Trees grow in all types of environments, and stream side or wetland areas can be some of the most challenging environments for trees to grow. While trees do need water, they face several challenges in a wet environment:
- While they also use water and sunlight, trees need oxygen. Trees share at least 60 percent of genetic information with humans, and breathe and use oxygen for energy. A flooded or very wet soil has little oxygen, so this makes root growth and function difficult.
- Wet environments are perfect for certain decay organisms to break down and damage trees.
- Periodically flooded or flowing streams and lakes face more disturbance, with wet and dry periods during the year increasing the stress to the surrounding trees. While a tree in a flat field may suffer from temperature changes, the environment around water changes more drastically, requiring much hardier trees.
- Some trees adapt to wet soils by having very superficial roots. These roots exchange oxygen at the top layer of soil and help the tree survive in a high water table. Species that characterize this include maples, sweetgum, magnolias and elms. Great examples of these superficial roots can be found in Bon Air Park along Four Mile Run, near the shelter, where we have some of our native red maple stands.
- The most common strategy to wet soils is to grow faster than any decay that may form, and heal over wounds caused by disturbance quickly. Eventually, these trees lose this battle, but they often pair the strategy by reproducing early in their age. These trees can be structurally unsound and often contain significant decay. Examples of trees like this are silver maple, American elm, and green ash. Barcroft Park is a great place to find many of these species along Four Mile Run throughout the park.
- Slow-growing, rot-resistant wood is one of the more long-term strategies to deal with the high disturbance of a waterlogged environment. The species using this strategy tend to be found in older environments where they have waited patiently, growing slowly, to take over the shorter-lived species over time. Some of these trees are the longest-living species in eastern North America, and include black tupelo, black locust, baldcypress (longest-living tree species in the east, up to 2,000 years) and arborvitae. While baldcypress and arborvitae aren’t directly native to Arlington, you can find blackgum and black locust growing along Ballston Pond.
Because of all their adaptations and their resistance to disturbance, many species that can handle tough environments like this can be appropriate trees for urban, compacted planting as well. Arlington uses many species commonly found along streams to beautify our streets and improve our tree canopy. We also plant many of these species to restore existing streams to improve retention of soil and clean our water in the short- and long-term.
To learn more about trees in Arlington, including our tree programs, proper practices and recommended trees for planting, visit environment.arlingtonva.us/trees.