RENFODA – JICA project
Chongrak Wachrinrat12,Somphat Khlangsap1, Ladawan Paungchit2, Sakhan Teejuntuk2 and Monton Jamroenprucksa2
[1] Trat Agroforestry Research Station (TAfRS), Kasetsart University Research and Development Institute (KURDI) 50 Paholyothin, Lardyao, Chattuchak, Bangkok 10900 Thailand email: fforcrw@ku.ac.th
2Department of Silviculture, Faculty of Forestry, Kasetsart University
Abstract
A study on the effect of thinning on the growth and yield of Acacia mangium and Dipteocarpus alatus was carried out in mixed stand of 5-year-old A. mangium and D. alatus at the Forest Industry Organization Takum Plantation, Trat Province. The data was collected in 2003, 2004 and 2005. The experimental design is randomized completely block design with three treatments and three replications: no thinning, 50% thinning and clearcutting. Each plot was 15 m x 30 m. The sample trees were cut to estimate various parts of aboveground biomass through allometric correlation to estimation of stand biomass. The growth of trees were measured and calculated two tears after thinning. The results showed that the average total stem biomass, commercial stem biomass, branch biomass and leaf biomass of 5-year-old A. mangium were 128.9, 127.2, 19.1 and 7.4 kg tree-1 or 59.7, 58.9, 8.8 and 3.4 t ha-1, respectively. The average total stem volume and commercial stem volume were 0.236 and 0.227 m3 ha-1 or 109.3 and 105.2 m3 ha-1, respectively. Thinning levels affected the growth of trees in terms of current annual increment (CAI) and relative growth rate (RGR) of diameter at breast height and height. It was showed that CAI and RGR in thinning plots were higher than no thinning plots. In addition, RGR of biomass of A. mangium also showed the same trend. However, D. alatus was found to be more sensitive to thinning levels than A. mangium. The study concluded that for short and long rotation species mixed planting, the thinning of 5 to 6-year-old short rotation species is recommended for increasing the growth rate and yield of trees.
Key words: thinning, growth, yield, mixed plantation, Acacia mangium, Dipterocarpus alatus
Introduction
A massive reforestation programme has long been recognized as an essential part for the sustainable management of forest resources in Thailand. In order to overcome the shortage of domestic wood consumption, several fast growing timber species have therefore been planted throughout the country. However, long rotation timber species are also high demanded. Mixed planting of short and long rotation timber species is generally recommended for several economical and environmental purposes. However, mixed planting pre-supposes a respect for the restrictions and special factors implicit in the species mixtures selected. Mixtures should be based on a matching of the species ecological requirements with the climatic, edaphic and topographical characteristics of the proposed planting site (Wormald 1992, Evans 1992). For management of mixed plantation, thinning is a practical method of intermediate cutting by releasing some trees from the stand to increase the growth rate of trees after thinning (Suwannapinant 1983). Furthermore, it can control pests and diseases and earn incomes before the final harvesting. In addition, thinning can be one of silvicultural methods to establish forest stands for short and long rotation species. Fast growing species mixed with native species is an important method of establishing multi-stories forests. The fast growing species could be thinned for economic incomes and in the process increase growing spaces to improve the growth of the native species.
The objectives of the present study are to study the growth and yield of Acacia mangium-Dipterocarpus alatus mixed plantation under different thinning regimes, and their use as basis for management in mixed plantation.
Methodology
This study was carried out in mixed stand of 5-year-old A. mangium and D. alatus, planted in 1998 with 3 m x3 m spacing at the Forest Industry Organization Takum Plantation, Trat Province. The experimental plot size was 54 m x108 m (0.5832 ha). The experimental design is the randomized completely block design with three treatments and three replications. Each plot was 15 m x 30 m. The treatments were thinning levels of A. mangium as follow:
– Control (no thinning)
– 50% thinning (thinning alternate row)
– Clearcutting (100% thinning).
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