Native plants are frequently defined as “those plant species present at the time of colonization by Europeans”.
Others like the Audubon Society go further and define “native plants as those that occur naturally in a region in which they evolved. They are the ecological basis upon which life depends, including birds and people. Without them and the insects that co-evolved with them, local birds cannot survive. For example, research by the entomologist Doug Tallamy has shown that native oak trees support over 500 species of caterpillars whereas ginkgos, a commonly planted landscape tree from Asia, host only 5 species of caterpillars. When it takes over 6,000 caterpillars to raise one brood of chickadees, that is a significant difference.
Unfortunately, most of the landscaping plants available in nurseries are alien species from other countries. These exotic plants not only sever the food web, but many have become invasive pests, outcompeting native species and degrading habitat in remaining natural areas.
Landscaping choices have meaningful effects on the populations of birds and the insects they need to survive. The bottom line is this—homeowners, landscapers, and local policy makers can benefit birds and other wildlife by simply selecting native plants when making their landscaping decisions.”