栎类次生林乔木的密度随高度级、径级的增加而递减，但树种丰富度却不随树木的密度增加而增加。
Tree density in the forest decreased with the increases of height class and diameter class, whereas species abundance did not increase.
为提高城市隔离片林生态效益及景观面貌，片林结构除简单的乔木层外，还应具有一定面积的复层混交种植结构。
Besides the simple arbor layer, the multilayer plantation structure should be adopted in order to enhance the ecological benefits and scene values of isolating greenbelts in Beijing.
草本植物则随着林隙环境条件的改变而出现较大的波动性，藤本植物和乔木的稳定性和连续性介于灌木和草本植物之间。
This indicated that the composition of shrub species remained relatively stable during the past 40 years of gap development, while the composition of herbaceous species fluctuated greatly.
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