Species alpha diversity of Pagbilao Grande Island vegetations, Quezon Province, Philippines

Five vegetation types were recorded from Pagbilao Grande Island (PGI), Quezon Province, Philippines, namely: 1. remnants of limestone or molave forest; 2. grassland-parang type; 3. coconut plantations cum brushlands/secondary forests; 4. mangrove-swamp forests, and 5. small strips of beach forest. A total of 251 vascular plant species belonging to 220 genera and 72 families were recorded from actual floristic surveys and vegetation analyses of PGI. This total number of species increased to 301 in 230 genera and 81 families with the inclusion of two study localities in mainland Pagbilao. About 41 percent of the island's total plant species belong to the weedy or ruderal types which are mostly annuals or biennials, hence their peak population densities were markedly seasonal in nature. These species are indicators of high level of disturbance of the landscape or ecosystem. Comparison among 26 study plots, 5 transect lines, 3 sites, and between 2 localities using the Shannon diversity index (H') revealed the following: 1. H' value ranged from 0.64 to 3.54 at plot level, the highest recorded in the ecotone of coconut plantation-secondary forest and grassland-parang type of vegetations; 2. at transect line level, H' value ranged from 2.51 to 3.90, the highest value recorded from same area with mixed vegetation types as in plot level; 3. at site level, H' value ranged from 2.51 to 4.26, the highest value was obtained from the island as a whole, and 4. at locality level, H' value ranged from 3.15 to 4.26. The entire study area had the highest H' value (=4.41) indicating a remarkably high level of plant diversity. Ten additional diversity indices - S, C, E, d, Dmg, Dmn, HB, HBe, N1 and N2, were used to evaluate the raw data obtained in this study. Majority of these measures supported the overall diversity trend shown by Shannon index. Additionally, the potential or actual uses and/or ecological roles of all taxa recorded in this study are also presented in this paper, including notes on some rare or endangered endemic taxa. A rare biological phenomenon involving formation of pistillate cones (megasporophylls) in Cycas revoluta-an introduced cycad of temperate origin is recorded for the first time. In the Philippines and probably elsewhere in the tropics, this cycad species is commonly asexually propagated by using plantlets or suckers from stem base of mature plants