Abstract

Productivity of tropical plantations varies widely, depending on site resources and species. The high growth rates achieved in some cases result from plentiful resources (water, nutrients, light), efficient species, favourable environmental conditions, and intensive management to control spacing, genetics and competition. In many situations, however, one or more key resources are scarce and growth is slow. These features affect both the rate of gross primary production (GPP) and the allocation of net primary production (NPP) to stem wood. Relatively small changes in GPP or allocation of NPP can greatly change stem wood production. Stem wood production typically increases in the early stages of plantation development as the leaf area and root-absorbing area of the trees increase. Productivity then peaks and declinesthe cause of this decline (while trees are still young and vigorous) remains poorly understood, but it is often associated with declines in stand leaf area and