Disturbance interactions can impact resilience mechanisms of forests

Authors


  • Corresponding Editor: R. Gardner.

Abstract

Interactions between multiple disturbances are of special concern in ecology due to their potential for non-linear behavior and long-lasting legacies on landscape structure and function. If multiple disturbances overcome the ecological resilience of a system, alternate stable states are possible. Increases in the frequency and severity of disturbance events as a result of climate change heighten this concern. This study directly addresses the question of ecosystem resilience in the face of multiple disturbances. We investigated a gradient of disturbance interaction severities between two events in a subalpine forest, a 1997 windstorm (variable severity) and a 2002 wildfire (high-severity). A third disturbance, salvage logging of blowdown (1999–2001) prior to the fire, served as a de facto experimental treatment. Ninety-nine study plots were established across the disturbance gradient, including fire-only areas for a baseline fire response. Modeling indicated that the combination of two severe disturbances created novel conditions which exceeded the resilience mechanisms of the system. Modeled mean fire residence time and temperature (First Order Fire Effects Model, FOFEM), as well as mean distance to potential seed sources, increased as a result of the interaction. Regeneration 8 years post-fire was essentially absent in medium- to high-severity blowdown + fire plots, whereas low-severity blowdown + fire and fire-only areas showed strong regeneration. Blowdown + salvage + fire had significantly higher regeneration than areas of comparable blowdown, suggesting that fuel loading drove the interaction. CART analysis supported this hypothesis. Multiple disturbances have the potential to create surprising situations and reduce the resilience of an ecosystem. Differential recovery as a result of a “novel disturbance” created by compounding events will likely have long lasting legacies across the landscape.

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