|Fragmentation means the breaking up of something into small, separated pieces. Over the last 200 years, Illinois forests became increasingly fragmented. Initially, settlers cleared the forest to create farms and harvest timber. Currently, new suburbs with housing developments and roads are splitting forests into ever smaller patches.
seventy per cent of all forest parcels in Illinois are between 40 and 200
acres in size, and the majority of remaining high
quality forests in Illinois are less than one hundred acres in size.
versus interior habitat
fragmentation decreases plant and animal diversity.
A small, fragmented forest parcel has a larger proportion of edge habitat
for its size than a larger forest.
of animals favor this area between two habitats, called edge habitat,
there are many species of forest animals, birds in particular, that require
larger, uniform blocks of land in order to breed and raise young successfully.
These animals are called "area-sensitive" species.
species need larger habitats
of this fragmentation is clearer when you consider the fact that many birds
that live deep within forests require up to 600 acres to thrive as a population.
Two of these species are the Ovenbird (Seiurus aurocapillus) and
Acadian Flycatcher (Empidonax virescens). The number of these species
has decreased because many of the forests fragments are too small for them.
species take their place
in edge habitat and a decrease of unbroken blocks of forest result in increases
in populations of species like deer and Brown-headed Cowbirds (Molothrus
||Edge habitat at Star Grove, Midewin Nation Tallgrass Prairie
Brown-headed Cowbirds take over the nests of native songbirds such
as the Ovenbird (Seiurus aurocapillus) (popup window with image)
reducing their ability to raise their young successfully.
Increased deer populations can damage the vegetation and structure of the forest. The quality of the habitat is reduced, leading to a decrease in the diversity (number of different types) of animals and plants that live there.
fragmentation also results in smaller, more isolated populations of plants
and animals. There are fewer corridors of forest connecting forest fragments.
When a population of an animal species is isolated in a small forest fragment,
unfortunate situations can occur.
It is difficult
for them to expand their habitat as they grow in number because the next
fragment is far away or unsuitable.
in this small group can only breed amongst themselves. The gene pool may
have or may develop weaknesses such as susceptibility to a disease or physical
weaknesses. The whole group could be more easily wiped out than a group
with a mixed gene pool.
If a flood
or fire disturbed this small habitat or eliminated it, the isolated group
would be less likely to survive than if they had a larger habitat or a
place to which to escape.