Effects of Tree Trunks on Estimation of Clumping Index and LAI from HemiView and Terrestrial LiDAR

Abstract

Estimating clumping indices is important for determining the leaf area index (LAI) of forest canopies. The spatial distribution of the clumping index is vital for LAI estimation. However, the neglect of woody tissue can result in biased clumping index estimates when indirectly deriving them from the gap probability and LAI observations. It is difficult to effectively and automatically extract woody tissue from digital hemispherical photos. In this study, a method for the automatic detection of trunks from Terrestrial Laser Scanning (TLS) data was used. Between-crown and within-crown gaps from TLS data were separated to calculate the clumping index. Subsequently, we analyzed the gap probability, clumping index, and LAI estimates based on TLS and HemiView data in consideration of woody tissue (trunks). Although the clumping index estimated from TLS had better agreement (R 2 = 0.761) than that from HemiView, the change of angular distribution of the clumping index affected by the trunks from TLS data was more obvious than with the HemiView data. Finally, the exclusion of the trunks led to a reduction in the average LAI by~19.6% and 8.9%, respectively, for the two methods. These results also showed that the detection of woody tissue was more helpful for the estimation of clumping index distribution. Moreover, the angular distribution of the clumping index is more important for the LAI estimate than the average clumping index value. We concluded that woody tissue should be detected for the clumping index estimate from TLS data, and 3D information could be used for estimating the angular distribution of the clumping index, which is essential for highly accurate LAI field measurements.

Differences in Soil Physicochemical Properties in Different-Aged Pinus massoniana Plantations in Southwest China

“…Leaf area index (LAI) was measured using HemiView that mainly consisted of a self-levelling mount, camera (Canon 80D), and HemiView canopy analysis software (Delta-T devices Ltd., Cambridge, UK). The procedure and method of HemiView can be found in the study by Bao et al [27].…”

Estimation of leaf area index using PROSAIL based LUT inversion, MLRA-GPR and empirical models: Case study of tropical deciduous forest plantation, North India

“…The plant canopy imagers recorded LAI observations were not corrected for clumping effects ( Chianucci et al, 2015 ). Clumping effects cause underestimation of LAI values ( Bao et al, 2018 ). We believe that the PROSAIL model prediction of LAI might have been further improved by providing a clumping effect corrected LAI range in the PROSAIL model.…”

Estimating Crown Structure Parameters of Moso Bamboo: Leaf Area and Leaf Angle Distribution

“…where P(θ) is the gap fraction of a canopy, which is generally obtained by hemispherical optical instruments such as in DHP [93,94]; and Ω(θ) is the clumping index, which is used for quantifying leaf spatial distribution within a canopy. Here, Ω(θ) is assumed as 1 to represent a random spatial distribution of leaves.…”