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

Abstract

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.

The magnitude, direction, and tempo of forest change in Greater Yellowstone in a warmer world with more fire

“…However, declines of ≥50% in tree density, basal area, forest extent, and aboveground carbon could occur within the coming 50 yr with a hot-dry future where fire resisters are less abundant. This rate of decline contrasts sharply with vegetation changes in the pollen record, where changes often take centuries (e.g., Calder and Shuman 2017, Crausbay et al 2017, Iglesias et al 2018, Stegner et al 2019. Our results support recent pleas for shifting from a "states-centered" to "rates-centered" approach to ecological management in which options to slow or accelerate rates of change gain prominence (Williams et al 2021).…”

“…Tracking future changes in GYE forests with empirical data then quantifying dissimilarity from reference conditions could detect the rise of novelty. Depending on the forest attributes and scales of interest, paleoecological records (e.g., Higuera et al 2011, Stegner et al 2019, dendroecological and chronosequence studies (e.g., Romme 1982, Romme and Despain 1989, Kashian et al 2005a, 2005b, and data on vegetation and ecosystem processes after the 1988 fires (e.g., Romme et al 2011) can all provide useful benchmarks. As climate and fire regimes begin to exceed historical ranges of variability (Westerling et al 2011, Higuera et al 2021, understanding where and why departures from historical disturbance-recovery dynamics lead to novel conditions is increasingly important.…”

Vegetation response to wildfire and climate forcing in a Rocky Mountain lodgepole pine forest over the past 2500 years

“…Few paleoecological studies have focused exclusively on reconstructing fire and vegetation relationships (Crausbay et al, 2017; Minckley et al, 2012; Minckley and Shriver, 2011), and even fewer have focused on creating high temporal resolution reconstructions of vegetation over the past 3000 years (Calder et al, 2017, 2019; Stegner et al, 2019), but these type of paleoenvironmental reconstructions are necessary to assess the resiliency of regions increasingly threatened by changes to coupled interactions between wildfire and climate (Calder et al, 2019). This study at Chickaree Lake provided the unique opportunity to investigate paleoecological vegetation dynamics on both millennial and decadal time scales.…”

“…Briles et al, 2012; Calder et al, 2015; Carter et al, 2017; Higuera et al, 2014; Millspaugh et al, 2000; Whitlock et al, 2011) assessed the impacts of fire on biogeochemical cycling (Dunnette et al, 2014; Leys et al, 2016; McLauchlan et al, 2014), and captured long-term changes in vegetation following glacial retreat (Brunelle et al, 2005; Lynch, 1996; MacDonald et al, 1991; Minckley et al, 2012). However, due in part to effort required to produce high-resolution pollen records, less is known about the decadal- to centennial-scale relationships between fire and vegetation in subalpine forests, particularly across periods of late-Holocene climate change (but see Minckley et al, 2011; Minckley and Long, 2016; Stegner et al, 2019).…”

Yellowstone's Old Faithful Geyser Shut Down by a Severe Thirteenth Century Drought

“…Droughts in the western United States and the Greater Yellowstone region commonly exhibit strong variability on interannual to multidecadal time scales, with recent decadal droughts being unusually severe due to regional warming (e.g., Calder et al, 2015;Cook et al, 2004;Gray et al, 2007;Martin et al, 2019aMartin et al, , 2019bMartin et al, , 2020Meko et al, 2007;Meyer & Pierce, 2003;Millspaugh & Whitlock, 1995;Stegner et al, 2019;Whitlock et al, 2008). Severe droughts of extended duration could have led to large variations in hydrothermal discharge and more specifically, to the frequency and intensity of geyser eruptions.…”