Abandoned Fishpond Reversal to Mangrove Forest: Will the Carbon Storage Potential Match the Natural Stand 30 Years after Reforestation?

Mangroves are essential carbon reserves, and their role in carbon sequestration is remarkable. However, anthropogenic pressures such as aquaculture development threatened this highly susceptible ecosystem. Thus, the need to rehabilitate abandoned aquaculture ponds is a must to offset the ecological losses over the economic gains derived from these mangrove land-use changes. Thus, we chose a reforestation site of a once heavily utilized fishpond devastated by a tsunami in the late 1970s in Zamboanga del Sur, Philippines. We then established a similar study plot in a nearby natural mangrove forest as a point of reference. We determined the heterogeneity in vegetation and estimated the aboveground and soil carbon storage capacities. We also examined the distinct changes in species composition and zonation from the seaward towards the landward zones. About 30 years after the abandoned fishpond rehabilitation, we found the tree density of the Rhizopora mucronata Lamk. and Avicenia marina (Forsk.) Vierh-dominated reforestation site was higher (271 trees ha⁻¹) compared to that of the Rhizophora apiculata Blume-dominated natural stand (211 trees ha⁻¹) (p < 0.05). The total aboveground biomass at the natural mangrove forest was 202.02 Mg ha⁻¹, which was close to that of the reforestation site (195.19 Mg ha⁻¹) (p > 0.05). The total aboveground C in the natural mangrove forest was 90.52 Mg C ha⁻¹, while that of the reforestation site was 87.84 Mg C ha⁻¹ (p > 0.05). Surprisingly, the overall soil C content at the natural forest of 249.85 Mg C ha⁻¹ was not significantly different from that of the reforestation site with 299.75 Mg C ha⁻¹ (p > 0.05). There was an increasing soil C content trend as the soil got deeper from 0–100 cm (p < 0.05). The zonation patterns established across the landward to seaward zones did not affect the aboveground and soil carbon estimates (p > 0.05). Our study highlights the effectiveness of abandoned fishpond rehabilitation and calls for continuous restoration of the remaining abandoned aquaculture ponds in the country because of their ability to sequester and store carbon. Lastly, their potential to store huge amounts of carbon that will counterbalance anthropogenic CO₂ emissions is likewise highlighted.