LB 9-84 - Divergent trends of biomass recovery between soft- and dense-wood species in tropical successional forests

Forest ecosystems are constantly changing in many parts of the globe due to anthropogenic and natural disturbances. Secondary forests recovering after disturbances currently comprise about half of the world’s tropical forests. Our understanding of functional changes, species composition, and biomass recovery of these secondary forests is improving yet insufficient for forest conservation and sustainable management of these ecosystems. The main objective of this research was to evaluate the successional trends in forest biomass recovery and tree species diversity, including some functional properties. We monitored the changes in tree species composition, stand structural characteristics, and biomass growth in a chronosequence of tropical secondary forests in the Yucatan Peninsula of Southeastern Mexico. Published allometric equations were used to calculate tree biomass stocks and Chapmann-Richard function to develop biomass growth models during forest succession. We also computed tree species diversity and similarity indices between forest successional groups (young, medium-aged, and old-growth forests). Results of this study demonstrate that stand structural properties changed gradually with forest age, while there was no clear trend in the increase or decrease of species diversity indices. During the succession, biomass accumulation followed a divergent trend between softer and denser wood species. Softer-wood tree species dominated younger secondary forests, while the contribution of denser wood species increased with the successional age of these forests. Softwood species (0.15 – 0.69 g cm-3) contributed around 68% of the total tree biomass in younger forests ( < 5 years) and 19% in old-growth forests ( >115 years). Meanwhile, densewood species (0.70 – 1.20 g cm-3) accounted for 32% of tree biomass in younger forests and 81% in old-growth forests. Sorensen´s similarity indices of species composition varied significantly between old-growth primary forests and secondary forests of different ages. Older secondary forests were more similar to primary forests in their species composition compared to younger ones, as evidenced by the basal area weighted Chao-Jaccard index. These results provide important insights into the role of species functional composition, especially the diversification of wood density trait, on biomass accumulation during tropical forest succession.