Vanessa Fox is a forest community ecologist. She has conducted research on songbirds, white-tailed deer, leaf litter decomposition, and vegetation in the DePauw Nature Park. Her research often has important conservation implications.
Where has all the leaf litter gone?
In 2004, Prof. Fox and her students noticed that there was very little leaf litter on the ground in the forests of the DePauw Nature Park. In 2006, Chad Byers '08, Charlotte Buehler '08, and Summer Drake '08 designed an experiment to investigate decomposition rates of leaf litter. Prof. Fox and her students found that the leaf litter decomposed very rapidly, in part because the leaves are highly palatable, with low tannin content, and in part because of super-abundant earthworm populations. The relative absence of leaf litter in the DePauw Nature Park was correlated with the absence of Ovenbirds in the park, a forest songbird that nests on the ground and constructs its nests out of leaf litter. The results of this research were published in 2010 in the journal Forest Ecology and Management (click here for pdf).
Are there too many deer in the Nature Park?
In 2006, the Nature Park Steering Committee discussed the issue of white-tailed deer in the Nature Park. Hunting is not permitted in the park, but hunting was permitted up until 2003 when the park was first established. Members of the steering committee expressed concern that the deer population would increase, given the absence of hunting pressure, and that the deer would overbrowse the vegetation, causing permanent damage to the forest structure and health. This type of pattern has been well documented in Indiana state parks. The solution in the state parks has been to open a limited deer hunting season to reduce the deer populations. The steering committee was interested in whether we should adopt this type of a strategy for the Nature Park.
The question arising from this research was “are there too many deer in the DePauw Nature Park?” With the help of Dana Dudle, her students in Conservation Biology, and Brien Holsapple, Prof. Fox and her students established eight permanent deer exclosures, each 5 × 5 meters in size, and eight adjacent control areas, also 5 × 5 meters in size in forests at the Nature Park. Prof. Fox and her students collected data on vegetation in the exclosures and control areas during spring and fall for four consecutive years, from 2008 to 2011. Analysis of the patterns showed that there were no differences in the vegetation between the exclosures and control areas. In other words, there were no effects of deer on the vegetation.
In addition to looking at potential changes in vegetation, Prof. Fox was also interested in estimating the size of the deer population in the Nature Park. She conducted surveys using infrared motion-sensitive cameras. Cameras were installed at various remote locations in the forests at the Nature Park and took hundreds of photographs over multiple years. Her results indicated that the deer population in the Nature Park is approximately four times higher than the park’s estimated carrying capacity. She consulted with wildlife biologists from the Indiana Department of Natural Resources about how to proceed. The DNR biologists recommended placing a greater emphasis on the vegetation data than on the deer population estimates. In other words, even if there are too many deer in the park, DePauw shouldn’t take action unless the deer are having negative effects on the vegetation. Prof. Fox and her students speculated that the effects of deer on vegetation in the park are mitigated by the landscape conditions surrounding the park. The park is surrounded mostly by agricultural fields. Deer may be feeding in adjacent agricultural fields and seeking shelter in the Nature Park, thus minimizing effects on vegetation within the park itself.
Prof. Fox wrote up the results of this research with three student co-authors, Kristen Frederick ’12, Emily Meadows ’12, and Ryan Kelly ‘12. This manuscript will be published in January 2014 in Natural Areas Journal.
How do undisturbed forests change over time?
Prof. Fox initiated a new research project in 2008. The goal of this project is to study the dynamics of forest structure and composition. She came up with the idea from reading about research published by Stephen Hubbell, an ecologist at UCLA, senior staff scientist at the Smithsonian Institution, and the author of The unified neutral theory of biodiversity and biogeography. In 1980, Hubbell initiated a project to investigate the long-term forest vegetation dynamics on Barro Colorado Island in Panama. Hubbell and his colleagues and students identified, measured, tagged, and mapped the location of all individual trees ≥ 1 cm in diameter in a 50-hectare tropical forest. Hubbell and his team have since revisited the site at least once every 5 years to document changes in the vegetation. This work became the foundation for the establishment of similar studies throughout the world, all using the same measurement protocols.
When Prof. Fox read about this approach, she thought why not try this in the DePauw Nature Park? There are several relatively large and undisturbed patches of forest within the park where this type of study could be conducted. She decided to establish two separate plots. Over a 4 year period, Prof. Fox and her students identified, measured, tagged, and mapped the location of all individual trees and vines ≥ 1 cm in diameter in approximately 2.6 hectares of forest. They have accumulated a data set on over 4,400 trees and over 1,400 vines. This year (in 2013), Prof. Fox and her students have returned to the plots to document the changes in vegetation. They are checking and re-measuring each individual tree and vine and documenting recruitment of new trees into the communities.
Do vines prefer trees based on phenology of leaf production?
One question that has arisen directly from this project is regarding the relationship between trees and vines. Prof. Fox's observations have shown that vines, specifically Virginia creeper and grape, grow more frequently on some tree species than others. Scott Meyer ’12, Danny Wetli ’12, and Prof. Fox spent a summer trying to figure out why this pattern occurred. After extensive reading of the literature, Prof. Fox came across the idea that vines grow more frequently in areas with more sunlight, i.e., along forest edges and in younger forests. She speculated that vines choose trees based on the phenological development of leaves during the spring. Walnut trees, for example, produce leaves later in the spring than sugar maple trees. Indeed, we found that vines grow more frequently on walnut trees than sugar maple trees, perhaps because of the higher light availability in the vicinity of these trees during early spring.