Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Phytoliths of Southeastern Vancouver Island, Canada, and their potential use to reconstruct shifting boundaries between Douglas-fir forest and oak savannah

Jenny L. McCune a,⁎, Marlow G. Pellatt b a Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada b Parks Canada, Natural Resource Conservation, Vancouver, BC, V6B 6B4, Canada article info abstract

Article history: Phytolith assemblages in terrestrial soils have the potential to reveal local shifts between open savannah and Received 24 January 2013 conifer forests in the past. On southeastern Vancouver Island, this could help quantify the range of variability Received in revised form 26 April 2013 of Garry oak savannahs prior to European colonization, and the degree of influence of indigenous people in Accepted 5 May 2013 maintaining open savannahs. We catalogued the phytolith morphotypes found in 72 of the most common Available online 12 May 2013 plant species in this system, and extracted phytoliths from two soil cores on either side of the boundary be- tween a conifer forest and an oak savannah. Grasses are the most prolific producers of phytoliths in savan- Keywords: fi Phytoliths nahs. In forests, Douglas- r(Pseudotsuga menziesii) produces large, distinctive asterosclereid phytoliths. Douglas-fir Phytolith assemblages from soil cores showed that phytoliths from grasses dominated, even in soils from Grassland the forest, where grasses are rare. However, the presence of asterosclereid phytoliths reliably distinguished Savannah between Douglas-fir forest and Garry oak savannah habitats within 20 m of the vegetation boundary. This Asterosclereid finding may be useful for reconstructing past vegetation not only on Vancouver Island, but also across a Canada large geographic area in North America where grasslands tend to be invaded by Douglas-fir following fire suppression. The use of the phytolith record from terrestrial soils at local sites where the history of human occupation is well-known could help establish the degree of influence of indigenous peoples in maintaining open savannahs on southeastern Vancouver Island. © 2013 Elsevier B.V. All rights reserved.

1. Introduction have shown that the extent of these savannahs was much greater just prior to European settlement, and that the remnants of this vegetation In many places across the Americas indigenous peoples had a long type now exist mainly in steep, rocky areas not suitable for agriculture and substantial influence on vegetation long before colonization by (Lea, 2006; Vellend et al., 2008; Bjorkman and Vellend, 2010). Oak Europeans (Denevan, 1992; Delcourt and Delcourt, 2004). However, savannahs on deep soil sites are highly susceptible to invasion by the there are serious debates concerning the degree and extent of this conifer Douglas-fir(Pseudotsuga menziesii; Fuchs, 2001). Palynological influence in time and space for particular regions (e.g. Vale, 2000; studies have shown that oak savannahs were established on southeast- Whitlock and Knox, 2002). It is very challenging to tease apart the ern Vancouver Island by approximately 8000 years ago, and persisted interacting effects of climatic and other non-human agents from cul- despite a cooling, moistening trend beginning about 6000 years ago tural impacts on vegetation over long time periods. Even with strong (Pellatt et al., 2001). Ethnographic and historical evidence suggests evidence from ethnography, dendroecology and palynology that the that on deep soil sites in particular, management by indigenous people activities of indigenous peoples were an important influence on veg- in the form of frequent, low-intensity prescribed burns maintained the etation structure, mysteries often remain about the details. open character of Garry oak savannahs (Turner, 1999; MacDougall et al., This is definitely true for the Garry oak savannahs of Vancouver 2004). However, the spatial and temporal extent of this influence, and Island, Canada. These savannahs represent the northernmost edge of the timing of transitions from open savannah to Douglas-fir forest or the range of the Garry oak tree (Quercus garryana), which stretches as vice versa prior to European settlement, is not clear. far south as northern California (Fig. 1). Historical ecological studies Phytolith analysis has the potential to increase our understanding of the history of vegetation change in this system. Phytoliths are plant

microfossils formed when hydrated silicon dioxide (SiO2·nH20) is de- ⁎ Corresponding author at: 3529-6270 University Blvd., Vancouver, BC V6T 1Z4, Canada. posited within and between the cells of a living plant (Pearsall, 2000; Tel.: +1 604 822 2133; fax: +1 604 822 6089. E-mail addresses: [email protected] (J.L. McCune), Prychid et al., 2003). The resulting cell-shaped silica casts are released [email protected] (M.G. Pellatt). upon decomposition of the plant, and can survive in sediments for

0031-0182/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2013.05.003 60 J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71

Fig. 1. Main map: the West Coast of North America showing Vancouver Island, with the range of Garry oak indicated in grey. Inset: Southeastern Vancouver Island and the Gulf Islands, showing Tumbo Island, the location of the soil samples. Lower right: photo of the boundary between oak savannah and Douglas-fir forest at the soil sampling location. Garry oak range map based on map by Erickson (2008).

thousands of years (e.g. Blinnikov et al., 2002). Phytoliths may be 2. Materials and methods transported by wind or water, but phytolith assemblages are derived from more local vegetation sources than pollen, which can travel for 2.1. Reference collection hundreds of kilometres (Jacobson and Bradshaw, 1981; Pearsall, 2000; Blinnikov et al., 2013). Therefore, phytoliths have the potential We collected tissue samples from common plant species of the to reveal vegetation changes on a local spatial scale. Phytoliths are not three main non-riparian vegetation types in the region: Douglas-fir produced by all plant taxa, but are particularly abundant in certain forests, Garry oak savannahs, and Douglas-fir/Arbutus forests, which plant families, and in some cases are specific to the level of genus are dominated by Douglas-fir but include a substantial component (Pearsall, 2000). In North America, phytoliths extracted from buried of arbutus (Arbutus menziesii) trees in the canopy. We selected spe- palaeosols and/or modern soil profiles have been used to infer past cies based on a vegetation survey of 184 20 × 20 m relevé plots sur- changes in vegetation in diverse regions including the Great Plains, veyed in 2009 (McCune and Vellend, in prep). For each of the three the Columbia Basin, Arizona, Utah, Minnesota, California, and Manitoba vegetation types, we collected samples of all species that had an aver- (Bartolome et al., 1986; Fisher et al., 1995; McClaran and Umlauf, 2000; age cover of at least 1% in all relevés in which they were present. We Kerns et al., 2001; Blinnikov et al., 2002; Boyd, 2002; Morris et al., supplemented our collection with the following: as many grass spe- 2010). cies as we could collect, including two native bunchgrasses that are The first steps in utilizing phytoliths to study long-term vegetation now very rare and one very rare exotic grass from the Panicoideae change are to establish a reference collection of the phytolith types sub-family; one species from the Juncaceae family; and a few recently produced by plants common to the region, and to determine whether introduced exotic non-grass species whose phytoliths could poten- the proportions of different phytolith types in surface soils can reli- tially be used as stratigraphical markers. In total we collected samples ably distinguish between current vegetation types (Fredlund, 2005). from 72 species in 28 plant families, including 13 herbs, 3 ferns, 15 Therefore, our study was designed to answer the following questions: shrubs, 10 trees, 1 sedge, and 30 grasses (Tables 1, 2). Samples were collected in the late spring or summer of 2010 or 2011 from mature (1) What are the phytolith types and type frequencies in common specimens, and air-dried until they could be processed. plants of Douglas-fir forests and Garry oak savannahs of We extracted phytoliths from plant tissue samples using the southeastern Vancouver Island? dry-ashing technique (Pearsall, 2000). We cut plant samples into (2) Do phytolith assemblages from terrestrial soils reliably differ- small pieces and separated inflorescences, fruit, and vegetative por- entiate between the two vegetation types? tions (stems and leaves). Shrubs and tree samples were separated (3) How sensitive are phytolith assemblages to vegetation into leaves (needles), twigs, fruit, and in some cases bark. We did boundaries? not collect below-ground plant parts except for the bulbs of camas J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71 61

(Camassia quamash and C. leichtlinii), which were the most important heavy liquid flotation procedure modified from Pearsall (2000) to ex- starch source for indigenous peoples prior to European colonization tract phytoliths. First we air-dried the soil sample overnight, and then (Turner and Bell, 1971). We rinsed herb and grass samples thoroughly filtered it through a 500 μm sieve. We weighed out approximately 5 g in distilled water and placed them in a drying oven at approximately of the filtered soil to process for phytoliths. We removed carbonates 70 °C overnight. We washed twigs and bark samples in a sonic bath by heating in 10% hydrochloric acid for 1 h. Following rinsing to re- for 30 min, and then placed them in a drying oven at approximately move the acid, we removed organic material with a five minute 70 °C overnight. We then placed each dried sample in an aluminum bleach treatment followed by heating in 30% hydrogen peroxide foil crucible, weighed it, and then incinerated it in a mufflefurnaceat until no further reaction was visible. This required several hours 500 °C for 30 min to several hours, until most material was white ash. for highly organic samples. We then dispersed clay particles by shak- Some plant samples retained blackened areas even after several hours ing for 24 h in a 0.1% solution of ethylenediaminetetraacetic acid in the furnace. After burning, we weighed each sample again and trans- (EDTA) disodium salt dihydrate. ferred it to a glass vial for storage. We removed clay particles by sedimentation in a 10 cm column of To examine the ash residue for phytoliths, we placed a small water for 9.3 h followed by removal of the supernatant. We repeated amount on a microscope slide and added a few drops of Canada bal- the sedimentation process at least 4 times. Finally, we separated sam. We examined each slide in its entirety using a Zeiss Imager M2 phytoliths using heavy liquid flotation with sodium polytungstate at light microscope at 400× magnification. We photographed, described 2.3 g/cm3 density. We decanted the supernatant (with suspended and categorized all phytoliths according to the International Code phytoliths), and then sank the phytoliths by adding distilled water for Phytolith Nomenclature (Madella et al., 2005). We classified the and centrifuging. We carried out this process six times to ensure com- abundance of each phytolith morphotype in each sample according plete flotation of phytoliths. We rinsed the final extract twice, and to the following scale: “rare” (1–2 per slide), “sporadic” (2–20 per then dried it at approximately 60 °C in a drying oven until all water slide), “common” (20–100 per slide), or “abundant” (>100 per had evaporated (2–3 days). We weighed the final extract and stored slide). We examined more than one slide for some species. it in glass vials.

2.2. Soil sampling across an ecotone 2.2.3. Phytolith counts We used an analytical balance to add between 0.5 mg and 1.2 mg 2.2.1. Soil collection of phytolith extract to a microscope slide (measured to the nearest We collected two 5 cm diameter soil cores from Tumbo Island, 0.1 mg). We then added 3–4 drops of Canada balsam, mixed the ex- which is part of the Gulf Islands National Park Reserve administered tract in thoroughly using a clean dissecting needle, and placed a by Parks Canada (Fig. 1). Tumbo Island is a small island, approximate- cover slip gently on top. We scanned the entire slide at 200× magni- ly 105 ha in area, which includes areas of Garry oak savannah, but is fication to count the large asterosclereid phytoliths produced by largely dominated by Douglas-fir forests. We chose an area on the Douglas-fir. We then counted other phytolith morphotypes at 400× southeastern side of the island that consists of Garry oak savannah magnification across a transect of 16–18 consecutive microscope nearest the shoreline, but switches abruptly to Douglas-fir/Arbutus fields from the centre of the cover slip to the edge. This resulted in a forest moving inland (Fig. 1). The oak savannah vegetation consists total count of between 205 and 1516 phytoliths, depending on the of sparse Garry oak trees with an understorey of mixed herbaceous sample. We estimated the number of each phytolith morphotype species and exotic grasses. The most abundant grass species is the (other than asterosclereids) per slide by first calculating the weighted introduced exotic sweet vernalgrass (Anthoxanthum odoratum). average number of phytoliths per field by weighting each field by its The Douglas-fir/Arbutus forest consists of a canopy dominated by distance from the cover slip centre. For example, the first field count- Douglas-fir, with some arbutus and Western red cedar (Thuja plicata), ed is one field distant from the cover slip centre, and there are eight and an understorey dominated by the shrub salal (Gaultheria shallon). fields equidistant from the centre, so we multiplied the counts for We took one core from the savannah vegetation 20 m from the this field by eight. The counts for the next field were multiplied by ecotone boundary, and one core from inside the Douglas-fir forest, 16, and so on. We then divided by the total number of fields to find also 20 m from the boundary. The soil is a shallow, well-drained, the average number of each morphotype per field. This gave more sandy loam developed over sandstone bedrock (Kenney et al., weight to fields more distant from the centre. We used this calculation 1988). We used an AMS multi-stage sediment sampler with a slide because no matter how well we stirred the extract into the Canada bal- hammer to extract the cores. The savannah core was approximately sam, phytoliths were usually more concentrated near the centre of 35 cm long and the Douglas-fir core was approximately 49 cm long. the cover slip, and we did not want to overestimate the actual number Our primary goals were to assess the assemblage of phytoliths of phytoliths per slide. We then multiplied this weighted average by present in a small sample of modern terrestrial soils in comparison the number of fields that would be needed to cover the entire area of to the phytoliths observed in our plant samples, and to determine the cover slip. whether surface soil phytolith assemblages can be used to distinguish We counted at least one slide for each 2 cm increment, and between present-day Douglas-fir forest and savannah vegetation. graphed the total count per gramme of dried soil and the percentage This was a necessary first step prior to any future wider study of of each morphotype against depth in the core. We also examined the soils in the region. However, given the use of phytolith assemblages total phytolith count per gramme of the final extract, but as this was proceeding downwards in soil cores for palaeoenvironmental recon- qualitatively very similar to the graphed amounts per gramme of soil struction in other studies, and the lack of any such studies in our re- we chose to display the latter only. We predicted that asterosclereids gion, we were also interested in observing patterns in phytolith would be significantly more abundant in the Douglas-fir forest core assemblages with soil depth. Although phytoliths have been shown to and phytolith morphotypes produced by grasses would be more be somewhat mobile in soil (e.g. Fishkis et al., 2010), there is also some abundant in samples from the oak savannah soil core. evidence that the average age of the phytoliths in a soil layer increases with depth (Alexandre et al., 1999), validating palaeoenvironmental 3. Results interpretations. 3.1. Phytoliths found in grasses 2.2.2. Phytolith extraction We divided each soil core into 2 cm increments and processed ap- Almost all of the grasses in our sample are from the Pooideae sub- proximately every other increment. We used a wet oxidation and family (members of Twiss et al.'s Festucoid class), and as expected 62 ..MCn,MG elt aaoegah,Pleciaooy aaoclg 383 Palaeoecology Palaeoclimatology, Palaeogeography, / Pellatt M.G. McCune, J.L.

Table 1 Phytolith types and type frequencies found in grass species of southeastern Vancouver Island. Taxonomy is according to Soreng et al. (2012). See photos of each phytolith type in Fig. 1.Inflorescences = inflor., leaves and stems = veg. A = abundant, C = common, S = sporadic, R = rare, blank cells indicate that phytolith type was not observed. Note that all species had hairs/hairbases and stomatal complexes, and most had silicified tracheids – these are not indicated here.

Subfamily Tribe Species Origin Plant Rondel “Saddle Bilobate Papillae Globular Sinuate Sinuate Dendriform Echinate Crenate Tuberculate/ Polygonal Scrobiculate Scrobiculate part (10 um) rondel” (“dumbbell”) ovate elongate elongate elongate elongate elongate echinate epidermal/ elongate elongate (≤25 um) (>25 um) elongate hairbases (≤30 um) (>50 um)

Danthonioideae Danthonieae Danthonia californica Native inflor. C A R A S C veg. A A A C R S Panicoideae Panicae Digitaria sanguinalis Exotic inflor. A A A A R R veg. A ASRR Pooideae Stipeae Achnatherum lemmonii Native inflor. A A C S C veg. A A A R S Bromeae Bromus carinatus Native inflor. A A A S S veg. R S S C Bromus hordeaceus Exotic inflor. C A A A A R R –

veg. C S C 59 (2013) 384 Bromus sterilis Exotic inflor. A A A A A veg. S S A C R R Bromus vulgaris Native inflor. A A A R S veg. S S A A S S

Hordeeae Elymus glaucus Native inflor. A A A C S C S – 71 veg. A A C C R Hordeum murinum Exotic inflor. A A A A R R veg. S R S S A Meliceae Melica subulata Native inflor. A S A C R veg. C C A S Poeae Agrostis exarata Native inflor. A C A A A C (CG1)a veg. A C A C R S Agrostis pallens Native inflor. A A A C R veg. A A A A Alopecurus arundinaceus Exotic inflor. A R A A C veg. AA A Anthoxanthum odoratum Exotic inflor. R A A A S A veg. S C R S Subfamily

Tribe Species Origin Plant Rondel “Saddle Bilobate Papillae Globular Sinuate Sinuate Dendriform Echinate Crenate Tuberculate/ Polygonal Scrobiculate Scrobiculate part (10 um) rondel” (“dumbbell”) ovate elongate elongate elongate elongate elongate echinate epidermal/ elongate elongate (≤25 um) (>25 um) elongate hairbases (≤30 um) (>50 um)

Arrhenatherum elatius Exotic inflor. A A C C C veg. S S C A Cynosurus echinatus Exotic inflor. S A R A R C R veg. A A A A A C Phalaris arundinacea Exotic inflor. A S R A veg. A C C A A Poeae (CG2)a Aira caryophyllea Exotic inflor. A A A S S R veg. A S C A R S Aira praecox Exotic inflor. A A A veg. A C S C R A R C Dactylis glomerata Exotic inflor. A A A C S veg. S A A R C Festuca occidentalis Native inflor. A A A A R R C

veg. A C C A S S 383 Palaeoecology Palaeoclimatology, Palaeogeography, / Pellatt M.G. McCune, J.L. Festuca roemeri Native inflor. A A A A R S S C veg. A A A A C Festuca rubra Exotic inflor. A A A A R S R veg. A R A A C Festuca subulata Native inflor. C A A C S C veg. A S A A C A Holcus lanatus Exotic inflor. A C A R veg. A C C A C Lolium perenne Exotic inflor. A A A A A S C veg. A A A A C C Poa bulbosa Exotic inflor. A A A A R S veg. A A A A S R Poa pratensis Native inflor. A A A A S S R S veg. A A A A A R C Vulpia bromoides Exotic inflor. A A S A A A S A S veg. A S S A R S Vulpia myuros Exotic inflor. A A S A A S C R veg. A S S A C S a CG1 and CG2 refer to “chloroplast group 1” and “chloroplast group 2” of the Poeae tribe. See Soreng et al. (2012). – 8 21)59 (2013) 384 – 71 63 64 J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71

Table 2 Phytolith types and type frequencies in non-grass species of southeastern Vancouver Island. Silica-based phytoliths are indicated in bold letters.A=abundant,C=common, S = sporadic, R = rare.

Family Species Origin Life form Phytoliths

Aceraceae Acer macrophyllum Native Tree Leaves: blocky CaOx (A), stomatal complexes (A) Seeds: rhombohedral CaOx (A) Twigs/petioles: blocky CaOx (C), spiky crystals (S) Apiaceae Sanicula crassicaulis Native Herb Stems/leaves: spherical CaOx (A) Aquifoliaceae Ilex aquifolium Exotic Shrub Stems and leaves: spherical CaOx (A) Araliaceae Hedera helix Exotic Shrub Branches/leaves/petioles: spherical CaOx (A) Asteraceae Hypochaeris radicata Exotic Herb Flowers: none observed Leaves: hairs (S), tracheids (R) Stems: none observed Berberidaceae Achlys triphylla Native Herb Flowers: puzzle piece epidermal (S) Stems/leaves: none observed Mahonia aquifolium Native Shrub Leaves: none observed Stems: none observed Mahonia nervosa Native Shrub Berries: none observed Leaves: rhombohedral CaOx (A) Twigs: none observed Betulaceae Alnus rubra Native Tree Leaves: spherical CaOx (A) Twigs: spherical CaOx (A) Caprifoliaceae Linnaea borealis Native Herb Stems/leaves/flowers: spherical CaOx (A) Lonicera hispidula Native Shrub Leaves: blocky mesophyll/epidermal cells (A, poorly silicified), spherical CaOx (A), puzzle piece epidermal (C, poorly silicified) Stems: spherical CaOx (A), scrobiculate elongate (S) Symphoricarpos albus Native Shrub Berries: spherical CaOx (C), rhombohedral CaOx (C) Leaves: spherical CaOx (A), tracheids (S) stems: spherical CaOx (A) Celastraceae Paxistima myrsinites Native Shrub Leaves: spherical CaOx (A), puzzle piece epidermal (S) Twigs: spherical CaOx (C) Cornaceae Cornus nuttallii Native Tree flowers/fruit: spherical CaOx (A), fusiform echinate 100–200 μm (A) Leaves: spherical CaOx (A), scrobiculate elongate (S) Twigs: rhombohedral CaOx (S), spherical CaOx (A), fusiform echinate 100–200 μm (A) Crassulaceae Sedum spathulifolium Native Herb Stems/leaves: spherical CaOx (A) Cupressaceae Thuja plicata Native Tree Bark: spiky crystals (A) Leaves: none observed Twigs: none observed Cyperaceae Carex inops Native Sedge Inflorescences: conical epidermal (C), echinate elongate (A), hairs (C), scrobiculate elongate (C), tracheids (C) stems/leaves: conical epidermal (A), crenate elongate (A), tuberculate/echinate elongate (S), hairs (S), scrobiculate elongate (R), stomatal complexes (C) Denstaedtiaceae Pteridium aquilinium Native Fern Leaves: puzzle piece epidermal (A) Stems: blocky CaOx (A), spherical CaOx (S), scrobiculate elongate (S), tracheids (S) Dryopteridaceae Polytichum munitum Native Fern Leaves: puzzle piece epidermal (S, poorly silicified) Stems: tracheids (S, poorly silicified) Ericaceae Arbutus menziesii Native Tree Leaves: blocky CaOx (A), tracheids (S) Gaultheria shallon Native Shrub Leaves: spherical CaOx (A) Twigs: rhombohedral CaOx (C), spherical CaOx (C), scrobiculate elongate (A, poorly silicified) Fabaceae Cytisus scoparius Exotic Shrub Leaves: none observed Twigs: none observed Trifolium dubium Exotic Herb Leaves/stems: blocky CaOx (A) Fagaceae Quercus garryana Native Tree Acorns: spherical CaOx (A) Leaves: blocky CaOx (A), spherical CaOx (A) Twigs: blocky CaOx (A), spherical CaOx (A) Juncaceae Luzula fastigiata Native Herb Stems/leaves: hairs (S), spiky papillae (C), scrobiculate elongate (C), sinuate elongate (C) Liliaceae Camassia leightlinii Native Herb Bulbs/roots: raphide CaOx (S), tracheids (R) Camassia quamash Native Herb Bulbs/roots: raphide CaOx (A) Camassia spp. Native Herb Flowers/seeds: raphide CaOx (R) Stems/leaves: raphide CaOx (A) Orchidaceae Epipactis helleborine Exotic Herb Flowers: raphide CaOx (A) Stems/leaves: blocky CaOx (C), raphide CaOx (C), scrobiculate elongate (A) Pinaceae Abies grandis Native Tree Needles: blocky mesophyll/epidermal cells (C, poorly silicified), blocky CaOx (C) Twigs: blocky CaOx (A), spiky crystals (R), tracheids (S) Pinus contorta Native Tree Needles: tracheary elements with bordered pits (S), pilate elongate (A), pilate oblong (A, sometimes seem to be melded with the pilate elongate cells), scrobiculate elongate (A) Twigs: scrobiculate elongate (A) Pseudotsuga menziesii Native Tree Needles: asterosclereids (R), blocky mesophyll/epidermal (S, poorly silicified) Twigs: blocky CaOx, 10 μm (A) Tsuga heterophylla Native Tree Cones: none observed Needles: none observed Twigs: scrobiculate elongate (A) Plantaginaceae Plantago lanceolata Exotic Herb Flowers: none observed Stems/leaves: scrobiculate elongate (A, poorly silicified) Polypodiaceae Polypodium glycyrrhiza Native Fern Stems/leaves: rhombohedral CaOx (S), papillate elongate (S), puzzle piece epidermal (S, poorly silicified), scrobiculate blocky mesophyll/epidermal (C), tracheids (R) J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71 65

Table 2 (continued) Family Species Origin Life form Phytoliths

Portulacaceae Claytonia perfoliata Native Herb Flowers/buds: none observed Stems/leaves: none observed Primulaceae Trientalis borealis ssp. latifolia Native Herb Stems/leaves: spherical CaOx (A), fusiform echinate 100–200 μm (S) Rosaceae Holodiscus discolor Native Shrub Buds: spherical CaOx (A) Leaves: spherical CaOx (A), tracheids (S) Twigs: spherical CaOx (A) Oemleria cerasiformis Native Shrub Fruits: none observed Leaves: spherical CaOx (A), puzzle piece epidermal (S), tracheids (S, poorly silicified) Twigs: spherical CaOx (A) Prunus laurocerasus Exotic Shrub Leaves: spherical CaOx (A), blocky mesophyll/epidermal cells (A, poorly silicified), tracheids (S) Stems: spherical CaOx (A), blocky mesophyll/epidermal cells (S, poorly silicified), rhombohedral CaOx (C) Rosa gymnocarpa Native Shrub Leaves: blocky CaOx (A), spherical CaOx (A), puzzle piece epidermal (C) Stems: blocky CaOx (A), spherical CaOx (C) Rubus armeniacus Exotic Shrub Flowers/fruit: spherical CaOx (A) Leaves: spherical CaOx (A) Stems: spherical CaOx (A) Rubus ursinus Native Shrub Leaves: rhombohedral CaOx (A) Stems: spherical CaOx (C)

rondels are abundant in most of these species (Table 1; Fig. 2a; Twiss epidermis multicells described by University College London re- et al., 1969). We did not differentiate between different rondel forms searchers in Agrostis gigantea husks (Fuller, 2007). The stems and leaves (e.g. “horned” versus “keeled” rondels). Bilobate short cells (also of D. sanguinalis had a rare occurrence of interesting Y-shaped called “dumbbells”; Fig. 2e) were restricted to the two native bunch- phytoliths located between bilobate cells (Fig. 2q). These may be the grasses, Danthonia californica (of the Danthoniodeae subfamily) and “cross-shaped and nodular” cells referred to by Metcalfe (1960, p. 162). Achnatherum lemmonii (of the Stipeae tribe), and to the Panicoid exotic Digitaria sanguinalis, which is highly rare in this region. The in- 3.2. Phytoliths found in non-grasses florescences of A. lemmonii also contained abundant cylindrical short cells, about the same diameter as rondels, but with concave ends and Most of the non-grass species we observed contained calcium ox- edges that appear ornamented with small round bumps (Fig. 2b,c). alate (CaOx) crystals (Table 2, Fig. 3p–u). These crystals are wide- We have nicknamed these “saddle rondels”. A few of our grass species spread in higher plants and can be diagnostic of certain taxonomic also had globular ovate phytoliths in varying abundance in their veg- groups (Pearsall, 2000; Franceschi and Nakata, 2005). However, etative tissue (Fig. 2d; Table 1). Unlike Morris et al. (2010), we did they are prone to dissolution in acidic environments, and therefore not find a consistent difference in rondel production between exotic they are difficult to recover from soil with extraction procedures and native grasses. Most of our grass species had abundant papillae that use strong acids to remove carbonates (Pearsall, 2000). One phytoliths in their inflorescence tissue (Fig. 2f). study (McClaran and Coder, 2003) failed to isolate them from soil In terms of elongate cells (long cells), morphology ranged from even when using an extraction protocol that did not use acid. Given smooth scrobiculate to dendriform (Fig. 2g–n). In all grasses more that the soils in our study region tend to be quite acidic (Kenney et al., than one of these elongate morphotypes were found, and the 1988), it is unlikely that CaOx crystals can be used in palaeoecological phytoliths in one plant species often grade between different orna- reconstructions from soil in this region. mentation types. Overall, dendriform elongates were more often Our samples contained four distinct shapes of CaOx crystals, the most found in inflorescence tissue than in vegetative tissue, while sinuate abundant of which are spherical, also known as druses (Fig. 3p,q; elongates were more common in vegetative tissue (Table 1). We sep- Franceschi and Nakata, 2005). We observed spherical CaOx crystals in arated sinuate elongate phytoliths into two lengths because they 12 of our 15 shrub species, three trees, four herbs, and one fern. We seemed to consistently fall within these two classes (Fig. 2g,h). Simi- found rhombohedral CaOx crystals of varying sizes in eight of our species larly, scrobiculate elongate cells were divided into two size classes (Fig. 3r,s) and blocky CaOx crystals in nine species (Fig. 3t). In our sam- (Fig. 2l,m). In general, elongate cells ranged in length from less than ple, we observed raphide CaOx crystals (Fig. 3u) only in species of the 25 μm to over 100 μm. Liliaceae and Orchidaceae families (Table 2). In addition to short cells and elongate cells, we often observed si- Silica-based phytoliths were relatively rare in our non-grass spe- licified tracheids (Fig. 2r), hairs and hairbases (Fig. 2s), and stomatal cies, but there were a few species with distinctive phytoliths. As complexes (Fig. 2t). Many species also had a class of phytolith we expected, we found asterosclereid phytoliths in the needles of have called “polygonal epidermal/hairbases”, as they appear to be Douglas-fir(P. menziesii), a conifer in the Pinaceae family (Fig. 3a). epidermal cells, but in some cases are subtended by hairs (Fig. 2o). Asterosclereid phytoliths are formed by the deposition of silica within We did not observe cuneiform bulliform cells (also known as “fan asterosclereids (also called stellate sclereids), which are large, shaped” phytoliths) in any of our ashed samples, although these phy- non-living lignified plant cells thought to provide structural support tolith types are frequently noted in grass species (Pearsall, 2000). It (Al-Talib and Torrey, 1961; Apple et al., 2002). They appear as could be that bulliform cells were poorly silicified in our samples branched bodies, with some of the branches often broken off in soil due to dry conditions (Parry and Smithson, 1964). In their study of (Fig. 3a,4). Rovner described them as “antler-shaped” (Rovner, grasses of the Great Basin, Morris et al. (2009) found bulliform cells 1983). These large, distinctive phytoliths were first noted in British in only two of 33 grass species they examined. Columbia in the early 1960s, when soil scientists came across the dis- Two phytolith types were unique each to only one grass species tinctive bodies in the silt fraction of a Vancouver Island soil (Brydon in our sample. We found abundant phytoliths in Agrostis pallens et al., 1963). Since then, Norgren (1973), Klein and Geis (1978) and inflorescences that appear to be elongate cells with regular thickened Blinnikov (2005) observed them in plant samples from Oregon, bands along their length (Fig. 2p). These resemble the abaxial New York, and Washington states, respectively. Due to the large 66 J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71

Fig. 2. Phytolith morphotypes found in grass species: (a) rondels, from vegetative tissue of Vulpia bromoides, (b) “saddle rondel” (side), from inflorescences of Achnatherum lemmonii, (c) “saddle rondel” (top), from inflorescences of A. lemmonii, (d) globular ovate, from vegetative tissue of Danthonia californica, (e) bilobate, from vegetative tissue of D. californica, (f) papillae, from inflorescences of Bromus carinatus, (g) sinuate elongate (≤25 μm), from vegetative tissue of Poa pratensis, (h) sinuate elongate (>25 μm), from vegetative tissue of Arrhenatherum elatius, (i) dendriform elongate, from inflorescences of Bromus hordeaceus, (j) echinate elongate, from vegetative tissue of A. lemmonii, (k) crenate elongate, from vegetative tissue of Festuca occidentalis, (l) scrobiculate elongate (≥50 μm), from vegetative tissue of Bromus vulgaris, (m) scrobiculate elongate (≤30 μm), from inflorescences of Festuca subulata, (n) tuberculate/echinate elongate, from vegetative tissue of F. occidentalis, (o) polygonal epidermal/hairbases, from in- florescences of B. carinatus, (p) banded elongate cells, from inflorescences of Agrostis pallens, (q) nodular phytoliths, from inflorescences of Digitaria sanguinalis, (r) tracheid, from vegetative tissue of Lolium perenne, (s) hair and hairbase, from inflorescences of F. subulata and (t) stomatal complex, from inflorescences of Festuca rubra. size of these phytoliths (up to 200 μm) we found them quite rare in 100 to 200 μm(Fig. 3d). Pinus contorta (Pinaceae) contains pilate ob- our ashed samples, such that we examined at least three slides before long phytoliths identical in appearance to the phytoliths reported by finding one. The relative abundance of asterosclereids in Douglas-fir Blinnikov (2005) and Norgren (1973) for Pinus ponderosa (Fig. 3f). needles can vary depending on the location of the needles along the Blinnikov did not report this morphotype in his examination of shoot axis (Al-Talib and Torrey, 1961), the age of the tree (Apple et P. contorta. Also found in P. contorta are pilate elongate phytoliths al., 2002), and the availability of silica in the soil upon which the (Fig. 3g) which sometimes seem fused with the oblong types tree is growing (Norgren, 1973). (Fig. 3h). The needles also contain sporadic tracheary elements with We confirmed the presence of the characteristic conical epidermal bordered pits (Fig. 3i), which Bozarth (1993) considers characteristic cells of the Cyperaceae family in our Carex species (Fig. 3b,c). This of the Pinaceae family. species also has crenate, scrobiculate, and echinate elongate cells, as Several of our non-grass species contained scrobiculate elongate were found in many grasses (see Fig. 2j–m). Luzula fastigiata, from phytoliths similar to those seen in grasses (see Fig. 2m). We noted the Juncaceae family, also has elongate cells resembling those of the sheets of brick-like blocky mesophyll or epidermal cells in five spe- Poaceae, including sinuate and scrobiculate elongate phytoliths cies, although these were often poorly silicified (Fig. 3l,m,n). These (Table 2). This species also has phytoliths that resemble spiky or pa- cells appeared pitted (scrobiculate) in the case of the fern Polypodium pillate papillae (Fig. 3o). glycyrrhiza (Fig. 3n). The silicified epidermal cells of eight of our Both Cornus nuttalli (a tree), and Trientalis borealis ssp. latifolia (an species resembled puzzle-pieces (Fig. 3j). We also noted silicified herb) have large fusiform echinate phytoliths, ranging in size from tracheids and stomatal complexes (Fig. 3k) in a few species (see J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71 67

Fig. 3. Phytolith morphotypes found in non-grass species: (a) asterosclereid, from needles of Pseudotsuga menziesii, (b) conical epidermal (top), from vegetative tissue of Carex inops, (c) conical epidermal (side), from vegetative tissue of C. inops, (d) fusiform echinate, from leaves of Cornus nuttallii, (e) spiky crystal, from bark of Thuja plicata, (f) pilate oblong, from needles of Pinus contorta, (g) pilate elongate, from needles of P. contorta, (h) pilate elongate/oblong, from needles of P. contorta, (i) tracheary element with bordered pits, from needles of P. contorta, (j) puzzle-piece epidermal, from leaves of Pteridium aquilinum, (k) stomatal complexes, from leaves of Prunus laurocerasus, (l) mesophyll, from leaves of P. laurocerasus, (m) mesophyll, from leaves of Lonicera hispidula, (n) mesophyll, from leaves of Polypodium glycyrrhiza,(o)“spiky papillae”, from tissue of Luzula fastigiata, (p) calcium oxalate spherical (large), from leaves of L. hispidula, (q) calcium oxalate spherical (small), from leaves of Alnus rubra, (r) calcium oxalate rhombohedral (large), from stems of P. laurocerasus, (s) calcium oxalate rhombohedral (small), from leaves of Mahonia nervosa, (t) calcium oxalate blocky, from twigs of P. menziesii and (u) calcium oxalate raphide, from bulbs/roots of Camassia quamash.

Table 2). Lastly, in three of our tree species we noted very fine, spiny remaining in the extract). Based on our examination of phytoliths in crystals in the twigs or bark (Fig. 3e). We are not certain if these are plant tissue, we counted five categories of phytoliths: asterosclereids, silica-based bodies. elongate cells, rondels, bilobates, and “other” phytoliths. The final cat- egory included hairs/hairbases, the conical epidermal cells from 3.3. Soil core analyses Carex, tracheids, and unknown potential phytoliths. This category was dominated by hairs/hairbases, with 59% of 192 total “other” The weight of our final extract ranged from 1.99% to 7.22% of the phytoliths being classified as hairs/hairbases. 8.3% were tracheids original dry soil sample (uncorrected for non-phytolith particles and 1% (2 out of 192) were Carex epidermal cells. We did not observe 68 J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71

Our samples were dominated by elongate phytolith types, which made up 60–83% of the estimated total number of phytoliths per slide (Fig. 6). They did not follow our prediction of being more abun- dant in the grass-dominated oak savannah core. At similar depths, elongates were usually more abundant in the forest core (Fig. 5). However, they did tend to represent a higher proportion of the total number of phytoliths per slide in the oak savannah core (Fig. 6). The second most abundant of the morphotypes were the rondels, which represented between 18% and 36% of total phytoliths per slide (Fig. 6). Rondels also tended to be more abundant in the forest core (Fig. 5), and to represent a higher percentage of total phytoliths than in the savannah core (Fig. 6). Bilobate phytoliths were quite rare in our samples, being between 0 and 3% of the estimated phytoliths per slide (Fig. 6). These grass- produced phytoliths were also unexpectedly more abundant and repre- sented higher proportions of total phytoliths per slide in the forest core samples than in the savannah core samples (Figs. 5, 6). The proportion Fig. 4. Asterosclereid phytolith extracted from the soil core located within the of phytoliths represented by the bilobate morphotype seemed to in- fi Douglas- r-dominated forest on Tumbo Island. crease with depth in the soil core, in particular in the savannah core, however the proportion remained relatively low in all cases (Fig. 6). any papillae, stomatal complex, “saddle rondels”, puzzle-piece epi- 4. Discussion dermal or P. contorta-type morphotypes in our soil samples. We also did not see any calcium oxalate crystals in our phytolith extract. 4.1. Documenting changes in savannah understorey composition As predicted, asterosclereids were consistently more abundant in the Douglas-fir forest core than in the savannah core, although they de- Garry oak savannahs in British Columbia today are dominated by clined sharply with depth, and were not found at the deepest increment introduced exotic grasses in the Pooideae subfamily (Fuchs, 2001; sampled, 46 cm (Figs. 4, 5). Excluding this depth, Douglas-firforest Maslovat, 2002). The understorey composition of these savannahs samples ranged from 382 to 5101 asterosclereids per gramme of soil, in the past is not known. Some researchers have suggested that the while oak savannah samples ranged from 0 to 128 asterosclereids per two native bunchgrasses, A. lemmonii and D. californica, were much gramme of soil. The maximum number of asterosclereids counted per more abundant prior to the introduction of agronomic grass species slide for oak savannah samples was 5, while Douglas-fir forest samples (Maslovat, 2002), while others suggest that there was a mosaic of ranged from 8 to 106 asterosclereids per slide (not counting the 46 cm mixed native grasses and forbs, with some areas dominated by depth; data not shown). Asterosclereids represented a maximum of camas (MacDougall et al., 2004). Phytolith research has the potential 0.19% of total phytoliths per slide (Fig. 6). to corroborate the former hypothesis, if the bilobate phytoliths found

Fig. 5. Estimated total number (in thousands of phytoliths) of (a) asterosclereids, (b) elongate phytoliths, (c) rondels and (d) bilobates per gramme of dry soil plotted against depth in the soil core. Black triangles represent the Douglas-fir forest core and open circles represent the Garry oak savannah core. Note that the scale of the y-axis differs for each phytolith morphotype. J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71 69

Fig. 6. Percentage of total estimated number of phytoliths per slide represented by (a) asterosclereids, (b) elongate phytoliths, (c) rondels and (d) bilobates plotted against depth in the soil core. Black triangles are the Douglas-fir forest core and open circles represent the Garry oak savannah core. Note that the scale of the y-axis differs for each phytolith morphotype.

only in the two native bunchgrasses are more abundant in the lower the relatively small grass phytoliths to be translocated into the nearby (older) layers of soils that have a well-established stratigraphy. Indeed, forest from the savannah before they are deposited in the soil. The orig- researchers in California have used the increased presence of bilobates inal “decay-in-place” model of phytolith deposition has been found in- in subsurface soils as evidence of the former dominance of native accurate in grasslands where wind, fire and herbivory can transport bunchgrasses on certain sites (Bartolome et al., 1986). On average, our grass phytoliths moderate to long distances (Piperno, 1988; Fredlund samples seemed to show an increase in bilobate morphotypes with and Tieszen, 1994; Kerns et al., 2001; Fredlund, 2005; Madella and depth (Figs. 5, 6), however we did not attempt any form of soil layer Lancelotti, 2012; Blinnikov et al., 2013). The location of our savannah dating to confirm that deeper soil layers are in fact older. We did not core is in shallow soil exposed to the nearby coastline and winds. find any silica-based phytoliths in any part of the camas plant, and Regardless of the cause, grass phytoliths in surface soils do not ap- therefore phytolith analysis cannot shed light on its abundance in pear to be accurate indicators of the shift between Douglas-fir forest the past. and oak savannah at this scale. More work is needed to determine if Nearly all the grass species we examined from the region produce grass-produced morphotypes are rarer in forest interiors, where a abundant rondels and elongate phytoliths. However, in our test soil source of grass phytoliths is more distant. We also plan to examine cores these morphotypes were as abundant or more abundant in soil cores from deep-soil savannah remnants that are farther away the forest core, where grasses were very rare. This finding is similar from coastal influence. to a study in southern Arizona, which found phytoliths characteristic of warm-season grasses to be abundant even in heavily forested areas 4.2. Asterosclereids as indicators of the presence of Douglas-fir where these grasses were absent (Kerns et al., 2001). Bozarth (1993) also found soils of boreal forest and aspen stands to be dominated by The large asterosclereid phytoliths produced in Douglas-fir grass phytoliths even though grasses were rare. This could be caused needles were significantly more abundant in the forest core samples, by two broad processes. First, we must consider that phytolith assem- and were found very rarely in the savannah soil core, just 20 m from blages are formed over decades to centuries, a process termed “inher- the forest boundary. This along with their very distinctive appearance itance” (Fredlund and Tieszen, 1994). This incorporation of phytoliths and their specificity to Douglas-fir makes them an excellent indicator into a soil layer may be affected by the rate of soil accumulation and/ of the local presence of Douglas-fir in the past, if a reliable soil chro- or erosion, shifts in the plant community over time, as well as the de- nology can be established. Care must be taken to establish that deeper gree of preservation of phytoliths due to soil chemistry or texture soil layers do in fact contain older phytolith assemblages. In our forest (Fredlund and Tieszen, 1994; Morris et al., 2010). A difference in one core, for example, a spike in asterosclereids, elongate and rondel or more of these factors between the two core locations could have phytoliths occurs at 31 cm depth in the core (Fig. 5), and this could caused differences in the concentration of grass phytoliths in the soil. result from a buried surface horizon. For example, the higher abundance of grass phytoliths in the forest Examination of surface soil samples from Douglas-fir forests of vary- core could be a result of greater preservation of phytoliths in the ing ages and tree densities is needed to determine whether the abun- Douglas-fir forest soil, or alternatively, the Douglas-fir forest may be a dance of asterosclereids can be used to indicate the density of forest in relatively recent formation on a soil that was previously dominated by an area. However, the presence of asterosclereids alone can be used to grass species. Secondly, conditions in the open savannah could permit document the encroachment of Douglas-fir into savannah areas over 70 J.L. McCune, M.G. Pellatt / Palaeogeography, Palaeoclimatology, Palaeoecology 383–384 (2013) 59–71 time in specificlocations.Thisfinding is applicable not only to the Garry composition on experimental plots at Cedar Creek, Minnesota. Quaternary Interna- tional 287, 101–113. oak savannahs of British Columbia, but across a large geographic area Boyd, M., 2002. Identification of anthropogenic burning in the paleoecological record of in which grasslands are infilling with Douglas-fir, including the the Northern Prairies: a new approach. Annals of the Association of American entire range of Garry oak (Fig. 1), as well as other regions of California Geographers 92, 471–487. Bozarth, S., 1993. Biosilicate assemblages of boreal forests and aspen parklands. In: (e.g. Cocking et al., 2012), Montana (e.g. Heyerdahl et al., 2006), and Pearsall, D.M., Piperno, D.R. (Eds.), Current Research in Phytolith Analysis: Applications New Mexico (e.g. Coop and Givnish, 2007). in Archaeology and Paleoecology. MASCA Research Papers in Science and Archaeology, Philadelphia, pp. 95–105. Brydon, J.E., Dore, W.G., Clark, J.S., 1963. Silicified plant asterosclereids preserved in 5. Conclusion soil. Soil Science Society of America Proceedings 27, 476–477. Cocking, M.I., Varner, J.M., Sherriff, R.L., 2012. California black oak responses to fire se- The most common plants of the Douglas-fir forests and Garry oak sa- verity and native conifer encroachment in the Klamath Mountains. Forest Ecology and Management 270, 25–34. vannahs of southeastern Vancouver Island produce a few distinctive Coop, J.D., Givnish, T.J., 2007. Spatial and temporal patterns of recent forest encroach- phytolith morphotypes. Most importantly, the grasses which dominate ment in montane grasslands of the Valles Caldera, New Mexico, USA. Journal of savannahs produce abundant elongate and rondel phytoliths, and Biogeography 34, 914–927. fi Delcourt, P.A., Delcourt, H.R., 2004. Prehistoric Native Americans and Ecological Douglas- r produces large, distinctive asterosclereid phytoliths. The Change: Human Ecosystems in Eastern North America since the Pleistocene. relative abundance of these phytolith types in terrestrial soil layers Cambridge University Press, Cambridge. has the potential to help document local shifts between open savannahs Denevan, W.M., 1992. The pristine myth: the landscape of the Americas in 1492. fi Annals of the Association of American Geographers 82, 369–385. and closed-canopy Douglas- r forests in the past. However, our test Erickson, W.R., 2008. Results and data from an ecological study of Garry oak (Quercus cores revealed that soil formed under Douglas-fir forests near grassy garryana) ecosystems in Southwestern British Columbia. Technical Report 043. savannahs can contain relatively high amounts of grass-produced B.C. Ministry of Forests and Range, Research Branch, Victoria (http://www.for. phytolith morphotypes even though grass is sparse in the forest gov.bc.ca/hfd/pubs/Docs/Tr/Tr043.htm). Fisher, R.F., Bourn, C.N., Fisher, W.F., 1995. Opal phytoliths as an indicator of the floris- understorey. More work is needed to determine whether this holds tics of prehistoric grasslands. Geoderma 68, 243–255. for deeper soils and in forested areas that are more distant from sources Fishkis, O., Ingwersen, J., Lamers, M., Denysenko, D., Streck, T., 2010. Phytolith transport fi fl – of grass phytoliths. in soil: a eld study using uorescent labelling. Geoderma 157, 27 36. fi Franceschi, V.R., Nakata, P.A., 2005. Calcium oxalate in plants: formation and function. Given the tendency of Douglas- r to invade deep soil savannahs in Annual Review of Plant Biology 56, 41–71. the absence of fire, the use of the phytolith record in terrestrial soils Fredlund, G.G., 2005. Inferring vegetation history from phytoliths. In: Egan, D., at sites where archaeological research has established the history of Howell, E. (Eds.), The Historical Ecology Handbook. Island Press, Washington, DC, pp. 335–362. human occupation and palynological research has documented re- Fredlund, G.G., Tieszen, L.T., 1994. Modern phytolith assemblages from the North gional vegetation history could provide important insights into the American Great Plains. Journal of Biogeography 21, 321–335. local variability of this ecosystem before European settlement, and Fuchs, M.A., 2001. Towards a Recovery Strategy for Garry Oak and Associated Ecosystems in fl Canada: Ecological Assessment and Literature Review. Environment Canada, Canadian the degree of in uence of indigenous peoples on local plant commu- Wildlife Service, Pacific and Yukon Region. nities in the past. Fuller, D., 2007. Archaeobotany: phytolith teaching and research images. Old World Reference Phytoliths version 1.3. University College London, London (http://www. homepages.ucl.ac.uk/~tcrndfu/phytoliths.html#poo). Acknowledgements Heyerdahl, E.K., Miller, R.F., Parsons, R.A., 2006. History of fire and Douglas-fir estab- lishment in a savanna and sagebrush-grassland mosaic, southwestern Montana, – The authors would like to thank T. Golumbia and R. Walker of the USA. Forest Ecology and Management 230, 107 118. Jacobson Jr., G.L., Bradshaw, R.H.W., 1981. The selection of sites for paleovegetation Gulf Islands National Park Reserve for arranging boat transportation studies. Quaternary Research 16, 80–96. to Tumbo Island. H. Roemer, C. Ziter, R. Germain and E. McLay assisted Kenney, E.A., van Vliet, L.J.P., Green, A.J., 1988. Soils of the Gulf Islands of British Columbia: in plant sample collection. A. Cang and A. Canela provided assistance volume 2, soils of North Pender, South Pender, Prevost, Mayne, Saturna, and lesser islands. B.C. Soil Survey Report no. 43. Agriculture Canada, Vancouver, BC. in the lab. Thanks to Dr. R. Evett for discussions of asterosclereid Kerns, B.K., Moore, M.M., Hart, S.C., 2001. Estimating forest-grassland dynamics using abundance, and A. Marsh for advice on the identification of phytoliths soil phytolith assemblages and delta C-13 of soil organic matter. Ecoscience 8, found in Agrostis and Digitaria. M. Vellend and two anonymous re- 478–488. Klein, R.L., Geis, J.W., 1978. Biogenic silica in the Pinaceae. Soil Science 126, 145–156. viewers provided helpful comments on an earlier draft. Soil samples Lea, T., 2006. Historical Garry oak ecosystems of Vancouver Island, British Columbia, were collected under Parks Canada Research and Collection Permit pre-European contact to the present. Davidsonia 17, 34–50. No. 10903. MGP appreciates financial support from Parks Canada MacDougall, A.S., Beckwith, B.R., Maslovat, C.Y., 2004. Defining conservation strategies and the Pacific Institute for Climate Solutions. JLM was supported by with historical perspectives: a case study from a degraded oak grassland ecosys- tem. 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