Beautiful, majestic, and dangerously overabundant, white-tailed deer (Odocoileus virginanus) have been an integral component of Ohio and the Eastern Deciduous Forest since the end of the Ice Age. For much of that time, their population was healthy and stable – Ohio’s forests provided plentiful food and cover, and large predators such as the wolf and cougar kept the deer numbers in check. Indigenous tribes hunted deer for food, tools, and trade, but it was not until widespread European settlement began in the late 1700s that the deer population began to dramatically change. Unrestricted hunting in the 1800s, along with a human population increase caused the deer population to plummet. By the early 1900s they were nearly extirpated from Ohio. Through a restocking effort, and the creation and enforcement of wildlife laws, their population climbed over the 1900s. In 1937, deer were found in just 28 Ohio counties; by 1956, they had expanded to occupy all Ohio counties. Statewide, their current fall population is approximately 725,000.
Today, white-tailed deer have a strong influence on the Glen Helen ecosystem. These grazers can eat over 7 pounds of foliage a day! As such, their presence on the landscape influences the distribution and abundance of herbaceous and woody plant species. Also, deer can rapidly reproduce, and in their role as ‘keystone’ herbivores, are able to restructure entire ecological communities. They are changing what plant species will be in Glen Helen in the future, and negatively impacting the biodiversity of the preserve.
Before European settlement, dry upland areas in Glen Helen were dominated by oaks and hickories. This is evidenced by relic 300-year old white oaks which can still be found in the tree canopy between the Yellow Spring and the Birch Creek Cascades. However, it is hard not to notice the replacements for these trees are not oaks or hickories. Baby white oaks are very desirable to deer, so you may see that lots of our young trees are forked or have multiple stems from being browsed, but you will rarely find a 2-year-old white oak.
Newly sprouted baby oak leaves are bright pink when they first emerge in the spring. This gives us the opportunity to find them, and when we do, we put up a cage to protect them from deer browse. You may have seen these cages in the north Glen. We currently have over 80 oaks caged, and we hope that some of these saplings will live as long as their parents. We have to be quick with the cages though! Last spring I found a baby oak, cherry, and maple all within a few feet of each other. I placed a makeshift marker of honeysuckle so that I could return to the location with fence and post materials. But when I returned, I found only the cherry and maple; the oak had been eaten by a deer. This differential palatability is shifting the tree community of Glen Helen – within our lifetime. Through this deer-enforced selection, our forest is changing toward a maple-dominated canopy. An unnatural shift like this creates a less resilient ecosystem through a reduction of biodiversity.
Before European settlement of Ohio, it’s estimated that white-tailed deer had population density of about eight per square mile. Considering that Glen Helen is approximately 1.7 square miles, the preserve might have supported around 14 deer. Recent studies have shown that at a population density of 10 per square mile, deer suppress herbaceous plants. At 16 per square mile, they suppress woody plant regeneration.
But how many deer do we have now? Until recently, we had no idea, but were confident that the preserve held more than the pre-settlement estimates. How many have you seen on a short walk in the Glen? Or along Corry Street?
In March 2018 we set out to get a population estimate of the deer in Glen Helen. We used a fixed wing unmanned aerial aircraft equipped with an infrared thermal camera to provide a “snapshot” of the population of a given day. We started flying on a frosty morning with hopes that we would have lots of contrast between the cold ground and the warm deer. The day-long survey accounted for 194 deer within the bounds of Glen Helen Nature Preserve.
This actually turns out to be a very conservative estimate, because tree cover and the topography of the Glen made it more difficult to identify deer compared to in an open field. Plus, an equipment malfunction cut our flight short by about 100 acres. Also, we surveyed the south Glen later in the day, when the temperature had warmed and the deer were harder to spot with thermal imaging. If we extrapolate the number of deer counted in the north across the entire property, we may actually have closer to 400 white-tails in the preserve.
Even with the low-end estimate, we can see that the population level is way, way out of equilibrium, with 194 deer compared to the 14 that may have been present on this landscape during pre-settlement conditions. How can the land support so many? In short, it can’t. In most cases, it appears that the deer are healthy (although that may be changing too). However, plants suffer to support this population. More deer equals fewer plants, more and more deer equals fewer and fewer and fewer plants. Fewer and less diverse plants, in turn, mean a drop in diversity and abundance of pollinators, of birds – and in the overall health of the ecosystem. I often wonder what amazing scenes of wildflowers and regenerating trees we would have if we had just half the deer population we have now. And, when we think about the health of our forest, we need to remember that young trees are as important as the big ones – they will carry the forest into the next generations.
As managers charged with the stewardship and protection of this natural space it is tough to watch the health and future of the Glen be eaten right in front of our eyes. We are not the only ones who are being touched by the damaging nature of our overpopulated White-tailed deer. In 2018, Ohio drivers had a 1 in 134 chance of having a deer collision, and the national average of cost per claim was over $4,300. Gardeners and landscapers in urban and rural areas know too well the trials and tribulations deer can cause their prized plants.
What to do about overpopulated deer in Glen Helen is one prong of a suit of problems stewards face when trying to safeguard the land and set the slate for the ecosystem to find a balance. Other considerations -- which all play and interact with each other – are invasive species occupying ecological niches and reducing biodiversity, the lack of a natural fire regime, the lack of top predators, and, humans creating disturbance through the creation of rogue trails. Balance and equilibrium are words I like to use when speaking about ecosystems and natural processes, as I have tried to illustrate with this article, a major component of our shared ecosystem is way out of balance.
-Ben Silliman, Glen Helen Land Manager