下层修枝对树种水分截留特性的影响

Effects of lower pruning on water interception of trees

本文以6种典型造林树种侧柏(Platycladus orientalis)、油松(Pinus tabuliformis Carr.)、栓皮栎(Quercus variabilis Blume)、五角枫(Acer elegantulum Bunge)、白皮松(Pinus bungeana Zucc.)和黄栌(Cotinus coggygria Scop.)为研究对象,目的在于探究下层修枝抚育处理对树种林冠截留特性的改变规律。实验采用自制的林冠截留量测定装置配合室内人工模拟降雨的方法,高精度地得出了林冠截留的过程数据。结果表明:1)下层修枝对于针叶树种的林冠截留特性影响大于阔叶树种,五角枫和黄栌对于下层修枝的响应不敏感; 2)修枝去除的下层枝叶中,阔叶树种下层叶的截留能力显著强于下层枝,而针叶树种下层枝和下层叶的截留能力相当; 3)在树下铺设密度为0. 35 kg/m^2枯落物之后,树木修枝前后的最大水分蓄持量和有效水分蓄持量减少量在10%以下。因此可知:针阔叶树种林冠截留特征对下层修枝响应强度不一,主要体现在针叶树种响应强度大于阔叶树种,下层枝和下层叶截留能力存在差异。林下铺设枯落物可以有效降低下层修枝对树木截流量的影响。

[Background]Lower pruning is one mainly method of forest tending.Canopy interception is an important process of forest hydrological cycle.Lower pruning can effectively change the characteristics of canopy interception.Few researches focus on this aspect.In this study,6 kinds of typical Beijing mountain afforestation tree species Platycladus orientalis,Pinus tabuliformis Carr.,Quercus variabilis Blume,Acer elegantulum Bunge,Pinus bungeana Zucc.and Cotinus coggygria Scop.are used to be the research objects,exploring the way of lower pruning treatments for characteristics changes in the canopy interception.[Method]The method of indoor simulated rainfall was adopted in the experiment.An equipment of canopy interception measurement was made to measure the amount of water interception.There are three parts of the equipment,a bench scale to measure the weight,a metal rain cover to block rain drops and barbed wire to put litters.We put the pot with experimental trees on the bench scale and then start raining.We read the weight on bench scale every 30 seconds.After one hour’s raining,continue reading the weight until the weight reading was unchanged.In this research we used weight to express the canopy interception.The final weight reading is the minimum interception(Cmin)of the tree.The maximum of bench scale during the raining is called the maximum interception(Cmax).We can get the data of canopy interception with higher precision in this way.After lower pruning,put trees on the equipment under the rainfall device to repeat experiment.After that,tree litters were put on the barbed wire.The thickness was 2 cm.We repeated the rainfall experiment.[Results]1)Lower pruning treatment influenced the conifer’s canopy interception more than that of broad-leaved tree.The maximum interception of coniferous species decreased by more than 50%.However broad-leaved tree species decreased by less than 20%.2)The interception ability of the lower layer leaves of broad-leaved trees was much stronger than that of the lower branches.While the interception ability of the lower and lower leaves of the coniferous trees was equal.The interception percentage of lower leaves of coniferous species was significantly less than that of broad-leaved species(P<0.05).Therefore,the interception percentage of lower branches was opposite.3)After laying tree litters of 2 cm,the difference of the maximum interception and the minimum interception between before and after lower pruning was below10%.[Conclusions]The results show that the interception characteristics of coniferous and broadleaved canopy vary with the intensity of the lower pruning,which is mainly reflected in that the coniferous tree species has stronger response strength than the broad-leaved tree species.Laying litters under the forest may effectively reduce the influence of lower pruning on the flow of trees.