Population Dynamics

Sudden, sharp increases in individual populations of native animals or plants can have serious consequences to the natural communities they and others depend on.

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White-Tailed Deer

White-tailed deer populations have skyrocketed in the eastern United States since the late 1900s due to several factors: suburbanization (which increases favorable edge habitats for deer and concentrates their breeding populations), a decline in hunting, and the lack of non-human predators.

Forests are resilient in providing the living requirements of many animals. But over-browsing by hungry white-tailed deer has multiple effects.

First, over-browsing severely reduces the number and diversity of native plants growing on the forest floor. This diminishes the quality of the natural communities as habitat for creatures that depend on the native groundcover for nesting, foraging, and protection—small mammals, eastern box turtles, and ground-nesting birds, for instance. Many sensitive species of songbirds cannot be found in areas where the understory has been removed by grazing.1

Perhaps even more importantly, as dense populations of deer consume too many woody tree seedlings and saplings, tree regeneration is threatened.2 Deer taste-preferences for certain tree seedlings can actually influence what a forest will look like in the future. Deer seem not to like American beech seedlings, while white oak seedlings seem to be a favorite, with many other oaks a close second. (Chestnut oak seedlings seem to be an exception: deer seem to snub them unless particularly hungry.) Putting them at a second disadvantage, oaks are very slow-growing compared to other tree species, leaving their tender leaves vulnerable to deer browse for several years; thus, many oaks won’t survive to maturity. Of course, many more oak seedlings take root than could ever be sustained in the forest canopy, so it is a natural process for animal browse and other pressures to limit the number of seedlings that make it to maturity. However, too many deer can leave too few young oaks to renew a forest as it ages.

A transition away from oak in a forest that has long been dominated by oak would not only change how the forest looks, it would also impact the animal communities that depend on the acorns they produce, the insects they host, and a myriad of other factors.

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How to deal with severe increases or drops in populations of native animals or plants is a challenge to resource managers. Why is it occurring? What is being impacted? What might happen if humans intervene? What might happen if they don't?

Everything in nature is interdependent, so the consequences of taking (or not taking) action must be carefully weighed. Often it takes months or years of study and sometimes public comment before a park embarks on a "preferred" course of action to intervene. Even then, staff has to be prepared to respond to results that no one could foresee.

Rock Creek Park in Washington, D.C. is taking seriously the importance of thoughtful stewardship of the white-tailed deer population, following an alarming population growth trend around the turn of the 21st century. After many years of study and public input, they embarked in 2013 on a Deer Management Plan for Rock Creek Park, with hopes of more sustainable forests and deer population within several years.3 4

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