Old Forests Face High Blaze Risk in Former Fire Zones

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A new analysis by scientists at Oregon State University and the USDA Forest Service Research & Development has found that the Pacific Northwest's mature and old-growth forests are most at risk of severe wildfire in areas that historically burned frequently at lower severity. The study highlights the impact of fire exclusion policies that began in the 1850s, which have allowed shade-tolerant and fire-intolerant species to move in, making the forests more vulnerable to stand-replacing wildfires as climate change intensifies.

Why it matters

Mature and old-growth forests are culturally, economically and ecologically significant, supporting biodiversity while storing vast amounts of carbon. Understanding where these forests are most vulnerable is essential for guiding risk mitigation efforts and returning forests to healthier fire regimes.

The details

The researchers used state-of-the-art modeling techniques to analyze federal forests in the 24 million acres of western Oregon, Washington and California covered by the Northwest Forest Plan. They found that 75% of the forest areas with the biggest risk of severe wildfire are places that used to see widespread low- and mixed-severity fires. The exclusion of fire from Northwest landscapes began with the disruption of Indigenous fire stewardship in the 1850s, and putting out wildfires became federal policy following the Great Fire of 1910.

• The disruption of Indigenous fire stewardship began in the 1850s.
• Putting out wildfires became federal policy following the Great Fire of 1910.

What they’re saying

What’s next

The researchers say developing land management strategies to address the loss of mature and old-growth forests to stand-replacing wildfire is crucial for maintaining these vital socio-ecological resources. This starts with quantifying the spatial footprint of fire exposure by combining geographic data with fire ecology analytics.