Blue Ridge Naturalist: Tallamy’s Oak

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Planting an oak to support caterpillars that feed birds is useless when ubiquitous and overly bright nighttime lighting keeps so many moths (such as this Luna Moth) from mating. (Note the numerous dead insects at the bottom of this light fixture that burned for days when the absent owner forgot it was on.) Photo: Marlene A. Condon.

Seed catalogs are arriving in the mail now, exciting gardeners with visions of the beauty they can enjoy during the upcoming growing season. Whether you are planning your next garden makeover or your first garden ever, I hope you are giving the natural world due consideration.

When you create a nature-friendly garden, your reward is extra beauty and excitement from the numerous kinds of critters that will visit or make your yard home. You can feel proud that you are providing desperately needed wildlife habitat.

If you are interested in helping wildlife, you may have heard and taken to heart Doug Tallamy’s advice to plant an oak tree. This University of Delaware ecology professor has been working hard to encourage folks all across the land to plant one.

Unfortunately, his message has been lost in translation as garden columnists and bloggers tend to misinterpret the advice and spread misinformation to the public. They often tell readers that planting an oak will provide food for over 500 species of Lepidoptera (moth and butterfly) caterpillars, which will provide an abundance of food for a chickadee (a cute bird anyone would want to assist) and its chicks.

However, a single oak tree is not going to live up to that expectation. Professor Tallamy is referring to the entire genus of oaks, comprising about 60 species of these trees in the United States. Your lonesome oak is only going to support a fraction of the species total promoted by the professor.

Should you still heed this ecologist’s advice? In many cases, the answer would be no, even if one tree did indeed host that many species of caterpillars.

If you own a small yard, it is never wise to plant a tree that is going to attain great height and breadth. As the tree grows ever bigger, its expanding area of shade will severely limit your ability to grow a variety of plants on your property that would create a thriving habitat. One tree does not a habitat make.

If you own a large property that can easily include one or more oaks without shading most of your land, is planting an oak tree the best thing you can do to bring nature home? Again, the answer is no.

Although Sudden Oak Decline (brought on by stressors, such as severe drought or ill-timed frost) has been occurring in the United States, we still have plenty of these trees in our area to feed the moth larvae and the few species of butterfly larvae that need them for sustenance. (You can verify this fact by visiting a forest near you.)

The real problem is not a dearth of oaks, but rather an overabundance of lights. They burn at night inside and outside of buildings (including homes), in parking lots, along roadways and walkways, and in many public parks. These lights attract moths (that comprise the majority of the 500-plus species mentioned by Professor Tallamy) that do not then fulfill their destiny of mating and producing the next generation.

Artificial lighting has been disastrous for these insects, which are such a hugely vital component of a properly functioning ecosystem throughout the various stages of their life cycles. As light pollution has increased, moth populations have plummeted.

Moths are practically nonexistent nowadays compared to when I was a child. When you have a dearth of moths, you have a dearth of caterpillars for those chickadees—no matter how many oak trees you plant.

Furthermore, in most people’s yards, Professor Tallamy’s oak becomes, essentially, nothing more than an invitation to reproductive failure for many kinds of moths and butterflies. Although some lepidopteran species manage to escape the effect of our artificial lighting to mate successfully, they leave behind offspring that overwinter underneath leaf litter that many people habitually remove.

When people take away the protection afforded by the fallen oak leaves, these caterpillars and pupae do not make it to spring when they would have transformed into adults. So again, when fewer adult insects exist to mate, fewer caterpillars will exist to feed those chickadees—no matter how many oak trees you plant.

If, as a society, we are to increase caterpillar numbers for the benefit of our birds (and other critters), we must alter many of our life practices. To accomplish this goal, you must recognize what is truly important in life (maintaining the health of the environment) and what is not (removing leaves from underneath trees and excessive artificial lighting).

If your yard is large enough and you can keep the leaf cover where it belongs, you might want to plant an oak tree as part of a multidimensional nature-friendly garden. However, living in agreement with nature is not quite as simple as Professor Tallamy suggests.

Please do not let yourself be fooled into believing that all it takes to make a significant difference in the numbers of moth and butterfly caterpillars is to plant an acorn.

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