Excessive Deer Populations Inhibiting Native Forest Plant Survival

An overabundance of deer in US forests are preventing a natural resurgence of native plant life, according to a new study.

Deer, which now have a US population density as much as 10 times higher than before European settlement in North America, are fond of eating these native plants, while eschewing the non-native garlic mustard plants.

Walking through many US forests today will reveal an abundance of garlic mustard plants, which deer do not eat, and significantly fewer native plants.

Researchers from the University of Pittsburgh wanted to see if there was a way for native forest plant populations to rebound, so they sectioned off multiple plots of land in the Trillium Trail Nature Reserve in Fox Chapel, Pa. These fenced-off plots, measuring nearly 200 square meters and established in 2003, were monitored over more than a decade. As deer were not able to breech the fences, the researchers were able to observe how the plant life reacted without the threat of being eaten by deer.

They observed that over time, native plants, such as trillium, would increase and the garlic mustard plant population would decline, trending towards zero.

In parts of the forest where deer could graze freely, garlic mustard was the dominant plant.

"When people walk in the woods where deer are overabundant, they don't realize what's missing," said research leader Susan Kalisz, a professor of evolutionary ecology at University of Pittsburgh. "They don't know what used to be growing there. They don't know that species are being lost and replaced by invaders."

Kalisz said that the overabundance of garlic mustard in the forests is a direct correlation with the overabundance of deer.

She contends that the effect is reversible through deer exclusion methods, but that the solution is not as simple as it seems. Deer management techniques differ from state to state, with some communities preferring to keep local deer populations high to appeal to hunters.

Kalisz and her collaborators published their study in the Proceedings of the National Academy of Sciences.