We examined the effects of retention density on plant DBH (diameter at breast height), height, volume growth, stand biomass, and stand economic benefit of Cunninghamia lanceolata plantation by Pingxiang, Guangxi Province. Four treatments of different retention density were set up a 14-year middle-aged Cunninghamia lanceolata plantation, 500, 750 and 1000 trees·hm-2, with stand without thinning as the control (1500 trees·hm-2). Results showed that DBH (20.55 cm), increment in height (15.70 m), and large-diameter timber volume (18.31 m3·hm-2) of the C. lanceolata plantation were the highest in 500 trees·hm-2 treatment. The volume of living trees was the highest in the control (199.63 m3·hm-2), which was significantly higher than that in 500 and 750 trees·hm-2. The biomass of arbor layer and ecosystem, as well as the economic benefit differed significantly across the treatments, with arborous biomass (90.72 t·hm-2), ecosystem biomass (94.97 t·hm-2), and economic benefit (1.184×105 yuan·hm-2) of 1000 trees·hm-2 treatment being significantly higher than others. Reducing stand retention density increased the DBH, plant height, timber diameter, proportion of large diameter timber, average volume and biomass of single timber, but it did not enhance the volume of living trees. The retention density of 1000 trees·hm-2 was the optimum for middle-aged C. lanceolata plantation. Compared with the control, it significantly increased the total stand volume, arbor biomass, ecosystem biomass, and economic benefit by 2.3%, 5.7%, 4.7%, and 5.8%, respectively.
在广西凭祥市热带林业实验中心青山实验场的杉木中龄人工纯林(14年生)中,以不间伐为对照(密度1500株·hm-2),研究不同保留密度(500、750和1000株·hm-2)对杉木人工林胸径、树高、蓄积生长量和林分生物量及经济效益的影响。结果表明: 500株·hm-2处理杉木人工林的平均胸径、树高生长量及大径材蓄积量均最高,分别达20.55 cm、15.70 m、18.31 m3·hm-2。对照林分活立木蓄积量最高(199.63 m3·hm-2),显著高于500、750株·hm-2处理。不同处理乔木层生物量、生态系统生物量和经济效益差异显著。1000株·hm-2处理乔木层生物量(90.72 t·hm-2)、生态系统生物量(94.97 t·hm-2)和经济效益(11.84万元·hm-2)显著高于其他处理。降低林分保留密度虽然能促进杉木胸径和树高的生长,提高林分的出材径级、大径材比例、单木平均材积和生物量,但不能提高活立木蓄积量。1000株·hm-2处理是杉木中龄林最适保留密度,林分的总蓄积量、乔木层生物量、生态系统生物量和经济效益分别比对照增加2.3%、5.7%、4.7%和5.8%。.
Keywords: Cunninghamia lanceolata plantation; biomass; economic benefit; retention density.