Comparing the spatial effects and longevity of key fuel treatments in California using spaceborne lidar data

Systematically comparing fuel treatment strategies' effects on vegetation and fuel structure is essential for mitigating wildfire risk, supporting forest management, and reducing climate-related impacts. While prescribed fire and mechanical activities have been compared using field data, large-scale comparisons across treatment types have been limited by inconsistent vegetation structure measurements. To address this gap, we integrate total of 29 million observations from NASA's Global Ecosystem Dynamics Investigation (GEDI) spaceborne lidar mission with 2870 records from two fuel treatment datasets for California. We assessed spatial and temporal effects of fuel treatments in California forests. We compared broadcast burns, mechanical fuel reduction, fuel breaks, right-of-way clearance, and forest stewardship to untreated zones using GEDI-derived metrics: aboveground biomass density (AGBD), canopy cover, ladder fuels, canopy height, and layering. Broadcast burns produced significant reductions across all metrics, with the largest decrease in AGBD and canopy height (13-18 %). Mechanical fuel reduction significantly reduced all metrics except canopy height, though with smaller magnitude (6-16%). Fuel breaks yielded the greatest reductions in canopy cover, layering, and ladder fuels (19-26 %) but showed limited effects on canopy height and no significant reduction in AGBD. Using a space-for-time substitution analysis, we found mechanical treatments maintain reductions for 9-15 years across crown fuel metrics, lasting 6-9 years longer than prescribed fire. Managed wildfires showed heterogeneous recovery, while forest stewardship exhibited gradual regrowth. These findings underscore the value of GEDI and future active remote sensing missions for monitoring fuel treatment outcomes. Understanding ecological responses to treatments supports optimizing forest management to reduce wildfire risk in fire-prone regions.