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Up, down, and Aaound: High-elevation Pines Respond to Warming in More Ways Than One

Photo of Limber pine seedlings are migrating upslope in the White Mountains, California, but at only a few locations. Such sites are characterized by the presence of ancient bristlecone pines (Pinus longaeva), which grew there in millennia past under favorable climates, but not at present. Limber pines at this location recruited during the period 1963-2000. White Mountain Peak (14,252'), California's third highest mountain, is in the background. USDA Forest ServiceLimber pine seedlings are migrating upslope in the White Mountains, California, but at only a few locations. Such sites are characterized by the presence of ancient bristlecone pines (Pinus longaeva), which grew there in millennia past under favorable climates, but not at present. Limber pines at this location recruited during the period 1963-2000. White Mountain Peak (14,252'), California's third highest mountain, is in the background. USDA Forest ServiceSnapshot : Under warming climates, models predict that high-elevation species will migrate up mountain slopes tracking cool conditions. With nowhere to go once they reach mountain summits, populations of subalpine and alpine species are projected to go extinct. Forest Service researchers found that subalpine limber pine (Pinus flexilis) in the U.S. Great Basin is indeed moving above upper treeline, but only at a few limited locations, and also is migrating downhill below lower treeline, as well as regenerating across forest borders into former meadows and shrublands at middle elevations. These findings suggest that limber pine has unexpected resilience to warming temperatures.

Principal Investigators(s) :
Millar, Constance I. 
Research Location : Western Great Basin mountains, California and Nevada
Research Station : Pacific Southwest Research Station (PSW)
Year : 2015
Highlight ID : 819

Summary

Limber pine (Pinus flexilis) is the dominant conifer of the subalpine zone in mountain ranges of the U.S. Great Basin. Models predict that high-elevation species will progressively migrate upslope with anthropogenically warming climates, and that populations will go extinct as they run out of habitat at mountain summits. Forest Service scientists studied seedling regeneration in limber pine in four mountain ranges of the western Great Basin and found that over the past 130 years, limber pine has regenerated upslope across upper treeline in a very limited number of locations. As importantly, seedlings are also regenerating below lower treeline, as well as across forest borders at middle elevations into former shrublands and meadows. Further, rather than the predicted continuous shifts responding to warming climates of the past century, seedling regeneration between 1883 and 2013 at all locations occurred in only one time interval: 1963-2000. This corresponded to a period of warm winters, cool summers, wet springs, and mild, wet autumns. In that successful tree regeneration requires about 10 years from seed-cone initiation to seedling establishment, migration of limber pine at least responds more complexly to climate than just a simple response to warming temperature. These complex conditions were met in the late 20th century in low, north ravines, mid-elevation meadows and shrublands where cold air pooled, and in a few locations above current upper treeline. The results suggest that limber pine has more resilience to warming temperatures than anticipated. ?

Forest Service Partners

External Partners

  • Robert Westfall and Diane Delany: USFS PSW Research Station, Albany, CA
  • Alan and Lorrie Flint, USGS, California Water Science Center, Sacramento, CA

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