Methods

Research was conducted at three sites, namely Thilla Ounté, Ngodjilème, and Thiaytou (Figure 22.1), from December 2000 to December 2001. These sites were part of an original group of 13. They were selected using a decision matrix derived from a stratified sampling procedure based on variations in soil types, agricultural activities, land use/land cover change as assessed through remotely sensed imagery, ethnic affiliation, village size, and proximity to major roads and markets.

One-day workshops on possible carbon sequestration projects were held with seven rural councils representing the 'communautés rurales' in the research area. A market study was also conducted to assess prices of all major goods purchased and sold by farmers. Crop statistics, climate records, and reports on experimental farming sites were used to complement data gathered in the field.

The methods used in the villages were highly participatory and are equivalent to 'participatory rural appraisals' (Chambers, 1997). They included resource mapping at the village level to identify land use types and infrastructure (Lightfoot and Noble, 1993); individual household resource mapping; change matrices to assess dynamics in land use and management practices over time (Freudenberger and Schoon-maker, 1994); Venn diagrams to identify institutions influencing access to key resources (Guijt and Pretty, 1992); agricultural calendars with household labor hours; wealth ranking to stratify village households into resource endowment groups (Bellon, 2001); structured and semistructured interviews, focus groups, and discussions; and formal surveys at the field and household level (Bernard, 1994).

Soil and biomass carbon measurements were taken on seven fields in each village. They were selected using a stratified random sampling procedure and included both infields and outfields. Infields (champs de case) are directly adjacent to village compounds and typically receive more organic matter input. Outfields (champs de brousse) are fields farther away from the compounds. Herbaceous litter and root samples were collected from 42 randomly positioned replicate quadrates, and soil samples from 84 replicate quadrates from 0 to 20 cm and 20 to 40 cm profiles. Tree biomass was measured at diameter at breast height. Samples were analyzed at the Institut Sénégalais de Recherches Agricoles/Centre National de Recherche Agronomique, using the Walkley-Black method for soil samples. Past, present, and future carbon stocks and dynamics, the impact of land use and management practices, and various climate change conditions were simulated with CENTURY, a biogeochemical model (Parton et al., 1994). A detailed description of the model scenarios and input data can be found in Tschakert (2004a) and Tschakert et al. (2004).

A farmer-based cost-benefit analysis (CBA) was also performed, using data from the market and household surveys and group discussions (Tschakert, 2004b). Income-expenditure profiles for 15 management options and three resource endowment groups were created in Microsoft Excel. Net benefits and net present values at a 20% discount rate were calculated for 1 hectare of land over a 25-year period. Results from the CBA were integrated into a household cash-flow model designed in STELLA, an object-oriented graphical programming language (High Performance Systems, 2000). Model sectors and parameters are explained in Tschakert (2004b).

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