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Reflecting reforestation over the past 100 years, forests presently dominate the Northeast's land cover. Currently, forests cover about 65% of the Mid-Atlantic region's land area. Specific states in New England have even more extensive forest cover; for example: Maine is 89% forested; New Hampshire, 88%; Vermont, 78%. Over the next 100 years, climate change could have a noticeable effect on these forests. One climate model study carried out by the World Wildlife Fund suggests that a warming of 4.5˚F over the next century would cause 44% of the current habitats of Maine and 35% of New Hampshire's to change.
The forests of the Northeast are important resources for local and regional inhabitants. The region's forests are a critical part of its watersheds, store vast quantities of carbon, provide habitats for wildlife, offer recreation (including hunting) venues for its residents and tourists, and supply the region's famous maple syrup. In addition, these forests generate wood and fiber that are used in the forest products industry. Wood products range from spruce-fir studs to birch toothpicks, plywood, trusses, furniture, veneer, pulpwood and paper, all of which presently succeed in the face of national or international competition.
Tree physiology and growth are influenced by many factors, such as physical climate (temperature and precipitation), chemical climate (air pollution and acid rain), soil type, availability of water, interactions with pests, strong winds, and ice storms. These many influences make it difficult to project the specific effects of climate change on Northeast forests. Nevertheless, changes in climate that could result in warmer winters, increased frequency of flooding, winter thaw/freeze events, and summer droughts are likely to affect the health and productivity of the forests of the Northeast causing an array of environmental, social, and economic impacts.
One critical impact of climate change could relate to carbon storage. The ability of trees to store carbon (in the form of wood and other structural and functional carbohydrates) is essential to both the productivity of forests and their economic value. In addition, by removing carbon dioxide from the atmosphere, forests help to offset carbon dioxide emissions. The forest ecosystems of New York and New England (NERA) contain about 4.2 billion metric tons of carbon and are increasing their carbon storage by about 20 million metric tons per year due to forest re-growth in many areas.
Over the past 30 years, the forested area in the Mid-Atlantic Region (MAR) has been fairly stable, but the amount of organic (living) material in the forests has increased through carbon storage as the forests have matured. However, as forests mature, the rate of carbon storage probably will begin to decline because mature forests store carbon at a slower rate than young, actively growing forests. Levels of carbon storage could be maintained if sustainable management practices, such as replanting and selective harvesting (choosing individual trees to harvest rather than clear-cutting a whole section of forest), are undertaken.
By acting as fertilizers and increasing water use efficiency, the increased carbon dioxide levels and nitrogen compounds in the atmosphere, associated with climate change, could increase growth rates for many species. If climate changes as projected, increased levels of carbon dioxide and soil nitrogen could trigger initial increases in forest growth. However, those positive factors could soon be counteracted by limited soil calcium or magnesium resulting in reduced forest growth.
More certain, however, is the harm likely to be posed to the region's forests by the projected increase in temperature, exposure to tropospheric (i.e., ground-level) ozone, and precipitation changes that together can directly effect tree growth and survival. The coastal and mountainous portions of New England and areas within the Appalachians, where exposure to tropospheric ozone is the highest, could be particularly affected by increases in concentration of this pollutant. Ozone levels are projected to increase as a result of rising temperatures.
Exposure to ground-level ozone is projected to decrease the primary productivity of forests by 2 to 17 %, which would reduce their ability to store necessary food and grow. Moreover, damage to needles and leaves from high ground-level ozone levels, combined with other pollutants and stresses, could contribute to forest dieback and decline. Also complicating the outlook for Northeast forests is acid rain (the sulfur and nitrogen compounds associated with climate change can combine in the atmosphere with cloud moisture and make acid rain and clouds) and relatively high levels of trace metal deposition from the atmosphere. Both are considered stresses to forest systems.
If the negative impacts overcome the positive effects of carbon dioxide fertilization and nitrogen deposited from the atmosphere, climate change could harm certain forests, tree types, and specific areas. Among the region's most vulnerable forest ecosystems are those growing at or near the minimum conditions for their competitive success and survival. Those already undergoing the stresses described above, isolated populations, those growing close to migration barriers (e.g., cities or mountains), and those with limited adaptive capabilities, could also be significantly affected. Vulnerable species include the red spruce and balsam fir, found at high elevations and already stressed by acid rain and winter injury, and the sugar maple, which no longer grows extensively south of New England.
Mature trees seem to be more susceptible to forest diebacks from thaw-freeze injuries than younger ones. One researcher found that forest diebacks in several northern hardwood species have been associated with various extreme or unusual weather events, including winter thaw followed by intense cold, spring and summer drought, summer heat stress, episodes of rapid warming, and increases in annual average temperatures. Combinations of stresses, such as winters without snow cover followed by deep freezes and summer drought, also could be damaging.
Looking at sugar maples over the last century, some studies found no evidence of widespread decline of this species in New England and New York while others found that large-scale die-offs have occurred when temperatures were warmer than normal. If the studies that suggest die-off associated with winter warmth are accurate, this would indicate that sugar maples are susceptible to summer droughts and mid-winter thaws that result in the loss of snow cover. Forests also could have to endure increased exposure to other stresses that can be directly or indirectly associated with climate change, such as fire, floods, windstorms, and the outbreak and increased ranges of pests and pathogens.
Changes in the composition and distribution of the plants and animals of the region are to be expected in connection with the impacts of climate changes on forests. The changes are likely to take place over several time scales. Trees and forests change slowly -- e.g., two to three centuries -- unless that change is accelerated by unexpected or secondary factors like fire, disease, and insects. But short-lived grasses and perennial plants can change quickly. Changes in the animal populations depend on whether the species require fast- or slow-changing vegetation types for habitat, or whether the physical environment puts limitations on their current populations.
In response to projected climate changes, the general geographical range of many tree species is projected to shift northward. By the end of the 21st century for example, the optimal range for some northeastern tree species could have moved 100 to 300 miles (or more) northward. However, historical records show that trees are generally only able to successfully develop at rates of about 8 to 31 miles per century depending on methods of seed distribution. Because of acorn distribution by blue jays, the presence of oaks may be able to move northward at a relatively rapid rate while maples will be slow moving because their seeds are dispersed by wind.
Seeds dispersed by birds are
often able to grow many miles from the parent tree, while wind-dispersed
seeds travel only a few feet from the parent tree. The difference in their
historical migration rates and the potential changes in their ranges raise
concerns that some tree species will not be able to keep up with the
climate alterations in their ranges without assistance. Climate models
suggest that one of the region's major forest types, Maple/ Beech/
Birch, is very likely to be completely displaced by more southern forest
types by the end of the 21st century. Maples are projected to
die-out in the NE region, except for isolated high elevation sites.
Climate change would also likely harm the products, such as maple syrup, coming from affected trees. New York and New England face the potential loss of maple sugar production because maple sap flows best when temperatures are less than 25˚F at night and when daytime temperatures are above 40˚F, temperature conditions that are very likely to be altered with climate change. In addition to daily fluctuations in the freeze-thaw cycle, prolonged periods below freezing are required to convert stored starch into sugar in the sap. This cold recharge period ensures that when the sap flows, it will be sweet.
Records for the past 100 years, and from some climate models, suggest that greater nighttime than daytime warming has occurred and is very likely to continue to occur; temperature increases of 3.6˚ and 7.2˚F are estimated to result in loss of optimal sap flow days of 17 and 39%, respectively. If warming occurs more in spring than in winter, buds are very likely to emerge early, resulting in bitter sap and a shorter, less productive season. Also, if the region's maple trees are in poor health, which could happen as a result of the stresses caused by climate change, the sap flow could be affected. Even though the winter of 2000/2001 was relatively typical in terms of snowfall, the sugar season was poor due to lack of the required daily temperature variations.
Forests provide wood, paper, and other forest products that are economically important by providing jobs and a way of life for many, especially in this region's rural areas. Forests also provide a variety of non-market benefits to the region and to society in general. They provide recreational opportunities, buffers for watersheds, habitat for a wide range of wildlife, enhanced biodiversity, and aesthetic appeal. Most of these non-market benefits are difficult to quantify and yet their loss could mean a significant change in the way of life for many.
Using one particular aspect as an example; the forests of the Northeast region are prized for their displays of fall colors, which draw many tourists to the area. Fall foliage is susceptible to the impacts of climate change in several ways, all of which could contribute to a less brilliant fall foliar display, as was experienced in the fall of 1998. Dead trees mute hillside colors, summer drought dims fall colors or causes early leaf drop, and longer fall seasons could result in fewer varieties being in color simultaneously. Shifts in species boundaries could lead to southern species such as oaks, which have brown leaves in the fall, replacing the brilliant hues characteristic of the Northeast forests today. The draw of the forests in the Northeast to tourists is also important regionally both for its economic impacts as well as its significance to the cultural identity of the region. More discussion about tourism and recreation in the forests of the Northeast follow in the section entitled Tourism and Outdoor Recreation.
Forestry and industries that rely on forests contribute significantly to the Northeast's economy. The potential economic impacts of climate change on northeastern forests could be far-reaching or negligible, depending on the climate changes that occur. MAR forest managers reported that whether they manage forests for watershed protection, harvest, aesthetics, or wildlife habitat, operating costs increase when extreme weather occurs. Thus, if the frequency of extreme events increases, as some models suggest, forest management operating costs are likely to increase even more.
The New England/New York region is responsible for approximately 75% of the total US maple sugar production and the regional value for 1997-1999 was $25 million. The Vermont share of this production (44%) supports 4,000 seasonal jobs and $105 million annually in related economic sectors. The US contribution to world wide maple syrup production is about 20%. Prior to the 1950s, the US accounted for 80% of worldwide production. In addition to its long-term decline, syrup production, for the US as a whole and this region specifically, has shown a recent variability with January-April temperatures. Generally, years with lower temperatures have shown increases in syrup production.
However, temperature is not the only important factor, and accounts for only about one third of the variation of syrup production. Other factors could include: pest infestations, drought, extreme events (e.g. ice storms), levels and timing of precipitation, growing conditions in the previous summer, technology, and changes in land values. Due to changes already occurring in many of these factors including climate, the bulk of the maple syrup production is moving away from New England into Canada. It is interesting to note that in 1928, the major syrup production center in the US was located in Garrett County, Maryland, whereas New England (specifically Vermont) had become the production center by the mid-1950s.
Manufacturing of wood-products accounts for 20 % or more of total industrial employment in some regions of the Appalachians. In the New England area, forest-based manufacturing employs some 86,000 residents, accounting for 12 % of the employment in Maine, 7 % in New Hampshire, 11 % in Vermont, and 2 % in New York. Payroll for these NE jobs equaled nearly $2.1 billion in 1990. Most of the wood-industry jobs are rural, with value-added jobs in nearby cities. These jobs and their contributions to the regional economy are important in specific areas but provide a lesser contribution to the economy as a whole because of the low wages associated with jobs in the forest industry.
Strategies to Address Potential Impacts on Forests
To contribute to maintaining the vigor of tree stands in the Northeast in the face of a changing climate, forest health could be monitored and managed in the following ways:
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