林龄是林分中林木的平均年龄，分为幼龄林、中龄林、近熟林、成熟林和过熟林。幼龄林是森林生长发育的幼年阶段，通常指Ⅰ龄级或Ⅱ龄级的林分，龄级指对林木按照林龄间隔一定的年限进行的分级，一般天然林每20年为一个龄级；人工林每10年为一个龄级。
加强中幼龄林抚育管理已是我国林业的紧迫任务。
It is emergent task to strengthen the management and tending of cultures in China forests.
因地制宜开展中幼龄林抚育、森林改造培育，提高森林质量。
Young forest management will be managed according to local conditions, with an emphasis on forest cultivation to improve forest quality.
林分直径分布，幼龄林呈倒“J”型，壮龄林近似于正态分布；
The stand diameter distribution of juvenile stand appears an inversed "J"form, and that of the half mature forest approximately a normal distribution.
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