Fire, vegetation and ecosystem processes in Yellowstone National Park
Lodgepole pine, disturbance, Yellowstone National Park, forest fire, nitrogen cycling, carbon dynamics, coarse wood, spatial heterogeneity, soils processes, microbial community composition
Our ongoing research on fire, vegetation and ecosystem processes includes long-term study of the 1988 fires. Wilderness areas like Yellowstone permit scientists to study ecosystems that have been minimally impacted by humans. Fires are likely to increase in number and size with global warming, and long-term studies may help scientists and land managers anticipate what may happen in the future. Our current research includes collaborators Bill Romme (Colorado State University) and Dan Tinker (University of Wyoming) and focuses on "Paths of recovery: landscape variability in forest structure, function and fuels 25 years after the 1988 Yellowstone Fires.” Understanding succession following severe wildfire is increasingly important for forest managers in western North America and it is critical for anticipating the resilience of forested landscapes to changing environmental conditions. Successional trajectories set the stage for future carbon storage, abundance and distribution of fuels, and habitat for many species. Early successional forests are increasing throughout the West in response to greater fire activity, but few long-term studies have considered succession following stand-replacing wildfires over large areas. With funding from the Joint Fire Science Proposal (view PDF of our proposal), we are re-sampling our long-term vegetation plots during 2012 and 2013 to test hypotheses in the context of three overarching questions:
(1) Are stand structure and function beginning to converge twenty-five years after the Yellowstone Fires, and what mechanisms may contribute to convergence or divergence? Heterogeneity in forest structure was the rule after the 1988 fires, and postfire lodgepole pine (Pinus contorta var. latifolia) densities ranged from zero to >500,000 trees/ha. The post-1988 cohort of lodgepole pine is reaching a time of critical transitions in structure and function. To quantify change in stand structure and function, we will re-sample vegetation in 90 plots (0.25 ha) representative of the range of conditions found within the burned area. To elucidate potential mechanisms underpinning vegetation changes, we will resample foliar nitrogen, cone production, and soil nutrients in 25 of the 90 plots.
(2) Are plant community composition and species richness converging or diverging across gradients in local fire severity, post-fire lodgepole pine density, elevation and soil type a quarter-century after the 1988 fires? A central objective in our research has been to understand the relative influence of contingent factors (e.g., local fire severity) vs. deterministic factors (e.g., elevation, soils) on postfire ecosystem development, and how these influences may change through time. We have also tracked selected plant species of concern (e.g., Populus tremuloides, Cirsium arvense) since the 1988 fires. We will re-sample community composition in the 90 plots, plus 300 plots within three 1 km x 1 km grids established in 1989, and 552 plots within nine burned patches established in 1990. These plots represent a broad range of fire severities, patch sizes, elevation/soil characteristics, and postfire pine sapling densities.
(3) How do canopy and surface fuels vary across the postfire landscape, and how will the variation in fuels influence potential fire behavior a quarter century post-fire? Successional dynamics ultimately generate the fuels available for future fires. From field data in the 90 plots and re-sampling of 11 fuels plots from 1997, we will quantify surface and canopy fuels across the postfire landscape then use the fuels data and the fire model NEXUS to estimate potential fire behavior. We will identify weather conditions under which certain fire behavior thresholds are crossed, e.g., moisture and wind values that permit torching or crowning to occur in young postfire forests.
Overall, results from the proposed study will enhance understanding of succession after one of the most notorious fires of the 20thC. Our findings will aid managers in evaluating other recent (and future) fires in the Mountain West; determining where postfire trajectories may lead to desirable vs. undesirable conditions; and anticipating potential fire behavior a quarter century after fire. Yellowstone’s postfire forests may serve as benchmarks for forests throughout the region and effective sentinels of change for the Rockies.