中文摘要：

采用空间代替时间的样地调查方法,利用异速生长方程和一元材积表计算不同林龄桦木林的生物量、生产力与材积,结果表明,桦木林乔木层及平均单株地上生物量均随林龄增加而增加,在50 a时达到最大; 生产力则先增加而后逐渐减少,乔木层30 a时生产力为7.88 t.hm-.2a-1,到40 a和50 a时,分别下降到5.17 t.hm-.2a-1和1.19.thm-.2a-1; 单株平均生产力在30 a时达到最大值1.13 kg.a-1,40 a时下降为0.96 kg.a-1,50 a时略有上升。林分蓄积量随林龄增加而增加,平均生长量在50 a达到最大值3.78 m.3hm-2,连年生长量在30 a时达到最大值6.07 m.3hm-2。平均单株材积增长速度随林龄增加而增加,50 a时平均生长量和连年生长量达到最大值。

英文摘要：

Aboveground biomass,ANPP and stem volume of coniferous plantations have been studied in many papers in subalpine region of Western Sichuan,China.However,very few were reported about natural secondary birch forests（Betula spp.）,which have become dominant types after over exploitation of old growth coniferous forests from 1950s to 1980s in this region.Aboveground biomass,aboveground net primary productivity（ANPP） and stem volume in birch forests with different stand age were calculated with allometric relationships and one-way tree volume models,respectively,by sampling stands with different age as a substitute for time series.The results indicated that aboveground biomass of tree layer as well as the average single tree increased with the increasing of stand age.Aboveground biomass of tree layer reached its peak at the 30 years old stand,that was 7.88 t·hm-2·a-1,and then slowed down gradually.Average individual aboveground biomass reached its maximum at the 30 years old stand,that was 1.13 kg·a-1.Stock volume of tree layer rose with the increasing stand ages,and the mean annual increment reached its maximum at the 50 years old stand,that is 3.78 m3·hm-2,while the current annual increment reached its peak at the 30 years old stand,that is 6.07 m3·hm-2.Average individual stem volume also rose with the increasing stand ages,both mean annual increment and current annual increment reached the peak at the 50 years old stands.