Jesse Minor University of Arizona School of Geography and Development Laboratory of Tree-Ring Research jminor@email.arizona.edu Spatio-temporal analysis of fire regimes in a Madrean Sky Island in southeastern Arizona Problem Statement Wildfire poses a suite of related problems for land managers and applied researchers. As a biophysical process, wildfire is well understood. As an ecological process, there are major unanswered questions involving post-fire recovery trajectories and the resilience of ecosystems to disturbances such as wildfire. Post-fire recovery trajectories are stochastic, as the responses of vegetation assemblages to disturbance depends on initial conditions and a suite of factors before, during, and after the fire event. Understanding the answers to basic questions can help inform more difficult and complex uncertainties that center on wildfire. One important question about wildfire centers on the time interval between fires at any given point on the landscape. This question can be addressed using paleoenvironmental proxy methods such as dendrochronological dating of fire scars, using fire atlases, and using satellite-based remote sensing techniques. Each method has its drawbacks: tree-ring based reconstruction of fire return intervals imperfectly captures fire perimeters. Fire atlases often contain only those fires registered as important, have short time series, and typically lack severity data. Satellite-based metrics capture fire perimeters and severity data, but have a short timescale as the remote sensing of fires dates only to the early 1980s.  (north aspect) Raster Analysis Model Objective The objective of this spatial analysis is to analyze burned areas using existing data sets to determine changes in burn frequency and severity across topographic variables and vegetation types. Fire severity data are used to determine reburn characteristics. The ultimate goal of this research project is to understand how changing fire regimes contribute to vegetation type conversions and altered trajectories of post-fire recovery. In turn, this project will yield information on ecological resilience in fire-prone ecosystem types. Next Steps and Further Analysis Overlapping fire perimeters will be intersected to determine the extent of the Madrean Sky Islands experiencing reburns in any given year. Mean fire return interval data calculated from this analysis will be compared to published tree-ring based estimations of mean fire return. Fire severity data covering the Madrean archipelago will be analyzed in association with LANDFIRE EVT and biophysical setting data, as well as topographic variables. Analysis will couple reburned area rasters with rasters containing slope, aspect, elevation, existing vegetation types, and biophysical setting to determine the factors causing particular changes in fire severity. This analysis will seek to identify changes in fire regimes initiated by type conversions in vegetation type. Data Sources This project uses publicly available data sources. Fire perimeter polygons were obtained from the USDA Forest Service’s Geospatial Data website. Fire severity data were downloaded from Monitoring Trends in Burn Severity (MTBS) (http://www.mtbs.gov/), and fires more recent than those available through MTBS were downloaded from the Burned Area Emergency Response (BAER) Imagery Support Data Download website (http://activefiremaps.fs.fed.us/baer/download.php). Other data are used to supplement analysis and for visualization purposes, such as a Digital Elevation Model obtained from the USGS National Map Seamless Server at http://seamless.usgs.gov/website/seamless/viewer.htm.