Dryobalanops aromatica is an emergent canopy tree species with hermaphroditic bee‐pollinated flowers. This species is distributed in the lowland dipterocarp forests of Malaya, Sumatra, Rhio Archipelago and Borneo. The flowering of many different dipterocarp species was observed in some parts of Brunei in 1991, and all over Brunei in 1992. The outcrossing rates of D, aromatica were estimated in 1991 and 1992 in the secondary forest, and in 1992 in the primary forest. Selective harvesting of D. aromatica has occurred in the secondary forest about 20 years ago. Four enzyme systems with a total of six isozyme loci were used to estimate the single locus and the multilocus outcrossing rates. The multilocus outcrossing estimates ranged from 0.794 to 0.856, with a mean of 0.816. These estimates are similar to those for other tropical tree species. Although the flowering density of D. aromatica in the secondary forest was lower than in the primary forest, the multilocus outcrossing estimates were not significantly different. The variation between years in the secondary forest was also not significant. These findings may be largely the result of the high flowering tree density of this species, even in the secondary forest. In this study, the outcrossing rates of D. aromatica were maintained by high flowering density regardless of the size structure or the topography of the habitat.
In northern Lao People's Democratic Republic, rising human population has drastically reduced the fallow period of slash-and-burn agriculture which has led to a considerable decrease in the carbon stock in these communities. We estimated chronosequential changes in the communities' carbon stocks, and established the relationship between the fallow period and fallow-period-average carbon stocks in three carbon pools of bamboo-dominated communities in hilly areas of the Luang Prabang Province, northern Lao People's Democratic Republic. Based on measurements by destructive sampling, we devised a model and root-to-shoot ratios for estimating bamboo biomass. In six secondary plant communities established after slash-and-burn cropping, we estimated community biomass using the above model and others, and measured deadwood and litter stocks. The communities' biomass and deadwood significantly increased with time after the last cropping and the former reached about 100 Mg ha -1 after 15 years, whereas litter stocks did not show significant trends over time. Extending the fallow period from 2 to 5 years would increase fallow-period-average carbon stock from 14.2 to 25.1 Mg C ha -1 . The overstory height was significantly correlated with biomass, deadwood, and litter carbon stocks of these communities. Based on our findings, changes in a community's carbon stocks can be estimated using the changes in overstory height, which should be taken into account in future studies to reduce uncertainty in estimating carbon stocks in tropical ecosystems.
This study examined the use of satellite sensor imagery for chronosequential assessment of land use and ecosystem carbon stock in slash-and-burn (S/B) regions of Laos. The segmentation approach was useful because the boundaries of S/B patches are subject to change due to natural or anthropogenic factors. Polygon-based classification using six optical bands of Landsat Enhanced Thematic Mapper Plus (ETM + ) imagery showed that S/B patches could be discriminated with high accuracy (0.98). Normalized difference spectral indices, NDSI[i, j]5[R j 2R i ]/[R j + R i ], using reflectances R j and R i at j and i nm wavelengths for S/B polygons during four consecutive years (1999)(2000)(2001)(2002) showed that NDSI [2215, 830], NDSI [1650, 830] and NDSI[660, 830] (5the normalized difference vegetation index, NDVI) values decreased significantly in S/B years compared to those under fallow conditions (by 0.21¡0.04, 0.20¡0.04 and 0.17¡0.03, respectively). Only slight differences were found before and after the S/B year, regardless of fallow length or biomass estimated by the allometry method. Relating reflectance signatures directly to fallow biomass was unsuitable, but these NDSIs were also useful for distinguishing S/B patches. Land-use history, including the community age of fallow vegetation, can be traced on a pixel basis using a superimposed set of segmented classified images.
We examined non-destructive methodologies for practicalities in monitoring anthropogenic greenhouse gas (GHG) emissions from tropical dry-land forest under the influence of various forms of human intervention. Spaceborne SAR withstood comparison with Landsat ETM+ in land cover classification of degraded tropical forest. For measurement of carbon stock and GHG flux per unit land area, the gain-loss method requires both growth rate and removal rate of forest carbon stock. However, the latter has rarely been obtained in tropical forest. For the stock-difference method, permanent sampling plot data can be used to estimate mean carbon stock per unit land area of each forest type. For cyclic land use that includes a clear-cutting stage such as slash-and-burn agriculture, chronosequential changes in carbon stock can be predicted by determining the time and spatial-distribution of cleared land. Changes in forest biomass by logging, storm-damage, etc., may be identified by monitoring the presence and diameter of the crowns of overstory trees. We developed five equations containing the parameter for crown diameter for estimating tree biomass. Overstory height can be a parameter for estimating ecosystem carbon stock of various plant communities, and forest height can be measured by airborne and spaceborne sensors, etc. Generic equations containing the parameter for overstory height are available for estimating community biomass of tropical and subtropical forests. PALSAR has an advantage over other remote systems by enabling frequent sensing and semidirect biomass estimation using backscattering coefficients. However, no reasonable remote sensing methods exist for monitoring the amount of carbon loss by forest conversion and logging in forests This paper reports the results obtained in the "Tropical Rain Forest Research Project (Phase II) (Japan International Cooperation Agency); Ministry of Education and Culture,
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.