| The forest canopy can affect the spatial distribution pattern of rainfall under forest,and weaken the direct erosion force of rainwater falling from high altitude to the ground.Studying the impact of the spatial morphological difference of the canopy on the interception function of forest trees can clarify the rainfall reduction mechanism of vegetation cover.,play the role of soil and water conservation,promote the management of forest resources,has important scientific significance.The 3D laser scanner can obtain the tree canopy point cloud,which provides the basis for the 3D reconstruction of the tree canopy and provides technical support for the characterization of the tree canopy difference.The study took 20 Eucommia ulmoides and 40 camphor trees in Fujian Agriculture and Forestry University as the research objects,and reconstructed the three-dimensional space of the forest canopy by observing and collecting the rainfall from June to November 2021 combined with the point cloud data obtained by the ground-based lidar scanner.Structure,select the tree canopy spatial morphological structure index,and study the impact and process of forest canopy morphological differences on rainfall interception.The main conclusions of the study are as follows:(1)During the observation period from June to November 2021,a total of 33 effective rainfall events occurred in the study area,the cumulative rainfall was 787.92 mm,the rainfall span was between4.14 mm and 261.0mm,and the average rainfall was 23.88 mm.During the observation process,the occurrence frequencies of light rain,moderate rain,heavy rain and heavy rain were found to be 9.09%,51.52%,24.24%and 15.5%,respectively.Among them,the frequency of moderate rain is the highest,and the frequency of light rain is low.During the study period,the cumulative penetration rain of Eucommia ulmoides was 506.12 mm,and the penetration rain of camphor was 541.48 mm;the stem flow of Eucommia ulmoides was 16.44 mm,and the stem flow of camphor was2.122 mm;the interception of Eucommia ulmoides was 268.63 mm,and the interception of camphor was 246.14 mm.(2)Based on the point cloud data obtained by the 3D laser scanner,the three-dimensional structure model of the canopy of 40 camphor trees and 20 Eucommia eucommia trees was reconstructed.Tree height,diameter at breast height,longest and shortest crown width,crown width area,crown length,contour line length and LAI value were selected as indicators to describe the spatial morphology of tree canopy.The extraction results showed that the longest tree heights of Eucommia ulmoides and Camphora were 8.50 m and 18.33 m,and the shortest tree heights were 3.50 m and 4.20 m,respectively;the longest diameters at breast height were 20.80 and 49.60 cm,and the shortest diameters at breast height were 5.80 cm and 11.10 cm,respectively.cm;the maximum crown widths are 28.26m~2 and 78.58m2,respectively,and the minimum crown widths are 1.70m2 and 4.95m2,respectively;the longest crown lengths are 6.99 m and 15.23 m,and the shortest crown lengths are 5.12 m and 2.61 m,respectively;The lengths of the long contour lines were46.97 m and 92.97 m,respectively,and the lengths of the shortest contour lines were 17.80 m and 30.52 m,respectively;the maximum LAI values were 3.8 and 4.79,and the minimum LAI values were 3.43 and 3.35,respectively.(3)Indicators such as slope,long crown radius and short crown radius are greatly affected by canopy morphology,and effective stratification is an important means to obtain these indicators.The horizontal layering mode with a unit interval of 0.5m is determined through experiments.The layering number of this layering mode is between 6 and 31 layers.It has a more detailed layering interval,and the extraction accuracy of indicators is higher.The standard of the layer depends on the slope that changes significantly,which can avoid the problem of double calculation of the slope.According to the stratified 3D model,it can be concluded that the maximum slopes are 2.74 and 21.42,and the minimum slopes are 0.44 and 0.38,respectively;the longest long crown radii in the single tree scale are 6.20 and 13.40 m,respectively,and the shortest long crown radii are The radii of the longest short crowns are6.00 m and 8.00m;the radii of the shortest short crowns are 0.90 m and2.10 m.(4)In light rain,the factors that have the greatest impact on penetration rainfall,stem flow and interception are the length of the contour line,and the correlation coefficient is 0.509,showing a very significant positive correlation;the longest crown radius,the correlation coefficient is-0.538,showing a very significant positive correlation.Very significant negative correlation;contour line length,the correlation coefficient is-0.495,showing a very significant negative correlation.During moderate rain,the most influential factors on through rainfall,stem flow and interception were the LAI value,the correlation coefficient was-0.451,showing a very significant negative correlation;the shortest crown length,the correlation coefficient was-0.500,showing a very significant negative correlation Correlation;LAI value,the correlation coefficient was 0.493,showing a very significant positive correlation.During heavy rain,the most influential factors on penetration rainfall,stem flow and interception were diameter at breast height,with a correlation coefficient of 0.375,showing a very significant positive correlation;the shortest crown length,with a correlation coefficient of-0.644,showing a very significant negative correlation;LAI value,the correlation coefficient was-0.339,showing a very significant negative correlation.During heavy rain,the most influential factor on through rainfall,stem flow and interception is tree height,with a correlation coefficient of 0.308,showing a very significant positive correlation;the shortest canopy length,with a correlation coefficient of-0.650,showing a very significant negative correlation;High,the correlation coefficient is-0.301,showing a very significant positive correlation.(4)Through principal component analysis,a comprehensive evaluation model for the characteristics of stratified and unstratified tree canopy morphological indicators was constructed respectively,and the effects of stratified and unstratified canopy spatial spatial shape on the tree canopy rainfall interception were compared.Results as follows:Comprehensive score of unstratified tree canopy morphological indicators = 0.2113 × contour line length + 0.1840 × diameter at breast height + 0.2175 × crown length + 0.2049 × crown width area + 0.1435× tree height + 0.0388 × LAI valueComprehensive score of stratified tree canopy morphological indicators = 0.0981 × longest crown width + 0.1473 × contour line length + 0.1460 × diameter at breast height + 0.1259 × crown length +0.0649 × crown width area + 0.1579 × tree height + 0.0534 × shortest crown width +0.1298×LAI value+0.0768×SlopeFrom the average relative accuracy RA,the values of the intercepted rainfall function quantification model fitted by the canopy without stratification are 83.82%,74.28%,66.94% and 80.09% in light rain,moderate rain,heavy rain and heavy rain,respectively;The RA values of the stratified canopy and interception fittings were 84.18%,75.88%,70.01% and 80.86%.Overall,the stratified model has higher fitting accuracy than the unstratified model under various rainfall intensities,indicating that stratification can more accurately characterize the canopy morphological difference,which is helpful for the realization of remote sensing quantification of rainfall interception function. |
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