Collaborative Research: Priority effects and persistent state shifts following wildfire and disease disturbance interactions

Humans change the behavior of wildfires, storms, diseases, and other disturbances. Altered disturbances can cause vegetation to permanently shift between types, such as from forest to shrubland. However, it is difficult to predict which parts of a landscape are vulnerable to shifts. This research examines how interactions between fires and an emerging plant disease may shift coastal forests to shrublands in the western U.S. This work will identify where and why forests are vulnerable to permanent conversion to inform disease and fire management. The research team will apply findings through relationships with the public, managers, tribal communities, and policymakers. This work will create a network across diverse research institutions to mentor students from underrepresented groups. This project will also support an innovative course that integrates art and science and publicly share a dataset that spans two decades. Although persistent state shifts have been described in many systems, empirical work has largely focused on demonstrating state permanence, rather than determining environmental variation in where transitions are likely. This research integrates an 18-year monitoring network, shrub-tree competition experiments that manipulate soil nutrient dynamics and other resource availability, and epidemiological and forest dynamics models. This integrated approach will: 1) quantify the sensitivity of forest-to-shrubland transitions to repeated fire and disease disturbances; 2) identify biogeochemical and disturbance-related feedbacks that destabilize forests and stabilize shrublands; and 3) examine where and when state shifts may occur across heterogenous, rapidly changing landscapes. This work will quantify the likelihood of persistent state shifts using a focal system that comprises plant traits relevant to disturbance-prone systems globally: coast redwood and mixed evergreen forests impacted by an introduced oomycete pathogen, Phytophthora ramorum. To date, there has been limited experimental evidence that diseases can trigger stable state transitions, despite their acute effects on plant mortality, resource competition, and biogeochemical cycles. This research will generate experimental and simulation-based tests of state shifts mediated by disease, while expanding the scope of a valuable longitudinal dataset in a long-lived forest system. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.