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Estimating below‐canopy light regimes using airborne laser scanning: An application to plant community analysis
摘要： Light is a key driver of forest biodiversity and functioning. Light regimes beneath tree canopies are mainly driven by the solar angle, topography, and vegetation structure, whose three‐dimensional complexity creates heterogeneous light conditions that are challenging to quantify, especially across large areas. Remotely sensed canopy structure data from airborne laser scanning (ALS) provide outstanding opportunities for advancement in this respect. We used ALS point clouds and a digital terrain model to produce hemispherical photographs from which we derived indices of nondirectional diffuse skylight and direct sunlight reaching the understory. We validated our approach by comparing the performance of these indices, as well as canopy closure (CCl) and canopy cover (CCo), for explaining the light conditions experienced by forest plant communities, as indicated by the Landolt indicator values for light (Llight) from 43 vegetation surveys along an elevational gradient. We applied variation partitioning to analyze how the independent and joint statistical effects of light, macro‐climate, and soil on the spatial variation in plant species composition (i.e., turnover, Simpson dissimilarity, βSIM) depend on light approximation methodology. Diffuse light explained Llight best, followed by direct light, CCl and CCo (R2 = .31, .23, .22, and .22, respectively). The combination of diffuse and direct light improved the model performance for βSIM compared with CCl and CCo (R2 = .30, .27 and .24, respectively). The independent effect of macroclimate on βSIM dropped from an R2 of .15 to .10 when diffuse light and direct light were included. The ALS methods presented here outperform conventional approximations of below‐canopy light conditions, which can now efficiently be quantified along entire horizontal and vertical forest gradients, even in topographically complex environments such as mountains. The effect of macroclimate on forest plant communities is prone to be overestimated if local light regimes and associated microclimates are not accurately accounted for.
关键词： canopy structure,forest biodiversity,remote sensing,light availability,microclimate,Ellenberg indicator value,beta diversity,hemispherical photography,biodiversity,airborne light detection and ranging LiDAR
更新于2025-09-11 14:15:04
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Evaluating Two Optical Methods of Woody-to-Total Area Ratio with Destructive Measurements at Five Larix gmelinii Rupr. Forest Plots in China
摘要： Accurate in situ leaf area index (LAI) estimates of forest plots are required to validate currently-used LAI map products. Woody-to-total area ratio (α) is a crucial parameter in converting the plant area index estimates of forest plots obtained by optical methods into LAI. Although optical methods for estimating the α of forest canopy have been proposed, their performance has never been assessed. In this study, five Larix gmelinii Rupr. forest plots with contrasting plot characteristics (i.e., tree age, tree height, management activities, stand density, and site conditions) were selected. The performance of two commonly used optical methods, namely, multispectral canopy imager (MCI) and digital hemispherical photography (DHP), in estimating the α of L. gmelinii forest plots was evaluated by using the reference α of the selected forest plots. The reference α of forest plots was measured via destructive method by harvesting two or three representative trees in each plot. Large variations were observed amongst the reference α of the selected forest plots (ranging from 0% to 56%). These α were also highly correlated with the site conditions and management activities in these plots. The effective α (αe) or α estimated using the leaf-on and leaf-off periods MCI or DHP images with or without consideration of the clumping effects of canopy element and woody components were 1.57 to 4.63 times the reference α in the five plots. The overestimation of α or αe was mainly caused by the preferential shading of woody components by the shoots in the leaf-on canopy. Accurate α estimates for the L. gmelinii forest plots with errors of less than 20% can be obtained from MCI when the clumping effects of canopy element and woody components are considered in the estimation.
关键词： plant area index (PAI),woody area index (WAI),leaf area index (LAI),forest canopy,clumping effect,multispectral canopy imager,digital hemispherical photography,woody-to-total area ratio
更新于2025-09-09 09:28:46
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[IEEE 2018 4th International Conference on Science and Technology (ICST) - Yogyakarta, Indonesia (2018.8.7-2018.8.8)] 2018 4th International Conference on Science and Technology (ICST) - The Comparison of Canopy Density Measurement Using UAV and Hemispherical Photography for Remote Sensing Based Mapping
摘要： Canopy density estimation based on the empirical method using remote sensing data needs field measurement of canopy density data. There are several methods to obtain canopy density data, and it can be divided into downward and upward measurement. Those two methods have different term used, and it is possible to produce different result. This study aims to compare aerial photography from UAV and hemispherical photography represent downward and upward method, respectively. The results showed downward method produces the higher canopy density than upward method. The regression analysis showed upward method provides the better method in canopy density estimation, however the term of downward measurement is more appropriate to canopy density term.
关键词： canopy density,hemispherical photography,aerial photography,Sentinel-2
更新于2025-09-04 15:30:14