Thinning and Managed Burning Enhance Forest Resilience in Northeastern California

Understanding and quantifying the resilience of forests to disturbances are increasingly important for forest management. Historical fire suppression, logging, and other land uses have increased densities of shade tolerant trees and fuel buildup in the western United States, which has reduced the resilience of these forests to natural disturbances. One way to mitigate this problem is to use fuel treatments such as stand thinning and prescribed burning. In this study, we investigated changes in forest structure in the Lassen and Plumas National Forests of northern California following a large wildfire. We used long-term field data and aerial photos to examine what management techniques can be effectively used to restore a healthy forest structure and increase the resilience of forests to drought and wildfires. Forest resilience was quantitatively modeled using the forest vegetation simulator and analyzed under varied thinning practices and fuel management scenarios. Results showed that trees below 1,219 m in elevation had the least mortality and gained the most biomass. Trees taller than 45.7 m lost the most biomass. We found that thinning basal area to 16.1 m²·hm⁻² resulted in the highest resilience score for California mixed conifer forest stands and thinning to 9.2 m²·hm⁻² resulted in the highest resilience score for Jeffrey pine stands. Structural diversity had a negative relationship with resilience score. Understanding forest structure, forest resilience, and the factors that make trees vulnerable to mortality will allow managers to better plan fuel treatments for these forests.