Prescribed fire and natural recovery produce similar long-term patterns of change in forest structure in the Lake Tahoe basin, California

In the context of concerns about degrading forest health, increasing fire activity, and practical restoration alternatives, we analyzed 20 years of data on the response of mixed conifer forest stands in the Sierra Nevada, California to two distinctly different management approaches. Specifically, we used a Bayesian hierarchical modeling approach to evaluate the direction and magnitude of changes in forest structure and fuel variables in areas treated with prescribed fire as well as untreated forest stands in the Lake Tahoe basin. Counter to many regional studies, our results indicated that treated and long-unaltered, untreated areas may be moving in a similar direction. Treated and untreated areas experienced declines in tree density, increases in the size of the average individual, and losses of surface fuels in most size classes. The number of large trees increased in untreated areas, but decreased in treated areas. Our results suggested that untreated areas may be naturally recovering from the large disturbances associated with resource extraction and development in the late 1800s, and that natural recovery processes, including self thinning, are taking hold. Given the high cost and broad extent of treatment required to restore forest health, management approaches that promote naturally recovering landscapes may complement ongoing and planned fuel reduction treatments. Deliberately managing for natural processes to proceed unimpeded may also be important for maintaining or increasing forest heterogeneity, resilience, and biodiversity.