Soil properties and tree diversity along elevational gradients in a tropical agroforestry landscape in the Philippines

Abstract

The Philippines is known for its archipelagic geography and tropical climate, which support a wide range of organisms. However, determining the relationship between soil physicochemical properties and tree diversity in agricultural landscapes has been less explored. This study assessed whether soil physicochemical characteristics influence tree species diversity in various agricultural regions of Tagnote Falls in Barangay San Antonio, Remedios T. Romualdez (RTR), Agusan del Norte across different elevation ranges, specifically in low (0–200 masl), moderate (201–400 masl), and high (401–600 masl) elevation ranges. The researchers collected soil samples to analyze their soil physicochemical properties: soil texture, soil pH, and macronutrient content (Nitrogen, Phosphorus, and Potassium). A total of 16 tree species were recorded across these areas. The study results showed that the Shannon diversity index reached 1.7042, indicating very low species richness, while Pielou's evenness index averaged 0.7832, indicating that organisms were distributed evenly among species. The Kendall's tau correlation analysis showed no significant relationship between tree species diversity and soil texture or soil macronutrients (Nitrogen, Phosphorus, and Potassium). Pearson's correlation analysis also found that tree diversity was not significantly related to soil pH. The distribution of tree species in the area is more influenced by environmental and ecological factors, including microclimate differences, landscape topography, biotic interactions, and historical land-use practices, rather than by soil physicochemical properties. Overall, the findings suggest that sustainable agroforestry and biodiversity conservation strategies should consider broader ecological drivers beyond soil physicochemical properties.