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Beware of Invaders in our Native Habitats

According to the Florida Fish and Wildlife Conservation Commission, Florida is now home to over 500 species of animals that are considered non-native (exotic). It’s even more shocking to consider that out of the 4,000 identified plants in Florida, about 1,200 are considered exotic species (UF/IFAS publication http://edis.ifas.ufl.edu/fr133). Many of these have become invasive problems for one reason or another and most of them have arrived via human transport mechanisms; some intentionally and some by accident.

Chinese Tallow Leaves

So how did some of our worst invasive exotics get here? Some of the plants were actually brought in with good intentions to serve as erosion control or livestock forage (kudzu and cogon grass), or ornamentals (coral ardisia, mimosa, Japanese climbing fern, Japanese honeysuckle, heavenly bamboo, Chinese privet, wisteria: all of which I see in Wakulla and Franklin County woodlands). Exotic animals are sometimes released by owners or escape from the exotic pet trade, as is the case with pythons, many species of lizards and the monk parakeet. Another subtler mode that many people do not consider is the release of ship ballast water in our ports that has come from oceans around the world. This is likely how we received larvae of the green porcelain crab in the Gulf, which is now common in our coastal waters on our oyster reefs. Sometimes when a species from another area is introduced it has a competitive advantage with fewer or no natural predators to keep it in check. Other times, our native species have no natural defense against newcomers to their neighborhood. This is the case with the Cuban treefrog which makes easy prey of our native treefrogs and has caused significant declines where it has become

Exotic Cuban Tree Frog

established. I have personally seen this species as far northwest as Carrabelle. In our area we have many examples of invaders that are very good at out-competing the natives. In the plant world, most people have heard about non-native hydrilla, that dominates some waterways and lakes to the point of detriment for natives. On land we can find monoculture stands of cogon grass that are very difficult to control. If you drive I-10 much you may have noticed dense stands of dark-green shrubs dominating miles of understory along the wood’s edge that are composed almost entirely of Chinese privet. Privet is a Ligustrum species that originated as a variegated (yellow and green leaf) ornamental in the nursery trade. It has reverted to its native green form and is now common in north Florida woodlands.

We even have exotic species of bacteria and fungi that are causing problems here. Many people are finding dead red bay trees in their woods of late. A fungus that is transmitted by an introduced ambrosia beetle is the culprit that causes laurel wilt disease and it is killing bay and sassafras trees throughout the southeast. Growers in the avocado industry of south Florida are very fearful of this occurrence since their trees are also in the laurel family. A bacterium from China is the cause of a devastating citrus disease called Huanglongbing (HLB) or citrus greening. There is currently no cure for the disease once a tree is infected. The disease is spread by a non-native Asian psyllid (insect) which is difficult for the backyard citrus grower to control. Commercial citrus production and the land area dedicated to citrus has dramatically declined in Florida since this disease appeared.

One key thing to remember is the distinction between the terms “exotic” and “invasive exotic”. Many of our most economically important and useful species are not from here. And that is fine as long as they don’t tend to escape our intended uses and begin negatively impacting our native ecosystems. One valuable information source for the home landscaper is the guide to Florida-Friendly Landscaping. Many of the recommended species are not native, but the key is that they are not invasive either. You can type in this long URL or simply use your search engine to find it on the web. https://ffl.ifas.ufl.edu/pdf/FYN_Plant_Selection_Guide_2015.pdf

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