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Fire Severity and Succession

Over the past 100 years, forest fires have impacted thousands of acres throughout the Great Basin. Unlike the fires of the past, today’s fires are larger and less frequent. The need to understand forest response to fire is important for improving management (controlled burns) and predicting ecological response (recovery and succession patterns).

In the Fish Lake National Forest, located in south-central Utah, the Twitchell Canyon fire burned 44,874 acres over a four month period (July-October 2010; Figure 1). On September 15, the fire had burned over 9,500 acres alone. This fire was the largest in the state that year, burning through multiple forested types with variable levels of severity. The impact that this fire had on forest ecosystems ranged from crown fires that killed all trees and understory vegetation to a smoldering fire that removed low growing plants and trees but preserved larger trees and removed partial understory structure.

Figure 1. Twitchell Canyon Fire east of Beaver, Utah burned over 44,000 acres and lasted from July to October 2010 (Photo courtesy of the US Forest Service 2010).

The ability of a forest to recover from fire is likely dependent on burn severity and forest mortality. Additionally, fire severity may influence long-term succession of plant communities. However, these responses are not well understood based on current literature. The Twitchell Canyon fire has provided an excellent opportunity to investigate forest successional following a largescale disturbance. We are using GIS to delineate patterns of fire severity and relate this to environmental variables and ecological patterns observed over time (Figure 2).

Figure 2. A) Fire severity representing low, moderate and high levels, B) Dominant vegetation types, and C) areas treated with seed and mulched.