What is an invasive exotic plant?
"Invasive" refers to a plant with a high reproductive output, early maturation, excellent seed dormancy, survival, and dispersal capabilities, and lack of natural predators/controls.
"Exotic" means many things to many people, but in the biological melting pot of warm temperate to tropical Florida, it means a plant or other organism not naturally native to the region's species-rich ecosystems.
A useful benchmark to consider is whether the plant was present prior to Spanish and subsequent European invasion in the early 16th century. Not all invasive plants are exotic (some native species are "weedy" and well adapted to disturbed habitats where they rapidly colonize), nor are all exotic plants invasive (some behave quite well and don't overrun their new surroundings).
BUT, those plants that are invasive exotics combine the double punch of agressive hardiness and few to no natural controls on their proliferation. Within any tract of publicly owned conservation land like St. Marks National Wildlife Refuge, where invasive exotic species are present, it becomes the responsibility of the land manager to provide the lacking natural control of such pest plants so that the native species don't unduly suffer from too much "foreign competion".
THE SCARY FACTS AND NUMBERS:
"One year's seeding, seven years weeding." - Old gardener's adage
- In the mid 1990's the economic impact of weeds on the U.S. economy was estimated to be $20 billion annually, ($15 billion agricultural, $5 billion non-crop damage).
- Nonnative species threaten approximately 66% of all threatened and endangered species
- Nonnative species are considered the second most important threat to biodiversity, only surpassed by direct habitat destruction.
- In Florida alone, nearly 30% of plant species growing in the state, excluding cultivated crops, are exotic species. That's 1200 different species of exotic plants with potential invasive properties (they've already met the first requirement of adaptability to local climate and soils)!
THE BIG THREE INVASIVE EXOTIC PLANTS AT ST. MARKS N.W.R.:
1. Cogongrass(Imperata cylindrica)
Description: This is a perennial grass with individual blades up to 4' tall, 1" wide and a conspicuously off-center mid vein. flower is a narrow, fluffy plume up to 8" long. growth habit within the Refuge is usually linear clumps up to several hundred feet long on roadsides, dikes, and disturbed land. Dead leafy material usually is a dense mat of dry tan leaves that appears to be "running" and bent over.
The Problem: Considered one of the world's 10 worst weeds, this pest plant infests millions of acres worldwide. On the Refuge, cogongrass was planted to control dike erosion in the 1940's and 1950's, and has spread throughout the dike system in the St. Marks unit. It threatens adjacent pine flatwoods as well as several rare and endangered plants (including corkwood, a rare endemic tree/shrub of the Gulf Coast, and a spikegrass found in only 2 other locations in the state). Easily spread through disturbance, wind-blown seed may travel up to 15 miles. Dense clumps crowd out all other native species.
Where is it from?: Southeast Asia, now found throughout the tropical and warmer regions of the wolrd.
What is the Refuge doing about it?: We are beginning a regime of prescribed burning (which actually encourages new leaf growth) , mowing to remove thatch, and selectively spraying new growth with herbicide that the plant transports to its root system. No known control is 100% effective, all treatments must be done multiple times. The Refuge is also applying for grant monies to help in control costs, developing a comprehensive plan of attack for all exotic species at St. Marks N.W.R., and participating in regional workshops to share knowledge and tactics as we search for more effective and species-specific control methods.
2. Chinese tallow tree (Sapium sebiferum)
Description: Chinese tallow is a medum-sized tree with distincive heart-shaped leaves that turn bright red in the Autumn (November-December in these parts), hence it's attractiveness as an ornamental landscape plant. Seeds are borne in conspicuous clusters that look like masses of popcorn kernels, giving rise to the other common name for this plant - popcorn tree. Seeds are covered with vegetable oil (tallow), giving them a waxy coated appearance.
The Problem: Like cogongrass, Chinese tallow ranks as a troublesome weed in other warm parts of the world, though it's full impact and importance is less well known. In the U.S., it is rapidly invading disturbed and natural areas in the Southeast from South Carolina to Texas, including 38 of Florida's 67 counties. There is significant concern that this tree is displaying a pattern of spread in Northern Florida similar to the explosive growth of Melaleuca in South Florida over the past four decades. Often established on disturbed upland sites as a result of human cultivation, Chinese tallow is readily carried into surrounding natural areas by birds that eat the copious seeds. Unfortunately for Northern Florida and the Refuge in particular, this pest thrives in wetland transitional areas, bottomland hardwood forests and edges, around ponds, and even out into relatively saline coastal marshes.
Where is it from?: As might be expected from the name, Chinese tallow is a native of China (Eastern China, to be specific), where it has been in cultivation for over a thousand years as a seed-oil crop.
What is the Refuge doing about it?: Refuge staff have begun systematically mapping the main population found thus far near the St. Marks Lighthouse, as well as documenting several outlying individuals around Refuge impoundments. In November 1998, the "main patch" of Chinese tallow was cut and pushed over with a small bulldozer, then burned in March of 1999 to destroy all potential seed producing individuals and allow for follow-up herbicide treatment of individual tree stems. Other Chinese tallow trees have been cut by hand and await herbicide treatment.
3. Japanese climbing fern (Lygodium japonicum)
Description: If it looks like a fern and it is climbing up a tree or smothering a bunch of trees in Florida, chances are that it's one of two species of Lygodium currently wreaking havoc in the state. In reality, this is quite a pretty, filmy, feathery fern that's a deep rich green in the growing season, and solid dark brown once killed back by Northern Florida's winter frosts. Often seen in roadside environments, especially in ditches and other wet areas climbing up nearby trees.
The Problem: Old World climbing fern (L. microphyllum) has viciously spread throughout South and Central Florida, often climbing over 50 feet as it smothers its host trees, and creating considerable fire danger as a "ladder fuel" capable of throwing burning embers hundreds of yards or more during prescribed burns and wildfires. Its close relative, Japanese climbing fern has not, until recently, been seen as such a terrible threat in Northern Florida, despite being quite widespread throughout the region. Recently, however, Japanese climbing fern has been observed displaying the same massive climbing/smothering characteristics as Old World climbing fern, leading land managers to wonder if the stage has now been set for established populations to become considerably more hostile to their surroundings.
Where is it from?: As with so many exotics, the name is self-evident.
What is the Refuge doing about it?: Refuge staff are presently mapping known locations of the Japanese climbing fern (which appear to be in isolated patches so far) both on the Refuge, nearby state and private lands, and adjacent roadways. With the implementation of a comprehensive exotic species plan, treatment will primarily consist of cutting the plants by hand, and basally applying herbicide to prohibit resprouting.
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