Branch angles are an important plant morphological trait affecting light interception within forest canopies.However,studies on branch angles have been limited due to the time-consuming nature of manual measurements u...Branch angles are an important plant morphological trait affecting light interception within forest canopies.However,studies on branch angles have been limited due to the time-consuming nature of manual measurements using a protractor.Terrestrial laser scanning(TLS),however,provides new opportunities to measure branch angles more efficiently.Despite this potential,studies validating branch angle measurements from TLS have been limited.Here,our aim is to evaluate both manual and automatic branch angle measurements of European beech from TLS data using traditional field-measurements with a protractor as a reference.We evaluated the accuracy of branch angle measurements based on four automated algorithms(aRchiQSM,TreeQSM,Laplacian,SemanticLaplacian)from TLS data.Additionally,we assessed different ways of manual branch angle measurements in the field.Our study was based on a dataset comprising 124 branch angles measured from six European beech in a European deciduous forest.Our results show that manual branch angle measurements from TLS data are in high agreement with the reference(root-mean-squared error,RMSE:[3.57°-4.18°],concordance correlation coefficient,CCC:[0.950.97])across different branch length positions.Automated algorithms also are in high agreement with the reference although RMSE is approximately twice as large compared to manual branch angle measurements from TLS(RMSE:[9.29°-10.55°],CCC:[0.830.86])with manual leaf points removal.When applying the automatic wood-leaf separation algorithm,the performance of the four methods declined significantly,with only approximately 20 branch angles successfully identified.Moreover,it is important to note that there is no influence of the measurement position(branch surface versus center)for branch angle measurements.However,for curved branches,the selection of branch measurement length significantly impacts the branch angle measurement.This study provides a comprehensive understanding of branch angle measurements in forests.We show that automated measurement methods based on TLS data of branch angles are a valuable tool to quantify branch angles at larger scales.展开更多
Vertical forest structure is closely linked to multiple ecosystem characteristics,such as biodiversity,habitat,and productivity.Mixing tree species in planted forests has the potential to create diverse vertical fores...Vertical forest structure is closely linked to multiple ecosystem characteristics,such as biodiversity,habitat,and productivity.Mixing tree species in planted forests has the potential to create diverse vertical forest structures due to the different physiological and morphological traits of the composing tree species.However,the relative importance of species richness,species identity and species interactions for the variation in vertical forest structure remains unclear,mainly because traditional forest inventories do not observe vertical stand structure in detail.Terrestrial laser scanning(TLS),however,allows to study vertical forest structure in an unprecedented way.Therefore,we used TLS single scan data from 126 plots across three experimental planted forests of a largescale tree diversity experiment in Belgium to study the drivers of vertical forest structure.These plots were 9–11years old young pure and mixed forests,characterized by four levels of tree species richness ranging from monocultures to four-species mixtures,across twenty composition levels.We generated vertical plant profiles from the TLS data and derived six stand structural variables.Linear mixed models were used to test the effect of species richness on structural variables.Employing a hierarchical diversity interaction modelling framework,we further assessed species identity effect and various species interaction effects on the six stand structural variables.Our results showed that species richness did not significantly influence most of the stand structure variables,except for canopy height and foliage height diversity.Species identity on the other hand exhibited a significant impact on vertical forest structure across all sites.Species interaction effects were observed to be site-dependent due to varying site conditions and species pools,and rapidly growing tree species tend to dominate these interactions.Overall,our results highlighted the importance of considering both species identity and interaction effects in choosing suitable species combinations for forest management practices aimed at enhancing vertical forest structure.展开更多
This paper presents the latest results of the radiation transfer model intercomparison(RAMI)of the realistic vegetation scenarios.RAMI-V included the same one-dimensional(1D)and 3D scenes of RAMI-IV phase and 2 new re...This paper presents the latest results of the radiation transfer model intercomparison(RAMI)of the realistic vegetation scenarios.RAMI-V included the same one-dimensional(1D)and 3D scenes of RAMI-IV phase and 2 new realistic ones,defined through a semiparametric(Savanna)and an empirical(Wytham Woods)approaches.The measurements to simulate were the bidirectional reflectance factor,directional-hemispherical reflectance,and bidirectional-hemispherical reflectance.In addition,the radiant flux transmission and absorption through and below the canopy and digital hemispherical photography were also proposed.The spectral bands were defined to mimic not only the ones of Copernicus optical missions,e.g.,for the Sentinel-3 Ocean and Land Colour Imager(OLCI)and Sentinel-2 Multispectral Instrument(MSI),but also the Moderate Resolution Imaging Spectroradiometer(MODIS).New solar and viewing geometry configurations were adopted from realistic satellite overpasses for different seasons and geographical locations.The role of internal consistency checks was reinforced to provide more reliable feedback to the participants in the early stage of the experiment and reduce the role of outliers in the model-to-model comparison and the identification of a surrogate reference.Over 4 of the 8 scenarios proposed,a set of models agreed within 2%uncertainty thresholds for most of the virtual measurements defined in the experiment.Specifically,they were the birchstand both leaf-on(HET09)and leaf-off(HET15)versions,and the structured canopy models consisting of a citrus orchard(HET14)and a poplar forest(HET16).It is noteworthy that less was among the models designated to set a reference benchmark across all chosen instances.Besides,dart,raytran,and wps were contributing to the benchmark in most of the experiment proposed,especially referring to total BRF and DHR,and total absorption,while for the transmittance the results were more dispersed.Dart,less,raytran,and wps contributed by submitting 100%,83.9%,99.4%,and 86.2% of the experiment proposed,respectively.The proficiency testing of the models was performed by means of the z′metric defined in ISO-13528.A custom reference,based on a selection of models that showed the best agreement,as well as a reference based on robust statistic were adopted.Above the aforementioned selected scenes,and assuming a compliance threshold of 3%(5%)for bidirectional reflectance(albedo)measurements,dart,less,and raytran were in agreement in all(more than 95%)cases.The approach based on the robust statistic described in ISO-13528 confirmed its relevance in interlaboratory comparison exercises where the benchmark is not defined a priori,allowing us to obtain proficiency results equivalent to those defined against the customized references.展开更多
基金supported by the Chinese Scholarship Council under Grant 202106910006.
文摘Branch angles are an important plant morphological trait affecting light interception within forest canopies.However,studies on branch angles have been limited due to the time-consuming nature of manual measurements using a protractor.Terrestrial laser scanning(TLS),however,provides new opportunities to measure branch angles more efficiently.Despite this potential,studies validating branch angle measurements from TLS have been limited.Here,our aim is to evaluate both manual and automatic branch angle measurements of European beech from TLS data using traditional field-measurements with a protractor as a reference.We evaluated the accuracy of branch angle measurements based on four automated algorithms(aRchiQSM,TreeQSM,Laplacian,SemanticLaplacian)from TLS data.Additionally,we assessed different ways of manual branch angle measurements in the field.Our study was based on a dataset comprising 124 branch angles measured from six European beech in a European deciduous forest.Our results show that manual branch angle measurements from TLS data are in high agreement with the reference(root-mean-squared error,RMSE:[3.57°-4.18°],concordance correlation coefficient,CCC:[0.950.97])across different branch length positions.Automated algorithms also are in high agreement with the reference although RMSE is approximately twice as large compared to manual branch angle measurements from TLS(RMSE:[9.29°-10.55°],CCC:[0.830.86])with manual leaf points removal.When applying the automatic wood-leaf separation algorithm,the performance of the four methods declined significantly,with only approximately 20 branch angles successfully identified.Moreover,it is important to note that there is no influence of the measurement position(branch surface versus center)for branch angle measurements.However,for curved branches,the selection of branch measurement length significantly impacts the branch angle measurement.This study provides a comprehensive understanding of branch angle measurements in forests.We show that automated measurement methods based on TLS data of branch angles are a valuable tool to quantify branch angles at larger scales.
基金Mengxi Wang holds a doctoral scholarship from the China scholarship council(CSC:202003270025)。
文摘Vertical forest structure is closely linked to multiple ecosystem characteristics,such as biodiversity,habitat,and productivity.Mixing tree species in planted forests has the potential to create diverse vertical forest structures due to the different physiological and morphological traits of the composing tree species.However,the relative importance of species richness,species identity and species interactions for the variation in vertical forest structure remains unclear,mainly because traditional forest inventories do not observe vertical stand structure in detail.Terrestrial laser scanning(TLS),however,allows to study vertical forest structure in an unprecedented way.Therefore,we used TLS single scan data from 126 plots across three experimental planted forests of a largescale tree diversity experiment in Belgium to study the drivers of vertical forest structure.These plots were 9–11years old young pure and mixed forests,characterized by four levels of tree species richness ranging from monocultures to four-species mixtures,across twenty composition levels.We generated vertical plant profiles from the TLS data and derived six stand structural variables.Linear mixed models were used to test the effect of species richness on structural variables.Employing a hierarchical diversity interaction modelling framework,we further assessed species identity effect and various species interaction effects on the six stand structural variables.Our results showed that species richness did not significantly influence most of the stand structure variables,except for canopy height and foliage height diversity.Species identity on the other hand exhibited a significant impact on vertical forest structure across all sites.Species interaction effects were observed to be site-dependent due to varying site conditions and species pools,and rapidly growing tree species tend to dominate these interactions.Overall,our results highlighted the importance of considering both species identity and interaction effects in choosing suitable species combinations for forest management practices aimed at enhancing vertical forest structure.
基金supported by EU Copernicus programfunded by the European Union(ERC-2021-STG grant agreement no.101039795)supported by the Estonian Research Council grant PRG1405。
文摘This paper presents the latest results of the radiation transfer model intercomparison(RAMI)of the realistic vegetation scenarios.RAMI-V included the same one-dimensional(1D)and 3D scenes of RAMI-IV phase and 2 new realistic ones,defined through a semiparametric(Savanna)and an empirical(Wytham Woods)approaches.The measurements to simulate were the bidirectional reflectance factor,directional-hemispherical reflectance,and bidirectional-hemispherical reflectance.In addition,the radiant flux transmission and absorption through and below the canopy and digital hemispherical photography were also proposed.The spectral bands were defined to mimic not only the ones of Copernicus optical missions,e.g.,for the Sentinel-3 Ocean and Land Colour Imager(OLCI)and Sentinel-2 Multispectral Instrument(MSI),but also the Moderate Resolution Imaging Spectroradiometer(MODIS).New solar and viewing geometry configurations were adopted from realistic satellite overpasses for different seasons and geographical locations.The role of internal consistency checks was reinforced to provide more reliable feedback to the participants in the early stage of the experiment and reduce the role of outliers in the model-to-model comparison and the identification of a surrogate reference.Over 4 of the 8 scenarios proposed,a set of models agreed within 2%uncertainty thresholds for most of the virtual measurements defined in the experiment.Specifically,they were the birchstand both leaf-on(HET09)and leaf-off(HET15)versions,and the structured canopy models consisting of a citrus orchard(HET14)and a poplar forest(HET16).It is noteworthy that less was among the models designated to set a reference benchmark across all chosen instances.Besides,dart,raytran,and wps were contributing to the benchmark in most of the experiment proposed,especially referring to total BRF and DHR,and total absorption,while for the transmittance the results were more dispersed.Dart,less,raytran,and wps contributed by submitting 100%,83.9%,99.4%,and 86.2% of the experiment proposed,respectively.The proficiency testing of the models was performed by means of the z′metric defined in ISO-13528.A custom reference,based on a selection of models that showed the best agreement,as well as a reference based on robust statistic were adopted.Above the aforementioned selected scenes,and assuming a compliance threshold of 3%(5%)for bidirectional reflectance(albedo)measurements,dart,less,and raytran were in agreement in all(more than 95%)cases.The approach based on the robust statistic described in ISO-13528 confirmed its relevance in interlaboratory comparison exercises where the benchmark is not defined a priori,allowing us to obtain proficiency results equivalent to those defined against the customized references.
