Forestry for mitigating the greenhouse effect : an ecological and economic assessment of the potential of land use to mitigate CO2 emissions in the Highlands of Chiapas, Mexico

The present study intends to answer some of the important questions that arise when translating projects that have an ecological potential to mitigate carbon excesses, into actual implementation of these projects in a farmer-dominated landscape. Farm and community forestry projects for greenhouse gas mitigation in such environments would involve numerous participants, a high variety of small-scaled systems spread over large areas, with individual adaptations of general management procedures due to personal interests, local conditions, and previous experiences. In this book the results are presented of a study to estimate the flux of carbon from the terrestrial ecosystems to the atmosphere from the 1970s and 1990s of an intensively impacted and highly fragmented landscape. About 20 x 10 6 MgC were released to the atmosphere during the period of time covered by the study. Approximately 34% of the 1975 vegetation carbon pool disappeared. A feasibility study was carried out to (i) identify farmer preferred and ecologically viable agroforestry/forestry systems and their ex ante carbon sequestration potential; and to (ii) assess the economic potential of carbon offsets of such systems.A total of five land-use systems were considered viable, while farmers presented local adjustments in preferred species, planting arrangements, and rotation times. The carbon sequestration potential varied highly between the systems and the regions (from 26.7 to 338.9 MgC ha -1 ). The total cost of one MgC ha -1 varied between $US 1.84 and 3.98 for the systems selected in the Tzeltal region and between $US 1.47 and 11.15 for the systems in the Tojolabal region. The differences in costs within the same region were due to differences in establishment and opportunity costs, whereas the differences between the two areas were due to differences in the carbon sequestration potential of the regions. The carbon sequestration potential of the Highlands of Chiapas was estimated, based on an incentive program that would stimulate small farmers and rural communities to adopt biomass-accumulating measures, such as agroforestry or improved forest management. It was estimated that 38 × 10 6 MgC could be sequestered for under $US 15 MgC -1 , of which 32 × 10 6 MgC by means of sustainable forest management. The choice of a baseline rate of biomass loss in the "business-as-usual" scenario remains a critical issue to estimate the carbon sequestration potential of forestry.The main sources of uncertainties observed in the calculations of the GHG-offset potential of a forestry project were related to: (i) classification of LU/LC types, with observed differences of up to around 8% in land cover estimations; (ii) estimation of C-stocks within each LU/LC type, with uncertainties varying from around 13 to 34% in total C-stock; (iii) historical evidence of LU/LC changes and related GHG fluxes applied in baselines, giving rise to uncertainties of up to about 16% in the estimation of fluxes, whereas varying baseline assumptions produced differences between 31 and 73% in the C-mitigation calculations, with levels of uncertainty in the differences of up to 74%; and (iv) simulation techniques used to calculate future baseline and project C-fluxes, which generated uncertainties of up to around 10% in overall C-mitigation estimations.A self-reporting system with on-site spot-checks is the most appropriate method to assess the impact on carbon fluxes of a farm-forestry project, which typically include a high diversity of small-scale systems and numerous participants. The monitoring and evaluation procedure outlined in this study, facilitates the collection of field data at low cost, helps to ensure that the systems continue to address the needs of farmers, and gives the farmers an understanding of the value of the service that they are providing.Any method to estimate carbon dynamics has to deal with sources and levels of variability and uncertainties in data. In this dissertation various approaches were used to estimate the impact of variability or uncertainty in data or assumptions. In Chapter 3, the standard deviation of collected biomass data was used as an indicator to estimate the confidence interval of the regional C flux. In Chapter 4, the uncertainty of information was dealt with by varying tree growth due to expected differences in site conditions. In Chapter 5, a sensitivity analysis was used to test the impact of baseline emission assumptions and capital interest rates on the cost of mitigating one Mg carbon. Varying baseline assumptions and carbon transfer parameters within a forest ecosystem was used in Chapter 6 to identify the most important sources of error in the C mitigation estimation of forestry projects.