Environmental and Physiological Constraints to Forest Yield

Abstract

Factors regulating biomass production concern the physical and biological processes controlling carbon gain and partitioning. These processes are the same in high- as in low-yielding stands. The specific site conditions in terms of climate and fertility, however, determine actual biomass production. In most temperate environments the major limiting factors for forest production are water and nutrients. Both factors greatly influence the amount of foliage produced and consequently directly affect the amount of radiation intercepted, hence also production. The size and life-span of the tree component in a forest ecosystem create special problems when trying to integrate the production processes in time and space. Analysis of the direct control of growth is made difficult by internal re-translocation of large quantities of carbon and nutrients. The basic information on the responses of plants to different environmental variables can only be extrapolated to the field by means of models. Such models must include known environmental effects on physiological processes, as well as secondary responses and feedback occurring on moving the level of the individual organ to stands and ecosystems. The morphological resolution should be commensurate with the level on which basic physiological measurements are made. Results from forest experiments, in contrasting environments, are presented and the reasons for differences in performance and yield discussed.