Early Eocene plant diversity and dynamics in the Falkland flora, Okanagan Highlands, British Columbia, Canada

ORIGINAL PAPER

Early Eocene plant diversity and dynamics in the Falklandflora, Okanagan Highlands, British Columbia, Canada

Robin Y. Smith & James F. Basinger &

David R. Greenwood

Received: 25 May 2011 /Revised: 11 September 2011 /Accepted: 20 September 2011 /Published online: 21 October 2011# Senckenberg Gesellschaft für Naturforschung and Springer 2011

Abstract The early Eocene fossil localities of the Okana-gan Highlands in British Columbia, Canada, and Wash-ington State, USA, span the Early Eocene ClimaticOptimum, the warmest period of the Cenozoic, and reflectmild but equable upland climates (mean annual temperature<15°C, cold month mean temperature >0°C). The Okana-gan Highlands region has been identified as a centre oftemperate plant family diversification in the northernhemisphere during the early Eocene. Here, we test thehypothesis of mid-latitude high diversity through rarefac-tion analysis of unbiased census collections from theOkanagan Highlands Falkland fossil locality, demonstratinglevels of diversity similar to those documented at hyper-diverse Eocene sites in South America when adjusted forsample size. An explanation for this diversity may lie in theupland character of the Falkland site, as altitudinalgradients provide a mosaic of microhabitats throughinteracting effects of topography and climate. Fine-scaletrends are also examined within the Falkland site, demon-

strating a shift in plant community composition over time toa more diverse flora, although the dominant taxa persistthrough the section in varying levels of abundance. Intra-site patterns in plant community structure and compositionare attributed to a combination of environmental factors,including disturbance and microhabitat diversity.

Keywords Fossil flora . Okanagan Highlands . BritishColumbia . Early Eocene Climatic Optimum . Diversity .

Rarefaction

Introduction

Shellito and Sloan (2006) described the Eocene world as a“lost paradise,” when tropical vegetation extended wellnorth of current ranges, and the poles were ice-free. Plantfossils yield information on terrestrial palaeoclimate thatcomplements geochemical proxies and provide an indicationof what the world can look like under very different globalclimate conditions. There is currently a particular interest instudying periods of Earth history that represent “greenhouse”climates (Royer 2008). One such key period is during theinterval of peak Cenozoic warmth in the early Eocene,approximately 53–50 Ma, referred to as the Early EoceneClimatic Optimum (EECO; Zachos et al. 2001, 2008).

The early Eocene fossil localities of the OkanaganHighlands in British Columbia, Canada, and WashingtonState, USA (Fig. 1) have received growing attention inrecent years as sources of diverse and well-preserved plantand insect fossil assemblages that provide a window onthis key interval of global warmth (e.g. Archibald andMathewes 2000; Archibald et al. 2010; DeVore et al. 2005;DeVore and Pigg 2007; Greenwood et al. 2005; Smith et al.2009). These sites, formed in similar lacustrine depositional

Electronic supplementary material The online version of this article(doi:10.1007/s12549-011-0061-5) contains supplementary material,which is available to authorized users.

R. Y. Smith (*)Department of Geological Sciences, University of Saskatchewan,114 Science Place,Saskatoon, SK S7N 5E2, Canadae-mail: [email protected]

J. F. BasingerDepartment of Geological Sciences, University of Saskatchewan,114 Science Place,Saskatoon, SK S7N 5E2, Canada

D. R. GreenwoodDepartment of Biology, Brandon University,270 18th Street,Brandon, MB R7A 6A9, Canada

Palaeobio Palaeoenv (2012) 92:309–328DOI 10.1007/s12549-011-0061-5

http://dx.doi.org/10.1007/s12549-011-0061-5

environments within a relatively short period of time ofapproximately 3 million years, provide comparative data withwhich to explore variation in biotic communities across timeand space (Archibald and Greenwood 2005). The fossil recordindicates that the early Eocene was characterised by generallywarm [i.e. mean annual temperature, (MAT) ≥15°C] andequable climates in North America, with winter temperaturestypically >0°C, even at high latitudes (Greenwood and Wing1995; Greenwood et al. 2010; Wing et al. 1991; Wing andGreenwood 1993). The Okanagan Highlands representrelatively cool upland environments (i.e. MAT <15°C) in thisgreenhouse context in the Eocene landscape of northwesternNorth America, although still with mild winter temperatures(cold month mean temperatures >0°C; Greenwood et al.2005; Smith et al. 2009).

The Eocene was a time of intense volcanic and tectonicactivity in the Interior of British Columbia, resulting in thedevelopment of a topographically diverse landscape thatincluded cool upland niches and the appearance of montaneforests (Greenwood et al. 2005; Wehr 1998; Wolfe 1987).The extent of microthermal climates in the region waslikely restricted during the early Eocene up to and includingthe EECO; therefore, the establishment of cool uplandenvironments provided an opportunity for the expansion ofmesothermal lineages into microthermal climates and theirsubsequent diversification (DeVore et al. 2005; DeVore andPigg 2007; Pigg and DeVore 2010; Wehr 1998; Wolfe1987) and the flourishing of microthermal taxa present asminor elements in lowland floras (Wehr and Hopkins1994). During the early Eocene, plant families such asAceraceae (now considered part of Sapindaceae s.l.),

Betulaceae and Rosaceae underwent rapid diversification,reflected in the fossil record of the Okanagan Highlands(DeVore et al. 2005; DeVore and Pigg 2010; Wehr 1995,1998; Wolfe 1987; Wolfe and Wehr 1987). This pattern ofdiversification, along with the coexistence of temperate andtropical taxa, is also seen in the insect fossil record of theOkanagan Highlands (Archibald and Mathewes 2000;Archibald and Farrell 2003; Archibald et al. 2010;Greenwood et al. 2005; Wehr 1998).

In the modern world, there is a well-documented latitudinalgradient in diversity, with the highest diversity in tropical low-latitude regions where there is abundant insolation and lowthermal seasonality (for a review, see Archibald et al. 2010).The Neotropics in particular show elevated species richnesseven relative to other tropical regions (Wilf et al. 2005). In theearly Eocene, global climate was characterised by a shallowerlatitudinal gradient in temperatures and a less pronouncedseasonal variation in mid-latitudes, as demonstrated by thepresence of frost-intolerant taxa, such as palms, in continentalinteriors of North America (Wing and Greenwood 1993;Greenwood and Wing 1995). Although a latitudinal gradientin plant diversity may have existed on a broad scale in theearly Paleogene (Harrington 2004), there is also evidence ofregional “hot spots” in diversity at mid-latitudes in bothNorth and South America (Archibald et al. 2010; Iglesiaset al. 2007; Johnson and Ellis 2002; Wilf et al. 2003, 2005).

In South America, high diversity in plant taxa has beenreported from macrofossils at the mid-latitude early tomiddle Eocene Laguna del Hunco and Río Pichileufú sitesin the Patagonia of Argentina (Wilf et al. 2003, 2005). Thisdiversity has been attributed to a combination of in situ

Fig. 1 Map showing study sitelocation (Falkland) in BritishColumbia, Canada, along withother Okanagan Highlands fossillocalities. a Outline map ofCanada, with GIS data providedby The Atlas of Canada(Department of NaturalResources Canada). b Detailedview of portion of BritishColumbia, Canada andWashington, USA, with selectOkanagan Highlands fossillocalities: 1 Driftwood Canyon,2 Horsefly, 3 McAbee,4 Quilchena, 5 Princeton/OneMile Creek, 6 Republic, WA

310 Palaeobio Palaeoenv (2012) 92:309–328

development associated with warm temperatures and theaddition of spillover of taxa from even more diverse lowerlatitudes (Wilf et al. 2005). The origins of Neotropicalrainforests have been traced as far back as the Paleocene inColombia and were well developed in lowland SouthAmerica by 58–55 Ma, supporting a trajectory of increasingdiversification over time following recovery from the end-Cretaceous extinction event in concert with early Paleogenewarming (Jaramillo and Dilcher 2000; Jaramillo 2002;Graham 2011; Wing et al. 2009). In the northern hemisphere,high diversity has been documented from macroflorasrepresenting lowland tropical rainforests in the Paleocene ofColorado (Johnson and Ellis 2002). Rose et al. (2011),however, found essentially flat diversity in the Paleocene ofNorth America for mammals, suggesting that full recoveryfrom the end-Cretaceous mass extinction was delayed formammals. Peppe (2010) also found delayed recovery offloristic diversity in the Williston Basin of the Northern GreatPlains of North America, where levels of diversity remainedlower than in the Cretaceous during the early to middlePaleocene, and even declined in conjunction with a mildcooling trend during this period. In contrast, Wing et al.(1995) found a gradual increase in plant diversity in the earlyto mid-Paleocene, and little correspondence between trendsin plant and mammal diversity. Studies of macrofloras fromthe Paleocene–Eocene Denver Basin in North America,however, have demonstrated considerable diversity gradientswithin a regional context (Johnson et al. 2003), matchingresults for Cretaceous dinosaurs in the same area (Vavrek andLarson 2010) and suggesting that high diversity might alsobe facilitated by local to regional level environmental factors,such as precipitation patterns and topography (Peppe 2010).

The Okanagan Highlands region has been identified as anorthern hemisphere centre for the diversification oftemperate plant families in a qualitative sense, indicatedby many first appearances in the fossil record (DeVore et al.2005; DeVore and Pigg 2007, 2010; Pigg and DeVore 2010;Wehr 1998). Here, we test this hypothesis quantitativelythrough rarefaction analysis of unbiased census collectionsfrom the Falkland fossil locality in the Okanagan Highlandsand demonstrate levels of diversity similar to thosedocumented at the hyperdiverse Eocene Patagonian siteswhen adjusted for sample size. This finding is consistentwith recent work on insect diversity in the OkanaganHighlands (Archibald et al. 2010). Fine-scale trends arealso examined within the Falkland site, with the resultsdemonstrating a shift in plant community over time to amore diverse flora dominated by angiosperms, although thedominant taxa persist through the section in varying levelsof abundance. The Okanagan Highlands fossil localitiesdemonstrate the importance of cool upland environments ina globally warm world, as well as the role of microhabitatdiversity in the landscape provided by altitudinal gradients.

Materials and methods

Plant macrofossils were collected from the early EoceneFalkland locality in south-central British Columbia, Canada(50.516°N, 119.628°W, 1369 m.a.s.l., Fig. 1). Falkland ispart of a series of correlative sites in British Columbia andWashington State known collectively as the OkanaganHighlands (Fig. 1) (Greenwood et al. 2005). Falkland hasbeen dated to 50.61±0.16 Ma, using U–Pb analysis ofzircons from a prominent volcanic ash layer within thefossil beds, placing the site in the waning phase of theEECO (Greenwood et al. 2005; Moss et al. 2005). Thepalaeoelevation of the site has been estimated, usingdifferences in both enthalpy and MAT compared to thoseat sea level sites, as being similar to or slightly higher thanthat of modern day; i.e. ≥ 1.3 km (Smith et al. 2009). Tribe(2005) reconstructed the palaeophysiography of the earlyEocene Southern Interior of British Columbia as similar inmany respects to the modern landscape, being a region ofupland plateaus and deeply incised valleys.

Macrofossils were collected using an unbiased censusapproach, whereby all specimens encountered in systemat-ically sampled quarries were collected and/or recorded.Two continuous and correlative vertical sections of approx-imately 2.5 m each were sampled in this manner. Inaddition, eight quarries of various sizes were censuscollected across the outcrop. Numerous specimens werealso collected from scree (without stratigraphic context) orfrom spot localities in situ in the outcrop in a selective(non-census) manner with the goal of improving thereference collection.

Based on site lithology and volcanic ash layers thatcould be traced laterally across the outcrop, the site wasdivided into three informal units (Smith et al. 2009; Fig. 2).The exposed outcrop is limited in vertical (approx. 3 m)and lateral (approx. 18 m) extent, representing a relativelyshort time interval, perhaps in the range of approximately6000–8000 years based on sediment accumulation rates(0.36–0.47 m/1000 years) from the coeval OkanaganHighlands Horsefly locality which features varved sedi-ments (Barton 1998), or more conservatively 103–104 years.A stratigraphic log of the outcrop (Fig. 2) reveals alacustrine sequence dominated by finely laminated clayand silt, with periodic influx of coarser material. Units 1and 3 comprise similar lithology: finely laminated, dark-grey, buff-weathering mudstone or shale, indicating low-energy deposition of sediments on the lake floor. Unit 2reflects a slightly higher energy environment with moreevidence of disturbance. Wave ripple marks appear brieflynear the base of Unit 2, coincident with the shift from finelylaminated claystone to muddy sandstone, suggesting achange in lake levels and shoreline position. A distinctivefish-kill layer is associated with the wave ripple marks in

Palaeobio Palaeoenv (2012) 92:309–328 311

Unit 2. Lithology immediately above the fish-kill layersuggests rapid sedimentation with high organic matter andash content. In addition to the wave ripple marks and thefish-kill layer, Unit 2 contains numerous ash layers,reflecting a period of active volcanism that would haveimpacted plant communities at the local and regional levels,both in terms of shaping the disturbance regime andpotentially modifying nutrient influx (Jolley et al. 2008).

As a first step towards understanding the Falkland fossilflora, specimens were sorted into discrete morphotypes,informal taxonomic categories based on aspects of mor-phology or leaf architecture (Johnson and Ellis 2002; Peppeet al. 2008). For dicotyledonous leaves, the approach andterminology outlined in the Manual of Leaf Architecture(Ellis et al. 2009) was followed, utilising database andspreadsheet resources developed by the Leaf ArchitectureWorking Group [see electronic supplementary material(ESM)]. Subsequently, the taxonomic literature was inves-tigated, and morphotypes were assigned to formal taxo-nomic categories where possible. Emphasis was placed onsituating the Falkland flora within the recent taxonomicliterature for the Okanagan Highlands, which has benefittedfrom careful study of particular plant groups (e.g. DeVore etal. 2005; Pigg et al. 2001, 2003, 2007; Radtke et al. 2005)and efforts towards whole-plant reconstructions utilisingassociated reproductive and vegetative material (e.g. Craneand Stockey 1985, 1987; Denk and Dillhoff 2005;Manchester and Dillhoff 2004; Schorn and Wehr 1986).

Census tally and other quantitative data as well asqualitative data derived from the macrofossil collectionwere divided into datasets of increasingly restricted criteria,suitable for the various types of analyses considered here(Table 1). For example, for the qualitative description of theplant communities at the Falkland site, the full dataset,including both census and biased collection specimens, areconsidered. For the quantitative analysis of trends indiversity, only census-sampled material is utilised. Thesedatasets are defined in Table 1. Datasets A and B(i) includethose specimens that were assigned to a “general” morpho-type category (e.g. toothed dicot, entire-margined dicot,conifer foliage, etc) due to a lack of taxonomicallydiagnostic features, poor preservation or incompleteness.These specimens remain in the full dataset as they provideinformation on the relative abundance of angiosperm andgymnosperm specimens, and it may be possible at somepoint in the future to assign them to specific morphotypes.Datasets B(ii), C and D exclude these general morphotypesas they undoubtedly lump multiple taxa and wouldtherefore skew an analysis of trends in diversity.

For the quantitative analysis of trends in diversity andplant community composition, several statistical methodsand diversity measures were explored. Alpha diversity inthe three units is measured via simple species richness

Fig. 2 Stratigraphic log of the Falkland site, showing three units sampledand the relative proportion of angiosperm and gymnosperm specimensrecovered in the three units [Dataset B(i)]. The time represented by thethree units is estimated to be approximately 6000–8000 years, or moreconservatively 103–104 years, based on sedimentation rates documentedat the coeval varved Horsefly site (see text). Cl clay, Si silt, Sa sand, vfvery fine, f fine, m medium, c coarse, vc very coarse


(number of morphotypes), along with a range of diversityindices. In order to assess trends within the site, as well ascompare Falkland with other relevant early Eocene sites,rarefaction analysis and non-metric multidimensional scal-ing (NMDS) were employed using the software packagePAST ver. 1.99 (Hammer et al. 2001). NMDS was chosenas an ordination technique to explore plant communityassociations in the three units. Importantly, NMDS has beenfound to perform well with ecological data that oftencomprises sparse data sets (with many zeros) with non-normal distribution patterns (McCune and Grace 2002). Inaddition, NMDS may be used with any distance measureand will preserve the rank order of among-sample similar-ities in the distance matrix on which it is based (McCuneand Grace 2002). These features make NMDS particularlywell suited to the examination of fossil datasets. Theordination was run on Dataset C (specimens from the twocorrelative stratigraphic sections). For the rarefactionanalysis, Dataset D (census dicots) from Falkland iscompared with census tally data from other mid-latitudeearly to middle Eocene lacustrine deposits reported in theliterature that have been sampled using an unbiased censusapproach (Table 2). We also ran the rarefaction analysisusing a more conservative subset of Dataset D, removingsome of the less-well-preserved singleton taxa and mergingsome taxa that may be variants of Alnus (see ESM).

Results

Overview of the Falkland fossil flora

Table 3 provides a preliminary list of plant taxa at theFalkland site, and the ESM contains a record of allmorphotypes, including those currently unassignable to

formally recognised taxa. Representative specimens areillustrated in Figs. 3 and 4. A minimum species estimatebased on foliage morphotypes includes 1 bryophyte, 5pteridophytes, 15 gymnosperms, 3 monocots, and 67dicots. Gymnosperms are dominated by taxa in Cupressa-ceae s.l., Pinaceae, and Ginkgoaceae (Fig. 3). Metasequoiaoccidentalis (Newberry) Chaney (dawn redwood) foliage isthe most commonly encountered fossil at the site, and seedand pollen cones are also present, although rare. Ginkgoadiantoides (Unger) Heer is also very common and oftenfeatures well-preserved cuticle. The fossil cuticle of G.adiantoides has been examined for both taxonomic featuresand to assess stomatal frequency as a proxy measure ofpalaeoatmospheric CO2 during the early Eocene (Smith etal. 2010).

Ferns and fern allies are rare features of the Falklandflora, represented by three specimens of fern pinnae (twotentatively assigned to Adiantum sp.), the floating fernAzolla and Equisetum. Monocot leaves lacking diagnosticfeatures apart from parallel venation are quite common atthe Falkland site, but their taxonomic affiliation remainsuncertain. The angiosperm dicot flora at Falkland is diverseand is particularly rich in taxa from families such asRosaceae, Betulaceae and Sapindaceae s.l. (Table 3, Fig. 4).In addition, there are many angiosperm families that arerepresented by a single taxon or few specimens at Falkland,contributing significantly to the diversity of the flora(Table 3).

Trends in diversity and plant community composition

Species richness, diversity and evenness

To assess species diversity in the three units at the Falklandsite, we use Dataset B(ii), which is limited to angiosperm

Table 1 Details of datasets used in analysis

Datasetidentifier

Shorthandreference

Description Number of specimens/no.of morphotypes

A Full dataset All specimens, including census and biased collections, all morphotypes 2052/138a 1560/133b

B(i) Census all All specimens collected from census-sampled quarries, including generalmorphotypes

1843/117a

B(ii) Census foliage All angiosperm and gymnosperm foliage specimens assigned to specificmorphotypes collected from census-sampled quarries; excludingreproductive morphotypes

1210/75b,c

C Stratigraphic sections All specimens assigned to specific morphotypes collected from the twocorrelative sections of approx. 2.5 m

964/94b,c

D Census dicots Including only dicot foliage morphotypes collected from census-sampledquarries; excluding general morphotypes FL99 and FL990

486/59b,c

a Including general morphotype categories: FL99 (toothed dicot foliage—general), FL990 (entire-margined dicot foliage—general), FL999(conifer foliage—general), FL9999 (monocot foliage—general) or FL9990 (reproductive or other plant part—general)b Excluding general morphotype categoriescMorphotypes FL21 and FL81 treated as a single morphotype, and morphotypes FL20 and FL23 treated as a single morphotype


and gymnosperm foliage morphotypes from census-sampled quarries. Reproductive morphotypes are excludedsince the extent of overlap with the foliage morphotypescannot be fully resolved. This dataset includes 1210specimens assigned to 75 morphotypes. Table 4 presentsselect measures of diversity, including species (morpho-type) richness, the Shannon–Wiener index (H), evenness(Pielou’s J), the Simpson index, Dominance and Fisher’s αfor systematically sampled quarries in the three units. Unit3, the youngest unit, demonstrates the highest diversity byany one of these measures. A t test for comparing theShannon–Wiener index from different sampling units(Hutcheson 1970; Zar 1999, formulas 8.62–8.65) demon-strates that the difference in diversity in pair-wise compar-isons of each of the three units is significant at α=0.05. Theevenness of diversity is similar across the three units butwith a trend to increased evenness in the upper unit, withPielou’s J ranging from 0.64 in Unit 1 to 0.73 in Unit 3. Abootstrapped comparison of this measure of evenness(calculated in PAST) demonstrates a significant differenceonly between Units 1 and 3, with adjacent units showing nosignificant difference in evenness.

Rarefaction analysis

In order to analyse changes in diversity over time at theFalkland site, rarefaction analysis was undertaken onabundance data from the three units, using the same datasetas for the determination of the diversity indices discussedabove; i.e. Dataset B(ii), angiosperm and gymnospermfoliage from census-sampled quarries. This analysis showsthat diversity is clearly highest in Unit 3 (Fig. 5). Unit 3 isthe youngest unit at the site and is also characterised by thecoolest climate (Table 5) and the lowest pCO2 estimates(Smith et al. 2010). The difference in rarefied richnessbetween Unit 1 and Unit 2 is not clear at this sample size asthe confidence intervals overlap, although there is asuggestion of a trend towards higher diversity in Unit 2.

Rarefaction data from Falkland (dicot leaf morphotypesonly, Dataset D) can be compared to those of other early tomiddle Eocene sites in North and South America reportedin the literature (i.e. Archibald et al. 2010; Johnson et al.2003; Wilf et al. 2003, 2005). In order to compare similarvolumes of material for the different localities, the Lagunadel Hunco site is presented by individual quarry (the four

Table 2 Details of early to middle Eocene mid-latitude fossil localities used for rarefaction analysis

Locality Age (Ma) Palaeolatitudea Number of dicotmorphotypes

Number ofspecimens

MAT (°C)b MAP(cm/year)c

Depositional setting Referenced

Falkland 50.61±0.16 ~54°N 59e 486e 7.3±2.08.7±4.8

121+52/-37149+125/-68

Lacustrine (upland) This paper

McAbee 52.90±0.83 ~54°N 23 125 10.1±3.0 108±35f Lacustrine (upland) 1, 2

Republic 49.42±0.54 ~51°N 58 1019 8.8±2.09.2±4.8

115±39f

135+111/-61Lacustrine (upland) 1, 3, 4, 5

Denver Basin(DMNH 2484)

~54 ~42°N 33 248 25.2 ±2.1 131+56/-40 Floodplain pond orsmall shallow lake

6

Río Pichileufú(RP-3)

47.46±0.05 ~46°S 39 213 19.2 ±2.4 N.A. Lacustrine 7

Laguna delHunco (LH)

51.91±0.22 ~49°S 132 3193 16.6 ±1.314.1 ±4.8

114+49/-34142+117/-64

Lacustrine 4, 5, 7

LH-2 51.91±0.22 ~49°S 61 609 18.2 ±1.9 105+45/-32 Lacustrine 4, 7

LH-4 51.91±0.22 ~49°S 53 1248 16.7 ±2.1 123+53/-37 Lacustrine 4, 7

LH-6 51.91±0.22 ~49°S 45 530 17.8 ±2.3 114+49/-34 Lacustrine 4, 7

LH-13 51.91±0.22 ~49°S 55 806 14.5 ±2.0 110+47/-33 Lacustrine 4, 7

MAT, Mean annual temperature; MAP, mean annual precipitation; N.A., data not availablea Palaeolatitude of the Falkland site calculated using the resources provided on the Ocean Drilling Stratigraphic Network GEOMAR website(http://www.odsn.de/odsn/index.html; note: website now offline). Palaeolatitude for Río Pichileufú is from Wilf et al. (2005). Palaeolatitudes forLaguna del Hunco and Republic are from Peppe et al. (2011). Other palaeolatitudes are estimated according to their modern position relative toFalkland, assuming roughly the same relative position in the early Eoceneb In all cases, the standard Leaf Margin Analysis (LMA) equation from Wing and Greenwood (1993) was used to estimate MAT as given in thesources listed, or calculated here in the case of Falkland (using Dataset A, all specimens). Where two estimates are given, the second is based onthe new global LMA equation in Peppe et al. (2011). Error is the greater of the standard error or 2°C (Wilf 1997)c Except where noted, MAP is calculated using the leaf area analysis equation in Wilf et al. (1998) as given in the sources listed, or calculated herein the case of Falkland (using Dataset A, all specimens). Where two estimates are given, the second is based on the new leaf area analysis equationin Peppe et al. (2011). Error is asymmetrical as it is converted from log values of the standard errord 1. Greenwood et al. (2005); 2. Archibald et al. (2010); 3. Passmore et al. (2002); 4. Wilf et al. (2003); 5. Peppe et al. (2011). 6. Johnson et al.(2003); 7. Wilf et al. (2005)e Based on Dataset D (data used for rarefaction analysis)f Estimated from bioclimatic analysis in Greenwood et al. (2005)


http://www.odsn.de/odsn/index.html

Table 3 Preliminary floral list for the Falkland site, with occurrence of taxa in units

Taxon or morphotaxon (organ; morphotype no.; reference specimen no.) Unit1

Unit2

Unit3

Scree

EQUISETALES

Equisetaceae

Equisetum sp. (A/F; FL098; US984-10292) – + + +

POLYPODIALES

Pteridaceae

?Adiantum sp. 1 (F; FL131; US959-10600) – – – +

?Adiantum sp. 2 (F; FL167; US960-10656) + – – –

Azollaceae

Azolla sp. (F; FL164; US959-10605) – – – +

Incertae sedis

Fern sp. 1 (F; FL146; US993-10479) + – – –

GINKGOALES

Ginkgoaceae

Ginkgo adiantoides (Unger) Heer (F; FL004; US981-10189) + + + +

Ginkgo dissecta Mustoe (F; FL096; US961-10642) – + – –

CONIFERALES

Pinaceae

Abies milleri Schorn and Wehr (F, CS, S; FL074, FL062, FL136; US986-10372, US967-9865, US998-10582) + + + +

Picea sp. (F, S; FL089, FL091; US959-10617, US959-10619) + + + +

Pinus sp. (F, SC, S; FL033, FL101, FL019; US997-10531, US959-10585; US967-9866) + + + +

Pseudolarix sp. (F, S; FL052, FL138; US992-10449, US997-10568) + + + +

Pinaceae sp. (PC; FL142; US970-9987) – – + –

Cupressaceae s.l.

Chamaecyparis sp. (SC; FL113; US959-10591) – – + +

Cupressinocladus interruptus (Newberry) Schweitzer (F; FL149; US997-10520) + – – +

?Glyptostrobus sp. (F; FL150; US985-10354) + + + –

Metasequoia occidentalis (Newberry) Chaney (F, SC, PC; FL012, FL059, FL139; US983-10262, US972-10117,US972-10107)

+ + + +

Sequoia affinis Lesquereux (F, PC; FL037, FL061; US970-9992, US969-9957) + + + +

Taxodium dubium (Sternberg) Heer (F; FL055; US973-10129) + + – –

Cupressaceae sp. 1 (F; FL031; US959-10611) + + + +

Cupressaceae sp. 2 (F; FL090; US969-9960) – – + –

Incertae sedis

?Cephalotaxaceae sp. (F; FL156; US967-9875) – + – –

Conifer foliage (F; FL064; US966-9842) – – + –

Conifer pollen cone (PC; FL036; US968-9892) – – + –

MONOCOTS

Monocot sp. 1 (F; FL005; US971-10069) + + + –

Monocot sp. 2 (F; FL123; US970-9985) + – + –

Monocot sp. 3 (F; FL130; US959-10599) – – – +

DICOTS

LAURALES

Lauraceae

Sassafras hesperia Berry (F; FL003; US959-10594) + + + +

?Lauraceae sp. (F; FL015; US972-10077) – + – +

PROTEALES

Platanaceae

Macginitea sp.a – – – –


Table 3 (continued)


Unit2

Unit3

Scree

Nelumbonaceae

Nelumbo sp. (F; FL165; US959-10613) – – – +

TROCHODENRALES

Trochodendraceae

Tetracentron sp. (F; FL161; US997-10572) – – – +

Trochodendron sp. (Fr; FL051; US970-9986) – – + –

Zizyphoides sp. (F; FL122; US965-9815) – + – –

SAXIFRAGALES

Cercidiphyllaceae

Cercidiphyllum/Joffrea sp. (Fr; FL053; US972-10096) – + – –

Grossulariaceae

Ribes sp. (F; FL088; US962-10644) + + + +

Hamamelidaceae

Hamamelidaceae sp. (F; FL141; US996-10513) – + – –

Iteaceae

cf. Itea sp. of Wolfe and Wehr, 1987 (F; FL115; US983-10264) + + + –

MALPIGHIALES

Salicaceae

?Salicaceae sp. 1 (F; FL028; US970-10007) – – + –

ROSALES

Rosaceae

Photinia pagae Wolfe and Wehr (F; FL114; US984-10298) + + + +

?Prunus sp. (F; FL163; US997-10547) – – + +

cf. Prunus sp. (Fl; FL166; US959-10630) – – – +

cf. Malus idahoensis Brown (F; FL013; US961-10643) – + + +

cf. Crataegus sp. (F; FL145; US959-10611) – – + +

?Holodiscus sp. (F; FL002; US970-10047) – – + –

cf. Spiraea sp. (F; FL040; US966-9854) – + + –

Rosaceae sp. 1 (F; FL093; US959-10607) + – – +

Rosaceae sp. 2 (F; FL132; US959-10602) – – – +

Ulmaceae

Ulmus okanaganensis Denk and Dillhoff (F; FL021, FL081; US967-9879, US988-10416)b + + + +

Ulmus sp. (Fr; FL032; US969-9964) + + + +

FAGALES

Fagaceae

Fagus langevinii Manchester and Dillhoff (F; FL044; US996-10504) – + + +

?Quercus sp. (F; FL079; US983-10259) – – + –

Betulaceae

Alnus parvifolia (Berry) Wolfe and Wehr (F, I; FL023, FL020, FL065; US962-10222, US972-10108,US959-10618)c

+ + + +

Betula leopoldae Wolfe and Wehr (F; FL034; US983-10261) + + + –

?Corylus sp. (F; FL026; US970-10015) + – + –

Betulaceae sp. 1 (I; FL006; US997-10533) – + + +

Betulaceae sp. 2 (I; FL124; US984-10335) + + + +

Myricaceae

Comptonia columbiana Dawson (F; FL001; US969-9941) – – + +

Juglandaceae

Juglandaceae sp. (F; FL011; US968-9915) – + + +


most productive quarries range in volume from 1.4 to2.0 m3 each; Wilf et al. 2005). Data for the site as a wholeis included for reference, but it does cover significantlygreater volume of outcrop (25 quarries over approx. 180 mvertical extent; Wilf et al. 2005) compared to the samplesfrom the other localities considered in the analysis. Thethree units at Falkland cover a vertical section of approx-

imately 2.5 m, the Republic sample 1.6 m (Passmore et al.2002) and the Denver Basin sample 1.0 m (locality 2484;Johnson et al. 2003), thus providing a good scale ofcomparison with the individual quarries at Laguna delHunco.

The rarefaction analysis (Fig. 6) shows highest diversityat Falkland, Laguna del Hunco (whole site), Laguna del

Table 3 (continued)


Unit2

Unit3

Scree

MALVALES

Malvaceae s.l.

Florissantia quilchenensis (Mathewes and Brooke) Manchester (Fl; FL042; US981-10196) + + + +

SAPINDALES

Anacardiaceae

Rhus malloryi Wolfe and Wehr (F; FL127; US982-10239) – – + –

Sapindaceae s.l.

Acer sp. 1 (F; FL050; US962-10221) – – + –

Acer sp. 2 (Fr; FL066; US985-10368) – + – +

Acer sp. 3 (Fr; FL095; US959-10620) – + + +

Aesculus sp. (F; FL069; US971-10066) + – + –

Bohlenia americana (Brown) Wolfe and Wehr (F; FL097; US987-10378) – + – –

Deviacer sp. (Fr; FL147; US989-10426) + – – –

Dipteronia brownii McClain and Manchester (Fr; FL108; US994-10483) + – – +

Koelreuteria arnoldi Becker (Fr; FL104; US959-10622) – – – +

ERICALES

Theaceae

?Gordonia sp. (Fr; FL162; US970-10016) – – + –

Ternstroemites sp. B of Wolfe and Wehr 1987 (F; FL022; US969-9955) – + + –

Incertae sedis

25 Indet. dicot toothed leaf morphotypes (FL009, US970-9988; FL010, US970-10020; FL014, US966-9840;FL016, US968-9896; FL018, US962-10650; FL029, US969-9977; FL030, US966-9850; FL039,US967-9869; FL049, US970-10008; FL054, US987-10386; FL056, US970-10027; FL057, US984-10304; FL067,US964-9803; FL080, US992-10443; FL082, US966-9843; FL084, US968-9930; FL086,US972-10120; FL100, US967-9865; FL110, US959-10632; FL111, US959-10633; FL116, US982-10230; FL140,US996-10508; FL143, US966-9843; FL153, US959-10631; FL160, US998-10579)

+ + + +

11 Indet. dicot entire leaf morphotypes (FL008, US980-10179; FL024, US963-9791; FL025, US963-9791; FL035,US972-10083; FL047, US979-10162; FL077, US967-9867; FL102, US959-10586; FL118,US993-10475; FL126, US984-10302; FL144, US982-10228; FL152, US984-10298)

+ + + +

Indet. dicot leaf type margin indistinct (FL134, US984-10312) +

15 Indet. reproductive structures (Fl, FL041, US970-10038; Fl, FL068, US980-10183; Fl, FL075, US969-9948;Fl, FL121, US984-10303; Fl, FL129, US965-9816; Fr, FL063, US968-9895; Fr, FL105, US959-10624; Fr, FL109,US959-10588; Fr, FL137, US980-10182; Fr, FL148, US983-10264; I, FL120, US993-10480; I, FL155,US966-9844; I, FL158, US959-10593; S, FL045, US959-10598)

+ + + +

Indet. moss sp. (F; FL103; US984-10297) +

Organs: A, axis; F, foliage; SC, seed cone; PC, pollen cone; CS, cone scale; S, seed; Fl flower; Fr, fruit; I, inflorescence/infructescence. Allmorphotype numbers are preceded by FL for Falkland. All specimen numbers are accession numbers from the University of SaskatchewanPaleobotany Collection (USPC). ?, tentative assignment to taxon; aff., morphological affinities to taxon; cf., no characters contradict assignment,but assignment uncertaina Reported by Greenwood et al. (2005) but not encountered during fieldwork for this studyb Two foliage morphotypes for this taxon (FL021 and FL081, representing elongation and young shoot leaves) are maintained in the morphotypedatabase, but are treated as a single species in all analysesc Two foliage morphotypes for this taxon (FL020 and FL023, representing mature and immature leaves) are maintained in the morphotypedatabase, but are treated as a single species in all analyses


Fig. 3 Representative specimens of the Falkland flora (gymnosperms,pteridophytes, monocots). All scale bars:1 cm. a Picea sp. defoliatedaxis, US959-10617; b Picea sp. seed, US959-10619; c Abies milleriseed, US998-10582; d Abies milleri, US986-10372; e Pinus sp. seed,US967-9866; f Pseudolarix sp. seed, US997-10568; g Abies millericone scale, US967-9865; h Pseudolarix sp., US992-10449; i Pinus sp.(5-needled), US959-10592; j Metasequoia occidentalis pollen cones,US972-10107; k Metasequoia occidentalis seed cone, US972-10117;

l Metasequoia occidentalis, US983-10262; m Cupressaceae sp.,US982-10255; n Chamaecyparis sp. seed cone, US959-10591; oSequoia affinis, US970-9992; p Sequoia affinis pollen cones, US969-9957; q Ginkgo adiantoides, US959-10610; r Ginkgo adiantoides,US981-10189; s Ginkgo dissecta, US961-10642; t ?Adiantum sp.,US960-10656; u ?Adiantum sp., US959-10600; v Equisetum sp.,US984-10292; w monocot, US971-10069


Hunco Quarry 2 (LH-2) and Río Pichileufú (RP-3). The RíoPichileufú quarry represents a relatively small sample size,and the rarefaction curve does not show the markedflattening that would indicate saturation of the collectioneffort; nevertheless, the preliminary RP-3 curve almostexactly tracks that of LH-2. The second cluster of sitesincludes Republic and the remaining Laguna del Huncoquarries (only LH-4 shown in Fig. 6). McAbee (OkanaganHighlands) and the Denver Basin localities also representrelatively small samples, but appear to fall within thesecond cluster.

Various diversity metrics suggest that the sites consid-ered here provide good comparative datasets (see Table S4in the ESM). In the samples included in the rarefactionanalysis, singleton taxa (morphotypes represented by asingle specimen) contribute significantly to diversity at allsites, ranging from 36% of the taxa at LH-2 to 47% of thetaxa at Republic, with Falkland falling near the middle ofthis range with 42% singleton taxa. The evenness ofdiversity at the various sites, as measured by Pielou’s J,ranges from 0.57 at Republic to 0.71 at LH-2, withFalkland (Dataset D) again falling within this range at0.69. The Okanagan Highlands sites (Falkland, Republic,and McAbee) show higher values for the Berger–Parkerindex (0.35, 0.44 and 0.44 respectively), which is thenumber of individuals in the dominant taxa relative to n,compared to Laguna del Hunco (0.23, 0.28 and 0.16 forLH-2, LH-4 and LH-All, respectively). At both Falklandand Republic, the dominant dicot taxon is Alnus parvifolia(Berry) Wolfe and Wehr.

The question of lumping versus splitting of morphotypesundoubtedly affects estimates of diversity. In order toprovide a more conservative estimate of diversity atFalkland, the rarefaction analysis was also run using amodified version of Dataset D in which some of the lesswell-preserved singleton taxa were removed, and some ofthe morphotypes that could represent variable foliage ofAlnus were merged. The modified dataset is described inESM Table S5 and presented with a conservative rarefac-tion analysis in ESM Fig. S1. This analysis does not alterthe results in any fundamental way but rather in degree, asthe more conservative Falkland dataset tracks the rarefac-tion curve of the second-most diverse quarry at Laguna delHunco (LH-13).

Plant community dynamics over time

In addition to tracking species richness and diversity overtime, the changing composition of the plant community atFalkland was investigated. To address this issue, NMDSwas employed to extract patterns in species abundance andplant community associations across the three units.Individual quarries are coded by unit in the ordination

graph (Fig. 7) and show a clustering by unit. In particular,Units 1 and 3 are quite distinct from one another, while thequarries from Unit 2 appear to be somewhat transitional,spanning the ordination space between the other two units.As described above, Unit 3 is more diverse than Units 1 or2, and the NMDS plot suggests that Unit 3 is distinct, atleast compared to Unit 1, in terms of plant communitycomposition.

Figure 8 presents a spindle diagram of the ten mostcommon taxa in the two correlative sections that weresampled using an unbiased census approach (Dataset C).With one exception, the juglandaceous leaf morphotype,which is only present in Units 2 and 3, all of these commontaxa were present in all three units, although their relativeabundance shifted over time. The two most abundant taxaat the site, Ginkgo adiantoides and Metasequoia occiden-talis, were present in all three units; however, both reachedpeak dominance in Unit 2 and were least abundant in Unit3. Ginkgo was notably absent in the quarry immediatelyabove the ash layer marking the transition between Unit 2and Unit 3. Ginkgo made up approximately 12% of thespecimens collected from Units 1 and 2 (based on DatasetB(i); all specimens from all census-sampled quarries) andonly approximately 3% of specimens from Unit 3.Similarly, Metasequoia dropped from 20–23% of speci-mens in Units 1 and 2, to approximately 13% of specimensin Unit 3. The other taxon that contributes to significantdifferences between the three units is Alnus parvifolia,which is present in all three units, but noticeably moreabundant in Unit 3 (12% of specimens in Dataset B(i) forUnit 3, compared to 7–8% in Units 1 and 2).

A contingency table (ESM Table S1) with counts ofangiosperm, gymnosperm and “other” taxa for the threeunits was used to test for the association between relativeabundance of angiosperm and gymnosperm specimens inthe three units, utilizing Dataset B(i). The chi-square testfor independence shows a highly significant association(p<0.001) between position in the section and relativeabundance of the major taxonomic groups. In Units 1 and2, angiosperm and gymnosperm specimens were found inroughly equal numbers, while Unit 3 shows a markedincrease in the relative abundance of angiosperms (Fig. 2).In all cases, dicots comprise the vast majority of theangiosperm specimens.

Discussion

Plant diversity at Eocene fossil localities

Several patterns emerge from the preceding analyses ofplant diversity within the Falkland site and among earlyEocene sites in North and South America. The results of the



rarefaction analysis (Fig. 6) demonstrate that the northernhemisphere mid-latitude Falkland site displays a diversitycomparable to that of the South American sites, despitehaving a cooler MAT. This finding agrees with recentdiscoveries on latitudinal gradients and insect diversity inthe early Eocene, indicating that equability of climate (i.e.low seasonality) contributed to the development of highlydiverse biotic communities even in areas with relatively lowtemperatures (Archibald et al. 2010). Falkland, like otherNorth American fossil localities in the early Eocene (Wingand Greenwood 1993), had an equable climate with a coldmonth mean temperature >0°C (Smith et al. 2009),indicating a lack of prolonged freezing temperatures.Therefore, even with a relatively cool MAT, Falkland wasable to support a highly diverse biotic community.

In their study of insect diversity, Archibald et al. (2010)also compared the diversity of the McAbee (OkanaganHighlands) flora to modern-day leaf litter samples fromboth the tropical rainforest (Ella Bay, Queensland, Aus-tralia) and temperate broadleaf-deciduous forest (HarvardForest, Massachusetts), and found the McAbee site to bemore similar to the tropical rainforest samples in terms ofdiversity. The Eocene Falkland site considered here meetsor exceeds the levels of diversity at McAbee (Fig. 6) andtherefore also compares favourably with modern tropicallevels of plant diversity at rarefied sample sizes. Data fromPanama and Brazil (Wing et al. 2009) confirm this, as therarefaction analysis shows Falkland dicot diversity to besimilar to that reported for a sample taken from a wetlakeshore on Barro Colorado Island, Panama (sample BCI-

D, Wing et al. 2009; Fig. 9). In contrast, the diversity of amodern temperate deciduous forest at mid-latitude (HarvardForest) is much lower than that at either the early Eocenesites or modern tropical sites (Archibald et al. 2010; Fig. 9).

Wilf et al. (2005) attributed the high diversity at Lagunadel Hunco and Río Pichileufú to the globally warmconditions of the Eocene, and the extension of Neotropicalinfluence to mid-latitudes in the southern hemisphere.Lowland tropical sites may have provided source materialfor the development of the mixed palaeofloras of Patagoniathat were able to accommodate both tropical taxa andcooler elements in their humid, frost-free conditions(Jaramillo and Dilcher 2000; Jaramillo 2002; Wilf et al.2005). In the Okanagan Highlands, similar conditions ofhumidity and frost-free winters likely prevailed, althoughunder generally cooler upland conditions. An explanationfor the high diversity at Falkland may lie partly in itsupland character. In the modern world, montane forests arehotspots of biological diversity (Körner 2004; Molau2004). An altitudinal transect may include a series ofclimatically different zones within a short distance (Körner2004). In addition, different slope exposures can createmicroclimate niches, and the interaction of climate withtopography creates a wide diversity of microhabitats(Killeen and Solórzano 2008; Körner 2004). The uppermontane rainforests of southern Ecuador (2700–2900 m a.s.l.)have been found to have extraordinarily high alpha diversityunder climate conditions that are relatively cool (MAT11–12°C) but with abundant moisture (approx. 300 cm/year)(Madsen and Øllgaard 1994).

The results presented here also suggest that not only wasdiversity high at the Falkland site, which is consistent withdata for other Okanagan Highland early Eocene sites, butthat there is evidence of a distinct and more diverse plant

Fig. 4 Representative specimens of the Falkland flora (dicots). Allscale bars:1 cm. a Tetracentron sp., US997-10572; b Joffrea sp. fruit,US972-10096; c cf. Prunus sp., US959-10630; d cf. Crataegus sp.,US959-10611; e Rosaceae sp., US959-10607; f Photinia pagae,US984-10298; g Fagus langevinii, US996-10504; h Ulmus okanaga-nensis, US967-9879; i Ulmus sp. samara (note preservation ofperipheral hairs), US959-10638; j Ulmus sp. samara, US969-9964; kBetula leopoldae, US983-10261; l Alnus parvifolia, US962-10222; mbetulaceous staminate inflorescence, US997-10533; n Alnus parvifoliapistillate infructescence, US959-10589; o Koelreuteria arnoldi,US959-10622; p Acer sp., US962-10221; q Acer sp. samara,US959-10620; r Acer sp. samara, US959-10623

�

Table 4 Select diversity measures for Falkland Dataset B(ii)

Measure of diversity Unit 1 Unit 2 Unit 3

Number of morphotypes 33 44 57

Number of individuals 313 454 443

Dominance (D) 0.19 0.14 0.10

Simpson’s index (1 − D) 0.81 0.86 0.90

Shannon–Wiener Index (H) 2.25 2.63 2.94

Pielou’s J 0.64 0.69 0.73

Fisher’s α 9.31 12.03 17.40

Fig. 5 Rarefaction analysis of three units at the Falkland site usingDataset B(ii), which is limited angiosperm and gymnosperm foliagefrom census quarries. See ESM for raw abundance data


community in the upper unit of the site. In particular, thereis evidence of increasing diversity of minor angiospermtaxa in the upper unit. The results of the NMDS ordination(Fig. 7) show a clustering of quarries in the three units,primarily in terms of the two end units of Unit 1 and Unit 3.If there were only a single plant community represented atthe site, we would expect to see the quarries spreadrandomly across the ordination space, irrespective of theirassignment to unit. While not perfect in terms of clusteringinto units, there is a distinct grouping (Fig. 7), especiallyvis-à-vis quarries from Units 1 and 3. The quarries fromUnit 2 appear to be transitional, and it is not possible toresolve whether the change from Unit 1 to 3 is continuousor abruptly defined by the unit boundaries, given theoverlap in clusters.

There are various factors that might have influenced thecomposition, stability and diversity of the Falkland flora.There is a limited vertical extent of outcrop at the Falkland site(approx. 3 m), likely representing a relatively short period oftime (in the range of 103–104 years). Evolutionary processescan likely be disregarded on this timescale. Other possiblefactors that warrant consideration include: (1) changes in

climate leading to shifts in the ranges of plant communitiesand in-migration from adjacent areas of lower or higheraltitude and/or latitude; (2) changes in the depositionalenvironment, leading to different taphonomic factors influ-encing the composition of the fossil assemblage; (3)patchiness in the local landscape due to microhabitatvariation and response to repeated disturbance events.

Climate and diversity

Leaf margin analysis (LMA) indicates that Falkland MATwas relatively cool compared to that of lower latitude sitesin North America and the mid-latitude South Americansites, but in the range typical for the Okanagan Highlands(Table 2). Peppe et al. (2011) caution that LMA may under-estimate MAT (≥4°C) versus a multivariate leaf physiog-nomic approach, and our estimates for Falkland certainlyare cooler than estimates from bioclimatic analysis orCLAMP (Smith et al. 2009; Table 5), but these authorsnoted that temperature trends detected using LMA withinthe same sedimentary basin, and potentially the samecontinental area, may reflect changes in the regional

Table 5 Details of fossil specimens collected at the Falkland site (Dataset A) and palaeoclimate estimates

Sample Unit 1 Unit 2 Unit 3 Screea Whole site

Plant specimens

Total (n) 508 662 738 144 2052

Identifiable to morphotype (n) 342 (67%) 528 (80%) 548 (74%) 142 (99%)e 1560 (76%)

Dicot leaves 81 180 247 58 566

Dicot reproductive 12 34 52 37 135

Monocots 7 8 19 1 35

Gymnosperm leaves 228 285 201 30 744

Gymnosperm reproductive 7 16 15 11 49

Ferns and horsetails 2 1 1 3 7

Other 5 4 13 2 24

Palaeoclimate

Dicot leaf morphotypes entire (%) 27.3% 17.6% 10.6% N.A. 20.0%

LMA Estimate of MAT (°C)b 10.2 ± 4.8 8.2 ± 4.8 6.8 ± 4.8 N.A. 8.7 ± 4.8

CLAMP Estimate of MAT (°C)c 13.0 ± 1.2 12.6 ± 1.2 11.8 ± 1.2 N.A. 12.8 ± 1.2

Mean area of dicot leaves, ln (mm2) 7.44 7.42 7.27 N.A. 7.36

Estimate of precipitation (cm/yr) based on eq. inWilf et al. (1998)d

127 +55/−38 126 +54/-38 116 +50/−35 N.A. 121 +52/−37

Estimate of precipitation (cm/yr) based on eq. inPeppe et al. (2011)d

152 +128/−70 151 +127/-69 145 +122/−66 N.A. 149 +125/−68

N.A., Not applicablea Stratigraphic context unknownb Calculated using the global LMA equation in Peppe et al. (2011). Standard error is 4.8°Cc Error is the standard deviation given in the CLAMP analysis, but is likely underestimatedd Error is asymmetrical as converted from log valuese Scree specimens were collected specifically to improve the reference collection of morphotypes, and therefore have a high percentage ofspecimens assignable to morphotype


temperature regime. Analysis of dicots from the three unitsat the Falkland site suggests that MAT was decreasing overtime (Table 5). It is unclear whether this decline representsa short-term fluctuation, or whether it is part of a longerterm trend in the waning phase of the EECO. This changein climate may have resulted in shifts in plant ranges fromadjacent areas, with taxa suited to cooler climates migratingfrom higher elevations or latitudes. However, intuitively wemight expect a cooling climate to mark a shift towards agreater abundance of conifers, rather than dicot taxa, whichis not the pattern observed in Unit 3. The precipitation atthe site was consistently high for the three units (>100 cm/year) based on leaf area analysis, with values for the threeunits not statistically distinguishable given the large errorranges (Table 5). It appears that cooler temperatures, whencombined with abundant moisture and mild winter temper-atures, did not hinder the development of a diverse plantcommunity. In contrast to Peppe (2010), we do not see acorrelation between declining MAT and declining diversity,although the Williston Basin study encompasses a muchlonger time period (millions, rather than thousands, of years)and so may be tracking trends at a broader scale. In addition,Peppe (2010) notes that local environmental factors may

modulate the climate–diversity relationship, as seen in otherparts of North America, such as the Denver Basin.

Depositional environment and diversity

There is a partial correspondence between the preserva-tional quality of fossils and the abundance and diversity offossil specimens in the three units. The macrofossils in Unit3 tend to be better preserved and more abundant than in thelower two units (Smith et al. 2009), and Unit 3 also has thehighest alpha diversity, as measured by various indices(Table 4). This raises the issue of whether the higherdiversity in Unit 3 is in fact a preservational bias, withtaphonomic factors overprinting the diversity signal. Differ-ences in preservational quality within leaf assemblagesoccur due to either altered energy regimes contributingvaried mechanical damage or altered oxidation states withinthe sediments (which is often correlated with the energy ofthe water-sediment interface), as well as physicochemicaldifferences between leaf taxa which influence susceptibilityto decay or biotic degradation (Steart et al. 2002, 2009).While we cannot absolutely reject a taphonomic hypothesis

Fig. 7 Non-metric multidimensional scaling (NMDS) ordination ofquarries at the Falkland site, Dataset C. Prior to analysis, some smallquarries with very sparse abundance data were amalgamated, but onlywhere the quarries were adjacent and in the same unit. This resulted ina total of 22 quarries in two correlative sections. Unit 1 is representedby nine quarries, Unit 2 by seven quarries and Unit 3 by six quarries.The Bray–Curtis distance measure (a quantitative form of theSørenson distance measure) was used to construct the distance matrix.The final stress of the two dimensional plot is 0.20. The proportion ofvariance explained by the two axes is 0.55 for axis 1 and 0.16 for axis2, giving a cumulative r2 value of 0.71

Fig. 6 Rarefaction analysis of dicot foliage at Falkland (Dataset D,see ESM for raw abundance data), Republic (data kindly provided byP. Wilf and K.R. Johnson), McAbee (Archibald et al. 2010), DenverBasin, Colorado (locality DMNH 2484; rarefaction curve fromJohnson et al. 2003), Laguna del Hunco (raw data in Appendix toWilf et al. 2005) and Río Pichileufú (rarefaction curve from Wilf et al.2005). See Table 2 for details of sampling localities. McAMcAbee,LHLaguna del Hunco, RPRío Pichileufú, DBDenver Basin. Note thatof the four Laguna del Hunco quarries discussed in the text, only themost and the least speciose (LH-2 and LH-4, respectively) areincluded in the rarefaction diagram, for readability of figure. Datafor the Laguna del Hunco site as a whole (25 quarries, Wilf et al.2005) are truncated to match the scale of the other data presented


to explain intra-site patterns in diversity, it is worth notingthat the lithologies in Units 1 and 3 are very similar(Fig. 2), suggesting similar depositional environments and

energy regimes, and the unit macrofloras reflect comparablesuites of taxa. If taphonomic factors were the primary causeof the differences in the observed fossil assemblages in thethree units, we would expect Units 1 and 3 to be rathersimilar, with a decrease in both diversity and fossil qualityin Unit 2. Instead, we see the most pronounced differencein all measures (fossil quality and diversity) between Units1 and 3, with Unit 2 intermediate in most values.

Disturbance, patchiness and diversity

Macrofossil assemblages tend to reflect local, rather thanregional, floras (Burnham 1989; Greenwood 1992; Steart etal. 2002). Consideration of pollen samples in floristicassessments can provide a window on the regionallandscape in which the plant community was situated. Adetailed assessment of the palynoflora of the Falkland siteis ongoing and will be presented elsewhere; however, initialresults from an earlier study offer some insight into thequestion of landscape dynamics. Moss et al. (2005)examined pollen samples from Falkland as part of aregional study of Okanagan Highlands sites. Their samplesare not placed in a stratigraphic context, but are noted tohave been in close lateral and vertical proximity. Despitethis, however, the three Falkland samples analysed showeda great deal of variation in relative abundance of three mainvegetation associations identified by Moss et al. (2005).Two of the samples showed similar proportions of the fir–spruce and birch–golden larch associations (35–55% and

Fig. 9 Rarefaction analysis of early Eocene Falkland dicots (DatasetD, see ESM for raw abundance data), early Eocene McAbee dicots(Archibald et al. 2010) and modern leaf litter samples from tropicalrainforests in Brazil (Rio Negro Waterfall and Rio Negro Stingray)and Barro Colorado Island, Panama (Wing et al. 2009) and from amid-latitude broad-leaved deciduous forest (Harvard Forest, MA,USA; Archibald et al. 2010). McAMcAbee, BCI-DBarro ColoradoIsland, Panama

Fig. 8 Spindle diagramshowing the abundance of the tenmost common taxa at the site inthe various quarries of the threeunits (quarries designated A–L)from Dataset C. Correlativequarries (i.e. those coveringroughly the same stratigraphicinterval measured relative to ashlayers) in the two sections wereamalgamated. The width of theblocks represents the number ofspecimens of each taxon found inthe correlative quarries of the twosections


45–65%, respectively, in the two samples), although withvariation in abundance of individual taxa within theseassociations. Their third sample, however, showed amarked shift towards dominance of the birch–golden larchassociation (92%) and the introduction of a minor palm–cypress element (approx. 3%).

Moss et al. (2005) suggested that differences in theFalkland pollen samples reflected local patchiness inmicrohabitat due to variation in the depth of the water-table or edaphic factors, and/or different seral stages inresponse to disturbance in the landscape. Similar explan-ations have been put forward to explain lateral and verticalchanges in plant community structure and composition atfossil sites representing taxodiaceous swamps in the Arctic(Greenwood and Basinger 1993), and these may also berelevant in the case of Falkland where there is evidence ofdisturbance through the stratigraphic record. The apparentincrease in abundance and diversity of dicots in Unit 3 (theyoungest of the three units) may reflect an intensifyingdisturbance regime at regional and local scales, withangiosperms more likely to form early seral stages of plantcommunities (Peppe et al. 2008).

At Falkland, Unit 2 encompasses the portion of theoutcrop that shows the most environmental disturbance, asit contains not only multiple volcanic ash layers (which arealso found in the other two units, but are less prominent)but also a horizon showing wave ripple marks, indicating apossible climate fluctuation affecting lake levels, followedby a distinctive fish-kill layer which includes numerousarticulated and disarticulated fish remains (Smith et al.2009). Volcanic activity has significant implications for thedevelopment of plant communities, depending on distancefrom the eruptive centre, the degree and frequency of theeruptions and the presence and location of biotic refugia(del Moral and Wood 1993; del Moral and Grishin 1999;Harris and Van Couvering 1995; Jolley et al. 2008).Succession and vegetation recovery following volcaniceruptions in modern environments is influenced by climate(and in particular moisture availability), substrate type, andlandscape factors, such as dispersal barriers and habitatpatchiness (del Moral and Grishin 1999). In addition,chance and stochastic events play a large role, and as aresult novel species combinations are often found involcanic environments, particularly in early stages ofsuccession (del Moral and Grishin 1999). Jolley et al.(2008) have examined the influence of volcanic activityon the nutrient availability for plant communities in thefossil record using material from the Miocene ColumbiaRiver flood basalts in northwestern USA. The plantcommunities documented in the interbed layers of thoseformations often show diverse and highly productiveplant assemblages that would have received large inputsof macronutrients from the weathering of volcanic

material in the surrounding landscape, transportedthrough the hydrological system during quiescent peri-ods (Jolley et al. 2008).

The Falkland site is clearly embedded in a volcanicallyactive landscape and may have received nutrient inputsthrough the weathering of volcanic materials (or airbornedeposition) in the high precipitation regime suggested byleaf area analysis (Table 5). Over time, volcanic soils maybecome depleted in nutrients, such as phosphorus andnitrogen (Jolley et al. 2008). The presence of nitrogen-fixing taxa, such as Alnus, abundant at Falkland and inparticular in Unit 3, would have enhanced the bioavailabil-ity of limiting nutrients, contributing to the recovery andsuccession of the plant communities following disturbance.While the scale of macrofossil sampling may not permit thecharacterization of individual disturbance and recoveryevents, it is important to consider the nature of thedisturbance regime in the three units (source, intensity andfrequency), as this was likely an important factor in shapingthe plant community over time. On-going work on theFalkland palynoflora sampled at fine, centimetre-scaleintervals may better elucidate the patterns of disturbanceand recovery in the sequence.

It is difficult to disentangle the influences of climate,disturbance and microhabitat variation, as these factors maybe linked to some extent. High diversity at mid-latitudesites in South America has been attributed in part to the in-migration of taxa from lower latitudes under conditions ofglobal warmth (Wilf et al. 2005). This pattern is not evidentat Falkland, as the unit with the highest diversity isassociated with the coolest MAT, and diversification inthe Okanagan Highlands appears to be centered ontemperate plant families, rather than on tropical in-migration. Perhaps a better analogy is the Denver Basin,where variation in topography and precipitation is linked toregional differences in plant diversity (Johnson et al. 2003;Peppe 2010). Microhabitat diversity has been suggestedbased on pollen evidence from Falkland (Moss et al. 2005)and may best explain the intra-site variation in diversity, incombination with the disturbance regime.

Conclusions

The fossil flora at the Falkland site is comparable indiversity to those at southern hemisphere hyperdiversesites, such as Laguna del Hunco and Río Pichileufú, despitehaving a cooler upland climate. However, at Falkland, thediversity is concentrated in temperate and deciduous planttaxa from families such as Pinaceae, Rosaceae, Betulaceae,Ulmaceae and Sapindaceae. Rather than reflecting the in-migration of taxa from higher diversity regions at lowerlatitudes, the Okanagan Highlands may represent the


epicenter of diversity for some lineages that later radiatedinto Asia and other parts of North America (DeVore andPigg 2010) as global temperatures cooled. The uplandenvironment, characterised by a mosaic of microhabitatsalong an altitudinal gradient, in combination with abundantmoisture and mild winters, may have provided theconditions that facilitated the development of a highlydiverse plant community.

There is evidence of a distinct plant community in theupper unit of the site, although dominant taxa, includingMetasequoia, Ginkgo and Alnus, are present in all threeunits with varying levels of abundance. The apparentincrease in abundance and diversity of dicots over timemay reflect an intensifying disturbance regime, with dicotsmore likely to form early seral stages of plant communitiesand better able to recover from repeated disturbance events.The changes in plant community structure and compositionobserved at the Falkland site are therefore best explained byresponse to disturbance events (e.g. increased abundance ofAlnus up-section, as volcanic activity increased) and lateralpatchiness in vegetation due to microhabitat variation in theupland landscape.

Acknowledgements This paper derives from a PhD thesis by RYS,supported through a Canada Graduate Scholarship to RYS from theNatural Science and Engineering Research Council of Canada(NSERC), and NSERC Discovery grants to DRG (DG 311934) andJFB (DG 1334). The authors would like to thank R. Wilson, B.Wilson, H. Wilson, S. Krasowski, K. Stouffer, J. Walberg and L.Johnson for assistance in the field. Thanks are extended to ourcolleagues S.B. Archibald, P.T. Moss, and R.W. Mathewes forhelpful discussions regarding the fossil biota of the site. Theauthors thank P. Wilf and K. Johnson for sharing raw abundancedata for Republic dicot specimens. R. Hebda and J. Kerik at theRoyal British Columbia Museum were helpful in obtainingpermission to collect at Falkland. We thank D. Peppe and twoanonymous reviewers for constructive comments and suggestionsthat greatly improved the manuscript.

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Early Eocene plant diversity and dynamics in the Falkland flora, Okanagan Highlands, British Columbia, Canada