Size-biomass relationships for Australian populations of the invasive rangeland shrub Parkinsonia aculeata L

Parkinsonia aculeata is an invasive, introduced shrub that is found in all mainland states of Australia except Victoria. It is especially prevalent north of the tropic of Capricorn. Size-biomass relationships were established for this species using data from 167 shrubs spread across eight sites in the Northern Territory and north-eastern Queensland. Above-ground dry weight (W, kg) can be predicted from plant height (H, m), canopy diameter (D, m) or stem cross-sectional area (A, cm2) using the equations: W = 0.025 H4.47 W = 0.091 D3.64 W = 0.022 A1.61 These relationships are linear when plotted on log-log scales. Although there was a significant effect of "site" on the log-log relationships between above-ground dry weight and size variables, the amount of information lost by not using site-specific equations is relatively small. These results provide reliable methods for estimating above-ground biomass in this species, the most robust being based on measurements of stem diameter at 20 cm above ground level.