马尾松人工纯林近自然化改造效果分析

目的 以马尾松人工纯林为对象，分析其近自然化改造后森林质量变化和树种发育情况，为此类人工纯林的近自然化经营提供参考和决策依据。 方法 2007年在广西凭祥中国林科院热带林业实验中心对马尾松纯林开展近自然改造试验并设置样地20块，其中经营样地16块、对照样地4块；于2007年第一次全面调查获得本底数据之后，冬季执行目标树抚育择伐；2008年春执行6个阔叶树种4种组合的林下补植作业；2016年实施第二次目标树抚育伐；2007年后，每2年执行1次样地复测调查，共获取了7期数据。对7期监测数据的重要值指数、平均胸径和纯生长量等指标进行统计，从树种组成、林分结构、林分生长等方面对马尾松人工林近自然化改造效果进行分析和评价。 结果 近自然化改造的马尾松人工纯林经过13 a后，林分逐步过渡到异龄复层混交林结构。林下补植的6个树种的重要值均处于前10名，林分中出现了安息香、油桐等树种的天然更新。近自然化改造的马尾松林的林木从5 cm起测径阶到55 cm径阶范围内均有分布，呈现出经营措施促进下快速形成混交异龄林格局的发展动态；而未作处理的对照林分依然呈同龄纯林的径级分布。就生长而言，近自然化改造林分生长量显著高于对照林分，并且林分生长量主要集中于较大径阶林木，实现了林分价值的显著提升。 结论 人工纯林近自然化改造中，调整树种组成是最关键的经营措施；扩大径级结构分布范围是针叶纯林近自然化改造的基本指标；近自然化改造显著提高了森林的生长量和蓄积量；同时促进了土壤微生物发育，改善了森林土壤和生态系统整体质量。

Analysis on the Effect of Close-to-nature Transformation of Pinus massoniana Pure Forest Plantation

Objective To provide the reference basis for decision-making for the close-to-natural management of plantations, the changes of forest quality and the development of tree species were analyzed after the close-to-natural transformation of Pinus massoniana. Method In 2007, 20 experimental plots for close-to-natural transformation of Pinus massoniana single species plantation were set up in the Tropical Forestry Experimental Center of Chinese Academy of Forestry in Pingxiang County, Guangxi , including16 operational plots and 4 control plots. In 2007, the first comprehensive survey was done to obtain basic data, and the implementation of selective cutting for target tree management was carried out in the winter of the same year. In the spring of 2008, trees of six broad-leaved species were planted in the stand. In 2016, the second felling for target tree tending was implemented. After 2007, the re- survey of the sample plot was carried out every 2 years, and a total of 7-phase monitoring data were obtained. Statistical calculation was made for the important value index (IVI), average diameter at breast height and pure growth of standing volume based on the monitoring data, and the effect of close-to-natural transformation of Pinus massoniana single species plantation towards multi-species mixed forest was analyzed and evaluated based on tree species composition, stand structure, stand growth, soil and microorganisms development in forest. Result After 13 years of close-to-natural transformation of Pinus massoniana pure plantation, the stand gradually transited to the structure of uneven-aged multi-species mixed forest. The IVI of the 6 tree species enriching planted under the forest were in the top 10 of IVI series, and the natural regeneration of Styrax tonkinensis and Vernicia fordii species appeared in the stand. The distribution of diameter at breast height of Pinus massoniana transformed forest was enlarged from 5 cm to 55 cm, showing the rapid development trend of mixed uneven-aged forest under the promotion of management measures. However, the untreated control stands still showed diameter class distribution of single species even-aged stand. The growth of the transformed stand was significantly higher than that of the control stand, and the growth of the stand was mainly concentrated in the trees with larger diameter, which improved the economic value of forest woods. In addition, the soil microbial content and soil physical and chemical properties of the transformed stand were significantly improved than those of the control stand. Conclusion Adjusting tree species composition is the most important management measure in Close-to-natural transformation of forest. Enlarging the distribution range of diameter class structure is the basic target of close-to-natural transformation of conifer even-aged plantation. Close-to-natural transformation increases significantly the forest growth, promotes the development of soil micro-organisms and improves the quality of forest ecosystem.