The use of native rain forest tree species in agroforestry systems is relatively new. In order to know the most suitable native tree species as well as exotic and fruit tree species, for use in such land use systems, there is a need to understand their nutrient requirements and effects on the soil. The study compared the levels of N, P, and K in native tree species, exotic tree species and fruit trees growing in acidic and calcareous agroforestry sites, and evaluated differences in nutrient status of soils under the three types of tree species. The tree species sampled included: Gmelina arborea, Swietenia macrophylla, and Tectona grandis for the exotic species; Dipterocarpus validus, Dracontomelon dao and Pterocarpus indicus for the native species, and Artocarpus heterophyllus, Chrysophyllum cainito, Persea americana, and Sandoricum koetjape for the fruit trees. Composite soil and leaf samples were collected for nutrient analysis.

Agroforestry is the land use system that combines trees and crops with or without animals on a given piece of land. It has been found to be effective in improving the productivity and biodiversity of degraded lands in the tropics. Degraded lands are generally characterized by low soil fertility status and unfavorable soil physical and chemical conditions (Asio, 1996; Steiner, 1996; and UNEP, 1990). Thus, the success of agroforestry on degraded lands greatly depends on the availability of mineral nutrients in the soil. This is because the trees and crops may fail to grow if there is deficient supply of essential nutrients in the soil. Nussbaum et al. (1995) reported that nutrient deficiency is the most important factor which limits the early growth of indigenous tree species on degraded soils. There are, however, certain plant species that are capable of thriving even in nutrient deficient environments. These are the slow growing wild plants which usually exhibit low absorption of nutrients (Chapin, 1980). Such plant species can be suitable for integration in agroforestry systems especially in degraded lands.

The use of rain forest or native tree species in agroforestry systems is relatively new, thus, limited information is available about their performance in such type of land use system. In a few demonstration sites in Leyte, the Germany-funded Applied Tropical Ecology Program (1991-1999) at Visayas State University, developed an agroforestry system called `rainforestation farming' that involves the use of rain forest tree species in combination with fruit trees and some other food crops to rehabilitate degraded acidic and calcareous lands (Margraf and Milan, 1996). The project showed that certain native tree species grow well in acidic sites but not in calcareous sites or vice versa. The same observation was true for the exotic tree species (i.e., non-native tree species).

Until now, the mineral nutrition of rain forest species (Wu et al., 2007) as well as certain exotic tree species widely used in reforestation projects, is poorly understood. The objectives of the study were to compare the levels of N, P, and K in native tree species (rain forest tree species), exotic tree species and fruit trees growing in acidic and calcareous sites in Leyte. The study also evaluates the differences in nutrient status of soils under the three types of tree species.

Soil And Water Sciences Journal, Agroforestry Systems, Artocarpus Heterophyllus, Mineral Nutrients, Nutrient Deficient Environments, Rainforestation Farming, Rain Forest Species, Exotic Tree Species, Reforestation Projects, Atomic Absorption Spectrophotometer, Organic Acids, Optimal Ratios.