Exploring Interactions Among Multiple Disturbance Agents in Forest Landscapes: Simulating Effects of Fire, Beetles, and Disease Under Climate Change

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Simulation Modeling of Forest Landscape Disturbances

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Interactions among disturbance, climate, and vegetation determine landscape patterns and influence ecosystem processes. Dynamic and reciprocal interactions among disturbances can also temporarily or persistently alter landscape trajectories, especially in new climate regimes. Ecological models are used routinely to explore ecological dynamics across heterogeneous landscapes, but few models are able to simulate effects of multiple interacting disturbance events. Projecting how multiple disturbance interactions might result in novel and emergent landscape behaviors is critical for addressing climate change impacts and designing land management strategies that are appropriate for future climates. In this chapter, we demonstrate the importance of interacting disturbances using an example from fire-dominated, pine forested ecosystems of the northern Rocky Mountains, USA, where mountain pine beetle (Dendroctonus ponderosae), white pine blister rust (Cronartium ribicola), and wildland fire interact with the vegetation and climate to create unique landscape behaviors. First, we synthesized the literature on the effects of these three disturbances and their interactions in the northern Rockies forests. Then we used the mechanistic landscape process model FireBGCv2 to simulate effects of multiple disturbance interactions on vegetation composition and basal area for two landscapes under current and projected future climates. Our findings are that (1) multiple disturbance interactions influence landscape patterns more than single or no disturbances; (2) disturbance responses are typically indirect feedbacks mediated through changes in vegetation and fuels; (3) disturbance interactions may overwhelm direct effects of climate changes or effects of a single disturbance on ecosystems, and (4) exploring disturbance interactions demands a mechanistic simulation approach to fully represent those important ecological processes that are directly and indirectly affected by disturbances and their interactions. Disturbances and their interactions must be addressed to properly assess future landscape changes under projected climate regimes.