INTRODUCTION The most important way to preserve trees is in natural forests and woodlands (584, 585). On site, or in situ, conservation is preferable to preservation in arboreta or in seed banks because it sustains the trees, and the many other organisms that depend upon them, in their natural environment. The interactions with pollinators and agents of seed dispersal are

maintained in forests, which are also vital in many places to sustain the natural environment. Forests help to control climate and rainfall, and are often essential to conserve watersheds. In any natural ecosystem the process of evolution and adaptation to change takes place naturally.