Fire and vegetation history on Santa Rosa Island, … · Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California

JOURNAL OF QUATERNARY SCIENCE (2010) 25(5) 782–797Copyright � 2009 John Wiley & Sons, Ltd.Published online 29 December 2009 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/jqs.1358
Fire and vegetation history on Santa Rosa Island,Channel Islands, and long-term environmentalchange in southern CaliforniaR. SCOTT ANDERSON,1* SCOTT STARRATT,2 RENATA M. BRUNNER JASS3 and NICHOLAS PINTER41 School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona, USA2 Volcanic Hazards Team, US Geological Survey, Menlo Park, California, USA3 9417 68 Avenue NW, Edmonton, Alberta Canada4 Department of Geology, Southern Illinois University, Carbondale, Illinois, USA

Anderson, R. S., Starratt, S., Jass, R. M. B. and Pinter, N. 2010. Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change insouthern California. J. Quaternary Sci., Vol. 25 pp. 782–797. ISSN 0267-8179.

Received 8 April 2009; Revised 30 September 2009; Accepted 6 October 2009

ABSTRACT: The long-term history of vegetation and fire was investigated at two locations – SoledadPond (275 m; from ca. 12 000 cal. a BP) and Abalone Rocks Marsh (0 m; from ca. 7000 cal. a BP) – onSanta Rosa Island, situated off the coast of southern California. A coastal conifer forest coveredhighlands of Santa Rosa during the last glacial, but by ca. 11 800 cal. a BP Pinus stands, coastal sagescrub and grassland replaced the forest as the climate warmed. The early Holocene becameincreasingly drier, particularly after ca. 9150 cal. a BP, as the pond dried frequently, and coastalsage scrub covered the nearby hillslopes. By ca. 6900 cal. a BP grasslands recovered at both sites.
Pollen of wetland plants became prominent at Soledad Pond after ca. 4500 cal. a BP, and at AbaloneRocks Marsh after ca. 3465 cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marshsomewhat later, probably by additional runoff from the highlands. Introduction of non-native speciesby ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declinesduring the early Holocene when minimal biomass suggests extended drought. A general increaseoccurs after ca. 7000 cal. a BP, and especially after ca. 4500 cal. a BP. The Holocene pattern closelyresembles population levels constructed from the archaeological record, and suggests a potentialinfluence by humans on the fire regime of the islands, particularly during the late Holocene. Copyright# 2009 John Wiley & Sons, Ltd.
KEYWORDS: palaeoecology; fire history; Channel Islands; pollen analysis; California.

Introduction

The northern Channel Islands, situated off the coast of southernCalifornia, are a westward extension of the Transverse Rangesinto the Pacific Ocean (Norris and Webb, 1990). ThoughAnacapa, Santa Cruz, Santa Rosa, and San Miguel are distinctislands today, the northern Channel Islands existed as a singleisland – Santarosae (Orr, 1968) – during the Last GlacialMaximum when sea level was �120 m lower (Siddall et al.,2003), and the distance from the mainland was �7 km (Kennettet al., 2008). Currently, local vegetation is dominated bygrasslands and shrublands, with patchy woodlands. During theLate Pleistocene, however, a forest more comparable to modernnorthern California existed at least on parts of Santarosae,including Pseudotsuga (Douglas fir), Pinus (pine) andCupressus(cypress) (Chaney and Mason, 1930; Anderson et al., 2008).Here we document the development of the vegetation and fire

* Correspondence to: R. S. Anderson, School of Earth Sciences and EnvironmentalSustainability, Box 5694, Northern Arizona University, Flagstaff, AZ, USA 86011.E-mail: [email protected]

regimes that have existed during the Holocene on Santa Rosa –the second largest island of the northern group.

Analysis of the vegetation history of Santa Rosa Island isimportant for several reasons. First, little is known about thelong-term ecology of the islands. The most detailed studiesinclude initial palaeobotanical research on Santa Cruz Island(Chaney and Mason, 1930), pollen analysis from a salt marsh(Cole and Liu, 1994) and an alluvial section (Kennett et al.,2008) on Santa Rosa Island, and from Daisy Cave on SanMiguel Island (West, 1994). Second, few details exist regardingthe long-term history of fire disturbance there. Cole and Liu(1994) produced a generalised history of lowland fire for SantaRosa Island, but a high-resolution record of fire for the islandshas not been published. Third, little is known about postglacialclimate changes on the islands. Various factors (Kennett et al.,2008) including climate changes (Anderson et al., 2008) havebeen implicated as the cause for the loss of the coastalPseudotsuga forest at the end of the Pleistocene, but the detailsof climate variability during the Holocene are largely unknown.Fourth, our understanding of the impact of humans – bothNative American and Euro-American – on the landscape isunclear. Did Native American fire use influence vegetation

PALAEOECOLOGY OF SANTA ROSA ISLAND 783

composition (e.g. Keeley, 2002) on the islands? The precisetiming of human settlement on Santarosae is not known, but itmost certainly began in the latest Pleistocene (Erlandson et al.,1996, 2007; Johnson et al., 2002).

Here we use pollen and charcoal stratigraphies from twosites, and a diatom stratigraphy from one, to determine theHolocene vegetation, climate and fire history of Santa RosaIsland, answering the following questions:

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hat were the changes in vegetation that occurred over anelevational gradient during the Holocene?

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ow has climate variability during the Holocene affected thenatural and unique island vegetation?
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hat is the history of fire on Santa Rosa Island? Does it differacross the elevational gradient?
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hat is the relationship, if any, between the history of humanoccupation and ecosystem disturbance – fire and speciesintroductions – on the island?
Increasingly, research on palaeohistorical vegetation anddisturbance regimes has attracted the attention of land managersand others, as the data provide baseline information useful forinformed decisions on management and potential restoration ofunique island habitats during a period of rapidly changing climate.Our goal is to understand this fragile island ecosystem that hasbeen under substantial human pressure for decades to centuries.

Setting

Santa Rosa Island and study sites

Santa Rosa Island (SRI) is the third, west to east, of the fournorthern Channel Islands (Fig. 1), lying �45 km off the Cali-fornia coast. It covers �21 400 ha (Cole and Liu, 1994). About

gure 1 Location of Santa Rosa Island in relation to the northern Channel Isnd (338 570 5500 N, 1208 050 5000 W) and Abalone Rocks Marsh (338 570

pyright � 2009 John Wiley & Sons, Ltd.

2000 m of late Tertiary rocks are exposed on SRI (Dibblee andEhrenspeck, 1998), which are overlain by a widespreadpackage of Quaternary deposits (Pinter et al., 2001), includingdune sands (Erlandson et al., 2005), and with a thick sequenceof Late Pleistocene fluvial deposits in canyons on the north sideof the island.

We studied the sediments from two small basins on SRI.Soledad Pond (informal name: SP) is a small ephemeral wetlandlocated in the middle of the island (338 570 5500 N, 1208 050 5000

W) in a saddle approximately 1.8 km from Soledad Mountainand 2.4 km from Black Mountain, at 275 m elevation (Fig. 1). Aberm at the northwest end of the wetland suggests it may haveoriginated after a landslide or slump. We also re-cored a smallcoastal salt marsh, informally known as Abalone Rocks Marsh(ARM; originally studied by Cole and Liu, 1994). ARM islocated at 0 m elevation, 338 570 2000 N, 1198 050 4500 W (Fig. 1).The age of the lowest deposits (ca. 6900 cal. a BP) suggests thatsediments began accumulating when postglacial sea-level riseslowed, then stabilised, after ca. 6000 a ago (Masters andAiello, 2007).

Modern climate

The climate of the Channel Islands is maritime Mediterranean,with moist winters and warm, dry summers, but with mildtemperatures and little fluctuation during the year (Junak et al.,2007). Long-term climate data for two stations near SRI (SantaBarbara (SB; 66 a), �1 m above sea level (a.s.l.); Anacapa Island(AI; 57 a), ca. 43 m a.s.l.) show typical annual patterns forcoastal southwestern California (Fig. 2). Average monthlytemperature varies from winter lows (18.48C (January), 16.18C(December)) to summer highs (25.28C (August), 22.18C (July,August)) at SB and AI, respectively (Western Regional ClimateCenter, http://www.wrcc.dri.edu). Average monthly precipi-

lands and southwestern coastal California, including photos of Soledad2000 N, 1198 050 4500 W)

J. Quaternary Sci., Vol. 25(5) 782–797 (2010)

Figure 2 57- and 66-year records of average maximum temperature and precipitation for Anacapa Island and Santa Barbara, respectively (data fromWestern Regional Climate Center)

784 JOURNAL OF QUATERNARY SCIENCE

tation varies from a high of 103.9 mm in February at SA, and111.3 mm in January at AI, to near absence during the monthsof June to September (Fig. 2).

The climate is also influenced by dynamics of the CaliforniaCurrent and the California Counter- (Davidson) Current(Moody, 2000; Herbert et al., 2001). The California Currentbrings colder water southward parallel to the coast, whereas theCalifornia Counter Current carries warmer water northward.The relative influence of these two currents has been animportant influence on the climate and vegetation along thecoast throughout the late Quaternary (Herbert et al., 2001).

Modern vegetation

Like other Channel Islands, introduction of livestock and othernon-native herbivores during the 19th century on SRIdrastically altered native floral communities due to severeovergrazing, leading to severe erosion of native soils (Corry,2006). SRI has nearly 518 known species, at least 22.2% (115)of which have been introduced over the last 500 a since thearrival of the first Euro-Americans (Junak et al., 1997). Today,grasslands dominate, including introduced Avena fatua (wildoat), Bromus diandrus (ripgut grass), Bromus rubens (red brome)and Hordeum spp. (barley), with remnant native species Stipaspp. (needlegrass) (Cole and Liu, 1994). Other vegetation typesinclude scrub, island chaparral, valley and foothill grassland,broadleaf woodland, conifer forest and coastal wetland (Junaket al., 2007). Common sage scrub species include Artemisiacalifornica (California sagebrush), Baccharis pilularis ssp.consanguinea (coyote brush), Encelia californica (Californiabrittlebush) and Salvia mellifera (black sage). In the Californiachaparral are Adenostema fasciculatum (chamise), Arctosta-phylos spp. (manzanita), Heteromeles arbutifolia (toyon),Ceanothus spp. (California lilac), and Rhus integrifolia (lemon-adeberry) (Cole and Liu, 1994). Quercus dumosa (Nuttall’sscrub oak), Q. agrifolia (encina) and Q. tomentella (island oak)are found in ravines and as isolated stands, whereas smallstands of Pinus torreyana (Torrey pine) and P. muricata (SantaCruz Island pine) also occur.

Cole and Liu (1994) detailed the vegetation of, andsurrounding, the Abalone Rocks saltmarsh. At SP, the dominantshrub is Baccharis pilularis. Common herbs include Xanthiumspinosum (spiney clotbur), Silybum maryanum (milk thistle),Gnaphalium luteo-album (weedy cudweed), Hirschfeldia

Copyright � 2009 John Wiley & Sons, Ltd.

incanum (short-podded mustard), Sonchus oleraceus (commonsow thistle), Polygonum arenastrum (common knotweed),Malva cf. parviflora (mallow), Conyza canadensis (horseweed),Petunia parviflora (wild petunia), Capsella bursa-pastoris(shepherd’s purse), Lactuca saligna (willow lettuce), Erodiumcicutarium (redstem filaree), Madia sp. (tarweed), Chenopo-dium ambrosioides (Mexican tea), Medicago polymorpha (bur-clover), Anagollis arvensis (scarlet pimpernel), Verbenalasiostachys (verbena), Sisyrhinchium sp. (sisyrhinchium),Sanicula arguta (sharp-toothed snakeroot), Cotula coronopifo-lia (brass buttons), Centaurea melitensis (tocalote) and Silenegallica (windmill pink). Grasses and rushes include Hordeummurinum (foxtail), H. geniculatus (Mediterranean barley),Polypogon monceliensis (rabbit’s-foot grass), Vulpia cf. octo-flora (six-weeks fescue), Bromus hordeaceus (soft chess),B. diandrus, Avena fatua, A. barbata, Lolium perenne (Englishryegrass), Agrostos cf. viridis (water bent) and Juncusmexicanus/balticus (rush) (terminology follows Junak et al.,1997).

Settlement history

SRI has one of the longest histories of settlement along theCalifornia coast. The earliest remains come from ArlingtonCanyon, dated to <12 000 a (Erlandson et al., 1996; Johnsonet al., 2002). By the Holocene, the archaeological record on thenorthern Channel Islands is extensive (e.g., Kennett andKennett, 2000; Erlandson et al., 2005; Kennett, 2005; Brajeet al., 2007; Glassow et al., 2007; Kennett et al., 2007). JuanRodriguez Cabrillo first claimed SRI (named ‘Nicalque’) forSpain in AD 1542–1543, recording at least three native villages(Kelsey, 1986; Woolley, 1996). By AD 1805 there were sevenrancherias on the island (Cole and Liu, 1994). The Mexicangovernment granted SRI to the Carrillo family in 1843, and thefirst sheep were brought there by AD 1844 (Cole and Liu, 1994;Woolley, 1996). The number of sheep on the island roserapidly, and they were the dominant herbivore there until theend of the 19th century, when Vail and Vickers bought theranch and replaced them with cattle. Throughout the 20thcentury, the ranch raised cattle, and in the 1920s and 1930s,imported Roosevelt elk and Kaibab mule deer for hunting. TheUS National Park Service purchased the property in 1986, andthe cattle were removed in 1999 (Woolley, 1996).



Methods

Fieldwork on SRI was conducted in June 1999. At SP, asediment column (SP 99-01) was collected from a pit in themiddle of the dry pond. The upper 210 cm of the column wassampled in continuous 10–20 cm blocks from the exposed pitface. Depths from 210 to 425 cm were collected in 5 cmsections with a bucket auger. We obtained three sediment coresfrom ARM using a Livingstone sediment corer, the longest (AB-99-03) being 676 cm. Each sediment column was eitherwrapped in plastic wrap, then aluminium foil (ARM and upperportion of SP), or placed in plastic Whirl bags (bottom portion ofSP). Sediments were transported to the Laboratory ofPaleoecology (LOP), Bilby Research Center, Northern ArizonaUniversity, and stored in a cooler.

In the laboratory we described the cores, and magneticsusceptibility was measured on the ARM core only, using aSapphire Instruments SI2 meter. Pollen analysis followed amodified Fægri and Iversen (1989) procedure, using 10 cm3

(SP) or 2 cm3 (ARM) of sediment. Processing includedpretreatment with (NaPO3)6 to deflocculate clays and theaddition of Lycopodium spores for calculation of pollenconcentration. Sediments were suspended in Na4P2O7 andsieved, then treated with HCl, HF, acetolysis solution anddensity separation in ZnBr2 (specific gravity 1.9). Samples werestained and suspended in silicone oil, and analysed at 400–1000� using a light microscope, with comparison to themodern pollen reference collection at the LOP. Because ofthe large number of species in the Asteraceae family on theChannel Islands (up to 95; Junak et al., 1995, 1997) we used ourreference collection to divide the Asteraceae into 11 pollensubgroups based on size and morphological characteristics(Table A.1 in Appendix). Complete pollen and spore counts arefound in the North American Pollen Database (http://www.ncdc.noaa.gov/paleo/napd.html).

For charcoal analysis, sediment subsamples (5 cm3 for SP;2 cm3 for ARM) were extracted at 2-cm intervals and dis-aggregated in water for several days. Each subsample was wet-sieved using a 250mm sieve, and examined and tallied using adissecting microscope (magnification of 10–70�). Charcoal wasidentified by reference to particle colour and texture – mostcharcoal particles are shiny black, and often retain cellularstructure. Charcoal influx (CHAR particles cm�2 a�1) wascalculated by multiplying the charcoal concentration (particlescm�3) by the sediment accumulation rate (SAR; cm a�1). In orderto reconstruct a local burning history, we analysed only the large-particle (>250mm) stratigraphy. Also, because of a variable SARin both the vernal pool (SP) and coastal marsh (ARM)environments, we used the charcoal stratigraphy to infer onlya generalised fire activity for each record. Complete charcoalcounts are found in the Global Charcoal Database (http://www.ncdc.noaa.gov/paleo/impd/paleofire.html).

Table 1 Radiocarbon ages for the Santa Rosa Island sites

Site Lab # Depth (cm) 14C Age (a BP) Medianage (cal.

SP 99-01 Beta-172056 210–215 4 100�50 4 6SP 99-01 Beta-172057 335–360 8 990�60 10 1SP 99-01 Beta-150252 415–420 10 160�110 11 8AR 99-03 Beta-177955 303–308 2 870�40 2 9AR 99-03 Beta-177956 433–434 3 740�50 4 0AR 99-03 Beta-177957 633–636 3 170�40 3 3


Diatoms samples (1 cm3) from ARM were processed usingstandard procedures (H2O2, HCl, HNO3, Na4P2O7). Due to thecoarse sediment component in each sample, samples wereallowed to settle for 30 s before a 50mL aliquot was removed.The sample material was dried on a slide and mounted inNaphrax. Microfossils were counted at 500–1000� using themethod of Schrader and Gersonde (1978). Due to the widerange of absolute microfossil abundance, a uniform area(1 cm2) from each slide was examined. Diatoms and chryso-phyte cysts were identified using standard references (Krammerand Lange-Bertalot, 1991a,b, 1997a,b; Snoeijs, 1993; Snoeijsand Vilbaste, 1994; Cooper, 1995; Duff et al., 1995; Snoeijsand Potapova, 1995; Sims, 1996; Snoeijs and Kasperoviciene,1996; Snoeijs and Balashova, 1998).

Radiocarbon samples for SP consisted of bulk sediments, asunburned macroscopic organic remains were extremely rarethere. For ARM, we were able to age pieces of charcoal directlyby AMS. Three methods were used to construct chronologiesfor the SP and ARM cores. First, 14C ages were calibrated (cal. aBP) using CALIB 5.0 (Stuiver et al., 1998) in the older part of therecords (Table 1), and the median probability age (Telford et al.,2004) was used to construct the age–depth profiles. Second,because of an anomalously young age for the bottom of the AR99-03 record (see below), we estimated the age of this record byextrapolating downcore from the upper 14C ages. Ourconfidence in this method is high since the stratigraphy andresulting sediment accumulation rate are nearly identical to theoriginal Cole and Liu (1994) core. Third, for the youngestportion of each record we used pollen stratigraphy andhistorical records to assign a calendar age to the time ofregional and local settlement by Euro-Americans. Settlementand expansion of cattle ranching within coastal Californiaoccurred by the late 1700s (Mensing and Byrne, 1998),documented by the first occurrence of pollen of weedy plants,including Erodium cicutarium. However, widespread sheepgrazing on the Channel Islands did not commence until ca. AD1850 (Roberts, 1991), and we use that age here.

Results

Soledad Pond

Sediment stratigraphy and chronology

The SP 99-01 record consists of 425 cm of silty clay (Fig. 3).Below 355 cm is sandy clay, with rock fragments near the baseof the section. Grey-brown clays with carbonate nodules occurfrom �355–180 cm, with highest carbonate accumulationbetween 300 and 250 cm. The upper �180 cm is organic clay,with increasing amounts of sand above �100 cm.

prob.a BP)

Age up(cal. a BP)

Age down(cal. a BP)

13C Matter dated

26 4 514 4 821 Unknown Bulk sediment57 10 147 10 235 Unknown Bulk sediment07 11 311 12 178 Unknown Bulk sediment96 2 871 3 081 �25.5 Charcoal AMS96 3 964 4 243 �25.2 Charcoal AMS98 3 332 3 470 �23.0 Charcoal AMS


Figure 3 Soledad Pond and Abalone Rocks Marsh stratigraphy and age–depth relationships (SP 99-01 and AR 99-03) and magnetic susceptibility (AR99-03 only) for the two study sites. Magnetic susceptibility (MS) is measured in electric magnetic units (emu; see text for explanation). Ages are either ina AD or in cal. a BP


The three calibrated radiocarbon ages (Table 1) were used todetermine the sediment chronology. From �417.5 to 347.5 cm(11 800 to 10 150 cal. a BP), the SAR is 1.08 mm a�1 and weused this rate to extrapolate the age of the bottom of the core tobe 12 000 cal. a BP). We assigned an age of AD 1850 (100 cal. aBP) to 100 cm depth based on the first occurrence of pollenassociated with sheep grazing (i.e. Erodium).


Pollen and charcoal

Four pollen zones are identified (Figs. 4 and 5) and Asteraceaepollen dominates throughout.

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one SP-1 (core bottom to �335 cm depth; ca. 12 000 to9150 cal. a BP). Pollen concentration is less in this zone than

Figure 4 Pollen percentage diagram of major pollen types for the Soledad Pond 99-01 profile. Percentages are shown in black, whereas silhouettesare �10. Ages are either in a AD or cal. a BP

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in any subsequent period (Fig. 4). Asteraceae pollen dom-inates (up to 90%), with dominant subgroups Lactuceae(chicory-type) and Baccharis (coyote brush) (Fig. 5). Poaceae(grass; to 7%) pollen is also important, along with Ambrosia(ragweed; to 3%) and coastal sage scrub species (e.g. Erio-gonum (buckwheat), Rosaceae (rose family)) and others(Polemoniaceae (phlox family) and Cyperaceae (sedge

gure 5 Pollen percentage diagram of differentiated members of the Asteraceapes). Percentages are shown in black, whereas silhouettes are �10. Ages are


family)). After ca. 10 760 cal. a BP (382 cm), Chenopodia-ceae (goosefoot family – Cheno-Am) increases (from traceamounts to over 5%).

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one SP-2 (335 to 275 cm depth; ca. 9150 to ca. 6900 cal.a BP). Pollen concentration during this period is variable (0 to>15 000 grains cm�3). However, pollen richness is less inthis zone than any other. Asteraceae pollen still dominates,
e for the Soledad Pond 99-01 profile (see text for explanation of polleneither in a AD or cal. a BP


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but other than small amounts of Baccharis and Solidago, it isnot diagnostic of any other subgroup (Fig. 5). Small amountsof Pinus (pine, to 3%) and Cheno-Am (to 2%) pollen occur,but most other types, including herbaceous (Poaceae, Cyper-aceae, Apiaceae (carrot family)) and shrubby (Eriogonum,Rosaceae, Fabaceae (legume family), Polemoniaceae) pol-len, disappear or become rare early in this zone, onlyreappearing near the end (Fig. 4).

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one SP-3 (275 to 100 cm depth; ca. 6900 cal. a BP to ca. AD1850). Pollen concentrations are variable (mostly below 100000 grains cm�3) and pollen richness increases once again.Most of the types found in the lowest zone SP-1 becomeimportant again, including Asteraceae, but also Baccharis,Solidago, Artemisia (sagebrush) and Lactuceae in the sun-flower family, along with members of the coastal sagescrub (Eriogonum, Rosaceae, Fabaceae, Polemoniaceaeand Caryophyllaceae (carnation family)) community. Poa-ceae pollen reappears and pollen of wetland plants (i.e.Cyperaceae and Apiaceae) is also prominent, particularlyafter ca. 4500 cal. a BP.
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one SP-4 (100 cm depth to core top; from ca. AD 1850 topresent). Pollen of the Asteraceae continues to dominate,with Baccharis, Solidago and Artemisia. However, Poaceaepollen and Pteridium (bracken fern) spores are most abun-dant during this time period, and pollen of Quercus (oak) andPinus also increases. Several pollen types indicative of graz-
gure 6 Charcoal influx (particles cm�2 a�1) for both the Soledad Pond 99-0ack line, whereas smoothed data are shown by the white line. Arrow showman habitation on SRI during the Holocene (after data presented by Ken


ing and pasturing, including Erodium (filaree), Plantago(plantain) and Ambrosia (ragweed), increase, along withCupressaceae (Cupressus) pollen. Sporormiella, a funguscharacteristic of herbivore dung (Davis and Shafer, 2006;Raper and Bush, 2009), also occurs in several samples.

The SP charcoal profile shows that charcoal was depositedthroughout the entire record (Fig. 6), indicating fire has beenimportant there for the last ca. 12 000 a. The changes throughtime largely parallel the vegetation changes, with modestcharcoal influx during the Lateglacial and earliest Holocene(zone SP-1), and minimal deposition during the early Holocene(zone SP-2). Charcoal influx increases slightly after ca.7000 cal. a BP, with a slightly increased influx after ca.4300 cal. a BP. Charcoal influx increases by an order ofmagnitude during the historic period (zone SP-4).

Abalone Rocks Marsh

Sediment stratigraphy, chronology, and magneticsusceptibility

The ARM record consists of 676 cm of alternating clays andsandy silts (Fig. 3). Sands are found below �640 cm, with

1 and Abalone Rocks Marsh 99-03 profiles. Actual data are shown by thes trend for the late Holocene. Long box on left is our interpretation of

nett, 1998, 2005; Kennett et al., 2009; and others)



laminated clays (�640–625 cm) and alternating clay and sandlayers to �520 cm depth. Silty clays occur from �520 to360 cm depth, grading into alternating layers of clay and sandsto �120 cm. Silty clays predominate from 120 to �8 cm, abovewhich is found organic silts.

Two upper calibrated radiocarbon ages occur in stratigraphicorder, whereas the lowest age appears to be too young(Table 1). We therefore reject this age. Using the medianprobability ages for each calibrated date to construct the age–depth curve, the SAR from �433.5 to 305.5 cm (4096–2996 cal. a BP) is 1.16 mm a�1, and we used this SAR toextrapolate to the core bottom at 676.0 cm, giving a bottom ageof ca. 6969 cal. a BP. As at SP, we assigned an age of AD 1850(100 cal. a BP) to 100 cm depth based on the increase inErodium pollen.

Magnetic susceptibility (MS) showed consistently highvalues, above 200 emu� 10�7, in the top 80 cm, during thehistoric period (Fig. 3). The high rate of sediment accumulationand high MS values suggest rapid erosion. Below 80 cm, MSvalues were generally lower.

Pollen, diatoms and charcoal

We base our discussion here on the two zones (one with twosubzones) identified from the pollen taxa, because sedimentscomparable in age to SP-1 and SP-2 were not recovered here.Numerous species of diatoms, chrysophyte stomatocysts,phytoliths, radiolaria and sponge spicules were recovered inthe diatom preparations (Table A.2 in Appendix). The quality ofpreservation of the diatoms is variable, reflecting changes in theamount of fresh water available on the marsh surface and thedistance of transport. This results in a bias towards more heavilysilicified species (Pinnularia borealis) and chrysophyte stoma-tocysts. The major late Holocene change in diatom stratigraphyis somewhat later (ca. 2500 cal. a BP) than for the pollen (ca.3500 cal. a BP).

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one AR-3a (bottom of core to �400 cm depth; ca. 6969 to3465 cal. a BP). In AR-3a pollen concentration is variable,averaging below 20 000 grains cm�3. Cheno-am pollendominates, but with high variability (�10–80%); Poaceaeis also important (�5–20%) (Fig. 7). Small amounts (�10%)of Pinus suggest presence nearby (either on the island or onthe coastal mainland), but not at the site. Quercus is presentin small amounts. Pollen types characteristic of sage scrubvegetation are common, including Eriogonum (to 5%), Arte-misia (10–20%) and others (Fig. 7). Baccharis dominates theAsteraceae group; other important Asteraceae types includeLactuceae, Helianthus, and Solidago. Pollen of wetlandplants (Alnus, Apiaceae, Cyperaceae) and spores of fernsare common (Fig. 7).

Diatoms in this zone are rare, and several samples arebarren (Fig. 8). Samples contain fragments of the marinediatom genera Thalassiosira and Coscinodiscus. A brackishspecies (Nitzschia commutata) and those that are found insubaerial environments, including soil (Hantzschiaamphioxys, Luticola mutica, Pinnularia borealis) are alsopresent. The diversity and abundance of phytoliths is rela-tively low in this zone.

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one AR-3b (400–100 cm depth; ca. 3465 cal. a BP to ca.AD 1850). Pollen concentration during this period is alsovariable (ca. 15 000–40 000 grains cm�3). Pollen percen-tages of Pinus and Quercus remain unchanged but hereBaccharis (35–60%) becomes dominant (Fig. 7). Sage scrubplants (i.e. Eriogonum, Artemisia, others) remain relatively

abundant, whereas Ipomopsis increases to �5%. Declinesoccur in Cheno-am (generally <15%), other Asteraceae(<2%) and Poaceae (generally <5%, but with individualspikes) (Fig. 7). The abundance and diversity of phytoliths(probably mostly derived from grasses) are lower and morevariable between 400 and 250 cm, paralleling the Poaceaepollen curve. The absolute number and diversity increase inthe upper part of zone AR-3b. Spores of several ferns andfern allies become more abundant during this zone, includ-ing Selaginella.

Zone AR-3a contains only a few diatoms, but the numberof specimens and species diversity is highest between 250 cmand 100 cm (Fig. 8). The dominant species are those that arefound in freshwater and subaerial environments (Hantzschiaamphioxys, Luticola mutica, Pinnularia borealis) and thosepreferring fresh and slightly brackish water (Navicula cincta,Nitzschia commutata).

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one AR-4 (100 cm to the core top; ca. AD 1850 to 1999).Pollen concentrations rise considerably (to 60 000 grainscm�3). Baccharis dominates initially, giving dominance toCheno-ams at the core top. Pollen of most sage scrub typesdecline, but one pollen type indicative of pasturing – Ero-dium – occurs, as well as pollen of other introduced trees,including Eucalyptus and Cupressus (Cupressaceae; Fig. 7).Several spore types reach their maximum percentages duringthis zone, including Pellaea, Adiantum, Botrychium andPolypodium californicum (Fig. 7). With the exception ofApiaceae, pollen of wetland plants (i.e. Cyperaceae, Typha,Salix) was not recovered. The total abundance of diatomsand chrysophyte stomatocysts declines from its maximum at100 cm to a low at 15 cm (Fig. 8). The abundance of subaerialspecies increases in the early part of the historic period at theexpense of slightly brackish species, and spores of vesicular–arbuscular fungi are also abundant.
Charcoal is found in nearly all of the ARM samples, and thereis great variability in deposition rates of charcoal through time(Fig. 6). In general, however, charcoal deposition is less duringAR-3a and increases to consistently higher influx during AR3b.Charcoal influx is generally high during the historic period ofAR-4.

Discussion

Vegetation history

The vegetation of the Late Pleistocene of southwesternCalifornia is only known from a handful of sites. Andersonet al. (2002) documented a middle Wisconsin (ca. 41 000 cal. aBP) site in Riverside County. Other sites of middle and lateWisconsin age include Mystic Lake Slough (Anderson, 2003)and the Rancho La Brea (Frost, 1927; Warter, 1976; Marcus andBerger, 1984; Shaw and Quinn, 1986; Stock and Harris, 1992;Ward et al., 2005), Carpenteria (>38 000 14C a BP; Chaney andMason, 1933; Fergusson and Libby, 1964) and McKittrick (ca.38 000–10 000 14C a BP; Mason, 1944; Berger and Libby, 1966)palaeofloras. In the southern San Joaquin Valley is the TulareLakebeds site (Atwater et al., 1986; Davis, 1999) spanning mostof Wisconsin. From marine cores in the Santa Barbara Basin,Heusser (1978, 1995, 1998) documented continuous change inupland vegetation for portions of southwestern California overthe last interglacial–glacial cycle. Conifers – Pinus, Abies andJuniperus or Cupressus – dominate the inland sites, unlike theflora of today, which is dominated by non-trees. Pollen of this


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Figure 8 Diatoms and other siliceous microfossils concentrations (numbers cm�2) for Abalone Rocks Marsh core 99-03


time period is similar to pollen deposited �800–1000 m highertoday in the mixed conifer forests of the San Jacinto and SanBernardino Mountains (Anderson and Koehler, 2003),suggesting that annual temperatures were 4–58C lower duringthe Last Glacial Maximum (Anderson et al., 2002).

The latest Pleistocene

The bottom pollen spectra from SP suggest that already by ca.11 800 cal. a BP a variety of plant communities existed nearthe site, including pine stands, coastal sage scrub andgrassland (Fig. 4). However, records from three coastal sitesdocument the occurrence of a coniferous forest during theLate Pleistocene on Santarosae. The Canada de los Sauces(Santa Cruz Island) florule (Chaney and Mason, 1930) datesfrom 12 840� 350 a BP (15 160 cal. a BP; Anderson et al.,2008) to 14 200� 250 a BP (17 020 cal. a BP; Fergusson andLibby, 1964). The florule consists of Pseudotsuga (taxifolia)menziesii (coastal Douglas fir), Pinus muricata forma remorata(Santa Cruz Island pine), and Cupressus goveniana (Gowencypress) forest with a diverse understory. Today, the site isdominated by introduced grasses, but Chaney and Mason(1930) compared the Pleistocene flora to modern coastalconifer forest near Fort Bragg, some 700 km north along theCalifornia coast. On SRI (Arlington Canyon; Kennett et al.,2008) and San Miguel Island (Daisy Cave; West, 1994), bothalso presently covered by introduced grasses, Pinus pollendominates the Late Pleistocene (<13 000 cal. a BP) sedimentsas well. These data suggest that pine (probably Pinusmuricata; West and Erlandson, 1994) covered parts of theisland during the Pleistocene and, with the subsequent declineof forest on the island, non-arboreal vegetation predominated.


Late Pleistocene pollen spectra from the Santa Barbara Basinto the west are dominated by Pinus and other conifers(Heusser, 1978, 1995, 1998), with Quercus and Alnus (alder).Dominated by pollen input from rivers and streams drainingthe nearby uplands, this confirms the importance of trees,particularly pines, in the coastal zone during the LatePleistocene. These regions are dominated by non-arborealvegetation today.

The minimal occurrence of conifer pollen in the SP sampledeposited during the latest Pleistocene suggests either that treespecies were confined mainly to the lower elevations of theIsland during this time, or that the transition to largely non-arboreal vegetation was relatively rapid. This was a period ofmajor change on the northern Channel Islands, both geo-graphically and in terms of human history. As sea level roseworldwide, the ancestral Santarosae island become separatedinto the four islands present today (Kennett, 1995), whereaswarmer, oxygen-poor waters developed in the adjacent SantaBarbara Basin (Kennett and Ingram, 1995). Human populationsalso increased for the first time on the islands (Johnson, 1977;Johnson et al., 2002), and their effects on vegetation shifts arenot yet fully explored.

The early Holocene

Palaeobotanical data from the early Holocene are very rare insouthern California. Pollen data from SP suggest increasinglydrier conditions during the early Holocene on SRI, particularlyafter ca. 9150 cal. a BP. Pollen richness declined and a lack ofaquatic pollen types indicates that the pond was dry moreoften than before. Coastal sage scrub, primarily coyote brush(Baccharis), covered the nearby hillslopes. Pollen data from



the Santa Barbara Basin (Heusser, 1978, 1995, 1998) suggestdrier, near-modern vegetation associations were establishedregionally along the coast by ca. 11 000 cal. a BP as well.Pollen is not preserved in early Holocene (ca. 10 800–7500 cal. a BP) Mystic Lake Slough sediments (Anderson,2003), which are calcareous silty clays with interspersed sandlayers, and a distinct zone of calcareous rhizoconcretions.This combination suggests arid conditions with generallylowered groundwater tables. These changes are also sugges-tive of progressive drying during the early Holocene. Incontrast, Kirby et al. (2005), Bird and Kirby (2006) and Birdet al. (2009) suggested wetter conditions at Lake Elsinore fromca. 9450 to 7670 cal. a BP, and also at Dry Lake in the SanBernardino Mountains from ca. 9000 to 7500 cal. a BP as aresult of a strengthened North American Monsoon. We find noevidence in our data for an increase in precipitation at thattime, although our chronology for the early Holocene may beinadequate to resolve this event.

The middle and late Holocene

By ca. 6900 cal. a BP grasslands had recovered not onlyaround higher-elevation SP, but also in the lowlands nearARM. Coastal sage scrub vegetation, characterised byabundant Baccharis-type pollen, was important at both sites.Small amounts of Pinus, Quercus and isolated chaparral andsage scrub (e.g. sagebrush/wormwood (Artemisia) and buck-wheat (Eriogonum)) plants are found throughout the record atSP. The Cole and Liu (1994) ARM record documented marinesediment input into the marsh during the early portion of thisrecord with high abundance of salt-tolerant plants, includingmembers of the Chenopodiaceae. This is largely confirmed inour pollen and diatom data. Diatom preservation is poor incoarser-grained sediments, leading to a biased assemblage.Fragments of the marine diatom genera Thalassiosira andCoscinodiscus in sediments deposited during this time wereprobably the result of aeolian or storm wave transport. Thebrackish species (Nitzschia commutata) may have existed onthe marsh surface, while those species that are found insubaerial environments, including soil (i.e. Hantzschiaamphioxys, Luticola mutica, Pinnularia borealis) wereprobably transported to the site or grew in seasonally moistsoils in higher parts of the marsh. By ca. 4500 cal. a BP anincrease in wetland plants at SP indicates higher groundwatertables, and a more frequent wetting of the pond sediments.These conditions continued largely intact around SP until thebeginning of the historic period.

Pollen dominance at ARM changed after ca. 3500 a ago tothe Asteraceae (Cole and Liu, 1994), paralleled in our study,but with Baccharis and sedges signifying increased freshwaterinput. In addition, our new analysis shows dominance also byother upland pollen types, including Eriogonum, Ipomopsis/Gilia and several of the subgroups of the Asteraceae. Manyspecies of ferns and fern allies become important during thistime period. For instance, spike moss (Selaginella cf. bigelovii)is nearly confined to this time and towards the recent. Thisperiod may reflect an increase in freshwater input into themarsh, and greater development of vegetation on thesurrounding uplands. The former interpretation is supportedby the occurrence of quillwort (Isoetes) spores, a pteridophyte,confined to freshwater and/or moist ground (Hickman, 1993).Evidence widespread in the western hemisphere (e.g. Rodbellet al., 1999; Sandweiss et al., 2001; Moy et al., 2002; Barronet al., 2003; Rein et al., 2005) suggests strengthening of ElNino–Southern Oscillation at this time. In southern California,


this would have led to increased winter precipitation and mayexplain the changes seen in the ARM record here.

The lag between the pollen and diatom data indicating anincrease in fresh water may be due to the location of themacrophytes and the means by which they obtain water. Theincreased moisture in the lower part of Zone 2 of Cole and Liu(1994) may indicate an increase in fog related to a change in seasurface temperature. While this may provide sufficient moisturefor vegetation, it may be insufficient to support the increasedfreshwater flow necessary for a robust diatom flora. Importantspecies present (Hantzschia amphioxys, Luticola mutica,Pinnularia borealis) occur in soil as well as in springs, andseasonally moist surfaces (Starratt, unpublished data).

During the middle and late Holocene, the Santa BarbaraBasin record suggests that Quercus woodlands and grasslandsdominated coastal communities, with expansion of the coastalsage scrub and chaparral communities. However, themaximum extent of the chaparral and coastal sage scrub(e.g., Artemisia, Rosaceae, Rhamnaceae, Anacardiaceae)occurred during the late Holocene (Heusser, 1978). At MysticLake Slough, middle Holocene sediments contain abundantwell-preserved pollen of grassland with sage scrub andchaparral vegetation types on the surrounding slopes (Ander-son, 2003). These overbank deposits suggest that water tableswere once again high. The Las Flores Creek (San Diego County)record, covering the last ca. 4800 a (Anderson and Byrd, 1998),shows pollen from riparian plants, including Typha (cattail)and sedges, is common throughout the section, but by ca. 3000 aago a vegetation mosaic including elements of the coastal sagescrub, chaparral and grassland communities was establishednear the site. The timing of late Holocene expansion of coastalsage scrub is nearly identical to the record from the Santa BarbaraBasin.

Historic period

The impact of Euro-American settlement and land use isdemonstrated through the introduction of non-native plantspecies to the island after ca. AD 1850 (Figs. 4 and 7). Theestablishment of the introduced Erodium, a plant spread bygrazing and pasturing (Mensing and Byrne, 1998), is found atboth locations and must have spread rapidly across the island.Sporormiella, a dung fungus associated with herbivores (Davisand Shafer, 2006), was recovered in the SP record. At least twoother herbaceous plants – Plantago and Ambrosia – expandedduring the historic period as well. Establishment of populationsof Cupressus macrocarpa (Monterey cypress) and later byEucalyptus (gum) is recorded in the ARM record. Eucalyptuswas widely planted in southern California after 1872 (Bulman,1988), and both species were subsequently planted near thehistoric ranch site at Beechers Bay to the northwest of themarsh. Cheno-Am pollen also increases in the later portion ofthe zone, and may represent an additional introduced species,such as one of the alien Chenopodium or Atriplex species nowcommon on the island (Junak et al., 1997). The number of fernand fern allies spores dramatically increases, with increases inBotrychium, Pellaea, Adiantum and Polypodium californicum,as well as several unidentified spores. Their expansion mayhave been facilitated by changing soil moisture conditions.

Erosion of upland soils, as shown by thicker sedimentpackages and higher magnetic susceptibilities, increasedsubstantially during the most recent 150 a – a 12-fold increasefor ARM and a nearly 36-fold increase for SP. The historic ratesof erosion into the basins are, as far as can be determined withour chronologies, unprecedented during the Holocene for thisisland. The increase in pollen and spore indicators of grazing



suggests this may be a result of the introduction of largenumbers of herbivores during this period.

Fire history

Sedimentary charcoal has been identified from many locationson the Channel Islands. Orr (1968) identified and collectedcharcoal on SRI dating well back into the Pleistocene, includingseveral radiocarbon-dead ages (>30–40 ka). Johnson (1977;San Miguel Island) and Brumbaugh (1980; Santa Cruz Island)identified charcoal in palaeosols and alluvial sections, whereasCole and Liu (1994) extracted charcoal from their original ARMcore. These studies and ours document the importance of fireduring the Holocene on SRI.

The SP sediments show high influx of charcoal (Fig. 6) duringthe period of transition from forested to non-forestedconditions. Declining influx during the early Holocene suggeststhat fire occurrence was probably at a minimum for the entirerecord. Based on our palaeovegetation interpretations, this wasa period characterised by extended drought, with minimalbiomass for burning on the island. This minimum in charcoalinflux lasted until ca. 7000 cal. a BP, at which time charcoalinflux, and therefore it is assumed fire, increased. Sediments ofthe early Holocene were not recovered from ARM, but by ca.7000 cal. a BP both pollen and charcoal were being depositedthere.

Although both sites show a subsequent general increase incharcoal through time, the patterns are very different at eachsite. Charcoal influx for ARM exhibits greater variability than atSP. Part of this can be explained by the finer sampling intervalsemployed for the ARM record than for SP (averaging 21 versus80 a between samples, respectively), but the samplingdifferential declines to 19 and 42 a between samples afterca. 4500 cal. a BP, during which time charcoal influx generallyincreases again in both records. Even so, the amounts ofcharcoal deposited in the SP record are less by a factor of 5–10than for ARM (Fig. 6).

So what factors could account for these patterns? We believethat the difference in charcoal deposition (less at SP, more atARM) is due to a combination of the dominant vegetation typeat each site and the characteristics of the drainage basin. For SP,a combination of a small drainage basin with no inflowingstreams, and dominance by grasslands with Baccharis on thesideslopes, produced little sedimentary charcoal. ARM, incontrast, has a large drainage basin and is open to the ocean. Inaddition, the pollen record suggests a greater variety ofvegetation types, including grassland and Quercus grassland,sage scrub with Baccharis, and conifer woodland nearby.Burning of these vegetation types could produce greatercharcoal, transported by streams to the marsh.

But the increase in charcoal through time at both sites couldbe explained by a combination of greater biomass developmentsince the middle Holocene, as seen in the pollen record, andpotentially an increase in influence of humans on the island.There is considerable debate about the impact of NativeAmerican burning on the California landscape (Keeley, 2002,2006). Ethnographic and historical accounts document regularuse of fire by the Chumash prior to its suppression in the 18thcentury (Timbrook et al., 1982), with Carroll et al. (1993)suggesting that the island Chumash or their predecessors mayhave set fires purposely for management of vegetationresources. By contrast, coastal California today has one ofthe lowest lightning fire frequencies in North America (Junaket al., 1995; see Keeley, 2002, 2006), and only 2–5% oflightning strikes actually result in fire (Minnich et al., 1993). Ifthis was true in the past, lightning ignitions alone may not have


been frequent enough to account for the abundance of charcoalin these sediments.

Human occupation of Santarosae and the adjacent main-land began as early as ca. 13 000 cal. a BP (Erlandson et al.,1987, 1996, 2008; Johnson et al., 2002; Kennett, 2005;Kennett et al., 2009). However, only a handful of sites arepresently known from the islands prior to ca. 8000 cal. a BP,probably indicating low populations (Kennett, 2005). Sub-sequently, populations began to expand here by 7500 cal. aBP (Kennett, 2005), as well as on the mainland (Glassowet al., 2007). This may have been driven by a periodicincrease in marine productivity, shown by lowered oceantemperatures (Glassow, 1993; Glassow et al., 1994). Duringthe middle Holocene, the number of sites increases in bothcoastal and inland settings (Kennett, 2005), including nearARM. In certain cases, middle Holocene sites overlie dunedeposits, which in turn overlie early Holocene sites (Kennett,2005) – additional evidence for an intervening dry period.Many middle Holocene sites from the island interior arelocated on ridge tops, not positioned close to perennial watersources (Kennett, 1998), suggesting somewhat wetter con-ditions island-wide at that time. In addition, the importance ofgrassland, woodland and sagebrush communities in the inlandis shown by the common occurrence of milling equipment anddigging-stick weights there at this time (Kennett, 1998).

The late Holocene ushered in a time of more complicatedsettlement patterns and improvements in watercraft, perhapsafter ca. 4000 cal. a BP on the coastal mainland (Glassow et al.,2007), but certainly by 3000 cal. a BP on SRI (Kennett, 2005;Kennett et al., 2009). This is indicated by a larger number ofcoastal villages in smaller drainages, and a greater number ofradiocarbon dates in general on SRI (Kennett, 2005). However,the number of interior sites declined during the late Holocene,even as presumed island population increased again after ca.1400 cal. a BP (Kennett, 2005; Kennett et al., 2009).

The similarity between the terrestrial biomass productivity(as shown by the pollen record), the charcoal particlestratigraphy and the archaeological records, with minimabetween ca. 9150 and 6900 (biomass and burning) or priorto ca. 7500 cal. a BP (settlement record), is evidence forsome form of human influence on landscape burning on SRIduring the Holocene. The case for this is even greater duringthe last 2000 a, as a global compilation suggests a decline inbiomass burning (Marlon et al., 2008). Humans almostcertainly were the primary source of ignition, considering therarity of lightning ignition of wildfires, at least on the modernislands.

Charcoal influx during the historic period remains high atARM, and is the highest in the entire SP record. This is curious,since no historically documented fires on SRI have beenrecorded since ca. AD 1850. Steven Viers (unpublished data,1999) examined two fire-scarred Pinus torreyana trees on SRI,with the last fires being recorded in the mid 19th century. This isconsistent with the establishment of ranching there. Whatmight account for these high accumulation rates? A strongpossibility is remobilisation of older sediments from slideslopesby grazing livestock during the historic ranching period.Sediment accumulation rates at both sites increased dramatic-ally during the historic period: �12 times the prehistoric rate atARM (0.087 cm a�1 vs. 1.0 cm a�1) and 36 times at SP(0.028 cm a�1 vs. 1.0 cm a�1). Some of this charcoal could havecome from burning of wildland and agricultural land on themainland, with deposition by offshore Santa Ana winds, whichtypically fan fires during the late summer and autumn insouthern California (e.g. Lessard, 1988; Keeley and Fothering-ham, 2003). The fire suppression and fire exclusion that havebeen so effective during the last century in western forests



(Brown et al., 2004; Stephens, 2005) does not apply toshrublands of southern and central coastal California, wherehuman ignitions account for the majority of fires (Keeley andFotheringham, 2003).

Conclusions

Holocene records of vegetation change and fire are rare in aridsouthwestern California, but our records for Santa Rosa Islandsuggest that, at least for coastal California, forest communitieswere replaced by mixed grassland and scrub communities byca. 12 000 cal. a BP. These events were certainly fostered bychanging climates at the end of the Pleistocene, and also bychanges in strength and position of coastal currents, which mayhave limited fog precipitation, an important auxiliary source ofmoisture along the north coast. The potential role of humans onthis newly colonised landscape is left open at this time. It isunclear what role, if any, rising sea level played in vegetationchanges at this time, but stabilisation of sea level along theCalifornia coast between ca. 8000 and 6000 cal. a BP (Mastersand Aiello, 2007) may have allowed sediment to accumulate atAbalone Rocks Marsh at this time.

Grasslands with Baccharis scrub dominated at higherelevations on Santa Rosa Island during the early Holocene,but between ca. 9150 and 6900 cal. a BP effective precipitationdeclined during the earliest Holocene, and Soledad Pond driedmore frequently. After ca. 6900 cal. a BP, however, effectiveprecipitation increased, with grassland and scrub communitiesdominating around Soledad Pond, and a variety of commu-nities, including grassland, oak grassland, pine woodland and

Table A1 Asteraceae pollen types for the Channel Islands

Asteraceae type Example genera

Ambrosia type Ambrosia, Iva, XanthiumArtemisia type ArtemisiaCirsium type Cirsium, Centaurea, ArctiumLactuceae type Cichorium, Lactuca, Taraxacum,

Hieracium, Microseris, (Rafinesquia),(Stepanomeria), Uropapus?

Baccharis type Baccharis, Brickellia, Conyza, Encelia,Erigeron, Grindelia, Gutierrezia, Heterotheca,Layia, Perityle, Pluchea, Senecio

Helianthus type Coreopsis, Helianthus, Madia, Viquiera

Chaenactis type Bebbia, ChaenactisSolidago type Aster, Euthamia, Gnaphalium, Solidago

Achillea type Achillea, Anthemis, Chrysanthemum, Cotula,Matricaria

Malacothrix type Malacothrix

Eriophyllum type Eriophyllum


coastal scrub growing near Abalone Rocks Marsh. The mostsignificant Holocene change in vegetation occurred during thehistoric period, with introduction of non-native speciesassociated with grazing on the island.

The fire history closely parallels both the vegetation historyand the archaeological record on Santa Rosa Island. Fires mayhave been more frequent during the latest Pleistocene–earliestHolocene transition, and less frequent during the dry early tomiddle Holocene. Fires probably increased after ca. 6900 cal. aBP, as both biomass and Native American settlement andcultural complexity increased. If natural ignitions by lightningwere as infrequent during the Holocene as they are today, thesecorrelations suggest that Native American burning was animportant ecosystem component on the northern ChannelIslands during the Holocene.

Acknowledgements We thank Dr Jan Van Wagtendonk (USGS) forbringing the opportunity to conduct fire and vegetation history on theChannel Islands to our attention; Kate Faulkner (NPS) and KathrynMcEachern (NPS) for assistance with logistics and paperwork; SarahChaney (NPS) for showing us around Santa Rosa Island, for locallogistical assistance, for help in obtaining the Soledad Pond profileand for identifying plants around Soledad Pond; Mitch Power (Univer-sity of Utah) (Soledad Pond and Abalone Rocks Marsh) and MichaelCleirigh (NPS) (Abalone Rocks Marsh) for help in the field; Dr HarryAlden (Smithsonian Institution) for macrofossil identification; AmyKelly (NAU) for laboratory assistance; Susan Smith, Douglas Hallettand Victor Leshyk (all NAU) for help with computer analysis anddiagram construction; and Mary McGann, John Barron, Douglas Ken-nett and an anonymous reviewer for thoughtful reviews. This researchwas supported by Cooperative Agreement 1443CA8000-8-0002 to RSAfrom the NPS. Much of this manuscript was written while RSA was onsabbatical at the Universidad de Granada (Espana), Departamento deEstratigrafıa y Paleontologıa. LOP Contribution # 113.

Appendix

Characteristics

Tricolporate, small spines, suboblate to spheroidalTricolporate, spheroidal to subprolate, thick exine in intercolpiumLarge (generally >40mm), spines broad at baseFenestrate (or pseudofenestrate)

Tricolpate or tricolporate, spheroidal, �25mm, spine gracile,spine length:breadth �1:1

Tricolporate, spine gracile (up to �5mm long), spine length:breadth �2:1, transverse furrow presentMassive spines, grain deeply lobateSpine density great, spine often bulbous at base, spine length:breadth �1:1, lightly lobateTricolporate, thick exine in intercolpium (much like Artemisia,but with stout spines), prolate to subprolate, tectum or collumellaegive intercolpium reticulate-like appearance between spinesTricolpate, large, suboblate to spheroidal, broad furrow, spinesnumerous but short. Similar to Lactuceae/Liguliflorae so perhaps pseudofenestrateLike Chaenactis type, but spine broad at base, and more massive


Table A2 Diatom species recovered from the Abalone Rocks Marsh core

Diatom Salinity preference

Achnanthes brevipes Agardh BrackishA. brevipes var. intermedia (Kutzing) Cleve BrackishAmphora granulata Gregory MarineAulacoseira granulata (Ehrenberg) Simonsen FreshCoscinodiscus marginatus Ehrenberg MarineCosmioneis pusilla (W. Smith) Mann and Stickle Fresh and brackishCymbella sp. FreshEpithemia adnata (Kutzing) Brebisson Fresh and brackishEunotia arcus Ehrenberg FreshE. monodon Ehrenberg FreshE. muscicola var. tridentula Norpel and Lange-Bertalot FreshE. pectinalis var. undulata (Ralfs) Rabenhorst FreshE. triodon Ehrenberg FreshGyrosigma acuminatum (Kutzing) Rabenhorst FreshHantzschia amphioxys (Ehrenberg) Cleve and Grunow Fresh and brackishLuticola mutica (Kutzing) Mann Fresh and brackishLyrella lyroides (Hendey) Mann MarineMeridion circulare var. constrictum (Ralfs) Van Heurck FreshNavicula cincta (Ehrenberg) Ralfs Fresh and brackishN. jaagi Meister FreshN. tripunctata (O.F. Muller) Bory FreshNitzschia bryophila (Hustedt) Hustedt FreshN. communis Rabenhorst FreshN. commutata Grunow Fresh and brackishN. filiformis (W. Smith) Van Heurck Fresh and brackishN. granulata Grunow Brackish and marineN. palea (Kutzing) W. Smith FreshN. scalpelliformis (Grunow) Grunow BrackishN. sociabilis Hustedt FreshOpophora schwartzii (Grunow) Petit BrackishParalia sulcata (Ehrenberg) Cleve Brackish and marinePinnularia appendiculata (Agardh) Cleve FreshP. borealis Ehrenberg FreshRhaphoneis surirella (Ehrenberg) Grunow Brackish and marineRhopalodia gibba (Ehrenberg) O. Muller FreshR. gibberula (Ehrenberg) O. Muller BrackishR. musculus Kutzing BrackishSellaphora bacillum (Kutzing) Mereschokwsky FreshS. laevissima (Kutzing) Mann FreshS. pupula (Kutzing) Mereschokwsky FreshStauroneis undulata Hilse FreshSurirella striatula Turpin BrackishSynedra acus (Kutzing) Lange-Bertalot FreshS. gaillonii (Bory) Ehrenberg MarineTabularia tabulata (Agardh) Snoeijs Fresh and brackishThalassiosira eccentrica (Ehrenberg) Cleve Marine


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Fire and vegetation history on Santa Rosa Island, … · Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California