Influence of bioclimatic variables on tree‐line conifer distribution in the Greater Yellowstone Ecosystem: implications for species of conservation concern

Abstract

Aim Tree-line conifers are believed to be limited by temperature worldwide, and thus may serve as important indicators of climate change. The purpose of this study was to examine the potential shifts in spatial distribution of three tree-line conifer species in the Greater Yellowstone Ecosystem under three future climatechange scenarios and to assess their potential sensitivity to changes in both temperature and precipitation.Location This study was performed using data from 275 sites within the boundaries of Yellowstone and Grand Teton national parks, primarily located in Wyoming, USA.Methods We used data on tree-line conifer presence from the US Forest Service Forest Inventory and Analysis Program. Climatic and edaphic variables were derived from spatially interpolated maps and approximated for each of the sites. We used the random-forest prediction method to build a model of predicted current and future distributions of each of the species under various climatechange scenarios. ResultsWe had good success in predicting the distribution of tree-line conifer species currently and under future climate scenarios. Temperature and temperature-related variables appeared to be most influential in the distribution of whitebark pine (Pinus albicaulis), whereas precipitation and soil variables dominated the models for subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii). The model for whitebark pine substantially overpredicted absences (as compared with the other models), which is probably a result of the importance of biological factors in the distribution of this species.Main conclusions These models demonstrate the complex response of conifer distributions to changing climate scenarios. Whitebark pine is considered a 'keystone' species in the subalpine forests of western North America; however, it is believed to be nearly extinct throughout a substantial portion of its range owing to the combined effects of an introduced pathogen, outbreaks of the native mountain pine beetle (Dendroctonus ponderosae), and changing fire regimes. Given predicted changes in climate, it is reasonable to predict an overall decrease in pinedominated subalpine forests in the Greater Yellowstone Ecosystem. In order to manage these forests effectively with respect to future climate, it may be important to focus attention on monitoring dry mid-and high-elevation forests as harbingers of long-term change.

Continued warming could transform Greater Yellowstone fire regimes by mid-21st century

“…54), and such dynamics have already been observed elsewhere (55)(56)(57). Warming temperatures alone are expected to cause declines in suitable habitat for some conifers now common in the GYE, even if precipitation also increases (58)(59)(60). In the GYE, projected changes in temperature reach the historical differences in temperature between subalpine forest (with an historical fire rotation >100 y) and lower montane forest (with an historical fire rotation <30 y) by the end of the century.…”

Autumn Snowfall Controls the Annual Radial Growth of Centenarian Whitebark Pine (Pinus albicaulis) in the Southern Coast Mountains, British Columbia, Canada

“…Climate change alone is predicted to reduce the distribution of Whitebark Pine in the USA by >90% by 2100 (Warwell et al 2007). More localized analyses indicate similar reductions (Romme and Turner 1991, Mattson and Reinhardt 1994, Bartlein et al 1997, Koteen 2002, Schrag et al 2007. A North American, rangewide analysis (McKenney et al 2007) predicts a 42% loss of range area for Whitebark Pine by 2100, However, this analysis, based solely on climatic variables, overestimates the current range extent and thus likely underestimates future range reduction.…”

“…At lower elevations, Whitebark Pine will face increased competition, particularly from Subalpine Fir and Engelmann Spruce, which are predicted to increase (Wilson 2001, Koerner 2003, Schrag et al 2007. This competition will reduce suitable sites for seedling establishment, leading to reduced regeneration rates and declining populations, and increase stress on mature trees, resulting in reduced seed production and increased susceptibility to White Pine Blister Rust and Mountain Pine Beetle.…”

“…Whitebark Pine distribution is heavily influenced by temperature (Arno and Hoff 1989, McKenzie et al 2003, Schrag et al 2007), especially at its upper elevational limits and thus is expected to be much affected by climate change. Model predictions with the 2X CO 2 scenario (Bradley et al 2004) indicate particularly intense summer warming at higher elevations and at latitudes between 35 o and 55 o N, which includes much of the range of Whitebark Pine.…”

Potential influence of wildfire in modulating climate-induced forest redistribution in a central Rocky Mountain landscape

“…3). Subalpine fir and Douglas-fir may be at risk because both require relatively moist soil conditions during the growing season, especially at middle and lower elevations, and hotter and drier temperatures can result in soil moisture stress (Ettl and Peterson 1995, Case and Peterson 2005, Schrag et al 2008. Although moderately drought tolerant, lodgepole pine is associated with climates of relatively cold nighttime and spring temperatures, and its frost-tolerant seedlings may provide competitive advantage over other conifers (e.g., Douglas-fir) in these areas (Lotan andCritchfield 1990, Coops et al 2005).…”