Abstract
BackgroundIn 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.ResultsBurn 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.ConclusionsWhile 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.
Highlights
In fire-adapted ecosystems of the western USA, prescribed fire is an essential restoration and fuel reduction tool
National Preparedness levels (PL) and the existing Northern California Geographic Area NWS (NOPS) PL are very similar, so we used NOPS PL preferentially in the Results Burn windows were especially rare during peak fire season (July to September) and December through January (Figs. 2 and 3)
While burn windows are less frequent in autumn than they are in the spring, managers often plan to conduct more complex prescribed understory burns in autumn because, (1) the historical fire season in the Sierra Nevada region was mostly summer through autumn, but summer has few burn windows; and 2) autumn precipitation events can assist with controlling prescribed fires, reducing the chance of fire escape (Fettig et al 2010)
Summary
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. In forests that historically experienced frequent, mostly low-severity fire (i.e., Fire Regime 1 forests [FR1], Hardy et al 2001), logging and fire exclusion have caused major changes, including loss of the large tree component, increases in stand density and surface and ladder fuels, as well as compositional shifts toward shade-tolerant and fire-intolerant tree species (Safford and Stevens 2017). Some studies have found that prescribed fire alone reduces surface and ladder fuels and is successful in mitigating the risk of crown fire under extreme weather conditions (Kilgore and Sando 1975; Stephens et al 2012)
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