Biomes of western North America at 18,000, 6000 and 0 14C yr bp reconstructed from pollen and packrat midden data

Journal of Biogeography,

27

, 555–584

© 2000 Blackwell Science Ltd

Original Article

Blackwell Science, Ltd

Biomes of western North America at 18,000, 6000 and 0

14

C yr

BP

reconstructed from pollen and packrat midden data

Robert S. Thompson

1

and Katherine H. Anderson

2 1

U.S. Geological Survey, Earth Surface Processes Team, Box 25046, MS980, Denver, CO 80225, USA,

2

Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80303, USA

Abstract

A new compilation of pollen and packrat midden data from western North America providesa refined reconstruction of the composition and distribution of biomes in western NorthAmerica for today and for 6000 and 18,000 radiocarbon years before present (

14

C yr

bp

).Modern biomes in western North America are adequately portrayed by pollen assem-

blages from lakes and bogs. Forest biomes in western North America share many taxa intheir pollen spectra and it can be difficult to discriminate among these biomes. Plantmacrofossils from packrat middens provide reliable identification of modern biomesfrom arid and semiarid regions, and this may also be true in similar environments in otherparts of the world. However, a weighting factor for trees and shrubs must be used toreliably reconstruct modern biomes from plant macrofossils.

A new biome, open conifer woodland, which includes eurythermic conifers and steppeplants, was defined to categorize much of the current and past vegetation of the semiaridinterior of western North America.

At 6000

14

C yr

bp

, the forest biomes of the coastal Pacific North-west and the desertbiomes of the South-west were in near-modern positions. Biomes in the interior Pacific North-west differed from those of today in that taiga prevailed in modern cool/cold mixed forests.Steppe was present in areas occupied today by open conifer woodland in the northern GreatBasin, while in the central and southern Rocky Mountains forests grew where steppe growstoday. During the mid-Holocene, cool conifer forests were expanded in the Rocky Mountains(relative to today) but contracted in the Sierra Nevada. These differences from the forests oftoday imply different climatic histories in these two regions between 6000

14

C yr

bp

and today.At 18,000

14

C yr

bp

, deserts were absent from the South-west and the coverage of openconifer woodland was greatly expanded relative to today. Steppe and tundra were presentin much of the region now covered by forests in the Pacific North-west.

Keywords

Packrat middens, pollen data, plant macrofossil data, plant functional types, biomes,

vegetation changes, western North America, last glacial maximum, mid-Holocene.

INTRODUCTION

Biomes represent broad physiognomic vegetation types that arebased on the co-occurrence of plant species that respond indi-vidualistically to climatic gradients and climatic change. Biomesdepict vegetation formations on a global basis based on the struc-ture, physiognomy and climatic adaptations of the plant func-tional types of which they are composed (Prentice

et al.

, 1992).Plant functional types (PFTs) are collections of plant taxa groupedby stature, leaf form, phenology and climatic adaptations. The

characterization of vegetation in terms of biomes providesthe basis for modelling past and future vegetation changes (e.g.Harrison

et al.

, 1995; Kutzbach

et al.

, 1998; Neilson

et al.

, 1998)and using the same terms for vegetation from different regionsfacilitates comparisons between the results of numericalclimate modelling and evidence of past vegetation (e.g. Jolly

et al.

, 1998a; Joussaume

et al.

, 1998; Williams

et al.

, 1998).Prentice

et al

. (1992) provided the original definitions ofPFTs and biomes used in this paper. Subsequent regionalsyntheses for Europe (Prentice

et al.

, 1996), the former SovietUnion and Mongolia (Tarasov

et al.

, 1998), China (Yu

et al.

,1998; Yu

et al.

, 2000), Africa and Arabia (Jolly

et al.

, 1998b;Elenga

et al.

, 2000), Beringia (Edwards

et al.

, 2000), and

Correspondence: Dr R. S. Thompson, U.S. Geological Survey, Earth SurfaceProcesses Team, Box 25046, MS980, Denver, CO 80225, USA. E-mail:[email protected]

JBI427.fm Page 555 Wednesday, November 1, 2000 12:20 PM

556 Robert S. Thompson and Katherine H. Anderson

© Blackwell Science Ltd 2000,

Journal of Biogeography

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, 555–584

Figure 1 Present-day climate of western North America. These four panels illustrate the biseasonal precipitation regime and the range of temperature and precipitation conditions experienced over this mountainous region. Modern mean temperature (top) and mean precipitation (bottom) in January (left) and July (right) over western North America.


Biome reconstructions for western North America 557



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Canada and the eastern United States (Williams

et al.

, 1998;2000) refined these definitions and methodology, and extendedthem into a wide range of climatic and vegetational circum-stances. In this paper, we use pollen and plant macrofossil datato portray biomes in western North America at 18,000 radio-carbon years before present (18,000

14

C yr

bp

the last glacialmaximum or LGM), 6000

14

C yr

bp

(the mid-Holocene), and0

14

C yr

bp

(today). We discuss the changes in biomes betweenthese time periods in terms of broad-scale changes in climate.

Western North America is treated separately from Canada andthe eastern United States for the following reasons: (1) it has anendemic flora that differs from those of Canada and the easternUnited States; (2) it has a unique data source (packrat mid-dens) and palynological settings in desert and mountain environ-ments that are different from the other two regions; (3) itsclimate has sharp gradients, is generally more arid than that ofthe eastern United States, and its winter temperatures are gener-ally milder than those of Canada or the north-eastern and mid-western United States; and (4) its mountainous terrain requiresspecial data analysis and can limit interpolation among sites.

Modern climate and vegetation

The modern climate of western North America has stronggeographical and elevational gradients in both temperatureand precipitation (Fig. 1). Winter precipitation from the NorthPacific supports wet environments in the Pacific Northwest,along the coast of California and in the northern RockyMountains. Rain shadows associated with the Sierra Nevada,Transverse and Cascade Ranges cause aridity in the interiorwestern United States. This aridity is offset in some areasnear the Mexico-United States border and in the southernRocky Mountains by summer monsoonal rainfall from sub-tropical sources. Seasonal and diurnal temperature ranges arelow in coastal regions, but are high in many parts of the aridand semiarid interior. These geographical gradients of climateinteract with the mountainous physiography of western NorthAmerica to create a mosaic of forest, woodland, steppe/grass-land, and desert vegetation. These patterns are depicted inFig. 2, where the categories representing potential naturalvegetation from Küchler (1964) have been grouped (Table 1)

Figure 2 Vegetation of the western United States based on the Küchler (1964) map of potential natural vegetation. The categories used by Küchler have been grouped to approximate the biomes used by Prentice et al. (1996) and this paper (with the exception of the steppe and grassland categories, which can be differentiated here but are more difficult to discriminate in pollen and macrofossil data).





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27

, 555–584

to approximate the biomes defined by Prentice

et al

. (1992).These categories are based on observations of the currentand historic vegetation and are purposefully simplified tofacilitate comparison between the fossil and modern data(for example, grassland and steppe are merged here as it isdifficult to distinguish these in the fossil record).

DATA AND METHODS

Pollen data

Pollen records provide quasi-continuous evidence of vegeta-tion change through time. These data are quantified as per-centages of each taxon for each spectrum in the record;however, modern pollen percentages frequently do not havelinear relationships with the abundances of species withinthe terrestrial vegetation. Pollen data are generally of lowtaxonomic resolution, and can usually be identified only atthe family or genus level. Fossil pollen data have been the

primary source of information on biomes in other regions,and their inclusion here allows some degree of comparabil-ity with previous studies. The pollen data included here arefrom original counts wherever possible, or were digitized frompublished diagrams when counts were unavailable. Raw pollencounts appear to provide a better discrimination betweennon-arboreal biomes (Jolly

et al.

, 1998b; Yu

et al.

, 2000), butdigitized data have been used to reconstruct biomes success-fully in other regions (e.g. Prentice

et al.

, 1996; Tarasov

et al.

,1998; other papers in this issue).

Packrat midden data

Packrats (

Neotoma

spp.) are small rodents that collect leaves,sticks, fruits and other materials from the area within tens-of-meters of their nests and bring these items into their homesfor food, nesting material, etc. Through time their nests canbecome cemented by their desiccated urine, and in dry cavesand rock shelters in western North America these urine-

Table 1 Present-day biomes in western North America interpreted from Küchler (1964; see Fig. 2).

Biome Küchler categories Key genera

tundra alpine meadows and barren Agrostis, Carex, Festuca, Poa

cool conifer forest spruce-cedar-hemlock forest, cedar-hemlock-Douglas fir forest, silver fir-Douglas fir forest, fir-hemlock forest, mixed conifer forest,redwood forest, red fir forest, lodgepole pine-subalpine forest, pine-cypress forest, western ponderosa forest, Douglas fir forest, cedar-hemlock-pine forest, grand fir-Douglas fir forest, western spruce-fir forest, eastern ponderosa forest, Black Hills pine forest, pine-Douglas fir forest, Arizona pine forest, spruce-fir-Douglas fir forest, Southwestern spruce-fir forest, western ponderosa forest, Oregon oak/California mixed evergreen forest

Abies, Cupressus, Picea, Pinus Pseudotsuga, Sequoia, Thuja, Tsuga

temperate deciduous/cool mixed forest

cedar-hemlock-Douglas fir forest, Oregon oak woodlands, California mixed evergreen forest, California oaklands, oak-juniper woodlands, mountain mahogany-oak (in part), northern floodplain forest

Arbutus, Cercocarpus, Juniperus, Populus, Pseudotsuga, Quercus, Salix, Thuja, Tsuga, Ulmus

open conifer woodland juniper-pinyon woodland, juniper woodland Artemisa, Juniperus, Pinus

xerophytic woods/scrub chapparal, coastal sagebrush, California oaklands (in part) Adenostoma, Arctostaphylos, Ceanothus, Eriogonum, Quercus, Salvia

grassland fescue-oatgrass, California steppe, California tule marshes, fescue-wheatgrass, wheatgrass-bluegrass, grama-galleta steppe, grama-tobosa prairie, wheatgrass-needlegrass shrubsteppe, galleta-three awn shrubsteppe, mesquite-buffalo grass, mesquite-acacia-savanna, foothills prairie, grama-needlegrass-wheatgrass, grama-buffalo grass, wheatgrass-needlegrass, wheatgrass-bluestem-needlegrass, wheatgrass-grama-buffalo grass, bluestem-grama prairie, sandsage-bluestem prairie, shinnery, northern cordgrass prairie, oak savanna, juniper-oak savanna, fescue-mountain muhly prairie

Acacia, Agropyron, Andropogon, Aristida, Artemisia, Bouteloua, Buchloe, Danthonia, Distichlis, Festuca, Hilaria, Juniperus,Muhlenbergia, Poa, Prosopis, Quercus, Setaria, Spartina, Stipa

steppe sagebrush steppe, Great Basin sagebrush steppe, saltbush-greasewood, mountain mahogany-oak (in part)

Agropyron, Artemisia, Atriplex, Cercocarpus, Quercus, Sarcobatus

desert mesquite bosques, blackbrush, creosote bush, creosote bush-bur sage, palo verde-cactus shrub, grama-tobosa shrubsteppe, ceniza shrub, grama-tobosa shrubsteppe, Trans-Peco shrub savanna

Cercidium, Colegyne, Flourensia, Franseria, Larrea, Leucophyllum, Opuntia, Prosopis





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, 555–584

cemented ‘packrat middens’ can be preserved for tens-of-thousands of years (see papers in Betancourt

et al.

, 1990 forfurther discussion). Packrat middens are unique to westernNorth America, although similar deposits left by other animalshave been found in arid regions in the Middle East, SouthAmerica, South Africa and Australia (Betancourt

et al.

, 1990).Plant remains from packrat middens: (1) can generally beidentified to the species level, and a given midden plant assem-blage appears to provide a detailed inventory of the speciesgrowing within 50 m (or less) of the packrat’s nesting site;(2) are extremely well-preserved and provide excellent materialfor radiocarbon dating; and (3) occur in assemblages thatappear to represent a short interval of time, perhaps as shortas the few years of an individual packrat’s life span. In sum,packrat middens provide a detailed inventory of plant speciesfor short intervals of time in the past.

Although vegetation assemblages preserved in packratmiddens have been studied since the 1960s, no uniform methodof quantification has been developed, and indeed there havebeen more quantification schemes than investigators in thefield. In any case, there is little evidence that relative abund-ance within the assemblages has much meaning, except toindicate the past presence or absence of a given plant speciesat a given midden site. In this paper we used data from theoriginal publications (USGS/NOAA NGDC Packrat Middendatabase) and converted the various quantification schemesinto a simple four-digit scale where: 0 = absent, 1 = rare (andpossibly a contaminant); 2 = present; and –9 = cannot deter-mine presence or absence (this usually pertains when theoriginal investigator published an incomplete list of plantspecies and it is thus not possible to determine if somethingis really absent). Packrat middens with very few reportedtaxa were omitted from the analysis.

Data sets

Modern pollen assemblages were obtained for 66 sites(Table 2). Raw pollen counts were obtained for 16 sites,and digitized data were used for the rest. Modern (and near-modern) packrat midden assemblages (35 samples) wereobtained from 18 sites (Table 3). To facilitate comparisonswith the older time slices, we used only the core tops ofpollen sediment cores for the 0

14

C yr

bp

time horizon. Wedid not use the diverse array of surface samples availablefor western North America. For packrat middens, we usedall samples with radiocarbon ages within the last 1000radiocarbon years.

The data set for 6000

14

C yr

bp

consists of 76 pollen sites(Table 2), of which 14 were obtained as raw pollen countsand 62 were digitized, and 34 packrat midden assemblages(23 sites) (Table 3). The data set for 18,000

14

C yr

bp

consists of 21 pollen sites (Table 2), of which 7 wereobtained as raw pollen counts and 14 were digitized, and17 packrat midden assemblages (13 sites) (Table 3). Withoriginal pollen data for the 6000

14

C yr

bp

time slice we usedthe pollen spectrum closest to 6000

14

C yr

bp

, whereasfor the digitized pollen data we interpolated to determinethe approximate 6000

14

C yr

bp

level. With packrat midden

data for 6000

14

C yr

bp

, we included all samples dated within1000 radiocarbon years of 6000

14

C yr

bp

(in other words,those samples that dated between 7000 and 5000

14

C yr

bp

).The same protocols were followed for the 18,000

14

C yr

bp

time slice.

Method of assigning biomes to pollen and packrat midden assemblages (biomization)

The biomization procedure has been fully described by Prentice

et al

. (1996) and Prentice & Webb (1998). There are four stepsin the biomization procedure: (1) assignment of individualplant taxa to plant functional types (PFTs); (2) specificationof the set of PFTs that can occur in each biome; (3) calculationof the affinity score of a given vegetation assemblage to everybiome; and (4) assignment of the vegetation assemblage tothe biome for which it has the largest affinity score. In caseswhere the affinity score for two or more biomes is equal, a tie-breaking rule is applied to determine the biome attributed tothe sample, following Prentice

et al

. (1996).We prepared separate plant taxon-PFT matrices for pollen

(Table 4) and for packrat midden assemblages (Table 5) basedon our knowledge of the ecology and biology of the individualplants, and on the descriptions of the flora and vegetationgiven in Benson (1982), Benson & Darrow (1981), Kearney& Peebles (1960), Little (1971, 1976, 1977), Thompson

et al

.(1999a, 1999b) and Turner

et al

. (1995). The pollen matrixincludes 74 individual pollen taxa and the packrat middenassemblage matrix includes 418 individual species.

We began with the PFT classification based on pollen dataused for Europe (Prentice

et al.

, 1996) and subsequently testedand modified for other northern hemisphere regions (e.g.Jolly

et al.

, 1998b; Tarasov

et al.

, 1998; Williams

et al.

, 1998;Yu

et al.

, 1998), and modified the pollen to PFT assignmentsto fit the North American situation. The PFT definitions, theassignment of individual pollen taxa to PFTs, and the assign-ment of PFTs to biomes are broadly consistent with the defi-nitions used in adjacent regions of North America by Williams

et al

. (2000) and Edwards

et al

. (2000).There are difficulties with the pollen-to-PFT relation in

western North America for conifers, as many pollen taxainclude both boreal and temperate species (most notably

Picea

,

Abies

and

Larix

). In Eurasia,

Larix

and

Picea

are con-fined to the boreal zone (Prentice

et al.

, 1996; Tarasov

et al.

,1998). However, both taxa also occur in more temperatesettings in North America (Little, 1971; Thompson

et al.

, 1999a,1999b). For example,

Larix lyallii

and

L. occidentalis

bothlive in temperate environments in the interior regions ofthe Pacific North-west, while

Picea sitchensis

occurs intemperate coastal forests from southern Alaska to northernCalifornia. We therefore allowed

Larix

to occur as both a borealsummergreen conifer (as in Eurasia) and a cool-temperateconifer, while

Picea

was classified as both a boreal evergreenconifer (as in Eurasia) and a cool-temperate conifer.

The species-level identifications of the midden plant macro-fossils led us to define five new PFTs: woodland conifer (wc),woodland shrub (ws), frost-sensitive desert shrub or succulent(ds2), desert shrub or succulent (ds) and steppe shrub (ss).





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Table 2

Characteristics of the 0, 6000 and 18,000

14

C yr

bp

pollen sites from western North America. Site names with asterisks indicate digitized data, those without an asterisk were taken from the North American Pollen Database from the sample level closest to the target age. Negative radiocarbon ages indicate dates that are younger than

ad

1950. Dating control (DC) codes are based on the COHMAP dating control scheme (Webb, 1985; Yu & Harrison, 1995). For sites with continuous sedimentation (indicated by a C after the numeric code), the dating control is based on bracketing dates where 1 indicates that both dates are within 2000 years of the selected interval, 2 indicates one date within 2000 years and the other within 4000 years, 3 indicates both within 4000 years, 4 indicates one date within 4000 years and the other within 6000 years, 5 indicates both dates within 6000 years, 6 indicates one date within 6000 years and the other within 8000 years, and 7 indicates bracketing dates more than 8000 years from the selected interval. For sites with discontinuous sedimentation (indicated by D after the numeric code), 1 indicates a date within 250 years of the selected interval, 2 a date within 500 years, 3 a date within 750 years, 4 a date within 1000 years, 5 a date within 1500 years, 6 a date within 2000 years, and 7 a date more than 2000 years from the selected interval. Biome codes (Biome) are given in Table 6. For mapping purposes some sites (indicated by ‡) which are too close to one another have been displaced slightly.

Site no. Site nameLat. (

°

N)Long. (

°

W)Elev. (m)

No. of

14

C dates DC

Age of chosen depth

Target age Biome References

Modern samples1 Alkali Creek* 38.75 106.83 2800 3 n/a n/a 0 OC Markgraf & Scott, 19813 Antelope Playa* 43.50 105.45 1450 3 n/a n/a 0 STEP Markgraf & Lennon, 19864 Balsam Meadows* 37.17 119.50 2005 6 n/a n/a 0 COCO Davis

et al

., 19855 Barrett Lake* 37.60 119.02 2816 6 n/a n/a 0 OC Anderson, 19906 Battle Ground Lake* 45.67 122.48 <300 11 n/a n/a 0 COCO Barnosky, 1985a

18 Como Lake* 37.55 105.50 3523 2 n/a n/a 0 OC Shafer, 198920 Cottonwood Pass Pond* 38.83 106.41 3700 3 n/a n/a 0 OC Fall, 198821 Creston Fen* 47.58 118.75 n/a 3 n/a n/a 0 OC Mack

et al

., 197622 Cub Creek Pond* 45.17 110.17 2500 3 n/a n/a 0 COCO Waddington & Wright, 197424 Cygnet Lake Fen 44.65 110.60 2530 6 n/a 0 0 OC Whitlock, 199326 Dead Man Lake* 36.24 108.95 2780 5 n/a n/a 0 OC Wright

et al

., 197328 Diamond Pond* 43.25 118.33 1265 11 n/a n/a 0 STEP Wigand, 198729 Divide Lake* 43.95 110.23 2628 3 n/a n/a 0 TAIG Whitlock & Bartlein, 199330 Dome Creek Meadow* 40.02 107.03 3165 5 n/a n/a 0 OC Feiler

et al

., 199731 Emerald Lake 44.07 110.30 2634 3 n/a 458 0 OC Whitlock, 199332 Exchequer Meadow* 37.00 119.08 2219 6 n/a n/a 0 COCO Davis & Moratto, 198837 Fryingpan Lake* 38.62 111.67 2720 5 n/a n/a 0 TAIG Shafer, 198940 Gold Lake Bog 43.65 122.05 1465 5 n/a 29 0 COCO Sea & Whitlock, 199542 Gray’s Lake* 43.00 111.58 1946 15 n/a n/a 0 OC Beiswenger, 199143 Great Salt Lake* 41.00 112.50 1280 1 n/a n/a 0 OC Mehringer, 198544 Guardipee Lake 48.55 112.72 1233 3 n/a –34 0 OC Barnowsky, 198945 Hager Pond* 48.67 116.92 860 12 n/a n/a 0 COCO Mack

et al

., 1978b, d46 Hall Lake* 47.82 122.30 104 6 n/a n/a 0 COCO Tsukada

et al

., 198147 Hay Lake, Arizona 34.00 109.43 2780 6 n/a 106 0 STEP Jacobs, 198548 Head Lake* 37.70 105.50 2300 6 n/a n/a 0 OC Shafer, 198949 Hedrick Pond 43.75 110.60 2073 5 n/a 0 0 OC Whitlock, 199350 Hidden Cave* 39.33 118.75 1251 16 n/a n/a 0 OC Wigand & Mehringer, 198551 Hoh Bog* 47.75 124.25 n/a 8 n/a n/a 0 COCO Heusser, 197853 Hurricane Basin* 37.97 107.55 3650 6 n/a n/a 0 STEP Andrews

et al

., 197554 Ice Slough* 42.48 107.90 1950 4 n/a n/a 0 OC Beiswenger, 198755 Indian Prairie Fen 44.63 122.58 988 5 n/a 350 0 COCO Sea & Whitlock, 199557 Jacob Lake 34.33 110.83 2285 3 n/a 25 0 STEP Jacobs, 198359 Keystone Iron Bog* 38.87 107.03 2920 7 n/a n/a 0 COCO Fall, 1985, 198860 Kirk Lake* 48.12 121.50 190 8 n/a n/a 0 COCO Cwynar, 198761 La Poudre Pass Bog* 40.48 105.78 3103 3 n/a n/a 0 STEP Short, 198562 Lake Cleveland* 42.32 113.63 2519 3 n/a n/a 0 OC Davis, 198156 Lake Isabel Bog* 40.07 105.62 3310 3 n/a n/a 0 OC Short, 198565 Lily Lake‡ 43.77 110.32 2469 2 n/a 0 0 OC Whitlock, 199368 Little Lake, Oregon 44.17 123.58 217 13 n/a 243 0 TUND Worona & Whitlock, 199569 Long Lake* 40.07 105.60 3210 5 n/a n/a 0 OC Short, 198570 Lost Lake, Montana 47.63 110.48 1019 5 n/a –35 0 STEP Barnosky, 198971 Lost Trail Pass Bog* 45.75 113.97 2152 16 n/a n/a 0 TAIG Mehringer

et al

., 197773 Marion Lake* 49.33 123.00 305 7 n/a n/a 0 COCO Mathewes, 197374 Mariposa Lake, WY 44.15 110.23 2730 3 n/a 0 0 OC Whitlock, 199375 Mayberry Well 33.70 108.30 2080 1 n/a 211 0 OC Markgraf, unpubl.76 Mckillop Creek Pond* 48.33 115.45 920 5 n/a n/a 0 COCO Mack

et al

., 198377 Mineral Lake* 46.73 122.20 436 7 n/a n/a 0 COCO Tsukada

et al

., 198178 Mission Cross Bog* 41.78 115.48 2424 7 n/a n/a 0 STEP Thompson, 198479 Molas Lake 37.75 107.68 3200 2 n/a 81 0 OC Maher, 1961



© Blackwell Science Ltd 2000, Journal of Biogeography, 27, 555–584

83 Nichols Meadow* 37.43 119.57 1509 2 n/a n/a 0 COCO Koehler & Anderson, 199485 Pangborn Bog* 48.83 122.58 n/a 3 n/a n/a 0 COCO Hansen & Easterbrook, 197488 Posy Lake* 37.95 111.70 2653 4 n/a n/a 0 COCO Shafer, 198989 Potato Lake* 34.08 111.50 2222 4 n/a n/a 0 OC Anderson, 199392 Rattlesnake Cave* 43.52 112.62 1996 1 n/a n/a 0 OC Davis, 198194 Ruby Marshes* 41.13 115.48 1818 25 n/a n/a 0 OC Thompson, 1992

100 Slough Creek Pond 44.93 110.35 1884 4 n/a 0 0 OC Whitlock & Bartlein, 1993102 Soleduck Bog* 47.92 124.47 73 1 n/a n/a 0 COCO Heusser, 1973103 Splains Gulch* 38.83 107.08 3160 4 n/a n/a 0 TAIG Fall, 1988105 Swamp Lake* 37.95 119.82 1554 5 n/a n/a 0 COCO Smith & Anderson, 1992106 Swan Lake* 42.33 112.42 1452 3 n/a n/a 0 OC Bright, 1966107 Teepee Lake* 48.33 115.50 1270 8 n/a n/a 0 COCO Mack et al., 1983109 Tioga Pass Pond* 37.92 119.27 3018 4 n/a n/a 0 STEP Anderson, 1990113 Waits Lake* 48.17 117.67 n/a 8 n/a n/a 0 CLDE Mack et al., 1978c, d116 Wessler Bog* 48.17 124.50 25 1 n/a n/a 0 COCO Heusser, 1973118 Williams Fen* 47.33 117.58 n/a 6 n/a n/a 0 STEP Nickmann, 1979119 Woski Pond 37.73 119.63 1212 3 n/a –36 0 COCO Anderson & Carpenter, 1991

6000 14C yr bp samples1 Alkali Creek* 38.75 106.83 2800 3 2C n/a 6000 OC Markgraf & Scott, 19813 Antelope Playa* 43.50 105.45 1450 3 1C n/a 6000 STEP Markgraf & Lennon, 19864 Balsam Meadows* 37.17 119.50 2005 6 2C n/a 6000 OC Davis et al., 19855 Barrett Lake* 37.60 119.02 2816 6 3C n/a 6000 OC Anderson, 19906 Battle Ground Lake* 45.67 122.48 <300 11 1C n/a 6000 COCO Barnosky, 1985a9 Big Meadow* 48.92 117.42 1040 8 2C n/a 6000 TAIG Mack et al., 1978a

10 Blacktail Pond* 44.97 110.60 2018 3 5C n/a 6000 OC Gennett, 197711 Bogachiel River Site* 47.88 124.33 533 2 7C n/a 6000 COCO Heusser, 197812 Bonaparte Meadows* 48.75 119.08 1021 14 1C n/a 6000 TAIG Mack et al., 197913 Buckbean Fen* 44.30 110.25 2363 4 2C n/a 6000 OC Baker, 197614 Carp Lake* 45.92 120.88 714 13 2C n/a 6000 COCO Barnosky, 1985b18 Como Lake* 37.55 105.50 3523 2 1C n/a 6000 OC Shafer, 198919 Copley Lake* 38.87 105.08 3250 7 1C n/a 6000 COCO Fall, 198820 Cottonwood Pass Pond* 38.83 106.41 3700 3 2C n/a 6000 COCO Fall, 198821 Creston Fen* 47.58 118.75 n/a 3 4C n/a 6000 OC Mack et al., 197622 Cub Creek Pond* 45.17 110.17 2500 3 7C n/a 6000 OC Waddington & Wright, 197424 Cygnet Lake Fen 44.65 110.60 2530 6 1C 6124 6000 OC Whitlock, 199325 Davis Lake* 46.58 122.25 282 16 1C n/a 6000 COCO Barnosky, 198128 Diamond Pond* 43.25 118.33 1265 11 n/a n/a 6000 OC Wigand, 198729 Divide Lake* 43.95 110.23 2628 3 3C n/a 6000 TAIG Whitlock & Bartlein, 199330 Dome Creek Meadow* 40.02 107.03 3165 5 2C n/a 6000 STEP Feiler et al., 199731 Emerald Lake 44.07 110.30 2634 3 4C 6018 6000 TAIG Whitlock, 199332 Exchequer Meadow* 37.00 119.08 2219 6 1C n/a 6000 COCO Davis & Moratto, 198837 Fryingpan Lake* 38.62 111.67 2720 5 1C n/a 6000 TAIG Shafer, 198938 Gardiners Hole* 44.92 110.73 n/a 2 4D n/a 6000 OC Baker, 198340 Gold Lake Bog 43.65 122.05 1465 5 2C 6147 6000 COCO Sea & Whitlock, 199542 Gray’s Lake* 43.00 111.58 1946 15 2C n/a 6000 STEP Beiswenger, 199143 Great Salt Lake* 41.00 112.50 1280 1 3D n/a 6000 OC Mehringer, 198544 Guardipee Lake 48.55 112.72 1233 3 5C 6166 6000 STEP Barnosky, 198945 Hager Pond* 48.67 116.92 860 12 1C n/a 6000 TAIG Mack et al., 1978b46 Hall Lake* 47.82 122.30 104 6 2C n/a 6000 COCO Tsukada et al., 198147 Hay Lake, Arizona 34.00 109.43 2780 6 6C 5639 6000 OC Jacobs, 198548 Head Lake* 37.70 105.50 2300 6 2C n/a 6000 OC Shafer, 198949 Hedrick Pond 43.75 110.60 2073 5 4C 6077 6000 OC Whitlock, 199350 Hidden Cave* 39.33 118.75 1251 16 2C n/a 6000 OC Wigand & Mehringer, 198553 Hurricane Basin* 37.97 107.55 3650 6 2C n/a 6000 TAIG Andrews et al., 197554 Ice Slough* 42.48 107.90 1950 4 3C n/a 6000 STEP Beiswenger, 198755 Indian Prairie Fen 44.63 122.58 988 5 2C 5919 6000 COCO Sea & Whitlock, 199559 Keystone Iron Bog* 38.87 107.03 2920 7 2C n/a 6000 COCO Fall, 1985, 198860 Kirk Lake* 48.12 121.50 190 8 3D n/a 6000 COCO Cwynar, 198761 La Poudre Pass Bog* 40.48 105.78 3103 3 2C n/a 6000 OC Short, 198562 Lake Cleveland* 42.32 113.63 2519 3 2C n/a 6000 OC Davis, 1981

Site no. Site nameLat. (°N)

Long. (°W)

Elev. (m)

No. of 14C dates DC

Age of chosen depth


Table 2 continued




63 Lake Emma* 37.90 107.63 3730 5 3D n/a 6000 OC Carrara et al., 198456 Lake Isabel Bog* 40.07 105.62 3310 3 2C n/a 6000 OC Short, 198564 Lake Washington* 47.67 122.22 6 5 4C n/a 6000 COCO Leopold et al., 198265 Lily Lake‡ 43.77 110.32 2469 2 2C 5892 6000 TAIG Whitlock, 199366 Lily Lake Fen‡ 43.77 110.32 2469 6 4D 6285 6000 OC Whitlock, 199368 Little Lake, Oregon 44.17 123.58 217 13 2C 5990 6000 COCO Worona & Whitlock, 199569 Long Lake* 40.07 105.60 3210 5 2C n/a 6000 OC Short, 198570 Lost Lake, Montana 47.63 110.48 1019 5 1C 5978 6000 STEP Barnosky, 198971 Lost Trail Pass Bog* 45.75 113.97 2152 16 1C n/a 6000 COCO Mehringer et al., 197773 Marion Lake* 49.33 123.00 305 7 2C n/a 6000 COCO Mathewes, 197374 Mariposa Lake, WY 44.15 110.23 2730 4 4C 6505 6000 OC Whitlock, 199376 Mckillop Creek Pond* 48.33 115.45 920 5 1D n/a 6000 TAIG Mack et al., 198377 Mineral Lake* 46.73 122.20 436 7 2C n/a 6000 COCO Tsukada et al., 198178 Mission Cross Bog* 41.78 115.48 2424 7 1C n/a 6000 STEP Thompson, 198479 Molas Lake 37.75 107.68 3200 2 7C 5818 6000 OC Maher, 196181 Mud Lake* 48.50 119.75 655 5 7D n/a 6000 OC Mack et al., 197983 Nichols Meadow* 37.43 119.57 1509 2 1D n/a 6000 OC Koehler & Anderson, 199485 Pangborn Bog* 48.83 122.58 n/a 3 5D n/a 6000 COCO Hansen & Easterbrook, 197486 Pinecrest Lake* 50.50 121.50 320 1 7D n/a 6000 COCO Mathewes & Rouse, 197588 Posy Lake* 37.95 111.70 2653 4 1C n/a 6000 OC Shafer, 198991 Rapid Lake* 42.62 109.20 3135 4 2C n/a 6000 OC Fall, 198892 Rattlesnake Cave* 43.52 112.62 1996 1 4D n/a 6000 OC Davis, 198193 Redrock Lake* 40.67 105.50 3095 7 1C n/a 6000 OC Maher, 197294 Ruby Marshes* 41.13 115.48 1818 25 1C n/a 6000 OC Thompson, 1992

100 Slough Creek Pond 44.93 110.35 1884 4 2C 6128 6000 OC Whitlock & Bartlein, 1993102 Soleduck Bog* 47.92 124.47 73 1 4C n/a 6000 COCO Heusser, 1973103 Splains Gulch* 38.83 107.08 3160 4 1C n/a 6000 COCO Fall, 1988105 Swamp Lake* 37.95 119.82 1554 5 4C n/a 6000 COCO Smith & Anderson, 1992106 Swan Lake* 42.33 112.42 1452 3 4C n/a 6000 STEP Bright, 1966107 Teepee Lake* 48.33 115.50 1270 8 1C n/a 6000 TAIG Mack et al., 1983109 Tioga Pass Pond* 37.92 119.27 3018 4 1C n/a 6000 OC Anderson, 1990113 Waits Lake* 48.17 117.67 n/a 8 2C n/a 6000 TAIG Mack et al., 1978c116 Wessler Bog* 48.17 124.50 25 1 7C n/a 6000 COCO Heusser, 1973118 Williams Fen* 47.33 117.58 n/a 6 1C n/a 6000 STEP Nickmann, 1979

18,000 14C yr bp samples6 Battle Ground Lake* 45.67 122.48 <300 11 2C n/a 18000 STEP Barnosky, 1985a8 Bechan Cave 38.00 111.00 1370 1 7D 18236 18000 OC Davis et al., 1984; Davis, 1990

11 Bogachiel River Site* 47.88 124.33 533 2 7C n/a 18000 STEP Heusser, 197814 Carp Lake* 45.92 120.88 714 13 1C n/a 18000 STEP Barnosky, 1985b25 Davis Lake* 46.58 122.25 282 16 3C n/a 18000 STEP Barnosky, 198126 Dead Man Lake* 36.24 108.95 2780 5 7C n/a 18000 OC Wright et al., 197327 Devlins Park* 40.02 105.55 2953 6 1C n/a 18000 OC Legg & Baker, 198033 Fargher Lake* 45.88 122.52 n/a 3 2C n/a 18000 COCO Heusser, 198342 Gray’s Lake* 43.00 111.58 1946 15 6C n/a 18000 OC Beiswenger, 199147 Hay Lake, Arizona 34.00 109.43 2780 6 6C 17770 18000 OC Jacobs, 198549 Hedrick Pond 43.75 110.60 2073 5 4D 17408 18000 OC Whitlock, 199351 Hoh Bog* 47.75 124.25 n/a 8 7D n/a 18000 TUND Heusser, 197857 Jacob Lake 34.33 110.83 2285 3 7C 18144 18000 OC Jacobs, 198358 Kalaloch* 47.55 124.33 35 3 6D n/a 18000 STEP Heusser, 197268 Little Lake, Oregon 44.17 123.58 217 13 2C 17618 18000 COCO Worona & Whitlock, 199575 Mayberry Well 33.70 108.30 2080 1 7C 18332 18000 OC Markgraf, unpublished NAPD77 Mineral Lake* 46.73 122.20 436 7 2D n/a 18000 STEP Tsukada et al., 198179 Molas Lake 37.75 107.68 3200 2 7D 18062 18000 OC Maher, 196183 Nichols Meadow* 37.43 119.57 1509 2 7C n/a 18000 OC Koehler & Anderson, 199489 Potato Lake* 34.08 111.50 2222 4 4C n/a 18000 OC Anderson, 199394 Ruby Marshes* 41.13 115.48 1818 25 1C n/a 18000 OC Thompson, 1992

Site no. Site nameLat. (°N)

Long. (°W)

Elev. (m)

No. of 14C dates DC

Age of chosen depth


Table 2 continued




Table 3 Characteristics of the 0, 6000 and 18,000 14C yr bp packrat midden sites from western North America. Dating control codes (DC) follow the scheme described in Table 2. Biome codes (Biome) are given in Table 6. For mapping purposes some sites (indicated by ‡) which are too close to one another have been displaced slightly.

Site nameSample code

Lat. (°N)

Long. (°W)

Elev. (m)

14C age

Targetage DC Biome References

Modern samplesAjo Loop 4 31.97 112.78 550 980 0 4D DESE Van Devender, 1987Ajo Loop 3A 31.97 112.78 550 990 0 4D DESE Van Devender, 1987Ajo Loop 2C 31.97 112.78 550 130 0 1D DESE Van Devender, 1987Ajo Loop 2B 31.97 112.78 550 30 0 1D DESE Van Devender, 1987Bison Alcove MOD 38.73 109.50 1317 405 0 2D OC Sharpe, 1991Bison Alcove MOD 38.73 109.50 1317 355 0 2D OC Sharpe, 1991Dog Canyon 1 32.83 105.92 1615 360 0 2D DESE Van Devender et al., 1984Dolores 4(1) 37.52 108.55 2100 900 0 4D OC Van Devender, 1985Dolores 3 37.52 108.55 2100 580 0 3D OC Van Devender, 1985Dolores 4(2) 37.52 108.55 2100 990 0 4D OC Van Devender, 1985Eureka View‡ #3 37.33 117.78 1450 535 0 3D DESE Spaulding, 1980Gatecliff #5 39.00 116.78 2319 0 0 1D OC Thompson & Hattori, 1983Greenwater Valley‡ G11C 36.17 116.60 1410 740 0 3D DESE Cole & Webb, 1985Greenwater Valley‡ G11A 36.17 116.60 1410 0 0 1D DESE Cole & Webb, 1985Greenwater Valley‡ G9D 36.17 116.60 1350 290 0 2D DESE Cole & Webb, 1985Greenwater Valley‡ G15 36.17 116.60 1380 0 0 1D DESE Cole & Webb, 1985Greenwater Valley‡ G7 36.17 116.60 1360 0 0 1D DESE Cole & Webb, 1985Greenwater Valley‡ G8 36.17 116.60 1340 0 0 1D DESE Cole & Webb, 1985Greenwater Valley‡ G6B 36.17 116.60 1350 270 0 2D DESE Cole & Webb, 1985Greenwater Valley‡ G11B 36.17 116.60 1410 400 0 2D DESE Cole & Webb, 1985Greenwater Valley‡ G4A 36.17 116.60 1350 200 0 1D OC Cole & Webb, 1985Hance Canyon‡ HC2B 36.03 111.97 1200 0 0 1D DESE Cole, 1981Hidden Forest #3B 36.57 115.10 2380 820 0 4D OC Spaulding, 1981Horse Thief Hills‡ #3(1) 37.35 117.80 1575 200 0 1D DESE Spaulding, 1980Horse Thief Hills‡ #3(2) 37.35 117.80 1575 200 0 1D DESE Spaulding, 1980Horse Thief Hills‡ #3(2) 37.35 117.80 1575 200 0 1D DESE Spaulding, 1980Horse Thief Hills‡ #2 37.35 117.80 1635 200 0 1D OC Spaulding, 1980Horseshoe Mesa‡ HM1B 36.03 111.98 1100 0 0 1D DESE Cole, 1981Kings Canyon KC7 36.80 118.80 1270 90 0 1D XERO Cole, 1983Kings Canyon MODINDUR 36.80 118.80 1270 0 0 1D XERO Cole, 1983McCullough Range 1(1)1 35.75 115.17 1045 960 0 4D DESE Spaulding, 1991Navar Ranch 18C 31.90 106.15 n/a 789 0 4D DESE Van Devender & Toolin, undatedSan Andres 1 32.83 105.92 1555 430 0 2D DESE Van Devender et al., 1984Sierra Bacha 3 29.83 112.47 100 320 0 2D DESE Van Devender et al., 1984Wide Rock Butte LEVEL1 36.12 109.33 2100 0 0 1D OC Schmutz et al., 1976

6000 14C yr bp samplesAjo Loop 1A 31.97 112.78 550 5240 6000 4D DESE Van Devender, 1987Chuar Valley CH1 36.17 111.92 1430 6830 6000 4D OC Cole, 1981Council Hall Cave #1A 39.33 114.10 2040 6120 6000 1D OC Thompson, 1984Eureka View #4(3) 37.33 117.78 1435 5435 6000 3D DESE Spaulding, 1980Eureka View #4(2) 37.33 117.78 1435 6795 6000 4D DESE Spaulding, 1980Eureka View #4(1) 37.33 117.78 1435 5595 6000 2D DESE Spaulding, 1980Fishmouth Cave 4 37.42 109.65 1585 6100 6000 1D OC Betancourt, 1984Grandview Point‡ GP4 36.00 111.98 2200 5510 6000 2D OC Cole, 1981Hornaday Mountains 1C 31.98 113.60 240 6065 6000 1D DESE Van Devender et al., 1990Lava Tube 99999 43.55 122.57 1640 5690 6000 2D STEP Bright & Davis, 1982Lubkin Canyon‡ 1 36.53 118.05 1264 5090 6000 4D STEP Koehler & Anderson, 1995Lubkin Canyon‡ 2 36.53 118.05 1264 5610 6000 2D OC Koehler & Anderson, 1995Lucerne Peak‡ #1 34.50 117.00 1097 5800 6000 1D DESE King, 1976Marble Canyon 1A 32.83 105.92 1580 5430 6000 3D DESE Van Devender et al., 1984McCullough Range 3(5) 35.75 115.17 1045 5060 6000 4D DESE Spaulding, 1991McCullough Range 3(1) 35.75 115.17 1045 5510 6000 2D DESE Spaulding, 1991McCullough Range 3(3) 35.75 115.17 1045 6480 6000 2D DESE Spaulding, 1991McCullough Range 3(4) 35.75 115.17 1045 6800 6000 4D DESE Spaulding, 1991Navar Ranch 1C1 31.90 106.15 n/a 6360 6000 2D DESE Van Devender & Toolin, undatedRhodes Canyon 4 33.18 106.60 1700 6330 6000 2D DESE Van Devender & Toolin, 1983Rhodes Canyon 6B 33.18 106.60 1700 6950 6000 4D DESE Van Devender & Toolin, 1983Sierra Bacha 1J 29.83 112.47 200 5340 6000 3D DESE Van Devender et al., 1994Sunset Cove‡ #1 34.50 117.00 972 5880 6000 1D OC King, 1976Tse an Bida Cave BI6B 36.00 112.00 1450 6800 6000 4D OC Cole, 1981Valleyview #1 39.50 114.72 2350 6250 6000 1D OC Thompson, 1984Valleyview #1 39.50 114.72 2350 6670 6000 3D OC Thompson, 1984Waterman Mountains 9D 32.35 111.45 760 5540 6000 2D DESE Andersen & Van Devender, 1991Waterman Mountains 9D 32.35 111.45 760 4845 6000 5D DESE Andersen & Van Devender, 1991Waterman Mountains 12A 32.35 111.45 760 6195 6000 1D DESE Andersen & Van Devender, 1991Waterman Mountains 12A 32.35 111.45 760 5920 6000 1D DESE Andersen & Van Devender, 1991Wellton Hills #5A 32.60 114.12 175 6600 6000 3D DESE Van Devender, 1973




Wellton Hills #5A 32.60 114.12 175 8150 6000 7 DESE Van Devender, 1973Wide Rock Butte LEVEL4 36.12 109.33 2100 6210 6000 1D COMX Schmutz et al., 1976Wolcott Peak 4 32.45 111.47 862 5350 6000 3D DESE Van Devender, 1973

18,000 14C yr bp samplesBig Boy 2 32.83 105.92 1555 18300 18000 2D OC Van Devender et al., 1984Chuar Valley‡ CH18C2 36.17 111.92 1770 18490 18000 2D COMX Cole, 1981Chuar Valley‡ CH18B 36.17 111.92 1770 18800 18000 4D OC Cole, 1981Eyrie #3(2) 36.63 115.28 1855 18890 18000 4D OC Spaulding, 1981Flaherty Mesa #2 36.48 115.25 1770 18790 18000 4D OC Spaulding, 1981Hance Canyon‡ HC4 36.03 111.97 1100 17400 18000 3D OC Cole, 1981Horseshoe Mesa‡ HM6 36.03 111.98 1450 18630 18000 3D XERO Cole, 1981Kings Canyon #5A2 36.80 118.80 1275 19130 18000 5D XERO Cole, 1983Kings Canyon #5A2 36.80 118.80 1275 17520 18000 2D XERO Cole, 1983Nankoweap‡ NA9C 36.25 111.95 2020 18130 18000 1D COCO Cole, 1981Nankoweap‡ NA9B 36.25 111.95 2020 17950 18000 1D COCO Cole, 1981Pontatoc Ridge #4B 32.35 110.88 1463 17950 18000 1D OC Van Devender & Thompson, unpublishedRampart Cave RatLayer 36.10 113.93 535 18890 18000 4D OC Phillips, 1977Streamview #2 39.33 114.10 1860 17350 18000 3D OC Thompson, 1984; Thompson &

Mead, 1982Vulture Canyon #6 36.10 113.93 645 17610 18000 2D OC Phillips, 1977Vulture Canyon #17 36.10 113.93 645 17100 18000 4D OC Mead & Phillips, 1981Willow Wash #4D 36.47 115.25 1585 17070 18000 4D OC Spaulding, 1981

Site nameSample code

Lat. (°N)

Long. (°W)

Elev. (m)

14C age

Targetage DC Biome References

Table 3 continued

Table 4 Assignments of pollen taxa from western North America to the plant functional types (PFTs) used in the biomization procedure.

Abbr. Plant functional type Pollen taxa

aa arctic /alpine dwarf shrub Alnus undiff., Betula undiff., Brassicaceae, Caryophyllaceae, Dryas-type, Fabaceae, Oxyria, Polygonum bistortoides-type, Potentilla-type, Ranunculaceae, Salix, Saxifragaceae, Thalictrum, Umbelliferae/Apiaceae

bec boreal evergreen conifer Abies, Piceabs boreal summergreen Alnus undiff., Betula undiff., Cornus, Larix, Larix/Pseudotsuga, Myricaceae,

Populus, Salix, Shepherdia canadensisctc cool-temperate conifer Abies, Larix/Pseudotsuga, Picea, Pseudotsuga, Taxaceae, Taxodiaceae (Other,

in California), Taxodiaceae/Cupressaceae/Taxaceae, Tsugadf desert forb Ambrosia-type, Brassicaceae, Caryophyllaceae, Chenopodiaceae/Amaranthus,

Ephedra, Eriogonum, Euphorbiaceae, Fabaceae, Nyctaginaceae, Ranunculaceae, Sphaeralcea-type, Tubuliflorae/Other Asteraceae, Umbelliferae/Apiaceae

ds desert shrub or succulent Not presentds2 frost-sensitive desert shrub or succulent Not presentec eurythermic conifer Cupressaceae/Taxaceae, Pinus, Taxodiaceae/Cupressaceae/Taxaceaeg grass Poaceaeh heath Ericaceaes sedge Cyperaceaesf steppe forb Ambrosia-type, Artemisia, Brassicaceae, Caryophyllaceae, Cercocarpus-type,

Chenopodiaceae/Amaranthus, Ephedra, Eriogonum, Fabaceae, Potentilla-type, Ranunculaceae, Sarcobatus, Saxifragaceae, Sphaeralcea-type, Tubuliflorae/Other Asteraceae, Umbelliferae/Apiaceae

ss steppe shrub Not presentts temperate summergreen Acer, Alnus undiff., Anacardiaceae, Aquifoliaceae, Carya, Ceanothus, Clethra, Cornus,

Fraxinus, Myricaceae, Ostrya/Carpinus, Populus, Quercus, Rhamnus, Salix, Ulmusts1 cool-temperate summergreen Betula undiff., Corylus, Fagus, Larix, Larix/Pseudotsuga, Tiliats2 intermediate-temperate summergreen Castanea, Celtis, Cephalanthus, Fabaceae, Juglans, Magnoliaceae, Morus, Nyssa,

Platanusts3 warm-temperate summergreen Celtis, Cephalanthus, Liquidambar, Nyssawc woodland conifer Not presentws woodland shrub Not presentwtc warm-temperate conifer Taxodiaceae (Other, in California), Taxodiaceae/Cupressaceae/Taxaceae, Taxodiumwte warm-temperate broadleaved evergreen Aquifoliaceae, Chrysolepis/Lithocarpus, Magnoliaceae, Quercuswte1 cool-temperate broadleaved evergreen Aquifoliaceaewte2 warm-temperate sclerophyll shrub Ceanothus, Chrysolepis/Lithocarpus, Quercus, Rhamnus




Table 5 Assignments of plant macrofossil (midden) taxa from western North America to the plant functional types (PFTs) used in the biomization procedure.

Abbr. Plant functional type Plant macrofossil taxa

aa arctic /alpine dwarf shrub Cirsium sp., Phlox sp.

bec boreal evergreen conifer Juniperus communis, Picea engelmannii, Picea pungens, Pinus flexilis

bs boreal summergreen Ribes cf. montigenum, Shepherdia canadensis, Shepherdia sp.

ctc cool-temperate conifer Abies concolor, Abies magnifica, Calocedrus decurens, Juniperus communis, Juniperus occidentalis, Juniperus scopulorum, Juniperus sp., Pinus flexilis, Pinus lambertiana, Pinus longaeva, Pinus ponderosa, Pseudotsuga menziesii

df desert forb Abutilon sp., Allionia incarnata, Amaranthus cf. albus, Amaranthus fimbriatus, Amaranthus sp., Amaranthus/Chenopodium, Ambrosia confertifolia, Ambrosia sp., Amsinckia intermedia, Amsinckia sp., Amsinckia tesselata, Amsinckia/Cryptantha, Amsonia sp., Argenome sp., Argythamnia lanceolata, Artemisia ludoviciana, Astragalus sp., Bahia absinthifolia, Boerhaavia sp., Boerhaavia wrightii, Brickellia arguta, Chaenactis sp., Chenopodium (cf.), Chenopodium sp., Chorizanthe brevicornu, Cirsium sp., Coldenia canescens, Cryptantha barbigera cf. Cryptantha maritima, Cryptantha racemosa, Cryptantha sp., Cryptantha virginensis, Cucurbita sp., Daucus pusillus, Descurainia sp., Dithyrea californica, Erigeron sp., Eriogonum fasciculatum, Eriogonum sp., Erodium sp., Eucnide urens, Euphorbia cf. polycarpa, Euphorbia micromera/polycarpa, Euphorbia sp., Gilia cf. latifolia, Gilia sp., Gutierrezia lucida, Gutierrezia sarothrae, Gutierrezia sp., Haplopappus brickelliodes, Hedeoma nana, Hedeoma sp., Helianthus sp., Heterotheca sp., Ipomoea or Convolvulus, Iva cf. ambrosiaefolia, Kallstroemia sp., Lappula redowskii, Lappula sp., Lepidium fremontii, Lepidium sp., Leptodactylon pungens, Lesquerella sp., Lotus sp., Lupinus sp., Machaeranthera sp., Mentzelia multiflora-type, Mentzelia sp., Mirabilis bigelovii, Mirabilis multiflora, Mirabilis sp., Oenothera (cf.), Oenothera pallida, Pectocarya cf. recurvata, Pectocarya heterocarpa, Pectocarya sp., Penstemon sp., Perityle emoryi, Physalis crassifolia, Physalis sp., Plantago insularis, Plantago sp., Polygonum sp., Portulaca oleracea, Psoralea sp., Salazaria mexicana, Salvia sp., Senecio sp., Sphaeralcea-type, Sphaeralcea ambigua, Sphaeralcea sp., Stanleya pinnata, Stephanomeria exiqua, Streptanthus sp., Streptanthus cordatus, Thysanocarpus sp., Tidestromia oblongifolia, Tidestromia lanuginosa, Verbena sp., Viguiera reticulata, Viguiera sp.

ds desert shrub or succulent Acacia greggii, Agave lecheguilla, Agave neomexicana, Agave sp., Agave utahensis, Aloysia wrightii, Ambrosia dumosa, Atriplex canescens, Atriplex polycarpa, Berberis haematocarpa, Brickellia desertorum, Brickellia longiflora, Brickellia or Eupatorium, Brickellia sp., Buddleja utahensis, Cactaceae undet., Ceanothus greggii, Celtis pallida, Choisya dumosa, Chrysothamnus nauseosus ssp. bigelovii, Chrysothamnus teretifolius, Coleogyne ramosissima, Coryphantha strobiliformus, Cowania mexicana (cf.), Croton sonorae, Dalea fremontii, Dalea sp., Dasylirion sp., Dasylirion wheeleri, Ditaxis lanceolata, Echinocactus horizonthalonius, Echinocereus sp., Encelia farinosa, Encelia frutescens, Encelia virginensis, Ephedra aspera, Ephedra nevadensis, Ephedra sp., Ephedra torreyana, Ephedra trifurca-type, Ericameria laricifolia, Eriogonum heermannii, Eriogonum sp., Fallugia paradoxa, Ferocactus-type, Ferocactus covellei, Forsellesia nevadensis, Forsellesia spinescens, Fouquieria columnaris, Fouquieria splendens, Grayia spinosa, Gutierrezia microcephala, Haplopappus cooperi, Haplopappus laricifolius, Horsfordia, Hymenoclea salsola, Hyptis emori, Janusia gracilis, Koeberlinia spinosa, Krameria grayi, Krameria parvifolia, Larrea divaricata, Lycium andersonii, Lycium cf. berlandieri, Lycium pallidum, Lycium sp., Machaeranthera tortifolia, Mammillaria tetrancistra, Menodora spinescens, Mortonia scabrella, Neolloydia johnsonii, Nicotiana trigonophylla, Nolina micrantha, Opuntia, Opuntia acanthocarpa, Opuntia arbuscula, Opuntia basilaris, Opuntia bigelovii, Opuntia chlorotica, Opuntia echinocarpa, Opuntia erincea, Opuntia fulgida, Opuntia imbricata, Opuntia kunzei, Opuntia leptocactus, Opuntia phaeacantha-type, Opuntia ramosissima, Opuntia sp., Opuntia versicolor, Peucephyllum schottii, Phoradendron californicum, Prosopis glandulosa, Prosopis juliflora, Prunus fasciculata, Prunus sp., Psoralea sp., Psorothamnus fremontii, Rhus diversiloba, Rhus microphylla, Salvia mohavensis, Salvia sp., Simmondsia chinensis, Solanum hindsianum, Tetradymia axillaris, Tetradymia spinosa, Thamnosma montana, Thamnosma sp., Trixis californica, Viquiera stenoloba, Yucca angustifolia, Yucca angustissima, Yucca baccata (cf.), Yucca baccata/torreyi, Yucca brevifolia, Yucca schidigera, Yucca sp., Yucca torreyi, Yucca whipplei, Yucca whipplei ssp. caepitosa




ds2 frost-sensitive desert shrub or succulent

Agave subsimplex, Bursera micophylla, Cactaceae undet., Carnegiea gigantea, Cercidium, Cercidium floridum, Cercidium microphyllum, Cereus giganteus, Ferocactus-type, Ferocactus acanthodes, Ferocactus cylindraceus, Jatropha cuneata, Lophocereus schottii, Olneya tesota, Pachycereus pringlei, Prosopis juliflora var. velutina, Prosopis velutina, Sapium biloculare, Stenocereus thurberi, Tetradymia sp.

ec eurythermic conifer Cupressaceae, Pinus sp.

g grass Agropyron cf. spicatum, Agropyron sp., Andropogon barbinodis/saccharoides, Aristida adscencionis, Aristida sp., Avena/Festuca-type, Bouteloua aristidoides, Bouteloua barbata, Bouteloua curtipendula, Bouteloua eriopoda, Bouteloua gracilis, Brickellia arguta, Bromus anomalus, Bromus rubens, Bromus sp., Bromus tectorum, Digitaria californica, Echinochloa crusgallii, Elymus sp., Enneapogon desvauxii, Eragrostis sp., Erioneuron grandiflorum, Erioneuron pulchellum, Festuca sp., Filago sp., Gramineae undet., Hilaria jamesii, Leptochloa dubia, Muhlenbergia microsperma, Muhlenbergia monticola, Muhlenbergia pauciflora, Muhlenbergia sp., Oryzopsis hymenoides, Oryzopsis sp., Panicum capillare, Panicum cf. hallii, Poa sandbergii, Poaceae undet., Setaria cf. leucophila, Setaria macrostachya, Sitanion hystrix, Stipa arida, Stipa cf. lobata, Stipa comata, Stipa neomexicana, Stipa occidentalis, Stipa sp., Stipa speciosa, Stipa arida cf., Tridens muticus

h heath Arctostaphylos pungens, Arctostaphylos sp.

s sedge Not present

sf steppe forb Allionia incarnata, Amaranthus cf. albus, Amaranthus sp., Amaranthus/Chenopodium, Ambrosia confertifolia, Ambrosia sp., Amsinckia sp., Amsinckia/Cryptantha, Angelica sp. cf., Argenome sp., Artemisia ludoviciana, Artemisia sp., Astragalus sp., Chaenactis sp., Chenopodium (cf.), Chenopodium sp., Cirsium sp., Cryptantha sp., Cryptantha virginensis, Cucurbita sp., Daucus pusillus, Descurainia sp., Ericameria cuneata, Erigeron sp., Eriogonum fasciculatum, Eriogonum sp., Erodium sp., Euphorbia sp., Gilia sp., Gutierrezia lucida, Gutierrezia sarothrae, Gutierrezia sp., Hedeoma nana, Hedeoma sp., Helianthus sp., Ipomoea or Convolvulus, Lappula redowskii, Lappula sp., Lepidium fremontii, Lepidium sp., Leptodactylon pungens, Lesquerella kingi, Lesquerella sp., Linum lewisii, Linum sp., Lithospermum sp., Lotus sp., Lupinus argenteus, Lupinus sp., Machaeranthera sp., Mentzelia multiflora-type, Mentzelia sp., Mirabilis bigelovii, Mirabilis multiflora, Mirabilis oxybaphoides, Mirabilis sp., Oenothera (cf.), Oenothera pallida, Pectocarya heterocarpa, Pectocarya sp., Penstemon breviflorus, Penstemon sp., Phacelia sp., Phlox sp., Physalis sp., Plantago insularis, Plantago sp., Polygonum sp., Portulaca oleracea, Psoralea sp., Senecio sp., Sphaeralcea-type, Sphaeralcea sp., Stanleya pinnata, Stephanomeria exiqua, Streptanthus sp., Streptanthus cordatus, Verbena sp., Viguiera sp.

ss steppe shrub Amelanchier sp., Amelanchier utahensis, Artemisia frigida, Artemisia sp., Artemisia spinescens, Artemisia tridentata, Atriplex canescens, Atriplex confertifolia, Atriplex polycarpa, Berberis fremontii, Berberis haematocarpa, Brickellia sp., Buddleja utahensis, Cactaceae undet., Ceanothus greggii, Ceratoides lanata, Cercocarpus ledifolius, Chamaebatiaria millefolium, Chrysothamnus greenei, Chrysothamnus nauseosus, Chrysothamnus nauseosus ssp. bigelovii, Chrysothamnus sp., Chrysothamnus teretifolius, Chrysothamnus viscidiflorus, Coryphantha strobiliformus, Cowania mexicana (cf.), Dasylirion sp., Dasylirion wheeleri, Echinocactus polycephalus, Echinocereus sp., Ephedra nevadensis, Ephedra sp., Ephedra torreyana, Ephedra trifurca-type, Ephedra viridis, Ericameria larcifolia, Eriogonum sp., Fallugia paradoxa, Forsellesia nevadensis, Grayia spinosa, Gutierrezia microcephala, Lycium pallidum, Mammillaria-type, Mammillaria microcarpa, Mammillaria sp., Menodora spinescens, Nolina micrantha, Opuntia, Opuntia arbuscula, Opuntia basilaris, Opuntia bigelovii, Opuntia chlorotica, Opuntia erincea, Opuntia fulgida, Opuntia imbricata, Opuntia leptocactus, Opuntia phaeacantha-type, Opuntia polyacantha, Opuntia sp., Opuntia spinosior, Opuntia whipplei, Petrophytum caespitosum, Psoralea sp., Purshia tridentata, Rhus diversiloba, Ribes cereum, Ribes sp., Ribes velutinum, Salvia carnosa, Salvia sp., Shepherdia argentea, Symphoricarpos spp., Symphoricarpos longiflorus, Tetradymia axillaris, Tetradymia sp., Tetradymia spinosa, Tidestromia oblongifolia, Yucca angustifolia, Yucca angustissima, Yucca harrimaniae, Yucca sp.


Table 5 continued




Woodland conifers include pinyon pine and woodland juniper,whereas the woodland shrub PFT includes species in thegenera Amelanchier, Berberis, Cercocarpus, Cowania, Fraxinus,Garrya, Prunus and Ribes, among others. Frost-sensitive desertshrubs or succulents include plants characteristic of the present-day Sonoran Desert, including species in the genera Agave,Bursera, Cereus, Cercidium and Ferocactus, among others. Thedesert shrub PFT includes less-frost-sensitive species includ-ing species in the genera Acacia, Celtis, Coleogyne, Daleaand Ephedra. Steppe shrubs include species in the generaArtemisia, Atriplex, Chrysothamnus, Ephedra, Gutierrezia andGrayia, among others.

We created a PFT to biome matrix (Table 6) to assign thePFTs in Tables 4 and 5 to the biomes defined in Prentice et al.(1992) and Prentice et al. (1996). In the case of tie-breaks,biomes are assigned in the order they appear in Table 6.

We identified a new biome (open conifer woodland: OC)

to represent the pinyon-juniper woodlands and subalpineconifer woodlands of the American Southwest, Great Basinand Colorado Plateau. This biome is characterized by theco-occurrence of eurythermic conifer, woodland conifer,woodland shrub, steppe shrub and steppe forb PFTs. The biomeoccurs in dry conditions near the lower moisture require-ments of conifers, and is associated with colder conditions thanthe xerophytic woods/scrub biome in Europe (Prentice et al.,1996), Africa (Jolly et al., 1998b) and southern California(see discussion above). The open conifer woodland biomecan be identified from both pollen and midden data.

The biomization procedure required some modificationswhen applied to the packrat midden data. In particular, thehighly localized sampling area represented by packrat mid-den assemblages, coupled with the depauperate arborealflora of much of the region, means that they characteristicallycontain relatively few fossil remains from trees and shrubs

Table 5 continued


ts temperate summergreen Amelanchier sp., Amelanchier utahensis, Ceanothus cuneatus, Ceanothus integerrimus, Celtis reticulata, Cercis occidentalis, Cercocarpus sp., Fraxinus anomala, Berberis repens, Ostrya knowltoni, Physocarpus alternans, Prunus sp., Ptelea trifoliata var. pallida, Quercus arizonica × Q. grisea, Quercus gambellii, Quercus grisea, Quercus sp., Rhus aromatica, Rhus aromatica or virens, Rhus diversiloba, Rhus sp., Rhus trilobata, Ribes cf. montigenum, Ribes sp., Rosa sp., Rubus sp., Sambucus neomexicana, Shepherdia sp.

ts1 cool-temperate summergreen Not present

ts2 intermediate-temperate summergreen Robinia neomexicana

ts3 warm-temperate summergreen Prosopis glandulosa

wc woodland conifer Juniperus deppeana, Juniperus erythrocarpa, Juniperus monosperma (cf.), Juniperus occidentalis, Juniperus osteosperma, Juniperus pinchotii, Juniperus scopulorum, Juniperus sp., Parthenium incanum, Parthenium sp., Pinus cembroides, Pinus discolor, Pinus edulis, Pinus edulis/remota, Pinus flexilis, Pinus monophylla, Pinus monophylla × P. edulis

ws woodland shrub Aloysia wrightii, Amelanchier sp., Amelanchier utahensis, Aplopappus cuneatus, Berberis fremontii, Berberis haematocarpa, Berberis repens, Berberis sp., Brickellia watsonii, Cactaceae undet., Ceanothus cuneatus, Ceanothus greggii, Cercocarpus betuloides, Cercocarpus intricatus, Cercocarpus ledifolius, Cercocarpus montanus, Cercocarpus sp., Chamaebatiaria millefolium, Cowania mexicana (cf.), Ericameria cuneata, Eriogonum heermannii, Eriogonum sp., Fendlerella utahensis, Forsellesia nevadensis, Forsellesia pungens, Fraxinus anomala, Garrya flavescens, Haplopappus laricifolius, Haplopappus nanus, Holodiscus dumosus, Holodiscus microphyllus, Jamesia americana, Mammillaria-type, Mammillaria grahamii, Mammillaria sp., Menodora spinescens, Opuntia polyacantha, Opuntia sp., Pediocactus mesae-verdae, Philadelphus microphyllus, Physocarpus alternans, Prunus fasciculata, Prunus sp., Psoralea sp., Ribes cereum, Ribes cf. montigenum, Ribes sp., Ribes velutinum, Rosa cf. stellata, Salvia carnosa, Shepherdia argentea, Shepherdia sp., Symphoricarpos spp., Symphoricarpos longiflorus, Tetradymia axillaris, Tetradymia spinosa, Thamnosma montana

wtc warm-temperate conifer Cupressus arizonicus, Pinus cembroides, Pinus discolor, Torreya californica

wte warm-temperate broadleaved evergreen Arctostaphylos pungens, Arctostaphylos sp., Cercocarpus betuloides, Cercocarpus sp., Quercus chrysolepis, Quercus pungens, Rhamnus crocea, Rhamnus crocea var. Ilicifolia, Umbellularia californica

wte1 cool-temperate broadleaved evergreen Not present

wte2 warm-temperate sclerophyll shrub Berberis sp., Ceanothus greggii, Quercus sp., Quercus turbinella, Quercus undulata, Vauquelinia californica




but an abundance of material from forbs, many of whichmay have been represented by only a few individual plants.If the standard method of calculating affinity scores wasapplied in this situation, it would be extremely difficult togenerate assignments to arboreal biomes. We therefore applieda weighting scheme to the packrat midden assemblages,whereby tree macrofossils were given a weighting of 3,shrub macrofossils were given a weighting of 2 and forbswere given a weighting of 1. These weighting factors weredetermined through experimentation: we tried several schemesand selected the weightings that provided the best biomiza-tion of present-day midden assemblages when comparedwith the mapped modern extents of biomes interpreted fromthe Küchler (1964) map of potential natural vegetation inNorth America. Except for these weighting factors, the calcu-lation of affinity scores and the assignment of packrat middensamples to biomes was done in the standard way.

RESULTS

Predicted vs. observed modern biomes

Pollen data provide the evidence for biome reconstructionsin the more northerly and higher elevation biomes (Fig. 3),whereas packrat middens are largely restricted to the south-western deserts, Great Basin and Colorado Plateau. The pollen-and macrofossil-based reconstruction of modern biomedistributions (Fig. 3) corresponds reasonably well with theobserved patterns in vegetation distribution (Küchler, 1964;Fig. 2). The desert, steppe, conifer forest and taiga vegeta-tion are correctly placed geographically. The predicted andobserved geographical patterns for selected biomes are asfollows.

TundraOnly one pollen site (Little Lake, OR; Worona & Whitlock,1995) is reconstructed as representing this biome and itoccurs within a present-day region of cool conifer forest.This misassignment is due to the high percentages of Alnus,Cyperaceae and Poaceae that occur at this site, presumablydue to historic land use.

TaigaIt is difficult to use pollen data to discriminate among thetaiga, cool conifer forest, cold mixed forest and cool mixedforest biomes in western North America. However, biomiza-tion of the modern pollen data does result in the correctplacement of taiga along the Idaho/Montana border and insouth-central Utah.

Cold deciduous forestThe core-top pollen spectrum from Waits Lake, WA (Macket al., 1978c), in a region of present-day cool conifer forest,is incorrectly assigned to the cold deciduous forest biome.This biome has an identical taxon list with the taiga, coolconifer, cold mixed and cool mixed forest biomes, exceptthat the cold deciduous forest biome lacks Picea and Abies.The Waits Lake surface spectrum is dominated by Pinuspollen with significant representations of Alnus and Larix.The allocation to cold deciduous forest occurs because Abiesis present in a very small amount and Picea is absent.

Cool conifer forestCool conifer forest is correctly reconstructed from pollenspectra in the Pacific Northwest and Sierra Nevada, as wellas in the northern panhandle of Idaho and in adjacentMontana. However, in the Yellowstone (Wyoming) region,Colorado and Utah, modern core-top pollen spectra fromthis biome (as mapped in Fig. 2) are often misassigned to theopen conifer woodland biome. Pinus, the most prolific pollenproducer in western North America, is present in both coolconifer forest and open conifer woodland as is Cupressaceae,which in these regions is represented by the genus Juniperus(another abundant pollen producer). Cool conifer forest includesmany taxa not present in open conifer woodland, including:(1) coniferous forest trees (Abies, Pseudotsuga, Picea);(2) riparian hardwoods with restricted geographical cover-ages and low representations in pollen spectra in these regions(Alnus, Betula, Cornus, Corylus, Salix); and (3) taxa that arepoorly recorded in pollen spectra (Ericaceae, Populus, Shep-herdia canadensis). Our data set indicates that most sites inthese cool conifer forests have less than 1% Pseudotsuga(although this tree is common in these forests), and at most

Biome Code Plant functional types

cold deciduous forest CLDE bs, ec, htaiga TAIG bec, bs, ec, hcold mixed forest CLMX bs, ctc, ec, h, ts1cool conifer forest COCO bec, bs, ctc, ec, h, ts1temperate deciduous forest TEDE bs, ec, h, ts, ts1, ts2, wte1cool mixed forest COMX bec, bs, ctc, ec, h, ts, ts1broadleaved evergreen/warm mixed forest WAMX ec, h, ts, ts3, wtc, wte, wte1xerophytic woods/scrub XERO ec, wc, ws, wte, wte2steppe STEP g, s, sf, ssdesert DESE df, ds, ds2, gtundra TUND aa, g, h, sopen conifer woodland OC ec, sf, ss, wc, ws

Table 6 Assignment of plant functional types (PFTs) to biomes used in the biomization for western North America.




Figure 3 Biomes for 0, 6000, and 18,000 14C yr bp in western North America. The 0 14C yr bp biomes are based on: (1) pollen assemblages from modern core tops from fossil pollen sites and lacustrine surface samples, and (2) packrat middens from the past 1000 radiocarbon years. Pollen sites are represented by a circle, midden sites by a triangle.




only a few percent of Abies and only rare Picea. The under-representation of major taxa in the pollen assemblage makesit difficult to obtain a correct biome assignment. Forexample, Edwards et al. (2000) have shown that it is difficultto correctly predict the extent of the Larix-dominated colddeciduous forests in eastern Siberia because Larix is chronic-ally under-represented in the pollen record. The cool coniferforest samples in the Rocky Mountains have an additionalproblem in that they contain significant amounts of Artemisia,Poaceae and other steppe taxa. These taxa occur in openconifer woodland but not in cool conifer forests. Their occur-rence at high elevation sites in the Rocky Mountains is pre-sumably due to pollen blown upslope from lower elevationhabitats. Collectively, the under-representation of key speciesof the cool conifer forest and the presence of steppe taxa inthe pollen spectra results in the misassignment of samples tothe open conifer woodland biome.

Open conifer woodlandThe distribution of open conifer woodland (Fig. 2) is reason-ably well captured in the biome reconstruction (Fig. 3), althoughpollen-based reconstructions overestimate the extent of thebiome in the central and northern Rocky Mountains. Pollenspectra in modern steppe/grassland environments in easternWashington, western Montana, central Wyoming, north-eastern Colorado and the Great Basin are also mistakenlycategorized as open conifer woodland. This is the reverseof the situation described in the preceding paragraph, ashere the long-distance blow-in of Pinus pollen (e.g. Mack &Bryant, 1974) combined with the local steppe/grassland taxain the pollen spectra, results in a wrong assignment to openconifer woodland. Packrat midden assemblages, with theirspecies-level inventory of plant remains, do not suffer thesame problems as pollen data in representing this biome.

Xerophytic woods/scrubThe single midden-based reconstruction of xerophytic woods/scrub in California is correctly placed. There are no pollenor midden records yet from the larger area of present-dayxerophytic woods/scrub in southern California (Fig. 2).

Steppe/grasslandThere are cases where the biomization of pollen data resultsin an incorrect categorization of steppe or grassland as openconifer woodland due to long-distance transport of coniferpollen. In other cases, such as the Ruby Marshes in north-eastern Nevada (Thompson, 1992), the pollen site itself islocated in steppe, but woodland vegetation occurs within afew kilometres. Here the steppe/grassland and open coniferwoodland biomes form a mosaic, and we do not considerthis to be a failed biomization from a regional perspective.

DesertThe modern hot deserts of the American Southwest andnorth-west Mexico are recorded only in packrat middenassemblages, as this environment is typically too arid for lakes.The present-day desert biome is correctly placed by the middendata, even in a situation such as the Grand Canyon where

pockets of modern desert occur (and are correctly recon-structed from the midden data; Table 3, Fig. 3) but are toosmall to appear on the present-day vegetation map (Fig. 2).

0 14C yr BP summaryAlthough there are minor problems with the assignment ofindividual sites to biomes, it is clear that the biomizationtechnique adequately captures the complex patterns in thevegetation of western North America and thus can be usedto reconstruct past changes in vegetation distribution withsome confidence. However, there are problems, including:(1) the differing taxonomic resolution and spatial coverageof pollen spectra and packrat midden plant assemblagesaffect the results in that middens provide an extremely localbut taxonomically precise view of biomes, whereas pollendata provide a more taxonomically generalized and regionalperspective (especially in mountainous regions where signi-ficant amounts of pollen from one vegetation association canblow into another); (2) present-day land use can skew pollenassemblages and lead to misassignments of surface pollensamples to biomes; (3) the depauperate tree flora can make itdifficult to segregate forest biomes, particularly because treessuch as Picea and Abies occur in both boreal and temperateplant assemblages; and (4) certain pollen types that are keymarkers for specific biomes (e.g. Pseudotsuga, Larix, andAbies) are under-represented in pollen assemblages.

The taiga, cool conifer, cold mixed and cool mixed forestbiomes in western North America are difficult to differentiateon the basis of pollen assemblages. All four share the followingtaxa: Abies, Alnus, Betula, Cornus, Cupressaceae, Ericaceae,Larix, Larix/Pseudotsuga, Myricaceae, Picea, Pinus, Populus,Salix, Shepherdia canadensis and the combined taxon Taxo-diaceae/Cupressaceae/Taxaceae. In their original definitions(Prentice et al., 1992, 1996), the cold mixed forest biome wascharacterized by the presence of the ctc1 PFT (see Table 5for key to abbreviations), whereas cool conifer forests werecharacterized by the bec PFT. In Europe, obligate ctc1 taxa(e.g. Cedrus and Taxus) are not common in the pollen recordsand the distinction between cold mixed and cool coniferforests largely rests on the presence of obligate bec taxa suchas Picea and Pinus (Haploxylon). Undifferentiated Picea isnot confined to ctc1 in western North America because it isalso considered a cool-temperate conifer, and Pinus (Haploxylon)in this region covers a range of environments from subalpineto open conifer woodland. Consequently, for western NorthAmerican pollen records, the cool conifer and cold mixedforest biomes have identical taxon lists and are assigned tothe cool conifer forest biome.

The pollen-based definition of the taiga biome lacks Corylus,Pseudotsuga, Taxaceae, Taxodiaceae and Tsuga, taxa thatare present in the cool conifer, cold mixed and cool mixedforest biomes. Most palynologists have not distinguishedPseudotsuga from Larix, nor Taxaceae and Taxodiaceae fromeach other or from Cupressaceae. Corylus is rarely recorded, andis never abundant, in western pollen records. In practice,then, it is the presence, absence, or abundance of Tsuga pollenthat allows us to distinguish taiga from the other three biomes.Tsuga is present only in the northern Rocky Mountains,




Cascade Range and Sierra Nevada, so it is only in thoseregions that one could potentially differentiate taiga from theother forest biomes. The cool mixed forest biome includesseveral taxa that are not present in the other three forestbiomes: Acer, Ceanothus, Fraxinus, Quercus, Rhamnus. Thesetaxa are usually found in minor amounts in pollen records inwestern North America, and it is probable that in most casesthe cool mixed forest biome cannot be reliably separatedfrom the other three forest biomes.

The mountainous terrain of western North America mayfurther confound attempts to differentiate taiga, cool conifer,cold mixed and cool mixed forest biomes in pollen spectra.Wind-blown pollen can be translocated from one vegetationassociation to another in a short geographical (but perhapslarge elevational) distance. In addition, many of the potentiallydistinctive taxa for these biomes are poor pollen producers (e.g.Acer, Ceanothus, Corylus, Fraxinus and Rhamnus) and may notbe recorded in pollen spectra from their native vegetation.

The taxonomic resolution of packrat midden macro-fossil assemblages makes it possible to segregate the speciescharacteristic of the forest biomes. Unfortunately, packratmiddens are not preserved in wet environments, and althoughcool conifer and cold mixed forest biomes are recognized infossil middens, the vast majority of the midden assemblagesreflect open conifer woodland, steppe and desert biomes.

Western North American biomes at 6000 14C yr BP

The predicted distribution of biomes across western NorthAmerica at 6000 14C yr bp (Fig. 3) is similar to the moderndistribution, in that forests were established in the PacificNorthwest, open conifer woodland occurred in the centralGreat Basin and the south-western deserts had reached theirmodern configuration. However, there are subtle regional dif-ferences between the reconstructed biomes at 6000 14C yr bpand the modern vegetation patterns. Three biomes werereconstructed from pollen data at one site each for 0 14C yr bp(cold deciduous forest, xerophytic woods/scrub, and,incorrectly, tundra), and none of these was reconstructedfrom the 6000 14C yr bp data. The other biomes recon-structed for 0 14C yr bp were present at 6000 14C yr bp inwestern North America and are discussed below.

TaigaTaiga is rare in the 0 14C yr bp reconstruction (Fig. 3) but ispresent at several sites in northern Idaho and adjacenteastern Washington and western Montana at 6000 14C yr bp(Fig. 3). Relatively small changes in pollen percentagesoccurred at the sites where taiga was replaced by cool coniferforest between 6000 and 0 14C yr bp. The key factor appearsto be the arrival, or increase in, Tsuga pollen in these records.Although this genus is present at relatively low levels (1–5%)in the modern spectra, the presence of this key taxon isdecisive in discriminating cool conifer forest from taiga.

At Waits Lake (Mack et al., 1978c), taiga at 6000 14C yr bpwas replaced by cold deciduous forest at 0 14C yr bp. Thesetwo biomes share all PFTs except bec (Tables 4 and 6), whichis represented only by Abies and Picea in western North

America. At Waits Lake, Abies was present at approximately1% in the mid-Holocene and was absent in the modern spec-trum, and this minor difference caused the shift from onebiome to another. At the Lost Trail Pass Bog site in westernMontana (Mehringer et al., 1977) slightly higher levels ofLarix/Pseudotsuga pollen at 6000 14C yr bp resulted in identifi-cation of cool conifer forest, and its decline to modern levelsled the biomization procedure to identify taiga (which lacksctc) from the present day spectrum. Taiga was identified insouthern Utah at both 0 and 6000 14C yr bp (Fig. 3).

Cool conifer forestFossil pollen data indicate that this biome attained its modernextent in the Pacific Northwest prior to 6000 14C yr bp(Fig. 3), and was also present in western Montana. It appar-ently covered more area than today in parts of Colorado andnorth-east Arizona because it was reconstructed for sitesthat were identified as having open conifer woodland at0 14C yr bp (although, as previously discussed, the reconstruc-tions for 0 14C yr bp are probably in error; the sites todayhost a depauperate form of cool conifer forest). For severalof the Colorado pollen records (e.g. Cottonwood Lake andKeystone Iron Bog: Fall, 1985, 1988), Picea and Abies pollengrains were more abundant at 6000 than at 0 14C yr bp, anddeclined as Pinus and Artemisia increased through the lateHolocene. This taxonomic shift from greater ctc pollen taxato increased ec and ss pollen resulted in the change inbiomes reconstructed between the two time periods. Theopposite trend occurred in the Sierra Nevada of California,where open conifer woodland was replaced by cool coniferforest after 6000 14C yr bp at several sites. Here ctc pollentaxa (Abies, Tsuga) arrived or increased between the mid-and late Holocene, while Pinus pollen declined.

Open conifer woodlandIn the Great Basin and Colorado Plateau regions, open coniferwoodland occupied essentially the same area at 6000 14C yr bpthat it occupies today. In south-eastern Idaho and adjacentWyoming, steppe was present at a few sites occupied today bywoodland. In the 0 14C yr bp reconstruction (Fig. 3), depau-perate cool conifer forests in the Rocky Mountains wereincorrectly reconstructed as open conifer woodland. This isprobably also the case in the same region for 6000 14C yr bp.

Steppe/grasslandPollen data indicate that this biome had the same geographicalrange at 6000 14C yr bp as it has today in the Great Basin,eastern Washington, Wyoming and on the Great Plains.

DesertBiomization of packrat midden plant assemblages indicatethat the south-western deserts had attained their modernnorthern limits by 6000 14C yr bp.

6000 14C yr BP summaryPollen and packrat midden data indicate that the mid-Holocene biomes of western North America were similar tothose of the present day. Cool-temperate conifer (ctc) trees




were more abundant than today in pollen records in theColorado Rockies, but less abundant in records in the interiorof the Pacific Northwest and in the Sierra Nevada. Smallshifts in the percentages of these trees between the two timeperiods caused apparent changes in biomes through time,although the overall region covered by conifer and mixedforests remained essentially the same between the two timeperiods. Steppe/grassland and desert biomes at 6000 14C yr bpoccupied largely the same areas as they do today.

Western North American biomes at 18,000 14C yr BP

While the environments of western North America appear tohave been quite similar at 0 and 6000 14C yr bp, they wereradically different at the last glacial maximum (LGM,18,000 14C yr bp). During the LGM, the Laurentide Ice Sheetcovered most of what is now Canada and montane glacierswere present in many of the western mountains. Large lakeswere present across the Great Basin and in parts of theSouthwest (e.g. Thompson et al., 1993). The reconstructedvegetation patterns were also very different (Fig. 3). Thetaiga and desert biomes were apparently absent. The remain-ing biomes are discussed below:

Cool conifer, cold mixed, and cold deciduous forestsIn the Pacific Northwest, biome reconstructions from pollendata indicate that the areas of modern conifer and mixedforests were largely occupied by steppe (although bec ele-ments were present) and perhaps even tundra at the LGM(Barnosky et al., 1987). However, cool conifer forests werepresent in western Oregon. This biome, along with coldmixed and cold deciduous forest, was identified from plantmacrofossils in packrat middens from various elevations inthe eastern Grand Canyon (Fig. 3).

Open conifer woodlandPollen and packrat midden data both indicate that thisbiome had a greatly expanded range (relative to today) atthe LGM, suggesting that the vegetation at that time wasvery open. The open conifer woodland biome occurred withinits current range in the Great Basin and Colorado Plateau,and was also present in the modern desert regions of theSouthwest. Pollen records indicate its presence in Coloradoand Wyoming, and there is little evidence that these are mis-assigned cool conifer forests as were the Holocene sites inthese states. Cool-temperate conifers (ctc) are largely absentfrom macrofossil records in the interior north of the GrandCanyon, so essential elements of the cool conifer forests appearto have been missing. In the Great Basin and surroundingareas, the LGM open conifer woodlands were characterizedby subalpine pines and by prostrate juniper with steppe plants.These woodlands were comprised of woodland conifers (pinyonpines and woodland junipers) in association with steppe andcold-tolerant desert elements in those areas that are deserttoday.

Xerophytic woods/scrubWarm-temperate sclerophyll shrubs (wte2) were recovered

from late Pleistocene packrat middens on the western side ofthe southern Sierra Nevada in California, near sites wherethese plants grow today. Warm-temperate sclerophyll shrubshave not been recovered from LGM sites elsewhere in westernNorth America.

TundraThis biome was reconstructed for one site in westernWashington, in a region where other sites were reconstructedas steppe (Fig. 3). The presence of lemming and reindeerfossils in southern Idaho and geomorphic evidence of frostwedges in Wyoming (Thompson et al., 1993 and referencestherein) suggests that this biome may have been more wide-spread in the northern interior of western North Americathan indicated by the currently available botanical data.

Steppe/grasslandSteppe elements were present in LGM vegetation acrosswestern North America during LGM time. However,eurythermic conifers were present (at least regionally) in thepresent domain of steppe in the Great Basin and surround-ing region, so pollen and macrofossil data from this regionare classified as open conifer woodland (Fig. 3). Steppe isreconstructed for the LGM for the presently tree-coveredwestern Washington.

Climatic implications of changes in biomes

The correspondence of biomes interpreted from the Küchler(1964) map of potential natural vegetation (Fig. 2, Table 1)with climatic parameters (MTCO: mean temperature of thecoldest month; GDD5: growing degree days on a 5 °C base;and α: a moisture index ranging from 0 = extremely dry to1 = extremely wet based on Thornthwaite & Mather, 1955,1957) are shown in Figs 4 and 5 and in Table 7. These climaticdata were obtained by using a 25-km equal-area grid ofpresent-day climate values (Bartlein et al., 1994; Thompsonet al., 1999a, 1999b) and assigning each grid point in westernNorth America to a biome based on the Küchler (1964) map.

Tundra is restricted to mountain tops and occurs whereMTCO is less than –2.5 °C, GDD5 is less than 1000 and α isgenerally above 0.75. The GDD5 upper limit for tundra seemshigh when compared to other regions (cf. Prentice et al., 1992);this could reflect the difficulty in estimating present-dayclimate at high elevations from the nearest low-elevation sites.However, preliminary analysis of tundra in Alaska suggeststhat tundra in that region commonly occurs with GDD5

values as high as 500–750. The cool conifer forest biome isthe most widespread forest vegetation in the western UnitedStates and occurs under a variety of climatic conditions(Table 7). It can occur under somewhat colder winter tem-peratures, and generally requires more moisture, than openconifer woodland. Open conifer woodland is comprised ofeurythermic conifers and steppe plants and can survive undercolder conditions than xerophytic woods/scrub and drier andwarmer climates than cool conifer forest. Xerophytic woods/scrub vegetation cannot survive freezing temperatures and,as its name implies, grows under warm and dry conditions.




Figure 4 Bivariate plots of the estimated modern climatic ranges of selected vegetation categories shown in Figure 2.




Grassland and steppe are not distinguished as separatebiomes in our reconstructions based on pollen and macro-fossil data. However, they are segregated on the Küchler (1964)map (Fig. 2), and Figs 4 and 5 illustrate their climatic dif-ferences. Grassland occurs on the Great Plains, in parts ofthe South-west, in the Central Valley of California and in theinterior Pacific North-west. Steppe is widespread across thesemiarid interior of the western United States from the GreatPlains to the lee of the Sierra Nevada and Cascade Ranges.Grassland survives under a wide variety of winter tempera-tures (MTCO –15 to +10 °C), and is associated with GDD5 of2000–4500 and α of 0.4–0.7. Steppe overlaps with grasslandin its climatic tolerances, but can live in drier environments (αas low as 0.15), has lower GDD5 requirements (GDD5 as lowas 1000) and does not occur under warm winter conditions(MTCO is below 0 °C). Desert occurs in the Southwest andin south-eastern-most California. It has lower moisturerequirements than steppe and grassland (α between 0.05 and0.4), higher GDD5 requirements (3000–6000) and MTCOabove freezing.

The climates associated with our 0 14C yr bp reconstructedbiomes are illustrated in Fig. 6 (see also Table 7b). Wherewe do not have precise elevational data for a site, we associ-ated the climate of the closest grid point on our 25-km gridwith the pollen or packrat midden site. Climatic ‘envelopes’for the Küchler-based biomes were visually interpreted fromFig. 4 and are included on Fig. 6 to allow comparisons ofthe climates of the Küchler-based biomes and the recon-structed biomes. The left-hand panels of Fig. 6 illustrate the

reconstructed climates for the cool conifer forest localities.Nearly all of the sites identified as belonging to this biomefall within the climate envelope from the Küchler-basedbiome, and thus it appears that the biomization assigns thesesurface pollen samples correctly.

The central panels of Fig. 6 plot the climates for the 0 14Cyr bp sites that were reconstructed as having open coniferwoodland vegetation. In these panels the climatic envelopes(from Fig. 4) for this biome are shown, along with those forcool conifer forest. Many sites in modern cool conifer forestin the northern Rocky Mountains were incorrectly placed inopen conifer woodland by the biomization procedure. Thedata in Fig. 6 show these sites occurring within the moisturerequirements of the cool conifer forest biome (which exceedthose of open conifer woodland) but at the cold end of thecool conifer forests. Inspection of these data indicate that thecool conifer forest sites that are misidentified as open coniferwoodland occur near the lower limits of the forest in relat-ively dry regions of north-eastern Nevada, central Utah andwestern Colorado. At the cold end of its tolerance many ofthe ctc trees are absent from this biome, and pollen spectraconverge on those of the open conifer woodland.

The right-hand panels of Fig. 6 illustrate the apparentmodern climates of sites reconstructed as steppe/grassland ordesert biomes at 0 14C yr bp. In this plot the steppe/grasslandand desert samples adhere closely to the freezing-line divideapparent in the Küchler-based data. However, sites withinboth biomes appear to exceed the permissible values for themoisture index. Here the assignment of nearest grid-point

Table 7 Climatic tolerances of biomes in western North America, based on (a) present-day potential natural vegetation and (b) present-day pollen and plant macrofossil assemblages. MTCO temperatures are approximated to the nearest 2.5 °C; GDD5 values to the nearest 500 growing-degree days; and α values to the nearest 0.05. The values in (a) were obtained through visual inspection and interpretation of Figs 5 and 6; the values in (b) through visual inspection and interpretation of Fig. 5. Cold deciduous forests and xerophytic woods/scrub are omitted from (b) because they only occur once.

(a)

(b)

BiomeMTCO min.

MTCO max.

GDD5 min.

GDD5 max.

α min.

α max.

cool conifer forest –12.5° 5.0° 500 2500 0.45 0.95xerophytic woods/scrub 2.5° 12.5° 2000 5000 0.30 0.70grassland –15.0° 7.5° 1500 5000 0.35 0.70steppe –10.0° 0.0° 1000 3000 0.15 0.55desert 0.0° 12.5° 3000 6500 0.05 0.40tundra –12.5° –2.5° <500 1000 0.75 1.00open conifer woodland –10.0° 5.0° 1000 3500 0.20 0.65

BiomeMTCO min.

MTCO max.

GDD5 min.

GDD5 max.

α min.

α max.

taiga –10.0° –7.5° 500 500 0.75 0.85cool conifer forest –7.5° 5.0° 500 2500 0.60 1.00grassland/steppe –10.0° 0.0° 500 2000 0.40 1.00desert 0.0° 7.5° 2000 6500 0.05 0.45open conifer woodland –10.0° 5.0° 500 3500 0.20 0.70




Figure 5 Histograms illustrating the univariate estimated modern climatic ranges of selected vegetation categories shown in Figure 2.

Figure 6 Bivariate plots of the estimated modern climatic ranges of the western North American biomes mapped for 0 14C yr bp in Figure 3. Pollen sites are represented by a circle, midden sites by a triangle.




climates may be causing difficulties, as in this region of highrelief we may be incorrectly using precipitation values fromhigher elevation sites.

Vegetation and climate of western North America at 6000 14C yr BP

The presence of cool conifer forest in the maritime region ofthe Pacific Northwest at 6000 14C yr bp suggests that relat-ively little climatic change occurred there between the mid-Holocene and the present. In the interior part of this region,the shift from taiga at 6000 14C yr bp to cool conifer and colddeciduous forests at 0 14C yr bp may reflect a shift to milderclimates in the late Holocene, with modern warmer wintersperhaps being the key factor. The reconstruction of coolconifer forests at several sites in Colorado and north-easternArizona that are characterized as open conifer woodland orsteppe in the modern reconstruction indicates that condi-tions were wetter than present at 6000 14C yr bp. In contrast,steppe was more extensive in the northern Great Basin at6000 14C yr bp compared to present, and sites in the SierraNevada that are in cool conifer forest today were in openconifer woodland during the mid-Holocene. These shifts invegetation imply drier than modern conditions in the north-ern Great Basin and Sierra Nevada at 6000 14C yr bp. Asnoted by Williams et al. (2000), warmer and drier climatesat 6000 14C yr bp are also reflected in the contraction offorests and expansion of grassland in the upper Midwest.

The contrast between drier conditions in these regions andwetter conditions in the southern Rocky Mountains has beennoted in previous reconstructions of the mid-Holocene climatesof western North America (e.g. Thompson et al., 1993), and,as discussed in that paper, appears to reflect an enhancedsummer monsoon circulation in the Southwest coupled withwarmer than modern conditions across most of westernNorth America (as illustrated in Fig. 1, the area of relativelymoist mid-Holocene climates lies within the modern track ofthe summer monsoon). Despite this proposed augmentationof the summer monsoon, the biome reconstructions implylittle discernible difference between 6000 and 0 14C yr bp inthe deserts of the Southwest.

Vegetation and climate of western North America at 18,000 14C yr BP

The occurrence of steppe and tundra at the LGM in now-maritime western Washington indicates conditions both colderand drier than today (Barnosky et al., 1987). Cold climatesassociated with steppe are also inferred for the northern GreatPlains near the Laurentide Ice Sheet (Williams et al., 2000).The presence of cool conifer forest in western Oregon at18,000 14C yr bp indicates that there was a strong tempera-ture and moisture gradient along the coast of the PacificNorthwest.

Open conifer woodland was present at most of the LGMsites from Wyoming south to the Mexican border, indicatingopen vegetation with MTCO remaining above –10 °C (Fig. 4).In the Great Basin and adjacent regions, this woodland

included xerophytic subalpine conifers instead of thecurrent dominance of woodland conifers, suggesting that theclimate was at the cold and dry end of the range of openconifer woodland. In contrast, this biome in the present-daysouth-western deserts included pinyon pine and woodlandjuniper, suggesting that the climate was cool (not cold) andwet relative to today. Open conifer woodland also occurredin the south-eastern United States during the LGM (Williamset al., 2000), and it is possible that it is favoured by the lowerlevels of atmospheric carbon dioxide that occurred in thelate Pleistocene (as may have occurred with dry-tropicalbiomes: Jolly & Haxeltine, 1997).

Overall, the distributions of biomes in western NorthAmerica at 18,000 14C yr bp are consistent with earlierpalaeoclimatic reconstructions (Thompson et al., 1993) andmodelling (Kutzbach et al., 1993, 1998; Thompson et al.,1993). Key factors of the LGM climate that differed signific-antly from today include: (1) a southward displacement ofthe westerlies, and their enhanced persistence through theyear; (2) virtual elimination of the present summer monsooncirculation; and (3) a strong temperature gradient through theinterior region, with very cold temperatures to the north andmild conditions along the Mexican border.

DISCUSSION AND CONCLUSIONS

The biomization method

Pollen and packrat midden data appear to provide realisticreconstructions of present-day biomes in western NorthAmerica. However, to achieve these results the weightinghad to be increased for trees (3x) and shrubs (2x) to be ableto reconstruct the woodland, forest and desert biomes. Ourability to differentiate among taiga, cool conifer forest, colddeciduous forest and cold mixed forest from pollen data islimited due to a depauperate flora and taxonomic overlapamong the PFTs. In addition, our ability to discriminatebetween cool conifer forest (at the cold end of its range) andopen conifer woodland appears to be limited by the very lowrepresentations of key ctc trees (especially Pseudotsuga) andby blow-in of pollen from steppe plants in regions of highrelief.

The new biome, open conifer woodland, provides a gooddescription of both the modern and late Pleistocene vegeta-tion of the semiarid interior of western North America. Itlikely occurs in other regions of the world. For example, thevegetation of the colder, drier parts of the circum-Mediterra-nean region is also characterized by an intimate mix of conifersand steppe vegetation (e.g. the juniper woodlands of interiorSpain and Greece: Polunin & Walters, 1985). However, vegeta-tion types that are apparently analogous to our open coniferwoodland biome occupy rather limited areas in Europe andthe Middle East today. This may explain why they were notclassified as a separate biome in the original biomization ofEurope (Prentice et al., 1996) and have not been recognizedin subsequent biomizations (e.g. Jolly et al., 1998b). Giventhat juniper woodlands may have been more widely distributedin Eurasia during other periods of the Late Quaternary, it




would be useful to re-examine the vegetation records fromthese other regions in the light of our recognition of openconifer woodlands as a distinct biome.

Single examples of plant macrofossils from a few siteshave been used to supplement pollen data in biomizations ofother regions (e.g. northern Russia: Texier et al., 1997; Africa:Jolly et al., 1998b). However, the biomization procedure hasnever been applied to assemblages of plant macrofossils orto an extensive plant macrofossil data set encompassing a rangeof different biomes. Our reconstructions show that identicalbiome reconstructions are obtained using plant macrofossilsand pollen spectra, when both types of data are availablefrom the same region. Specifically, the changing extent of openconifer woodland since the LGM is clearly documented fromboth pollen and plant macrofossil sites. The comparabilityof biome reconstructions from the two data sources opensup new possibilities for the systematic mapping of vegetationchanges during the Late Quaternary in more arid regionswhere pollen data are sparse. Although packrat middens areunique to western North America, similar deposits have beenfound in, e.g. the Middle East (Fall et al., 1990), South Africa(Scott, 1990) and Australia (Nelson et al., 1990), as well asin South America. The systematic exploitation of the macro-fossil records from these deposits could substantially enhanceour understanding of the Late Quaternary dynamics of aridregions.

Pollen and plant macrofossils record vegetation at ratherdifferent spatial scales: pollen data provide regional recon-structions of vegetation changes at a coarse level of taxo-nomic precision, while macrofossil data provide records ofmore local changes based on species-level identifications.Potentially, these differences in spatial resolution could beexploited in several ways. For example, macrofossil data couldbe used to determine whether specific taxa represented in apollen record were locally present or were derived by long-distance transport. Takahara et al. (2000) have shown thatthe upslope transport of pollen from extra-local vegetationleads to incorrect biome reconstructions for nearly half ofthe pollen records from Japan. The use of plant macrofossildata to establish local presence, in conjunction with pollendata, could therefore substantially improve biome recon-structions in mountainous regions. In cases where differentspecies within a genus are characteristic of different biomes,such as is the case with different species of Pinus, Abies andPicea in western North America, it may also be possible toexploit the higher taxonomic resolution of plant macrofossildata to guide biomizations at pollen sites (Jolly et al., 1998b;Takahara et al., 2000).

Changes in the distribution of PFTs in western North America since the last glacial maximum

Plant species have responded to changes in climate andatmospheric chemistry in individualistic fashions over thetime since the LGM (Thompson, 1988). We have exploredaspects of this history in regard to changes in biomes. Aspectsof the vegetation history of western North America can bealso seen in the changing affinity scores of PFTs. For example,

boreal evergreen conifers (bec) were present across most ofthe region at 18,000 14C yr bp (Fig. 7), except for the present-day low elevation deserts of the Southwest. By 6000 14C yr bpthis PFT attained its modern range in the Rocky Mountainsand Pacific Northwest, and lost much of its late Pleistocenehabitat in the Southwest. Woodland conifers (wc) alsochanged their distributions through time: they lived in themodern south-western deserts at 18,000 14C yr bp and dis-persed northward and upward in elevation to near theirmodern limits by 6000 14C yr bp (as they lost their late Pleis-tocene habitats in the south-western deserts).

The steppe shrub PFT (ss) was important across its modernrange at 18,000 14C yr bp, and was also present in the PacificNorthwest and the south-western deserts (Fig. 8). Thisimplies that this complex of species has been a major constituentof western vegetation under both late Pleistocene andHolocene climatic regimes. In contrast, taxa from the desertshrub or succulent PFT (ds) were minor components of westernvegetation at the LGM, and have expanded into their mod-ern range during the Holocene. Collectively the histories ofthe four PFTs in Figs 7 and 8 illustrate differing patterns ofPFT response to climatic change. Some, such as the steppeshrub PFT, have maintained near-modern geographical (althoughperhaps not elevational) ranges since the LGM, whereas othershave modified their geographical ranges to greater or lesserextents.

Vegetation and climate changes in western North America in the Late Quaternary

The vegetation reconstructed through the objective biomiza-tion method in western North America is in good agree-ment with more informal reconstructions for 18,000, 6000and 0 14C yr bp (e.g. Thompson et al., 1993). The biomizationprocedure provides a uniform method of describing vegeta-tion changes through time, as well as providing a potentialmeans to identify underlying climatic causes. Geological andbiological data indicate that the present-day climatic patterns(Fig. 1) of western North America were greatly changed atthe LGM. For example, the present-day climate of westernWashington State in the Pacific Northwest is characterizedby high levels of precipitation and mild temperatures. Thiswas apparently not true at 18,000 14C yr bp; instead glacial,faunal and vegetational data suggest that this region experi-enced dry climates with cold winters (Barnosky et al., 1987;Thompson et al., 1993). In contrast, the desert regions ofthe Southwestern United States today have hot and dryclimates, whereas palaeolacustrine, faunal and vegetationaldata indicate that the climate was relatively cool and moistat 18,000 14C yr bp (Street-Perrott et al., 1989; Thompsonet al., 1993), apparently due to a southerly displacement (relat-ive to today) of the westerlies. The biomes reconstructed forboth of the regions at the LGM fit well within this framework,with the cold dry climates of the Pacific Northwest beingassociated with steppe and tundra, and the cool moist climatesin the Southwest with open conifer woodlands (Fig. 3). Thereconstructed biomes for the mid-Holocene are also wellaligned with previous palaeoclimatic syntheses. Particularly




Figure 7 Affinity scores for selected plant functional types in western North America for 18,000, 6000, and 14C yr bp. The upper series of panels illustrates the occurrence of boreal evergreen conifers including species of Picea, Abies and Larix. The lower series illustrates the past occurrence of species of pinyon pines and woodland junipers (woodland conifers). Pollen sites are represented by a circle, midden sites by a triangle.




Figure 8 Affinity scores for selected plant functional types in western North America for 18,000, 6000, and 0 14C yr bp. The upper series of panels illustrates the occurrence of steppe plants, such as Artemisia, whereas the lower series illustrates shrub and succulent species that are now largely confined in hot deserts. Pollen sites are represented by a circle, midden sites by a triangle.




noteworthy are the contrasting changes in biomes in thesouthern Rocky Mountains and Sierra Nevada. The formerarea apparently fell within a region of greater-than-modernsummer monsoonal precipitation at 6000 14C yr bp (Fall,1988; Thompson et al., 1993), while the latter area experi-enced greater-than-present drought at this time (Anderson,1987; Thompson et al., 1993). The reconstructed biomesreflect this pattern, with the Rocky Mountains having moresites covered with cool conifer forest at 6000 14C yr bp thantoday, while several present-day cool conifer forest sites inthe Sierra Nevada were open conifer woodland in the mid-Holocene (Fig. 3).

ACKNOWLEDGMENTS

This paper is a contribution to BIOME 6000. Sandy Harrisongraciously provided editorial advice and motivation. Ourassignment of pollen taxa to PFTs was made in consultationwith Pat Anderson, Pat Bartlein, Mary Edwards, Eric Grimm,Steve Jackson, Colin Prentice, Pierre Richard, Tom Webb,Cathy Whitlock and Jack Williams. We thank Jack Williamsfor the software used in the biomization procedure, and TomWebb, Dan Muhs and Jack Williams for detailed and con-structive reviews. We thank Laura Strickland for her help indata preparation. Silvana Schott provided a detailed technicaledit of the manuscript. We are grateful to Colin Prentice foradvice on the application of the biomization procedures towestern North America and for comments on an earlier draftof the manuscript.

REFERENCES

Anderson, R. S. (1987) Late-Quaternary environments of theSierra Nevada, California. PhD Thesis, University of Arizona.

Barnosky, C. W., Anderson, P. M. & Bartlein, P. J. (1987) Thenorthwestern U.S. during deglaciation: vegetational historyand paleoclimatic implications. North America and adjacentoceans during the last deglaciation (ed. by W. F. Ruddimanand H. E. Wright Jr), The Geology of North America, Vol. K-3,pp. 289–322. Geological Society of America, Boulder, Colorado.

Bartlein, P. J., Lipsitz, B. B. & Thompson, R. S. (1994) Modernclimatic data for paleoenvironmental interpretations. AmericanQuaternary Association Program and Abstracts of the 13th BiennialMeeting, 19–22 June, p. 197. University of Minnesota, Minneapolis.

Benson, L. (1982) The cacti of the United States and Canada.Stanford University Press, Stanford.

Benson, L. & Darrow, R. A. (1981) Trees and shrubs of theSouthwestern Deserts. University of Arizona Press, Tucson.

Betancourt, J. L., Van Devender, T. R. & Martin, P. S. (1990)Fossil packrat middens: the last 40,000 years of biotic change.University of Arizona Press, Tucson.

Edwards, M. E., Anderson, P. M., Brubaker, L. B., Ager, T.,Andreev, A. A., Bigelow, N. H., Cwynar, L. C., Eisner, W. R.,Harrison, S. P., Hu, F.-S., Jolly, D., Lozhkin, A. V., MacDonald,G. M., Mock, C. J., Ritchie, J. C., Sher, A. V., Spear, R. W.,Williams, J. & Yu, G. (2000) Pollen-based biomes for Beringia18,000, 6000 and 0 14C yr bp. Journal of Biogeography, 27,521–554.

Elenga, H., Peyron, O., Bonnefille, R., Prentice, I. C., Jolly, D.,

Cheddadi, R., Guiot, J., Andrieu, V., Bottema, S., Buchet, G.,de Beaulieu, J. L., Hamilton, A. C., Maley, J., Marchant, R.,Perez-Obiol, R., Reille, M., Riollet, G., Scott, L., Straka, H.,Taylor, D., Van Campo, E., Vincens, A., Laarif, F. & Jonson, H.(2000) Pollen-based biome reconstruction for southern Europeand Africa 18, 000 yr bp. Journal of Biogeography, 27, 621–634.

Fall, P. L. (1985) Holocene dynamics of the subalpine forest incentral Colorado. American Association of Stratigraphic Paly-nologists, Contributions Series, 16, 31–46.

Fall, P. L. (1988) Vegetation dynamics in the southern RockyMountains: Late Pleistocene and Holocene timberline fluctu-ations. PhD Thesis, University of Arizona, Tucson.

Fall, P. L., Lindquist, C. A. & Falconer, S. E. (1990) Fossil hyraxmiddens from the Middle East: a record of paleovegetationand human disturbance. Fossil packrat middens: the last40,000 years of biotic change (ed. by J. L. Betancourt, T. R.Van Devender and P. S. Martin), pp. 408–427. University ofArizona Press, Tucson.

Harrison, S. P., Kutzbach, J. E., Prentice, I. C., Behling, P. &Sykes, M. T. (1995) The reponse of northern hemisphereextratropical climate and vegetation to orbitally-inducedchanges in insolation during the last interglacial: results ofatmospheric general circulation model and biome simula-tions. Quaternary Research, 43, 174–184.

Jolly, D. & Haxeltine, A. (1997) Effect of low glacial atmo-spheric CO2 on tropical African montane vegetation. Science,276, 786–788.

Jolly, D., Harrison, S. P., Damnati, B. & Bonnefille, R. (1998a)Simulated climate and biomes of Africa during the LateQuaternary: comparison with pollen and lake status data. LateQuaternary climates: data syntheses and model experiments(ed. by T. Webb III). Quaternary Science Reviews, 17, 629–657.

Jolly, D., Prentice, I. C., Bonnefille, R., Ballouche, A., Bengo, M.,Brenac, P., Buchet, G., Burney, D., Cazet, J.-P., Cheddadi, R.,Edorh, T., Elenga, H., Elmoutaki, S., Guiot, J., Laarif, F.,Lamb, H., Lezine, A.-M., Maley, J., Mbenza, M., Peyron, O.,Reille, M., Reynaud-Farrera, I., Riollet, G., Ritchie, J. C.,Roche, E., Scott, L., Ssemmanda, I., Straka, H., Umer, M.,Van Campo, E., Vilimumbalo, S., Vincens, A. & Waller, M.(1998b) Biome reconstruction from pollen and plant macro-fossil data for Africa and the Arabian peninsula at 0 and 6 ka.Journal of Biogeography, 25, 1007–1027.

Joussaume, S., Taylor, K. E., Braconnot, P., Mitchell, J. F. B.,Kutzbach, J. E., Harrison, S. P., Prentice, I. C., Broccoli, A. J.,Abe-Ouchi, A., Bartlein, P. J., Bonfils, C., Dong, B., Guiot, J.,Herterich, K., Hewitt, C. D., Jolly, D., Kim, J. W., Kislov, A.,Kitoh, A., Loutre, M. F., Masson, V., McAvaney, B., McFarlane, N.,de Noblet, N., Peltier, W. R., Peterschmitt, J. Y., Pollard, D.,Rind, D., Royer, J. F., Schlesinger, M. E., Syktus, J., Thompson, S.,Valdes, P., Vettoretti, G., Webb, R. S. & Wyputta, U. (1998)Monsoon changes for 6000 years ago: results of 18 simulationsfrom the Paleoclimate Modeling Intercomparison Project (PMIP).Geophysical Research Letters, 26, 859–862.

Kearney, T. H. & Peebles, R. H. (1960) Arizona flora. Universityof California Press, Berkeley.

Küchler, A. W. (1964) Manual to accompany the map PotentialNatural Vegetation of the conterminous United States. Ameri-can Geographical Society Special Publication, 36, 1–16.

Kutzbach, J. E., Gallimore, R., Harrison, S. P., Behling, P., Selin,R. & Laarif, F. (1998) Climate and biome simulations for thepast 21,000 years. Late Quaternary climates: data syntheses




and model experiments (ed. by T. Webb III). QuaternaryScience Reviews, 17, 473–506.

Kutzbach, J. E., Guetter, P. J., Behling, P. J. & Selin, R. (1993)Simulated climatic changes: results of the COHMAP climate-model experiments. Global climates since the last glacialmaxium (ed. by H. E. Wright Jr, J. E. Kutzbach, T. Webb III,W. F. Ruddiman, F. A. Street-Perrott and P. J. Bartlein),pp. 24–93. University of Minnesota Press, Minneapolis.

Little, E. L., Jr (1971) Atlas of United States trees, 1. Conifersand important hardwoods. Miscellaneous Publication 1146.U.S. Department of Agriculture, Forest Service. U.S. GovernmentPrinting office, Washington, D.C.

Little, E. L., Jr (1976) Atlas of United States trees, 3. Minor westernhardwoods. Miscellaneous Publication 1314. U.S. Departmentof Agriculture, Forest Service. U.S. Government Printingoffice, Washington, D.C.

Little, E. L., Jr (1977) Atlas of United States trees, 4. Minoreastern hardwoods. Miscellaneous Publication 1342. U.S.Department of Agriculture, Forest Service. U.S. GovernmentPrinting office, Washington, D.C.

Mack, R. N. & Bryant, V. M., Jr (1974) Modern pollen spectrafrom the Columbia Basin, Washington. Northwest Science,45, 183–194.

Mack, R. N., Rutter, N. W., Valastro, S. & Bryant, V. M., Jr(1978c) Late Quaternary vegetation history at Waits Lake,Colville River Valley, Washington. Botanical Gazette, 139,499–506.

Mehringer, P. J., Jr, Arno, S. F. & Petersen, K. L. (1977) Postglacialhistory of Lost Trail Pass Bog, Bitterroot Mountains, Montana.Arctic and Alpine Research, 9, 345–368.

Neilson, R. P., Prentice, I. C. & Smith, B. (1998) Simulatedchanges in vegetation distribution under global warming.Regional impacts of climate change: an assessment of vulner-ability (ed. by R. T. Watson, M. C. Zinyowera, R. H. Moss &D. J. Dokken), pp. 439–456. Cambridge University Press,Cambridge.

Nelson, D. J., Webb, R. H. & Long, A. (1990) Analysis of stick-nest rat (Leporillus: Muridae) middens from central Australia.Fossil packrat middens: the last 40,000 years of biotic change(ed. by J. L. Betancourt, T. R. Van Devender and P. S. Martin),pp. 428–434. University of Arizona Press,Tucson.

Polunin, O. & Walters, M. (1985) A guide to the vegetation ofBritain and Europe. Oxford University Press, Oxford.

Prentice, I. C. & Webb III, T. (1998) BIOME 6000: recon-structing global mid-Holocene vegetation patterns frompalaeoecological records. Journal of Biogeography, 25, 997–1005.

Prentice, I. C., Cramer, W., Harrison, S. P., Leemans, R., Monserud,R. A. & Solomon, A. M. (1992) A global biome model based onplant physiology and dominance, soil properties and climate.Journal of Biogeography, 19, 117–134.

Prentice, I. C., Guiot, J., Huntley, B., Jolly, D. & Cheddadi, R.(1996) Reconstructing biomes from palaeoecological data: ageneral method and its application to European pollen data at0 and 6 ka. Climate Dynamics, 12, 185–194.

Scott, L. (1990) Hyrax (Procaviidae) and dassie rat (Petromuri-dae) middens in paleoenvironmental studies in Africa. Fossilpackrat middens: the last 40,000 years of biotic change(ed. by J. L. Betancourt, T. R. Van Devender and P. S. Martin),pp. 398–407. University of Arizona Press, Tucson.

Street-Perrott, F. A., Marchand, D. S., Roberts, N. & Harrison, S. P.

(1989) Global lake-level variations from 18,000 to 0 years ago:a palaeoclimatic analysis. Technical Report. U.S. DOE/ER/60304–H1 TR046. U.S. Department of Energy, Washington DC.

Takahara, H., Sugita, S., Harrison, S. P., Miyoshi, N., Morita, Y.& Uchiyama, T. (2000) Pollen-based reconstructions ofJapanese biomes at 0, 6000 and 18,000 14C yr bp. Journal ofBiogeography, 27, 665–683.

Tarasov, P. E., Webb, T., III, Andreev, A. A., Afanas’eva, N. B.,Berezina, N. A., Bezusko, L. G., Blyakharchuk, T. A.,Bolikhovskaya, N. S., Cheddadi, R., Chernavskaya, M. M.,Chernova, G. M., Dorofeyuk, N. I., Dirksen, V. G., Elina, G. A.,Filmonova, L. V., Glebov, F. Z., Guiot, J., Gunova, V. S., Har-rison, S. P., Jolly, D., Khomutova, V. I., Kvavadze, E. V., Osi-pova, I. M., Panova, N. K., Prentice, I. C., Saarse, L.,Sevastyanov, D. V., Volkova, V. S. & Zernitskaya, V. P. (1998)Present-day and mid-Holocene biomes reconstructed frompollen plant macrofossil data from the Former Soviet Unionand Mongolia. Journal of Biogeography, 25, 1029–1053.

Texier, D., de Noblet, N., Harrison, S. P., Haxeltine, A., Jous-saume, S., Jolly, D., Laarif, F., Prentice, I. C. & Tarasov, P.(1997) Quantifying the role of biosphere-atmosphere feed-backs in climate change: a coupled model simulation for 6000yr b.p. & comparison with palaeodata for northern Eurasiaand northern Africa. Climate Dynamics, 13, 865–881.

Thompson, R. S. (1988) Western North America—vegetationdynamics in the western United States: modes of response toclimatic fluctuations. Vegetation history (ed. by B. Huntleyand T. Webb III), pp. 415–458. Kluwer Academic Publishers,Dordrecht.

Thompson, R. S. (1992) Late Quaternary environments in RubyValley, Nevada. Quaternary Research, 37, 1–15.

Thompson, R. S., Anderson, K. H. & Bartlein, P. J. (1999a) Atlasof relations between climatic parameters and the distributions ofimportant trees and shrubs in North America—introductionand conifers. US Geological Survey Professional Paper, 1650-A, 1–269. US Geological Survey Press, Denver.

Thompson, R. S., Anderson, K. H. & Bartlein, P. J. (1999b) Atlasof relations between climatic parameters and the distributionsof important trees and shrubs in North America—hardwoods.US Geological Survey Professional Paper, 1650-B, 1–423. USGeological Survey Press, Denver, CO.

Thompson, R. S., Whitlock, C., Bartlein, P. J., Harrison, S. P. &Spaulding, W. G. (1993) Climatic changes in the western UnitedStates since 18,000 yr b.p. Global climates since the last glacialmaximum (ed. by H. E. Wright Jr, J. E. Kutzbach, T. Webb III,W. F. Ruddiman, F. A. Street-Perrott and P. J. Bartlein),pp. 468–513. University of Minnesota Press, Minneapolis.

Thornthwaite, C. W. & Mather, J. R. (1955) The water balance.Publications in Climatology, 8, 1–104.

Thornthwaite, C. W. & Mather, J. R. (1957) Instructions andtables for computing potential evapotranspiration and thewater balance. Publications in Climatology, 10, 181–311.

Turner, R. M., Bowers, J. E. & Burgess, T. L. (1995) Sonoran desertplants: an ecological atlas. University of Arizona Press, Tucson.

Webb, T., III (1985) A global paleoclimate data base for 6000 yrB.P. DOE/eV/10097-6. US Department of Energy, Washington,DC.

Williams, J. W., Summers, R. L. & Webb, T., III (1998) Applyingplant functional types to construct biome maps from easternNorth American pollen data: comparisons with model results.Quaternary Science Reviews, 17, 607–627.




Williams, J. W., Webb, T., III, Richard, P. J. H. & Newby, P.(2000) Late Quaternary biomes of Canada and the easternUnited States. Journal of Biogeography, 27, 585–607.

Worona, M. A. & Whitlock, C. (1995) Late Quaternary vegeta-tion and climate history near Little Lake, central CoastRange, Oregon. Geological Society of America Bulletin, 107,867–876.

Yu, G. & Harrison, S. P. (1995) Lake status records fromEurope: data base documentation. NOAA PaleoclimatologyPublications Series Report 3, 1–451. NOAA, Boulder, Colorado.

Yu, G., Prentice, I. C., Harrison, S. P. & Sun, X. (1998) Pollen-based biome reconstructions for China at 0 ka and 6 ka.Journal of Biogeography, 25, 1055–1070.

Yu, G., Chen, X., Ni, J., Cheddadi, R., Guiot, J., Han, H.,Harrison, S. P., Huang, C., Ke, M., Kong, Z., Li, S., Li, W.,Liew, P., Liu, G., Liu, J., Liu, Q., Liu, K.-B., Prentice, I. C.,Qui, W., Ren, G., Song, C., Sugita, S., Sun, X., Tang, L., VanCampo, E., Xia, Y., Xu, Q., Yan, S., Yang, X., Zhao, J. &Zheng, Z. (2000) Palaeovegetation of China: a pollen data-basedsynthesis for the mid-Holocene and last glacial maximum.Journal of Biogeography, 27, 635–664.

REFERENCES FOR THE DATA SET

Anderson, R. S. (1990) Modern pollen rain within and adjacentto two giant sequoia (Sequoiadendron giganteum) groves,Yosemite and Sequoia national parks, California. CanadianJournal of Forest Research, 20, 1289–1305.

Anderson, R. S. (1993) A 35,000 year vegetation and climatehistory from Potato Lake, Mogollon Rim, Arizona. Quater-nary Research, 40, 351–359.

Anderson, R. S. & Carpenter, S. L. (1991) Vegetation change inYosemite Valley, Yosemite National Park, California, duringthe protohistoric period. Madroño, 38, 1–13.

Anderson, R. S. & Van Devender, T. R. (1991) Comparison ofpollen and macrofossils in packrat (Neotoma) middens: achronological sequence from the Waterman Mountains ofsouthern Arizona, U.S.A. Review of Palaeobotany and Paly-nology, 68, 1–28.

Andrews, J. T., Carrara, P. E., King, F. B. & Stuckenrath, R.(1975) Holocene environmental changes in the alpine zone,northern San Juan Mountains, Colorado: evidence from bogstratigraphy and palynology. Quaternary Research, 5, 173–197.

Baker, R. G. (1976) Late Quaternary vegetation history of theYellowstone Basin, Wyoming. U.S. Geological Survey Profes-sional Paper, 729-E, 1–43.

Baker, R. G. (1983) Holocene vegetational history of the westernUnited States. Late Quaternary environments of the UnitedStates (ed. by H. E. Wright Jr), pp. 109–126. University ofMinnesota Press, Minneapolis.

Barnosky, C. W. (1981) A record of Late Quaternary vegeta-tion from Davis Lake, southern Puget lowland, Washington.Quaternary Research, 16, 221–239.

Barnosky, C. W. (1985a) Late Quaternary vegetation nearBattle Ground Lake, southern Puget Trough, Washington.Geological Society of America Bulletin, 96, 263–271.

Barnosky, C. W. (1985b) Late Quaternary vegetation in theSouthwestern Columbia Basin, Washington. QuaternaryResearch, 23, 109–122.

Barnosky, C. W. (1989) Postglacial vegetation and climate in the

northwestern Great Plains of Montana. Quaternary Research,31, 57–73.

Beiswenger, J. M. (1987) Late Quaternary vegetational historyof Grays Lake, Idaho and the Ice Slough, Wyoming. PhDThesis, University of Wyoming, Laramie.

Beiswenger, J. M. (1991) Late Quaternary vegetational historyof Grays Lake, Idaho. Ecological Monographs, 61, 165–182.

Betancourt, J. L. (1984) Late Quaternary plant zonation and cli-mate in southeastern Utah. Great Basin Naturalist, 44, 1–35.

Bright, R. C. (1966) Pollen and seed stratigraphy of Swan Lake,southeastern Idaho: its relation to regional vegetational his-tory and to Lake Bonneville history. Tebiwa, 9, 1–47.

Bright, R. C. & Davis, O. K. (1982) Quaternary paleoecologyof the Idaho National Engineering Laboratory, Snake RiverPlain, Idaho. American Midland Naturalist, 108, 21–33.

Carrara, P. E., Mode, W. N., Meyer, R. & Robinson, S. W. (1984)Deglaciation and post-glacial timberline in the San JuanMountains, Colorado. Quaternary Research, 21, 42–55.

Cole, K. L. (1981) Late Quaternary environment in the easternGrand Canyon: vegetational gradients over the last 25,000years. PhD Thesis, University of Arizona, Tucson.

Cole, K. L. (1983) Late Pleistocene vegetation of Kings Canyon,Sierra Nevada, California. Quaternary Research, 19, 117–129.

Cole, K. L. & Webb, R. H. (1985) Late Holocene vegetationchanges in Greenwater Valley, Mojave Desert, California.Quaternary Research, 23, 227–235.

Cwynar, L. C. (1987) Fire and the forest history of the NorthCascade Range. Ecology, 68, 791–802.

Davis, O. K. (1981) Vegetation migration in southern Idahoduring the Late Quaternary and Holocene. PhD Thesis, Uni-versity of Minnesota, Minneapolis.

Davis, O. K. (1990) Caves as sources of biotic remains in aridwestern North America. Palaeogeography, Palaeoclimatology,Palaeoecology, 76, 331–348.

Davis, O. K., Agenbroad, L., Martin, P. S. & Mead, J. I. (1984)The Pleistocene dung blanket of Bechan Cave, Utah. Contri-butions in Quaternary vertebrate paleontology: a volume inmemorial to John E. Guilday (ed. by H. H. Genoways &M. R. Dawson). Special Publication of Carnegie Museum ofNatural History, 8, 267–282. Carnegie Museum of NaturalHistory, Pittsburgh, Pennsylvania.

Davis, O. K., Anderson, R. S., Fall, P. L., O’Rourke, M. K. &Thompson, R. S. (1985) Palynological evidence for earlyHolocene aridity in the southern Sierra Nevada, California.Quaternary Research, 24, 322–332.

Davis, O. K. & Moratto, M. J. (1988) Evidence for a warm dryearly Holocene in the western Sierra Nevada of California:pollen and plant macrofossil analysis of Dinkey and Excheq-uer Meadows. Madroño, 35, 132–149.

Fall, P. L. (1985) Holocene dynamics of the subalpine forest incentral Colorado. American Association of Stratigraphic Paly-nologists, Contributions Series, 16, 31–46.

Fall, P. L. (1988) Vegetation dynamics in the Southern RockyMountains: Late Pleistocene and Holocene timberline fluctua-tions. PhD Thesis, University of Arizona, Tucson.

Feiler, E. J., Anderson, R. S. & Koehler, P. A. (1997) Late Quater-nary paleoenvironments of the White River Plateau, Colorado,USA. Arctic and Alpine Research, 29, 53–62.

Gennett, J. A. (1977) Palynology and paleoecology of sedi-ments from Blacktail Pond, Northern Yellowstone Park,Wyoming. MS Thesis, University of Iowa, Iowa City.




Hansen, B. S. & Easterbrook, D. J. (1974) Stratigraphy and paly-nology of Late Quaternary sediments in the Puget Lowland,Washington. Geological Society of America Bulletin, 85, 587–602.

Heusser, C. J. (1972) Palynology and phytogeographical signific-ance of a late-Pleistocene refugium near Kalaloch, Washington.Quaternary Research, 3, 284–304.

Heusser, C. J. (1973) Modern pollen spectra from MountRainier, WA. Northwest Science, 47, 1–8.

Heusser, C. J. (1978) Palynology of Quaternary deposits of thelower Bogachiel River area, Olympic Peninsula, Washington.Canadian Journal of Earth Sciences, 15, 1568–1578.

Heusser, L. E. (1983) Contemporary pollen distribution incoastal Oregon. Palynology, 7, 19–42.

Jacobs, B. F. (1983) Past vegetation and climate of the MogollonRim area, Arizona. PhD Thesis. University of Arizona, Tucson.

Jacobs, B. F. (1985) A middle Wisconsin pollen record fromHay Lake, Arizona. Quaternary Research, 24, 121–130.

King, T. K., Jr (1976) Late Pleistocene-early Holocene history ofconiferous woodlands in the Lucerne Valley Region, MohaveDesert, California. Great Basin Naturalist, 36, 227–238.

Koehler, P. A. & Anderson, R. S. (1994) The paleoecologyand stratigraphy of Nichols Meadow, Sierra National Forest,California, USA. Palaeogeography, Palaeoclimatology, Palae-oecology, 112, 1–17.

Koehler, P. A. & Anderson, R. S. (1995) Thirty thousand yearsof vegetation changes in the Alabama Hills, Owens Valley,California. Quarternary Research, 43, 238–248.

Legg, T. E. & Baker, R. G. (1980) Palynology of Pinedale sedi-ments, Devlins Park, Boulder County, Colorado. Arctic andAlpine Research, 12, 319–333.

Leopold, E. B., Nickmann, R. J., Hedges, J. I. & Ertel, J. R.(1982) Pollen and lignin records of Late Quaternary vegeta-tion, Lake Washington. Science, 218, 1305–1307.

Mack, R. N., Bryant, V. M., Jr & Fryxell, R. (1976) Pollensequence from the Columbia Basin, Washington; reappraisalof postglacial vegetation. American Midland Naturalist, 95,390–397.

Mack, R. N., Bryant, V. M., Jr & Pell, W. (1978d) Modern forestpollen spectra from Eastern Washington and Northern Idaho.Botanical Gazette, 139, 249–255.

Mack, R. N., Rutter, N. W., Bryant, V. M., Jr & Valastro, S.(1978a) Late Quaternary pollen record from Big Meadow,Pend Oreille County, Washington. Ecology, 59, 956–965.

Mack, R. N., Rutter, N. W., Bryant, V. M., Jr & Valastro, S.(1978b) Reexamination of postglacial vegetation history inNorthern Idaho: Hager Pond, Bonner Co. Quaternary Research,10, 241–255.

Mack, R. N., Rutter, N. W. & Valastro, S. (1979) Holocenevegetation history of the Okanogan valley, Washington.Quaternary Research, 12, 212–225.

Mack, R. N., Rutter, N. W. & Valastro, S. (1983) Holocenevegetational history of the Kootenai River valley, Montana.Quaternary Research, 20, 177–193.

Mack, R. N., Rutter, N. W., Valastro, S. & Bryant, V. M., Jr(1978c) Late Quaternary vegetation history at Waits Lake,Colville River Valley, Washington. Botanical Gazette, 139,499–506.

Maher, L. J., Jr (1961) Pollen analysis and postglacial vegeta-tion history in the Animas Valley Region, Southern San JuanMountains, Colorado. PhD Thesis, The University of Minnesota,Minneapolis.

Maher, L. J., Jr (1972) Absolute pollen diagram of RedrockLake, Boulder County, Colorado. Quaternary Research, 2,531–553.

Markgraf, V. & Lennon, T. (1986) Paleoenvironmental historyof the last 13,000 years of the eastern Powder River Basin,Wyoming, and its implication for prehistoric cultural patterns.Plains Anthropologist, 31, 1–12.

Markgraf, V. & Scott, L. (1981) Lower timberline in centralColorado during the past 15,000 yr. Geology, 9, 231–234.

Mathewes, R. W. (1973) A palynological study of postglacialvegetation changes in the University Research Forest, south-western British Columbia. Canadian Journal of Botany, 51,2085–2103.

Mathewes, R. W. & Rouse, G. E. (1975) Palynology and pale-oecology of postglacial sediments from the Lower FraserRiver Canyon of British Columbia. Canadian Journal ofEarth Science, 12, 745–756.

Mead, J. I. & Phillips, A. M., III (1981) The Late Pleistoceneand Holocene fauna and flora of Vulture Cave, GrandCanyon, Arizona. Southwestern Naturalist, 26, 257–288.

Mehringer, P. J., Jr (1985) Late-Quaternary pollen records fromthe interior Pacific Northwest and Northern Great Basin of theUnited States. Pollen records of Late-Quaternary North Amer-ican sediments (ed. by V. M. Bryant Jr and R. G. Holloway),pp. 167–190. American Association of Stratigraphic Palynol-ogists Foundation, Dallas, Texas.

Mehringer, P. J., Jr, Arno, S. F. & Petersen, K. L. (1977) Postglacialhistory of Lost Trail Pass Bog, Bitterroot Mountains, Montana.Arctic and Alpine Research, 9, 345–368.

Nickmann, R. J. (1979) The palynology of Williams Lake Fen,Spokane Co., Washington. MS Thesis, Eastern WashingtonState University, Spokane, Washington.

Phillips, A. M. (1977) Packrats, plants, and the Pleistocene ofthe Lower Grand Canyon, Arizona. PhD Thesis, University ofArizona, Tucson.

Schmutz, E. M., Dennis, A. E., Harlan, A., Hendricks, D. &Zauderer, J. (1976) An ecological survey of Wide Rock Buttein Canyon de Chelly National Monument, Arizona. ArizonaAcademy of Science, 11, 114–125.

Sea, D. S. & Whitlock, C. (1995) Postglacial vegetation andclimate of the Cascade Range, central Oregon. QuaternaryResearch, 43, 370–381.

Shafer, D. S. (1989) The timing of Late Quaternary monsoonprecipitation maxima in the Southwest United States. PhDThesis, University of Arizona, Tucson.

Sharpe, S. E. (1991) Late-Pleistocene and Holocene vegetationchange in Arches National Park, Grand County, Utah andDinosaur National Monument, Moffat County, Colorado.MS Thesis, Northern Arizona University, Flagstaff, Arizona.

Short, S. K. (1985) Palynology of Holocene sediments, ColoradoFront Range: vegetation and treeline changes in the subalpineforest. American Association of Stratigraphic PalynologistsContribution Series, 16, 7–30.

Smith, S. J. & Anderson, R. S. (1992) Late Wisconsin paleoecologicrecord from Swamp Lake, Yosemite National Park, California.Quaternary Research, 38, 91–102.

Spaulding, W. G. (1980) The presettlement vegetation of theCalifornia Desert. California Bureau of Land Management,Desert Planning Staff (Quaternary Research Center), Riverside,Seattle, WA.

Spaulding, W. G. (1981) The Late Quaternary vegetation of a




southern Nevada Mountain Range. PhD Thesis, University ofArizona, Tucson.

Spaulding, W. G. (1991) A middle Holocene vegetationrecord from the Mojave Desert of North America and itspaleoclimatic significance. Quaternary Research, 35, 427–437.

Thompson, R. S. (1984) Late Pleistocene and Holocene environ-ments in the Great Basin. PhD Thesis. University of Arizona,Tucson.

Thompson, R. S. (1992) Late Quaternary environments in RubyValley, Nevada. Quaternary Research, 37, 1–15.

Thompson, R. S. & Hattori, E. M. (1983) Packrat (Neotoma)middens from Gatecliff Shelter and Holocene migrations ofwoodland plants. Anthropological Papers of the AmericanMuseum of Natural History, 59, 157–167.

Thompson, R. S. & Mead, J. I. (1982) Late Quaternary environ-ments and biogeography in the Great Basin. Quaternary Research,17, 39–55.

Tsukada, M., Sugita, S. & Hibbert, D. M. (1981) Paleoecologyin the Pacific Northwest I. Late Quaternary vegetation andclimate. Verhandlungen der Internationalen Vereingung furtheoretische und angewandte Limnologie, 21, 730–737.

Van Devender, T. R. (1973) Late Pleistocene plants and animalsof the Sonoran Desert: a survey of ancient packrat middens insouthwestern Arizona. PhD Thesis, University of Arizona, Tucson.

Van Devender, T. R. (1985) Late Holocene plant records fromthe Dolores River Area, Montezuma County, Colorado.Dolores Archaeological Program: studies in environmentalarchaeology (ed. by D. A. Breternitz), pp. 203–206. U.S.Dept. of the Interior, Denver, CO.

Van Devender, T. R. (1987) Holocene vegetation and climate inthe Puerto Blanco Mountains, Southwestern Arizona. Quater-nary Research, 27, 51–72.

Van Devender, T. R., Betancourt, J. L. & Wimberly, M. (1984)Biogeographic implications of a packrat midden sequencefrom the Sacramento Mountains, South-Central New Mexico.Quaternary Research, 22, 344–360.

Van Devender, T. R., Burgess, T. L., Felger, R. S. & Turner, R. M.(1990) Holocene vegetation of the Hornaday Mountains ofnorthwestern Sonora, Mexico. Proceedings of the San DiegoSociety of Natural History, 2, 1–19.

Van Devender, T. R., Burgess, T. L., Piper, J. C. & Turner, R. M.(1994) Paleoclimatic implications of Holocene plant remainsfrom the Sierra Bacha, Sonora, Mexico. Quaternary Research,41, 99–108.

Van Devender, T. R. & Toolin, L. J. (1983) Late Quaternaryvegetation of the San Andres Mountains, Sierra County, New

Mexico. The prehistory of Rhodes Canyon, survey and miti-gation (ed. by P. L. Eidenbach), pp. 33–54. Human SystemsResearch Inc.,Tularosa.

Van Devender, T. R., Toolin, L. J., (undated) The Holocenedevelopment of vegetation in the western Hueco Mountainsand Fort Bliss Army Base, El Paso County, Texas. UnpublishedReport. Dept. Geosciences, University of Arizona, Tucson.

Waddington, J. C. B. & Wright, H. E., Jr (1974) Late Quaternaryvegetational changes on the east side of Yellowstone NationalPark. Quaternary Research, 4, 175–184.

Whitlock, C. (1993) Postglacial vegetation and climate ofGrand Teton and southern Yellowstone National Parks. Eco-logical Monographs, 63, 173–198.

Whitlock, C. & Bartlein, P. J. (1993) Spatial variations ofHolocene climatic change in the Yellowstone region. QuaternaryResearch, 39, 231–238.

Wigand, P. E. (1987) Diamond Pond, Harney County, Oregon:vegetation history and water table in the eastern Oregondesert. Great Basin Naturalist, 47, 427–458.

Wigand, P. E. & Mehringer, P. J., Jr (1985) Pollen and seedanalyses. The archaeology of Hidden Cave, Nevada (ed. byD. H. Thomas). Anthropological Papers of the AmericanMuseum of Natural History, 61, 108–124.

Worona, M. A. & Whitlock, C. (1995) Late Quaternary vegeta-tion and climate history near Little Lake, central Coast Range,Oregon. Geological Society of America Bulletin, 107, 867–876.

Wright, H. E., Jr, Bent, A. M., Hansen, B. S. & Maher, L. J., Jr(1973) Present and past vegetation of the Chuska Mountains,Northwestern New Mexico. Geological Society of AmericaBulletin, 84, 1155–1180.

BIOSKETCHES

Robert S. Thompson is a geologist with the Global Change and Climate History Team of the U.S. Geological Survey who studies late Cenozoic vegetation and climate change, primarily in western North America.

Katherine H. Anderson is a research associate with the Institute for Arctic and Alpine Research (INSTAAR) at the University of Colorado. She applies quantitative techniques to reconstruct past climates from pollen and plant macrofossil data in North America.


Documents

Biomes of western North America at 18,000, 6000 and 0 14C yr bp reconstructed from pollen and packrat midden data