The risk that exotic forest trees may escape the area on which they are tested or cultivated and turn invasive has long been underestimated in the forestry sector. Invasive species can be damaging for a number of natural or agricultural ecosystems, including native forests and the biological diversity they contain. They can be particularly damaging during forest regeneration but can also negatively affect mature forests.
It is difficult to predict which species are likely to cause serious damage if introduced. At present, the best guide to potential invasiveness is identification of species that have already caused problems when introduced elsewhere. Reliable information is thus critically important for assessing the risk of invasiveness.
In 2002, CAB International conducted a global review for FAO on the phenomenon of naturalization and invasiveness of forest tree and shrub species. The study, carried out through database searches and literature review, found 1 121 tree species reported introduced, naturalized or invasive in particular situations, of which 442 were reported as invasive forest trees (Haysom and Murphy, 2003). It is important to keep in mind, however, that different authors defined these terms in various ways.
The data set, which is being prepared for posting on the FAO Forestry Web site, can be a valuable tool for use by plant protection and quarantine officers, forest managers, agricultural support programmes and environmental protection institutions and groups. Intentional introduction of exotic plants, including trees and shrubs, will increasingly be subject to preliminary risk assessment for potential invasiveness. In this respect, a list of reported introduced, naturalized and invasive trees posted on the Internet, even if indicative and not authoritative, will find several applications in forestry, ornamentals, urban forests, agroforestry and trees outside forests. Such a list is a necessary tool in any national or international biosecurity and plant protection strategy.
Haysom, K.A. & Murphy, S.T. 2003. The status of invasiveness of forest tree species outside their natural habitat: a global review and discussion paper. Forest Health and Biosecurity Working Paper FBS/3E. Rome, FAO. Available on the Internet: www.fao.org/DOCREP/006/J1583E/J1583E00.HTM