COS 128-3
Increases in native, not exotic, species plus succession promote biotic homogenization in the sand plain plant communities of central Wisconsin
Fire can strongly affect plant community structure and composition. Fire suppression through the 20thcentury has thus greatly shaped plant community structure and composition in fire-dominated systems across North America. The lack of baseline data limits our ability to infer the long-term effects of fire suppression on plant community assembly. Here, we use unusually detailed baseline data from the 1950s to track changes in the over- and under-story composition of plant communities growing on sandy glacial lake bed sediments in central Wisconsin. We hypothesized that fire suppression will favor more shade-tolerant species and more closed canopy conditions in these communities. We expected this to reduce alpha, beta and gamma diversity as species composition among sites converge and exotic species invade. We particularly expected shade-tolerant and fire sensitive species to increase while shade-intolerant and fire-adapted species declined.
Results/Conclusions
Sand plain plant communities in central Wisconsin have undergone dramatic changes in species structure and composition over the past 54 years. As predicted, beta diversity has declined, reflecting biotic homogenization. However, both alpha and gamma diversity unexpectedly increased. Increases in canopy coverage and native species primarily drove this biotic homogenization. Increases in exotic species richness actually promoted biotic differentiation rather than biotic homogenization across these sites, reflecting opportunistic invasions and their relative rarity. Increasing species were mostly woody, abiotic pollinated and shade tolerant, suggesting that succession following fire suppression mainly drove these changes. Our findings highlight the importance of fire in shaping plant communities and the importance of long-term studies for understanding plant community assembly.