Biomass valorization in the management of woody plant invaders: The case of Pittosporum undulatum in the Azores

As one cause for biodiversity loss, invasive alien species are a worldwide threat. However, exotic woodland can also have an enormous biomass potential. The goal of this study was to evaluate the available aboveground biomass (AGB, including trunk, branches and foliage) of the widespread woody plant invader Pittosporum undulatum in the exotic woodland in São Miguel, Terceira and Graciosa islands (Azores archipelago), in order to assess its potential for energetic valorization. We used different modeling approaches in combination with forest inventory data to estimate total AGB. We sampled 127 stands dominated by P. undulatum, estimated stand density, measured diameter at breast height, basal area, tree height, and number of branches at breast height in a total of 5872 trees, and determined the AGB of 674 trees. Allometric equations were used to estimate AGB from dendrometric traits (R2 = 0.88). Although it was possible to predict stand biomass based on stand density and on dendrometric traits, there was no clear relationship between AGB and topographic and climatic variables. Using average estimates of AGB, the areas classified as dominated by P. undulatum in the forest inventory, and a rotation period of 26 years, we calculated a total annual available AGB of 1570, 2594 and 11903 Mg. year−1 for Graciosa, Terceira and São Miguel islands, respectively. The employed methods and the results obtained in this work provide the means for a more accurate evaluation of the woody biomass resources, opening new perspectives for the management of woody plant invaders.