The North American tree-ring fire-scar network

Ellis Q. Margolis, U.S. Geological Survey, New Mexico Landscapes Field Station, Santa Fe, NM and Christopher H. Guiterman, Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ

Background/Question/Methods
Fire size and severity continue to increase across large parts of North America, driven by a combination of climate change and effects of human land use. Instrumental records are too short to fully understand patterns, trends, and drivers of fire that are necessary to model future fire. Tree-ring fire scars provide centuries-long records of fire regimes, including fire frequency, season, size, and fire-climate relationships. We compiled fire-scar records from > 100 researchers across the continent to produce the first North American tree-ring fire-scar network. We describe the network in-terms of six components, geography, spatio-temporal patterns, vegetation, topography, climate, and humans, to identify patterns as well as opportunities for future research.
Results/Conclusions
The network includes 2,593 sites and 35,606 fire-scarred trees. There is good spatial coverage across much of North America back to 1700 (1500 in western North America). Multiple landscapes contain > 1,000 fire-scarred trees, providing the potential for area burned reconstructions and analysis of fire regime scaling properties. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to sub-tropical forests in southern Mexico. The network includes 90 different fire-scarred tree species, although it is dominated by gymnosperms in the genus Pinus. Fire scars are found from 0 to > 4,000 m above sea level and on a range of slopes and aspects. The core climate space of the fire-scar network and of modern fires are similar, suggesting the potential for a limited range of climate conditions associated with fire occurrence. Influence of indigenous and non-indigenous human land use on fire regimes likely varied in place and time. Contrasting patterns of fire across the U.S./Mexico border indicate how humans can have important effects on fire regimes and vegetation at broad scales. Many areas that are now densely populated have evidence of historical wildfire, indicating the potential for catastrophic consequences when they burn again. Detailed future analyses of the hundreds of thousands of annually- to sub-annually dated records of fires spanning centuries across the continent will further advance our understanding of the interactions between fire, climate, topography, vegetations, and humans in North America. Fire affects many aspects of ecosystems (e.g., hydrology, vegetation structure and composition, and biogeochemical cycles); therefore, we anticipate this new network will promote cross-disciplinary collaborations among research communities and data networks to address the challenges of rapidly changing fire regimes.