Riparian communities are those that exist on or near the bank of the river. These plants are the ones we typically see in floodplains. The Gorge has several different kinds of riparian communities. Some exist in almost desert-like conditions, where soils are dry and well-drained because they are gravelly. Wet bottomland forests of moist, rich soil support other types of communities.
In the Potomac Gorge, there are six types of globally rare riparian communities. Riparian habitats, like most habitats, are defined by three conditions:
- Soil Moisture. Mesic soils are part-dry and part-wet; if they are more wet than dry, they can be called wet mesic. Dry mesic soils are more dry than wet. Hydric soils are just wet; xeric soils are simply dry. All of these soils are present in the Gorge.
- Soil Composition. As backyard gardeners know, soils range from organically rich to rocky mineral. In the Gorge’s riparian zones, mineral soils are found in low places such as rocky washes, where pools form after high water, and in gravel and cobble bars that form as the Potomac carries sediments downstream.
- Vegetation. The types of plants that dominate in each of the Gorge’s riparian areas depend on its soils and moisture content. They range from savanna grasses and herbs, to shrubs and forests.
When you walk the trails, the Potomac Gorge will come alive for you if you learn to recognize these shifts in communities—sometimes subtle, sometimes vivid.
Non-native and invasive plants are perhaps the biggest threat to the survival of the Gorge’s native riparian communities. Like aggressive weeds in a backyard garden, invasive plants can completely overwhelm an entire ecosystem. Another threat, which compounds the damage by non-native plants, is the over-abundant deer browsing in these fragile riverine habitats.