基于林分生长量的沙地樟子松初植造林密度确定

Confirmation of initial planting density of Pinus sylvestris var.mongolica in sandy land based on stand growth

为研究樟子松不同初植密度林分成熟龄后生长因子之间的差异,对不同初植密度的27块林分造林40年后的生长量进行比较分析,结果表明,林分由初植密度10000~833株·hm^-2演变到现存密度2542~390株·hm^-2,关系式为:D现=705.651×ln(D初)-4360.7(R^2=0.81);成熟龄樟子松人工林保存率随初植密度的增大而降低,关系式为:R r=-0.0036×D初+54.758(R^2=0.61);胸径随现存密度的增大而降低,关系式为:DBH=-0.0044×D现+22.423(R^2=0.75);树高随现存密度的增大而增高,关系式为:H=0.0005×D现+9.8537(R^2=0.05),但密度增大到一定程度之后树高不再增高,而是维持在一定范围内上下波动;现存林分的胸径、树高、冠幅生长量存在显著差异。以樟子松成熟龄人工林的胸径生长量为指标,考虑到樟子松更长久的固沙防护周期,初植密度以833株·hm^-2为宜,株行距以3 m×4 m为宜。樟子松为强阳性树种,栽植时不宜丛植。樟子松的生长抚育间伐以单株树冠之间互不相搭为标准进行作业为好。在沙地樟子松人工林同龄林中如用克拉夫特林木分级法判别林木级别,用胸径一个指标区分就可以保证准确性,便于操作。

Growth trait differences of mature Pinus sylvestris var.mongolica forests with different initial planting densities were researched by comparing growth amounts of 27 forest stands with different initial densities 40 years after planted.Results indicated that:the density of 27 experimental sites of Pinus sylvestris var.mongolica evolved from the initial planting density of 10000~833 plants·hm^-2 in 1980 to the current density of 2542~390 plants·hm^-240 years after afforestation,the equation is D current=705.651×ln(D initial)-4360.7(R^2=0.81).The survival rates of mature plantation decreased with the increasing of initial planting densities,the equation is R r=-0.0036 D current+54.758(R^2=0.61).The DBH decreased with the increasing of current densities,the equation is DBH=-0.0044 D current+22.423(R^2=0.75).The tree height increased with the increasing of current density firstly,the equation is H=0.0005 D current+9.8537(R^2=0.05).When the density increased to a certain extent,the tree height fluctuated within a certain range.There were significant differences in DBH,tree height and crown width among existing stands.According to DBH increasement in mature forest of P.sylvestris var.mongolica,considering the longer sand-fixation protection cycle,the better initial planting density was 833 plants·hm^-2 and the better planting spacing was 3 m×4 m.P.sylvestris var.mongolica is a heliophilous species,and it should not be group planted.The thinning of P.sylvestris var.mongolica was better based on the criterion that the tree crowns of individual plants do not overlap with each other.In even aged P.sylvestris var.mongolica plantation of sandy land,if the Kraft tree grading method was used to classify the tree grade,DBH index could be selected to ensure the accuracy and to simplify the operation.