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冠层间隙率和叶片聚集度指数对植被拦截光和冠层辐射传输过程有重要影响。叶片往往以树冠的形式聚集在森林中,而树冠在诸多森林冠层几何光学模型中有重要作用。之前的研究主要集中于树冠的形状(例如圆柱、圆锥、椭球、圆锥+圆柱等)特征对冠层间隙率和叶片聚集度的影响。然而,树冠的结构特征除了包括形状特征外,还包括尺寸特征。事实上,树冠的尺寸特征是植被在长期进化过程中与自然环境相互作用的结果,且比树冠形状特征具有更明显的地理空间特征。本文首先修改了前人常用的用于描述树冠分布的泊松分布模型,其次,利用超几何模型更为真实地、定量地描述树冠之间的排斥效应和树冠的分布情况;最后,以椭球树冠为例,设定了从“瘦高”型到“矮胖”型等7种尺寸的树冠,分别通过固定树冠半径和树冠体积两种途径探讨了树冠尺寸特征对冠层间隙率和叶片聚集度的影响。结果表明:(1)无论固定树冠半径,还是固定树冠体积,树冠尺寸特征对冠层间隙率和叶片聚集度指数的影响,均比树冠形状特征对间隙率和叶片聚集度指数的影响明显;(2)树冠的尺寸对冠层间隙率和叶片聚集度的影响非常显著,且具有明显的规律性。树冠在观测方向的投影面积越大,冠层间隙率越小,叶片聚集指数度越大,冠层内叶片越趋于泊松分布。
Canopy gap and leaf aggregation index have an important influence on vegetation interception and canopy radiation transmission. Leaves tend to gather in the forest in the form of canopy, while canopy plays an important role in many canopy geometrical optics models. Previous studies have focused on the effects of canopy shape (eg, cylinder, cone, ellipsoid, cone + cylinder, etc.) on canopy porosity and degree of leaf aggregation. However, the structural features of the crown include dimension features in addition to the shape features. In fact, the dimensional features of the canopy are the result of the interactions between the vegetation and the natural environment during the long-term evolution and have more obvious geospatial characteristics than the canopy shape features. In this paper, we first modify the Poisson distribution model commonly used to describe canopy distribution. Secondly, we use the hypergeometric model to describe the exclusion effect and canopy distribution more truly and quantitatively. Finally, For example, the tree canopy was set up from seven kinds of crown such as “lean ” type to “stout ” type, and the effects of canopy size on canopy clearance Effect of rate and degree of leaf aggregation. The results showed that: (1) The effect of canopy size on canopy gap and leaf clustering index was more obvious than that of canopy shape on the gap percentage and leaf clustering index, both for fixed crown radius and fixed crown volume. 2) The crown size has a significant effect on the canopy gap and the degree of leaf aggregation, and has obvious regularity. The larger the projected area of canopy in the observation direction, the smaller the canopy gap, the larger the index of leaf aggregation, the more the leaves in the canopy distributed Poisson.