Mid-Atlantic Forest Ecosystem Vulnerability Assessment

This chapter describes the assessment area and purpose of this document. It also describes the forest communities assessed in later chapters and summarizes current forest threats and management trends. This information lays the foundation for understanding how shifts in climate may contribute to changes in forest ecosystems, and how climate may interact with other stressors on the landscape.

• Of the nearly 60 million acres of land in the assessment area of the Mid-Atlantic region, about 32 million acres is forested. Private individuals, corporations, and conservation organizations own 74 percent of the forest land, and the remaining forest is owned by Federal, State, and municipal entities. Oak/hickory and maple/beech/birch are the most abundant forest-type groups across the area.

• Historical land use and past management practices have resulted in second-growth forests that are young compared to pre-European settlement conditions.
• Current major stressors and threats to forest ecosystems in the Mid-Atlantic region include:
• Fragmentation and land-use change (e.g., energy, agriculture, or residential development)
• Shifts in natural disturbance regimes (e.g., shifts in fire regimes, drought frequency, or flood frequency)
• Forest diseases and insect pests
• Establishment of nonnative invasive plant species
• Establishment of nonnative invasive plant species
• Sea-level rise
• Extreme weather events
• Herbivory
• The forest products and forest-related recreation industries are major contributors to the regional economy, and an increasing amount of forest land is managed according to a sustainability certification standard.
• Net forest growth (gross growth minus mortality) is nearly three times as great as removals. Private forest lands, which include both industrial and nonindustrial ownerships, accumulate the most growing stock.
• Eleven forest communities are used to describe the forests in the Mid-Atlantic region. The descriptions of forest communities were based on macrogroups defined in the Northeast Terrestrial Habitat Classification System, but were revised as part of the expert elicitation process.

Many of the climatic changes that have been observed across the world over the past century are also evident in the assessment area. This chapter summarizes our current understanding of observed changes and current climate trends across the MidAtlantic region, with a focus on the last 100 years.

• Temperature minimums (lows) and maximums (highs) have increased. Minimum temperatures have increased more than maximum temperatures in every season except spring, with the greatest increase in temperature during the winter.
• Precipitation patterns have changed across the region, with the most change occurring in fall (increase of 3.2 inches). The number of intense precipitation events has increased.
• Sea levels have risen in the Mid-Atlantic faster than global sea levels, about 12 inches since 1900 along the Atlantic coastline.
• Climate change is also indicated by observed changes in biological processes, such as growing season length, shifts in flowering phenology, and changes in wildlife emergence and migration.

This chapter describes climate projections for the assessment area over the 21st century. Temperature and precipitation projections are derived from downscaled simulations of climate models. Published scientific literature provides the basis for describing possible trends in a range of climate driven processes, such as extreme weather events and snowfall.

• Temperatures are expected to increase over the next century, under a range of climate scenarios and in all seasons.
• Precipitation is projected to increase in winter and spring across a range of climate scenarios. Projections of summer and fall precipitation are more variable.
• Localized soil moisture deficits are expected to become more frequent.
• The growing season length is expected to increase by up to 1 month.
• The number of hot days is expected to increase and the number of cold days is projected to decrease.
• Intense precipitation events are expected to become more frequent.
• Streamflow and flooding potential are expected to increase in the winter and spring, and decrease in the summer and fall.
• Sea level in the Mid-Atlantic is projected to rise by up to 7 feet by 2100, resulting in more flooding and storm surge.

This chapter, drawing on information from a coordinated series of model simulations and published research, summarizes the potential impacts of climate change on forests in the MidAtlantic region.

• Many mesic forest species, including American beech, eastern hemlock, eastern white pine, red spruce, and yellow birch, are among those projected to have reductions in suitable habitat, growth potential, and biomass under a high degree of warming over the next century.
• Many species are expected to lose regeneration potential over the next century, but mature individuals could continue to grow for much longer in the absence of other mortality factors.
• Many southern species—species with ranges extending largely south of the Mid-Atlantic region, including post oak, scarlet oak, and southern red oak—are projected to increase in suitable habitat and biomass within the MidAtlantic region.
• The forest impact models used in this assessment isolate the effects of climate change on tree species’ growth and habitat, and do not account for many other factors that influence forests.
• Scientific literature was used to provide additional information on the effects of climate change on other factors such as:
• Moisture stress
• Acid deposition and carbon dioxide fertilization
• Altered nutrient cycling
• Invasive species, insect pests, and forest diseases
• Herbivory on young regeneration
• Interactions among these factors

This chapter focuses on the vulnerability of major forest ecosystems in the Mid-Atlantic region to climate change (Table 1). Detailed vulnerability determinations are provided for 11 forest ecosystems with an emphasis on dominant species, features that define a system (drivers), and features that disturb a system (stressors).

The adaptive capacity of each forest ecosystem was also examined as a key component to overall vulnerability. Adaptive capacity is the ability of a species or ecosystem to accommodate or cope with potential climate change impacts with minimal disruption (Glick et al. 2011, IPCC 2007).

We further rated the evidence used in assessing vulnerability as well as the level of agreement between sources of evidence. We consider a system to be vulnerable if it is at risk of a species composition change leading to a substantially different character for the forest system, or if the system is anticipated to suffer substantial declines in acreage, health, or productivity. General trends in climate change impacts and adaptive capacity factors for the Mid-Atlantic region are also captured in overarching synthesis statements.

Potential impacts of climate change on ecosystem drivers and stressors

• Temperatures will increase (robust evidence, high agreement). All global climate models agree that temperatures will increase with continued increases in atmospheric greenhouse gas concentrations.
• Growing seasons will lengthen (robust evidence, high agreement). There is strong agreement that projected temperature increases will lead to longer growing seasons in the MidAtlantic region.
• The amount and timing of precipitation will change (robust evidence, high agreement). There is strong agreement that precipitation patterns will change across the Mid-Atlantic region.
• Intense precipitation events will continue to become more frequent (robust evidence, high agreement). There is strong agreement among climate models that the number of heavy precipitation events will continue to increase in the Mid-Atlantic region. If they do increase, impacts from flooding and soil erosion may become more damaging.
• Sea levels will continue to rise (robust evidence, high agreement). There is substantial evidence that ongoing sea-level rise will continue to affect low-lying coastal areas and increase potential impacts from flooding, saltwater intrusion, and storm surge.
• Soil moisture patterns will change in response to temperature and precipitation (medium evidence, high agreement). Warmer temperatures and altered precipitation are expected to change soil moisture patterns throughout the year, but there is uncertainty about the direction and magnitude of the changes at specific locations.
• Forest vegetation may face increased risk of physiological drought during the growing season (medium evidence, medium agreement). Warmer temperatures can lead to decreased soil moisture even without an associated decrease in precipitation, resulting in a temporary inability for a tree to meet water demand.
• Climate conditions will increase wildfire risk by the end of the century (medium evidence, medium agreement). Some national and global studies suggest that conditions favorable for wildfire will increase, but few studies have specifically looked at wildfire risk in the MidAtlantic region. Wildfire risk will also depend on ignition, fire weather, ecosystem type, topography, fragmentation, and other regional characteristics.
• Certain insect pests and pathogens will increase in occurrence or become more damaging (medium evidence, high agreement). Evidence indicates that an increase in temperature, longer growing seasons, and more frequent disturbances will lead to increased threats from insect pests and pathogens, but research to date has examined relatively few species.
• Many invasive plants will increase in extent or abundance (medium evidence, high agreement). Evidence indicates that increases in temperature, longer growing seasons, and more frequent disturbances will lead to increases in many invasive plant species.

Potential impacts of climate change on forest communities

• Northern and remnant boreal tree species will face increasing stress from climate change (medium evidence, high agreement). Ecosystem models agree that these species may have reduced suitable habitat and biomass across the Mid-Atlantic region. These species may be less able than temperate forest species to take advantage of longer growing seasons and warmer temperatures.
• Habitat will become more suitable for southern species (medium evidence, high agreement). All three forest impact models project an increase in suitability and growth for southern species such as post oak, scarlet oak, and southern red oak compared to current climate conditions.
• Forest composition will change across the landscape (medium evidence, high agreement). Forest impact model results predict that habitat and biomass of individual tree species will change, and that tree species will respond uniquely. However, few studies have specifically examined how assemblages of species may change.
• Tree regeneration and recruitment will change (medium evidence, high agreement). Seedlings are more vulnerable than mature trees to changes in temperature, moisture, and other seedbed and early growth requirements; they are also expected to be more responsive to favorable conditions.
• Forest productivity will increase during the next several decades in the absence of significant stressors (medium evidence, medium agreement). Some studies have examined the impact of climate change on forest productivity within the Mid-Atlantic region, but they disagree on how other factors such as species composition, stand age, disturbance, or pollution may interact to influence productivity. Changes are not expected to be consistent within a species, and the diversity of forest site conditions across the landscape suggests that changes will be spatially variable.

Adaptive capacity factors

• Low-diversity forest communities are at greater risk (medium evidence, high agreement). Studies have consistently shown that diverse systems are more resilient to disturbance, and low-diversity ecosystems are more vulnerable to change.
• Most tree species in isolated or fragmented landscapes will have reduced ability to migrate to new areas in response to climate change (limited evidence, high agreement). The dispersal ability of most individual tree species is reduced in fragmented landscapes, but the degree of landscape fragmentation in the future is an area of uncertainty.
• Species or systems that are limited to particular environments will have less opportunity to migrate in response to climate change (limited evidence, high agreement). Our current ecological understanding indicates that migration to new areas may be impossible for tree species and forest communities with narrow habitat requirements.
• Forest communities that have high tolerance to disturbance will be at lower risk of decline from shifting climate extremes (medium evidence, high agreement). Basic ecological theory and other evidence suggest that communities adapted to disturbance will be at lower risk of declining on the landscape. However, some communities may tolerate only a narrow range of conditions related to a disturbance and may be susceptible to different, or more frequent and severe, disturbances.

This chapter summarizes the implications of potential climate change impacts on important facets of forest management and planning in the Mid-Atlantic region, such as impacts on timber output, wildlife, or cultural resources. We point out key implications, ongoing research, and sources for more information on how climate change is expected to affect these topics. This chapter does not make recommendations as to how management should be adjusted to cope with these impacts, because impacts and responses will differ by ecosystem, ownership, and management objective.

• Climate change will present risks to forest management such as more disturbance, as well as opportunities such as longer growing seasons.
• Over the next century, climate change is expected to have profound effects on forest ecosystems, which will in turn lead to habitat changes for a variety of plant and animal species; management of forest-dependent plants and animals may face additional challenges as the climate shifts.
• Land conservation planning is expected to include more emphasis on climate adaptation strategies related to carbon mitigation, refugia for at-risk species and habitats, landscape connectivity for migration corridors, and water supply protection.
• Changes in climate and extreme weather events are expected to affect infrastructure such as roads, bridges, and culverts on forest lands throughout the region.
• The timing of activities, including timber removal, prescribed fire, and recreation, may need to be shifted as temperatures and precipitation patterns change.
• Responses to increased risk of wildfire may require more resources to reduce fuel loads, suppress fires after ignition, and manage ecosystems affected by wildfire.
• Climate change is expected to increase respiratory allergies and diseases, gastrointestinal illnesses, heat stress, and vector-borne diseases.