Auburn University professor co-authors BioScience study re-examining role of mesophication in declining prominence of oak landscapes in US

An Auburn University professor has published a study reviewing the commonly held hypothesis—mesophication—that fire exclusion is responsible for reducing the prominence of oak trees across the central and eastern United States.

Heather Alexander, assistant professor of forest ecology in the School of Forestry and Wildlife Sciences, served as lead author of a multi-institution study that investigated mesophication, a condition that occurs when forests become shadier, moister and less flammable. This enables encroaching species to create conditions favorable for their own persistence at the expense of pyrophytic, or fire-tolerant, species.

The paper, “Mesophication of Oak Landscapes: Evidence, Knowledge Gaps, and Future Research,” was recently published in the journal, BioScience.

“While many forest ecologists and land managers accept the mesophication hypothesis as evidence for the compositional shifts in eastern U.S. oak forests, the reason for these changes is not clear, and many questions remain,” said co-author Alison Paulson, a postdoctoral researcher at University of California, Davis.

Within the study, the authors examine these gaps and suggest future research to consider which tree species and tree traits create self-perpetuating conditions, and under what conditions tree-level processes might affect forest flammability at broader scales.

“Our goal is to promote research that can better inform restoration and conservation of oak ecosystems experiencing structural and compositional shifts across the region,” said Alexander.

Declining oak landscapes raise concerns about the long-term consequences for a variety of ecosystem services.

Oak trees strongly influence precipitation distribution and nutrient cycling through their crown, bark and leaf litter traits. “This is not only important for the local ecosystem, but also at a broader watershed scale for human use and consumption,” said co-author Courtney Siegert, associate professor of forest hydrology at Mississippi State University.

Oaks are also a foundation genus because of their dominance and pronounced effects on ecosystem processes.

Oak acorns are food for at least 96 avian and mammal species. In addition to acorns, leaves and bark are important food for insect herbivores, providing an essential base for terrestrial food chains which support countless wildlife species that use open-canopied areas for nesting, brooding cover and foraging.

“We know from research on sites that have transitioned away from oak dominance in the region, these areas tend to be much less diverse wildlife communities and many species of conservation concern are lost without many gained,” said co-author, Marcus Lashley, an assistant professor in the Department of Wildlife Ecology and Conservation at the University of Florida.

“Dr. Alexander and her team have identified critical areas of research that will increase our understanding of the factors that influence oak loss so that we can preserve these incredibly important ecosystems,” said Janaki Alavalapati, dean of the School of Forestry and Wildlife Sciences.

The collaborative effort was undertaken by authors from Auburn University, Mississippi State University, University of Mississippi, University of Georgia, University of Florida, University of California, Davis, Pennsylvania State University and Tall Timbers Research Station, representing various expertise, including fire ecology, forest hydrology, tree ecophysiology, wildlife and plant ecology.

For more information about this research, visit Fire University to listen to a podcast and YouTube episode.