Brandon Collins, Michelle Coppoletta, Scott Stephens and I have been working for the past three years to understand a consistent, puzzling pattern in wildfire data: that fires are more severe on land owned by industrial timber companies than on land managed by public agencies.

Using a unique airborne LiDAR dataset, we identified and mapped individual trees across 460,000 hectares in the Sierra Nevada, an area which subsequently burned in five large wildfires including the Dixie Fire, the largest single fire in California’s recorded history.

Using this data, we examined: (i) which forest structures are most associated with high-severity fire; (ii) whether these forest structures are more common on private industrial land; and (iii) how extreme fire weather driven by climate change mediates the effect of management.

We found that fires were more severe in dense, spatially homogenous forests with high ladder fuels – characteristics more common on private industrial than adjacent public land.

Critically, we also found that the effects of forest structure on fire severity were amplified in extreme weather conditions!

This is an important result because it indicates that management practices which reduce tree density and ladder fuels, and increase variability, will remain effective even as extreme weather conditions become more prevalent under climate change. Indeed, these efforts will only become more urgent.

Overall, the paper suggests that the forest structures created through plantation forestry -- dense, homogenous stands with high ladder fuels -- elevate the risk of high-severity fire. However, although public lands fared better in our dataset, they still have a massive fire severity problem.

Mitigating the severity of future fires requires a coordinated effort across ownership boundaries. In particular, strategies like mechanical thinning which reduce the density of trees and foster structural variability are critical.