Air pollution can affect woodlands in a number of different ways
- Acid Deposition
Rainwater is naturally acidic due to dissolved CO2, but man-made emissions (usually Sulphur and Nitrogen dioxides from combustion) can increase this to a point where it becomes harmful to growing plants. Emission control measures have reduced the prevalence of SO2 and NO2 significantly over recent years. Most of the SO2 and NO2 produced in Britain comes from power stations and large industrial units, but cars and heavy vehicles are also important sources of the oxides of nitrogen. Forest Research has a page which explains in more detail here.
Trees can be an effective barrier to particulate emissions from industry and busy roads. However, these particulate deposits can cause damage to woodlands in a number of ways:soil quality can be affected if the particulates contain heavy metals or other compounds poisonous to plants;
particles can clog leaf pores leading to reduced photosynthetic ability;
in extreme cases, particles can coat the leaf surface causing abrasions and reducing the leaf’s light capturing ability. Further information on air pollution is available from Forest Research here.
- Low Level Ozone
Ozone (O3) at high altitude is an important component of the atmosphere, absorbing harmful UV radiation from the sun. However, it can also be formed as a result of incomplete combustion of hydrocarbon fuels. At low altitude Ozone is a serious contributory factor to smog and can cause irritation to eyes and lungs in humans. Low Level Ozone also causes “scorching” to vegetation and can lead to premature leaf loss. Further information on air pollution is available from Forest Research here.
Soil and Groundwater Pollution
Contamination of the soil can lead to damage to tree roots and a range of impacts on plant health. It is rare to find serious soil contamination in established woodlands, but new woodlands and regenerated brownfield sites may encounter problems. Woodlands which are adjacent to sources of pollution, such as landfill sites, may become affected due to the movement of contaminants in ground and surface water. If you have concerns about an area of woodland, we recommend contacting Forest Research for more detailed advice. Some specific issues can include:
- Spray Drift
Salt spray from the sea and gritted roads can cause a decrease in soil fertility and harm vegetation as can drift from herbicide application on neighbouring land.
- Heavy Metals
Research has shown that trees can be effective in absorbing heavy metal elements from the soil, and there is considerable interest in this property for site remediation. You should bear in mind though, that these heavy metals will be present in the wood ash after burning, and make sure that it is disposed of safely (rather than contaminating other sites with the same problem.)
- Organic Pollutants
Some trees species are also effective at removing organic contaminants from the soil (such as solvents, petrochemicals, wood preservatives, explosives and pesticides) the organic components of these contaminants will be completely destroyed by burning, but a heavy metal component may remain in the ash if present.