不同生境栓皮栎天然更新幼苗植冠构型分析

栓皮栎存在于秦岭南坡的多种林分中,生活在不同生境中的个体往往形成不同的树冠形态和构型特征。为了说明不同生境条件下栓皮栎幼苗的植冠构型变化,采用典型抽样法,对秦岭南坡3种生境中(林冠下、林隙、林缘)的栓皮栎天然更新幼苗的侧枝、叶片特征及其空间分布进行了调查分析,结果表明:3种不同生境中栓皮栎幼苗植冠形态发生了明显的可塑性变化,(1)林冠下的幼苗明显为开阔型树冠,林隙和林缘处的幼苗树冠相对紧密;(2)幼苗的1级侧枝密度与分枝角度在3种生境下均差异显著(P0.05);从Ⅰ到Ⅳ层,林冠下幼苗的分枝角度在冠层内变化幅度不到5°,而林缘处幼苗的分枝角度变化高达40°;发生5个以上1级侧枝的概率以林冠下最大,为0.6;(3)从林缘、林隙到林冠下,幼苗的叶长、叶宽、单叶面积、叶面积指数逐渐降低,数量叶密度和比叶面积则逐渐增大,与其它两种生境相比,林冠下幼苗的叶片逐渐向树冠上层集中,且以更高序的侧枝为主要着生枝条;(4)林隙中栓皮栎幼苗的树高、地径明显优于林缘和林冠下,缩短了苗木进入主林层的时间,林隙对栓皮栎种群更新有利。在今后栓皮栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化的提供有利条件。

Architectural analysis of crown geometry of Quercus variablis BL. natural regenerative seedlings in different habitats

Quercus variabilis distributes widely in a variety of forest stands on the south slope of Qinling Mountains, and this tree species often displays variety crown morphological and architectural features in different habitats. In order to illustrate the crown architectural variation of Q. variabilis seedlings in different habitats and understand the response and adaptation mechanisms of plant to different environment conditions, the typical sampling method was implemented, and the characteristics of lateral branch and leaf, as well as their spatial distribution for Q. variabilis seedlings, which grew in three different habitats (under canopy, forest gap and forest edge), were investigated in Shanyang in September 2012. The result showed that the crown morphological features of Q. variabilis seedlings changed in response to three kinds of habitats. (1) The seedlings under canopy had significantly broad crown, while the crown was relatively dense and narrow in forest gap and edge (P < 0.05), this was displayed by the crown width of seedlings, which were 22.8, 32.1 and 45.6 cm in forest edge, forest gap and under canopy respectively, and such a change in crown structure was an advantageous adaptation for enhancing light interception. (2) The density of first-order-branch and the branch angle were both different significantly among three kinds of habitats (P < 0.05), from I to IV stratum,the branch angle of seedlings under canopy were the widest, and the amplitude of variation didn''t exceed 5°, while the same parameter in forest edge decreased gradually and the amplitude of variation reached up to 40°. meanwhile, the probability of forming more than 5 first-order-branches for seedlings under canopy was the largest, the maximum was 0.6, and the mean branching number could be up to 5.1. (3) Affected by the lateral branches distribution, the leaves distribution of seedlings were different among three habitats. the leaf morphological charecteristics of Q. variablis seedlings including leaf length, leaf width, leaf area and leaf area index gradually decreased from forest edge, forest gap to under canopy, while quantitative leaf density and leaf area per unit dry mass showed reverse trend. Compared with the other two habitats, the seedling leaves in under canopy tended to distribute in upper crown and insert on the higher order branches, and this distribution pattern of branches and leaves could enhance the light interception of the seedlings in this kind habitats. (4) The height and collar diameter of seedlings in forest gap were obviously greater than those in other two habitats, this advantage could shorten the time of seedlings entering into the main storey, so forest gap was advantageous to the population regeneration and cultivate the large diameter timber of Q. variabilis, and this might be caused by the better radiation condition, air temperature and soil moisture etc., which were benefit to the growth of seedlings, In the future, appropriate thinning techniques should be used to increase the number of the forest gap and provide favorable conditions for regeneration and structure optimization of Q. variabilis forests.