There are several impacts expected to occur in forested areas due to global warming, including increased timber production in some areas; regional variability; changes in nontimber production; impacts with fire, insects, and extreme events; changes in forest health; social and economic impacts; and changes in biodiversity.
According to the IPCC, current modeling efforts show that climate change will increase global timber production if there is an increase in forest growth as a result of higher CO2 concentrations in the atmosphere, as well as a northward expansion of forest habitat in the Northern Hemisphere as temperatures warm and ecosystems migrate poleward. Economists in the United States do not predict a significant economic impact to forestry as a result of this poleward shift of forests due to the larger reserves of existing forests, technological change in the timber industry, and the ability to adapt in the United States.
Although the IPCC does predict an overall increase in timber production, they do caution that there will be regional variability due to local factors such as precipitation, temperature, humidity, soil type, and severe weather events. In California, for example, they project that initially (around 2020) climate change will increase harvests by causing an increased growth; but by 2100 there will be reductions in areas of softwood growth. They also predict there will be substantial negative impacts to other products from forests, such as seeds, nuts, resins, plants used in pharmaceutical and botanical medicine, cosmetics, and hunting resources.
The IPCC has also identified the need to further evaluate, revise, and fine-tune climate models and their predictions for forests, specifically the effect of CO2 on tree growth. Some scientists think that projections of future tree growth may be overestimated in forest growth models. In one model devised by Richard J. Norby of the Environmental Sciences Division at the Oak Ridge National Laboratory, a 550 ppm CO2 was used in the model, which yielded a net increase in productivity of 23 percent in young tree stands; but when this model was compared to an actual 100-year stand, there was not that much growth evident, suggesting the model greatly overestimated the accelerated growth effect of CO2. Some scientists with the IPCC have suggested that other factors may also play roles that have not been accounted for in the model, such as land disturbances, air pollutants, and nutrient limitations.
Other identified limitations with current models include a need to include key ecological processes. What are needed are Dynamic Global Vegetation Models (DGVMs) to enable better predictions of climate-induced vegetative changes by simulating forest biomass, composition of species types, water and nutrient cycling, and the effects of wildfires.
Current models today indicate that increased temperatures and longer growing seasons will increase both aridity and additional fire risk. Models for the United States have predicted a 10 percent increase in the severity of fire. Other models, using a three-times greater increase in CO2, project a 74 to 118 percent increase in area burned in Canada by the end of the 21st century.
In many forests, one of the most pressing issues is forest health. Even today, due to warmer temperatures, many forests in the western United States have experienced great infestations of bark beetle that have killed off thousands of acres of previously healthy forest. As global warming continues to intensify, pest and disease outbreaks will continue to be major sources of natural disturbance.
According to the IPCC, the effects will range from defoliation and growth loss to timber damage to massive forest diebacks. Climate change will shift current boundaries of insects and pathogens and also modify tree physiology and tree defense. This is one area that still needs improvement in modeling.
Other potential impacts to forests identified by the IPCC that will vary on a region-by-region basis include reduced access to forest land; increased costs for road and facility maintenance; damage to trees by wind, snow, frost, and ice; higher risks of wildfires and insect outbreaks; and the negative economic effects of wetter winters and earlier thaws to the logging industry.
Another way models need to be improved is by being able to portray the interactions among these multiple disturbances. As one impact occurs, it weakens the forest and increases its vulnerability so it is then even more susceptible to damage from other impacts. For instance, if strong winds damage trees by breaking branches, crowns, and trunks, it leaves the stand more vulnerable to damage from insect outbreaks and wildfires. In other cases, such as in the southwestern United States, prolonged drought increases species mortality, leaving these areas prone to insect and pathogen damage and wildfires. The Amazon is another
Wildfire is one of the projected negative impacts to forests as global warming continues. (BLM)
area where this is a major potential problem. Current deforestation, forest fragmentation, wildfire, and increased drought episodes make this region vulnerable to even more massive deforestation if the climate becomes warmer and drier.
According to data from the IPCC, social and economic impacts through the relocation of forest economic activity (as forests migrate) will affect businesses, landowners, workers, consumers, governments, and tourism. Areas where production increases will receive benefits; areas where there are decreases will have negative impacts. In areas where wood prices decrease, consumers will benefit while producers will suffer losses.
According to the FAO, people who will lose the most as far as forest resources are concerned are those who live in extreme poverty in developing countries and depend on forest resources for their livelihood, approximately 1,080,000,000 people. For these people, their income is tied directly to not only wood products but also to nontimber forest products as well, such as fuel, forest foods (nuts, fruits), and medicinal plants. Because forests also provide for the health needs of about 80 percent of the population, a health-related crisis threatens these communities. When a medicine man dies in the rain forest, it is like losing thousands of years worth of knowledge about the medicinal qualities of the plants in the rain forest.
Forest biodiversity will also be affected by global warming. Worldwide, there are potentially from 30 to 80 million species of plants and animals. The tropical rain forests, which cover only 7 percent of the Earth's landmass, provide habitat for more than half of them. Currently, only about 1.5 million species have been identified and named, leaving an enormous amount of life-forms still waiting to be discovered and studied. Many of these species are so specialized that they exist in very small, isolated ecosystems. This fact makes them extremely vulnerable to extinction in light of deforestation; if their habitat is cut down, they are eliminated. According to N. E. Stork of the Rainforest Action Network, up to 137 species are disappearing worldwide per day.
This represents not only an alarming loss of biodiversity, but also a potential source of medicine that could ultimately end up being a cure for life-threatening diseases such as cancer, AIDS, or many other serious diseases. Within the ecosystem itself, many organisms are losing species that they depend on, which means they also face extinction within the ecosystem, potentially causing a far-reaching ripple effect as food chains and biomes disintegrate.
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