| Popis: |
Holding approximately 89,000 Tg of organic carbon, tropical peatlands are one of the largest pedological sinks of carbon (Page et al., 2011). Waterlogged conditions in undisturbed peatlands reduce heterotrophic respiration and provide environments in which organic matter accumulates (Moore et al., 2013). However, from 1990 to 2010, the forest cover in the peatlands of South East Asia fell from 77% to 36%; at this rate of decline, all of the undisturbed peatlands are likely to have disappeared by 2030 (Li et al., 2007; Koh et al., 2011; Miettinen et al., 2011). Land-use changes in these ecosystems can have important consequences for carbon (C) budgets (Page et al., 2002; Hooijer et al., 2010). Recently a number of studies have been carried out on tropical peatlands (e.g. Couwenberg et al., 2010; Hergoualc'h and Verchot, 2011; Hirano et al., 2012; Jauhiainen et al., 2005, 2012; Li et al., 2007; Melling et al., 2005; Page et al., 2009), but some parts of the C budget are yet to be quantified. In order to fill these gaps in our knowledge, the goal of this work was to assess heterotrophic and total soil respiration, litterfall, litter decomposition and evaluate peat properties in an intact peat swamp forest, a transitional logged drained forest and an oil palm plantation located on the same alluvial peat plain. This in-situ research lasted two years, and heterotrophic and total soil respiration were separated using the trenching method. Our results from the carbon dioxide flux monitoring in the three land uses showed that the trenched plots provided a good proxy for heterotrophic respiration. The annual integrated total soil respiration was lower in the intact and drained forest than in the oil palm plantation, at 20.2 ±3.4, 18.7 ±1.1 and 26.4 ±1.7 Mg C ha-1 y-1, respectively. A similar pattern was seen in the heterotrophic respiration for the same land uses, 9.6 ±7.7, 15.7 ±1.0 and 22.9 ±2.0 Mg C ha-1 y-1, respectively. When extrapolated to the landscape, the percentage of heterotrophic 4 respiration appeared to have significantly increased following drainage, even before the conversion to oil palm, with percentages of 47.6 ±10.1, 83.9 ±7.3, 86.6 ±1.9 for intact forest, drained forest and oil palm plantation, respectively. The average litterfall in the three land uses was not significantly different, at 26.3 ±4.1, 23.2 ±4.2 and 18.6 ±3.5 kg dry litter ha-1 d-1 respectively. Overall, the C fluxes results produced in this thesis point towards a negative C balance (i.e. net ecosystem loss of C) for the drained forest, a pronounced negative C balance for the oil palm plantation and a near neutral balance for the intact forest. Other relevant findings in the study were: (1) the impacts of N fertilizer application in the oil palm plantation lasted only a few days and were unlikely to have significant consequences on the annual C budget; (2) concerns over the diurnal variability of carbon dioxide fluxes are not particularly pertinent in these tropical peatlands; and (3) the principal soil property affected by drainage and land-use change was the abundance of logs in the soil. In summary, the results produced in this thesis represent noteworthy data about the C budget and C dynamics in tropical peatlands and will help decision making by policy makers and land managers for sustainable use of these ecosystems. |
