Soil respiration is a carbon flux that is indispensable for determining carbon balance despite variations over time and space in forest ecosystems. In Kanchanaburi, western Thailand, we measured the soil respiration rates at different slope positions-ridge (plot R), upper slope (plot U), and lower slope (plot L)-on a hill in a seasonal tropical forest [mixed deciduous forest (MDF)] to determine the seasonal and spatial variations in soil respiration on the slope. The heterotrophic (organic layer and soil) and autotrophic (root) respiration was differentiated by trenching. Soil respiration rates showed clear seasonal patterns: high and low rates in rainy and dry seasons respectively, at all plots, and tended to decrease up the slope. Soil respiration rates responded significantly to soil water content in the 0-30 cm layer, but the response patterns differed between the lower slope (plot L) and the upper slope (plots R and U): a linear model could be applied to the lower slope but exponential quadratic models to the upper slope. The annual carbon dioxide (CO 2 ) efflux from the forest floor was also associated with the slope position and ranged from 1908 gC m À2 year À1 in plot L to 1199 gC m À2 year À1 in plot R. With ascending position from plot L to R, the contribution of autotrophic respiration increased from 19.4 to 36.6% of total soil respiration, while that of the organic layer decreased from 26.2 to 9.4%. Mineral soil contributed to 46.3 to 54.4% of the total soil respiration. Soil water content was the key factor in controlling the soil respiration rate and the contribution of the respiration sources. However, the variable responses of soil respiration to soil water content create a complex distribution of soil respiration at the watershed scale.

Soil respiration is a crucial carbon flux for determining carbon balance in the forest ecosystem. In Kanchanaburi, western Thailand, we measured soil respiration at different stand ages (1, 6 and 21 year-old) of teak (Tectona grandis) plantations. There were no significant differences in soil respiration among plots of different ages. Soil respiration rates showed a clear seasonal pattern of a high rate in the rainy season from April to November and a low rate in the dry season from December to March. The contribution of organic layer, roots and soil to total soil respiration was 17, 15 and 68%, respectively, in the 6 year-old teak plantation (T-Y plot). Total soil respiration rate was significantly correlated with soil water content in the 0-30 cm layer. The annual amount of CO 2 efflux from the forest floor was estimated to be 1,062-1,154 gC m -2 y -1 in the teak plantations in 1997. In 1998, annual CO 2 efflux declined to 80% of that in 1997 in the T-Y plot, probably due to low rainfall.

A well-known principle of conservation biology is that larger areas can support larger wildlife populations and thereby reduce the risk of extinction. To be effective in conserving rare species, protected areas need to be sufficiently large to include at least a minimum viable population, though few, if any, are large enough to support all of the species they intend to help conserve. To address this concern, Thailand has become a leader in establishing complexes of protected areas and surrounding lands, designed to facilitate their planning and management on an ecosystem basis. The 20 protected area complexes established in Thailand to date cover both terrestrial and marine protected areas, in virtually all parts of the country. They potentially can connect protected areas through conservation corridors that include privately owned land or land managed by other government agencies (such as Forestry, Fisheries, and Military) to connect protected areas, thereby expanding their effective size. These corridors enable the movement of plants and animals between protected areas, as well as physically linking the habitats. Protected area complexes provide opportunities for adapting to climate change and enable closer collaboration between protected areas and local communities, thereby supporting rural development.

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