Invasive Species

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There are many benefits to planting natives in the garden. Native plant species co-evolved with native animal life, especially insects. Insects and other invertebrates feed on native plants, and in turn, provide food sources for other animals in the food web of Piedmont and Sandhills ecosystems. But what about all of the non-native plants in our landscapes?

Non-native plant species are called exotic species. Their natural range originated outside of the southeast United States. Many exotic species come from temperate Eurasia, which has a climate and ecosystems most similar to our own. Hostas (Hosta spp.) and crape myrtles (Lagerstroemia spp.) for example, are originally from Asia but have been cultivated and selectively bred in Europe and North America for many decades. An exotic species becomes naturalized when it has become established outside its native range (i.e. not deliberately planted by humans). Chickweed and white clover are common naturalized exotics but are not considered invasive species.

A species becomes invasive if it outcompetes and displaces native species, causing ecological and economic damage. By displacing natives, invasive species can disrupt local ecosystems by interfering in the food web, representing a major threat to biodiversity. Invasive plants cause an estimated $35 billion in damage annually, affecting agriculture, forestry, and personal property.

There are several features that contribute to an exotic species becoming invasive. Invasives are well adapted to our local climate and environment. Their native ranges tend to have similar temperature extremes, precipitation levels, and seasonal cycles. Invasive plants also lack natural enemies in their new environment, meaning there are not the pathogens, pests, and herbivores that normally keep populations in check in their home range. Exotic species that have a rapid life cycle, produce copious seeds, and/or spread vegetatively by stolons or rhizomes are more like to become invasive. Kudzu (Pueraria spp.), an invasive leguminous vine native to Japan, has become common in disturbed sites in the southeast thanks in part to its ability to spread rapidly by stolons.

Currently, the most notorious and troublesome invasive agricultural weed in the southeast, especially for vegetable growers, is Palmer’s amaranth (Amaranthus palmeri). A relative of beet, spinach, and quinoa, Palmer’s amaranth is capable of producing one hundred thousand to one million tiny, easily dispersed seeds per plant, tolerates a variety of soils, is drought resistant, and can grow three inches in a day! Its rapid growth and fecundity also means it can evolve quickly: Palmer’s amaranth is now resistant to several classes of herbicides.

Some invasive species were introduced accidentally by global shipping and trade, but many were introduced intentionally before we understood their negative ecological affects. In fact, you may have several invasive species already in your landscape already. Chinese privet (Ligustrum sinense) is a large evergreen shrub that was widely planted for hedges. It escaped the home landscape thanks to bird dispersal, and has since become a major problem in moist bottomland forests and streamsides, forming dense thickets that shade out most native herbaceous understory species. English ivy (Hedera helix) is a popular ground cover and ornamental vine, especially in the Piedmont, where it has likewise outcompeted and displaced native wildflowers. Other common invasive species found in the home landscape include, mimosa (Albizia julibrissin), Japanese (Wisteria floribunda) and Chinese wisteria (W. sinensis), Japanese honeysuckle (Lonicera japonica), and multiflora rose (Rosa multiflora). Nandina domestica is a shrub commonly found in suburban border plantings. Fruiting varieties have the potential to become invasive, so avoid Nandina unless you are planting a dwarf variety that does not produce fruit.

For a complete list of invasive plant species in North Carolina, visit the NC Invasive Plant Council website, or contact your local N.C. Cooperative Extension Center. We can help you identify invasives and give recommendations for their control and removal. The NC State Extension’s Wildlife Friendly Landscape website also has an extensive list of common invasive plants and suggested alternative native species that perform similar functions in the landscape and support local wildlife.

Matt Jones is Horticulture Agent with North Carolina Cooperative Extension in Chatham County.