National Assessment of
Alaska's forests are renewable resources that help maintain wildlife habitat, yield domestic and international forest products and encourage tourism. Alaska's forests could also potentially sequester more carbon as they grow more under favorable conditions such as warmer temperatures. Forests cover 129 million acres of Alaska, about one third of the State. Past climate changes and the resulting short-term forest responses (e.g., increases in productivity) could provide insights into how Alaska's forests would respond to future climate change. However, over the longer term, climate change is likely to bring large landscape-level vegetation changes to both forest and tundra regions in Alaska.
Alaska is home to two types of forests, classified as coastal temperate rainforests (about 10%) and boreal forests. Coastal temperate forests are located in the southeast and south-central regions of Alaska, covering roughly 13 million acres -- 19% of the world's coastal temperate forests. Climate change could positively impact these forests -- through increases in average tree growth and forest productivity, diversity in species, and expansion of forests into the boreal zone and the tundra. And yet, future climate change associated with increases in the incidence of destructive winds and insect infestations and in increases in summer moisture deficit could compromise Alaska's coastal forests.
Boreal forests, which cover 17% of the Earth's land surface area, are found in Alaska's south-central and interior regions. Models consistently project large-scale transformation of Arctic landscapes, where the northern edge of the boreal forest advances into the tundra. Even with these projections, concerns for Alaska's boreal forests from projected climate changes include: a loss in the moisture needed for forest growth; insect-induced tree mortality; increased risk of large fires; interference with the reproduction of white spruce, a biological and economic concern; and the changes caused by permafrost thaw e.g., slumping of land and wetland development from thaw water.
Potential impacts of projected climate change in Alaska's forests are examined below, with social and economic impacts -- closely related -- addressed jointly. Strategies that could prove useful in addressing these impacts concludes the discussion.
Recent warming in Alaska has increased average growing degree-days by about 20% over the state, bringing apparent increases in forest productivity on sites that are not moisture limited -- principally in the southern coastal forest, but also including some regions of the boreal zone. At the northern margin of the boreal forest, the present climate already favors forest expansion into the tundra zone, particularly on the Seward Peninsula. The potential for such expansion is estimated as 35 miles per °F of climate warming. On sites that are moisture-limited, which occur through much of the interior, recent warming has apparently increased moisture stress and reduced productivity. Near Fairbanks the average number of days exceeding 80°F annually has tripled since 1950, imposing moisture stress on white spruce stands that result in loss of productivity with warm, dry summers. It has been suggested that the past 20 years have seen the greatest moisture stress and lowest productivity of the 20th century through much of the interior boreal forest.
Substantial changes in patterns of forest disturbance, including insect outbreaks, blowdown (from strong winds), and fire, have also been observed in both the boreal and southeast coastal forest. A sustained outbreak of spruce bark beetles since 1992 has caused over 2.3 million acres of tree mortality on the Kenai Peninsula, the largest loss from a single outbreak documented in the history of North America. The association of warmer temperatures with both accelerated beetle development times and increased tree vulnerability through moisture stress makes it likely that recent warming contributed to the outbreak. Outbreaks of defoliating insects in the boreal forest, including spruce budworm, coneworm, and larch sawfly, have also increased sharply in the 1990s, affecting a cumulative total of 800,000 acres. Susceptibility of interior forests to insect attack could also have increased due to canopy breakage from the heavy snow loads typical of warmer winters.
In Southeast forests, warmer winters since the 1970s with more precipitation falling as rain have reduced the frequency of low and moderate-elevation avalanches, allowing mountain hemlock to colonize alpine tundra. Reduced low-elevation snowpack has also likely contributed to the extensive decline of yellow cedar in the coastal forests, due to freezing of their shallow root systems during winter cold spells with no insulating snow cover. Over the same period, the southern coastal forests have also seen a marked increase in the frequency of gale-force winds, which is the primary disturbance in these forests. The southern coastal forests have also experienced outbreaks of the defoliating western black-headed budworm that appear to be triggered by warm dry summers.
Forest fire frequency and intensity have increased markedly since 1970. The 10-year average of boreal forest burned in North America, after several decades of around 2.5 million acres, has increased steadily since 1970 to more than 7 million acres annually. Boreal forest fire reached extreme values in both Eurasia and North America in 1998, with over 27 million acres burned in total, 10 million in North America. It is suggested that substantial climate-related changes for the coastal forest could occur over several decades, including the appearance of new fungi and a significant fire risk for the first time in the observed record.
Boreal forests and tundra ecosystems also contain large stores of carbon in their soils. These soils can act as either sources or sinks of greenhouse gases, depending on temperature and moisture conditions. As temperatures rise and soils thaw and dry, they become more susceptible to release of CO2. Where drainage is poor and the soil remains wet after thawing, emissions of methane could increase.
Each of these changes is capable, in turn, of effecting other changes in Alaska's environment. The declining frequency of severe snow, for instance, has allowed Sitka black-tailed deer better access to winter forage plants, heightened the survival of deer populations, and reduced the regeneration rate of Alaska yellow cedar, which is the preferred grazing vegetation of deer.
About 21 million acres, or 16% of total forest, is classified as productive, capable of average growth of 20 cubic feet per acre per year. About 4 million acres, nearly all of it in the coastal forest, is outside protected areas and has the productivity of 50 cubic feet/acre-year necessary to support commercial harvest with road construction. The state's timber harvest increased from 600 to 1,100 million board feet from 1986 to 1990, and has since declined to about 500 million board feet. Employment and income in the industry followed the same pattern, peaking at 4,000 jobs and $200 million in 1990, declining to 2,500 jobs and $130 million by 1997. While the declines of the 1990s principally reflect two causes: the closure of two SE Alaska pulp mills and the depletion of Native Corporation timber inventories, changes in Alaska's forests, primarily from climate changes, could have significant social and economic implications. For example, the majority of saw logs from private coastal forestland are exported to supply strong markets (logs from public lands cannot be exported). Decreased yields from these forests could jeopardize a way of life and the only source of income for many. Moreover, Alaska's boreal forests, in addition to supporting a strong traditional culture among the world's lowest density of human settlement in any of its major forest areas, support growing timber and mineral extraction. As with coastal forests, compromises to boreal forests could threaten the cultural values and livelihoods of those living in these areas.
A major change in Alaskan settlement geography since 1970, promoted by policies including large-scale private transfer of public lands and extensive road-building, has greatly increased dispersed settlement in forest land. At the same time, other policies to transform native villages into permanent communities created more than 60 communities with significant costly infrastructure surrounded by boreal forest. These trends have greatly increased the vulnerability of people and settlements to forest fires. A single major fire in June 1996, for example, burned 37,000 acres of forest and peat, causing $80 million in direct losses and destroying 450 structures including 200 homes. As many as 200,000 Alaskan residents could now be at risk from such fires, with the number increasing further as outlying suburban development continues to expand.
Strategies to Address Potential Impacts on Forests
For large-scale ecological and landscape transformations, no effective adaptation strategies are likely to be available. However, many strategies could be pursued to lessen the economic effect of present and potential climate-change impacts on Alaska's forests and the communities that depend on them. They could include any of the following options:
To help offset climate-induced increases in fire risk in commercially valuable forests or near settlements -- recognizing that any strategy based on expanded fire suppression will carry its own ecological costs and also risks being ineffective in the long term, because by removing risk from property owners it would sustain incentives to build in fire-prone areas -- one could:
An alternative approach would create incentives to reduce private risk -- this approach would represent a radical departure from historical policies in the region but could include:
The following actions could assist in recovering or avoiding some of the potential economic losses related specifically to forestry:
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