Drivers of forest change in the Greater Yellowstone Ecosystem

Questions Global climate change is predicted to cause widespread shifts in the distribution and composition of forests, particularly in mountain environments where climate exerts strong controls on tree community arrangement. The upslope movement of vegetation has been observed in association with w...

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Published in:Journal of vegetation science 2022-07, Vol.33 (4), p.n/a
Main Authors: Blomdahl, Erika M., Speer, James H., Kaye, Margot, Zampieri, Nicole E., Rochner, Maegen, Currey, Bryce, Alving, Denise, Cahalan, Gabriel D., Hagedorn, Ben, Li, Hang, Oelkers, Rose, Pelletier, Lissa, Thapa, Ichchha, Willson, Kevin, Woodward, Brian D., DeRose, R. Justin
Format: Article
Language:English
Subjects:
Abies lasiocarpa
Aging
Aridity
Beetles
Climate change
Climate prediction
Composition
Demography
dendrochronology
Dendroctonus ponderosae
Drought
ecotone shift
Ecotones
Elevation
Forest ecosystems
Forests
Growing season
Mortality
Mountain environments
mountain pine beetle
Pest outbreaks
Pine
Pine trees
Pinus albicaulis
Pinus contorta
Plant species
Seedlings
Transition zone
Treeline
Understory
Vegetation
whitebark pine
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Summary:Questions Global climate change is predicted to cause widespread shifts in the distribution and composition of forests, particularly in mountain environments where climate exerts strong controls on tree community arrangement. The upslope movement of vegetation has been observed in association with warming temperatures and is especially evident in ecotones—the transition zones between vegetation types. We explored the role of drought and tree mortality on recent changes in high‐elevation forests. Location Greater Yellowstone Ecosystem, USA. Methods We established 19 forest demography plots along an elevational gradient spanning dominant high‐elevation vegetation types. Results Tree establishment dates indicated the upslope movement of Pinus albicaulis (whitebark pine) treeline and ecotone shift from meadow to forest starting in the 1950s. An expansion of the growing season likely contributed to the upward expansion of the treeline. Comparisons between overstory and understory tree composition suggested ongoing succession in the absence of fire at lower elevations, namely the replacement of Pinus contorta (lodgepole pine) by Abies lasiocarpa (subalpine fir). P. contorta seedlings were distributed at higher elevations than overstory trees of the same species, suggesting some potential for upslope movement with warming conditions; P. albicaulis seedlings, conversely, were distributed throughout all elevations of the transect. Significant tree mortality occurred in Pinus spp. and disproportionately affected P. albicaulis, as a result of a regional Dendroctonus ponderosae (mountain pine beetle) outbreak (2008–2012). Mortality events were strongly associated with drier than average conditions 2–3 years prior to tree death. Conclusion Rising sensitivity to arid conditions in the mid‐20th century amid already dense, aging forests appears to have increased susceptibility to beetle‐induced mortality during the most recent drought. Tree species in the study area responded individually to global change stressors, which acted on these forests in complex ways and led to both ecotone shifts and stability. This work highlights the interplay between succession, forest disturbances and climate‐related growth responses in driving forest compositional change in subalpine and treeline environments. We investigated tree species compositional change in subalpine forests of the Greater Yellowstone Ecosystem. Using forest demography and tree‐ring data sampled along an elevational g
ISSN:1100-9233
1654-1103
DOI:10.1111/jvs.13141