In this study which we conducted at the VSU-GTZ reforestation project site (see photo) in Mt. Pangasugan, Leyte, Philippines, we looked at the influence of two native tree species- Parashorea plicata and Dipterocarpus warburgii- on the nature and rate of changes on the chemical properties of a highly weathered soil following a change in land use from Imperata grassland to plantation of indigenous tree species. Monthly sampling of carefully selected plots in two sites (dominated by native or indigenous species) was carried out to evaluate temporal as well as spatial variations in important soil chemical properties. In addition, rates of litter decomposition of the two species were also investigated on the sites.
We found significant monthly variations of soil pH, organic matter content, total N and available P. Significant differences between sites were also observed for organic matter, total N as well as Ca and Mg contents suggesting individual tree species effects. For most of the soil properties evaluated, irregular fluctuations at certain times of the year characterized by periods of high and low availability. This suggests a highly dynamic nutrient cycling within the system.
The influence of these native tree species could be attributed to its litter contribution to the soil. In both sites, some centimeters thick of organic layer could be observed on the soil surface throughout the year. An evaluation of decomposition revealed high rates for both species. This result suggests that aside from being dynamic, the cycling of nutrients also tends to be efficient. This efficient cycling of nutrient may also help explain why these native tree species appeared to grow well despite the inherently low levels of nutrients in this old, highly weathered soil.
Kelly JM and PA Mays. 1999. Nutrient supply changes within a growing season in two deciduous forest soils. Soil Sci Soc Am J 63: 226-232.
Sueta JP, VB Asio and AB Tulin. 2007. Chemical dynamics of a highly weathered soil under indigenous tree species in Mt. Pangasugan. Annals of Tropical Research 29: 73-89.