The plants and animals that naturally exist in a place evolved together, adapted together and coexist for mutual benefit. Birds, insects and other animals help pollinate plants and distribute seeds. Plants provide food and shelter for the animals.

When you start adding exotic or nonnative species, or subtracting native species, you disrupt the balance. Native creatures may not be able to get nourishment from nonnative plants, and indigenous plants may not be able to compete with invasive alien plants.
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The native plant society strongly recommends physical methods for getting rid of plants, as opposed to using herbicides. But where plant stands are large or hard to control by clipping or pulling, chemicals may well be the last resort.