How much damage does invasive plants do to the enviroment?

Question

How much damage does invasive plants to to the enviroment?
What kind?

Answer 1

They can be devastating...the worst case is Caulerpa, a green alga that has wiped out much of the biodiversity and productivity of the Mediterranean.

Answer 2

A general answer:
Invasives are a subdivision of Exotics: plants not native to a given area. Invasives outcompete native vegetation for habitat. This is "bad" for the native habitat- because it won't be there anymore.
Generally, invasives do quite a bit of damage.

Answer 3

Chinese Tallow trees in the U.S. have spread rampantly in the east and south. They sprout up in grasslands transforming them into forests. The grassland animals have to move or die. Not all animals can adapt to a change like that in their habitat. Tallows are fast growing and relatively short lived comparatively speaking. If a young oak is growing next to a tallow the same height, the tallow will soon out grow the native oak eventually shading it and possibly causing it to die from not enough sunlight. Tallows live maybe 25-30 years where some oaks can live well over 100 years.

Answer 4

Kudzu was introduced as an ornamental plant in the American South but it has since run rampant. It grows very fast and chokes out native species.