Effects of Thinning on Growth and Yield of Acacia mangium Willd. under Naturally Regenerated on Abandoned Mining Area in Phang nga Forestry Research Station

Abstract

The studies on effects of thinning on growth and yield of Acacia mangium Willd. naturally regenerated  in abandoned mining area  were carried out at  Phang nga Forestry Research Station , Takuapa district, Phang-nga province. Randomized complete block design (RCBD) with 3 replications was used in these experiments.  Four densities of trees at remained after 2-years-old thinning were 1,150, 2,250 and 3,000 trees/ha and control considered as treatments. Experimental plot size was set as 10x20 m² for all treatments. Growth performances, i.e., diameter at breast height (DBH) and total height (H) were measured annually for 4 years. Aboveground biomass was estimated by using allometric equations. Growth data of thinned trees were analyzed the differences between treatments by analysis of variance (ANOVA) and Duncan’s Multiple Range Test.

The results showed that density at 1,150 trees/ha of 6 years old was highest both DBH and H, 11.89 cm and 17.30 m, respectively. For aboveground biomass, density at 2,250 trees/ha had highest figures followed by density of 3,000, 1,150 trees/ha and control having the figures of 87.44, 82.69, 67.37 and 59.50 tons/ha, respectively. Current annual increment (CAI) of the 1,150 trees/ha density had highest increment. However, after 6 years old thinning should be repeated because stand density is too high leading to strong competition and growth limitation.

Keywords:  Thinning, Growth, Yield, Acacia  mangium Willd., Abandoned Mining Area, Phang nga Forestry Research Station