Photographic exposure affects indirect estimation of leaf area in plantations of Eucalyptus globulus Labill
Photographic exposure affects indirect estimation of leaf area in plantations of Eucalyptus globulus Labill
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DOI：
10.1016/s0168-1923(99)00139-2
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发表时间：
2000-02-05
影响因子：
6.2
通讯作者：
Adams, MA
中科院分区：
文献类型：
--
作者：
Macfarlane, C;Coote, M;Adams, MA
用于估计叶面积的间接方法的校准通常基于小数据集，并且通常是特定于物种的，甚至可能是特定于林分的。我们使用 Licor LAI-2000 植物冠层分析仪 (PCA) 作为参考来校准基于半球摄影的叶面积测量。使用西澳大利亚州 10 个 6-8 年生塔斯马尼亚蓝桉 (Eucalyptus globulus Labill.) 种植林，研究采样位置、摄影曝光和图像处理的变化对使用半球摄影估算的叶面积（或叶面积指数，L）的影响。我们还将我们对 L 的摄影估计值与通过破坏性采样（异速生长）在均匀分布和高度聚集的蓝桉林中获得的估计值进行了比较。改变一档曝光量会影响估计的 L 大约 13%，但我们确认可以通过测量冠层外的曝光量来大致预测正确的曝光量。在测量树冠外曝光不切实际的情况下，我们建议使用根据恒定曝光拍摄的摄影图像估计的 L 与通过其他方式得出的实际 L 之间的经验推导关系。通过摄影方法获得的 E. globulus 的平均倾斜角（68.7 度+/- 2.5 s.e）与其他研究中对桉树物种的估计值非常吻合。由于种植园内树冠的非随机排列，采样位置显着影响平均倾斜角。在双行间隔很近且双行间间隙较宽的高度丛集的林分中，用摄影方法将 L 低估了 16-30%，这可能是由于树冠水平上树叶丛集较多的结果。我们的结论是，在 E. globulus 和可能其他树冠分布均匀的阔叶树种中，枝条或枝条水平上的叶子丛集不太可能是间接估计 L 的重要误差源。使用 PCA 时，蓝光散射可能会导致 L 的大幅低估。在具有“极端”架构的看台中，基于光拦截的间接方法可能会大大低估 L，但即使在这些看台中，定位传感器以消除大间隙也可能允许准确估计 L。 (C) 2000 年由 Elsevier Science B.V 出版，保留所有权利。
Calibrations of indirect methods for estimating leaf area are usually based on small data sets and are often species-specific and may even be stand-specific. We used the Licor LAI-2000 plant canopy analyser (PCA) as a reference to calibrate leaf area measurements based on hemispherical photography. Ten stands of 6-8 year-old, plantation grown Tasmanian bluegum (Eucalyptus globulus Labill.) in Western Australia were used to investigate the effects of variations in sampling position, photographic exposure and image processing on leaf area (or leaf area index, L) estimated using hemispherical photography. We also compared our photographic estimates of L with those obtained via destructive sampling (allometry) in both evenly spaced and highly clumped stands of E. globulus. Varying exposure by one stop affected estimated L by approximately 13% but we confirmed that correct exposure can be approximately predicted by metering exposure outside the canopy. In situations where metering exposure outside the canopy is impractical, we recommend the use of empirically derived relationships between L estimated from photographic images made at a constant exposure and actual L derived from other means. Mean tilt angle obtained for E. globulus from the photographic method (68.7 degrees +/- 2.5 s.e.) agreed well with estimates for Eucalyptus species from other studies. Owing to the non-random arrangement of crowns within plantations, sampling position significantly affected mean tilt angle. In highly clumped stands with closely spaced double rows and wide inter-double row gaps, underestimation of L by 16-30% with the photographic method was probably the result of greater foliage clumping at the crown level. We concluded that, in stands of E. globulus and probably other broadleaf species with evenly distributed crowns, foliage clumping at the shoot or branch level is unlikely to be a significant source of error in indirect estimates of L. Scattering of blue light may result in large underestimates of L when using the PCA. In stands with 'extreme' architecture, indirect, light interception-based methods are likely to greatly underestimate L, although, positioning the sensor so as remove large gaps from view may allow accurate estimates of L even in these stands. (C) 2000 Published by Elsevier Science B.V All rights reserved.