Forests and Health 179
Forests prevent erosion and reduce flooding
By adding leaves to the soil, providing shade for plants that grow beneath
the trees, and holding soil in place with their roots, trees prevent erosion and
reduce flooding. They slow rainwater and spread it across the ground, so it will
sink into the soil rather than run off.
When forests are cleared, soil washes into rivers
and streams. When storms come, the soil is no
longer able to absorb and hold the rainwater.
Instead, the water flows faster across the land,
causing floods. Keeping trees and forests
standing is an important way to
protect the natural flow of water
through the watershed. (For an
activity that shows what rain does
to bare soil, see page 289.)
Forest diversity and health
In a forest, it is easy to see
the web of life (see page 27)
because a healthy forest
contains many different
kinds of plants and animals.
This diversity of life protects
people’s health in many ways.
Bees and other insects that live
in trees pollinate crops so they
flower and produce fruit. Wasps
and ants eat insects that attack
crops. Bats and birds eat mosquitoes
that spread malaria, yellow fever, and
other diseases. Other forest animals keep
rats, fleas, flies, and ticks under control by
hunting them or competing with them, and
prevent them from spreading disease.
When human settlements are built in or close
to degraded forests, the number and variety of
animals are reduced because their sources of shelter
and food become less plentiful and less diverse.
Also, the animals that remain are forced to live in
closer contact with people. This leads to a greater
possibility that animal diseases will be passed to
people. By maintaining enough forest to support a
variety of plants and animals, we protect human health.
A Community Guide to Environmental Health 2012