Why are native, rather than exotic, plants so essential for our environment?
Native plants are essential because they support specialization – relationships in nature that have been established over tens of thousands to millions of years. For example, caterpillars of Monarch butterflies specialize on milkweed. No milkweed, no Monarchs. There are more than 150 species of butterflies in Southern California; the caterpillars of most of the species specialize on native plants. (Footnote 3)
Scientists know that, in nature, specialization is the rule. Specialization is illustrated by the fact that up to 90% of leaf-eating insect species (such as caterpillars of butterflies) can eat only native plants. (Footnote 2) These insects turn leaf matter into protein and feed the food web. There are about 10% of leaf-eating insect species that are generalists and can eat exotic plants, but planting exotics eliminates habitat for the 90% and makes places virtually sterile but for a handful of generalist species. Native plants are essential for biodiversity because of the specialized relationships between plants, insects and animals that have developed over time.
In North America, 96% of terrestrial bird species rear their young on insects – mostly caterpillars. No native plants = virtually no insects = virtually no baby birds. 430 species of North American birds are at risk of extinction (State of the Birds, 2016), and there are 50% fewer song birds today than 40 years ago, mainly due to loss of habitat. (Footnote 5) Birds need native plants for the insects they support, the shelter and nesting material they provide, and the seeds, nuts, fruits or berries they produce.
The relationship between native plant habitat and support for birds holds true for terrestrial food webs in general. In California, for example, native oaks support more than 5,000 species of beneficial insects and animals. (Footnote 6) The non-native ginkgo supports only four species. In our urban and suburban areas, we support healthy food webs and functioning ecosystems by landscaping with native plants.