Effects of tree diversity and stand structure on above-ground carbon storage in evergreen broad-leaved and deciduous forests in Southeast Vietnam

Understanding the relationship between tree species diversity and above-ground carbon (AGC) storage in tropical forests is essential for a sustainable flow of ecosystem goods and services. Although tropical forests of Vietnam are of particular interest due to their high biodiversity and carbon density, few studies have evaluated the relative importance of species composition, tree species diversity and forest structure on AGC storage by forest vegetation type. In this study, we tested for the influence of taxonomic diversity, forest structure and species composition on AGC storage in evergreen broad-leaved and deciduous forests of Southeast Vietnam. Data was collected within 137 rectangular plots (25 m × 20 m), randomly selected across a deciduous forest (DF) and four evergreen broad-leaved forest (EB) categories, with different stand­ing volumes levels: very poor (EBG), poor (EBP), medium (EBM) and rich (EBR). In total, we identified 3687 individuals from 110 tree species belonging to 46 families in 6.85 hectares of sampled area. AGC stor­age significantly differed among forest categories, ranging from 14.81 Mg ha−1 in EBG to 146.74 Mg ha−1 in EBR. There was higher AGC in the medium diameter class (20-40 cm), except for EBR where there was higher AGC within individuals of 40-60 cm in diameter. Taxonomic diversity was weakly correlated with AGC while stand structure (stem density and maximum diameter) were strongly correlated. Our results suggest that maintaining the abundance distributions of remnant tree species, particularly that of large trees, is one important method to enhance AGC storage in the tropical ecosytems of southern Vietnam.