Complex Response of White Pines to Past Environmental Variability Increases Understanding of Future Vulnerability

<div><p>Ecological niche models predict plant responses to climate change by circumscribing species distributions within a multivariate environmental framework. Most projections based on modern bioclimatic correlations imply that high-elevation species are likely to be extirpated from their current ranges as a result of rising growing-season temperatures in the coming decades. Paleoecological data spanning the last 15,000 years from the Greater Yellowstone region describe the response of vegetation to past climate variability and suggest that white pines, a taxon of special concern in the region, have been surprisingly resilient to high summer temperature and fire activity in the past. Moreover, the fossil record suggests that winter conditions and biotic interactions have been critical limiting variables for high-elevation conifers in the past and will likely be so in the future. This long-term perspective offers insights on species responses to a broader range of climate and associated ecosystem changes than can be observed at present and should be part of resource management and conservation planning for the future.</p></div

(A) Location of pollen and charcoal records in the Greater Yellowstone region (brown shade) and modern distribution of whitebark pine (green shade) (www.geomapapp.org) [15].

<p>Postglacial trends in (B) <i>Pinus</i> subgenus <i>Strobus</i> pollen percentages, and (C) charcoal abundance at the study sites. The presence of macrofossils of <i>Pinus</i> subgenus <i>Strobus</i> is shown with ‘+’.</p

Environmental and conifer history in the Greater Yellowstone region over the last 15,000 years, including trends in January (blue) and July (red) insolation anomalies [44], snowpack dynamics inferred from δ¹⁸O variations at Crevice Lake [19] (note that the y-axis is reversed), fire activity (CHAR) and pollen abundance (%), and the first recorded presence of mountain pine beetle (<i>Dendroctonus</i> spp.) [46].

<p>Carbonate δ¹⁸O variations at Crevice Lake are interpreted as changes in spring snowmelt that affect the isotopic composition of the Yellowstone River. Low (more negative) δ¹⁸O values correspond with more humid winters [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124439#pone.0124439.ref019" target="_blank">19</a>]. Pollen and charcoal regional trends are estimated by GAMs applied to the charcoal influx pollen percent and data. Standard errors are shown in gray.</p

Study sites.

<p>Study sites.</p

Synthesis of key environmental proxies from the AG11 core (Asi Gonia, Crete, Greece), Cretan historical information (compiled from [25]), and Mediterranean recent Late Holocene climate data [7, 67].

<p>a) Vegetation: summary pollen diagram and richness-evenness curve; b) Grazing: fungal spore accumulation rate; c) Fire: frequency and mean peak magnitude inferred from charcoal accumulation rate (CHAR) analysis; d) Sediments: LOI analysis and sediment accumulation rates.</p

Complete percentage pollen and spore diagram from the AG11 core (Asi Gonia, Crete, Greece).

<p>Taxa excluded from the TLP sum are in grey; LDT* = long-distance pollen (Pollen of pines and trees absent in the modern ecosystems of Crete is likely to result from long-distance transport onto the island [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156875#pone.0156875.ref053" target="_blank">53</a>]); c = clump of pollen grains indicating the proximity of the plant of origin; the white bar indicates the presence of oak macro-remains (leaf, acorn) in the peat.</p

Photograph of a big plane tree growing on a dry-stone wall bordering the peat deposit (photo: T. Pedrotta, May 2012).

<p>Photograph of a big plane tree growing on a dry-stone wall bordering the peat deposit (photo: T. Pedrotta, May 2012).</p

Age-depth model of the AG11 sequence (Asi Gonia, Crete, Greece) developed with Bacon 2.2 (acc.mean = 3.5 (yr cm^-1) and acc.shape = 0.50; [29]).

<p>Age-depth model of the AG11 sequence (Asi Gonia, Crete, Greece) developed with Bacon 2.2 (acc.mean = 3.5 (yr cm^-1) and acc.shape = 0.50; [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156875#pone.0156875.ref029" target="_blank">29</a>]).</p

Saprophytic and dung fungal spore taxa and summary pollen diagram from AG11 core (Asi Gonia, Crete, Greece).

<p>Saprophytic and dung fungal spore taxa and summary pollen diagram from AG11 core (Asi Gonia, Crete, Greece).</p

Macro-charcoal data from the AG11 core (Asi Gonia, Crete, Greece) and reconstructed fire regime parameters: fire episodes, fire-episodes frequency, fire-episodes magnitude (CHAR residual-peak), and mean fire-episodes magnitude.

<p>Macro-charcoal data from the AG11 core (Asi Gonia, Crete, Greece) and reconstructed fire regime parameters: fire episodes, fire-episodes frequency, fire-episodes magnitude (CHAR residual-peak), and mean fire-episodes magnitude.</p