EFFECT OF THINNING ON GROWTH AND YIELD OF EUCALYPTUS CAMALDULENSIS DEHNH. PLANTATION

Abstract

Effect of thinning on growth and yield of Eucalyptus camaldulensis plantation were investigated at Ratchaburi Forest Experiment Station, Ratchaburi Province. The data collection was done during 1992 to 1995 at 1 year before thinning (7-year old) and 2 and 3 years after thinning (9 and 10-year old). The whole experimental site was consisted of 2 x 2 m spacing, 4 plots of thinning in alternate rows and 4 plots of unthinned plantations. In each plot, diameter at ground level (D₀), diameter at 30 cm level (D₃₀) and diameter at breast height (DBH) of trees were measured. Sprouts coppiced from the thinned stumps were sampled 10 clumps per plot representing the mean stump size of each plot then D₀ and DBH of sprout in sample clumps were measured. Growth parameters in forms of current annual increment and relative growth rate of diameter, height, biomass and yield of trees, sprouts and total trees and sprouts were analyzed. The results revealed that after thinning for 3 years, current annual increment of diameter and height in thinned plots as well as their relative growth rates showed larger values than in unthinned plots. Mean biomass in trees left after thinning of stem biomass and total above ground biomass in thinned plots were larger than in unthinned plots but mean branch biomass and leaf biomass were smaller. Yield of trees left after thinning in forms of aboveground biomass in unthinned plots were higher than in thinned plots. Yield of trees combined with sprouts in thinned plots were large but still smaller than in unthinned plots. Relative growth rate of total trees left after thinning and sprouts in thinned plots were found to be higher than in unthinned plots. It is then concluded that when stand was 7-year old with 2 x 2 m spacing, the row thinning is more suitable than unthinning. Although the number of trees remained only half of unthinned plots, they showed higher growth rate than in unthinned plots for about 2 times. The future production of the thinned plots is expected to increase to the same level as in unthinned plots.