Allometric estimation of above-ground biomass and leaf area in managed Grevillea robusta agroforestry systems

Non-destructive methods for determining the biomass and leaf area of indivi dual trees throughout their growing cycle are an essential tool in agrofore stry research, but must be capable of providing reliable estimates despite the influence that management strategies such as pruning may have on tree f orm. In the present study, allometric methods involving measurements of the diameter of all branches provided reliable estimates of canopy leaf area a nd biomass for grevillea trees (Grevillea robusta A. Cunn.; Proteaceae) gro wn as poles, but proved unsuitable for routine measurements because of thei r time-consuming nature. An alternative, less laborious method based on mea surements of trunk cross-sectional area immediately below the first branch of the canopy provided satisfactory allometric estimates of leaf area and c anopy biomass. Trunk biomass was determined from measurements of tree heigh t and diameter at breast height using established methodology based on the assumption that trunk volume may be calculated using a quadratic paraboloid model; biomass was determined as the product of trunk volume and the speci fic gravity of the wood. The theoretical basis, development and validation of allometric methods for estimating tree growth are discussed and their wi der applicability to other agroforestry systems is assessed.