Comparative evaluation of biodiversity and carbon sequestration of fruit tree- and forest tree-based agroforestry systems in Caraga Region, Philippines

Fruit tree-based and forest tree-based agroforestry systems in Buena Vista, Agusan del Norte, Caraga Region [Philippines] with relatively, similar topography and geographical characteristics were evaluated to compare their capacity to sequester and stone carbon and to determine whether plant diversity has influence on soil carbon stock. Plant diversity was higher in the lanzones-based agroforestry system (H=1.01). Low diversity index was recorded in falcata-based agroforestry system (H=0.64) due to the invasive and dominant characteristics of Wedelia trilobata which hindered the growth of other plant species. Higher species richness was also recorded in lanzones-based at 15.00 while falcata-based had only 6.67 because of the multi-layered canopy which allowed sunlight penetration necessary for the growth and development of the under storey plant species. Falcata trees had higher biomass than lanzones in the upperstorey stratum while lower for the understorey stratum because it had less diverse understorey plant species. Although not significantly different (p-value = 0.3964), the total carbon stored in the falcata-based agroforestry systems was slightly higher (55.80 tC/ha) than in the lanzones-based agroforestry systems (54.38 tC/ha). Falcata trees were only 4 years old while the lanzones trees were 30 years old at sampling time. Annual C sequestration in lanzones-based was only 1.81 tC/ha/yr while 13.96 tC/ha/yr for falcata-based agroforestry systems. Carbon stored in the upperstorey, floor litters, soil depths, and the interaction of area and soil depths were also found not significantly different in the two agroforestry systems. However, carbon stored in the soil was higher in the falcata-based than in the lanzones-based agroforestry systems. Carbon content of floor litters was negatively correlated with plant density (r= -0.08973) and diversity (r= -0.72284). The creeping nature and dense biomass formed by Wedelia trilobata conserved the floor litters which led to higher soil organic carbon in the falcata-based agroforestry systems.