While some of us value plants in our landscapes primarily for the beauty they provide, we may not realize that plants are in fact critically important components of food webs and essential to the life cycles of birds and insects.
Author Doug Tallamy explains, “almost all North American birds other than seabirds – 96 percent – feed their young with insects.” These insects require host plants on which to lay their eggs, plants with which they have evolved over millennia.
Replacing native plants (those species that have evolved with surrounding plants and animals, each influencing the evolution of the other) with species from other places can hinder the ability of some of these insects to reproduce. One example can be seen in a comparison of the flowering dogwood (Cornus florida), which is native to Orange County, and the kousa dogwood (Cornus kousa), which is native to Korea, China, and Japan. The flowering dogwood supports 117 species of moth and butterfly larvae, while the kousa dogwood supports none.
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Some gardeners point out that they also frequently observe insects on their non-native plants. For instance, butterflies can often be seen drinking nectar from the flowers of the non-native butterfly bush (Buddleia davidii). While this may be beneficial food for the butterflies, unfortunately no species of butterfly native to North Carolina will use the butterfly bush as a host plant on which to lay its eggs. Better choices to provide breeding support for butterflies include oak-leaf hydrangea (Hydrangea quercifolia), redbud (Cercis canadensis), and fringe-tree (Chionanthus virginicus), to name a few.
Unfortunately no species of butterfly native to North Carolina will use the butterfly bush as a host plant on which to lay its eggs.
Native plants are also important to our economy. Insects pollinate many of the foods we enjoy eating. As of 2009, pollination of U.S. crops by native insects was valued at more than nine billion dollars.
Some individual species, such as the monarch butterfly, have an estimated economic value in the billions of dollars. These insects will cease to exist without the correct host plants on which to lay their eggs. In fact, researchers estimate that the monarch butterfly population has declined by 80 percent over the past 21 years. The decline is attributed in large part to the disappearance of the milkweed plants on which the species relies, resulting in the U.S. Fish and Wildlife Service considering the monarch butterfly for protection under the Endangered Species Act (ESA).
In contrast to the high economic value of natives, many non-native species can be economically and environmentally devastating; such species are categorized as invasive by the federal government. They include English ivy, Japanese honeysuckle, autumn olive, tree of heaven, and multiflora rose. Nearly half of the species listed for protection under the ESA are in trouble due at least in part to invasive species.
Far from the economic good of natives, invasive species are estimated to cost the U.S. more than 120 billion dollars in damages annually. It can take decades to determine that a species is invasive, and such a finding does not automatically lead states to ban the sale of the species.
While not all non-native plants are invasive or damaging to the environment, it is wise to understand whether a plant is invasive or in some way damaging to pollinators. In addition, it would certainly be good to avoid planting non-natives on a broad scale.
A number of resources exist to help residents figure out which native plants will thrive in your yard or garden. The N.C. Botanical Garden (http://ncbg.unc.edu/) offers plant lists, classes, tours, family and youth programs, and knowledgeable people to help you in your hunt (not to mention a beautiful garden to stroll through to see spectacular natives year-round). In addition, from June to Oct. 3, the Botanical Garden is offering workshops, exhibits, talks and tours that highlight the importance of pollinators and what can be done to help secure a stable future for them.
Plant lists and local nurseries that specialize in species native to our region can also be found through the North Carolina Native Plant Society (http://www.ncwildflower.org/).
About the series
This is the latest in an occasional series of articles by the Orange County Commission for the Environment. Each article highlights an environmental issue of interest to the residents of Orange County. The commission is a volunteer advisory board to the Board of County Commissioners. Additional information can be found in the Orange County State of the Environment 2014 report at bit.ly/1mTE5K2