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Managing the effects of forests on the diversity of wildlife

For many forest landowners in northern Michigan, wildlife habitat management ranks as a primary ownership goal.

While white-tailed deer, black bear, ruffed grouse, American woodcock, and other game species are usually of primary interest, the majority of vertebrate wildlife species in our forests are non-game species.

In fact, most of our forest wildlife are secretive, cryptic, and/or migratory, spending only the breeding season in northern Michigan. To introduce the reader to some of those species and how specific forest structures provide wildlife habitat, below I will describe a hypothetical forest wildlife community inhabiting a hypothetical 40-acre forest property during late spring.

Our imaginary forested property has 30 acres of northern hardwoods and 10 acres of lowland conifers. The property has both mature trees (40 feet tall or more and 40-100 years old) and immature trees (seedlings and saplings less than 20 feet tall).

The northern hardwood forest is comprised of big-tooth aspen, red maple, and sugar maple, with a few scattered large eastern white pine and red oak trees. It once had eastern hemlock and white spruce, but those species were removed decades ago and are no longer represented. White ash was also part of this forest, but non-native, invasive emerald ash borer killed all the trees. The lowland conifers include black spruce, balsam fir, tamarack, and northern white-cedar.

The first wildlife species encountered on our property is the gray treefrog. Because our property has “vernal ponds” (seasonally wet spots that dry out come summer in the northern hardwoods) and some standing water in the lowland conifers, a number of different species of amphibians exist on the property.

Our gray treefrog is one of the more cryptic. We hear it, but don’t see it. The color of its skin blends in perfectly as it sits on a limb of a red maple on the edge of the northern hardwood patch. Only the trained ear can discern the odd song of the species from other sounds in our forest. The male’s odd song will attract a female that will lay eggs in our vernal ponds and other standing water.

The next wildlife species we encounter on our property is a strikingly colored, and consistently vocal, male American redstart.

The small, migratory songbird is one of the more common forest bird species in the eastern U.S., and males are dramatically colored, with orange, black, and white.

Our male is defending a breeding territory in a one-acre patch in our northern hardwood forest, spending most of its time in young maple saplings less than an inch in diameter.

Its mate, yellow-brown and secretive, is sitting on three eggs in a small nest in a sapling sugar maple only six feet off the ground. When the young hatch, they will be fed protein-rich insects collected by both parents. Because of the water and the cover in the adjacent lowland conifers, there are lots of insects in our forest, and the young grow quickly. Come August, they all will migrate to the Caribbean.

Our final two wildlife species are using one tree, just different parts of it.

A large big-tooth aspen has formed a perfect crown into which a great-horned owl pair nested the previous February.

Now, the two chicks are nearly full grown and are out of the nest, looking for small mammals as prey. Because the aspen is over 100 years old, decay has started to cause some of its limbs to break off and fall to the forest floor.

Here, the fallen limbs provide cover for an array of plant, fungi, and animal species, including the pygmy shrew that hides from the owl.

The shrew is a member of the second-smallest species of mammal in the world, and is most active at night. Because of its high metabolism, it eats continuously and is now searching for insects and other invertebrates that are using the fallen limb, as well.

All told, our 40-acre property provides conditions for many more wildlife species than space allows us to mention here.

While game management can provide habitat for some non-game species, forest wildlife diversity is usually a result of complexity provided by “composition” (the mix of tree species) and “structure” (the vertical and horizontal arrangement of live and dead trees) specific to a given forest site.

Composition and structure for the present and the future can be a focus of forest planning and management.

And, if identified as a landownership goal, forest planning that takes into account natural models of how forests form and function can provide a blueprint for maintaining forest wildlife diversity.

Greg Corace is the forester for the Alpena-Montmorency Conservation District. For more information, including sources used in this article, contact him at greg.corace@macd.org or 989-356-3596, ext. 102.

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