Introduction

Miller, James H.; Manning, Steven T.; Enloe, Stephen F. 2010. A management guide for invasive plants in southern forests. Gen. Tech. Rep. SRS–131. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 120 p.

Only recently has the extent of invasive plant occupation in the Southern United States and elsewhere in the world been realized. Coming rather quickly in the past 10 to 50 years, the extent and spread of nonnative plant species has taken many people by surprise, and it is still not comprehended by most citizens and policymakers. One thing is starkly apparent, however, forest, preserve, and right-of-way managers and landowners need to act fast to stop the rapid encroachment of nonnative invasive plants, eradicate infestations, and restore native communities.

It was only in 1999 that President Clinton issued the executive order defining an “invasive species” and mandating specific Federal actions. The definition of an invasive species in that order is: (1) a species that is nonnative (or alien) to the ecosystem under consideration, such as the Southeast, a specific State or subregion; and (2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health (Executive Order 13112, signed February 3, 1999, by President Clinton).

Thus, a plant invader is any plant species that occurs outside its area of origin and that has become established, can reproduce, and can spread without cultivation and causes harm. Prevention, management, and strategies for control of nonnative plants of the Southeast are addressed in this book and their identification in the companion volume, “A Field Guide for the Identification of Invasive Plants in Southern Forests” (Miller and others 2010 and slightly revised 2013). Two other invaluable books for identifying and managing invasive plants in Florida, which are not covered here, are “Identification and Biology of Nonnative Plants in Florida’s Natural Areas” (Langeland and others 2008) and “Control of Non-Native Plants in Natural Areas of Florida” (Langeland and Stocker 2009).

The damages and impacts of nonnative invasive plants have not been completely determined, but the following are generally recognized:

Nonnative invasive plants

• Limit or stop productive land management andre generation of forests and grasslands.
• Displace and permanently decrease biodiversity and wildlife habitat.
• Alter vital ecological processes such as soil formation,watershed function, and pollination of native plants.
• Limit land access for recreation such as hiking, fishing, hunting, and bird watching.
• Produce overabundant pollen that causes widespread allergenic reactions in humans.
• Present extreme fire hazards to forests, preserves,and homes.
• Can be poisonous to humans and livestock.
• Harbor plant diseases and animal.
• Cause psychological anxiety through a sense of the inability to control our surroundings.

Not all nonnative plants are invasive, and a few are among our most valued crops, e.g., wheat, barley, oats, and a Native American introduction from Mesoamerica, corn. Other nonnative grasses are the mainstay forage species, although most of these are invasive in forests or forest openings, such as Bermudagrass [Cynodon dactylon (L.) Pers.], bahiagrass (Paspalum notatum Flueggé), Johnsongrass [Sorghum halepense (L.) Pers.], and tall fescue [Schedonorus phoenix (Scop.) Holub]. Plant breeding programs over the past 100 years have yielded numerous varieties of each crop and forage species that give landowners plants with increased productivity, useable yields, and tolerance to a wider range of growing conditions and predators. This in turn increases their invasiveness.

Over the past 50 years, the explosion in the number of ornamental and horticultural species and abundant varieties has yielded benefits to many aspects of modern society, such as landscape beautification and rapid-growing shade trees and shrubs, but have taken their toll on our natural ecosystems. The social costs of annual maintenance control of these introduced invasive species have skyrocketed in our yards, parks, green spaces, and along rights-of-way as well as forests, grasslands, and wildlands.

Nonnative plants become invasive for many reasons. The following are among the traits that help nonnative species establish and spread:

• Early introduction in the 1700s and 1800s as ornamentals or forages, resulting in a long period of spread, hybridization, and adaptation (Hundreds of thousands of small farmers planted ornamentals around their houses, and the plants remained after the great exodus in the late 1800s and early 1900s to cities.)
• Rapid early growth rates that outpace native cohorts
• Few native predators and a resiliency to predation by insects, pathogens, and mammals
• Production of abundant fruit and seed at a young age
• Seed that is readily spread by wind, water, birds, and mammals
• Seed that can remain viable in the soil for 1 year and even up to decades
• Roots or rhizomes that persist and resprout after topkill following herbicide applications, cutting, or burning and that grow outward to yield intensified and dense infestations
• Capability to establish and spread in sites of periodic disturbance, such as along ever expanding forest edges, on rights-of-way, along stream and river banks, and in abandoned crop and pasture lands
• Capability to adapt and spread in a new site through a “set-and-wait” strategy until conditions are suitable
• Wide tolerance to shade, drought, soil conditions, and flooding that gives a decided advantage over native plants
• Capability of forming exclusive (or limited species) dense infestations through their high amount of leaf area that is often evergreen or appears earlier in spring and sheds later in fall compared to native species
• Capability of suppressing other plant seed germination and growth by releasing allelopathic chemicals (through the invasive plant’s foliage and roots)
• Alter biogeochemical cycles and soil micobial communities that favor invaders over native plants

Cogongrass seedheads.

The more of these traits a nonnative species might have, the greater its likelihood of success in establishing itself and spreading, as well as resisting control and eradication.

Recently escaped plants can remain at low levels of scattered occurrence known as the “lag phase” but then come into an era of rapid increasing spread. Invasive traits can be enhanced through hybridization with native or nonnative plants of the same genus. There are nonnative plants at every stage of invasion in the Southeast, while across the region none are yet at the “maximum occupation” phase. Many currently “naturalized” plants in the early lag phase will likely become invasive due to selective adaptation and hybridization as well as increased disturbed habitat for establishment.

The objective of this book is to provide useful information on current management strategies and procedures for 56 recognized plants that have invaded forests, natural areas, pastures, rights-of-way, orchards, grasslands, and wetlands of the Eastern United States. This book also covers the principles of invasion and how we can organize, plan, and enact prevention and management programs.