The Impact of Large Deer Populations on Local Woodland Ecosystems

Adrian Fisher lays out the complex and many-layered ways in which an over-abundance of white-tailed deer can alter local ecosystems beyond recognition and potentially beyond recovery. It is a worthy, science-based read.

I first realized this in a direct, experiential way while birding at a large, protected woodland habitat in Central Illinois. Like the local Des Plaines River Forest Preserve tracts, these woods ran along a relatively wild river, encompassing both bottomland and some upland forest habitats, together with patches of open prairie here and there.

What amazed me was how quickly and easily I encountered species I had never seen or heard in the Des Plaines River or nearby preserves: A mourning cloak butterfly. A weevil. An ebony jewelwing dragonfly. Abundant Culver’s root, Starry Campion, Canadian anemone and Jewel weed covering the forest floor. More indigo buntings than I could keep track of and, to top it all off, the daytime call of a barred owl. It was, simply enough, a richer natural environment.

Perhaps most significantly, I observed only one white tailed deer.

The tract, along the Mackinaw River, is actively managed by a dedicated staff and volunteers, through the removal of invasive underbrush and controlled burns. Significantly, the land mangers also allow seasonal deer hunting, once a year in the fall. The resulting diversity and abundance of woodland forbs in the understory was in striking contrast to most Cook County woods, where it is rare to find a healthy stand of spring ephemerals or almost any woodlands flowers not browsed to the ground. They are ideal forage for deer, and stand little chance when the latter become too numerous.

Neither do oak saplings, the mainstay of our local forests, and without which the forest as we know it cannot reproduce itself, transforming instead into something that can no longer support the many organisms that depend on oak trees for food and shelter. Fisher concludes:

What does recovery of woodlands take? Clearly, if at all possible, deer should be managed before tipping points are reached, because at that point recovery to anything resembling the prior state might actually be impossible, or only achievable with intensive human intervention. The basic prescription requires a reduced deer population for an extended period of time, coupled with replanting, reseeding, and control of non-native invasive plants. Yet, since ecological restoration can only arc with time’s arrow towards new states of dynamic equilibrium, there is no going back to what once was. The ecosystem will become, inevitably, something different from what it would have been had deer been kept at appropriate levels all along. In addition, global warming and climate disruption are already warping the patterns of relationships in local ecosystems, so it is difficult to accurately predict how our woodlands will behave in even the near future. Yet all climate change mitigation schemes rely on the existence of healthy natural areas. With careful, attentive management and care, a given landscape can recover a great deal of biodiversity, though composition and complexity will change as conditions change. So much depends on what we do, right here, right now.

Read the whole thing:

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