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Impacts of air pollution on forest ecosystems

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  1. Introduction.
  2. Subarctic boreal forests.
    1. Air pollution causes.
    2. Air pollution concerns.
    3. Air pollution effect.
  3. Wet tropics.
    1. Air pollution causes.
    2. Air pollution concerns.
    3. Air pollution effects.
  4. Semiarid forests.
    1. Air pollution causes.
    2. Air pollution concerns.
    3. Air pollution effects.
  5. Temperate forests.
    1. Air pollution causes.
    2. Air pollution concerns.
    3. Air pollution effects.
  6. Conclusion.

Air pollution problems are international in scale. All forests worldwide experience some degree of air pollution exposure above preindustrial levels. Atmospheric transport processes do not recognize geographic borders, but sources of pollutants, the pollutants of concern, and the speci?c effects of pollutants vary greatly depending on human cultural activities and natural climate patterns. For example, heavy-metal contamination is a result of poorly controlled mining and industrial emissions; when coupled with frequent rainfall, dispersion is minimized and local deposition is maximized. Deposition of suspended particles is most frequently a problem in forests in dry climates adjacent to agricultural areas where atmospheric conditions allow suspended particles to remain airborne for long periods of time. Ozone is a secondary pollutant formed from auto- mobile exhaust (nitrogen oxides) and volatile organic carbon from a variety of chemical, combustion, and natural processes. The reaction requires ample sunlight, thus ozone is a serious problem in urbanized areas in sunny climates. Air pollution effects on forests can, therefore, best be understood by looking at climate zone and the human cultural activities of agriculture, urbanization, and industrialization. Although there are many natural sources of air pollutants, such as vegetation ?res, windstorms, and volcanic eruptions, for the purposes of this article we shall focus on human caused or anthropogenic, sources of air pollutants and their effects on forest ecosystems.

[...] Air pollution effects Clearly, burning to remove vegetation alters the immediate landscape but the effects of smoke on ecosystems downwind have only recently been addressed. The huge ?res in Southeast Asia during the late 1990s and the annual burning of the cerrado grasslands in central Brazil offer examples of intentional and unintentional ?re effects on native forests. Serious increases in tropospheric ozone have been documented as a result of cerrado ?res. Concentrations measured are equivalent to those measured outside large urban centers (100?200 ppb). [...]

[...] Air pollution effects Ozone effects on semiarid forests are well documented in the Mediterranean climates of south-western North America, southern Spain, and Italy. Short- term exposures to ozone concentrations greater than 150 ppb can cause acute damage symptoms on many plant species. Long-term, chronic exposures to 50 ppb result in reduced growth of sensitive species and foliar mottling of many forest tree species. The primary sites of uptake and injury are the stomata of actively photosynthesizing leaves. When the stomata are open for gas exchange, ozone readily gains access to the stomatal cavity and mesophyll of foliage. [...]

[...] However, in the last several decades, many nations have recognized the serious effects of air pollution on forests and have taken steps to reduce or eliminate many of the pollutants through legislation and technology. Reduction in sulfur emission in the industrialized mid-west and northeastern parts of North America has resulted in measurable reductions in ambient concentrations and deposition to adjacent forests. Improved metal-smelting technologies have greatly curtailed atmospheric deposition of heavy metals in Canada, Europe, and parts of Asia. Improvements in energy production ef?ciency for heating, cooking, and transportation have reduced urban smoke emissions when compared to the air quality at the turn of the century. [...]

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