Watershed rehabilitation potential of Calliandra (Calliandra calothyrsus Meissn.) in Manolo Fortich, Bukidnon, Philippines

This study analyzed the contribution of Calliandra calothyrsus Meissn. in rehabilitating ecosystems function in the degraded areas of Manolo Fortich, Bukidnon. Landscape Function Analysis (LFA) was used to determine stability, infiltration, nutrient cycling, vegetation structure and habitat complexity, while the Shannon- Wiener was used for species diversity. Benefit-cost analysis (BCA) on the use of Calliandra for watershed rehabilitation was compared with a pure stand of fast-growing Brazilian fire tree (Schizolobium parahyba (Vell.) S.F. Blake). There were four seral stages of Calliandra: RA1 (1-year old Calliandra), RA4 (4-year old Calliandra), RA6 (6-year old Calliandra), and RA12 (12-year old Calliandra) that were compared with a grassland (GL) and a nearby secondary forest (SF). Results of the LFA showed that stability, infiltration and nutrient cycling indices were highest in SF at 84.7, 79.4 and 79.8, respectively. Indices for RA12 approaches that of the SF having values of 84.5, 65.3 and 64.4 for stability, infiltration and nutrient cycling, respectively. The use of Calliandra as a pioneer species in watershed rehabilitation hastened the biogeochemical functions of the rehabilitated sites and approaches the functions of SF with increase in age. Pearson correlation showed that only pH and CEC have influenced the biogeochemical functions of the study areas. pH was positively highly correlated with stability (p = 0.867) but negatively correlated with infiltration (P =-0.808) and nutrient cycling (P =-0.773) indices. CEC was negatively correlated with all indices at 0 = -0.541, p = -0.761 and o = -0.735 for stability, infiltration and nutrient cycling, respectively. RA12 showed the highest basal area, had the tallest trees as exhibited by the tree height when compared with RA1, RA4 and RA6 and even GL and SF. RA12 received silvicultural treatments employed in plantation such as proper spacing that was absent in SF, hence, taller and larger trees were measured. Shannon-Wiener diversity indices showed that SF consistently had higher H' (2.697, 2.904, 2.808 and 2.231) for all plot sizes (1 x Im, 2 x 2m, 5 x 5m and 10 x 20 m) when compared with the rehabilitation sites (RA1, RA4, RA6 and RA2) and the GL. Habitat complexity showed that RA12 and SF had the highest score for tree canopy (70%), logs, rocks, debris, litter (70%) and permanent water adjacent to the area indicating that the vegetation is able to support faunal population in the area. Cashflows developed for Calliandra when used in watershed rehabilitation using a 15% discount rate showed a positive net present value (NV) of PhP 202,090 and a benefit-cost ratio (BCR) of 14. On the other hand, planting Brazilian fire tree with 10 years rotation gave an NPV of PhP 56.522 and a BCR of 1.62. Calliandra cannot compete with tall timber trees and growth is negatively affected by shading as shown in RA12, hence, did not pose problem on Calliandra eradication.