Simulation of a fire-sensitive ecological threshold: A case study of Ashe juniper on the Edwards plateau of Texas, USA
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abstract
A model was developed to represent the establishment of a fire-sensitive woody species from seeds and subsequent survival and growth through five size classes. Simulations accurately represent structural changes associated with increased density and cover of the fire sensitive Ashe juniper (Juniperus ashei, Buckholz) and provide substantial evidence for multiple steady states and ecological thresholds. Without fire, Ashe juniper increases and herbaceous biomass decreases at exponential rates until a dense-canopy woodland is formed after approximately 75 years. Maintenance of a grass- dominated community for 150 years requires cool-season fires at a return interval of less than 25 years. When initial cool-season fires are delayed or return intervals are increased, herbaceous biomass (fuel) decreases below a threshold and changes from grassland to woodland become irreversible. With warm season fires, longer return intervals maintain grass dominance, and under extreme warm-season conditions even nearly closed-canopy stands can be opened with catastrophic wildfires.
