plant species are defined as plants not present in Illinois prior to European
settlement. This includes plants that settlers brought from surrounding
states and Europe.
change the habitat
species have a negative impact on native plant communities. Exotics are
generally aggressive and spread quickly to replace native plant and wildlife
habitat. They thrive well because they have no natural pests or predators
in their new home.
Exotic species can have a dramatic effect on the appearance of a community. After invasion, the original community is changed and degraded. The combination of original species present is changed and the original balance is often difficult to restore, even with the eradicaiton of the invader.
of native species
by non-native plant species often results in the elimination or loss of
native species, both plant and animal, if there is no intervention to stop
rose (Rosa multiflora)
one fifth of plants now growing in Illinois are exotic. They include
trees, shrubs, vines, and herbs. Of these, the shrubs pose the greatest
threat to Illinois forests.
of shrubs introduced to improve wildlife habitat (but took over native
shrubs) are common buckthorn (Rhamnus cathartica), autumn olive
umbellata), amur honeysuckle (Lonicera maackii), and multiflora
rose (Rosa multiflora).
woody shrubs, such as privet (Ligustrum obtusifolium), were introduced
as ornamentals. Japanese honeysuckle (Lonicera japonica), a woody
vine for lawns and gardens, was introduced both as wildlife cover and as
an ornamental. This vine thrives in gaps in the canopy where light enters.
It deforms trees. It can retard the regrowth of a forest by killing young
saplings in a forest opening.
of Heaven (Ailanthus altissima)
weed trees also pose a threat to native species and species diversity.
In Illinois, the most common problem trees are:
alba). It grows rapidly. The leaves are the natural food for silkworms.
The tree was introduced from Japan in a nineteenth century effort to support
silk production in the United States. White mulberry seeds are dispersed
by birds. The plant is drought and disease resistant. It hybridizes with
native red mulberry, and can eventually replace them.
altissima) pictured above. It grows very fast, takes over its site with a thicket of closely growing trees up to 80 feet tall. It produces large amounts of seeds and a toxin that prevents other species of plants from growing in the vicinity.
ginnala). It is an small maple tree with brilliant color in the fall. It was imported from Asia as a garden ornamental, but it produces large clumps of seeds that escape to the wild and result in groves of fast-growing trees if seeds sprout in well-drained soil. As with any exotic, they may replace native species in the wild.
tree (Koelreuteria paniculata). These trees were introduced from
Asia, mostly as ornamentals and for cover. They grow in any kind of soil,
tolerate extreme temperatures, poor drainage, and drought. They produce
seedlings by the thousands, so they are likely to invade natural areas
and replace native species.
all the herbaceous (non-woody) exotics invading Illinois forests, garlic
mustard (Alliaria petiolata) poses the greatest threat. Garlic mustard
invades established forests, produces great amounts of seed and chokes
out the native herbaceous layer.
herbaceous non-native invaders include:
media). It is widespread throughout the state. It spreads by stem rooting where the stem is in contact with the ground and by seeds that land on an open spot on the ground. It grows in a thick mat as large as 50 cm in diameter. It can choke out neighboring plants and increase the conditions that promote fungal disease.
smartweed (Polygonum despotism var. longisetum). It looks like grass when it sprouts, and grows in clumps like grass. It reproduces with seeds and horizontal roots to grow 1 to 3 feet tall. It is a perennial that may live 3 or more years. It spreads to invade other species' habitat.
hederacea L. var. micrantha). It has vining stems that creep
as the plant spreads. It invades quickly.
pests are also more likely to have a bigger impact in smaller, fragmented
forests. These insect pests include:
growth forests often include non-native trees, which in turn provide habitat
for non-native insects associated with those trees and are potentially
damaging to the native vegetation.
moth (Lymantria dispar), which feeds on a variety of trees, especially
the European elm bark beetle, which harbored the fungus that wiped out elm forests in the 1950s.