supposed to be healthy for plants and trees. It provides them with water, which is essential for their growth. So why is some rain killing and
damaging the forests? Because the raindrops contain sulfuric, nitric and other acids. These acids originate in sources such as gasoline
and diesel used in cars, fossil-fuel-fired electric power plants, industrial boilers, and residential furnaces. When high concentrations of
acidic compounds from such sources mix with atmospheric moisture, they create acids which are deposited in precipitation. This process
creates acid rain.
Above: Traffic is one of the leading causes of air pollution. Below: Large cities build up concentrations
of air pollution, and surrounding areas experience poorer air quality, a fact which affects both people and forests. Photo credit Corel Photo Clipart CD.
Acid rain harms forests in several ways. One
detrimental effect of the rain is that the leaves are damaged. For example, the wax on the leaves is worn away, making them less
resistant to more rain and insects. The leaves also lose nutrients, leading to the eventual demise of the tree. Furthermore, the fallen
leaves do not decompose as quickly because acid rain causes many organisms living in the soil to have diminished respiration rates.
This in turn increases the ammonia in the soil because the nutrients that are usually released in decomposition are not being made.
Emissions from industry, plus those from vehicles, are the largest sources of air pollution. Photo credit Corel Photo Clipart CD.
This decrease of nutrients prevents the forest
from growing. Acid rain also stifles new growth and kills many of the seedlings. Another effect from acid rain is that the tree's growth is
decreased because the microorganisms that live near it die. Acid rain also causes physical damage to the roots, decreasing the rate of
growth and eventually leading to the death of the tree. Acid causes the pH level in the soil to fall and when it reaches 4.0, aluminum and other
metals are leached out of the soil. The aluminum is filtered through the roots, damaging them, and causing the tree's death.
By the time industrial gases fall on the forests,
the rain they come down in may be ten or twenty times as acidic as normal (pre-industrial) rain. But the problem doesn't end there.
The soil, and lakes and ponds also become acidic. Toxic heavy metals--cadmium, lead, zinc, etc.-- and other substances
show up in the soil.
Serious acid rain problems have been caused
by industrial emissions in parts of the East and Northeast of the United States, and eastern Canada, as well as Eastern Europe.
Sometimes these emissions come from far away, carried on prevailing winds. And in their movements through the atmosphere they can
be altered by ultraviolet light and contact with other chemical compounds.
In Germany, the name "Waldsterben" (forest
death) has been given to the effects of atmospheric pollution that has killed stands of Norway spruce, fir, and European beech. The
so-called "Black Triangle", an industrial area between Dresden, Germany, and Wroclaw, Poland and Prague, Czech Republic has
experienced such severe acid rain that the soils can no longer grow forests.
Pollution affects different forests in different ways. Some are so severely damaged that many or
all of the trees begin to die. Some of these forests that have suffered major declines due to pollution are described here.
find out more...
The United States and 24 other nations have agreed
to keep the nitrogen oxide emission levels at 1987 rates as a part of the Long-Range Transboundary Air Pollution Agreement. The Clear
Air Act was intended to cut in half sulfur dioxide emissions from power plants by the year 2000.
Alternative forms of transportation can be used by more people at once, and therefore create far less air pollution than cars. Photo credit Corel Photo Clipart CD.
In cars, catalytic converters are used to lessen
the emissions of harmful exhaust. Pollutants from factories and such are caught in filters or changed into less dangerous liquid or solid
of pollution kill the animals in the forest, and when even one important predator or prey species disappears, the entire ecosystem can
disintegrate. Almost 40% of the endangered freshwater fishes in North America are at risk because of water pollution. Much of that water
pollution has come from pulp mills, where wood chips are manufactured into pulp and paper products. The toxic organochlorine
compounds ruin fish habitat. Often, pollutants collect in increasing quantities over time, and have long-lasting effects that at first go
unnoticed. By the time chemicals are determined to be the cause of plant and animal deaths, it is often too late to prevent more damage.
Once an area is contaminated with pollutants, it is very difficult to clean it up.
often sprayed on newly cleared and replanted areas, to keep down the growth of brush and help keep insects from eating new trees.
However, no one knows what the long-term effects will be of spraying these pesticides on forest soils.
Beneficial insects and even essential
micro-organisms within the soil are undoubtedly also harmed. However, very little is known about the actual effects on these unseen
creatures, and there is not enough evidence to convince many people that the pesticides may seriously damage forest ecosystems.
When chemical pesticides kill too many insect
predators, the insects they feed on suddenly experience a population explosion. In these unnaturally large numbers, any species can
become a pest; the pesticides have effectively created a new pest where there were previously only harmless insects.
are then brought in to control these new pests. The large amounts of pesticides now in the environment mean that some species are beginning
to become resistant to them, and still more pesticides are needed to combat these creatures.
In a short-term economic view,
pesticides still save money and for this reason have more benefits than drawbacks. However, the drawbacks include such a serious
potential impact on all forest life, and on top of this are often a danger to human health, that we may not continue to depend on them as
much as we do now.
[water] [roots & leaves] [soil] [fungi] [insects] [climate] [forest types] [forest life] [fish] [riparian zones] [wood & forest products] [pests] [forests through time]
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