CHAPTER 1

1.1 INTRODUCTION

Invasive plants are the most discussed group of plants and were subjected to many new research areas. Ecologists define invasive species in various ways and using various terms to introduce invasive species. Ecologists and researches concern about their impacts on ecosystems, economy and human health when creating definitions. Invasive plants are a group of plant which result in various negative impacts on ecosystem when they are introduced to a new environment beyond their native range by either intentionally or unintentionally. It is believed that they reduces the diversity of the native plant species of the introduced area and changes the ecosystem processes of the introduced area.
In many books, review articles, and researches various terms are using to introduce invasive species such as exotic, non-indigenous, alien, weeds etc. Yet it is doughtful which term is most suitable to explain invasive species. Some believe that invasion is a stage of the succession process and believe that characteristics of the pioneer plant species which are the first colonizers in succession process are similar to that of the invasive plants.
In contrast some plant species which are considered as invasive plants are still using in many forest management practises. So it is important to investigate whether they are really invasive, or whether they really negatively impact on ecosystem and to understand what are their impacts on ecosystem, in order to have a