Measurement and prediction of biomass and carbon content of Pinus pinaster trees in farm forestry plantations, south-western Australia

Abstract A total of 148 Pinus pinaster trees from 18 farm plantations in south-western Australia were destructively sampled to develop biomass and carbon mass prediction equations for inventory application. Sampling covered a range of ages (1–47-year-old), sizes (e.g. DBH 0–47 cm) and spacings (close- and open-spaced arrangements). Equations were developed to predict biomass and carbon mass of whole-trees and tree components (stems, crowns, tops and roots) as functions of stem diameter (DBH), tree height ( h ) and height to crown base ( h c ) or basal stem diameter ( d 10 ) of small trees. One equation was sufficient to predict biomass (or carbon mass) of both close- and open-spaced trees as a function of DBH and h c . For developing prediction equations a weighted non-linear (WNL) model was always best if DBH was included in the predictor variables. Either a log-transformed allometric (LTA) model or the WNL model were best for predictions as a function of d 10 , but a weighted combined variable (WCV) model was never best. Root:shoot (R:S) ratio decreased with increasing tree size in both close- and open-spaced trees but was higher in open-spaced trees than close-spaced trees of the same size. From literature review, we conclude that increased partitioning of biomass to roots in open-spaced stands may be due to increased light availability or, more likely, more pronounced root thickening on open-spaced trees in response to greater mechanical stress from wind sway.