Impacts of global change and conservation solutions on fire-dependent plant communities
By Audrey Wilson, Master’s student, Wildlife Ecology & Conservation Department
An errant spark from a poorly extinguished campfire or carelessly discarded cigarette can trigger a devastating fire. Fire can be one of the most important drivers that shapes and maintains an ecosystem, however. Dr. Ellen Damschen and her lab in the Department of Zoology at the University of Wisconsin-Madison study the role of fire and other forces in determining local diversity in fire-dependent systems.
The beginning of Dr. Damschen’s career followed an unusual trajectory. As an undergraduate at Luther College in Decorah, Iowa, she double-majored in Music and Communication. She had always excelled at the flute, but by graduation knew that she did not want to pursue a career in performance. Inspired by a lifetime love of the outdoors, she enrolled in biology classes and secured an internship at the Cedar Creek Ecosystem Science Reserve. She went on to complete a PhD in Zoology with a minor in Botany at North Carolina State University.
Dr. Damschen’s work is aimed at addressing the relative influences of local and regional processes that shape an ecosystem by using plant species to address these important ecological questions. The work is conducted in grasslands and savannas of the Midwest and Southeast, focused on areas with nutrient-poor soils and a history of frequent fire.
For many years, naturally occurring fires have been suppressed because of the threat that uncontrolled flames pose to humans, along with the misguided assumption that fire is “bad.” Using historic data, Dr. Damschen and her team evaluated the changes in species richness and composition that have occurred in prairies and oak savannas where fire has been suppressed. Looking at data from the 1950s, 1980s, and 2012, they found that the number of plant species remained constant over the years. The real story lies in the composition of species; here, they found dramatic change. Exotic and woody species flourished in the absence of fire, while rare and sensitive species declined. Many species that dominated the landscape in 1950 have declined or disappeared, while some of the most common species in 2012 were not present at all in 1950. They also found evidence that the rate of change accelerates over time, as there was considerably greater change in composition between 1987 and 2012 than there was between the 1950s and 1987.
Next, Dr. Damschen wanted to understand what was driving the changes in plant species composition beyond the lack of fire. Her team found that between 1950 and 1987, the area of each patch of habitat had little effect on species composition. But by 2012, the rate of plant species extinction within a patch was strongly correlated with patch size; small patch size led to more species disappearing. The same study also found that in patches that were burned more frequently, extinctions were lower and there were more colonizations, or new species moving in. As expected, they found that fires reduced the number of woody and exotic species able to creep in and displace other plants.
Including prescribed burns in the management of fire-dependent ecosystems is increasingly common-but can adding a fire regime salvage all habitats that have suffered in the absence of fire? The short answer to this question is no. Although ecosystems are resilient, there is a threshold that, once crossed, the ecosystem cannot be restored to its pristine state with fire management alone. Sometimes other methods, such as mechanical or chemical treatments, might need to be combined with prescribed fire. This is important for land managers to consider when they work to restore fire-dependent ecosystems.
Not all species are equally likely to persist when conditions in a habitat are less than optimal; slow-growing plants, for example, are often more susceptible to local extinction than those that reproduce quickly. One factor that is particularly important for less persistent species with lower tolerance for stress is habitat connectivity. When habitat patches are more connected, sensitive or rare species are more likely to thrive. On the other hand, the success of generalist species is largely independent of connectivity. The effects of connectivity are amplified for sites managed with prescribed fire, an important reminder that the interaction of factors molding a community can be more significant than any one factor.
Dr. Damschen’s work revolves around the principle that many ecological questions must be addressed at a large scale. One of her projects focused on habitat corridors and was based at the Savannah River site, a large research facility that provides the perfect opportunity to examine landscape-scale questions. There has historically been a lot of debate in the field of ecology surrounding the pros and cons of habitat corridors in human-modified landscapes. Dr. Damschen specifically tackled the issue of the role corridors play in altering wind patterns. Wind is an important disperser, scattering seeds and enabling many species of plants to colonize new areas. Using elaborate models and sophisticated software programs, the team identified considerable changes in wind dynamics within corridors. Connected patches had increased wind dispersal, and the alignment of corridors with the predominant wind direction also had a strong effect. After studying the models, Dr. Damschen and her collaborators released glow-in-the-dark seeds to validate the results in the field. They collected and mapped the seeds and were able to corroborate the conclusions of the computer models – wind dispersal of seeds is improved in habitat corridors.
Dr. Damschen’s work highlights the need to address ecological questions at a large scale, both geographically and temporally. We look forward to her future work tying climate change to these phenomena!