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Growth and Yield of Thinned Stands and Coppices of Eucalyptus camaldulensis (Dehn.) and of Intercropped Rice (Oryza sativa L.) in Thailand
Dissertation Abstract:
The role of thinning in Thailand's forest village plantations was assessed. Specifically, the study sought to investigate the post-thinning situation in four- and seven-year-old Eucalyptus camaldulensis plantations, particularly the response of tree stands and upland rice. Tree stands, with an initial spacing of 2 m x 8 m, were thinned to three spacing leve ls: 4 m x 8 m, 2 m x 16 m, and 8 m x 8 m.
Thinning affected tree growth and microclimate, particularly in relation to light intensity, and likely affected the productivity of intercropped rice. However, thinning did not affect the growth of coppices in the same way that the age of the plantations did not affect coppice growths.
Based on the growth parameters, namely: relative growth rate (RGR), leaf weight ratio (LWR), leaf area ratio (LAR), leaf area index (LAI), and crop growth rate (CGR), th inning of stands with an original spacing of 2 m x 8 m (S0) to 4 m x 8 m (S), 2 m x 16m (S2) , and 8 m x 8 m (S) showed better growth in both the four- and seven-year-old plantations. However, trees in the seven-year-old plantation were more sensitive to thinning than those in the four-year-old plantation. Trees in the four-year-old plantation showed significant difference only between the highly thinned (S) and unthinned (S0) stands, but trees in the seven-year- old plantation showed significant differences between the thinned group (S1 S2, and S) and the unthinned stand (S0). The performance of the coppices with regard to thinning had no marked difference either between those from four-year-old stumps or those from different stands. Under the 2m x 8m spacing, the maximum productivity of stands in the four-year-old plantation was 25-28 t/ha, while that of stands in the seven-year-old plantation was 57.5-67.5 t/ ha. Thinning increased light transmission to the stands through LAI modification. It increased light transmission from 61.8 in S0 to 71.7, 72.9, and 78.3 percent in S1, S2, and S3 of four-year-old plantation, and from 54.3 in so to 58.0, 61.0, and 7.6 percent in S1, S2, and S3 of seven-year-old plantation, respectively. The relationship oflight transmission ratio (LTR) and LAI can be expressed as follows: In (L TR) = 4.4118- 0.215 I (LA!) with r2 = 0.919.
Due to the extreme drought that occurred during the anthesis or flowering of the rice (September), very low grain yield was obtained (1.1 - 12.3 kg/ha). However, using total biomass as the parameter, the productivity of the rice plants intercropped in the four-year-old plantation was greater than those in the seven-year-old plantation. Similarly, those in the area between the tree rows of each stand had greater productivity than those near the tree row. This was attributed to greater light intensity in the four-year-old plantation and in the area between the tree rows.
The study recommended that thinning should not be applied in four-year-old plantations if the purpose is only to enhance growth of tree stands. But for purposes of intercropping, thinning of 4 m x 8 m or 2m x 16m is reasonable. In addition, thinning was shown to be essential in seven-year-old plantations, whether or not intercropping is desired. For intercro pping purposes, thinning of 8 m x 8 m or wider is recommended.
The expected grain yield of intercropped rice was not met because of the exceptionally low rainfa ll distribution in 1987, when the experiment was conducted. Thus, intercropping with upland rice was not conclusive and, therefore, cannot be recommended.