Leaf area index of boreal forests: Theory, techniques, and measurements
Leaf area index of boreal forests: Theory, techniques, and measurements
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DOI：
10.1029/97jd01107
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发表时间：
1997-12-26
影响因子：
4.4
通讯作者：
Plummer, S
中科院分区：
文献类型：
--
作者：
Chen, JM;Rich, PM;Plummer, S
叶面积指数（LAI）是森林生态系统的一个重要结构特征，因为绿色叶片在控制植物冠层中的许多生物和物理过程中起着重要作用。在生态生理学、大气-生态系统相互作用和全球变化的研究中，需要精确的叶面积指数估算。本文的目的是评估叶面积指数的几个研究小组使用不同的方法获得的广泛的北方森林类型的国际北方生态系统-大气研究（BOREAS）的支持。这些方法包括破坏性取样和光学仪器：跟踪辐射和冠层结构（TRAC），LAI-2000植物冠层分析仪，半球摄影，和Sunfleck Ceptometer。后三个计算叶面积指数从测量的辐射透射率（间隙分数）使用反演模型，假设一个随机的空间分布的叶子。结果表明，这些仪器低估了叶面积指数的北方森林的立场，树叶丛生。TRAC通过测量林隙大小分布来量化丛生效应。对于落叶林分，从TRAC测量的丛生指数包括所有尺度的丛生效应，但对于针叶林分，它只解决了比嫩枝（针叶的基本集合）更大尺度的丛生效应。为了确定针叶树枝条内的叶子丛生，使用了摄像机和旋转光表系统。在确定小针叶树针叶表面积的主要困难已在很大程度上克服了使用一个精确的体积位移法。半球摄影的优点是它也提供了一个永久的图像记录的檐篷。通常情况下，叶面积指数福尔斯的范围从1到4杰克松和白杨森林和黑云杉从1到6，我们的比较研究提供了最全面的一套叶面积指数估计可用于北方森林，并表明，光学技术，结合有限的直接叶取样，可以用来获得快速和准确的叶面积指数测量。
Leaf area index (LAI) is a key structural characteristic of forest ecosystems because of the role of green leaves in controlling many biological and physical processes in plant canopies. Accurate LAI estimates are required in studies of ecophysiology, atmosphere-ecosystem interactions, and global change. The objective of this paper is to evaluate LAI values obtained by several research teams using different methods for a broad spectrum of boreal forest types in support of the international Boreal Ecosystem-Atmosphere Study (BOREAS). These methods include destructive sampling and optical instruments: the tracing radiation and architecture of canopies (TRAC), the LAI-2000 plant canopy analyzer, hemispherical photography, and the Sunfleck Ceptometer. The latter three calculate LAI from measured radiation transmittance (gap fraction) using inversion models that assume a random spatial distribution of leaves. It is shown that these instruments underestimate LAI of boreal forest stands where the foliage is clumped. The TRAC quantifies the clumping effect by measuring the canopy gap size distribution. For deciduous stands the clumping index measured from TRAC includes the clumping effect at all scales, but for conifer stands it only resolves the clumping effect at scales larger than the shoot (the basic collection of needles). To determine foliage clumping within conifer shoots, a video camera and rotational light table system was used. The major difficulties in determining the surface area of small conifer needles have been largely overcome by the use of an accurate volume displacement method. Hemispherical photography has the advantage that it also provides a permanent image record of the canopies. Typically, LAI falls in the range from 1 to 4 for jack pine and aspen forests and from 1 to 6 for black spruce, Our comparative studies provide the most comprehensive set of LAI estimates available for boreal forests and demonstrate that optical techniques, combined with limited direct foliage sampling, can be used to obtain quick and accurate LAI measurements.