Aboveground biomass and productivity of nitrogen-fixing tree species in the Philippines

Abstract

Aboveground biomass and productivity traits of two nitrogen-fixing exotic species (Acacia auriculiformis A. Cunn. ex Benth. and Acacia mangium Willd.) and one nitrogen-fixing native species (Pterocarpus indicus Willd.) were compared in this study using 10 and 20-year-old age classes. Parameters measured were stand density, basal area, importance value index, aboveground biomass and carbon, annual litterfall, aboveground net primary productivity (ANPP), leaf area index (LAI), specific leaf weight (SLW), and nitrogen productivity. Results of the study showed that ANPP and nitrogen productivity were higher in the 20-year-old A. auriculiformis(6.28 tons ha-1 yr-1 and 267.23 kg kg-1 yr-1, respectively) and A. mangium (6.43 tons ha-1 yr-1 and 221.72 kg kg-1 yr-1, respectively) stands which were attributed to their higher values of litterfall and aboveground biomass and carbon. Also, SLWwas much higher in the 10- and 20-year-old A. auriculiformis (244 and 245 cm2g-1, respectively) and 20-year-old A. mangium (255 cm2g-1) than P. indicus stands. The density of woody species (>5 cm DBH) was highest in the 20-year-old A. mangium stand (1,492 trees ha-1) and lowest in the 10-year-old P. indicus stand (592 trees ha-1). Acacia auriculiformis and A. mangium showed better performance in the field which serves as a basis in recommending them for reforestation in the Philippines. These species are very important in the initial establishment of the plantation and could be considered as priority species to lessen the vast degraded areas in the country. Key words: Aboveground net primary productivity, exotic species, native species, nitrogen productivity, rehabilitation.