Las Cruces, New Mexico
In Northeast swamp forests, introduced pathogens have eliminated the American elm.
In Hawaii, there has been a strawberry guava invasion. Dr. Huenneke began with two hypotheses: Is establishment of the vigorous invasion by this plant the result of soil disturbance caused by feral pigs? Is establishment by seed, dependent on processing by animals? The answers to both questions turned out to be no.
A number of other factors turned out to be relevant. Natives can't survive being covered by plant litter while nonnatives can survive under litter for years and then send up a shoot through the layer and establish themselves. Breakage is another factor; 27% of natives break and just half of these survive, compared to a 98% survival rate by nonnatives.
In New Mexico, grasses were altered by cows and the vegetation is now much like that of the deserts further south. Invasion of mesquite is accompanied by degradation of soil, formation of dunes, and massive disturbance, but does not seem to be accompanied by pervasive invasions.
There is a native thistle which has hybridized with invader thistle species. The Forest Service is now considering listing this native thistle as a noxious weed. The evolution of weedy behavior in this native thistle is a result of its hybridization with the nonnative varieties. Human impacts may have contributed to the development of this behavior.