Vegetation-environment relationships in the forests of Chitral district Hindukush range of Pakistan

We investigated the composition of plant communities to quantify their relationships with environmental parameters in the Chitral Hindukush range of Pakistan. We sampled tree vegetation using the Point Centered Quarter （PCQ） method while understory vegetation was sampled in 1.5-m circular quadrats. Cedrus deodara is the national symbol of Pakistan and was dominant in the sampled communities. Because environmental variables determine vegetation types, we analyzed and evaluated edaphic and topographic factors. DCA-Ordination showed the major gradient as an amalgam of elevation （p〈0.05） and slope （p〈0.01） as the topographic factors correlated with species distribution. Soil variables were the factors of environmental significance along DCA axes. However, among these factors, Mg2＋ , K ＋ and N2＋ contributed not more than 0.054% 0.20% and 0.073%, respectively, to variation along the first ordination axis. We conclude that the principal reason for weak or no correlation with many edaphic variables was the anthropogenic disturbance of vegetation. The understory vegetation was composed of perennial herbs in most communities and was most dense under the tree canopy. The understory vegetation strongly regulates tree seedling growth and regeneration patterns. We recommend further study of the understory vegetation using permanent plots to aid development of forest regeneration strategies.

Vegetation-environment relationship in Pinus wallichiana forests of the Swat Hindukush range of Pakistan

Understanding the influence of environmental variables on the spatial distribution of ecological communities is essential to predict the response of vegetation to various environmental drivers.Ecological theory suggests that multiple environmental factors shape local species assemblages and should influence the various components of community structure and composition in different ways.This study aimed to classify Pinus wallichiana dominated forests in the Swat Hindukush range mountains to understand the relative influence of multiple environmental filters on its composition and structure.These forests represent the most typical of the species distribution in northern Pakistan and were not subjected to any phytosociological study.For this purpose,thirty forest stands,spanning a wide range of physical habitats were sampled using 10910 m plots and the importance value index was calculated.The floristic and environmental data were subjected to Ward’s agglomerative cluster analysis for objective classification and ordinated with NMS ordination for pattern description and testing the vegetation–environmental relationships.Three floristically and ecologically distinct communities were recognized along the topographic gradient(elevation,r=0.377;slope,r=0.5548)coupled with soil physical(clay,r=0.2782;silt,r=0.3225)and chemical properties(pH,r=0.4975;lime,r=3982).An elevation gradient of 100 m separated the low(Pinus wallichiana–Quercus dilatata community)and middle elevations forest stands(P.wallichiana pure population)from the highland population type(Pinus wallichiana–Cedrus deodara community).The floristics and structure of these forest types respond directly or indirectly to topographic and soil variables which were evidenced from the floristic composition,species richness,and community physiognomy.These characteristics of the communities changed from heterogenous,dense stands to sparsely dispersed conifers,broadleaved-evergreen,and deciduous vegetation types along the environmental gradients.We concluded that several factors explained the spatial pattern.Thus,we predict that elevation coupled with soil physical and chemical properties could be considered if the ultimate goal is the restoration and conservation of these forests.We also recommend broad-scale phytosociological study on P.wallichiana forests including multiple sampling from diverse locations to define the floristic diversity and to better understand its ecological requirements.

Long-range Dependence Characteristics of Forest Biological Disasters in China against the Background of Climate Change

Forest biological disasters(FBD) seriously impact energy flow and material cycling in forest ecosystems,while the underlying causes of FBD are complex. These disasters involve large areas and cause tremendous losses. As a result,the occurrence of FBDs in China( CFBD) threatens the country's ability to realize its strategic target of increasing both forested area(40 million ha) and forest volume(1.3 billion m^3) from 2005 to 2020. Collectively,China has officially named this effort to increase forest area and volume the "Two Increases" as national goals related to forestry. Based on Hurst index analysis from fractal theory,we analyzed the time series of the occurrence area and related data of FBDs from 1950 to 2007 to quantitatively determine the patterns of the macro occurrence of FBDs in China. Results indicates that,the time series of( CFBD) areas is fractal( self-affinity fractal dimension D = 1. 3548),the fluctuation of( CFBD) areas is positively correlated( auto-correlation coefficient C = 0. 2170),and the occurrence of the time series of( CFBD) is long-range dependent( Hurst index H =0. 6416),showing considerably strong trend of increases in FBDC area. Three different methods were further carried out on the original time series,and its two surrogate series generated by function surrogate in library t series,and function Surrogate Data in library in Wavelet software R,so as to analyze the reliability of Hurst indexes. The results showed that the Hurst indices calculated using different estimation methods were greater than 0. 5,ranging from 0. 64 to 0. 97,which indicated that the change of occurrence area data of FBDs was positively autocorrelated.The long-range dependence in forest biological disasters in China is obvious,and the spatial extent of FBDs tended to increase during this study period indicating this trend should be expected to persistent and worsen in the future.

Mid and late Holocene forest fires and deforestation in the subalpine belt of the Iberian range,northern Spain

The conversion of subalpine forests into grasslands for pastoral use is a well-knownphenomenon, although for most mountain areas the timing of deforestation has not been determined. The presence of charcoal fragments in soil profiles affected by shallow landsliding enabled us to date the occurrence of fires and the periods of conversion ofsubalpine forest into grasslands in the Urbión Mountains, Iberian Range, Spain. We found that the treeline in the highest parts of the northwestern massifs of the Iberian Range(the Urbión, Demanda, Neila, and Cebollera massifs) is currently between 1500 and 1600 m a.s.l., probably because of pastoral use of the subalpine belt, whereas in the past it would have reached almost the highest divides(at approximately 2100–2200 m a.s.l.). The radiocarbon dates obtained indicate that the transformation of the subalpine belt occurred during the Late Neolithic, Chalcolithic, Bronze Age, Iron Age, and Middle Ages. Forest clearing was probably moderate during fires prior to the Middle Ages, as the small size of the sheep herds and the local character of the markets only required small clearings, and therefore more limited fires. Thus, it is likely that the forest recovered burnt areas in a few decades; this suggests the management of the forest and grasslands following a slash-andburn system. During the Middle and Modern Ages deforestation and grassland expansion affected most of the subalpine belt and coincided with the increasing prevalence of transhumance, as occurred in other mountains in the Iberian Peninsula(particularly the Pyrenees). Although the occurrence of shallow landslides following deforestation between the Neolithic and the Roman Period cannot be ruled out, the most extensive shallow landsliding processes would have occurred from the Middle Ages until recent times.

Seamless integration of above-and undercanopy unmanned aerial vehicle laser scanning for forest investigation

Background:Current automated forest investigation is facing a dilemma over how to achieve high tree-and plotlevel completeness while maintaining a high cost and labor efficiency.This study tackles the challenge by exploring a new concept that enables an efficient fusion of aerial and terrestrial perspectives for digitizing and characterizing individual trees in forests through an Unmanned Aerial Vehicle(UAV)that flies above and under canopies in a single operation.The advantage of such concept is that the aerial perspective from the above-canopy UAV and the terrestrial perspective from the under-canopy UAV can be seamlessly integrated in one flight,thus grants the access to simultaneous high completeness,high efficiency,and low cost.Results:In the experiment,an approximately 0.5 ha forest was covered in ca.10 min from takeoff to landing.The GNSS-IMU based positioning supports a geometric accuracy of the produced point cloud that is equivalent to that of the mobile mapping systems,which leads to a 2–4 cm RMSE of the diameter at the breast height estimates,and a 4–7 cm RMSE of the stem curve estimates.Conclusions:Results of the experiment suggested that the integrated flight is capable of combining the high completeness of upper canopies from the above-canopy perspective and the high completeness of stems from the terrestrial perspective.Thus,it is a solution to combine the advantages of the terrestrial static,the mobile,and the above-canopy UAV observations,which is a promising step forward to achieve a fully autonomous in situ forest inventory.Future studies should be aimed to further improve the platform positioning,and to automatize the UAV operation.

Rain Forests in Subtropical Mountains of Dominican Republic

This article presents a study of the cloud forest dominated by the Prestoea montana (R. Graham) Nichols. This is a hyperhumid forest located in ravines and shaded areas with cloud condensation, and at heights ranging from 350 - 1250 masl. This type of forest is always found in thermal and mesotropical belts, without ever reaching the supratropical belt. This study was based on works published by other authors and on our own field sampling. The article begins by describing the geological, bioclimatic, biogeographic and floristic aspects of the areas in the study, specifically the hyperhumid areas in the central and eastern mountains. Due to the scarcity of phytosociological works on this area, we apply a statistical treatment to compare our communities with other associations described in Cuba. This comparison reveals that these forest groups are floristically quite distant from each other, both with regard to alliance and association species. We therefore propose two new communities: Cyathea furfuracea Baker and Prestoea montana (Grah.) Nichol;Ormosia krugii Urb. and Prestoea montana (Grah.) Nichol.

Early performance of two tropical dry forest species after assisted migration to pine-oak forests at different altitudes:strategic response to climate change

Assisted migration has been proposed as a strategy for adaptive management of forest species in response to expected effects of climate change,but it is controversial for several reasons.Tropical dry forests are among the most threatened ecosystems in the world.In Mexico,historically,land-use change and deforestation have been decreasing forest cover,and climate change is shifting the potential distribution of different forest types,exacerbating the risk of local extinctions.Assisted altitudinal migration could be a feasible strategy for reducing local extinctions in response to climate change and lack of landscape connectivity.Our objective was to evaluate survival and growth of Albizia plurijuga and Ceiba aesculifolia,two tropical deciduous forests species in Mexico.We transplanted 4-month-old seedlings to experimental raised beds at three altitudes(2100,2400 and 2700 m a.s.l.),exceeding their upper regional limit of distribution(2000 m a.s.l.).We also tested seed germination at each altitude.We monitored the experiment for 10 months.For both species,as altitude increased and cold weather was more prevalent,plant performance declined.Within species,differences in individual growth were significant among altitudes.Overall survival was 18.5%for A.plurijuga and 24.5%for C.aesculifolia.Both species had higher survival and better growth at lower altitude,and no seedling emergence at any altitude.We conclude that assisted migration can be implemented for each species by an upward attitudinal shift within,and not exceeding,400 m beyond their present upper altitudinal limit of distribution.Our results indicate that for many species that show altitudinal gradients at regional scales,unless current climate conditions change,the potential to establish outside their range is minimal.

基于iForest与KDE的雷达目标最优距离门估计

针对脉冲相干式毫米波雷达在人体生命体征信号检测中胸廓目标的距离门突变和切变问题,提出一种基于孤立森林(iForest)与核密度估计(KDE)的雷达目标最优距离门估计方法。为有效评估目标信号的距离门检测准确度,设计了人体呼吸模拟装置,建立目标信号跟踪与测量评估方法;基于iForest与KDE算法对目标最优距离门选取进行实验研究。结果表明,静态下误差率最高为5.17%;动态下误差率为8.30%。为进一步验证其有效性,对人体进行呼吸检测,并且提取的人体呼吸信号杂波少,信噪比高,能够有效提取呼吸信号特征。因此,基于iForest与KDE算法在目标最优距离门选取具有较好的估计能力,为该类型毫米波雷达非接触生命体征提取提供了有效的目标跟踪方法。

Forest Biodiversity Assessment in Peruvian Andean Montane Cloud Forest

Cloud forests are unusual and fragile habitats, being one of the least studied and least understood ecosystems. The tropical Andean dominion is considered one of the most significant places in the world as regards biological diversity, with a very high level of endemism. The biodiversity was analysed in an isolated remnant area of a tropical montane cloud forest known as the "Bosque de Neblina de Cuyas", in the North of the Peruvian Andean range. Composition, structure and dead wood were measured or estimated. The values obtained were compared with other cloud forests. The study revealed a high level of forest biodiversity, although the level of biodiversity differs from one area to another: in the inner areas, where human pressure is almost inexistent, the biodiversity values increase. The high species richness and the low dominance among species bear testimony to this montane cloud forest as a real enclave of biodiversity.

城市森林结构多样性预测冠下地面温度的潜力研究

城市森林冠层具有调控城市森林微气候的能力,但现有研究尚未阐明冠层结构对冠下地面温度的影响及其预测潜力。文章基于无人机机载激光雷达(UAV-LiDAR)提取哈尔滨林业示范基地的城市森林冠层结构多样性特征指标,探究单一结构多样性特征对冠下地面温度的影响,以及结构多样性多因子组合对温度的预测潜力。结果表明:1)城市森林结构多样性的8个特征因子与冠下地面温度呈显著相关关系(P<0.05),其中深间隙(DG)、深间隙分数(DGF)、覆盖分数(CF)、间隙分数分布(GFP)表征了结构多样性的覆盖/开放度特征;冠层高度标准差(H_(std))、冠层高度最大值(H_(max))、95%分位点高度(ZQ_(95))表征了高度特征;垂直复杂指数(VCI)表征了异质性特征。2)城市森林冠层结构多样性的覆盖/开放度特征对冠下地面温度的响应更强(R^(2)为0.15~0.5),强于高度指标(R^(2)为0.14~0.19)以及异质性指标(R^(2)=0.14)。3)结合高度指标、覆盖/开放度指标以及异质性指标的多因子预测模型2(R^(2)=0.61,RMSE=0.51,MSE=0.26,AIC=62.74),对于冠下地面温度的预测性能更优。研究明晰了城市森林结构多样性的多因子变量及其特征组合预测冠下地面温度的潜力,为城市森林冠层结构调控内部小气候环境研究提供了科学参考。

林区机载LiDAR点云的多分辨率层次布料模拟滤波

针对现有机载LiDAR(light detection and ranging)点云滤波方法在地形起伏剧烈的林区适用性不足的问题,提出一种多分辨率层次布料模拟滤波方法。首先,通过多尺度形态学开运算选择大量种子地面点;然后,基于种子地面点,使用布料模拟法由低至高逐层构建参考地形,以快速获取高分辨率参考地形;最后,基于点至参考地形的高差区分地面点和非地面点。利用国际摄影测量和遥感学会提供的数据集和参考方法,评估该方法性能。利用在中国、美国多个代表性林区的点云数据,评估该方法的可推广性。结果表明,该方法的Kappa系数和运行时间是83.72%和34.11 s,精度和效率较经典布料模拟滤波方法提高10.49%和52.17%。相比8种参考方法,该方法能够获得更高精度,并且具有稳定的可推广性。

新疆森林火灾时空分布特征及其与气候的关系

基于森林火灾报表数据(1999—2020年)和中国火灾网络数据(2005—2018年),利用相关分析、相对重要性分析等方法,分析了新疆森林火灾时空规律,探讨了过火面积与气候的关系。结果表明:80%的火灾发生在13:00—17:00,3—9月是火灾起数高发月份(占全年89.62%),8—9月是过火面积较高月份(占全年79.59%),森林火灾起数和过火面积自1999年以来均呈现下降趋势,且过火面积下降趋势显著。空间范围80°~88°E,43°~48°N是森林火灾发生的主要区域。8—9月过火面积主要受气温日较差(原始数据:r=0.49,P<0.05;去趋势数据:r=0.68,P<0.05)和最高温(原始数据:r=0.47,P<0.05;去趋势数据:r=0.54,P<0.05)的影响。森林火灾主要是人为引起的,2017—2020年(58.46%)比1999—2016年(71.73%)人为火源比例下降13.27%。研究结果可为新疆森林火灾监测预警提供科学依据,即当预测8—9月最高温度较高的时候,需加强重点时段和关键地区的火源管控。

Influence of food availability,plant productivity,and indigenous forest use on ranging behavior of the endangered samango monkey(Cercopithecus albogularis schwarzi),in the Soutpansberg Mountains,South Africa

Understanding the determinants of ranging patterns in species susceptible to habitat fragmentation is fundamental for assessing their long-term adaptability to an increasingly human-dominated landscape.The aim of this study was to determine and compare the influence of ground-based food availability,remotely sensed plant productivity,and indigenous forest use on the ranging patterns of the endangered samango monkey(Cercopithecus albogularis schwarzi).We collected monthly ranging data on two habituated samango monkey groups,from February 2012 to December 2016,from our field site in the Soutpansberg Mountains,South Africa.We used linear mixed models to explore how food availability,plant productivity,and indigenous forest use influenced monthly ranging patterns,while controlling for group size,number of sample days and day length.We found that as more areas of high plant productivity(derived from remotely sensed EVI)were incorporated into the ranging area,both total and core monthly ranging areas decreased.In addition,both total ranging area and mean monthly daily path length decreased as more indigenous forest was incorporated into the ranging area.However,we found no effect of either ground-based food availability or remotely sensed plant productivity on ranging patterns.Our findings demonstrate the behavioral flexibility in samango monkey ranging,as samangos can utilize matrix habitat during periods of low productivity but are ultimately dependent on access to indigenous forest patches.In addition,we highlight the potential of using remotely sensed areas of high plant productivity to predict ranging patterns in a small ranging,forest-dwelling guenon,over ground-based estimates of food availability.

早侏罗世粗中粒黑云母二长花岗岩岩石地球化学、LA-ICP-MS锆石U-Pb年代学特征及成因——以大兴安岭北段潮满林场地区为例

以大兴安岭北段额尔古纳地块北缘潮满林场地区粗中粒黑云母二长花岗岩为研究对象,采用地质调查、岩石地球化学和LA-ICP-MS锆石U-Pb年代学方法,分析粗中粒黑云母二长花岗岩岩石学、主量元素、微量元素和年代学等特征,探讨成因及构造环境。结果表明:潮满林场地区粗中粒黑云母二长花岗岩具有Ⅰ型花岗岩特征,属于弱过铝质高钾钙碱性花岗岩;粗中粒黑云母二长花岗岩中SiO_(2)的质量分数为68.92%~72.44%,Na 2O的质量分数为4.65%~4.85%,K_(2)O的质量分数为3.33%~4.41%,Al_(2)O_(3)的质量分数为15.25%~16.75%,里特曼指数为0.95~2.84;稀土元素总量的质量分数为(101.24~152.40)×10^(-6),轻、重稀土元素分馏明显,轻稀土元素富集,重稀土元素亏损,其中富集Rb、Th、Ce、Zr等元素,相对亏损Ta、Nb、P、Ti等元素。粗中粒黑云母二长花岗岩岩浆来源于新增生下地壳物质的部分熔融,形成于早侏罗世(192.1±1.6)Ma。研究区早侏罗世粗中粒黑云母二长花岗岩的形成环境为与蒙古—鄂霍茨克洋南向俯冲—碰撞作用相关的活动大陆边缘火山弧环境。该结果为研究大兴安岭北段潮满林场地区粗中粒黑云母二长花岗岩岩体构造背景和年代学提供依据。

六盘山区辽东栎林分结构对各植物层生物量的影响

[目的]量化宁夏六盘山区辽东栎次生林各植物层(乔木层、林下植物层(草本和灌丛)、枯落物层)生物量随郁闭度及林分密度的变化,确定能使各层生物量均维持在较高水平的最佳林分结构,以充分发挥森林多种功能。[方法]基于野外调查样地数据,利用上外包线分析法确定辽东栎林各层生物量对林分密度和郁闭度的响应规律,并经综合权衡后确定最佳郁闭度范围。[结果]随郁闭度和林分密度增加,乔木层生物量先快速增加,在郁闭度0.75和密度1050株∙hm^(−2)时分别达到292.3和296.9 t∙hm^(−2),分别为其外包线最大值的80%和82%,之后增速变缓;林下植物层生物量先缓慢下降,在郁闭度0.75和密度1150株∙hm^(−2)时分别达到9.08和9.17 t∙hm^(−2),分别为其外包线最大值的89%和86%,之后快速减小;枯落物层生物量先逐渐增加,在郁闭度0.75时达到33.34 t∙hm^(−2),为外包线最大值的97%。综合分析各层生物量随郁闭度的变化表明,需维持林冠郁闭度在0.75~0.79左右,才能使林分各层生物量都保持在各自上外包线最大值的80%以上。[结论]在宁夏六盘山区,要使辽东栎林的乔木层、林下植物层、枯落物层的生物量均维持在较高水平,需维持林冠郁闭度在最佳范围0.75~0.79左右,这可用于指导该地区及类似地区的辽东栎林多功能经营。

基于新一代信息技术的温带森林生态系统碳通量精准计量

【目的】森林碳通量估算存在巨大不确定性,其科研应用缺乏信息化技术支撑。本研究旨在改变传统低效的森林信息采集和处理方式,深化森林碳通量研究与信息化技术的融合,探索科研范式变革与实现途径。【方法】融合物联网、近地面遥感、人工智能和大数据等新一代信息化技术,组建多功能数据中心,开展复杂地形下森林碳通量精准计量示范研究。【结果】引入分形维数等指数,提出量化地形复杂度的新参数;建立双季激光雷达点云单木分割方法,提取小流域33万株单木全量结构信息;数字模拟风格局,识别三种风模式;解析CO_(2)浓度信号频域特征,在机器学习框架下计量森林碳通量,不确定性降至15.9%。【局限】仍基于经典涡度协方差法模型,区域尺度森林碳通量计量尚未开展,需边界层气象学、森林生态学、遥感科学等学科及信息化前沿技术的深度融合。【结论】发展了森林碳通量计量与信息化手段融合的技术方法,探索了传统森林生态与林学科研范式变革的实现途径,成功在辽东典型温带森林进行示范。

森林公园范围调整及影响评价--以吉林三岔子国家森林公园为例

随着我国自然保护地体系的建立,吉林三岔子国家森林公园也正面临新的机遇与挑战。本文简要介绍了森林公园自然概况及景观资源,梳理了森林公园现存的主要矛盾,阐述了森林公园范围调整的必要性,并从四个方面对森林公园调整范围后的影响进行评价。

基于级联循环网络的林木生长参数预测

【目的】树木的生长参数在林木性状评估、森林碳汇计量和优化森林经营策略等方面具有重要的意义。从激光雷达数据中精准提取林木生长参数并对树木未来生长参数进行预测,以期为林业数字化发展提供技术支持。【方法】本研究提出了一种基于人工智能的林木生长参数提取与预测方法,该方法以南京林业大学中的樱花、银杏、鹅掌楸、水杉4个树种为实验对象。首先,采用机载激光雷达获取4个树种样地的点云数据,并通过单株分割算法提取单棵树木点云。其次,基于圆拟合及高斯滤波的方法自动的从2016、2018、2020年的单棵树点云中提取胸径、树高、冠宽等生长参数,并辅以样地调查数据(2015、2017、2019、2021、2022年),构建不同树种的单棵树生长参数时间序列作为深度学习网络的训练样本集。最后,构造由两层门控循环单元(GRU)的林木生长参数预测深度学习网络,并引入注意力模块以弥补传统循环神经网络捕获长期依赖关系的不足。该网络以2015-2021年单株树木生长参数时间序列作为输入,依托训练数据及随机梯度下降算法使网络参数逼近真实树木生长情况,并用以预测2022年单棵树木的生长参数。【结果】深度学习网络在树高预测上表现最好,决定系数R^(2)均不低于0.83,均方根误差(E_(RMS))均小于0.50 m,在4种树中银杏树的预测结果最优(R^(2)=0.95,E_(RMS)=0.31 m)。在胸径、冠宽等参数的预测上,深度预测网络仍有着良好的表现,R^(2)均不低于0.81,胸径E_(RMS)小于2.50 cm,冠宽E_(RMS)小于0.32 m。在与线性回归和LSTM网络等林木参数预测方法的比较中,本模型预测效果良好(R^(2)≥0.86),误差较小。【结论】级联循环神经网络可有效地预测未来树木的生长情况,提高林木生长参数的预测精度,同时GRU和注意力机制的引入在林木参数的时序预测中有一定的鲁棒性,为森林的智能管理与可视化分析提供了新的思路。

近地面激光雷达点云密度对森林冠层结构参数提取准确性的影响

基于激光雷达技术获取冠层结构为森林生态学研究增加了新的维度。搭载于多旋翼无人机的近地面激光雷达相比于固定翼有人机的机载激光雷达,能够更加灵活高效地获取森林群落样地高密度点云。但在实际操作中,往往出现局部低密度点云数据,影响了冠层结构参数提取的准确性。使用4块森林动态样地的近地面激光雷达点云数据;利用航带分解方法分析各样地低密度样方成因;采用点云抽稀模拟算法计算并拟合偏差曲线,对比不同样地、参数和取样尺度间的点云密度对冠层结构参数提取准确性的影响;根据偏差曲线计算各条件下保证参数提取准确性的最低点云密度。结果发现:1)低密度区域主要受地形或(和)近地面遥感设计规划的影响。地形复杂的测区(西双版纳和古田山样地),遥感规划难度大,整体难以获取高密度点云(在30点/m^(2)左右),容易在沟谷和高海拔处出现低密度样方。平坦测区(长白山两块样地)虽可获取高密度点云(均超过150点/m^(2)),但欠佳的遥感规划设计导致长白山1测区北部出现1hm^(2)低密度区域。2)冠层参数提取准确性随点云密度减少而迅速降低,呈负指数幂函数关系。这一变化趋势在不同参数和尺度间差异较大,但在各样地间无显著差异。3)根据偏差曲线拟合结果,点云密度达到16点/m^(2)可以实现5—20 m取样尺度下冠层结构参数提取准确度达95%。综上,为更好的将近地面激光雷达技术应用在森林生态学研究中,应注重外业遥感作业方案的合理性,充分考虑地形的影响,在源头把控数据质量;如果数据存在低密度点云的情况,应适当放宽取样尺度并慎重提取对点云密度较为敏感的冠层结构参数。