Forest [FAR1]

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.

These forests are also prevalent across the region on a wide variety of soils and landforms. Not all areas are expected to be affected equally, and in general, areas that are north-facing, at higher elevations, or are farther north in the region are expected to undergo less change and may continue to support spruce-fir forest in the future. At the same time, spruce-fir forests that are farther south may have a reduced capacity to cope with future conditions, particularly where past land use or management has already impaired the system.

These forests tend to have relatively low diversity and be dominated by a relatively small number of northern and boreal species. Forests with lower species diversity may be more vulnerable. Further, management often favors the hardwood component in these forests, and additional stress or disturbance may continue to shift forest composition toward hardwood species.