Lightning is the main source of natural fire, and lightning fire and other types of forest fires together constitute the global forest fire system. It is generally believed that lightning fire, as a natural fire source, has nothing to do with human beings and is different from man-made fire sources, but in fact, human activities have inextricable links with the occurrence of lightning fire. Since 2019, due to the severe impact of COVID-19 lockdowns, non-essential activities and mobility have decreased, which has led to a significant decrease in pollutant concentrations and lightning. In this paper, we linked the lightning fire with modernization process of human beings, the expansion of habitation, the change of underlying surface, the development of prediction technology and firefighting technology, and the laws and regulations of the country, to explore the impact of human activities on the occurrences of lightning and the forest lightning fire. Lightning is the fire source of the three elements in lightning fire occurrence, the lightning that can cause lightning fire is mainly cloud-to-ground lightning. The human activities in recent decades have profoundly affected the content of aerosols in environment. Aerosols are the main factors affecting lightning, and the large amount of pollution aerosols emitted from urban areas, soot aerosols emitted from biomass combustion and urban heat island effect have all increased the probability of lightning occurrence. The average annual ground lightning density of different land cover types is obviously different, and the construction land has the highest average annual ground lightning density. Intense lightning in forest areas has a higher density and slope. Most of the forests are located in high altitude areas, which is consistent with previous studies showing high lightning frequency in high altitude areas. The lightning in forests is intenser, steeper and more destructive, so forest areas are prone to lightning strikes. Lightning has the characteristic of selective discharge, that is, it will discharge into some special areas, which are also known as lightning selection areas, such as the place groundwater is exposed to the ground, where different conductive soils are connected, and where there are underground metal mines, such as copper and iron mines, and underground lake and water reservoir areas. Lightning strikes are caused by changes in soil conductivity caused by human activities such as mining waste rock sites, reservoir construction on mountain tops, and power transmission lines in mountainous areas. At the same time, due to the abundant trees in the mountainous area, it is also important to avoid the resulting lightning fire. With the development of lightning monitoring technology, a lightning location monitoring system has been established in some areas of China. Especially in 2021, the National Forestry and Grassland Administration launched the "Enlisting and Leading" emergency science and technology project of forest lightning fire prevention and control, and the project team has constructed a lightning fire sensing system in the Daxing'anling region with three-dimensional lightning full-wave detection network as the main body, covering the forest area of the Daxing'anling forest region, which can accurately locate the location of cloud-to-ground lightning in real time, improve the monitoring and warning ability of lightning fires, and improve the efficiency of lightning fire discovery. National laws and regulations indirectly affect lightning fires by affecting forest cover and climate change. This paper is expected to provide reference for the occurrence, prevention and control of forest lightning fire in the future, and provide a basis for the formulation of corresponding policies.

Objective: The occurrence of lightning fire is comprehensively affected by lightning, meteorological conditions, forest fuel, terrain, etc. Various factors are coupled and act together. After the launch of "forest lightning fire prevention and control emergency technology project", a full waveform three-dimensional lightning detection network covering the Daxing'anling Mountains has been built. Combined with the national basic meteorological station, lightning fire meteorological monitoring station, watchtower and ground patrol, the network can be used to carry out collaborative monitoring and early warning of lightning, weather and lightning fire occurrence. The number of mass lightning fires caused by dense lightning processes accounted for most of lightning fires in the spring fire season of 2022. Based on the data of the lightning fire sensing system, this paper aims to analyze the quantitative characteristics of various factors causing lightning fires, and clarify the mechanism of the influence of various factors in the dense lightning process on the occurrence of lightning fires. Method: Based on the lightning fire sensing system, the monitored lightning indicators, meteorological factors and lightning fire occurrence indicators were systematically analyzed. This study also analyzed the basic situation of lightning fire occurrence in Daxing'anling Mountains during the spring fire season in 2022, the impact of dense lightning on lightning fire occurrence, the quantitative characteristics of lightning that caused lightning fire, as well as the lightning location accuracy and lightning fire smoldering period. Result: In 2022, a total of 22 lightning fires occurred during the spring fire season in Daxing'anling Mountains, of which 18 were caused by dense lightning processes. The ground lightning and cloud lightning had one peak respectively in the positive and negative current area. The negative ground lightning accounted for 82.82% of the total number of ground lightning, and the ground lightning formed a high-frequency interval at -8~-50 kA. The number of lightning fires caused by negative ground lightning was the largest, which accounted for 70% of the total number of ground lightning, and accounted for 84.5% of the negative ground lightning. The positive ground lightning that formed a high-frequency range at 10~30 kA accounted for 12.7% of the total ground lightning, and 74.2% of the positive ground lightning, which was much lower than the number of negative ground flashes. The average current intensity of lightning fire in spring fire season was -22.72 kA, the strongest current was -48.34 kA, and the weakest current was -8.70 kA. The occurrence time of lightning that causes lightning fires was relatively concentrated, and lightning fires were mostly ignited around noon. There was a rapid temperature rise before the dense lightning that caused the lightning fire occurred. With the decline of air humidity and the increase of wind speed, the daily maximum temperature was basically the same as the occurrence time of the lightning that caused the lightning fire. It was also the period of time when the lowest relative humidity and the highest wind speed appeared. The smoldering period of lightning fire in spring fire season was from 0.56 to 17.62 h. The accuracy of lightning detection and location was 165~884 m, with an average accuracy of 394.5 m. There were two lightning fires with lightning wood positioning coordinates, and the positioning accuracy reached 165 m and 170 m. The fuels in the fire site were mainly waste mountain grassland, dry wetland meadow, as well as some coniferous forests, coniferous and broad-leaved mixed forests and burned slashes. Conclusion: The mass lightning fires caused by dense lightning processes account for the majority of lightning fires. The occurrence of mass lightning fires requires the coupling of dense lightning processes with extreme weather conditions of drought, as well as fuel available. When the lightning process is not synchronized with the precipitation process or the precipitation is less, and there is a rapid warming process in the early stage, and the intensive lightning process is accompanied by a drop in temperature, the lightning fires often occur in this period. In the process of lightning fire monitoring and early warning, we should pay special attention to the dense lightning process under drought conditions.

Objective: Lightning fire is the biggest cause threatening the safety of forest resources in Daxing'anling Mountains. This study aims to provide a scientific basis for lightning fire monitoring, early warning, prevention and suppression by analyzing the occurrence pattern of lightning in the Daxing'anling Mountains. Method: Based on the monitoring data with the VLF/LF 3D lightning location system from 2019 to 2021 in Daxing'anling Mountains, the quantity of lightning (intra-cloud lightning, IC; cloud to ground lightning, CG; positive lightning, PL; negative lightning, NL), current intensity, height of IC, and the temporal and spatial distribution of lightning activities were analyzed. Result: 1) A total of 710 487 times of lightning were detected in Daxing'anling Mountains (321 667 times in Heilongjiang Daxing'anling Mountains and 388 820 times in Inner Mongolia Daxing'anling Mountains) from 2019 to 2021, with an average of 236 829 times per year. The lightning in Daxing'anling Mountains was mainly negative CG, in which the IC: CG ratio and PL: NL ratio were roughly 1:5. The current intensity of PL and NL in Daxing'anling Mountains ranged from 4.5 to 371 kA, and from -501.7 to -4.5 kA, respectively, and the absolute value of the current intensity of most lightnings was concentrated between 4.5 and 50 kA. The average IC height in Daxing'anling Mountains was 4.72 km, of which 88.09% was mainly below 10 km. 2) The average number of lightning days in Daxing'anling Mountains was 127 days per year. Lightning started at the end of April and ended in mid and late October, mostly from May to August, of which July was a concentrated high incidence period. The occurrence of lightning showed a single peak change pattern in a single day. Lightning started to increase at 10:00, and the high incidence period was from 12:00 to 17:00. After 18:00, the number of lightning gradually decreased, and the total amount of lightning decreased significantly from midnight to early morning. 3) The distribution of lightning in Daxing'anling Mountains was spatial aggregation. On the whole, the lightning density in Daxing'anling Mountains of Heilongjiang was significantly higher than that in Daxing'anling Mountains of Inner Mongolia. High density lightning areas were mostly distributed in Daxing'anling Mountains of Heilongjiang, such as Huzhong, Tahe, Hanjiayuan, Xinlin, Nanwenghe Nature Reserve and Jiagedaqi. 4) Low intensity negative CGs, which are easy to cause lightning fires, were mainly concentrated in Xilinji, the south of Tuqiang, most area of Tahe, the north of Huzhong, and Nanwenghe Nature Reserve in Heilongjiang Daxing'anling Mountains, and the north of Mangui, a small part of Hanma and Jinhe in Inner Mongolia Daxing'anling Mountains. Conclusion: The occurrence of lightning in Daxing'anling Mountains has obvious spatial-temporal heterogeneity. Based on the occurrence pattern of lightning and specific types of lightning that are prone to fire, it is suggested that targeted monitoring, early warning and early deployment are effective means to prevent major lightning fires.

Objective: Since the implementation of the second phase (2001-2020) Shelter Forest Program in the Three North Region, huge ecological benefits have been achieved, but there are still problems in some areas, and even ecological degradation has occurred. Focusing on the structure, quality and service of the ecosystem, comprehensively and quantitatively evaluate the changes in the ecosystem, and clarify the impacts of the implementation of the fourth and fifth periods of the program on the restoration of the ecosystem, intend to provide a scientific and pertinent theoretical basis for the rolling implementation of the program. Method: This paper is based on the comprehensive evaluation method of "historical dynamic background-restoration status-restoration index" to construct the ecosystem macro-structure change index (EMSCI), ecosystem quality change index (EQCI), ecosystem service function change index (ESCI), and ecosystem restoration index (ERI) for a comprehensive evaluation of the spatial and temporal changes in structure, quality and key service functions of the ecosystem in the Three-North Program region. The spatial overlay analysis function was used to clarify the process of ecosystem changes and quantitatively evaluate the extent of ecosystem restoration. Result: 1) In the second phase of the Three-North Shelter Forest Program, ecosystem type has changed significantly with an overall dynamic degree of 12.22% and the forest coverage continued to increase with an area accounting for 10.18%. Moreover, the forest coverage increase in the fourth period (16 000 km²) was greater than that in the fifth period (6 900 km²). 2) The quality of the ecosystem has been significantly improved. The vegetation coverage and vegetation net primary productivity have increased by 0.038 and 82.33 gC·m^-2a^-1, with a growth rate of 24.50% and 34.96%, respectively. Moreover, 20.15% of the area continues to improve. 3) Compared to historical background, the service function of the ecosystem has been improved significantly. Water conservation per unit area, the amount of carbon sequestered per unit area, the amount of soil conservation per unit area and the amount of windbreak and sand fixation per unit area has been increased by 12 500 m³·km^-2, 134.19 gC·m^-2a^-1, 6.76 t·hm^-2a^-1 and 9.81 t·hm^-2a^-1, respectively, with a respective growth rate of 45.89%, 34.96%, 74.29% and 24.96%.The degree of soil water erosion, and wind and sand erosion damage is reduced, with the water erosion modulus increased 23.88% (the average annual precipitation increased in recent years compared to the previous period, resulting in an increase in the amount of erosion and the amount of retention), and the wind erosion modulus decreased by 25.58 t · hm^-2a^-1, leading to the reduction of damages by wind erosion by 46.49%. Finally, there are 15.83% area ecosystem service functions continued to improve. 4) The restoration of the ecosystem is very significant, with 21.95% and 20.29% area has continued to improve and remain stable. Conclusion: Through the implementation of successive periods of the Three-North Shelter Forest Program, significant improvements have been achieved, the ecosystem have recovered well and entered a sustained, stable and healthy development trend in farmlands in the Northeast and North China Plains, the Inner Mongolia Plateau and the Loess Plateau with improved forest coverage, increased average vegetation coverage, increased average net primary vegetation productivity, and ecosystem service functions such as water holding capacity per unit area, carbon sequestration by vegetation, soil conservation capacity and wind-breaking and sand-fixation capacity have been significantly improved. However, the northwest desert area is still relatively fragile, and the ecosystem status has not been effectively improved. In Tianshan Mountains, Zhungeer Basin, Qaidam Basin, the agricultural and pastoral areas in southern Xinjiang basin, Bashang Plateau, the desert and semi-desert grassland areas in western Inner Mongolia where the ecosystem is fragile, the increase of forest area is slowing down, the area of grassland is decreasing and the desert area is still increasing. Therefore, the prevention and control of grassland desertification is still the focus of future program implementation.

Objective: Sensitivity analysis of the ecophysiological parameters in ecological process models was conducted to improve the accuracy of model simulations by optimizing these parameters. Method: The carbon fluxes observed during 2016-2018 in Hippophae rhamnoides plantation in the Loess Hilly region was used to optimize the parameters of Biome-BGC model and evaluate its applicability and accuracy. The extended fourier amplitude sensitivity test method was used to analyze the first-order sensitivity and total sensitivity of the 27 selected ecophysiological parameters in this model. The effects of these parameters alone or their interactions on the accuracy of simulated carbon fluxes were investigated. The total sensitivity parameters were selected based on high level (> 0.2) and medium level (0.1-0.2) criteria. Path analysis was conducted to calculate the positive and negative effects of these parameters on the Biome-BGC model. Result: The result showed that after optimizing the parameters, the Biome-BGC model was effective at simulating the seasonal dynamics of the carbon fluxes in the H. rhamnoides plantation. Sensitivity analysis indicated that the ratio of new fine root carbon relative to leaf carbon and the ratio of shady leaf area relative to sun leaf area (SLA_{shade: sun}) exhibited high total sensitivity to the gross ecosystem productivity (GEP), ecosystem respiration (RE), and net ecosystem productivity (NEP) in the plantation. The ratio of new fine root carbon relative to leaf carbon also exhibited high first-order sensitivity to the carbon fluxes. Path analysis suggested that the ratio of fine root carbon relative to leaf carbon had significant and negative effects on GEP, RE, and NEP in the H. hamnoides plantation (P < 0.001) through its effects on the relative carbon and nitrogen contents of the leaves and fine roots. In addition, the ratio of shady leaf area relative to sun leaf area had significant and positive effects on the carbon fluxes (P < 0.001) through its effects on the intensity and area of light on the leaves. Both the plant photosynthesis and respiration processes were directly influenced by the relative carbon and nitrogen contents of the leaves and fine roots, and light intensity and area. Conclusion: The ratio of new fine root carbon relative to leaf carbon and the ratio of shady leaf area relative to sun leaf area were highly sensitive parameters to simulate GEP, RE, and NEP through Biome-BGC model in a H. rhamnoides plantation in the loess hilly region. Optimizing these sensitive parameters can improve the accuracy of carbon fluxes simulation of Biome-BGC model.

Objective: The aim of this study was to explore the effect of herbage inter-planting on the stability of soil microbial community of Camellia oleifera plantations in southern red soil region. These findings would provide the theoretical basis for sustainable management of C. oleifera plantation. Method: The structure of soil microorganisms of C. oleifera plantations respectively with tending and weeding (TF), preserving natural weeds (TZ), inter-planting of Coreopsis basalis (TJ) and inter-planting of Paspalum notatum (TB) was studied by high-throughput sequencing method, the abundance pattern of soil microbial community was analyzed by using brokenstick, Zipf, Mandelbrot and other models, and the community aggregation process was inferred by zero modeling method. The stability of microbial community was evaluated by the average variation degree of community, and the interaction between microbial communities was predicted by network analysis. Result: There were differences in soil nutrients and enzyme activities under different herbage inter-planting treatments. The contents of total carbon, total nitrogen, available nitrogen, and available phosphorus were the highest in TF treatment, and there was no significant difference in soil nutrients and enzyme activities between TF and TB. The composition of soil microbial community under TF, TJ, and TB treatments were similar. Among them, Proteobacteria and Acidobacteria were the dominant phyla, accounting for more than 50% of the total soil microbial. Koribacteraceae was the dominant family, accounting for more than 12% of the total. The dominant phyla of TZ treatment were Proteobacteria and Bacteroidetes, accounting for 55.1%, and the dominant family was comamonadaceae, accounting for 12.8%. Zipf Mandelbrot model had the best fitting effect on soil microbial abundance pattern. The species structure of soil microbial community under TZ treatment was the most balanced, with a small decrease in abundance and a weak dominance of dominant species in soil microbial community. The balance of community structure in TF and TB treatments was poor. There were significant differences in the stability of soil microbial communities among different herbage inter-planting treatments. The average variation degree value (AVD) of TF treatment was 0.411, indicating that the stability of soil microbial communities was the strongest. The AVD value of TZ treatment was 0.634, indicating that the stability of soil microbial communities was the worst. The absolute value of beta nearest taxon index (βNTI) between each treatment was bigger than 2, indicating that the change of microbial community was a deterministic assembly process, and the change of microbial community structure was mainly affected by decisive factors. The β diversity of microbial community was significantly positively correlated with the environmental distance. When the genetic difference was eliminated, the environment still had a significant indigenous effect on community construction, while the genetic distance and the genetic distance to eliminate the environmental distance had no significant indigenous effect on community construction, that is, habitat filtering had an effect on the construction of soil microbial community in C. oleifera plantation. Delftia, Methylotenera, Rhodoferax, Sphingobium and Veillonella were the core genera for maintaining the network stability under herbage inter-planting treatments. The effects of soil environment on dominant flora were studied, and the results showed that Proteobacteria and Chloroflexi were not sensitive to environmental changes, and the effect of total potassium content on Acidobacteria was extremely significant, while that on Actinobacteria and Firmicutes was significant. Total phosphorus content had a significant effect on Firmicutes. Conclusion: The herbage inter-planting had an effect on the stability of soil microbial community in C. oleifera plantations in red soil area in southern China. Soil potassium content significantly affected the structure and stability of microbial community, and P. notatum is more suitable for herbage inter-planting in C. oleifera plantations. It is not suitable to inter-plant natural weeds in C.oleifera plantations, which can reduce soil nutrient content and soil microbial community stability. Although tillage and tending weeding improved the stability of soil microbial community, its composition pattern was not balanced. The long-term clearing and weeding would cause the loss of rare populations and may weaken the ecological service function.

Objective: In order to provide a theoretical foundation and basic data for forestry workers to protect and sustainably utilize forest resources, we explore the effects of topography and soil factors on the decay of Korean pine (Pinus koraiensis) living trees, and illustrate the distribution patterns of decay trees. Method: In a monitoring block of 30 hm² typical mixed broadleaved-Korean pine forest at Fenglin National Natural Reserve, Heilongjiang, we selected 329 living trees of Korean pine from 62 plots, consisting of 73 young trees (10 cm≤ DBH < 30 cm), 104 adult trees (30 cm≤ DBH < 50 cm) and 152 old trees (DBH ≥50 cm). We used Resistograph to detect the decay, and measured topographical factors and soil physical-chemical proprieties of sample trees. At individual tree level, we used Mann-Whitney U test to compare comparisons of soil physical-chemical proprieties between healthy and decay trees; at plot level, we used Spearman correlation analysis to explore the relevance between soil physical-chemical proprieties and decay rate, we used Kruskal-Wallis test and Post hoc test to explore influence of topographic factors on decay rate. And we used canonical correspondence analysis to explore the distribution of decay of living Korean pine trees. Result: 1) The average decay rate of Korean pine was 35.87%, and the decay rates of young trees, adult trees and old trees were 42.1%, 39.2%, and 29.2%, respectively. 2) The soil total carbon of the decay trees is significantly lower than healthy trees. And the soil ammonium of the decay trees is significantly higher than the healthy trees(P < 0.05); 3) There is an extremely significant negative correlation between soil volumetric moisture content, total nitrogen, total carbon and total phosphorus content and the decay rate of living Korean pine trees, and a significant negative correlation between total potassium, available phosphorus content and the decay rate. 4) The decay rate of living Korean pine trees on different topographic positions and aspects is significantly different (P < 0.05). The decay rate is significantly higher on upper slope than on lower slope (P < 0.05), and significantly lower on semi-shady slope than on semi-sunny slope. 5) Topographic position and soil phosphorus content are the most important factors associated with decay of living Korean pine trees in different growth phases. Young healthy Korean pine distribute in edaphic condition with higher nitrate nitrogen content, but adult and old decay trees always distribute in edaphic condition with higher ammonium nitrogen content. Conclusion: In Xiaoxing'an Mountains, the decay rate of living Korean pine trees is high, and most severe on upper slope and shady slope, semi-sunny slope. The decayed Korean pine in different growth stages were mostly distributed at higher topographic position with lower contents of soil nutrients and moisture. But nitrogen forms have different effects on Korean pine at different growth stages. The results provide a scientific basis and basic data for the protection and sustainable utilization of Korean pine.

Objective: Water-holding capacity of litter layer is an important part for hydrological effect evaluation of forest land. Quantitative evaluation of hydrological characteristics of litter layer of typical sparse plantations in Loess ridge hilly region can provide a theoretical basis for ecological reconstruction and structure optimization of forest and grass vegetation in the study area. Method: Six kinds of artificial forests were selected, including pure forest of Armeniaca sibirica, Amygdalus davidiana, and Caragana intermedia, A.sibirica and Hippophae rhamnoides mixed forest, A. sibirica and C. intermedia mixed forest, and A. sibirica, A. davidiana and Medicago sativa mixed forest. A standard plot of 20 m×20 m was set up in each of artificial forests, and five subplots of 1 m×1 m were set up at the four corners and the center of the plot to collect litter samples. The field investigation and indoor soaking method were used to compare and analyze the stock volume, water-holding capacity and dynamic change pattern of all litter on the surface and mixed with soil in each of artificial forests. Result: The result showed that: 1) The total litter volume of the six artificial forests ranged from 1.05 t·hm^-2 to 4.01 t·hm^-2, with the highest in pure forest of A. sibirica and the lowest in pure forest of A. davidiana. The proportion of litter volume in soil to total litter volume varied from 11.43% to 25.00%. Except for pure forest of A. sibirica, the total volume of the mixed forest was all greater than that of the pure forest. 2) In terms of the water-holding capacity of the surface litter and the litter in the soil of the six kinds of artificial forests, the maximum water-holding capacity of A. sibirica pure forest was the highest (15.75 t·hm^-2), and the maximum water-holding rate of A. sibirica and C.intermedia mixed forest was the highest (264.65%). 3) During the water absorption prosess, the dynamic changes in litter water-holding capacity and water absorption rate in the six kinds of artificial forests changed rapidly at the early immersion stage, reached saturation and tended to be stable at 24 hours. The variation of water-holding capacity and water absorption rate were in accordance with the natural logarithm equation and power fuction equation, respectively, and reached a very significant level (P < 0.01). 4) In terms of the effective water retention capacity and effective water retention rate of the six stands, the surface litter of A. sibirica pure forest had the strongest effective water retention capacity, and the soil litter of A. sibirica and C.intermedia mixed forest had the strongest effective water retention capacity. The total effective water retention capacity of litter in A. sibirica pure forest was the highest (11.08 t·hm^-2), followed by A. sibirica and C.intermedia mixed forest (7.67 t·hm^-2). Conclusion: In the Loess ridge hilly region of Ningxia, the comprehensive performance of litter water holding capacity of A. sibirica pure forest, and A. sibirica and C. intermedia mixed forest is better than that of the other stands. The result can provide a theoretical basis for the scientific evaluation of soil and water conservation benefits of litter and the optimization of forest and grass vegetation structure in local ecological restoration.

Objective: The difficulties and the large registration error of the 3D point cloud registration in forested area present a challenge. Taking different types of forest point cloud data from different perspectives and platforms (ground-based and airborne) as input, and aiming at high-precision fusion of forest point cloud data, an automatic marker-less registration algorithm of point cloud for multi-types of data under forest semantic environment was proposed, focusing on point-pair matching with the single wood object as semantic feature. Method: Firstly, according to the data characteristics of different types of point clouds, the tree positions are extracted respectively. For the side view (ground-based) point cloud, based on the deviation between the main direction dispersion and the vertical angle of the main direction of the point cloud, non-trunk point cloud is eliminated, and the connected component segmentation method of voxel-based partition is used to identify the trunk of individual tree, and the place with the maximum point density of voxel vertical distribution of the single tree trunk point cloud is determined as the planar position of the tree. For the top view (airborne) point cloud, the canopy height model (CHM) is extracted, and then the marker controlled watershed method is used to segment CHM to extract individual trees and the canopy vertex is identified as the planar position of individual trees. Then, taking the extracted positions of individual trees as feature points, the registration matrix is obtained based on Laplace spectral map matching theory, and the 4-DoF (degree of freedom) point cloud coarse registration is completed. Finally, the side view point clouds are precisely registered by using the main trunk matching and the side view and top view point clouds are precisely aligned by using the global iterative closest points (ICP) method. Result: The experimental result show that the registration accuracy between point cloud obtained from ground perspective views is better than that of ground side view and airborne top views point clouds. The average coarse registration error between point clouds from both ground perspective was 0.24 m, and the average error of precision registration was 0.08 m. The average error of coarse registration between side view and top views point cloud was 1.07 m, and the average error of global ICP is 0.44 m. After airborne point cloud and side-looking point cloud are matched through the main trunk, the average error is further improved to 0.36 m. Conclusion: This study followed from coarse to fine registration routine, integrating many kinds of individual tree detection algorithms designed for ground-based and airborne point cloud. We design a framework for multiple source types of point cloud registration, and the experimental result prove the feasibility of the scheme, which is suitable for various forested environment. The marker-less automatic registration algorithm applicable to multi-type point cloud data provides precision and more complete data that is critical to forest resource investigation and evaluation.

Objective: The aim of this study was to screen out superior clones of Eucalyptus from five locations in Guangxi, Guangdong and Hainan by analyzing the genetic diversity of growth traits and evaluating the interaction between genotype and environment. Method: The data of tree height, DBH and volume, preserving rate and forest stock of 3.5-year-old Eucalyptus clones was collected, The single factor analysis of variance and multiple comparison were conducted for each trait with the collected data from the five locations. Then, a linear mixed model was established for single-location and multi-locations analysis of variance. The variance components of each trait and the BLUP values of each clone were obtained by taking clones and clones×repeats (locations) as random effects, so as to calculate the genetic parameters of each trait. Finally, AMMI model and BLUP-GGE model were integrated to select elite clones and suitable environment. Result: 1) This study showed that there were significant differences in each growth trait among different parents, clones and locations (P < 0.01). Among the different parents, the traits of E. pellita×E. wetarensis were relatively better, and its volume and annual average forest stock were 0.069 0 m³ per plant and 26.6 m³·hm^-2a^-1, respectively. Among the different clones, EC245 was the best, and the volume and annual average forest stock were 0.090 9 m³ per plant and 118.46 m³·hm^-2a^-1, respectively, but the preserving rate (77.8%) was relatively lower. Among the different locations, the clones in Leizhou area had the best growth performance with the average volume and preserving rate of 0.083 6 m³ per plant and 85.5%, respectively, while those in Haikou area had the worst growth performance with the average volume and preserving rate of 0.023 8 m³ per plant and 55.5%, respectively. 2) The analysis of variance with data from multiple locations and genetic parameters showed that the interaction between each trait and the environment reached a significant level (P < 0.01), and the repeatability of each trait ranged from 0.717 4 to 0.869 5. Among the effect sizes of different traits, the environmental effect size (43.2%) and interaction effect size (17.0%) of tree height were much greater than those of other traits, and the environmental effect size (26.5%) and interaction effect size (8.8%) of DBH were the lowest, indicating that tree height was susceptible to environmental effects, while DBH was relatively stable. In different locations, tree height repeatability ranged from 0.653 9 to 0.901 8, DBH repeatability ranged from 0.679 1 to 0.930 1, volume repeatability ranged from 0.680 8 to 0.936 0, and annual average forest stock repeatability ranged from 0.481 1 to 0.925 0, indicating that volume was suitable as the target trait in selection. 3) The interaction analysis between genotype and environment showed that the result of AMMI and BLUP-GGE biplots based on volume traits were slightly different. Both models agreed that Leizhou was the ideal environment and EC245 was the high volume clone, followed by EC234 and CM1509. AMMI model showed that EC244, EC228 and EC238 had the higher stability, and EC245 was the lowest, and EC245 was screened as the clones with high volume and low stability. However, the BLUP-GGE model showed that EC244, EC232 and EC224 had higher stability, and EC238 was the lowest, and EC245 was screened as a high volume and medium stability clone. Conclusion: According to the comprehensive evaluation, EC245 was a clone with high volume and medium stability, and it has good growth performance in all locations.

Objective: Xylem water transport is the basis of photosynthetic process and tree growth. Exploring the effect of hydraulic efficiency on gas exchange and growth performance will help to deepen the understanding of the internal relationship between hydraulic efficiency and gas exchange and growth, and provide a theoretical basis for the breeding of new drought-resistant forest varieties. Method: The 2-year-old seedlings of six poplar hybrid clonesPopulus alba 'I-101'×(P. alba×P. Glandulosa '84K') were used to measure gas exchange parameters (net photosynthetic rate A_net, stomatal conductance g_s, reference stomatal conductance g_s-ref, water use efficiency WUE), leaf water status (midday leaf water potential Ψ_md), hydraulic efficiency (whole crown hydraulic efficiency K_CL, main branch hydraulic efficiency K_MSL and root hydraulic efficiency K_RL), stomatal characteristics (stomatal density SD, stomatal length SL, stomatal area index SPI) and growth parameters (ground diameter absolute growth rate AGRD and relative growth rate RGRD). Results: 1) Six poplar clones showed significant difference in hydraulic efficiency, and the changes of the hydraulic efficiency of roots, main branches and crowns were consistent, that is, the clones with high or low hydraulic efficiency had higher or lower K_RL, K_MSL and K_CL. 2) The change in Ψ_md was closely related to that of g_s. After Ψ_md decreased to -1.1 Mpa, g_s decreased sharply, resulting in a corresponding decrease in A_net. AGRD was significantly positively correlated with A_net. 3) SL was significantly positively correlated with K_CL, K_MSL, g_s-ref, AGRD and RGRD, and SD was significantly negatively correlated with K_MSL, A_net and AGRD. 4) K_CL and K_MSL were significantly correlated with g_s-re, and K_CL had a stronger correlation with g_s-ref, indicating that higher hydraulic efficiency was beneficial to stomatal opening. 5) K_CL was significantly positively correlated with K_MSL, and K_MSL was always greater than K_CL (about 37.3% higher on average). K_CL and K_MSL were significantly positively correlated with AGRD and RGRD, among which K_CL had a stronger correlation with RGRD. Conclusion: In this study, ,it is found that the hydraulic efficiency of each part of the tree is coordinated at the intraspecific clonal level, and the hydraulic efficiency of the root system, main branch, crown can reflect the ability of the tree to transport water. The water transport efficiency is closely related to the gas exchange process of leaves, and the structural characteristics of leaf stomata are coordinated with the water transport capacity. Efficient water transport improves the leaf water status, promotes stomatal opening, and improves carbon assimilation capacity, and thereby promotes growth.

Objective: This study aims to explore the influence of different preparation and analysis methods on the determination of volatile oil composition and the contents, and reveal the dynamic changes of the contents in the Torreya grandis 'Merrillii' aril during the seed growth and development, as so to provide the rationale for the utilization of the aril. Method: Steam distillation (SD) and headspace solid phase microextraction (HS-SPME) techniques were used and optimized for the sample preparation The gas chromatography-mass spectrometry (GC-MS) was used to determine the volatile components and the contents in the aril during the growth and development of T. grandis seeds. Result: 1) Based on GC-MS analysis, SD was more suitable for the sample preparation of volatile oil from T. grandis seeds in terms of the component and content. 2) The SD-GC-MS analysis showed that there were 47 volatile oil components in the aril, including 21 terpenes (limonene, α-pinene, δ-juniene, etc.), 15 terpene alcohols (linalool, borneol, elemol, etc.), three terpene esters (bornyl acetate, pine oil acetate, and geranyl acetate), and eight other compounds (piperone, antioxidant 264, palmitic acid, etc.). 3) The volatile components in the aril during seed growth and development showed certain regular changes. Among them the content of camphene, β-pinene, and terpinolene increased from May to September; the content of such ingredients as α-pinene, cypressene, and myrcene gradually rose to the peak value from May to August and then declined. The monoterpenoids and sesquiterpenoids showed an obvious negative correlation during May to June and from August to September, while the monoterpenoids and sesquiterpenoids showed an increasing trend from June to July because the aril was growing. PCA suggested that the volatile oil components of aril in May were similar to those in June Conclusion: The extraction condition for T. grandis 'Merrillii' aril is the ratio of material to liquid set as 1:10, and soak time as 1 hour, extraction time as 4 hours. Through the SD-GC-MS detection, 47 compounds were identified, with a total of 13 483.14 μg·g^-1. The main ingredients include limonene and α-pinene compounds. The volatile components in the aril of T. grandis 'Merrillii' are significantly different at different seed growth and development stages. The number of compounds increased from 35 in May to 47 in September. Sesquiterpenoids and oxygenic derivatives increased, and the total content of essential oil increased first and then decreased from May to September. The composition and content of essential oil in the aril were similar from May to June and July to August, but they were significantly different from those in September.

Objective: The activity rhythm of wildlife is to adapt to the changing environmental conditions, reflecting its ecological selection in the time dimension and the timely utilization of resources. Species with similar affinities and sympatric distribution will adjust their activity time, as a survival strategy, to reduce the interspecific competition. Research on their activity rhythms can help to reveal the mechanism of species coexistence, and is of great significance to strengthen the conservation and management of wild animals. This study aims to deeply understand the daily activity rhythms of multiple pheasants in Fanjingshan National Nature Reserve, and explore their time allocation mode and coexistence mechanism of the sympatric pheasants. Method: We monitored five sympatric pheasant species with 61 infrared camera traps in Fanjingshan from April 2017 to December 2020, and analyzed the daily activity rhythms of the five species of pheasants. Result: 1) The five monitored pheasant species (Syrmaticus ellioti, Tragopan temminckii, Chrysolophus pictus, Bambusicola thoracica, Pucrasia macrolopha) were all diurnal with two activity peaks at morning and dusk, respectively. 2) Only the daily activity rhythm of Tragopan temminckii was significantly different from that of other pheasants. 3) The daily activity rhythm of both Chrysolophus pictus and Pucrasia macrolopha was affected by altitude variation. 4) There was significant seasonal difference in daily activity rhythm of P. Macrolopha in the seasonal change from breeding period to non-breeding period. 5) For those pheasants with distinct sexual dimorphism, the overlapping degree of daily activities of male and female individuals in the reproductive period was higher than that in non reproductive period. Their daily activity rhythms and time allocation were more similar in breeding period. Conclusion: Through the study on the daily activity rhythm of five species of syndromic pheasants in Fanjing Mountain National Nature Reserve, it is found that the characteristics and difference of the daily activity rhythms of the five sympatric pheasant species are the result of interaction of the environmental factors and the interspecific competition, and are also affected by the breeding time and reproductive strategy.

Objective: To compare the effects of different milling parameters on the milling quality and milling force of particleboard by milling melamine impregnated paper veneer particleboard with a carbide single tooth shank milling cutter, and to provide a theoretical basis for the utilization of particleboard quality milling processing. Method: The effect of tool front angle, milling line speed and milling depth on the milling quality and milling force of particle board was investigated by comparing the milling result of different milling parameters with a single-shank milling cutter using tool front angle, milling line speed and milling depth as independent variables; regression analysis was used to determine the significance of each milling parameter, and a mathematical model of milling force and surface roughness during the milling process was established. The optimum range of milling parameters was established and verified by test. 1) The surface roughness of particle board milling decreases with increasing tool speed; 2) The milling force decreases with increasing tool front angle, decreases with increasing milling line speed and increases with increasing milling depth; 3) The effects of tool front angle, milling line speed and milling depth on tangential milling force and milling quality are statistically significant, and the interaction of tool front angle, milling line speed and milling depth has a significant effect on tangential milling force and milling surface roughness. 4) When the tool front angle, milling line speed and milling depth are 5°, 9.42 m·s^-1 and 1.5 mm respectively, the energy consumption in the machining process can be effectively reduced and the surface quality improved on the basis of ensuring the milling efficiency. Conclusion: The milling parameters such as tool front angle, milling line speed and milling depth have certain influence on the milling quality and milling force of particle board, and these parameters can be used in the industrial production of veneered particle board materials to obtain higher production efficiency.

With an ever-increasing consumption of non-renewable resources, the construction of green cycle and low-carbon economy has become the top priority of the sustainable development of all walks of life throughout the world. The bamboo industry is one of the major industries that are very unique to China. With the implementation of three low-carbon emission reduction policies of "carbon peak, carbon neutralization and carbon trading" and the "plastic ban" policy, bamboo fiber, as a type of natural green fiber, is seeing resurgence in interests leading it to becoming a current research hotspot. Bamboo fiber has the characteristics of high strength, low density, good elasticity, wear resistance, breathability, renewable, and degradable. Compared with glass fiber and carbon fiber, it is easy to degrade and has less degradable carbon emissions. It can be used as a reinforcing phase of composite materials to partly replace plastics and has huge economic potential. However, the current preparation method used to produce bamboo material and bamboo fiber do result in a lot of pollution, so that bamboo fiber loses its environmental advantages; there are also still many problems in the preparation of bamboo fiber, such as lignin residues, short fiber length, hairiness, uneven thickness and so on. These processing issues restrict the high value-added application of bamboo fiber in textile and composite materials. Based on a large number of scientific studies, this paper focus on the development of environmentally friendly bamboo fiber preparation method. The basic properties of these method were compared and the advantages, disadvantages and key technical difficulties of various method were analyzed. Thus, the preparation of bamboo fiber was prospected. The innovation of new environmentally friendly preparation technology and the upgrade of high-efficiency automation equipment are important development directions for realizing the integrated development of raw materials, equipment and processes, improving the performance of bamboo fibers, reducing product costs, and expanding the development of high value-added products of bamboo fibers.

Objective: This study aims to explore the potential of nutrient content in sap flow for nutritional diagnosis of Betula platyphylla plantation, so as to explore a more economical and convenient method for tree nutritional diagnosis. Methods: The 12-year-old B. platyphylla plantation was targeted, a relatively flat site was selected, and a sample plot (30 m×120 m) was set up. Forty sample trees with normal growth and free of diseases and insect pests were randomly selected. Three kinds of materials including tree leaves, topsoil occupied by individual trees and sap flow in early spring were collected before leaves were completely spread. Then the correlation coefficient between the nutrient content of the three kinds of samples and tree growth was analyzed to determine the feasibility of sap flow used for nutrition diagnosis. Results: The element contents in sap flow from high to low were total carbon (TC) (4.03±0.16 g·L^-1), total nitrogen (TN) (60.66 mg·L^-1±4.02 mg·L^-1), total potassium (TK) (34.41 mg·L^-1±2.14 mg·L^-1) and total phosphorus (TP) (5.84 mg·L^-1±0.52 mg·L^-1). There was a significant positive correlation between tree height and TC content in soil, leaves and sap flow (P < 0.05). Stepwise regression analysis showed that TC content in sap flow had the greatest contribution to tree height (R²=0.145). Among the three diagnostic materials, only the contents of TN and TP in sap flow were positively correlated with DBH (P < 0.05). Stepwise regression analysis showed that only the TP content of sap flow had a significant contribution to DBH (R²=0.187). Conclusion: The results of correlation analysis and stepwise regression analysis indicate that sap flow can be used for nutrition diagnosis of B. platyphylla, and the analysis shows that the trees with poor growth are limited by C and P. The study provides a feasible method for tree nutrition diagnosis before complete leaf development, which is more reliable than soil and leaf nutrition diagnosis, and the diagnosis time can be advanced.

Objective: The objective was to investigate the effects of biodiversity, DBH structure and topography on the temporal stability of biomass and clarify the main driving factors for the temporal stability of biomass at different spatial scales. Method: Based on two large fixed sample plots in Jiaohe, Jilin, the influences of different spatial scales was quantitatively analyzed by randomly sampling 20 m×20 m, 40 m×40 m, and 60 m×60 m plots. Three types of nested models were constructed using generalized additive models: stability~biodiversity + DBH structure (model 1), stability-biodiversity + topographic factors (model 2), stability-biodiversity + DBH structure + topographic factors (model 3), and compared with stability~biodiversity (model 0). The relative contributions of different explanatory factors are evaluated by the variation of Akaike information criterion (△AIC), the variation of Bayesian information criterion (△BIC), the variation of adjusted determination coefficient (△R_adj²) and the variation of deviance explained (△DE). Result: The analysis of the generalized additive model shows that at the three scales of 20 m×20 m, 40 m×40 m, and 60 m×60 m, the relative contribution rates of biodiversity are 15.18%, 12.66%, and 47.64%, respectively; the relative contribution rates of DBH structure are 11.30%, 72.38%, and 23.48%, respectively; the relative contribution rates of topography are 73.52%, 14.96%, and 28.88%, respectively. Biodiversity and DBH structure are only significantly correlated with the temporal stability of biomass on the 60 m×60 m scale (P < 0.05). Among them, species richness and Faith phylogenetic diversity index are significantly negatively correlated with the temporal stability of biomass. The maximum diameter at breast height and basal area per hectare are significantly positively correlated with the temporal stability of biomass, and the coefficient of variation of diameter at breast height is significantly negatively correlated with the temporal stability of biomass. Among the topographic factors, the aspect is significantly related to the temporal stability of biomass at the 20 m×20 m scale, and the elevation and slope are significantly related to the temporal stability of biomass at the 60 m×60 m scale. The explanation rate of the deviation of the above explanatory variables on the temporal stability of biomass increases with the spatial scale. The driving factor for the temporal stability of volume is basically the same as the temporal stability of biomass. Conclusion: The relative influences of topographic factors, DBH structure and biodiversity have significant scale effects on the temporal stability of biomass and shift along different spatial scales. Topographical factors play a major role in the temporal stability of biomass at the scale of 20 m×20 m. DBH structure plays a major role in the temporal stability of biomass at the scale of 40 m×40 m and biodiversity plays a major role in the temporal stability of biomass at the scale of 60 m×60 m. The results provide a theoretical basis for improving the stability of the northeast coniferous and broad-leaved mixed forest ecosystem.