A preliminary assessment of utilizable biomass in invading Acacia stands on the Cape coastal plains
The biomass (woody material and foliage) of invasive Australian wattles (Acacia cyclops, A. saligna and A. mearnsii) was estimated in stands where crown cover exceeded 50% on the west coast, Agulhas and Eastern Cape coastal plains. Tree-level models were constructed to estimate biomass of the different plant components of A. cyclops and A. saligna from stem diameter at knee height. An existing volume regression equation for A. mearnsii was adapted and the estimated volumes, based on diameter at breast height, and tree height, were converted to mass. Sample plots were used to estimate mass per unit area by tree component, species and region. Satellite remote sensing conservatively estimated the densely (>50% cover) infested areas at >100 000 ha. The total green (wet) woody biomass with a minimum diameter of 2.5 cm was estimated to be almost 10 Mt or 12 million m3. This is equivalent to the annual intake of roundwood by South African pulp, paper and board mills. A substantial quantity of raw material is therefore available for charcoal, wood composites and paper. Other products could possibly be developed from bark and foliage. Large-scale utilization of biomass will be a demanding task, with potential risks. Risks include environmental damage, and the creation of a dependency, and these will need to be managed carefully.