Mesophication is the process by which xeric plant communities transition to mesic communities due to the lack of fire. Xeric plant communities harbor unique plant, animal and insect communities that have become more uncommon over the past 100 years due to fire suppression. The first stage of mesophication occurs with densification (canopy closure and increased shade in existing forest patches) and woody encroachment of open areas. This subsequently alters understory conditions and creates change in the community (i.e., transition of species present). Fire has been excluded from the Moquah Barrens Research Natural Area (RNA), located in the pine barrens of northwest Wisconsin, since its establishment as one of the first RNAs by the U.S. Forest Service in 1935. In 1934, the RNA was composed of open grasslands, blueberry-sweet fern, aspen, mixed hardwoods, and jack pine. Reports document that the vegetation community has changed over time. Our project investigated whether these changes reflect mesophication. We studied woody density and community composition changes between 1979 and 2016 using plots established in 5 community types in the RNA: jack pine, aspen, aspen-oak-birch complex, oak-pine, and grassland.
Results/Conclusions
Preliminary results indicate that mesophication effects depended on community type. Tree density (stems/ha) decreased in jack pine and aspen-oak-birch communities, but increased in the other types (aspen, oak-pine, grassland). Compositional importance values of the tree species indicated that red maple (mesic sp.) and pin oak (xeric sp.) increased in importance while red oak, quaking aspen, and paper birch declined; jack pine importance was unchanged. In the tree sapling layer, there was an increase in sapling density in the jack pine community and a decline in the other types. The increase in sapling density in the jack pine community was due to mesic red maple and juneberry (a shrub). Importance values of the sapling species indicated that red maple, juneberry, and pin oak increased in importance while quaking aspen and paper birch declined; jack pine importance was unchanged. Shrub density increased in all communities except aspen where shrub density declined. Overall, the density and composition changes in trees, saplings, and shrubs in the RNA indicate that mesophication has occurred over the 80 years of fire exclusion, and resulted in greater importance of mesic species within all forest layers and higher densities of understory mesic saplings and shrubs. These changes likely affect the biodiversity, habitat, and trophic interactions that depend on xeric ecosystems.