Nutrient Cycling in a Eucalyptus obliqua (L'hérit.) Forest. III. Growth, Biomass, and Net Primary Production

Abstract

The biomass of Eucalyptus obliqua forest in south-eastern Australia was estimated over a 22-year period by using allometric relationships in which tree diameter was the independent variable. Biomass increased from 24 kg m-2 at a stand age of 44 years to 37 kg m-2 at 66 years. Maximum net primary production (NPP) was 1.4 kg m-2 year-1. Biomass accumulation ratios (biomass/NPP) follow a trajectory with age which fits closely R. H. Whittaker's work in temperate forests of the United States. It is proposed that the growth of forests is regulated within three definable and sequential stages: (i) growth of the photosynthetic display and of the metabolic transport system, (ii)development of heartwood as a support structure system, and (iii) maintenance of the ecosystem through the production of litter. Essential to this view is the recognition of heartwood formation as a growth-regulating process rather than as the end-result of an ageing process.