Improving Productivity, Profitability and Sustainability of Degraded Grasslands Through Tree-Based Land Use Systems in the Philippines - Smallholder Tree Growing for Rural Development and Environmental Services - page 279

Claveria is located 40 km northeast of Cagayan de Oro. It lies on an undulating
plateau between a coastal escarpment and mountainous interior, ranging in eleva-
tion from 200 to 500 m above mean sea level. The soil in the site is well-drained
oxisol, acidic (pH between 4.5 and 5.0), and has a soil profile depth of more than
1 m (Garrity and Agustin 1995). The study site has an average annual rainfall of
2,000 mm for a 5-year period (Limbaga 1993). The wet season is from May to
October while the dry season occurs for the rest of the year. The majority of the
crops planted include root crops, tomato, and maize, with maize being the dominant
crop and is used as staple food and animal feed. Tree farming of fast-growing tree
species (e.g., Gmelina arborea , Acacia mangium , and Eucalyptus deglupta ), is
emerging in the area.

14.2.3 Estimation of Carbon Sequestration

Carbon flow (in the form of CO 2 ) in crop or forest production depends on two proc-
esses: fixation (assimilation) and emission processes. The former represents the
biomass growth in living crop/trees (in CO 2 equivalents) due to photosynthesis,
while the latter represents the biomass decay of the wood (in CO 2 equivalents),
resulting from natural mortality or human related removals and end-uses. For this
study, the carbon flow for each land use system was estimated using SCUAF by
simulating the net carbon gains/losses from plant-soil system carbon and annual
emissions from decaying biomass.
The SCUAF model simulated the changes in plant-soil system carbon annually
as the difference between total carbon gains and losses for each system. Gains for
plant-soil system carbon are from the atmosphere like photosynthesis or net pri-
mary production, and from additions of organic material from outside the system.
Soil carbon arising from organic matter or leaf litter decomposition is accounted for
in the gains from photosynthesis. Carbon losses, on the other hand, are those from
harvest, burning, erosion and oxidation. The mathematical derivation for the calcu-
lation of net carbon flow is given in Appendix 1.

14.2.4 Land Use Systems Modeled in the Study

The study modeled six land use systems based on the existing and potential land
use transformation pathways for Imperata grassland (Table 14.1). Farmers at the
study site practiced these systems singly or in a portfolio of farming systems as a
household livelihood strategy of reducing income risks.
IMPLUS refers to Imperata -dominated grasslands that have not undergone any
burning or cultivation. In the modeling exercise, 100 percent of the area of the one-
hectare farms was devoted to Imperata and 95 percent of above-ground biomass
was consumed by grazing animals (cattle) during the year while the remaining parts