Long-term effects on forests

These are but a few examples of the invasive species that have affected the United States’ forest ecosystems. As world trade intensifies, scientists predict that more and more tree diseases, pests, and weed plants will find their way into this country. Fast-moving and usually hard or impossible to cure or eradicate, these exotic species have destroyed countless trees in forests, cities and suburbs. The results can be seen not only in landscapes stripped of some of their most beautiful species but in changes to how forest ecosystems work and in the economic value of this natural resource. (33)

Invading species can alter a variety of forest ecosystem properties such as productivity, nutrient cycling, natural disturbance regimes, and soil and vegetation structure. Nitrogen-fixing invaders can change soil chemistry, fire-prone exotics can change fire regimes, and deep-rooting invasive species can lower water tables in ecosystems (7). Scientists say one lesson that has come from invasive infestations and blights is the importance of diversity, particularly in planted landscapes. Monocultures (such as elms or pine plantations or monocrop agriculture) are particularly ripe for epidemic destruction by an invasive species. (33) Loss of native plant biodiversity also can lead to changes in the physical structure of the ecosystem and a reduction in habitat available to native bird and insect species. (34)

Cures on a forestwide scale are, in general, impossible. Curbing the spread of pathogens is difficult, as many travel as tiny wind-borne or water-borne spores or on insects flying from tree to tree. (33) Weedy plants often have huge rooting systems and prolific seed production; herbicide applications will eliminate native forest species as well. Insects are prolific reproducers and can move quickly through the landscape, so pesticide use is many times fruitless and like herbicides, can harm native species instead of the target invasive.

"I get concerned about what the forests of the future will look like," said Dr. Craig G. Lorimer, a forest ecologist at the University of Wisconsin. "To have so many diseases cause so many problems over such a short period of time is really unprecedented. You get this impression that clear-cutting is the most devastating thing… and it's not. This is much more serious." (33)



	Long-term effects on forests

Home Overview of Invasives Case studies in US forest ecosystems Insects BWA Gypsy moth Plants Tree of heaven Kudzu Pathogens Chestnut blight Dutch elm disease Long-term effects on forests Conclusions References Useful links	These are but a few examples of the invasive species that have affected the United States’ forest ecosystems. As world trade intensifies, scientists predict that more and more tree diseases, pests, and weed plants will find their way into this country. Fast-moving and usually hard or impossible to cure or eradicate, these exotic species have destroyed countless trees in forests, cities and suburbs. The results can be seen not only in landscapes stripped of some of their most beautiful species but in changes to how forest ecosystems work and in the economic value of this natural resource. (33) Invading species can alter a variety of forest ecosystem properties such as productivity, nutrient cycling, natural disturbance regimes, and soil and vegetation structure. Nitrogen-fixing invaders can change soil chemistry, fire-prone exotics can change fire regimes, and deep-rooting invasive species can lower water tables in ecosystems (7). Scientists say one lesson that has come from invasive infestations and blights is the importance of diversity, particularly in planted landscapes. Monocultures (such as elms or pine plantations or monocrop agriculture) are particularly ripe for epidemic destruction by an invasive species. (33) Loss of native plant biodiversity also can lead to changes in the physical structure of the ecosystem and a reduction in habitat available to native bird and insect species. (34) Cures on a forestwide scale are, in general, impossible. Curbing the spread of pathogens is difficult, as many travel as tiny wind-borne or water-borne spores or on insects flying from tree to tree. (33) Weedy plants often have huge rooting systems and prolific seed production; herbicide applications will eliminate native forest species as well. Insects are prolific reproducers and can move quickly through the landscape, so pesticide use is many times fruitless and like herbicides, can harm native species instead of the target invasive. "I get concerned about what the forests of the future will look like," said Dr. Craig G. Lorimer, a forest ecologist at the University of Wisconsin. "To have so many diseases cause so many problems over such a short period of time is really unprecedented. You get this impression that clear-cutting is the most devastating thing… and it's not. This is much more serious." (33)