To study the feasibility of determining the mean annual aboveground biomass gain of tropical seasonal forests at the national scale, we estimated the gain (i.e., increase due to growth of living trees) and loss (i.e., decrease due to tree death) of aboveground tree stand biomass (stand AGB) using 49 permanent sample plots distributed nationwide for 139 observation periods from 2005 to 2015 in Cambodia. In a linear mixed-effects model, stand AGB gain was predicted to increase with the initial stand AGB: Stand AGB gain＝0.0165 Stand AGB+2.20 (n＝139, P<0.0001, R2＝0.4531, RMSE＝2.84), where Stand AGB gain is the sum of tree AGB growth (Mg ha－1 year－1), and Stand AGB is the sum of initial tree AGBs (Mg ha－1). The mean estimated stand AGB gain was 4.79Mg ha－1 year－1 for an average initial stand AGB of 155.5Mg ha－1. The annual stand AGB loss was<20% of the initial stand AGB and the influence of stand AGB loss on stand AGB gain was negligible. The 2006 IPCC Guidelines for National Greenhouse Gas Inventories assigned stand-age-dependent values of default annual stand AGB gain for tropical natural forests. However, age is difficult to determine in tropical trees. Our stand-age-independent approach based on the stand AGB offers a practical method for assessing the AGB gain of tropical natural forests.
Agarwood is one of the most valuable non-timber forest products harvested from the heart of the mountains of Southeast Asian tropical rain forests. Some species of trees in the genus Aquilaria (Thymelaeaceae) accumulate resins in parts of their trunks. Agarwood has a long history as a trade good, although ecological data and economic assessments regarding agarwood harvesting in natural habitats are lacking. The author performed field surveys in the upper reaches of the Baram River in Sarawak, Malaysia, to assess the possibility of harvesting natural agarwood sustainably. In 2004, the habitat density of Aquilaria beccariana around village L was less than one tree per ha, and only relatively mature trees produced resins in their trunks. The introduction of commercial logging and hill rice cultivation damages the habitat of A. beccariana. Thus, the conservation of primary forests is essential for natural agarwood harvesting. The local Penan people only harvest the portions of the trees where resins accumulate, which allows the trees to survive. However, exploitative agarwood harvesting has begun in this area since the early 2010s, as a result of intrusions by outsiders. Thus, one cannot assume that all agarwood harvesting in Sarawak is being conducted sustainably. Meanwhile, in areas with no traces of outside intruders, the number of mature agarwood-producing trees has been maintained, suggesting that the method of agarwood harvesting used by the villagers is sustainable. To ensure that agarwood harvesting is sustainable, traceability that is based on more strictly defined and more detailed information regarding all of the steps in the agarwood supply chain is required.
Indigenous oil-degrading bacteria (ODB) were screened from two islands, Iriomote, Japan and Con Dao, Vietnam. These islands are considered predicted contamination sites from oil spillage on a nearby busy transportation route. The aim of this study was to compare the degradation abilities of bacterial isolates from the two different study areas for crude oil, n-alkanes, and polycyclic aromatic hydrocarbons. Comparing the two study areas, the numbers of the total bacteria and ODB showed the same distribution tendencies. There were no differences between Iriomote and Con Dao in the counts of the total bacteria and ODB in sediment samples, while those in seawater samples were statistically lower for Iriomote than for Con Dao. A total of 45 isolates, 25 from Iriomote and 20 from Con Dao, belonging to 18 genera, were isolated. Among 11 genera detected on Iriomote, the dominant genera were Achromobacter, Pseudomonas, and Ochrobactrum. Among 11 genera from Con Dao, the dominant genera were Pseudomonas and Microbacterium. The degradation ability of the isolates was studied for crude oil, two kinds of n-alkanes, and two kinds of polycyclic aromatic hydrocarbons (PAHs). The numbers of the isolates that degraded more than 50 percent of the crude oil and n-alkanes and 25 percent of the PAHs present in the media were higher for Iriomote (3, 11, and 2, respectively) than for Con Dao (2, 4, and 1, respectively). It is noteworthy that the isolates of Pseudomonas putida and Ochrobactrum anthropi could degrade more than 40 percent of the oil and n-alkanes and more than 25 percent of the PAHs present in the media.
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