Eastern hemlock is the dominant tree species in southeastern Kentucky’s deep ravines and along mountain streamsides. It is also commonly found in shaded riparian zones and moist cliff line habitat throughout the rest of eastern Kentucky. Isolated populations have been found west of Elizabethtown in Hardin County and in the Green River valley around Mammoth Cave National Park. It is the most shade-tolerant evergreen in the eastern United States and the shade it casts greatly influences the forest microclimate. The hemlock is a very long-lived tree and it supports a unique ecosystem that depends on the cool, moist conditions it maintains. A great variety of birds roost, nest or forage in the dense canopies and several, including the black-throated green and Blackburnian warblers are almost exclusively associated with hemlock forests. Other species that are found in association with hemlocks include plants such as Fraser’s sedge which requires cool, moist soils to flourish. Hemlock trees also have a role in moderating the flow and temperature of streams, enabling a wide variety of aquatic organisms that need cool, shaded water to survive through the warmer, drier summer months. The hemlock’s extensive, fibrous root systems hold the soil and help maintain stable stream banks.

All of the impacts from the loss of hemlocks in Kentucky’s forests cannot be envisioned at this time. However, with their decline, changes in the forest structure from the canopy to the forest floor will become apparent. Increased sunlight will raise soil and water temperatures; decreases in soil moisture and available water flow in summer months will take a toll on the plants and animals that have evolved with the dense hemlock cover. Vegetation composition will shift to species that are more drought-tolerant as conditions become drier. Bird diversity and abundance may decline as hardwood trees and invasive non-native plants colonize the areas once occupied by hemlocks. The large influx of woody debris from fallen trees will change water chemistries, further damaging their ability to support aquatic life. Stream banks may destabilize as tree roots decay, adding more silt to choke the streambeds. No other species can replace the hemlock tree and assume its ecological role.