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Structure and Floristic Diversity of the Vegetation on an Ultramafic Hill in Surigao del Sur, Philippines
Dissertation Abstract:
An exhaustive floristic inventory was conducted in three 1-hectare plots in a forest logging concession area on the eastern slopes of the Diwata Mountains in Surigao del Sur, Mindanao, Philippines. Each plot was subdivided into 25 quadrats of 20 x 20 m2. All plants within each plot with stem diameter of > 5 cm were marked, tagged, identified, and mapped. The plot design and the marking, tagging and mapping of the plants followed the procedure outlined in the biodiversity monitoring software BIOMON. The population structure, importance values, and species association were also analyzed for each plot. Soil samples and leaf tissue samples of the five dominant species in each plot were analyzed for chemical composition of metallic elements. Biodiversity indices were computed using the software program BIOPRO.
The main plot (Plot 1) was in a forest on ultramafic rocks and the other two plots (Plot 2 and Plot 3) were in lowland dipterocarp forests. A total of 281 species and 124 families of vascular plants were identified in all three plots or an average of 141 species plot-1. Trees represented the most diverse life form averaging 94.9 percent of the total number of individual per plot for all life forms. Average stem density for trees (dbh > 5 cm) (excluding palms and pandans) was 1370 trees ha-1, with a total density for all life forms estimated to 13,218 plants ha-1. The total basal area for the plots ranged between 31.98-m2 ha-1 for the ultramafic forest and 35.21-37.78 m2 ha-1 for the dipterocarp forest.
Species diversity was greatest in Plot 2 with a Shannon-Weiner diversity index of 2.228 and 169 species and 48 families. About 49.41 percent of the species were also unique for the plot. However, Fisher’s log series index was highest for Plot 1, the ultramafic forest, with value of 64.10 among the different plots studied and greater evenness of 0.794. These values indicate that the flora of the ultramafic forest was more diverse than the dipterocarp forests in Plot 2 and Plot 3. The number of individuals (21,154) representing various life forms was also recorded highest for the ultramafic plot. This figure was about twice the values for the dipterocarp plots.
Most species were only locally abundant for all plots. In Plot 3, 42 percent of the species were represented by only a single individual tree; in Plot 1, 23.8 percent and Plot 2, 36.6 percent. The three most dominant species in each plot were Plot 1 – Pandanus copelandii, Calophyllum blancoi, and Terminalia surigaensis; Plot 2 – Shorea palosapis, S. negrosensis, and Mallotus hirsutus; and Plot 3 – S. palosapis, Oncosperma gracilipes, and Canarium barnesii. P. copelandii was found significantly associated with Teijsmanniodendron ahernianum in Plot 1, while C. barnesii with Myristica nitida, and M. nitida with Syzygium brevistylum were found to be highly associated in Plot 3. Except for three individuals at the edge of the plot, no other dipterocarp trees were found in Plot 1, the ultramafic forest.
