No abstract

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).

Enrichment planting is often suggested as a means of enhancing the productivity of logged rainforest. However, little is known about the long-term survival and growth of these trees. In this study, we used historical data from enrichment planting trials ranging from 15 to 32 years old to examine the survival and growth of 16 tree species across different sites in north Queensland, Australia. The results complement and extend current knowledge on the potential role of enrichment planting from a production perspective. A key finding was that the initial level of post-logging overwood did not appear to affect the immediate survival of enrichment plantings, but in the longer term (up to 30 years) survival decreased as post-logging overwood and regrowth increased. This suggests that removal of overwood should take place at the time of enrichment planting. A further key finding was that despite regular tending to remove vegetation adjacent to the plantings, competition from saplings and trees that were situated outside the tended area emerged as a major source of competition in some plots. By implication, the success of enrichment planting may depend on removal of competition from the entire logged area, not just adjacent to enrichment plantings. Results between individual species and trials varied widely. The best development of Flindersia brayleyana resulted in a mean tree diameter of 32.5 cm at age 22 for the 100 tallest trees per hectare. Although Eucalyptus grandis, Eucalyptus microcorys, and Eucalyptus pilularis all failed—as expected, because they do not normally grow in rainforest—Corymbia torelliana, Cardwellia sublimis, Araucaria bidwillii, Khaya senegalensis, Flindersia amboinensis, and Swietenia macrophylla also failed although they grow naturally in similar sites. In other trials, tree height and basal area growth were often poor. For example, Khaya ivorensis grew to a basal area of only 1.3 m2/ha and a mean height of 7.7 m at age 10, and Flindersia ifflaiana only grew to a basal area of 0.7 m2/ha and a height of 7.9 m, also at age 10. Overall, these results emphasise the necessity of site–species matching before enrichment planting begins and the necessity of post-planting monitoring and remedial tending.