Abstract Airborne laser scanning (ALS) is a tool that can be used to monitor canopy height changes when data acquisitions are done at successive times. However, ALS is subject to some limitations in forested environments. One of these is that height growth measured between two times can be due to vertical crown growth of trees or to lateral growth of branches. The latter process gives canopy height change values unrelated to actual stem elongation. Lateral growth is a source of uncertainties in height change analyses because canopy height models do not contain information on the source of the growth. Lateral infilling of open space in the canopy and vertical crown growth are important processes in the gap dynamics of temperate deciduous forests. Small gaps are expected to close more often by lateral growth of branches while larger gaps can sometimes close by the vertical crown growth of seedling and saplings. Yet, few studies have examined growth patterns in and out of gaps in temperate deciduous forests. We studied both unmanaged and managed temperate deciduous forests in southern Quebec, Canada using a multi-temporal ALS dataset. A Bayesian stochastic model of three-dimensional dynamics was developed to classify whether measured height growth was due to lateral growth or vertical crown growth. A generalized additive model was also constructed to relate vertical crown growth to the height of trees. Between 10.6% and 13.7% of the canopy height model's pixels changed value due to lateral growth. There was no clear temporal trend for the frequencies of lateral growth in the managed forests chronosequence. Frequencies of lateral growth were also comparable between unmanaged and managed sites. Treetops of dominant trees grew slowly while crown edges of those trees grew both vertically and laterally. Our results show that canopy structure recovery in managed forests occurs through faster vertical crown growth of trees

中文翻译：

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使用多时相机载激光扫描解开管理和非管理温带落叶林冠层高度增加的原因

摘要 机载激光扫描 (ALS) 是一种工具，可用于在连续时间完成数据采集时监测冠层高度变化。但是，ALS 在森林环境中受到一些限制。其中之一是两次之间测量的高度增长可能是由于树木的垂直树冠生长或树枝的横向生长。后一个过程给出与实际茎伸长无关的冠层高度变化值。横向生长是高度变化分析中不确定性的一个来源，因为冠层高度模型不包含有关生长来源的信息。冠层空地的横向填充和树冠垂直生长是温带落叶林间隙动态的重要过程。预计小间隙会因树枝的横向生长而更频繁地闭合，而较大的间隙有时会因幼苗和树苗的垂直树冠生长而闭合。然而，很少有研究调查温带落叶林中间隙内外的生长模式。我们使用多时相 ALS 数据集研究了加拿大魁北克南部的未管理和管理的温带落叶林。开发了三维动力学的贝叶斯随机模型，以对测量的高度增长是由于横向增长还是垂直冠增长进行分类。还构建了一个广义的加性模型，将垂直树冠生长与树木高度联系起来。由于横向生长，冠层高度模型的像素值在 10.6% 到 13.7% 之间发生了变化。管理林时间序列的横向生长频率没有明显的时间趋势。未管理和管理站点之间的横向生长频率也具有可比性。优势树的树梢生长缓慢，而这些树的树冠边缘垂直和横向生长。我们的结果表明，管理林中的冠层结构恢复是通过树木更快的垂直树冠生长而发生的