Most remain in limited populations in their new environment but occasionally a species thrives too well, wreaking havoc on the native ecosystem.
Ecosystems are complex associations of organisms that have evolved together over time.
There are numerous checks and balances on each individual species in its natural environment. When that happens, it can change a native ecosystem forever. These noxious weeds are aggressive and can damage natural areas in a number of ways. Some simply outcompete native plants for nutrients, water, or light. Others actually change ecosystem processes such as nutrient cycling, hydrology, wildfire cycles, and in some cases by interbreeding with native plants.