Floral Diversity and Soil Property Changes as Affected by Rehabilitation in Volcanic ash-Laden Areas in Cabangan, Zambales

Abstract

Comparative Assessment conducted between the floral diversity and soil properties of rehabilitated volcanic ash-laden areas in Cabangan, Zambale sand grassland area in Barangay Cadmang, Cabangan, Zambales. Quadrant sampling method was used in vegetation sampling for trees and understorey while line intercept method was used in vegetation sampling for ground cover. Diversity was determined using Shannon-Weinner Diversity index. Dominant species were also determined by computing the importance value of each species. Composite soil samplings were collected from the area and its physical and chemical properties were analyzed at the ERDB Soils Laboratory.

Thirteen years after the establishment of species screening trials in the Pinatubo volcanic-ach laden areas in Cabangan, Zambales results showed that the species planted accelerates the rate of ecological succession in the once-degraded area. Ecological transformation is evident in the rehabilitated area compared with grassland areas with no rehabilitation measures undertaken. Among the twelve species planted, nitrogen-fixing trees such as Agoho (Casuarina equisetifolia); Narra (Pterocarpus indicus); Mangium (Acacia mangium); Rain tree (Samanea saman); Auri (Acacia auriculiformis) survived very well in the area while Gmelina (Gmelina arborea) and Dapdap (Erythrina orientalis) also survived but at a lower survival rate. Bagras (Eucalyptus deglupta), Mahogany (Swietenia macrophylla), Salago (Wilkstroemia speciosa), Bayog (Dendrocalamus merillianus) and Kauatan-tinik (Bambusa spinosa) failed to survive in the harsh volcanic-ash laden area.

In rehabilitated volcanic-ash laden areas, floral diversity is higher diversity compared with natural grasslands where there are no rehabilitation measures done. The rehabilitated area has a species richness of 59 compared to grassland with only 8. The diversity index of trees, understorey and ground cover species in the rehabilitated area revealed that it is higher compared to the grassland adjacent to it.

Soil analysis revealed changes in the soil chemical properties of the rehabilitated areas in Barangay Cadmang, Cabangan, Zambales. Nitrogen and Potassium content of the soil decreased from very high to very low N and very high to low K. The nitrogen and potassium in the soil might have been absorbed by the plants and now locked up in the biomass resulting in the decrease of the nutrients. For Phosphorus, there is a significant increase from very low to very high possibly due to mineralization. No significant changes on the pH, Calcium and Magnesium content of the soil were observed.