What is secondary forest?

The recognition that tropical secondary forests are the tropical forests of the future has led to a rapid expansion in the literature. Unfortunately it has also resulted in an expansion in the meaning of the term 'secondary forest' which risks rendering it virtually useless. This is a relatively minor inconvenience for ecologists and foresters, who have the time, knowledge and experience to find out what is actually meant in a particular case. Imprecise terminology can, however, be a major stumbling block in communicating with decision makers at all levels and with the general public, tropical and extra-tropical. What is secondary forest? A recent review defined man-made secondary forests as 'those formed as a consequence of human impact on forest lands', excluding plantations (Brown & Lugo 1990). Unfortunately, virtually all tropical forests have suffered some form of human impact - all, if one includes the impact of anthropogenic changes in atmospheric composition. The question is: how much disturbance is needed to make a forest secondary? The most widespread human impacts on tropical forests are: hunting, logging for timber (usually very selective), firewood collection (typically less selective), and clearance for agriculture (including pasture). Nobody has suggested that even total removal of all large vertebrates by hunters makes a forest secondary, although the long term impact of such defaunation may be at least as great as many more visible disturbances. In contrast, forests damaged by logging or firewood collection are often included with forest regrowth on abandoned agricultural land as 'secondary forest' (e.g. Brown & Lugo 1990, Wadsworth 1987,