Forest

Insect pests such as the hemlock and balsam woolly adelgids currently affect this ecosystem and have the potential to increase when winter temperatures no longer limit populations.

Although this ecosystem generally receives the highest rainfall in the Central Appalachians, a decrease in precipitation, combined with higher temperatures, may negatively impact spruce regeneration.

Changes in winter processes could affect this high-elevation ecosystem more than others; interacting effects of reduced snow cover (warm temperatures) or increased snow cover (lake effect) would alter soil freezing conditions.

Suitable habitat for this ecosystem is already limited to the highest elevations in the Central Appalachians and the range of this ecosystem may contract as climate change forces species upward. This ecosystem is dependent on very moist conditions, and persists only in the coolest, wettest, and highest elevation sites in mountainous sections.

Red spruce and balsam fir (the keystone species in this ecosystem) are limited to the Allegheny Mountains and the Northern Ridge and Valley sections, and models project suitable habitat and growth potential to decline dramatically for both species under both climate scenarios. Balsam fir has the lowest adaptive capacity of all the species in this ecosystem, largely due to its fire- and drought-intolerance and susceptibility to balsam woolly adelgid and other insect pests.

In the cooler and moister sites, hemlock is a keystone species that has been declining and is projected to decline further. For these forests, the loss of hemlock is likely to change the species assemblage dramatically, with fast-growing generalists like red maple or a variety of invasive species likely to overtake the newly vacated niche.

Increased flashiness followed by dry periods could cause amplification of the current hydrologic cycle, potentially increasing the spread and establishment of current and newly introduced invasive species.

Many riverine species in this forest type were modeled only by the Tree Atlas; thus evidence is somewhat limited regarding dominant species. Suitable habitat is projected to remain stable or increase for sycamore, river birch, black walnut, and boxelder. Silver maple is projected to decrease under low climate scenarios and increase under high climate scenarios. Hemlock and red maple were modeled by all three models.

Wildfire, currently episodic and human-caused, could increase under drier conditions, although the extent would be limited by the fragmented nature of small stream ecosystems. Mortality and damage from drought or storms may result in increased coarse woody debris, contributing to wildfire fuels.

Potential changes to the precipitation regime could intensify peak stream flow and shift the timing to earlier in the spring. Reduced precipitation in the summer and fall would result in drier conditions, increasing the potential for late-summer drought. Moisture deficits have the potential to create dry vegetation conditions late in the growing season, stressing hydrophilic seedlings and supporting wildfire conditions. Drought-stressed trees may be more susceptible to diseases such as thousand cankers and elm yellows, and insect pests such as hemlock woolly adelgid.