科尔沁沙地不同密度(小面积)樟子松人工林生长状况

在内蒙古科尔沁沙地丘间片林中选择不同密度的樟子松样地,对樟子松在不同栽植密度条件下的生长情况进行了研究.由于受多年降水偏少的影响,科尔沁沙地的樟子松出现了大量枯梢继而死亡的现象,而这种现象与林地的密度存在很强的相关性.样地林木的死亡率随林地密度的加大呈幂函数关系增加,原先最高密度情况下的林地,保存到现在的活木数量反而最少;林木的平均死亡年龄、最早死亡年龄、冠幅、树高和胸径随林地密度的增加而减小.虽然在其它一些区域的研究结果表明,树高较少受竞争的影响,但是在半干旱区,树高仍然与密度相关.枯梢林木的比例在高密度的样地大于低密度的样地,枯梢对低密度样地的林木基本上没有大的影响.各样地的冠幅和胸径比相差不大,平均只有0.297,以此指标衡量,该地可能更适合单一樟子松林的种植.综合来看,科尔沁沙地的气候和土壤条件适合栽植樟子松,但初始密度应控制在2800株/hm2以下,并应根据生长情况在进入生长高峰期后对林木进行适时间伐,20a龄期的林木其密度保持在2100株/hm2左右比较适宜.

Growth of small area Pinus sylvestris var. mongolica artificial forest under different densities in Horqin Sandy Land, North of China

Pinus sylvestris var. mongolica is one of important tree species, widely introduced into the arid and semi-arid zone in the northeast of China for shelterbelt establishment and timber production. However, in some places, this introduced pinus died with twigs and leaves wilted at first. In order to understand the cause of wilting and death, different plots were chosen to study the growth of the pinus associated with density, rainfall in Horqin Sandy Land of Inner Mongolia, China. The results showed that growth of the pinus related strongly to forest density. Death rate increased in power function with increasing of density. In the plot of the highest density, there were the least alive trees because of the highest death rate by now. The averaged death age, first death age, crown dimension, height and stem diameter decreased with increasing of density. The height still related to density in arid zone, though size-density theory showed that height growth was relatively unaffected by competition. Twig wilting was mainly attributed to high density. In plots of low density, proportion of twig-wilted trees was lower and there was nearly no obvious influence on growth of trees. There was not significant difference of crown dimension to stem diameter in the plots, and averaged value was only 0.297. Thus, according to Dawkins' report, we think that this region may be more suitable for monoculture than mixed forest. Anyway, climate and soil condition in this region are suitable for planting the pinus. The original density should be controlled under 2800 trees/hm2. At the same time, intermediate cutting should be taken into account when growing-peak is coming. It is reasonable that the density is about 2100 per hectare when tree age is 20 years old approximately.