Species niche differences shape our high-elevation forest communities.
Above: Mountain pine beetle and white pine blister rust have heavily impacted this whitebark pine forest in the Mt. Rose Wilderness Area outside of Reno, Nevada, USA.
In recent decades, increasing temperatures and prolonged drought have been linked to widespread tree mortality across the western United States. High-elevation forests are especially vulnerable due to their isolation on mountaintops, where interactions among different populations and potential for migration are limited. Losses of our high-elevation forests would have dire consequences for ecological and anthropogenic communities since these forests stabilize snowpack and regulate the downstream water supply in our arid region. These ancient forests contain the longest lived trees in the world (>4000 years old!) that have survived through significant climatic changes in the past. However, we are in a period of unprecedented climate change and novel disturbance impacts that raise concerns about the future of these beloved, ancient forests.
Cover article: (Free to read online for a year.)
Hankin, L.E. and Bisbing, S.M. (2021) Let it snow? Spring snowpack and microsite characterize the regeneration niche of high-elevation pines. J Biogeogr. 48:2068-2084. https://doi.org/10.1111/jbi.14136
Disturbance impacts and associated restoration strategies have been focused in the Rocky Mountains due to the extent of forest decline there, however, we don’t know how vulnerable these same species are within the Great Basin, where isolated tree populations deal with both extreme water stress and cold-temperature stress. Under these stressful conditions, opportunities for tree regeneration are rare, therefore we wanted to better understand the conditions that favor regeneration of high-elevation five-needle pines to be able to anticipate climate change- and disturbance-induced shifts in forest extent and composition near the upper treeline.
A Great Basin bristlecone pine sapling grows from under a downed tree with lightning-killed snags standing nearby in the White Mountains of California. Great Basin bristlecone pine is an edaphic specialist, preferring calcareous rock types found in only a few mountain ranges in the Great Basin.
Great Basin forests are fascinating because they exist atop mountain sky islands that rise dramatically out of the arid sagebrush-filled valleys. There is so little information about many of these remote areas that conducting data collection was filled with unknowns and adventures. Many times we had to resort to “old school” paper maps just to figure out a way to access the forests and sites within. There is no better way to get to know a place though, and we were surprised at the ecological diversity and beauty at every turn. Furthermore, the abundance of regeneration within these harsh environments was a humbling reminder of the resilience of these tree species. Given the accessibility challenges within the Great Basin, we are excited to be able to contribute forest monitoring data to the nation-wide efforts to conserve five-needle pine species, especially monitoring potential advancements in mountain pine beetle and white pine blister rust impacts.
As we now better understand divergent species’ strategies for persisting in these harsh environments, we get to dive deeper into how they deal with different climate conditions and what conditions may go beyond their capacity to survive. Ultimately, forest persistence will rely on natural tree regeneration and seedling traits has been tied to establishment success, so our next steps are characterizing the range of seedling traits in different Great Basin tree populations, and how these might link to seedling performance and survival under changing climate conditions. Our study showed divergent responses to snowpack conditions for more specialist whitebark and bristlecone pines, and a clear generalist strategy of limber pine – responses that are likely tied to adaptive traits. With this ongoing work, we hope to guide the selection of the best seed sources for restoration that promote resilience to climate extremes and support the persistence of this beloved and important forest type.
Lacey Hankin, PhD Candidate
Program in Ecology, Evolution, and Conservation Biology, Dept. of Natural Resources & Environmental Sciences, University of Nevada – Reno
Bisbing Lab website: https://www.sarahbisbing.com