Abstract

Transects of 500X100 m were marked in 6 teak [Tectona grandis] plantations (14-65 yr old) in different Forest Divisions in Kerala to represent different slope positions. Within each transect 100X100 m plots were marked and top height and girth measured for a group of 5-7 dominant trees per plot. The site quality (site index) of each plot was calculated based on the height attainable at 50 yr old (close to the harvesting age). Among the plots 2 were from site quality (SQ) I (30.5-36.6 m), 4 from SQ II (24.4-30.4 m), 12 from SQ III (18.3-24.3 m) and 11 from SQ IV (12.2-18.2 m). Soil samples were taken from a pit at the centre of each dominant group of trees, and various physical and chemical properties determined for different depths (0-20, 20-40 and40-60 cm). The contents of sand, silt, clay, organic C, exchange acidity and exchangeable bases were adjusted for gravel content and values for the different depths composited for analysing their relations with SQ. Since there were age differences between the transects a one-way classification was done into 11 age/SQ groups in order to peform the analysis, which was done with respect to altitude and slope, as well as for soil properties. There were significant differences in soil properties between groups. Increases in gravel and exchange acidity and decreases in sand, silt, pH and exchangeable bases resulted in a lower SQ along (and generally across) transects. Trends with bulk density, clay and water holding capacity were inconsistent. In a multiple linear regression analysis, soil variables accounted for 31 of the variation in top height, and age 63. Partial regression coefficients indicated the important effects of gravel, sand, pH and exchange acidity