Post-fire vegetation and climate dynamics in low-elevation forests over the last three millennia in Yellowstone National Park

Conifer forests of the western US are historically well adapted to wildfires, but current warming is creating novel disturbance regimes that may fundamentally change future forest dynamics. Stand-replacing fires can catalyze forest reorganization by providing periodic opportunities for establishment of new tree cohorts that set the stage for stand development for centuries to come. Extensive research on modern and past fires in the Northern Rockies reveals how variations in climate and fire have led to large changes in forest distribution and composition. Unclear, however, is the importance of individual fire episodes in catalyzing change. We used high-resolution paleoecologic and paleoclimatic data from Crevice Lake (Yellowstone National Park, Wyoming, USA), to explore the role of fire in driving low-elevation forest dynamics over the last 2820 yr. We addressed two questions: 1) did low-elevation forests at Crevice Lake experience abrupt community-level vegetation changes in response to past fire events? 2) Did the interaction of short-term disturbance events (fire) and long-term climate change catalyze past shifts in forest composition? Over the last 2820 yr, we found no evidence for abrupt community-level vegetation transitions at Crevice Lake, and no evidence that an interaction of climate and fire produced changes in the relative abundance of dominant plant taxa. In part, this result reflects limitations of the datasets to detect past event-specific responses and their causes. Nonetheless, the relative stability of the vegetation to fires over the last 2820 yr provides a local baseline for assessing current and future ecological change. Observations of climate-fire-vegetation dynamics in recent decades suggest that this multi-millennial-scale baseline may soon be exceeded.