Climate change in southeast Alaska

Climate change in southeast Alaska are changes which occur in southeast Alaska as average temperatures rise as a result of global warming.

The temperate rainforest that covers this area is a result of humid summers and transient snow cover in winter. The conifers that thrive in this moist climate are free from fire risk as compared to the forests to both the north and south.

Warmer weather will lengthen the growing period of the trees and the increase in evapotranspiration is likely to outweigh the increase of precipitation. Assuming a scenario involving a mid-range increase in emissions, the average temperature may rise by about 3 °F by the year 2040 and by 6 °F by 2080. The trees will grow more vigorously but fungi that cause rot will also thrive, there is likely to be an increase in windthrow, and fire risk may rise.

With winter temperatures increasing, the type of precipitation will change. Lack of snow cover on the ground will expose tree roots to colder soils, and yellow ceder is already showing the result of this with many trees dying. The melting of glaciers in the watershed is likely to accelerate and will cause hydrological changes that will impact the wetland habitats and the distribution of wildlife. Animals such as the black-tailed deer, moose and mountain goat may benefit from less snow cover, while such mammals as the northwestern deer mouse that tunnels under the snow are likely to be disadvantaged.

Alaska's temperate rainforest

The temperate rainforest in southeast Alaska, in the Tongass National Forest is a perhumid (always wet) temperate rain forest.^[1] A perhumid temperate rainforest is a rainforest that receives above ten percent of its annual rainfall during the summer. Another contributing factor to define a perhumid rainforest is transient snow must be present in the winter with mean annual temperatures of 7 °C. These qualities define the rain forest as cool and temperate.^[2]

Southeast Alaska's temperate rainforest (present)

At present, the southeast Alaskan temperate rainforest is strongly dominated by old growth stands.^[3] The vegetation is strongly represented by a series of conifers; Sitka spruce, western hemlock, mountain hemlock, amabilis fir, shore pine, western red cedar and Alaska yellow cedar.^[4] This forest, unlike its neighboring regions to the north and south, is completely safe from fires. Fire is virtually nonexistent in the southeast region due to the moist and cool climate. Small scale windthrow is the main disturbance that affects the rain forest in this region.^[3] Temperatures and precipitation in the southeast region of Alaska for the year of 2011 have matched what a typical temperate rainforest needs to be defined as one by DellaSala. Juneau, Alaska, received 66.40 inches of precipitation and averaged 40.6 °F during 2011. Snowfall, as will be discussed in further detail later, is an important player for the temperate rainforest in this region, and the Juneau area received 115.9 inches which, converted to its liquid equivalent is 11.59 inches.^[5] The weather characteristics of the southeast region match up very well with what a temperate rainforest needs as defined by DellaSala.

Emission scenario for the future

In order to predict how climate change might affect the southeast region of Alaska, there must be a standard of how the data will be collected and interpolated. The models used in the Scenarios Network for Alaska and Arctic Planning (SNAP) research took in to account a steady increase in carbon dioxide emissions from fossil fuel combustion over the first several decades of the 21st century. As the implementation of low-emission energy alternatives becomes more prevalent, a projected decline in CO₂ emissions will occur. According to SNAP, this scenario is a moderate estimate. This scenario will be the standard for how the temperate rainforest in the southeast region will be impacted in the coming decades.

Climate change predictions

The southeastern region is projected to become warmer over the next century. Warmer temperatures in this region mean additional length to the growing season. These two changes in the ecosystem are likely to result in increase in evapotranspiration, enough to outweigh the increase of precipitation that is also predicted to occur throughout the region. Many scientists have already discovered typical signs of climate change in wetland drying and glacial recession.

Precipitation and temperature

Assuming a mid-range emission scenario described as, a world of rapid economic growth, a global population that peaks mid-century, rapid introduction of new and more efficient technologies, and a balance between fossil fuels and other energy sources. By using this scenario presented by the Scenarios Network for Alaska and Arctic planning, there is a predicted increase in average annual temperature by about 3 °F by the year 2040, increasing to 6 °F by 2080. The final result would be an increase of average annual temperature of about 42 °F to close to 48 °F over the southeast region of Alaska. More importantly than average annual temperature rises, is seasonal temperature rise. Particularly winter temperatures. Winter temperatures could dramatically rise to 42 °F from the average of 36 °F. With winter temperatures increasing, the type of precipitation will change.

Disturbances

Windstorms are the most relevant disturbance regime that impacts the southeast temperate rainforests. Stand-replacing wind storms happen in 100-year intervals and wind throw as a main disturbance will continue to be one of the main disturbances in the coming years. Wind protected areas that support old growth stands will become more prone to wind throw events. Stem decay and other disease agents have smaller impacts on these stands and are to be considered a finer scale and exclusive disturbance. With rising temperatures comes longer growing-season, and is predicted to increase growth rates of these fungi. Combined wind-throw events and fungi disturbances generate concern for persistence of old growth stands throughout the region. Decreasing old growth stands paves the way for an increase of early successional species taking over a greater proportion of area.^[6] One species of tree, yellow-cedar, has already been observably impacted by the changing climate. The main disturbance to yellow-cedar in the northern part of the southeast region is lack or depletion of snow-pack. The yellow-cedar has been dying throughout an area of 200,000 hectares over the last 100 years.^[6] The yellow-cedar's fine root system is susceptible to cold soil temperatures; temperatures below −5 °C are lethal. Snow pack acts as an insulator to the trees root system. Rising temperatures means earlier snow-melt and later freeze-up dates. When insulated by snow, the temperature barrier remains in place and the tree's roots can survive. Onset of early spring freezing episodes will be detrimental to the yellow-cedar population.^[6]

These changing climate factors are predicted to have a substantial influence on the condition of wildlife habitat. With increase in temperatures and a decrease of wetlands and streams raises the likelihood of fire risk, which is a prominent issue concerning the temperate rainforest.^[6]

The major biophysical factor that is prevalent in many areas that contain temperate rainforests is snow and glaciers. The continual warming in this region poses major hydrological changes that may impact the rainforest in the future. These hydrological changes will impact place species distribution and wildlife habitat.^[6]

Wildlife

Climate change effects on the wildlife in temperate rainforests in the southeast region will be influenced by decreasing snow-pack and lengthening of the growing-season. Snow depth impacts foraging and herbivore animals such as blacktailed deer (Odocoileus hemionus), moose, and mountain goat (Oreamnos americanus). Protection by snow-pack is taken advantage of by the northwestern deer mouse (Peromyscus keeni); decreasing snow-pack creates habitat concern for the deermouse. Conversely, less snow for less of time means bigger area of winter range for the blacktailed deer; this would create the availability of high quality foods in spring for the black tailed deer, which would ultimately decrease winter mortality.^[6]

References

• DellaSala, Dominick A. "Just What Are Temperate and Boreal Rainforests?" Temperate and boreal rainforests of the world ecology and conservation. Washington, D.C.: Island Press, 2011. 1–41. Print.
• DellaSala, Dominick A.. "Temperate and Boreal Rainforests of the Pacific Coast of North America". Temperate and boreal rainforests of the world ecology and conservation. Washington, D.C.: Island Press, 2011. 41–81. Print.
• "Juneau Climate Summary". Juneau Climate Summary. N.p., n.d. Web. 10 Nov. 2013.
• Scenarios Network for Alaska and Arctic Planning, University of Alaska [2013]. Impacts of Climate Change on Southeast Alaska
• Wolken, J. M., et al. 2011. "Evidence and implications of recent and projected climate change in Alaska's forest ecosystems". Ecosphere 2(11):124. doi:10.1890/ES11-00288.1