Typhoon Damage Assessment of Natural and Planted Mangroves in Bais Bay, Negros Oriental, Philippines

Category 5 Typhoon Odette, internationally known as Rai, devastated the Central Philippines in December 2021, causing immense damage to the country’s infrastructure, agriculture, and ecosystems. Coastal vegetative ecosystems, which include mangroves, are exposed to strong wind and wave energy during extreme weather events. Considering their importance in providing a myriad of ecosystem services to coastal communities, the post-typhoon assessment of mangroves will serve as a guide to future rehabilitation efforts. On August 13 and 14, 2024, 8 months after Typhoon Odette, the community structure characteristics (species composition, stem density, basal area, and regeneration potential) and damage severity of planted and natural mangrove forests were assessed in eight 10x10 m permanent plots located in Bais Bay, Central Philippines. Trees inside the plots were observed for signs of damage and were ranked in terms of damage severity. The differences in damage between natural and planted stands were statistically significant at χ2=5.113; p=0.02. There was a weak association between stand type (natural or planted) and damage incidence (φ= -0.110), with reforested sites being more associated with damaged trees. Rhizophora stylosa showed low resilience, having the highest mortality rate of 15 trees, 14 of which were in planted sites. Most of the R. stylosa stands also failed to show refoliation 8 months after the typhoon, in contrast to Sonneratia alba and Avicennia marina trees which displayed refoliation as well as new stem sprouts despite also sustaining damage. Results of the study indicate that future mangrove planting projects should aim to plant a diverse set of mangrove species while following the correct species zonation of the forest (i.e., storm-resilient Sonneratia alba and Avicennia marina in seaward zones and Rhizophora in midward zones) to increase resiliency, especially in areas vulnerable to typhoons. Adequate space conducive for lateral growth should also be provided between planted trees.