The Mangrove survey team of the ECAN Zoning Project conducted its survey of the mangrove areas in the coastal areas of Puerto Princesa from March 28 to May 10, 2005. The survey laid out 195 in different locations selected as sampling sites. The survey recorded 18 true and 20 associate mangrove species belonging to 14 families and 27 genera of vascular plants.
Mangrove species which were found to be widely distributed include: Rhizophora apiculata (Ra), Rhizophora mucronata (Rm), Ceriops tagal (Ct),Xylocarpus granatum (Xg), Bruguiera gymnorrhiza (Bg), Sonneratia alba(Sa),Rhizophora stylosa (Rs),Heritiera littoralis (Hl) ,Bruguiera cylindrica (Bc), and Ceriops decandra.
The most dominant and important species recorded is Rhizophora apiculata (Ra). It is also the most frequent and dense mangrove species recorded. The other species most frequently encountered and with characteristically dense cover are Bruguiera gymnorhiza (Bg), Ceriops tagal (Ct), Sonneratia alba (Sa), Rhizophora mucronata (Rm), Xylocarpus granatum (Xg), Rhizophora stylosa (Rs), Sonneratia caseolaris (Sc), Bruguiera cylindrica (Bc).
In terms of species diversity, the top five (5) most diverse sampling sites are Macarascas (2 sampling sites), Sicsican, Kamuning, and Dos Palmas. Almost all sampling sites in Puerto Princesa City ranges from very low-to-low relative values of biodiversity indices using the Shannon index of measure. Likewise, the evenness of distribution of species abundances was low in all transects.
Based on the results of the survey, the mangrove forest conditions in Puerto Princesa can be aptly summarized as follows:
- Most of the sampling sites in Puerto Princesa City have an open/logged-over stocking mostly in pole sizes; only Bahile has adequate stocking and six sampling sites have moderate stocking: transects Bagong Silang, Macarascas; Manalo River, Manalo; Bacungan River, Sta. Cruz; San Jose Plantation, San Jose; Naglaom, Mangingisda; and Puntod River, Kamuning.
- Mangrove forests in the City have generally low volume forest stand; only 17 transects (9%) out of 125 transects have moderate to high volume stands;
- Intact mangrove forest with old growth stands were recorded in the following sampling sites:
- Honda bay: boundary of Salvacion (near boundary of Manalo, Tapol River, Siñaran), Sta. Cruz (Kalatubog river), Bacungan River and San Jose.
- Ulugan bay: barangays Bahile and Macarascas.
- Puerto Princesa bay: Lulubog – lilitaw island, Barangay Sicsican, Tawiran and Zigsag, Luzviminda
There are mangrove plantation in Concepcion, Tanabag, Dos Palmas, Snake Island, Starfish Island, Manalo, Sta. Lourdes, Bacungan and San Jose. The Plantation in barangay Manalo had robust growth, taller and high survival rate.
Based on the 1986 aerial photographs of NAMRIA, mangrove forest cover was estimated to be about 5,917 hectares. The ECAN Zoning Project, using 2004 SPOT5 imageries, measured the area of remaining mangrove cover in Puerto Princesa City to be 5,737 hectares. The decrease of 180 hectares over a period of 18 years or about 10 hectares per year is attributed to the rampant cutting of trees for fuel wood, charcoal making and housing materials. Clearing of mangroves for fishpond development substantially contributed to the receding forest cover. The decrease in mangrove cover over the same period could have been bigger if not for the efforts of the DENR, LGU, NGOs and POs to reforest denuded areas. About 1,344 hectares of mangroves were rehabilitated during the period 1900-1995 with a survival rate of 55% as reported by the DENR.