抚育间伐对北京山区侧柏人工林林下植物多样性的短期影响

侧柏人工林是北京山区主要生态公益林，由于林分密度普遍偏大，树木长势弱，林下植被稀疏，生物多样性锐减，林分质量普遍较差，难以全面发挥生态功能.抚育间伐作为森林经营中一项基础性措施，对于提高侧柏人工林质量，恢复林下植物多样性，加速退化生态系统的重建具有重要意义.研究抚育后侧柏林下植物多样性的动态变化，为合理的抚育技术提供依据，2004年在北京山区分别选择低山阳坡薄土、阳坡厚土、半阳坡厚土3种立地类型的侧柏人工林进行弱度、中度、强度间伐（修枝、割灌试验），共设置样地41块.2005和2006年夏季对林下植物多样性变化情况进行了调查研究，结果表明:抚育后第1年和第2年的林下植物种类、数量、Simpson多样性指数（D）、Shannon-Wiener多样性指数（H′）和林下植物总生物量都随着抚育强度的增大而增加，林下植物垂直结构也随抚育强度增大而分布明显；强度抚育2年后，阳坡薄土、阳坡厚土和半阳坡厚土侧柏林下灌木分别增加4、5、5种，草本增加13、10、8种，并促使侧柏林下植物向旱中生、中旱生转变；中度、强度抚育后各立地条件的侧柏林下植物生物量均可达到5 t/hm2以上.从短期影响效果看，中、强度抚育有利于植物多样性的提高. 

Short-term effects of tending on the undergrowth diversity of Platycladus orientalis plantations in Beijing mountainous areas

The Platycladus orientalis plantation is one of the major non commercial plantations in Beijing mountainous areas. Due to the generally high stand density, the forests could not grow well. There is very little vegetation undergrowth, the biodiversity is degrading, and the general quality of the stand is in poor condition. The ecological functions of the plantations hence cannot be fully activated. Tending, as the fundamental method of forest management, has significant effects in improving the general quality of plantations, recovering the undergrowth diversity and reconstructing the deteriorated ecosystem. In order to investigate the dynamic variance of the undergrowth and to provide reference for reasonable tending, in 2004, 41 sample plots in the low hill sunny slope with thin soil, sunny slope with thick soil and half sunny slope with thick soil, were selected in Beijing mountainous areas and light, medium and heavy tending on each sample plots were conducted, respectively. In the summers of 2005 and 2006, changes of the undergrowth diversity were investigated and analyzed. The results showed: 1) in the 1st and 2nd tending years, the species and quantity of undergrowth, Simpson index (D), Shannon Wiener biodiversity index (H′) and the total amount of the undergrowth biomass all increased along with enhancing tending intensity; and the distribution of vertical structure of the community became more significantly as the tending intensity was enhanced; 2) after two years of heavy tending, the shrub species increased in the sunny slope with thin soil, sunny slope with thick soil and half sunny slope with thick soil by 4, 5 and 5, and these numbers for the herb species increased by 13, 10 and 8 respectively. Besides, the heavy tending has an effect in improving the undergrowth’s turning to xeromesophytes and meso xerophytes; 3) after the medium and heavy tending, the undergrowth biomass can reach more than 5 t/hm2. Among the short_term effects, the medium and heavy tending are more favorable to the increase of plant diversity.