For many systems, regular disturbances can help maintain distinct ecological states. When these disturbance regimes are altered by humans or climate change, ecosystems states can shift. For example, many grasslands and savannas require regular fire to maintain the dominance of herbaceous species, and when fire is absent woody species can expand and become dominant. Grasslands and savannas are economically and ecologically important systems, so understanding successional trajectories following the removal of fire will help us understand if these systems will be able to persist into the future. Using historical resurvey data, long-term climate records, and site management histories, we document and assess the amount of successional change associated with the loss of fire and climate change in 50 prairie and savanna sites across Wisconsin, USA that were originally surveyed in the 1950s were resurveyed in the 2010s.
Results/Conclusions
Substantial community change has occurred over the past 60 years, and much of this change is related to management history. Species extinction probabilities between the 1950s and 2010s were 4 times lower in sites maintained with fire than those who received little to no fire. Fire frequency had the largest influence on species persistence, but winter climate change also differentially influenced species, with spring-blooming species suffering more at sites that experienced greater changes in winter weather. Many historical savanna sites have become closed-canopy woodlands as both fire and grazers were absent in recent decades. Changing the disturbance regimes in these prairies and savannas has weakened reinforcing cycles that maintain open habitats and often results in succession to closed canopy woodlands. Climate change, such as warming winter temperatures, also had species-specific influences that shape the patterns of community change.