Deer Exclosure Creates Plant Life

If you are walking down the Yellow Trail near Big Pond you might have noticed a fenced rectangular structure 8-feet high about 100-feet off the trail in the woods. An informational sign marks the spot on the trail. The exclosure was constructed by volunteers with donated materials in 2007. This exclosure is designed to keep deer out so that any resulting changes in forest vegetation can be documented.

Throughout our region deer exist today at a much higher population than they did pre-settlement. This is the case whether you are located in a place where hunting occurs. Due to overpopulation deer have changed our forests. Because deer are everywhere, what we think of as a “normal” forest is actually one that has had all of the palatable understory species selectively removed. The remaining dominant plants are species that are unpalatable to deer.

To understand what our pre-settlement forests may have looked like, deer exclosures allow plants to grow without the presence of deer. In the exclosures plants are protected from deer, but the large mesh of the fence allows egress by pretty much all of the other animal species present in our forests and, of course, seeds and pollen can enter freely also. Inside the exclosure seedlings can grow, leaves can expand, stems can lengthen, and flowers and fruits can develop without getting nipped by the relentlessly hungry deer. This summer, if you look inside the deer exclosure you will see that the herbs and shrubs are taller, denser and support more flowers and fruits than those outside of the exclosure.

However, you might ask, “What about the species that have disappeared because the deer ate them all?” Although many species are difficult to find in our forests today, some of these species have persisted underground as seeds. Viable seeds that persist in the soil are collectively called the seedbank, which may remain viable for many years. If provided with the appropriate conditions, these seeds will germinate and, if located inside a deer exclosure, the seedlings may survive and grow. For this reason, you may see species inside the exclosure that do not occur outside of the exclosure.

So what has happened since the deer exclosure was built in 2007? We established four 1-square-meter study plots inside the exclosure and another four 1-square-meter study plots nearby but outside of the exclosure.

Each year we record the percent cover, density and height of each plant species in each of the plots. In 2008, an average of 53 percent of the study plots outside of the exclosure supported vegetation, but this had decreased to 45 percent by 2012. In 2008 this “outside” vegetation was composed of 28 species across all four plots, and this was unchanged in 2012, but three of the species had disappeared and three new species had appeared.

On average, plants were about 1 inch taller in 2012, as a result of increased height by ferns and several shrub species. Lastly, the number of individual plants in the “outside” plots increased slightly.

Now let’s compare this with the changes that occurred in study plots inside the exclosure. In 2008 the “inside” plots had 30 species, and by 2012 this had increased to 38 species with the loss of one species and the gain of nine new species.

In 2008 the “inside” plots were on average 56 percent covered with vegetation, and by 2012 this had increased to 76 percent. The plants had on average increased in height by more than 2 inches, however, the number of individual plants in a plot increased only slightly.

Thus, plants in plots inside the exclosure were wider and taller, and there were quite a few new species, but there were not more individual plants than in 2008. New species included sarsaparilla (Aralia nudicaulis) which was also new outside of the exclosure, wintergreen (Gaultheria procumbens), fly honeysuckle (Diervillia lonicera), and several grasses and sedges.

Tree seedlings were also more common inside the deer exclosure. About 80 percent of the plant species that were flowering and fruiting from 2008 to 2012 occurred inside the deer exclosure. The presence of non-native species was negligible both inside and outside the exclosure.

You can see that the deer exclosure provides a good snapshot and pilot study of the dramatic effects of deer upon our native forest vegetation. It is likely that our forests are very different than they used to be. In the absence of deer the vegetation became more diverse, occupied more of the forest floor, and flowered and fruited more often. However, it is possible that the particular location of the deer exclosure is unusual, and this would have happened with or without the fence. For this reason, the construction of multiple deer exclosures in differing habitats would better enable us to speculate with certainty how deer are changing our forests.

Jonathan and Priscilla Titus are professors at SUNY Fredonia. They and their students have been using the deer exclosure at Audubon as a resource during their classes. Plans are drawn for more exclosures on the property. Audubon is located at 1600 Riverside Road, just off Route 62 between Warren and Jamestown. The trails are open from dawn to dusk, and the center is open from 10 a.m. until 4:30 p.m. daily. Information can be had by calling 569-2345 or visiting jamestownaudubon.org.