Invasive Species

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Invasive species are non-native plants or animals that have been introduced, usually by humans, into an environment that is not equipped to support them.


Invasive Animal Species

The most common invasive animal on the refuge is the feral hog.   Feral hogs are common on the refuge and can be detrimental to nesting bird success. The hogs degrade habitat and can contribute to land loss by damaging healthy plants that hold the soils in many areas together.  The SW LA National Wildlife Refuges contract with USDA Wildlife Services to control/manage feral hogs through year round ground trapping and shooting, and scheduled aerial shooting efforts. We have been working together in this effort since 2007.

Another invasive animal present on the refuge is the Nutria.  This rodent was first trapped on the refuge in the winter of 1941-42, and at the time refuge personnel wished they had more of them to control vegetation.  The nutria has displaced the native muskrat in many of Louisiana's coastal marshes and they can cause harm to fragile marshes when they occur in high densities. When warranted, harvest is used to control the population.

Invasive Plant Species

Several invasive plant species are present on the refuge. The Chinese tallow tree is the most prevalent. It is found on canal and impoundment spoil banks and may be found on ridges. It is an introduced ornamental that has escaped to become the dominant woody species in Louisiana coastal marshes. Larger tallow trees can be controlled by herbicide application or cleared, and small plants can be removed by burning woody growth before it reaches maturity.

Salt Cedar is found sparsely along canal banks and ridges throughout the refuge. It was introduced from Europe and can be an aggressive invader on dewatered, disturbed wetlands and especially on hydraulically deposited soils. Drought conditions contribute to its establishment and propagation. Methods of control include long-term deep flooding or application of herbicides licensed for aquatic use.

Water hyacinth has been found on the refuge when water conditions are fresh. This South American and African plant was introduced as an ornamental that reproduces quickly and has no natural predator in the United States. Repeated application of the herbicide 2-4-D is the most practical method of reducing infestations; outside of saltwater which it cannot tolerate.

Giant salvinia is native to South America occurs on the refuge when water conditions are fresh. It is a small free-floating plant that grows in clusters and develops into dense, floating mats or colonies in quiet water, undisturbed by wave action.  This plant quickly builds up during fresh periods but is quickly eliminated during saltwater periods.

Eurasian milfoil is rapidly colonizing areas that have converted from emergent marsh to open water, and has been found to be one of the most common species near terraces placed in an open water area in Unit 7. Though Eurasian milfoil is not native and is of less value to wildlife than other aquatic species, its presence is desired over the absence of vegetation in recently disturbed open water areas.