Tree Physiology Advance Access originally published online on June 24, 2009
Tree Physiology 2009 29(8):1069-1080; doi:10.1093/treephys/tpp042
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Woody-to-total area ratio determination with a multispectral canopy imager
1 School of Geography, State Key Laboratory of Remote Sensing Science, Jointly Sponsored by Beijing Normal University and the Institute of Remote Sensing Applications of Chinese Academy of Sciences, Beijing Normal University
2 Corresponding author (gjyan{at}bnu.edu.cn)
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Abstract |
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Leaf area index (LAI) – defined as one half of the total green leaf area per unit ground surface area – can be determined by direct or indirect methods. Three major sources of errors exist in indirect LAI measurements: within-shoot clumping, beyond-shoot clumping and non-photosynthetic components. The effect of non-photosynthetic components on LAI measurements can be described by the woody-to-total area ratio, 
; however, no convenient and efficient indirect methods have been developed to estimate , especially the variations in with zenith angle 
, (). We describe the development and use of a multispectral canopy imager (MCI) to estimate and () by considering the effects of non-random distributions of canopy elements and woody components and the overestimation of needle-to-shoot area ratio on woody components. The MCI, which mainly comprises a near-infrared band camera (Fujifilm IS-1), two visible band cameras (Canon 40D), filters and a pan tilt, was developed to measure clumping index, woody-to-total area ratio and geometric parameters of isolated trees. Two typical sampling plots (Plots 1 and 5) chosen from among 16 permanent forest experiment plots were selected for the estimation of and (). The non-random distributions of canopy elements and woody components were estimated separately at eight zenith angles (from 0° to 70° in increments of 10°) using MCI images based on the gap size distribution theory. The visible/near-infrared image pairs captured by the MCI were able to discriminate among sky, leaves, cloud and woody components. Based on three methods of estimation, we obtained woody-to-total area ratios of 0.24, 0.19, 0.19 for Plot 1 and 0.23, 0.18, 0.17 for Plot 5. If clumping effects were ignored, values were overestimated by as much as 21% and 24% at Plots 1 and 5, respectively. We demonstrated that () varied with the zenith angle, with variations in the range of 3–33% at Plot 1 and 2–65% at Plot 5. A new formula for the precise determination of LAI is proposed.
Keywords: clumping index, leaf area index, near-infrared photography, non-photosynthesis components, plant area index, woody area index, woody-to-total area ratio
Received December 4, 2008; Accepted May 17, 2009
* Present address: School of Geography, Beijing Normal University, 19 Xinjiekou Wai Street, Beijing, PRC.