The overall health and persistence of Pinus albicaulis is of international concern due to Cronartium ribicola, Dendroctonus ponderosae, altered fire regimes and climate change. Refugia have long been studied to better understand how populations persist during periods of unfavorable or rapid environmental change. Palaeobotanical records indicate plant populations are also known to retract to extreme and unusual soils. We applied these concepts to identify genetic macrorefugia (1-km) within known, regional climates. Selected samples represent the US Northern Rockies. Soils data were obtained from the USGS. Baseline (1981-2010) and mid-century (2011-2040) climate data were obtained from AdaptWest. Spatially explicit adaptive layers were developed using geostatistical-hybrid regression for blister rust resistance, drought tolerance and late winter cold hardiness; genetic diversity was characterized by ordinary kriging. Layers were linearly integrated and categorized from high-to-low to identify grids with desirable genetic attributes. A limestone filter was subsequently applied. Stable climatic filters (≤ 1⁰C change in temperature and ≤ 10% change in precipitation) included two representative concentration pathways (RCP4.5 and RCP8.5). Lower bounds of model uncertainty were described by mean annual temperature (MAT) and mean annual precipitation (MAP); upper bounds were described by mean coldest month temperature (MCMT) and precipitation as snowpack (PAS).
Results/Conclusions
Midcentury (2040) stable MAT and MAP indicated the presence of macrorefugia for only 1.1% of the interior distribution for RCP4.5 and no suitable locations for RCP8.5. Stable MCMT and PAS indicated macrorefugia for 36.4% of the interior distribution for RCP4.5 and 24.4% for RCP8.5. Potential refugia occupied a more narrow range of elevation and climate, with a downward shift in elevation (320 m), cooler annual temperatures (3.1⁰C), higher precipitation (205 mm) and warmer winter temperature (2.4⁰C). This qualitative, bottoms-up approach to identifying macrorefugia supports viable populations to avoid inbreeding depression (n=100) and maintain evolutionary potential (n=1000). Wilderness areas are widely held as germplasm repositories for plant populations. While an average of 85% of present day interior P. albicaulis occurs in designated wilderness, our results indicate less than 1% of the projected refugia are located within the boundaries of these unmanaged areas. These findings have far-reaching implications for prioritizing areas for active restoration and conservation if P. albicaulis is expected to continue to provide a valuable food source for dependent wildlife and to function as a foundation and keystone species.