William & Mary

High anxiety

Higher than a deer can jump

Higher than a deer can jump:  Mary Seward, a graduate student in biology, can’t reach the top of a deer-proof enclosure seven feet off the forest floor. Seward and other students helped construct a number of deer exclosures in the College Woods.

Deer are eating rare plants in the College Woods, but is there something else going on?

What was once lush is now sparse.

A team of biologists at William & Mary has begun a long-term experiment to determine what is behind the degradation of the College Woods ecosystem.

Harmony Dalgleish, assistant professor of biology, and Martha Case, College Conservator of Botanical Collections, agree that deer are part of the problem in College Woods. But there’s more going on in William & Mary’s 600-acre nature preserve than hungry deer. Many factors may contribute to the recent loss of plant species diversity and general degradation of the understory, but at least part of the problem is heavy deer browsing.

Dalgleish and four other biology professors have set up several experimental patches in the College Woods, each surrounded by deer-proof fencing. The idea is to get a handle on how much blame the deer should shoulder for the loss of plant life and also to gauge how quickly the flora can recover in a deer-free environment.

Remarkable floral diversity

The problem deserves attention. For its size, the College Woods are remarkable for holding a wide variety of plants, including a number that are rare on the Coastal Plain of Virginia. Case explains that the College Woods’s singular habitat began to develop in the Pleistocene epoch, when the climate distribution was more continuous from the mountains to the ocean and the land overall was much cooler. Over the millennia, the land broke into pockets of cooler and warmer habitat. In some warmer places, these cool habitat pockets still exist and maintain more northern and mountainous species. The College Woods is one such place.

Case, who is also an associate professor of biology, said that the variety of topography in the College Woods enables an interesting set of plants to grow and even thrive. To begin with, the College Woods holds several species of oaks and hickories, as well as beech, sour gum, sweet gum and about a dozen other trees. In addition, Case explained that the College Woods holds species such as Actaea pachypoda, an herb also known as doll’s eyes and Cornus alternifolia, alternate-leaf dogwood—plants more commonly found in Virginia mountain ranges. Out of their main range, such plants can be found in niche environments such as found in the College Woods.

The botanists explain that the species of most concern require very specific habitats to thrive. Many plants that were once easy to find in the College Woods have become hard, if not impossible, to locate.

“My graduate student Caitlin Cyrus is looking at plants that were collected in the College Woods 40 and 20 years ago to try and get an idea on what’s going on,” Case said. “She’s had to look a whole lot harder for things than before.”

Remarkable floral diversity
Botanist Harmony Dalgleish leads a crew making deer-resistant enclosures to protect target plots in William & Mary’s College Woods.

Meanwhile, Dalgleish has been heading up the deer-exclosure effort. There are eight patches enclosed by deer fencing around Lake Matoaka. Dalgleish set up the experiment with the aid of students like Mary Seward, who is currently working under Dalgleish as a graduate student. These patches are designed to keep deer out in order to see if their absence makes it possible for various plants to rejuvenate from dormant seeds in the seed bank. Dalgleish does not intend for this to be a short-term experiment. 

“I was very ambitious and I bought the fencing that’s supposed to last twenty years,” Dalgleish said. “I’m hoping that this will be a long term experiment.”

The experiment was supported by the Morton Science Lab Fund, an endowment set up to provide annual support for science faculty who are pursuing “creative and innovative ideas that will enrich and augment science labs.”

There are many benefits to conducting this experiment over a long period of time. Dalgleish explained that deer have heavily browsed the College Woods for several years and the damage to the vegetation is extensive. Even if the deer were removed, these patches may take several years to start showing signs of rejuvenation.

“The browse pressure is just really heavy so it may take a long time to get vegetation back,” Dalgleish said.

 There are fifteen species of orchids that are known to exist in the College Woods. According to Case, these plants take a decade or more to reach maturity and are incredibly picky about where they grow; many will not even survive in gardens for long.

Other scientists also have the benefit of adding on additional side experiments. The more data that is collected over time, the more likely it is that other variables can be tested. Dalgleish explained that light is a large factor in the College Woods. Plants need light to grow, but several areas of the College Woods have a very well developed canopy, which makes it difficult for light to reach the forest floor. Smaller seedlings are unable to grow in this environment.

The ability to test multiple variables at once would not be possible with a shorter experiment. A long-term experiment will allow Dalgleish and her students to see the influence of other factors on the decline of the College Woods vegetation.

“If five years has passed and vegetation is still not growing in the deer-fence patches, that is strong evidence that other factors are at play, such as light and we can begin to test for that,” Dalgleish explained.

Deer in the frame

However, Dalgleish and Case both have strong evidence to suggest that the deer are the primary cause. They point out that deer are eating holly and beech, neither of which deer prefer. Dalgleish explained that the deer have browsed the forest floor to the extent that they have started to run out of resources. The deer are smaller, scrawnier and malnourished.

“This isn’t good for the forest, but it isn’t good for the deer either,” said Dalgleish.

The problem is not simply that the deer are eating too many plants, but that the plants are growing back smaller and smaller each year. The deer are eating the plants so quickly that they are unable to store enough regenerative material to grow back to their original height the next year.

There are multiple pressures that have caused the deer populations to skyrocket. According to Case, humans have greatly depleted their habitats, forcing larger numbers to congregate in smaller areas with fewer resources.

“We haven’t just doubled the deer populations, we have increased the deer herds by 10 fold or more” Case said.

Since deer can eat ninety percent of the species that exist on the College Woods floor, over-browsing will have drastic consequences on the forest dynamics. The botanists point out that not only will plants be pushed to elimination in these areas, but other organisms that rely on these plants for survival will also die out. Birds, butterflies, beetles, and various other insects use these plants as integral parts of their lifecycle, and the elimination of their existence has potential to be very detrimental.

“We really are on the cusp of complete extinction of many different species in the College Woods,” Case said. “There is the possibility that the entire structure of the woods will change and we will lose everything that happens to be dependent on that primary diversity. Humans are now altering the landscape at such a rapid pace that there is no evolutionary history known that can compensate for this kind of rapid destruction.”

Dalgleish is hoping that this experiment will help become an outreach with the community. Now more than ever, the deer population is a human problem. Case explained that as humans replaced cougars, coyotes and wolves as the top predators, so it is now a human responsibility to control the deer. The scientists understand that deer culling is a hard sell.

“A large part of people’s reservation with killing deer is social, there is sort of a feeling that we need to protect the deer,” Dalgleish said. “No one wants to kill Bambi.”

Case also thinks that human involvement is essential. “I think it’s very safe to say the preservation of the forest isn’t going to happen without human intervention. We can’t just put a fence around it and say to nature: ‘Ok you’re on your own’ because we have too much influence on too many areas.”

Throwing a fence around all of the College Woods is not feasible. It’s also counterproductive, the scientists say: The woods need to be grazed to some extent, otherwise, the canopy would grow far too dense and no light would reach the forest floor, completely eliminating the understory.

 In the case of the College Woods, along with many areas along the Eastern coast, a happy medium must be reached with the deer populations in order to maintain stability and prevent the collapse of ecosystems.