Woodland Decline Undermines Resilience in Fire-Adapted Landscapes.

Open-canopy forests and woodlands are a foundational component of historically fire-adapted landscapes, yet their persistence under contemporary climate and fire regimes remains poorly understood. Here, we leverage historical aerial photogrammetry integrated with contemporary satellite imagery to assess landscape change, vegetation transitions, and ecological stability over a century (1930s-2020s) for a large regional landscape of the Interior Northwest. We found woodlands declined by more than 40% across the region and exhibited high rates of type conversion, with roughly half converting to closed-canopy forests and a quarter transitioning to grass- and shrub-dominated ecosystems. Forest area, in contrast, remained relatively stable over the same period as woodland-to-forest conversion compensated for forest losses. The widespread decline in woodlands demonstrates that they exist as a metastable state, created and maintained only under stable, low- and mixed-severity fire regimes. The loss of these keystone ecosystems portends the erosion of landscape resilience-as remaining woodlands disappear, their ability to buffer for forest losses will decline as well, increasing the risk of abrupt and persistent ecosystem transitions under shifting fire regimes and warmer future climates.