Thesis (Ph.D.)--Chulalongkorn University, 2007

The study was conducted to assess carbon (C) stock potential in forest, reforestation and agricultural land-use types and reliably estimate the impact of land use on C stocks in Nam Yao sub-watershed (19degree05'10"N, 100degree37'02"E), Nan province, Thailand.The carbon stocks of aboveground, litter, belowground, and soil organic carbon within forest, reforestation and agricultural land were estimated through field data collection. Results revealed that total carbon stock of forests was significantly greater than the reforestation and the agricultural land (P < 0.05). In the forest, total carbon stock of hill evergreen forest was the greatest (398.43 +- 25.16 Mg C ha[superscript-1]), followed by aboveground carbon, litter carbon, belowground carbon, and soil organic carbon as of 150.07 +- 12.58, 6.86 +- 0.58, 19.56 +- 0.20 and 221.94 +- 1.66 Mg C ha[superscript-1], respectively. In the reforestation, total carbon stock of the 26-year-old reforestation was the greatest (205.67 +- 10.33 Mg C ha[superscript-1]), followed by aboveground carbon, litter carbon, belowground carbon, and soil organic carbon as of 40.70 +- 6.36, 2.22 +- 0.13, 11.14 +- 0.18 and 151.61 +- 3.66 Mg C ha[superscript-1], respectively. In agricultural land, total carbon stock of the 6-year-old fallow land was the greatest (120.21 2.43 Mg C ha[superscript-1]), followed by aboveground carbon, litter carbon, belowground carbon, and soil organic carbon as of 5.91 +- 1.21, 0.15 +- 0.01, 1.01 +- 0.07 and 113.14 +- 2.26 Mg C ha[superscript-1], respectively. Internal comparison of the average total aboveground carbon : total belowground carbon : soil organic carbon ratios (TAGC : TBGC : SOC), was 7:1:12, 3:1:14 and 6:1:106 for the forest, the reforestation and the agricultural land, respectively. This study found that land-use changes and/or land management practices resulted in carbon stocks losses, especially, aboveground carbon and soil carbon. The aboveground carbon pool is highly responsive to land-use changes while the soil organic carbon is more resistant than other pools. Results indicated that significant carbon stocks can occur in forest ecosystem conservation, restoration and reforestation.It is important for decreasing carbon dioxide in the atmosphere and climate change.