Changes in Soil Nitrogen, Phosphorus, and Carbon Stocks in a Forest Ecosystem at Different Successional Stages in Leyte, Philippines

Forests play a vital role in the global carbon cycle since these are sources and sinks of carbon. This study was conducted to evaluate the changes in soil carbon stocks and some essential nutrients of different succession stages in two different soil types in Leyte Province. A space-fortime substitution approach was done in this study. Measurements of the physical, chemical, and biological properties of the soils were done following standard methods. The sites were characterized as Ultisol (Site 1 – Baybay, Leyte) and Andisol (Site 2 – Ormoc City). Results showed no significant differences among all the soil properties in the different forest succession stages in each site. However, variation in soil properties between sites was clearly observed. Site 2 had higher soil porosity and water holding capacity, but had lower bulk density than Site 1. Soils in Site 2 were more acidic, had higher total organic carbon, total N, and CEC but had pot, lower exchangeable bases and CEC than in Site 1. Both sites had low eff available P. The C:N ratios in all forest successions were significantly lower in Site 1 than in Site 2. This conforms to the results of substrate-induced respiration, where Site 1 was more active in CO evolution than Site 2. 2 Moreover, the soils in Site 2 significantly contained more SOC stocks (108- -1 -1 180 Mg C ha ) than in Site 1 (49-76 Mg C ha ). However, SOC stocks did not vary significantly in both sites. This result implies that the determination of soil physico-chemical properties is important in evaluating the changes of C:N ratios as well as of SOC stocks. In this study, Andisols had higher potential in storing organic C than Ultisols.