Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation
Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation
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DOI：
10.1111/oik.02858
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发表时间：
2016-07
期刊：
影响因子：
3.4
通讯作者：
T. Aakala;K. Shimatani;Toshihiro Abe;Y. Kubota;T. Kuuluvainen
中科院分区：
文献类型：
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作者：
T. Aakala;K. Shimatani;Toshihiro Abe;Y. Kubota;T. Kuuluvainen
树木的轻觅食是形成森林群落的基本过程。在异质光环境中，这种行为表现为树木生长的可塑性和结构不对称性的发展。研究了邻体结构和定向太阳辐射对北方芬诺斯堪的那亚（Fennoscandia）演替后期高纬度（67-68°N）森林树冠水平不对称性的相对影响。我们将树冠不对称性描述为树冠向量（即从茎中心到树冠中心的水平向量），这是我们根据田间树冠周长测量从树冠图中获得的。为了解开两个主要的决定因素，树间竞争和方向性的冠层以上的太阳辐射在高纬度地区的影响，我们采用圆形统计模型，利用圆柱分布，这些数据组成的冠不对称的方向和强度。在单株树水平上，我们的模型预测了当前林分结构的树冠不对称向量，当不对称强度（即树冠向量长度）较高时，预测效果会更好。竞争是2/3树木树冠不对称的主要决定因素，当我们将太阳辐射的方向性纳入模型预测时，模型预测得到了改善。在林分水平上，这些不对称性导致了投影冠层面积的小幅增加和空间结构的规则性增加。我们的圆形统计建模方法提供了一个定量评估的相对重要性，太阳辐射和邻里的立场结构的方向性，这两个因素如何发挥作用，在高纬度森林树冠不对称的形成。这种方法进一步证明了循环统计模型在响应变量既有方向又有强度的生态研究中的适用性。
Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67–68°N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.