南亚热带人工针叶纯林近自然改造早期对群落特征和土壤性质的影响

Community characteristics and soil properties of coniferous plantation forest monocultures in the early stages after close-to-nature transformation management in southern subtropical China

借鉴近自然森林管理理念,用阔叶林或针阔混交林替代南亚热带大面积人工针叶纯林已被认为是一种有效的森林培育方式。1993年,在位于广西凭祥的中国林业科学研究院热带林业实验中心伏波试验场营造了马尾松和杉木纯林。为了提高针叶纯林的生产力和维护生态平衡,2007—2008年间,运用近自然森林培育技术,分别在间伐后的马尾松和杉木纯林中套种等量混合的当地优质乡土树种红椎(Castanopsis hystrix)和香梓楠(Michelia gioii)苗木,套种密度均为405株/hm2(以下简称"马尾松近自然林"、"杉木近自然林")。选择邻近地块相同林龄、相似立地条件的未经改造的马尾松、杉木人工纯林作为对照(以下简称"未改造纯林"),研究了马尾松和杉木人工针叶纯林近自然改造早期对群落特征和土壤性质的影响,以期为马尾松和杉木人工林的可持续经营提供科学依据。研究结果表明:(1)近自然林中马尾松和杉木的密度、胸高断面积均显著低于各自未改造纯林(P<0.05),但其平均胸径均高于各自未改造纯林,其中马尾松达显著差异(P<0.05)。(2)近自然林成年树(DBH≥10 cm)的林木株数少于未改造纯林,树种仍以马尾松和杉木占据绝对优势地位,而近自然林小树(5 cm≤DBH<10 cm)和幼树(1 cm≤DBH<5 cm)的物种数、株数均多于未改造纯林,套种的红椎和香梓楠已经成为近自然林中重要值最大的幼树物种,红椎和香梓楠在马尾松近自然林中的生长状况优于杉木近自然林。(3)马尾松近自然林灌木层和草本层的物种丰富度指数、Shannon-Wiener指数、Simpson指数和Pielou指数与其未改造纯林均无显著差异;杉木近自然林灌木层的丰富度指数和草本层的Pielou指数显著高于其未改造纯林(P<0.05),其他指数则没有显著差异。(4)马尾松和杉木近自然林的土壤容重、总孔隙度、全磷、全氮、全钾和速效钾与各自未改造纯林没有显著差异,但马尾松近自然林的土壤有机碳含量和pH值显著低于其未改造纯林(P<0.05),杉木近自然林的速效磷含量显著低于其未改造纯林(P<0.05)。

Mixed conifer-broadleaved plantations within a framework of close-to-nature forest management can be a good ilvicultural alternative to large-scale monocuhures of coniferous plantations in southern subtropical China. In 1993,monocuhure stands of Pinus massoniana and Cunninghamia lanceolata were established on the Fubo Forest Farm, which is located in Pingxiang County of Guangxi. To improve the productivity of the coniferous plantation forest monocultures and maintain their ecological balance, close-to-nature silvicultural technology was employed in 2007--2008. In this process,the native species Castanopsis hystrix and Michelia gioii were interplanted in thinned P. massoniana and C. lanceolata stands （hereinafter referred to as the P. massoniana close-to-nature forest and the C. lanceolata close-to-nature forest） ,with a density of 405 trees/hm^2. In this study, P. massoniana and C. lanceolata plantation forest monocultures based on similarities in topography, soil texture, stand age, and management history were chosen as the reference to study the effects of close-to-nature transformation management in the early stages on the forest community structure and biodiversity, and soil properties, with the expectation of providing scientific reference points and a basis for the sustainable management of P.massoniana and C. lanceolata plantation forests. The results showed that ： （ 1 ） The stand density and basal area of the P. massoniana and C. lanceolata close-to-nature forests were both significantly lower than those in corresponding plantation forest monocultures （P 〈 0.05 ）, but their average DBH was higher than in the plantation forest monocultures and the average DBH of P. massoniana was significantly different （P〈0.05）. （2） The stem number of adult trees （DBH≥10 cm）of the close-to-nature forests was lower than that in the plantation forest monocultures, and P. massoniana and C. lanceolata were still the dominant species, while the tree number and species number of trees （5≤DBH〈 10 cm） and young trees （ 1 ≤ DBH〈5 cm） of the close-to-nature forests were both higher than those in the plantation forest monocultures. The inter-planted C. hystrix and M. gioii turned out to be the young tree species with the highest importance value, and they grew better in the P. massoniana close-to-nature forest than in the C. lanceolata close-to-nature forest. （3） Species richness index, Shannon-Wiener index, Simpson index and Pielou index in the shrub and herbaceous layers of the P.massoniana close-to-nature forest were not significantly different from those in the P. massoniana plantation forest monocultures. The species richness index of the shrub layer and the Pielou index of the herbaceous layer of the C.lanceolata close-to-nature forest were significantly different from those in the C. lanceolata plantation forest monocultures （ P〈O. 05 ） while the other indexes showed no significant differences. （4） Bulk density and total porosity in the soil profile,and soil total P, total N, total K and available K all showed no significant differences between the close-to-nature forests and the plantation forest monocultures, but the organic carbon content and pH value of the P. massoniana close-to-nature forest were significantly lower than those in the plantation forest monocuhures （P〈O. 05 ）, while soil available P in the C. lanceolata close-to-nature forest was significantly lower than in the plantation forest monocultures （P〈O. 05 ）.