Retrospective analysis of burn windows for fire and fuels management: an example from the Lake Tahoe Basin, California, USA

Abstract

Background: In fire-adapted ecosystems of the western USA, prescribed fire is an essential restoration and fuel reduction tool. There is general concern that, as the fire season lengthens, the window for conducting prescribed burns will contract unless management changes are made. This could occur because a number of conditions must be met before prescribed fire can be used in the field, and those are most common during the spring and autumn when the need for fire suppression response has been historically less. To assess patterns of potential prescribed burning feasibility, this study evaluated three conditions: (1) permission to burn as granted by air quality regulators; (2) weather within burn plan prescription; and (3) availability of operational and contingency resources. Our 21-year analysis (1999 to 2019) combines three independent datasets for a daily comparison of when prescribed fires could have been implemented (henceforth, burn windows) in the Lake Tahoe Basin (LTB) and analyzes seasonality, interannual variability, and trends. Results: Burn windows were most frequent during spring, followed by autumn, with the fewest burn windows during the summer and winter. Burn windows lasting multiple days occurred infrequently. Two- to three-day burn windows did not often occur more than twice per month over the study period, and longer burn windows were very rare. Interannual variation was considerable. Finally, an abrupt increase in burn windows was detected in 2008. This was determined to be related to a methodological change by air quality regulators and not to any changes in climate or resource availability. Conclusions: While this case study focuses on the LTB, the analysis was performed with readily available data and could be applied easily to other land management units, demonstrating a valuable method for planning and prioritizing fire and fuels management activities. This type of tool can also identify areas for research. For example, if there were unused burn windows during the winter and early spring—or they were projected to increase—research into the ecological impacts of winter and spring burning may allow managers to more confidently adapt to changing climate. Moreover, this analysis demonstrated that modest and reasonable regulatory changes can increase opportunities for prescribed burning.