Simulation of the Consequences of Different Fire Regimes to Support Wildland Fire Use Decisions

Abstract

The strategy known as wildland fire use, in which lightning-ignited fires are allowed to burn, is rapidly gaining momentum in the fire management community. Managers need to know the consequences of an increase in area burned that might result from an increase in wildland fire use. One concern of land managers as they consider implementing wildland fire use is whether they can meet the goals in the land management plan for the desired distribution of forest structural stages across the landscape with further increases in fire. These questions were explored for a 49,532 ha landscape on the Boise National Forest in Idaho that typically experiences mixed-severity and stand-replacing fires. The landscape simulation model TELSA was used to evaluate how increases in fire frequency and area burned might affect landscape composition and structure. Information about frequency, annual area burned, and size-class distributions of fires derived from a fire atlas for the northern Rocky Mountains were used to define the fire regime parameters for five different simulation scenarios. Scenarios with higher fire frequency and area burned resulted in landscapes dominated by earlier successional forest stages and only small patches occupied by large trees. Simulated variability in area occupied by different tree-size classes on this landscape was much greater than the desired ranges defined in the land management plan for the forest at large. A measure of dissimilarity (Euclidean Distance) from desired composition was used to evaluate scenarios for their relative ability to achieve long term land management goals. The lowest values of Euclidean Distance were for a scenario that represents a substantial increase in fire over 20th century fire regimes. Euclidean Distance increased for scenarios with very high rates of burning, implying an upper limit to the desired amount of fire for this landscape. These findings could be used to develop guidance for achieving desired conditions with wildland fire use.