Prescribed fire is used in fire-adapted ecosystems to reintroduce lost disturbance processes. Controlled burns create a mosaic of habitat features in the landscape for species endemic to these systems, and management often targets fire regimes that minimize population loss due to mortality effects. While observed population responses of animals following disturbance are often described, population models that use vital rates to understand and predict how spatially-different disturbance regimes affect population dynamics are limited. Integrating vital rates into mechanistic population models is a necessary advancement to test the viability of disturbance-based management plans with rare, sensitive species.
We used population growth rate as a metric to test how an endangered butterfly metapopulation responds to seven fire management scenarios of varying spatial scales and disturbance intensity. Specifically, we asked if fine-scale disturbance is better for population growth rate, and if it decreases extinction risk of small populations. Further, we tested if fine-scale disturbance decreases the importance of immigrant butterflies in driving population recovery of sites post-fire. To answer these questions, we developed a spatially-explicit agent-based model for a Fender's blue butterfly metapopulation in Oregon, USA. Our model introduces fire disturbance as a dynamic effect on habitat quality and vital rates to predict population growth rate under different prescribed burn regimes in a real landscape.
Results/Conclusions
Fine-scale disturbance increases population growth rate and decreases extinction risk for an endangered butterfly. Prescribed fire that disturbs an entire population significantly decreases growth rate compared to no-fire management, and increases extinction risk of small populations. We found that lower-intensity fire buffers population stability, while higher-intensity fire causes extremes in population growth rate in response to management scenarios. The importance of immigrant butterflies in driving population recovery after fire is significantly higher in burn plans that disturb an entire population.
Our results demonstrate how fire-sensitive animal populations respond and recover from prescribed fires, and suggest optimal fire management strategies that use fine-scale disturbance in the landscape are better for population growth rate. Management approaches that do not partition disturbance within populations increase extinction risk and reliance on immigrant individuals for population recovery, and suggests burn plans should be applied at finer scales in the landscape to achieve boosts in population growth for species of concern.