In the Executive Summary of the National Invasive Species plan (NISMP) the term “invasive species” was defined as:
-“a species that is non-native to the ecosystem under consideration and whose introduction causes, or is likely to cause, economic or environmental harm or harm to human health”
(see www.invasivespeciesinfo.gov)”.
Michael Davie details some of the critical characteristics of invasive species, and the problems caused by them, in a recent article in “The Arboricultural Consultant” (“From Experience: Controlling Invasive Plant Species”). These characteristics and problems are detailed and expanded below.
Characteristics of invasive plant species.
1. They mature early, produce many seeds, and usually the fruits are of low nutritive value;
2. They are fast growing and long-lived (kudzu vines can grow at a rate of up to 18”/day);
3. They have a long photosynthetic period, e.g., many are ‘evergreen’ such as English Ivy and Privet;
4. There is a lack of natural biological controls.
Problems
A number of key, invasive species are killing both young and old trees and causing widespread urban deforestation in the Atlanta area with an associated loss of biodiversity. Just as critical, they are also preventing the normal process of forest replacement by suppressing the secondary succession, i.e., stopping the process by which the mature trees of the forest generate the seedlings and saplings necessary to their replacement. The Schools experiential learning activities with appropriately qualified Apprentices and Volunteers specifically include:
1. Cutting various invasive vines and lianes away from infested trees. The predominant invasive lianes are English Ivy (Hedera helix), Chinese Wisteria (Wisteria chinensis), Japanese Honeysuckle (Lonicera japonica) and the notorious kudzu (Pueraria montana). Poison Ivy (Rhus radicans), Poison Oak (R. toxicodendron), and Poison Sumac (R. vernix) are native species but they are removed also as they can be severely poisonous on contact; A Poison Ivy infestation has encased a tree and seeded the surrounding area creating a dense field of Poison Ivy in the ‘A’ layer. Garden in Sandy Springs, north Atlanta.
2. Cutting down shrubs such as the privet, Lagustrum sinense, and the olives of the genus Eleagnus. Eradication of both vines and shrubs may involve the use of the “Cut-Treat” approach to killing root systems (see Miller, 2003) as well as physical removal.