Study Of Carbon Stock In Timber Forests Of Various Management Types Based On Terrestrial Laser Point Cloud

Forests are an important part of terrestrial ecosystems,and forest vegetation structure parameters under different management practices can effectively reflect the state of material and energy cycles in terrestrial ecosystems,as well as the level of terrestrial productivity,which plays an irreplaceable role in global carbon sinks and carbon cycles.Therefore,the correct and accurate assessment of forest carbon stock is of great significance to global ecosystem research.Traditional vegetation carbon stock statistics are based on a large amount of ground-truthing data,which is labor-intensive,material-intensive and time-consuming.Terrestrial laser scanning（TLS）technology enables forest scenes to be recreated,allowing millimeter-level 3D information to be obtained for the study area,and enabling efficient,automated,periodic measurements of forest structure information.In terms of research content,we used southern Chinese timber forest species as research objects（mainly Cunninghamia lanceolata and Liriodendron chinense）,compared the growth of Cunninghamia lanceolata plantation with four mixed management and Liriodendron chinense plantation with three density management,and conducted dynamic monitoring of Liriodendron chinense plantation samples for three periods,aiming to provide a research basis for efficient management and management of planted timber forests.Firstly,point cloud characteristics such as tree measurement factors as diameter at breast height,tree height,volume and cumulative percentage of height were extracted based on single wood point clouds to provide accurate data for the subsequent study.Secondly,we analyzed the differences of tree measurement factors and height accumulation percentages of different composite management types and multi-density management plantations,and established the tapper equation to realize the analysis of stem shape and timber species output,and used the biomass method to estimate the forest biomass and forest carbon stock of each management type to explore the ecological and economic benefits of planted timber forests under various management methods.Finally,the point cloud extracted tree measurement factors were used to analyze the change of Liriodendron chinense plantation from2014 to 2019,and a dynamic prediction model of timber volume was established with the point cloud feature parameters,in order to find a more convenient method for estimating standing timber volume and provide a more efficient way for forest carbon stock estimation.In terms of methodological exploration,this paper used Terrestrial laser point cloud data as the basis,fitted trunk diameter by least squares method,extracted tree height using fusion software,and designed extracted characteristic parameters（height cumulative percentage）.In order to evaluate the effects of different management types（mix-forest of Cunninghamia lanceolata and multi-densities of Liriodendron chinense）,the differences in their growth structures were analyzed by using the extracted diameter at breast height,height and height cumulative percentage from the point cloud,and a taper equation model was developed based on the extracted upper diameters and a wood yield table was compiled to compare and analyze the differences in their stem shapes and wood yield of the species,while their biomass and carbon stocks were estimated by using the biomass conversion factor method.The ecological and economic benefits of the researched species were evaluated.The study also analyzed the growth changes in 2014,2018,and 2019 of the Liriodendron chinense plantation based on the tree measurement factors and characteristic parameters extracted from the point cloud.The main research results are as follows:1、Compared with the Cunninghamia lanceolata pure stands,the average diameter at breast height,average tree height and average volume of Cunninghamia lanceolata decreased under mixed management（Cunninghamia lanceolata-Sarcandra glabra,Cunninghamia lanceolata-Manglietiastrum sinicum,Cunninghamia lanceolata-Phoebe bournei）.Mixed management forest Cunninghamia lanceolata-Manglietiastrum sinicum had less effect on the diameter at breast height,tree height and volume of Cunninghamia lanceolata（22.8cm,18.65m,0.3995m3,respectively）,which were similar to the values of Cunninghamia lanceolata pure stands（23.5cm,19.13m,0.3991m3,respectively）.The modified four-parameter Schumacher model was used to model the taper equations of the four mixed-managements forest and to plot the stem curves,which showed that the stem shape of Cunninghamia lanceolata-Manglietiastrum sinicum was closer to that of the pure forest,while the stem shape of Cunninghamia lanceolata-Sarcandra glabra and Cunninghamia lanceolata-Phoebe bournei were closer and the stem curves were located below the pure forest.The volume of large-diameter timber production of Cunninghamia lanceolata-Manglietiastrum sinicum was the largest,while Cunninghamia lanceolata-Sarcandra glabra and Cunninghamia lanceolata-Phoebe bournei declined compared to the pure forest.The above results showed that Cunninghamia lanceolata-Manglietiastrum sinicum not only facilitated the cultivation of large-diameter timber compared with pure forests,but also promoted the growth of accumulation,biomass and carbon stock,and also achieved the purpose of increasing economic and ecological benefits.2、The diameter at breast height,height and volume of the study area decreased with the increase of silvicultural density,showing an inverted"J"curve.The mean diameter at breast height,tree height and volume at high density plantation stand were significantly smaller than those at medium and low densities plantation stand,and slightly larger at low density plantation stand than at medium density plantation stand.The cumulative percentage of height（Hz）showed differences among multiple density management types and was consistent with the differences in tree mensuration factors.The cumulative length and volume of large-diameter wood of high-density were the smallest,followed by medium-density and close to low-density,and the small-diameter wood（72.14%）accounted for most of the wood yield of high-density Liriodendron chinense,forest stand while the highest wood yield of large-diameter wood was in medium-density Liriodendron chinense forest stand（24.73%）.The storage volume,biomass and carbon stock of Liriodendron chinense increased with the increase of stand density,and the storage volume,biomass and carbon stock of high-density Liriodendron chinense plantation stand were the largest,followed by medium-density.The above results show that,taking into account large-diameter timber,medium-diameter timber,ecological benefits and economic benefits,medium-density plantations have the highest overall benefits.3、During the monitoring periods of 2014,2018 and 2019,the average diameter at breast height of the Liriodendron chinense plantation increased by 1.91cm,the average tree height increased by 1.82m,and the average volume increased by 0.11m³.The diameter grade order distribution shifted from 25cm to 30cm;the cumulative percentage of height（Hz）was sensitive to the change of volume and was highly correlated with volume.The 3-stage volume prediction model with H₂₅ and DBH as variables can be used for wood volume prediction,with R² greater than 0.9 and RMSE smaller,and there is no significant difference between the model predicted value and the point cloud measured value;the timber volume model established can be used for the prediction of timber volume change of Liriodendron chinense,and the model predicts the timber volume change of each diameter order in three periods,and there is an obvious linear relationship between its predicted value and the point cloud measured timber volume change value,with R² of 0.9891;the cumulative percentage of height（Hz）can reflect the change of upper diameter with increasing tree height.The Hz curves of the two analyzed trees showed an inflection point at H₂₅ and a second inflection point at H₅₀,and the heights of the two inflection points were consistent with the inflection point range of the two analyzed trees.