Fires in subalpine forests of the Greater Yellowstone Ecosystem often burn in a mosaic pattern, resulting in heterogenous environments that shape the initial years of succession. However, whether species composition in the long term is associated with microclimatic conditions is mostly unexplored. Our lab has examined successional trends in post-fire communities over 30 years after the 1988 Yellowstone fires using permanent plots (n = 275) on southerly slopes of Henderson Mountain (HM) and northerly slopes of Mt. Washburn (MW). In each location, plots were grouped into study sites with similar environmental conditions, including mesic-burned, mesic-unburned, xeric-burned, and xeric-unburned. In 2016-2017, we remeasured plots for plant species richness and conifer regeneration and deployed microclimate sensors on a random subset of plots (n = 19) for ~60 days during the growing season to characterize seasonal soil temperature (ST) and soil moisture (SM) at each study site. Microclimatic parameters were estimated using bootstrapping. We asked the following questions: 1) How variable are SM and ST, particularly in burned relative to unburned study sites? 2) What is the floristic composition at each study site nearly 30 years after fire? 3) Is species composition associated with specific microclimatic conditions?
Results/Conclusions
Preliminary analyses indicate that ST at HM was more variable in burned sites (-4 – 61°C) than in unburned sites (1 – 27°C), which may be related to low conifer regeneration in the former group. Average SM was consistently greater in mesic-burned and mesic-unburned sites compared with their xeric counterparts (0.09 versus 0.055 m3/m3, respectively). The dry-burned site had the most variable ST, lowest average SM, and was dominated by grasses, including blue wild rye (Elymus glaucus). Mesic-unburned and xeric-unburned sites showed the lowest variability in ST, possibly related to closed tree canopies, and harbored unique species not found in burned sites, including Labrador tea (Ledum glandulosum) and heartleaf twayblade orchid (Listera cordata). At MW, ST showed similar variation between burned and unburned sites (2 – 41°C), which may be related to high conifer regeneration and coarse woody debris cover in burned sites. Average SM was greatest in the mesic-burned site (0.11 m3/m3). Nonetheless, species composition was similar among all sites, which were dominated by grouse whortleberry (Vaccinium scoparium). Microclimate may be related to post-fire species composition in areas with minimal deadfall or where conifer regeneration is slow (HM) but appears less important in areas where regenerating tree canopies have reduced microclimatic variability (MW).