Non-Forested Wetlands

This forest type is often found in areas that have a high degree of past or current human disturbance, and fragmentation, invasive species, or other threats that can reduce the adaptive capacity of particular locations. Many forests are located in fragmented landscapes. A history of fire suppression and reduced light reaching the forest floor has facilitated a shift to more mesic conditions and associated hardwood species (e.g., red and sugar maple, American beech, tuliptree).

Studies suggest that insect pests may increase in northern forests due to increased metabolic activity in active periods and increased winter survival. Many insect species are limited by extremely cold temperatures, and evidence suggests that several insect species may increase in a warmer climate, including the hemlock woolly adelgid. Trees stressed by heat, drought, or disturbance are also typically more vulnerable to insect pests and diseases. Emerald ash borer and Dutch elm disease are expected to continue to limit ash and elm species.

There are many invasive plant species, insect pests, and forest diseases that have negative impacts on lowland and riparian hardwoods, many of which are expected to increase through the direct and indirect effects of climate change. Invasive species such as Japanese stiltgrass and buckthorn are existing threats to these forests, and invasive species are expected to increase in abundance under climate change, particularly where forests are disturbed.

This forest system contains many tree species that are tolerant of warmer temperatures and are located in the central to northern portion of their range in New England and northern New York. Multiple forest impact models tend to agree that these species are likely to increase in suitable habitat and biomass across a range of climate scenarios by the end of the century. Species such as American elm, eastern cottonwood, and silver maple are expected to gain suitable habitat across the assessment area under a range of climate futures.

Many species in riparian and lowland forests can tolerate intermittent wet and dry conditions, and
they can tolerate periodic floods and moisture stress. Extended droughts would cause significant damage
to shallow-rooted species, but increased winter and spring precipitation could buffer summer droughts
in low-lying areas on the landscape.

Climate change has the potential to substantially alter the hydrologic regimes in lowland and riparian systems. These hardwood forests are adapted to annual and seasonal water table fluctuations; however, more intense and variable precipitation events may present risks to this system through excessive flooding, inundation, streambank erosion, or prolonged droughts between heavy precipitation events. Extended droughts could cause significant damage to shallow-rooted species, but increased winter and spring precipitation may buffer summer droughts in low-lying areas on the landscape.

These are northern species near their southern range limits in New England and northern New York. Multiple forest impact models tend to agree that these species are more likely to decline in suitable habitat and biomass across a range of climate scenarios by the end of the century. Impacts from climate change are projected to be less severe in the northern part of the assessment area, such as in Maine, allowing the dominant species to persist in some areas.

Changes in snowfall amount and duration throughout the assessment area may change the wintertime foraging behavior for herbivores such as moose, white-tailed deer, and snowshoe hare. Moose are expected to be negatively affected by numerous changes in the future, including heat stress and increased parasitism from winter ticks. In contrast, deer may benefit in many parts of the region as warmer winter temperatures and reduced snow depth increase access to winter forage.

Sphagnum moss, the primary source of peat in these systems, may be susceptible to warmer conditions. Warmer growing seasons may increase evapotranspiration rates and reduce the rate of peat accumulation in these forests, and peat layers may begin to erode as decomposition rates increase.

Lowland conifer forests function in a relatively narrow window of hydrologic and soil conditions. These conditions are expected to be perturbed in a variety of ways, including through increased severe precipitation events and flooding, increased risk of drought, and changes in the water table or relative influence of precipitation versus groundwater. In general, drier conditions would be expected to have a greater negative impact than excess moisture. Organic soils could decompose more quickly under warmer and drier conditions.