Global change is shifting disturbance regimes that may rapidly change ecosystems, sometimes causing ecosystems to shift between states. Interactions between disturbances such as fire and disease could have especially severe effects, but experimental tests of multi-decadal changes in disturbance regimes are rare. Here, we surveyed vegetation for 35 years in a 54-year fire frequency experiment in a temperate oak savanna–forest ecotone that experienced a recent outbreak of oak wilt. Different fire regimes determined whether plots were savanna or forest by regulating tree abundance (r2 = 0.70), but disease rapidly reversed the effect of fire exclusion, increasing mortality by 765% in unburned forests, but causing relatively minor changes in frequently burned savannas. Model simulations demonstrated that disease caused unburned forests to transition towards a unique woodland that was prone to transition to savanna if fire was reintroduced. Consequently, disease–fire interactions could shift ecosystem resilience and biome boundaries as pathogen distributions change.
Bibliographical noteFunding Information:
We thank Kally Worm for assistance with data collection and Robert Jackson for useful discussion. This research was supported by the National Science Foundation (NSF) Long-Term Ecological Research (LTER) grants DEB-0620652, DEB-1234162, and DEB-1831944, Biological Integration Institutes grant NSF-DBI-2021898 and USDA grant 2018-67012-28077.
© 2021 The Authors. Ecology Letters published by John Wiley & Sons Ltd.
- Alternative states
- forest model
- fungal pathogen
- plant disease
- tree rings