Estimating leaf area distribution in savanna trees from terrestrial LiDAR measurements

Béland, Martin; Widlowski, Jean-Luc; Fournier, Richard; Côté, Jean-François; Verstraete, M. M.

doi:10.1016/j.agrformet.2011.05.004

Cited by 227 publications

(217 citation statements)

References 28 publications

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“…However, other better-performing crown base metrics may be identified in the future, perhaps using laser intensity data to identify live crown. Seielstad et al (2011) andBéland et al (2011) have each shown that laser intensity data can be used to distinguish foliage from branch wood in both conifer and broadleaf specimens using similar instruments and techniques.…”

Section: Discussionmentioning

confidence: 99%

Conifer crown profile models from terrestrial laser scanning

Ferrarese¹,

Affleck²,

Seielstad³

2015

Silva Fenn.

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• Crown models are derived from terrestrial laser data for 3 NW USA conifer species.• Crown models require only crown length for implementation.• Beta and Weibull curves fit to 95th percentile widths describe crown extent.• Crown profile curves are species-specific and not interchangeable.• Crown shape is not strongly conditioned by tree size or site. AbstractRegional crown profile models were derived for three conifer species of the interior northwestern USA from terrestrial laser scans of eighty-six trees across a range of sizes and growing conditions. Equations were developed to predict crown shape from crown length for Pseudotsuga menziesii, Pinus ponderosa, and Abies lasiocarpa from parametric curves applied to crown-length normalized laser point clouds. The 95th width percentile adequately described each crown's outer limit; alternate width percentiles produced little profile shape variation. For P. menziesii and P. ponderosa, a scaling parameter-modified beta curve gave the most accurate fit (using cross-validated Mean Absolute Error) to aggregated 95th width percentile points. For A. lasiocarpa, beta and Weibull curves (equivalently modified) produced similar results. For all species, modified beta and Weibull curves fit crown points with less error than conic or cylindrical profiles. Crown profile curves were species-specific; interchanging among species increased error significantly. Laser-derived crown base metrics provided objectivity and consistency, but underestimated field-derived base heights through inclusion of dead branches. Profile curve parameters were not correlated with tree or stand characteristics suggesting that crown shape is not strongly conditioned by size and site factors. However, laser sampling necessarily favored more open growing conditions, potentially under-representing variations in crown shape associated with social position. Overall, Terrestrial Laser Scanning (TLS) lends itself to detailed measurements of external crown architecture with occlusion-imposed limits to characterization of internal features. Yet, the time and cost of collecting and processing individual tree data precludes use of TLS as a common field sampling tool.

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Section: Discussionmentioning

confidence: 99%

Conifer crown profile models from terrestrial laser scanning

Ferrarese¹,

Affleck²,

Seielstad³

2015

Silva Fenn.

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“…However, similar to the α‐value, the voxel size has to be chosen with care as it can have a significant effect on the measured property, in particular when computing volumes. With respect to tree crowns, voxel grids have been used to compute leaf area index and foliage (Béland, Widlowski, Fournier, Côté, & Verstraete, 2011), crown plasticity (Seidel, Leuschner, Müller, & Krause, 2011), crown competition (Metz et al., 2013), and CVs (Fernández‐Sarría et al., 2013; Metz et al., 2013). Often, α‐shape and voxel grid approaches are used in combination (Fernández‐Sarría et al., 2013; Metz et al., 2013; Seidel et al., 2011), mainly because they enable faster point cloud processing and simplification.…”

Section: Introductionmentioning

confidence: 99%

A high‐resolution approach for the spatiotemporal analysis of forest canopy space using terrestrial laser scanning data

Hess

Härdtle

Kunz

et al. 2018

Ecology and Evolution

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Forest canopies and tree crown structures are of high ecological importance. Measuring canopies and crowns by direct inventory methods is time‐consuming and of limited accuracy. High‐resolution inventory tools, in particular terrestrial laser scanning (TLS), is able to overcome these limitations and obtain three‐dimensional (3D) structural information about the canopy with a very high level of detail. The main objective of this study was to introduce a novel method to analyze spatiotemporal dynamics in canopy occupancy at the individual tree and local neighborhood level using high‐resolution 3D TLS data. For the analyses, a voxel grid approach was applied. The tree crowns were modeled through the combination of two approaches: the encasement of all crown points with a 3D α‐shape, which was then converted into a voxel grid, and the direct voxelization of the crown points. We show that canopy occupancy at individual tree level can be quantified as the crown volume occupied only by the respective tree or shared with neighboring trees. At the local neighborhood level, our method enables the precise determination of the extent of canopy space filling, the identification of tree–tree interactions, and the analysis of complementary space use. Using multitemporal TLS data recordings, this method allows the precise detection and quantification of changes in canopy occupancy through time. The method is applicable to a wide range of investigations in forest ecology research, including the study of tree diversity effects on forest productivity or growing space analyses for optimal tree growth. Due to the high accuracy of this novel method, it facilitates the precise analyses even of highly plastic individual tree crowns and, thus, the realistic representation of forest canopies. Moreover, our voxel grid framework is flexible enough to allow for the inclusion of further biotic and abiotic variables relevant to complex analyses of forest canopy dynamics.

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“…The new approach presented in this research, referred to as the 'intensity-based' method, defines gap fraction in a given angular range (GF) as (Equation (2)): (2) where m indicates the number of laser hits expected (with no gaps) and Int corrected refers to intensity values corrected with respect to the ranging information recorded by TLS. Assuming that canopy elements present Lambertian scattering properties, intensity values captured by LiDAR systems are dependent on the target reflectance, the portion of the laser beam occupied by the target and the distance from the sensor at which they are triggered [22].…”

Section: Background Theorymentioning

confidence: 99%

Testing the Application of Terrestrial Laser Scanning to Measure Forest Canopy Gap Fraction

2013

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Terrestrial laser scanners (TLS) have the potential to revolutionise measurement of the three-dimensional structure of vegetation canopies for applications in ecology, hydrology and climate change. This potential has been the subject of recent research that has attempted to measure forest biophysical variables from TLS data, and make comparisons with two-dimensional data from hemispherical photography. This research presents a systematic comparison between forest canopy gap fraction estimates derived from TLS measurements and hemispherical photography. The TLS datasets used in the research were obtained between April 2008 and March 2009 at Delamere Forest, Cheshire, UK. The analysis of canopy gap fraction estimates derived from TLS data highlighted the repeatability and consistency of the measurements in comparison with those from coincident hemispherical photographs. The comparison also showed that estimates computed considering only the number of hits and misses registered in the TLS datasets were consistently lower than those estimated from hemispherical photographs. To examine this difference, the potential information available in the intensity values recorded by TLS was investigated and a new method developed to estimate canopy gap fraction proposed. The new approach produced gap fractions closer to those estimated from hemispherical photography, but the research also highlighted the limitations of single return TLS data for this application.

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Estimating leaf area distribution in savanna trees from terrestrial LiDAR measurements

Cited by 227 publications

References 28 publications

Conifer crown profile models from terrestrial laser scanning

Conifer crown profile models from terrestrial laser scanning

A high‐resolution approach for the spatiotemporal analysis of forest canopy space using terrestrial laser scanning data

Testing the Application of Terrestrial Laser Scanning to Measure Forest Canopy Gap Fraction

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