This spring, Callie Oldfield (Biodiversity Fellow C’15) and I initiated a long-term wildflower study in Dick Cove as part of a Conservation Biology group project. The goal was to determine whether excluding Sewanee’s hordes of white-tailed deer (Odocoileus virginianus) from certain areas of the forest would allow wildflowers, which were once richly abundant in the cove but have recently been munched into oblivion, to regenerate. In February of 2013 we set up five exclosures made of nylon fencing, two on either side of the cove and one in the cove bottom, and then, since the wildflowers were in no rush, we waited. It’s hard to predict how long this wait will be, or if the wildflowers will come back at all. Most are rhizomatous plants, so they can survive a certain amount of herbivory as long as there are sufficient nutrients stored in their root structures, but the Dick Cove plants have experienced a dangerous level of browse. The plants within our fences may take decades to return to their full glory, and even then they will face the struggles of a changing forest and a changing climate. However, we have hope for these little herbaceous plants; their delicate, ephemeral blossoms fail to represent the hardiness that is present in their persistent root structures.
Our fencing experiment was focused mainly on wildflowers, yet we knew that excluding deer from certain areas would also benefit the trees. Though wildflowers are a favorite treat, a hungry deer will munch on almost anything it can reach, including tree seedlings and saplings. This continued herbivory on trees’ early life stages causes an imbalance in the population; if no saplings are allowed to mature, the forest’s natural regeneration processes cannot take place. By excluding deer, we allow saplings to retain leaves, photosynthesize, and grow.
Last Thursday Callie and I returned to Dick Cove with Conservation Biology professor Dr. Jon Evans to check up on our exclosures. While yanking out some Japanese spireae (an invasive that is slowly creeping its way into the coves) along the trail, we discussed the changes that have taken place in the forest since spring. The most noticeable of these, besides the many happy blooms and busy insects, was the intense shade created by the lush summer canopy. Here and there bright patches of sunlight blazed in where a big tree had fallen, but most of the forest floor was deprived of direct sun by the greedily photosynthesizing giants above. This greenish shade is quite pleasant for the passing hiker, yet it poses another concern for our understory forest friends. The wildflowers get a jump-start on spring growth, shooting up from their wintry roots as soon as the weather is warm enough and then finishing up their main food production for the year just as the trees begin to leaf out. Saplings, on the other hand, arrive in the middle of the game and must compete for precious light with their huge parents. As we approached our first exclosure, we couldn’t help but notice the puny amount of light that permeated through the canopy, not to mention the almost complete absence of young trees. The wildflowers there might do just fine, safe from hungry vertebrates, but fencing alone may not be enough to help the saplings.
Crossing the streambed to the other side of the cove, we came upon two more exclosures (and their respective un-fenced control plots). Nearby a huge oak lay fallen, letting sunlight pour into an open space roughly the size of one of our plots. A miniature grove of tulip poplar saplings was basking in the photons, surrounded by many ankle-high chestnut oaks. What a nice sight! These had yet to be gobbled up by deer and were taking full advantage of this breach in the canopy, just as saplings are expected to do. With the future of these little hopefuls in mind, we tentatively decided on an addition to the original Dick Cove project: fencing in some of the natural light gaps in the forest to protect the regenerating trees from being browsed in their most vulnerable state. Manipulating the forest in this way may seem unfair to the white-tails, but many such decisions must be made in order to rectify the ecosystem’s natural balances, particularly in this age where it is not mountain-lions and forest fire, but humans, who have hold of the land. Protecting Dick Cove’s flora will not only require management of the deer populations (I personally would not mind seeing local venison featured in the University dining hall), but also careful consideration of the many other factors, like light availability, that play a role in the forest’s ecology.