Photo: American Sycamore trees, Margaret Fisher
American Sycamore trees, “Ghosts of the Woods,” Margaret Fisher
In the winter, as you drive across the American Legion Bridge or across many of our creeks, you may be startled to see large numbers of trees with bright white trunks and branches. You may worry that climate change has struck and left them bleached. Worry no more: those are American Sycamore trees, sometimes known as the Ghosts of the Woods, whose bark normally peels as the trees get taller, leaving a white and brown pattern that shows best once the leaves have fallen. These congregations of sycamores help us notice that our seventy or so locally native tree species are not randomly distributed throughout the woods but rather are living in natural plant communities. As our region ramps up the Plant NOVA Trees campaign, understanding natural communities can help us design our landscaped environments to better support our local ecosystem.
Sycamores and other trees that live in wet soil can survive there because their roots can tolerate low oxygen conditions. They don't necessarily need a lot of water and can thrive in the low oxygen conditions of many of our dry, compacted lawns. Unlike non-natives, these native trees will provide food for vast numbers of caterpillars and thus for the birds and other critters that eat insects. The contributions of native trees to the food web, combined with the increasing numbers of beautiful species available for sale, are why they are the default choice in all but the harshest of our built environments. Planting any native tree is a very good way to contribute to our region’s effort to expand the tree canopy.
Having said that, though, is it possible for us to do even better by taking plant communities into account? Again, trees are not randomly distributed in the woods, and neither are the birds and other critters that depend on combinations of specific plants. It is not within our power to fully restore the ecosystems which we have destroyed, but we might at least nudge them in the right direction by grouping plant species that would naturally live together on the terrain we have occupied.
If your yard has wet or compacted soil, an American Sycamore could be a great choice. But what if you live on a dry hillside and your soil is not compacted? In that case, you might prefer to choose trees and accompanying understory plants that are more representative of a hillside natural community. For example, Mockernut Hickory, Flowering Dogwood and Maple-leafed Viburnum underplanted with Virginia Creeper and Blue-Stemmed Goldenrod would give you the start of an Acidic Oak-Hickory Forest, a very common plant community around here.
Woodland plant community, Arlington Public Library
Dozens of plant communities have been identified in Northern Virginia, but only a few of them are very common. How can you tell which is most appropriate for your property? This is no easy task, even for experts, not only because it is highly technical but because humans have altered the landscape in many places beyond recognition. However, you might be able to make a reasonable guess based on the elevation of your yard in relation to the nearest creek. You can then look at a plant list for the relevant community and decide which ones you might like to add to your property, given its current light, soil and moisture conditions. Just as in nature, as your trees grow and shade out the understory, sun loving plants will give way to shade tolerant ones, providing future residents with a haven from the heat, far more useful than a sun-scorched lawn in this warming world.
Details about the plant community concept (and about how you can find someone to help you implement it) can be found on the Plant NOVA Natives website. Even if you have no planting plans, if you have a passing familiarity with our native trees and other plants, reading about our natural communities can add to your pleasure as you walk through our woods and notice the patterns.