Disentangling the relationship of aboveground biomass, structure and tree diversity in a mixed Acacia plantation in Northern Vietnam

Abstract

A diversification strategy of introducing two or more species is becoming increasingly prevalent in forest plantations previously dominated by single-species compositions. Improving productivity and enhancing other ecosystem services are the main reasons for this conversion. While mixing effects in temperate forests and plantations are well supported by empirical data, such information is scarce for tropical forest plantations. We analyzed the quantitative aboveground biomass - structure - tree diversity relationship in a tropical mixed-forest plantation in Northern Vietnam to gain insight into ecosystem service provision trade-offs. The study site was located in an abandoned Acacia mangium and Acacia auriculiformis (established in 2012) plantation in Northern Vietnam. A one-hectare permanent plot was installed in which all trees were identified individually by species, measured (diameter and height), and georeferenced. The descriptive analysis found that the study area contains 110.66 tons/ha of biomass in the aboveground tree compartments. The structural and species diversity analysis indicated high richness and high evenness compared to other forest plantations in the study area. A set of models was fitted and ranked to determine the relationship between aboveground biomass and structural and specific diversity. The results indicate that the Shannon index and height differentiation index were significant for both species while basal area was only significant for the Acacia mangium model. According to the model sensitivity analysis, aboveground biomass – and therefore carbon concentration – decrease as species diversity increases.