Evaluation of species suitability of established reforestation areas of Ganano watershed, Diffun, Quirino (Philippines)

Species preferences by farmers and wood processors are reflective of their needs and intentions. From a prioritized list of 13 reforestation species preferred by both groups, four were selected and assessed of their suitability. They are gmelina, carabao mango, mahogany and Benguet pine. Out of these, the only suited species and their total suitable area in Ganano watershed are as follows: Gmelina, 8,513.75 hectares; carabao mango, 1,359.50 hectares; and mahogany, 1,146.50 hectares. The suitable area of carabao mango totally overlapped with that of gmelina. The size and distribution of suitable areas of each species were evaluated as to political jurisdiction, land use and DENR [Department of Environment and Natural Resources] projects. Within DENR projects, the areas suited to species are as follows: gmelina, 2,848.00 hectares; carabao mango, 238.50 hectares; and mahogany, 17.5 hectares. Species preferences of people do not have a good match with the distribution of suitable areas of their chosen species in their barangays [villages]. The result of species suitability assessment for gmelina was validated on 10-year-old plantations of the species located within the watershed. Results of analysis showed that areas mapped as suitable and unsuitable are significantly different from each other based on their total merchantable volume but not on the survival percentage and total height of trees. The optimal solution to the linear programming model formulated to allocate for reforestation suitable areas of each species within DENR projects with the objective of maximizing profit subject to a set of constraint was as follows: gmelina, 2,502.08 hectares; carabao mango, 238.50 hectares; mahogany, 17.50 hectares; and profit, P368,994,600.00. The computed average profit from the plantation was P133,786.76 per hectare. The resources found limiting are the area suited to mahogany and carabao mango and the permissible soil loss. Results of sensitivity analysis showed general direct relationship between the NPV [net present value] and the above-mentioned limiting resources with profit. Future effects of reforestation on the hydrology of the watershed 2-3 years after plantation establishment are expected to be as follows: evapotranspiration loss and soil moisture storage within the root zone will increase; soil moisture storage within the unsaturated zone will decrease; and groundwater storage will remain unaffected