1 Introduction



A large number of woody plant species have been introduced to various tropical regions, but only a fraction (around 1%) of them have spread into new habitats and even fewer have become serious pests. Here we consider how land managers can detect invasive woody plant species, assess their threat to native vegetation, and manage and control them if this is necessary. Of particular importance is the gathering of information on the invasive plant and the ecosystems it invades prior to decision making.



In many parts of the world introduced woody plants have become invasive and have necessitated some form of management. The resources needed to control invasive plants can be very large, for example in 1991 the Australian Federal Government provided AS$2 million to mechanically and chemically control Mimosa pigra to halt its spread and protect a nearby World Heritage site from invasion (Miller et al. 1992).


  Emphasis is placed on the management of alien species in protected areas rather than man-made habitats. Protected area is a term used to include all areas of natural or semi-natural vegetation in which the conservation of the natural community is a major objective, and it therefore includes areas designated as national parks, nature reserves, wildlife conservation zones and so on. The management of land outside a protected area can often be crucial to the conservation objectives within it, and to broader conservation goals within a country. Land outside protected areas, and forestry plantations and amenity areas in particular, often act as the main seed source for a number of invasive woody plants. Therefore, control of alien plants outside protected areas can be very important.
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