Biotic and abiotic factors control aboveground biomass (AGB) and the structure of forest ecosystems. This study analyses the variation of AGB and stand structure of evergreen broadleaved forests among six ecoregions of Vietnam. A data set of 173 1-ha plots from 52 locations in undisturbed old-growth forests was developed. The results indicate that basal area and AGB are closely correlated with annual precipitation, but not with annual temperature, evaporation or hours of sunshine. Basal area and AGB are positively correlated with trees [ 30 cm DBH. Most areas surveyed (52.6%) in these old-growth forests had AGB of 100-200 Mg ha-1 ; 5.2% had AGB of 400-500 Mg ha-1 , and 0.6% had AGB of [ 800 Mg ha-1. Seventy percent of the areas surveyed had stand densities of 300-600 ind. ha-1 , and 64% had basal areas of 20-40 m 2 ha-1. Precipitation is an important factor influencing the AGB of old-growth, evergreen broadleaved forests in Vietnam. Disturbances causing the loss of large-diameter trees (e.g., [ 100 cm DBH) affects AGB but may not seriously affect stand density. Keywords Aboveground biomass Á Carbon storage Á Climatic variables Á Ecoregion Á Edaphic variables Á Oldgrowth forest Project funding: This word is funded by Vietnam Ministry of Science and Technology under Grant number ÐTÐL.XH.10/15, Vietnam National Foundation for Science & Technology Development (106-NN.06-2016.10), and International Foundation for Science (J-1-D-4602-3).
Differences in light capture strategies of tropical monsoon trees were examined with a focus on the function of hierarchical leaf cluster structure. Specifically, morphological differences in leaf clusters were examined among ecological functional groups of tree species. The three-dimensional distribution of leaves within 62 crowns of 21 species in or above the canopy layer was estimated using a terrestrial laser scanner. Leaf clusters with hierarchical structure were identified within each crown, and the thickness and inclination of a leaf cluster were calculated. The light capture property of the crown was examined using the light extinction coefficient and the directional dependency of light capture. An ordination technique was used to organize crown architecture into two axes: one corresponding to the directional dependency of light capture, which separates leaf phenological types, and the other representing the spatial scale contributing to light capture, which separates growth forms. Similar leaf cluster shapes at various spatial levels ranging from small leaf clusters to crowns caused specialization of crown directional dependency, which was clearest in emergent species. In deciduous species, flatter leaf clusters at various spatial levels were specialized to efficiently capture overhead light, whereas rounder leaf clusters at various spatial levels in evergreen species were specialized to uniform light capture from all directions. Different light capture strategies among functional groups in tropical monsoon forest would be related to drought stress response.
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