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Cavity Trees

Bayou-Diversity (10 February 2019) The title of this short essay could be “Holey Trees.” It is not about the spiritual aspects of a forest (i.e. “Holy Trees”) but rather the presence or absence of cavity trees in a forest. In the realm of commercial forestry, trees with holes are undesirable. They take up space where more valuable, sound trees can grow. For that reason cavity trees have been all but eliminated on millions of acres. It’s that money thing.

But in southern woodlands, trees with cavities once occurred naturally at varying frequency across the landscape. Cavities form when trees are injured or diseased; animals, especially woodpeckers, excavate holes in living and dead trees. As vital components of a forest, cavity trees provide nesting, roosting, and denning habitat for many types of wildlife. At least 85 species of birds in North America are dependent on cavities. In this region many of our most popular birds nest in cavities including the eastern bluebird, Carolina wren, Carolina chickadee, tufted titmouse, prothonotary warbler, tree swallow, purple martin, and wood duck. Most owls in the U.S. nest in cavities. These species are secondary cavity nesters in that they don’t excavate their own holes but rather use those made by woodpeckers or other natural causes such as decay. It is ironic that many of these species, whose populations decline when cavity trees are removed, are also insectivorous and play an important role in controlling forest insect pests.

Local mammals are also dependent on tree cavities. Squirrels, opossums, raccoons, skunks, mink, and gray foxes den in tree hollows. Research on area wildlife refuges has revealed Rafinesque's big-eared bats, which also help control harmful insect populations, prefer to roost in hollow water tupelo trees. Large, hollow cypress trees have been identified as important denning and birthing sites for Louisiana black bears.

Even though appropriate man-made nest boxes designed for particular species can be beneficial on a small scale, the obvious answer to this conservation dilemma is to promote and preserve naturally occurring cavity trees. Research indicates 2 to 3 such trees per acre can enhance biodiversity and foster healthy forests. Holey trees are not without value.


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