Whitehead David, Grace Jennifer C., Godfrey Martin J. S.
Forest Research Institute, Private Bag 3020, Rotorua, New Zealand.
Tree Physiol. 1990 Dec;7(1_2_3_4):135-155. doi: 10.1093/treephys/7.1-2-3-4.135.
The architectural arrangement and leaf area of representative branch units, on one branch complex from each cluster on the stem, were measured on six trees in a widely spaced 7-year-old Pinus radiata D. Don plantation. There was a linear relationship between leaf area and the basal area of branch complexes. Assuming similarity in the arrangement of branch units within concomitant branch complexes at each cluster, the 3-dimensional distribution of leaf area density (leaf area per unit volume) in an array of cubic cells, each 10(-3) m(3), comprising the volume of each tree crown, was reconstructed. The fraction of cells in which foliage was present varied from 0.08 to 0.23 in the crowns with the highest (Tree 4) and lowest (Tree 3) degree of clumping, respectively. This difference was related to the number, length, and leaf area per unit length of Order 3 branch units, in particular. The actual distributions of leaf area density were used with a simple radiative transfer model to estimate the probability of penetration of beam and diffuse photosynthetically active radiation (PAR) through individual tree crowns. The average probability of beam penetration was greater for the tree with the most clumped foliage than for the tree with the least clumped foliage. For both trees, the average probabilities of penetration were greater than the values that would have resulted if a random distribution of foliage had been assumed. The negative binomial model was used to estimate an index of foliage dispersion for the tree crowns. For beam PAR, the index of foliage dispersion was 3.3 and 2.3 for the trees with the most, and the least clumped foliage, respectively. These results were supported by analysis of the architectural arrangement of foliage in the tree crowns. For two days in summer, the assumption that leaf area density was randomly distributed would have resulted in a 20 to 30% overestimation of intercepted PAR flux by the tree crowns.
在一片间距较大、树龄为7年的辐射松人工林中，对6棵树上取自树干上每个枝条簇的一个枝条复合体上具有代表性的枝条单元的结构排列和叶面积进行了测量。叶面积与枝条复合体的基部面积之间存在线性关系。假设每个枝条簇中相伴枝条复合体内部的枝条单元排列相似，在由10⁻³立方米的立方体单元阵列（构成每棵树冠体积）中，重建了叶面积密度（单位体积叶面积）的三维分布。在树冠聚集程度最高（树4）和最低（树3）的树冠中，有叶细胞的比例分别在0.08至0.23之间变化。这种差异尤其与3级枝条单元的数量、长度以及单位长度的叶面积有关。叶面积密度的实际分布与一个简单的辐射传输模型一起用于估算光合有效辐射（PAR）的直射光和散射光穿透各个树冠的概率。叶簇最密集的树的直射光穿透平均概率大于叶簇最稀疏的树。对于这两棵树，穿透的平均概率均大于假设树叶随机分布时所得到的值。使用负二项式模型来估算树冠的叶簇分散指数。对于直射PAR，叶簇最密集和最稀疏的树的叶簇分散指数分别为3.3和2.3。这些结果得到了对树冠中叶簇结构排列分析的支持。在夏季的两天里，假设叶面积密度随机分布会导致树冠对PAR通量截获量的高估20%至30%。
