抚育间伐对白桦天然次生林生长及林下植物多样性的影响

采用样地调查的方法，对白桦次生林抚育间伐(F-T:平地，强度间伐；S-T:坡地，弱度间伐)3 a后林分生长、径级结构和林下植物多样性进行研究。结果表明，抚育后乔木群落和白桦种群的平均胸径、平均冠幅有增加趋势，但不显著（P>0.05），树高无显著变化。对位于平地的林分进行强度间伐后，乔木群落大径组(25 cm≤DBH＜37 cm)比例提高8%，白桦种群大径组比例提高5%。对位于坡地的林分进行弱度间伐后，乔木群落大径组和白桦种群大径组比例分别提高5%和23%。抚育后，林下灌木层物种丰富度降低，F-T、S-T灌木层物种数分别比各自对照降低了42.9%和52.9%，草本层物种丰富度升高，F-T、S-T分别增加了22.2%和71.4%。珍珠梅、白花碎米荠、猴腿蹄盖蕨、蚊子草和宽叶薹草的重要值均增加，红松、东北茶藨子、花楷槭，刺玫蔷薇、细叶苔草和羽节蕨的重要值均降低。抚育后灌木层Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数均降低，草本层各指数均升高。综上，从短期(3 a)效果看，抚育间伐有促进白桦次生林径向生长和提高大径组比例的趋势，利于林下草本植物的更新和多样性的提高，而灌木层更新受阻，多样性降低。

Effects of Thinning on the Growth and Plant Species Diversity in Betula platyphylla Natural Secondary Forest Stand

Natural secondary forests of Betula platyphylla occurring in Linkou of Heilongjiang were surveyed after 3 years of thinning with two intensities,i.e.,intensive thinning in flat ground (F-T) and low intensity thinning in slope site (S-T).The stand growth,diameter structure characteristics and plant diversity were examined.The results showed that the mean DBH and crown width of arbor community (AC) and B.platyphylla population (BP) increased,but not significantly (P>0.05),and there was no significant change in tree height growth.The large DBH class (25 cm≤DBH＜37 cm) of AC and BP tended to increase in thinned stand.The proportion of large diameter group (25 cm≤DBH<37 cm) of AC increased by 8%,and the proportion of large diameter group of increased by 5% after intensive thinning in F-T,and the figures increased by 5% (AC) and 23% (BP),respectively after low intensity thinning in S-T.The richness of shrub decreased by 42.9% (F-T) and 52.9% (S-T),respectively,while the species number in herb layers increased by 22.2% (F-T) and 71.4%(S-T),respectively.The importance values of Sorbaria sorbifolia,Cardamine leucantha,Athyrium brevifrons,Filipendula palmate,Carex siderosticta all increased,while the importance values of Pinus koraiensis,Ribes amdsjuricum,Acer ukurunduense,Rosa davurica,Carex rigescens,Gymnocarpium dryopteris all decreased.After thinning,the Simpson diversity index,Shannon-Wiener index and Pielou evenness index of shrub layer decreased,while those of herb layer increased.Among the short-term effects (3 a),there was a tendency that the thinning treatment could promote the radial growth of B.platyphylla secondary forest and increase the proportion of large DBH class,and the thinning was able to promote natural generation and plant diversity of herb layer,while those of shrub layer decreased.