Many species are introduced to areas outside of their natural range, and are hence non‑native, but not all of these will become invasive. Many will not be able to adapt to the new environment at all, and may eventually die-off. Most plants consumed by Sri Lankans originate from other parts of the world. Even today, hundreds of new plant and animal species are brought to Sri Lanka for various purposes. This process is not confined to Sri Lanka as it happens all over the world.
What happens to these introduced species? Some species are confined to human habitats such as home gardens, botanical gardens or farmlands, or end up in fish tanks or cages as pets. A few of them are able to escape, from where they are intended to be confined, and mix with other species and habitats. Although most of these species are not able to survive in such new environments, a very small portion of them manage to persist in their new homes. Out of this small portion of species, a blend with the natural ecosystems and maintain their populations, without causing harm to native biodiversity. Some of them grow rapidly in human settlements, especially in farmlands, and cause damage to agricultural crops and livestock. These are known as pests and weeds.
Lastly, a very small number of introduced species are able to survive, colonize and disperse beyond their areas of introduction and beyond their purpose of introduction, by suppressing man-made and natural ecosystems, and replacing native plant and animal species. Such species are known as Invasive Alien Species (IAS).
There are a number of invasive alien plant and animal species in Sri Lanka. They are currently causing the loss of millions of rupees to our economy in several ways. They are also suppressing our unique biological diversity and ecosystems. The aim of this manual is to provide valuable information on IAS, and to provide guidelines on identification and management practices.
This book is especially designed to cater to the managers and policy makers who are responsible for the management and control of IAS. It is anticipated that this descriptive manual will share a wide range of knowledge relevant to the design and practice of effective invasive alien control programmes.