Forestry

Invasive Plants in Alabama Forests

Non-native invasive plants

Plants are considered non-native if they were introduced to an area by human activity, either accidentally or on purpose.  Non-native plants are not inherently harmful.  In fact, many agricultural crops and ornamental plants are non-native and are extremely beneficial to our economy and well-being.  However, some non-native plants escape cultivation and become weedy pests.  It is estimated that approximately 1 in 10 introduced non-native plants escape cultivation, 1 in 10 of those becomes naturalized and 1 in 10 of those becomes invasive (Williamson and Fitter 1996).  A non-native species is considered invasive when its introduction causes or is likely to cause economic harm, environmental harm or harm to human health (Executive Order 13112).  Kudzu is probably the most notorious non-native invasive plant in Alabama but it certainly isn’t the only invasive pest plant for which we need be concerned.

Impact of invasive species

Non-native invasive species can have numerous impacts within natural areas, production forest lands, pastures, right of ways, roadsides, and urban green spaces. Invasive plant infestations can out-compete native species, eventually displacing or killing them. Reductions in native plant biodiversity and health in turn lead to reduced availability of wildlife food and habitat. Some invasive species also have additional negative effects on ecosystem functions, such as fire regimes, water cycles, soil characteristics, and the regeneration of forests and other natural areas. Ultimately, infestations reduce crop and forest productivity, impact wildlife, hamper hunting, fishing and other outdoor activities and reduce ecosystem functioning.

In addition to costs associated with harm to the environment and reduced land productivity, invasive plant control costs billions of dollars each year. Unless caught early, control of invasive plant infestations can take years of herbicide applications and/or extensive cutting, mowing, mulching or pulling. Preventing the establishment of invasive plants and catching infestations when still small are the most cost-effective ways to help slow the spread of invasive plants across the landscape.

Common characteristics of invasive plants

Characteristics often observed in invasive plants are rapid and aggressive growth, production of numerous seeds that are spread easily by wind, birds or water, and the ability to grow under many different conditions. They often have long lived seeds that persist in the soil until disturbance triggers germination. Some have roots and rhizomes that readily sprout and can be spread by flood waters or on vehicles and equipment.  In addition, the natural diseases and herbivores that typically keep plant populations in check are absent in the new range. This is not to say that all plants with these characteristics are, or will become, invasive.  However, since it may take decades for a plant species to become a recognized invasive pest, it is best to be extra cautious when growing plants that share these characteristics. 

Invasive plant species in Alabama

The Alabama Invasive Plant Council (ALIPC) has compiled a list of plant species considered to be invasive in Alabama. The intent of the list is to rank plants based on their invasive characteristics, foster early detection of invasive plants so that landowners, managers and stewards can implement a rapid response action to prevent them from becoming established and spreading, and to educate the general public and others about invasive plants. The list has no regulatory authority, but provides information for to inform decision making.  

Trees

Shrubs

Vines

Grasses

Forbs

Plants of Concern (showing signs of being invasive)

Invasive Plant Control

The approach used to control a specific invasive species depends on the characteristics of the species, the size of the plants, the size of the infestation, the site, and the resources available for the job. Sources of information for control options include:  ‘A Management Guide for Invasive Plants in the Southeast and the Southeast Exotic Pest Plant Council Invasive Plant Manual.

An important aspect of understanding the spread of invasive plants and ultimately their control is having access to up-to-date information about plant distributions. The Early Detection and Distribution Mapping System (EDDMapS) provides distribution maps and lists of invasive plants reported by county.  Citizen scientists and other volunteers can provide valuable information about invasive plant distributions, especially newly emerging species. Click here to learn more about how you can map invasive plants, or download the free app for easy mapping in the field.     

Forest management practices and invasive species

As recently as a decade twenty years ago, forest land managers had little reason to be concerned with non-native invasive plants as the threat was not high and, if present, invasive species generally were restricted to forest edges. However, as forest lands are being negatively impacted by invasive species. Currently, over 50 of the species listed by the Alabama Invasive Plant Council (ALIPC) occur in, and could negatively impact, natural and managed forests. Cogongrass, Japanese climbing fern, Japanese stiltgrass and Chinese tallowtree are of particular concern to forest managers due to their rapid spread, negative impact on forest productivity and difficulty of control.
Any forest management practice that disturbs the soil, increases light levels to the forest floor, removes native vegetation and/or involves the use of off-site equipment can favor the establishment, growth and spread of invasive species.  These practices include thinning, release treatments, harvesting, site preparation and burning.   The establishment of food plots can also introduce invasive species through intentional planting or use of contaminated equipment.  Streamside management zones may serve as a haven for invasive species which may spread to adjacent lands. Pine straw production strategies can create conditions favorable to the establishment and growth of Japanese climbing fern, and bales and equipment from infested stands can spread the fern long distances.
The brochure ‘Invasive Plant Responses to Silvicultural Practices in the South’ reviews forest management practices and potential impacts on invasive plants, and is summarized below:

  • Learn to identify invasive plants and incorporate their management into any land-use plan.
  • Prevent introduction of invasive plants into uninfested sites.
  • Contain and treat new infestations of invasive plants. For many species, a single plant can initiate an infestation. Controlling small infestations (sometimes simply removing a single plant) is easier and more cost effective than trying to control well-established, rapidly spreading infestations.
  • Minimize transport of invasive plants from infested to uninfested areas. Clean vehicles and equipment and avoid working in infested areas when seeds are present or when soil conditions allow movement of roots or rhizomes.  
  • Minimize soil disturbance as invasive plants often prefer disturbed ground.  Monitor areas where soil has been disturbed.
Maintain desirable species. Establishing and maintaining competitive, desirable plants along roadsides and disturbed areas prevents or slows establishment of invasive plants.

Landscaping and invasive species

Many invasive plants are escaped ornamentals. Managers of natural areas suggest that homeowners and landscapers consider not planting known invasive species, especially if the site is in an area where seeds and/or aggressive plants can easily spread into nearby woods, fields or other natural areas. 

Additional information about invasive plants can be found at the following links: