Urbanization, species invasions, and climate change are contributing to biodiversity losses across the globe. Against this background of multiple, interacting threats, conservation increasingly relies on hands-on actions to provide refugia where species have the best chance of survival. However, even the best designed conservation strategies are vulnerable to unpredictable, catastrophic events. Following the intense disturbance imposed by Hurricane Irma, we had the unique opportunity to test how habitat management interacted with the hurricane to affect population dynamics of rare species. We studied the population growth of a rare, fire-adapted plant, pineland croton (Croton linearis). Working two years before Hurricane Irma’s landfall, we created an experiment on Big Pine Key in which we simulated fire with mechanical understory removal. We estimated croton vital rates and population growth rates in the year of clearing and in no-disturbance controls. For comparison purposes, we used croton monitoring data from Everglades National Park to estimate croton vital and population growth rates in fire years and in years with no disturbance. Both study sites were impacted by Hurricane Irma in September 2017. Following the storm, we estimated vital and population growth rates in our experimental plots on Big Pine Key, and in the Everglades.
Results/Conclusions
Where Hurricane Irma’s impact was most intense on Big Pine Key, croton survival rates depended on whether or not plots were mechanically cleared prior to the hurricane. Previously cleared plots had higher hurricane survival relative to those that had not (Tx*Irma interaction: χ2=14.25, df=1, p<0.001). In Everglades, where Hurricane Irma was less intense, its effects on survival of croton plants was less pronounced. Croton survival was highest in no-disturbance years, and fire and hurricane survival rates were not different (Disturbance Type: χ2=23.91, df=2, p<0.001). Population growth rates mirrored the pattern in survival rates. On Big Pine Key, hurricane lambda in mechanically cleared plots was almost twice our estimate for control plots. In the Everglades, fire initially reduced the population growth rate which then rebounded in the year of the hurricane, much as we might expect in the absence of a hurricane as a population recovers from a fire. Our results show quantitatively that human-driven habitat management increases population resilience to an anthropogenically-driven, catastrophic, weather event. In the context of increasing threat of major hurricanes, appropriately managing landscapes that harbor rare species has the potential to increase species’ resilience to subsequent storm events. With poor management, stronger hurricanes will accelerate extinction.