The Drivers of Forest Stress in the Greater Yellowstone Ecosystem

Authors: James Speer*, Indiana State University, Margot Kaye, Pennsylvania State University, Bryan Black, University of Arizona, Grant Harley, University of Idaho, Stockton Maxwell, Radford University, Christopher Gentry, Austin Peay State University, Justin DeRose, University of Utah, Matt Bekker, BYU, Jodi Axelson, University of British Columbia, Adam Csank, University of Nevada, Reno, Georg Van Arx, WSL, Rob Wilson, University of St. Andrews, Maegen Rochner, University of Louisville, Joey Pettit, University of Utah, Lauren Stachowiak, Eastern Washington University, Sabrina Brown, Defiance University, Peter Brown, Rocky Mountain Tree Ring Research, Karen Heater, Unviersity of Idaho, Bethany Coulthard, University of Nevada, Las Vegas, Becky Brice, USGS, Jessie Pearl, USGS, Laura Smith, University of Tennessee
Topics: Biogeography, Paleoenvironmental Change, Climatology and Meteorology
Keywords: Greater Yellowstone Ecosystem, Dendrochronology, Global Change
Session Type: Virtual Paper
Day: 4/9/2021
Start / End Time: 6:15 PM / 7:30 PM
Room: Virtual 30
Presentation File: No File Uploaded

Forests are changing around the world due to stress from global change. We examined multiple forest sites in the Shoshone National Forest, during North American Dendroecological Fieldweek events in 2014, 2017, 2018, and 2019. We sampled over a thousand trees from 14 sites to reconstruct temperature, streamflow, spruce budworm outbreaks, fire, mortality dates, and regeneration patterns. We used innovative techniques such as blue intensity, stable isotopes, and quantitative wood anatomy, combined with traditional tree-ring research. We were able to reconstruct over 1,000 years of snowpack, stream flow, and temperature. We reconstructed six fires from 1584-2017 CE that affected sites across an elevational gradient. Mountain pine beetle caused massive mortality in whitebark pine between 2008 and 2012 while spruce budworm outbreaks occurred five times from 1751-2017 CE. Outbreaks have been increasing in duration and the current outbreak is the most severe on record. Whitebark pine is establishing further upslope than was previously recorded, resulting in the conversion of high elevation meadows to young forests. Whitebark pine from above and subalpine fir from below are regenerating underneath lodgepole pine forests, suggesting a contraction of the lodgepole pine zone in the future. We documented a switch from temperature minimum as the dominant climatic parameter in high-elevation tree growth to drought stress around the 1950s and insect outbreaks may be speeding the conversion to new vegetation types. Overall, the long-term perspective from tree rings shows that recent climate, disturbance, and forest regeneration are outside the natural range of variability in the Greater Yellowstone Ecosystem.

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