间伐强度对马尾松人工林冠下套种树种生长的影响

  目的  研究间伐强度对马尾松人工林冠下套种阔叶树生长的影响，为马尾松人工纯林向针阔混交林转化和阔叶树种潜在价值的开发提供科学依据。  方法  以广西凭祥马尾松人工林为研究对象，设置3种不同间伐强度（80%、50%和30%）的试验样地，间伐后冠下套种大叶栎、红锥、灰木莲、格木4种阔叶树，分析间伐强度对阔叶树胸径、树高和冠幅生长的影响，并利用相关分析检验影响套种树生长的关键因子。  结果  不同强度间伐9年后阔叶树的结构特征和生长状况存在显著差异，大叶栎和灰木莲的生长量随间伐强度的增大而增加，格木受采伐强度影响不显著。不同强度间伐后大叶栎的胸径、树高生长速度均为最快，且伐后3年就出现快速生长；红椎的冠幅生长在80%和50%强度增加较快，间伐5年后生长加快；格木在间伐后9年间生长最慢。相关性分析表明，马尾松林分密度、林下灌木盖度、土壤厚度和土壤有机质对套种阔叶树的生长均有显著影响。  结论  间伐后林分的生长空间和环境条件得到有效的改善，林下套种的阔叶树都出现了不同程度的快速生长，但也因间伐强度和树种特性的不同而产生差异，不同树种在中高强度的间伐下，生长速度更佳。在制定“间伐 + 套种”的经营措施时，应该考虑适当延长间伐间隔时间和树种生态学特性，马尾松人工林中高强度间伐（80%或50%）后，建议选用大叶栎、灰木莲进行冠下套种，发挥适应性强和生长迅速的优势，提升人工林的生态功能；低强度（30%）间伐后宜套种红椎和格木以培育长周期、高价值的大径材。 

Effects of thinning intensity on the growth of interplanting broadleaved trees under Pinus massoniana plantation

  Objective  This paper analyzes the thinning effect of replanting tree species of Pinus massoniana plantation in southwestern Guangxi, southern China in order to provide a better guidance and theoretical basis for scientific and reasonable management.  Method  Four kinds of artificial replanting tree species were used as the research objects to study the growth of replanting tree species under Pinus massoniana plantation after three thinning intensities (80%, 50%, 30%), and to analyze the influence of stand and habitat factors.  Result  The thinning intensity had a significant impact on the growth of interplanting broadleaved trees. The thinning intensity significantly affected the growth of broadleaf trees, and the growth of Castanopsis fissa and Manglietia glauca increased with thinning intensity increasing, but the influence of cutting intensity on Erythrophleum fordii was not significant. The DBH growth of Castanopsis fissa was higher than that of other three tree species, and the peak appeared in the third year or so. The effect of thinning intensity on the growth of Erythrophleum fordii was accelerated in 30% thinning intensity after nineth years. Castanopsis fissa and Castanopsis hystrix were suitable to grow under 50% thinning intensity, and the increase of DBH appeared in the fifth year. The main factors affecting the growth of replanted trees were tree density, organic matter and soil thickness, showing significant differences in replanted trees (P < 0.05).  Conclusion  Different tree species have better growth rate under medium and high intensity thinning. Castanopsis fissa and Castanopsis hystrix can make full use of the space left behind by high-intensity thinning, give full play to the advantages of rapid growth and improvement of forest soil, while Erythrophleum fordii and Castanopsis hystrix can keep the growth rate continuously by the environmental conditions created by Castanopsis fissa and Manglietia glauca. It is suggested that Quercus griffithii and Manglietia glauca are suitable tree species in the thinning intensity (80% or 50%), Castanopsis hystrix and Erythrophleum fordii are suitable tree species under the 30% thinning intensity of Pinus massoniana plantation.