Introduction

Based on their ecological status, we can distinguish the forest stands as undisturbed natural forests, disturbed or degraded natural forests, and plantations. The plantations can be further categorised into those of indigenous or exotic species, and those consisting of a single species (usually called monoculture) or more than one species (usually called mixed plantation). Foresters, forest entomologists and plant ecologists have strong traditional views on the risk of pest susceptibility of these different types of natural and man-made forest stands. Speculation was unavoidable in the past because the practice of forestry could not wait for conclusions based on long-term experiments. Now that fairly adequate data have accumulated, it is possible to make a critical assessment of the hypotheses and their theoretical foundations. Three commonly held views and their underlying hypotheses are examined here. These views are (1) that natural, mixed-species tropical forests are free of pest problems (in contrast to forest plantations); (2) that plantations of exotics are at greater risk of pest damage than plantations of indigenous species and (3) mixed plantations are at lesser risk of pest damage than monocultures.

Do plantations suffer greater pest damage than natural forests? And if so, why?

That plantations suffer greater pest damage than mixed-species natural forests is a well-accepted axiom in forestry, although contrary to the conventional wisdom, tropical forests are not free of pests.