Soil properties variation in a small-scale altitudinal gradient of an evergreen foothills forest, Ecuadorian Amazon Region

The aim of this study was to evaluate variation in the soil physical and chemical properties in a small-scale elevation gradient at 601 to 1000 m above sea level (m.a.s.l) in an Evergreen Andean-Amazonian forest. The soil sampling was divided into four elevation zones, establishing five permanent monitoring plots (PMP) for each one, where soil physical and chemical properties were determined at depths of 0-10 cm and 10-30 cm. For the altitudinal soil-gradient relationship analysis, multivariate statistical methods were used. The results suggest that some soil properties - such as bulk density (BD), saturated hydraulic conductivity (K sat ), total porosity (TP), soil organic matter (SOM), total nitrogen (TN), available phosphorus (P), potassium (K + ) and exchangeable calcium (Ca 2+ ) were significantly affected by altitude. Soil pH, Al 3+ and exchangeable acidity did not follow any defined pattern with respect to the altitudinal gradients. SOM, TN, Ca 2+ , K sat , TP and retention porosity (RP) exhibited an increase according to altitudinal gradient, whereas soil bulk density, K + and P showed an inverse behavior, with higher values at the lower elevation gradient. The principal components analysis (PCA) and the redundancy component analysis (RDA) also revealed a clear separation of soil properties among altitudinal gradient and confirmed that these variables were necessary in order to explain variation in the soil physical and chemical properties as an elevation gradient function.