Pattern of species diversity and carbon stocks along the intertidal zones of protected mangrove forest in southern Philippines

This study examined the composition, structure, and carbon storage of the Pangasihan Mangrove Forest Reserve in the Philippines. The reserve, spanning 64 hectares, was established in the 1990s and comprises natural and planted mangrove species dominated by Sonneratia alba, Avicennia marina var. rumphiana, and Rhizophora apiculata. Sampling was conducted along three transects covering the tidal gradient, with three sampling plots established along each transect. Trees with a diameter at breast height (DBH) ≥ 5cm were inventoried, and vegetation analysis was performed to determine species importance value, species richness, and diversity indices. Biomass estimation for carbon stock utilized published allometric equations and specific wood density values were applied. Carbon stock estimates were converted to CO₂ equivalents. Based on the result, the richness and abundance of mangrove species in the different intertidal zones is higher in the landward zone than in the seaward and middle ward zones. Species richness indices were 1.58, 1.00, and 3.37, while the diversity index is generally low at 1.57, 1.53, and 2.25 for seaward, middle ward, and landward, respectively. The carbon stocks from mangrove tree biomass in different intertidal zones were higher in the seaward region with computed values of 777, 422, and 488 t ha^-1 and carbon stock densities of 350, 190, and 219 t C ha^-1 for seaward, middle ward, and landward, respectively. This study generated valuable insights on which zone has higher species diversity and carbon stock, which could be helpful in the planning and management of the study area.