Honeysuckle is killing forests and ivy is helping, especially in the northeast/midwest. Kill all that shit, help stop it from spreading. And try to volunteer for local groups that are clearing invasive species. It's pretty amazing seeing a forest before and after invasive species have been removed.
In the Southwestern US tamarisk trees are a huge problem, they spread really fast along rivers and streams and their leaves have a lot of salt in them and shed constantly so they choke out native plant species. When I was a kid I used to play in the river a lot and I can remember tamarisk trees were the only thing that grew there, any other type of tree or plant was pretty much nonexistent. Luckily though there is a species of beetle that feeds on tamarisk and nothing else, they were brought in a few years ago to control the tamarisk population and they seem to be helping a ton. They cleared out all the dead tamarisk trees and now the riverbanks are filled with cottonwoods, willows, and reeds, it's really nice to see.