Ecology of Understory Plants of Forests Over Limestone in Samar Island, Philippines

Abstract

Understory plant species diversity was assessed within forests over limestone across municipalities of Paranas, Taft, and Guiuan in Samar Island, Philippines. Edaphic factors were analyzed and subjected to cluster and ordination analysis. A total of 26 understory plants were recorded, 6 fern species belonging to 6 genera in 6 families and 20 flowering plants belonging to 13 genera in 9 families. Based on the forest floor census, the highest species richness occurs in Paranas, with 18 understory plant species followed by Taft with 12 and Guiuan with 5. Community awareness together with the help of Environmental agencies such as the Department of Environment and Natural Resources and the Local Government Unit is instrumental towards plant species protection and conservation. Lower species diversity in Guiuan may be attributed to generally poor soil characteristics. Soil pH across sites was slightly acidic. Generally, the percent organic matter (OM) was high in all plots but was highest in Guiuan (16.44%) and lowest in Taft (9.61%). Variation in average soil OM across sites can be explained by differences in vegetation cover, amount of leaf litter, and continuous rain-promoting decomposition. Similarly, total N and P are high and above threshold levels in all plots. Total average N was recorded to be highest in Guiuan (0.63) and lowest in Taft (0.47). Interestingly, most of the analyzed edaphic factors are not typical of forests over limestones. Understory plant species recorded from Paranas and Taft are highly affected by Fe and EC. Plant species from Guiuan, on the other hand, is positively correlated with pH, OM%, N%, P, Cl, K, Cu, Mn, Mg, Na, and Zn. Understanding key environmental factors is important in biodiversity assessment and indicates overall environmental quality.