Native, introduced, and invasive species

Heather N. Kolich, ANR Agent, UGA Extension Forsyth County

A walk through our local parks, state forests, and even our own backyard reveals a rich mixture of plants and wildlife. Typically, some will be native species and others are specimens imported from foreign regions. Is one type better than the other?

In certain circumstances, both native and introduced species can become invasive. In a stable ecosystem, native species exist in balance. Activities that disturb land, such as fire, cultivation, or development, break the balance. Both native and introduced plants take advantage of disturbed lands to proliferate. If a plant, animal, fish, or disease-causing pathogen produces economic, environmental, or human health harm, it is classified as invasive.

Introduced species have been imported intentionally and accidentally. Some non-native species became food staples and are quite beneficial. Corn seeds were hand-carried to new regions as Paleoindian and Archaic peoples slowly migrated northward from Central America and Mexico. Beans arrived in similar fashion from Brazil and Guatemala in later eras. Spanish explorers and missionaries brought Asian peach trees to the Americas. Even that all-American fruit, the apple, hails from the mountainous regions of Kazakhstan. And honeybees, evident in the Old World from the Tertiary period or earlier, first arrived in North America in 1622 as part of a shipment of livestock from the Virginia Company in London to the Jamestown colonists. These and other introduced species are vital to our national prosperity and are welcome additions to the fabric of our national landscape.

Other introduced species, however, can have harmful environmental effects. When introduced without competing species and predators that keep their numbers in check in their native lands, non-native species may adapt to the new environment so well that they overrun or out-compete native species. Their spread can significantly diminish the biodiversity of an area, including plants and the wildlife that depend on native plants for food, habitat, and nesting materials.

If the altered ecosystem can’t support existing wildlife, insects and animals move out, taking with them their pollination and seed dispersal services that are critical to forest sustainability. As native plants decline, introduced plants can create a monoculture of vegetation across large areas. The loss of biodiversity—whether through planned cultivation or unplanned colonization by noxious species—has extensive negative effects on ecosystems.

Invasive species are often economically damaging, too. They diminish the productivity of important crops and raise the cost of production. Furthermore, when invasive species hitchhike along with exported goods, international commerce suffers. After Honduran officials discovered seven kudzu bugs in a 2012 shipment of poultry from Georgia, they halted receipt of container shipments from Georgia and surrounding states.

Many of our invasive plant species arrived as ornamental plants. Through overplanting, neglect, and other means, they “escaped” cultivation and began invading our forests. The Georgia Forestry Commission compiles a “Dirty Dozen” list of non-native invasive plants each year. Below is a comparison of the top culprits of 2013, when I first began writing about invasive plants, with the 12 most prevalent in Georgia’s forests in the current (2021) report.

Chances are good that at least one of these invasive plants has claimed ground in your yard. Over the next few weeks, we’ll look more closely at some of these species and how we can slow or stop their spread.