Forested watershed

This ecosystem exists in many variations within a relatively small proportion of the Central Appalachians, but is extremely altered by habitat destruction, fragmentation, and disconnection of floodplain forests from rivers and streams (e.g., by roads or infrastructure that impedes the flow of water).

Drought-stressed trees may become more susceptible to insect pests such as emerald ash borer and diseases such as thousand cankers and elm yellows. Mortality of ash species from emerald ash borer is likely to eliminate this species by mid-century, reducing overall native species diversity.

The high number of invasive species out-competing natives has already reduced the adaptive capacity of this ecosystem. Dependence on periodic inundation, combined with competition from invasive species, may result in a reduced ability of native tree species to tolerate a variety of amplified or new disturbances.

Wildfire, currently episodic and human-caused, could increase under drier conditions, although the extent would be limited by the fragmented nature of riparian and floodplain ecosystems.

Many riverine species in this forest type were modeled only by the Tree Atlas; thus evidence is somewhat limited regarding dominant species. Black willow, green ash, sweetgum, and sycamore are projected to increase in suitable habitat over much of the Central Appalachians. Silver maple had mixed results, but is projected to generally decrease in suitable habitat under low climate scenarios and increase under high climate scenarios.

Episodic precipitation is likely to result in more intense storms, and subsequent flooding events. Although this ecosystem is highly dependent on disturbance and a regular influx of seeds, nutrients, and water during periodic flooding, increases in flood intensity or more frequent drought may not be tolerated by many species, especially in the early growth stages. Many riverine species in this forest type depend on high moisture availability, and are especially threatened by discrete periods of dry soil conditions.

Increased drought risk, especially during the growing season, may increase susceptibility to red oak borer, ambrosia beetle, gypsy moth, armillaria root rot, and other insect pests and diseases. Tree-of–heaven, Japanese stiltgrass, and garlic mustard, which often out-compete native herbs and shrubs in this ecosystem, are expected to do well in warmer temperatures.

This ecosystem supports a high number of tree species, is widely distributed, representative of a range of habitat conditions, and is likely to expand on the landscape.

Many species are tolerant of dry soil conditions and fire, although young regeneration may be sensitive to severe drought and fire. Low-severity late-season drought generally favors oak species, although severe drought may hinder regeneration, or combine with other stressors to make individuals more susceptible to mortality or reduced productivity.

A history of fire suppression and timber harvesting has facilitated a shift to more mesic soils and associated hardwood species (e.g., sugar maple, American beech, tulip tree). Increased fire frequency could help regenerate oak species and restore the understory composition. However, very frequent fires have the potential to kill young seedlings of any species, even those species that have relatively fire-resistant, thick bark as adults.