More tree growth reduction due to consecutive drought and its legacy effect for a semiarid larch plantation in Northwest China

Extreme climate has increasingly led to negative impacts on forest ecosystems globally,especially in semiarid areas where forest ecosystems are more vulnerable.However,it is poorly understood how tree growth is affected by different drought events.In 2006–2009,the larch plantations in the semiarid areas of Northwest China were negatively affected by four consecutive dry years,which was a very rare phenomenon that may occur frequently under future climate warming.In this study,we analyzed the effect of these consecutive dry years on tree growth based on the data of the tree rings in the dominant layer of the forest canopy on a larch plantation.We found that the tree-ring width index(RWI)in dry years was lower than that in normal years,and it experienced a rapidly decreasing trend from 2006 to 2009(slope=-0.139 year^(-1),r=-0.94)due to water supply deficits in those dry years.Drought induced legacy effects of tree growth reduction,and consecutive dry years corresponded with greater growth reductions and legacy effects.Growth reductions and legacy effects were significantly stronger in the third and fourth consecutive dry years than that of single dry year(p<0.05),which might have been due to the cumulative stress caused by consecutive dry years.Our results showed that larch trees experienced greater tree growth reduction due to consecutive dry years and their legacy effect,and the trees had lower recovery rates after consecutive dry years.Our results highlight that consecutive dry years pose a new threat to plantations under climate warming,and thus,the effect of climate extremes on tree growth should be considered in growth models in semiarid areas.

Tree allometry responses to competition and complementarity in mixed-species plantations of Betula alnoides

Tree allometry plays a crucial role in tree survival,stability,and timber quantity and quality of mixed-species plantations.However,the responses of tree allometry to resource utilisation within the framework of interspecific competition and complementarity remain poorly understood.Taking into consideration strong-and weakspace competition(SC and WC),as well as N_(2)-fixing and non-N_(2)-fixing tree species(FN and nFN),a mixedspecies planting trial was conducted for Betula alnoides,a pioneer tree species,which was separately mixed with Acacia melanoxylon(SC+FN),Erythrophleum fordii(WC+FN),Eucalyptus cloeziana(SC+nFN)and Pinus kesiya var.langbianensis(WC+nFN)in southern China.Six years after planting,tree growth,total nitrogen(N)and carbon(C)contents,and the natural abundances of^(15)N and^(13)C in the leaves were measured for each species,and the mycorrhizal colonisation rates of B.alnoides were investigated under each treatment.Allometric variations and their relationships with space competition and nutrient-related factors were analyzed.The results showed a consistent effect of space competition on the height-diameter relationship of B.alnoides in mixtures with FN or nFN.The tree height growth of B.alnoides was significantly promoted under high space competition,and growth in diameter at breast height(DBH),tree height and crown size were all expedited in mixtures with FN.The symbiotic relationship between ectomycorrhizal fungi and B.alnoides was significantly influenced by both space competition and N_(2) fixation by the accompanying tree species,whereas such significant effects were absent for arbuscular mycorrhizal fungi.Furthermore,high space competition significantly decreased the water use efficiency(WUE)of B.alnoides,and its N use efficiency(NUE)was much lower in the FN mixtures.Structural equation modeling further demonstrated that the stem allometry of B.alnoides was affected by its NUE and WUE via changes in its height growth,and crown allometry was influenced by the mycorrhizal symbiotic relationship.Our findings provide new insights into the mechanisms driving tree allometric responses to above-and belowground resource competition and complementarity in mixed-species plantations,which are instructive for the establishment of mixed-species plantations.

Predicting Users’ Latent Suicidal Risk in Social Media: An Ensemble Model Based on Social Network Relationships

Suicide has become a critical concern,necessitating the development of effective preventative strategies.Social media platforms offer a valuable resource for identifying signs of suicidal ideation.Despite progress in detecting suicidal ideation on social media,accurately identifying individuals who express suicidal thoughts less openly or infrequently poses a significant challenge.To tackle this,we have developed a dataset focused on Chinese suicide narratives from Weibo’s Tree Hole feature and introduced an ensemble model named Text Convolutional Neural Network based on Social Network relationships(TCNN-SN).This model enhances predictive performance by leveraging social network relationship features and applying correction factors within a weighted linear fusion framework.It is specifically designed to identify key individuals who can help uncover hidden suicidal users and clusters.Our model,assessed using the bespoke dataset and benchmarked against alternative classification approaches,demonstrates superior accuracy,F1-score and AUC metrics,achieving 88.57%,88.75%and 94.25%,respectively,outperforming traditional TextCNN models by 12.18%,10.84%and 10.85%.We assert that our methodology offers a significant advancement in the predictive identification of individuals at risk,thereby contributing to the prevention and reduction of suicide incidences.

Stand structure and height-diameter relationship of a degraded Populus euphratica forest in the lower reaches of the Tarim River, Northwest China

Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a dominant tree species along the Tarim River watershed, plays an irreplaceable role in the sustainable development of regional ecology, economy and society. However, as the result of climate changes and human activities, the natural riparian ecosystems within the whole river basin were degraded enormously, particularly in the lower reaches of the river where about 320 km of the riparian forests were either highly degraded or dead. In this study, we presented one of the main criteria for the assessment of vitality of P. euphrafica forests by estimating the defoliation level, and analyzed forest structure and determined the height-diameter （height means the height of a tree and diameter means the diameter at breast height （DBH） of a tree） relationship of trees in different vitality classes （i.e. healthy, good, medium, senesced, dying, dead and fallen）. Trees classified as healthy and good ac- counted for approximately 40% of all sample trees, while slightly and highly degraded trees took up nearly 60% of total sample trees. The values of TH （tree height） and DBH ranged from 0-19 m and 0-125 cm, respectively. Trees more than 15 m in TH and 60 cm in DBH appeared sporadically. Trees in different vitality classes had different distribution patterns. Healthy trees were mainly composed more of relatively younger trees than of degraded tress. The height-diameter relationships differed greatly among tress in different vitality classes, with the coefficients ranging from 0.1653 to 0.6942. Correlation coefficients of TH and DBH in healthy and good trees were higher than those in trees of other vitality classes. The correlation between TH and DBH decreased with the decline of tree vitality. Our results suggested that it might be able to differentiate degraded P. euphratica trees from healthy trees by determining the height-diameter correlation coefficient, and the coefficient would be a new parameter for detecting degradation and assessing sustainable management of floodplain forests in arid regions. In addition, tree vitality should be taken into account to make an accurate height-diameter model for tree height prediction.

Hurricane disturbances, tree diversity, and succession in North Carolina Piedmont forests, USA

Windthrow plays a critical role in maintaining species diversity in temperate forests. Do large-scale strong wind events(i.e., tropical cyclones, including hurricanes,typhoons and severe cyclonic storms) increase tree diversity in severely damaged forest areas? Do hurricanes(tropical cyclones that occurs in the Atlantic Ocean and northeastern Pacific Ocean) lead to altered relative abundance of shade-tolerant and shade-intolerant species? Did historic hurricanes alter the succession trajectory of the damaged forests? We used nearly 70-year tree demographic data to assess the effects of two major hurricanes on woody species diversity in Piedmont forests, North Carolina, USA. Species richness(S) and Shannon–Wiener's diversity index(H') were used to evaluate the changes in tree diversity. The changes in composition were assessed with Nonmetric Multidimensional Scaling. The pre-hurricane successional phase can strongly influence both the damage severity and subsequent responses. Although there is often an immediate drop in diversity following a hurricane, understory tree diversity quickly increases to levels that exceed those prior to the disturbance. This leads to an increase in diversity in stands that were substantially damaged. Hurricanes significantly decrease the dominance of shade-intolerant canopy species while increasing preestablished, more shade-tolerant species. We conclude that large, and infrequent hurricanes help to maintain local tree diversity, but also accelerate the increase in dominance of understory species such as red maple and beech.

Genetic diversity and relatedness analysis of nine wild species of tree peony based on simple sequence repeats markers

Tree peony has nine wild species,but the evolutionary relationship of them is still unclear.Here,a total of 274 specimens from 22 natural populations of nine wild species were collected,and their genetic diversity and similarity was analyzed based on Simple Sequence Repeats(SSR)molecular markers.A total of 106 alleles were generated based on 20 primers and with an average of 5.3 alleles per primer.Shannon’s information index(I)ranged from 0.6333 to 1.7842,and the average of Nei’s genetic diversity coefficient(H)was 0.5771.Polymorphism Information Content(PIC)value varied from 0.29 to 0.77,ten of these primers had high polymorphism(PIC≥0.50).All the above genetic parameters of primers reflect more rich genetic diversity information compared with other researches using SSR molecular markers to study the genetic diversity of tree peony wild species.At the population level,the lowest and highest degree of genetic diversity occurred in Paeonia ludlowii-P1 and P.delavayi-P3 population,respectively.Whereas at species level,the genetic diversity of 9 wild peony species was as follows:P.lutea>P.delavayi>P.rockii>P.qiui>P.ostii>P.decomposita>P.potaninii>P.spontanea>P.ludlowii.Furthermore,cluster analysis at species level divided the nine wild tree peony species into two branches.In branch I,the closest phylogenetic relationship was found between P.ostii and P.rockii,followed by P.spontanea,P.qiui,and P.decomposita.In branch II,the closest relationship occurred between P.lutea and P.delavayi,followed by P.potaninii and P.ludlowii.Clustering results supported the division of tree peonies into two subsects(Delavayanae and Vaginatae),it also supported P.potaninii and P.ludlowii as independent species.The results provided novel insight into the genetic diversity and phylogenetic relationship of nine wild tree peony species.It will help formulate comprehensive protection measures of wild germplasm resources and select proper parents for distant hybridization in the future.

An improved area-based approach for estimating plot-level tree DBH from airborne LiDAR data

The diameter at breast height(DBH) of trees and stands is not only a widely used plant functional trait in ecology and biodiversity but also one of the most fundamental measurements in managing forests. However, systematically measuring the DBH of individual trees over large areas using conventional ground-based approaches is labour-intensive and costly. Here, we present an improved area-based approach to estimate plot-level tree DBH from airborne Li DAR data using the relationship between tree height and DBH, which is widely available for most forest types and many individual tree species. We first determined optimal functional forms for modelling heightDBH relationships using field-measured tree height and DBH. Then we estimated plot-level mean DBH by inverting the height-DBH relationships using the tree height predicted by Li DAR. Finally, we compared the predictive performance of our approach with a classical area-based method of DBH. The results showed that our approach significantly improved the prediction accuracy of tree DBH(R^(2)=0.85–0.90, rRMSE=9.57%–11.26%)compared to the classical area-based approach(R^(2)=0.80–0.83, rRMSE=11.98%–14.97%). Our study demonstrates the potential of using height-DBH relationships to improve the estimation of the plot-level DBH from airborne Li DAR data.

Development and application of microsatellite markers within transcription factors in flare tree peony(Paeonia rockii)based on next-generation and single-molecule long-read RNA-seq

Tree peonies native to China are a precious crop with ornamental,medicinal and edible oil properties,of which flare tree peony(Paeonia rockii)is one of the most significant germplasms in Paeonia.The development and application of expressed sequence tag-simple sequence repeat(EST-SSR)markers are very valuable for genetic and breeding applications,but EST-SSR resources for the genus Paeonia are still limited.In this study,we first reported the development of SSRs within transcription factors(TFs)in P.rockii based on next-generation sequencing(NGS)and single-molecule long-read sequencing(SMLRS).A total of 166 EST-SSRs containing six nucleotide repeat types were identified from 959 candidate TFs associated with yield,with an average of one SSR per 5.83 unigenes.In total,102(61.45%)pairs of primers produced amplification products in the two RNA-seq cultivars.Among them,58(56.86%)pairs of primers from 18 gene families(AP2,b HLH,HSF,etc.)were identified to be polymorphic both in the parents of a linkage mapping population and in eight randomly selected accessions of P.rockii.Further,the 58 EST-SSRs indicated a high level of informativeness with PIC values ranging from 0.32 to 0.91(mean 0.70)after assessment in 37 tree peony accessions.Transferability studies indicated that the amplification ratio of the 58 pairs of primers ranged from 89.66 to 100%across seven species of Paeonia.In addition,a genetic relationship study was performed in 62 accessions.Cluster analysis using the neighbour-joining(NJ)tree demonstrated that major clusters corresponded to the known pedigree trees.Taken together,these newly developed EST-SSRs have a potential use in the conservation of tree peony germplasm and marker-assisted selection(MAS)breeding.

Estimating Pinus palustris tree diameter and stem volume from tree height,crown area and stand-level parameters

Accurate and efficient estimation of forest growth and live biomass is a critical element in assessing potential responses to forest management and environmental change. The objective of this study was to develop models to predict longleaf pine tree diameter at breast height （dbh） and merchantable stem volume （V） using data obtained from field measurements. We used longleaf pine tree data from 3,376 planted trees on 127 permanent plots located in the U.S. Gulf Coastal Plain region to fit equations to predict dbh and V as functions of tree height （H） and crown area （CA）. Prediction of dbh as a function of H improved when CA was added as an additional independent variable. Similarly, predic- tions of V based on H improved when CA was included. Incorporation of additional stand variables such as age, site index, dominant height, and stand density were also evaluated but resulted in only small improvements in model performance. For model testing we used data from planted and naturally-regenerated trees located inside and outside the geographic area used for model fitting. Our results suggest that the models are a robust alternative for dbh and V estimations when H and CA are known on planted stands with potential for naturally-regenerated stands, across a wide range of ages. We discuss the importance of these models for use with metrics derived from remote sensing data.

Climate forcing of tree growth in dry Afromontane forest fragments of Northern Ethiopia:evidence from multi-species responses

Background: Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high priority to facilitate sustainable management of the remnant dry forests. In this study, we examined the long-term climate-growth relations of main tree species in the remnant dry Afromontane forests in northern Ethiopia. The aim of this study was to assess the dendrochronological potential of selected dry Afromontane tree species and to study the influence of climatic variables (temperature and rainfall) on radial growth. It was hypothesized that there are potential tree species with discernible annual growth rings owing to the uni-modality of rainfall in the region. Ring width measurements were based on increment core samples and stem discs collected from a total of 106 trees belonging to three tree species (Juniperus procera, Olea europaea p. cuspidate and Podocarpus falcatus). Thesubsp. collected samples were prepared, crossdated, and analyzed using standard dendrochronological methods. The formation of annual growth rings of the study species was verified based on successful crossdatability and by correlating tree-ring widths with rainfall. Results: The results showed that all the sampled tree species form distinct growth boundaries though differences in the distinctiveness were observed among the species. Positive and significant correlations were found between the tree-ring widths and rainfall, implying that rainfall plays a vital role in determining tree growth in the region. The study confirmed the formation of annual growth rings through successful crossdating, thus highlighted the potential applicability of dendroclimatic studies in the region. Conclusions: Overall, the results proved the strong linkage between tree-ring chronologies and climate variability in the study region, which further strengthens the potential of dendrochronological studies developing in Ethiopia, and also has great implications for further paleo-climatic reconstructions and in the restoration of degraded lands. Further knowledge on the growth characteristics of tree species from the region is required to improve the network of tree-ring data and quality of the chronology so as to successfully reconstruct historic environmental changes.

Identification of refactoring opportunities for source code based on class association relationships

In order to deal with the complex association relationships between classes in an object-oriented software system,a novel approach for identifying refactoring opportunities is proposed.The approach can be used to detect complex and duplicated many-to-many association relationships in source code,and to provide guidance for further refactoring.In the approach,source code is first transformed to an abstract syntax tree from which all data members of each class are extracted,then each class is characterized in connection with a set of association classes saving its data members.Next,classes in common associations are obtained by comparing different association classes sets in integrated analysis.Finally,on condition of pre-defined thresholds,all class sets in candidate for refactoring and their common association classes are saved and exported.This approach is tested on 4 projects.The results show that the precision is over 96%when the threshold is 3,and 100%when the threshold is 4.Meanwhile,this approach has good execution efficiency as the execution time taken for a project with more than 500 classes is less than 4 s,which also indicates that it can be applied to projects of different scales to identify their refactoring opportunities effectively.

Height-Diameter Relationship of Some Forest Species Exploited for Wood in the Natural Tropical Forest of the Congo Basin

To enrich knowledge on the growth dynamics of commercial forest species in the Congo Basin, a study was conducted in Cameroon, within a community forest in savannah forest transition zone (Zone 1) and within FMU 10 052 in dense semi-deciduous humid forest (Zone 2). It aimed to obtain, in 8 species, the height (H) of the tree from its diameter (D) more accessible: Entandophragma cylindricum (Meliacea), Eribroma oblongum, Sterculia rhinopetala et Triplochiton scleroxylon (Malvaceae);Erythrophleum suaveolens et Piptadeniastrum africanum (Fabaceae), Milicia excelsa (Moraceae) et Terminalia superba (Combretaceae). The destructive method was used. After felling and flushing out a tree, the dendrometric parameters were measured and/or calculated. In Zone 1, 6 species including T. scleroxylon were calibrated using 30 trees of each. In Zone 2, 45 trees of E. cylindricum, 99 of E. suaveolens and 82 of T. scleroxylon constituted the sample. At the 5% threshold (95% confidence interval), the height-diameter relationship is a linear model. In all species, the height of a tree is predicted by measuring its diameter through linear regression. In Zone 1 regression equation is: H(m) = 28.13 + 19.09 * D(m) for T. scleroxylon;H(m) = 12.35 + 30.38 * D(m) for S. rhinopetala;H(m) = 23.09 + 26.42 * D(m) for E. oblongum;H(m) = 14.86 + 20.92 * D(m) for P. africanum;H(m) = 14.98 + 24.78 * D(m) for T. superba and H(m) = 1.55 + 32.37 * D(m) for M. excelsa. In Zone 2, the relationship is: H(m) = 27.40 + 14.21 * D(m) for T. scleroxylon;H(m) = 7.79 + 20.18 * D(m) for E. cylindricum and H(m) = 20.08 + 9.74 * D(m) for E. suaveolens (probability associated with F < 0.0001). The influence of site parameters (biotic and abiotic) on the height-diameter relationship should be more studied in multilayers forests specifically in the Congo Basin.

What Happens after the Gap?— Size Distributions of Patches with Homogeneously Sized Trees in Natural and Managed Beech Forests in Europe

A novel but simple approach for describing stand structure in natural and managed forests driven by small-scaled disturbances is introduced. A primeval beech forest reserve in Slovakia and two beech stands in Germany with different management histories were studied, and their forest stand texture was analysed in terms of tree coordinates, stem diameter, and crown radius. Neigh-bouring trees of similar size with estimated contact of their crowns were assigned to tree groups. The study goal was to estimate the number and size of such homogeneous patches. In all cases, the number of tree groups in a particular diameter class decreased exponentially as group size increased. Single trees were predominant. Compared to simulated random tree distributions, the natural stand exhibited a more clumped distribution of small trees and more regular distribution of larger ones. The natural forest generally had smaller groups than the managed even aged stand, but the smallest group sizes were found in the uneven-aged selection forest. The simple analytical approach provided new spatial insights into neighbourhood relations of trees. The continuous scale from single trees to larger tree groups is an important achievement compared to other analytical methods applied in this field. The findings may even indicate a certain degree of self-organization in natural forests. Due to the limitations associated with each method or statistical models, a joint consideration of 1) gap dynamics, 2) forest developmental stages, and 3) size classes of homogeneous tree groups is recommended. Relevant to forest practitioners, the size class distributions enhance an understanding of the complex stand structures in natural forests and therewith support an emulation of natural forest dynamics in managed beech forests.

Phylogenetic analysis of 48 gene families revealing relationships between Hagfishes, Lampreys, and Gnathostomata

It has become clear that the extant vertebrates are divided into three major groups, that is, hagfishes, lampreys, and jawed vertebrates. Morphological and molecular studies, however, have resulted in conflicting views with regard to their interrelationships. To clarify the phylogenetic relationships between them, 48 orthologous protein-coding gene families were analyzed. Even as the analysis of 34 nuclear gene families supported the monophyly of cyclostomes, the analysis of 14 mitochondrial gene families suggested a closer relationship between lampreys and gnathostomes compared to hagfishes. Lampreys were sister group of gnathostomes. The results of this study supported the cyclostomes. Choice of outgroup, tree-making methods, and software may affect the phylogenetic prediction, which may have caused much debate over the subject. Development of new methods for tackling such problems is still necessary.

Tree View在高校学生管理系统中的应用

文章介绍以Delphi5.0为开发语言、SQLServer为后台、运行于Windows2000下、C/S模式(客户/服务器模式)的高校学生管理信息系统(MIS)中TreeView的应用,并简述了TreeView在基于Web程度开发中的应用。。

职住地建成环境对轨道交通通勤行为的非线性影响机制研究——以武汉市为例

改革开放以来中国大城市快速蔓延导致了职住分离及交通拥堵等问题,倡导轨道交通等绿色交通方式出行成为大城市缓解通勤压力的重要手段。当前研究主要以居住地作为地理背景考察建成环境对轨道交通通勤的作用,但较少探索就业地建成环境的影响。本研究以武汉市为例,通过189个轨道站点的刷卡数据识别轨道交通通勤人员并构建通勤出行链,通过梯度提升决策树(GBDT)解析职住地涉及建成环境和轨道站点的30个特征因素对通勤客流量和通勤时间的非线性影响机制。研究发现:①居住地通勤客流量表现为较集中的点状分布,就业地通勤客流量则呈现显著的“中心-外围”结构,职住地两端通勤时间的空间格局均呈中间低、外围高的分布特征;②职住地周边建成环境因素对轨道交通通勤客流量和通勤时间普遍存在非线性影响及阈值效应,整体而言居住地建成环境的相对影响程度高于就业地,但就业地“公司企业数”是影响通勤客流最重要的要素,就业地“与城市中心距离”则是影响通勤时间的首要因素;③职住地周边同一建成环境因素,对于通勤客流量和通勤时间的影响可能截然相反,这与城市轨道交通网络建设和社会实际发展状况相关。研究结果可以更好地理解职住地建成环境与轨道交通通勤行为的关联,有助于促进城市轨道交通和城市职住空间的协调发展。

基于GBDT的望奎县农田土壤有机碳主控因子研究

利用多源公开数据,针对于2012年搜集到的农田土壤有机碳(SOC)数据,通过梯度增强决策树(GBDT)探究SOC的主控因子,揭示SOC空间分异机理.选择国家商品粮食生产基地县和全国产量大县-望奎县作为研究区域,结果表明,GBDT模型相较于一元线性回归模型在所有的自变量上均具有更好的预测效果,总体的R^(2)为0.958,表明该模型能够很好地解释目标变量的变异;碱解氮、有效磷、气温、土壤微生物多样性、速效钾、土壤pH和降水量依次是影响有机碳含量最为显著的几个因素,其中碱解氮以33.85%的影响权重位居最高;7个环境协变量均观察到对SOC的阈值效应,且均具有两个阈值.研究发现任意两个变量都不是独立的,均存在相互作用的负值效应.表明环境变量对SOC含量的影响是一个复杂的交互作用,而不是简单的叠加.侧面证明了过度施肥并不会达到增加土壤肥力的作用,而会造成资源浪费和农田生态污染问题.

凉水保护区红松与主要伴生树种的空间关系

空间关系是影响森林生长与群落演替的重要因素,种间关系是其重要组成部分,研究空间关系有利于了解森林群落的生长更新、功能作用与演替进程。利用移动窗口法对凉水自然保护区10.4 hm^(2)样地不同径级的红松与主要伴生树种做空间相关性研究,并进行多尺度比较,得到不同尺度下不同径级红松与主要伴生树种个体的空间关系特征。研究结果表明:(1)红松与伴生树种的相互关系复杂多样,多种相互关系并存,表现出阔叶红松林群落结构的复杂性与稳定性。大径级红松压制同径级伴生树种,二者呈极显著负相关,但其对小径级伴生树种有庇荫作用,二者呈极显著正相关。(2)红松与主要伴生树种的相互关系在不同尺度、径级上均有极显著差异。尺度越大,红松与主要伴生树种的相关系数变化速率越小;伴生树种的径级越大,红松与主要伴生树种的相关系数变化速率越大。(3)红松与伴生树种的相关性具有尺度特征,主要表现在大尺度(≥60 m)范围上,在小尺度(<60 m)上相关性较弱。红松与伴生树种在相同径级与不同径级的结合方式上表现出不同的空间关系。同径级的红松与伴生树的种间关系多表现为负相关,不同径级的红松与伴生树种种间关系多表现为正相关。(4)以种间关系确定样方最小面积,凉水保护区临界样地面积为60 m×60 m。该研究集中于不同尺度下不同径级的红松与伴生树种的种间关系,解释优势种红松与伴生树种在森林的空间关系以及群落结构特征,为东北地区阔叶红松林的森林管理提供参考意见。

紫椴红松林群落主要乔木树种种间关系

以吉林松花江三湖国家级自然保护区紫椴红松林为研究对象,采用总体相关性检验(VR)、χ^(2)检验、联结系数(AC)、共同出现百分率(PC)和点相关系数(Ф)分析群落主要乔木树种在5个层级(Ⅰ级幼苗、Ⅱ级幼树、Ⅲ级小径树、Ⅳ级中径树、Ⅴ级大树)的种间关系。结果表明:主要乔木树种总体相关性为显著正联结,各层级VR介于0.84~1.59;χ^(2)检验结果显示,紫椴-红松在各层级均为不显著联结,二者在Ⅰ、Ⅲ、Ⅳ层级为正联结,在Ⅱ和Ⅴ层级为负联结。主要树种种间关系大多不显著,由Ⅰ级幼苗至V级大树不显著联结种对数占比增加;在Ⅱ和Ⅳ层级,负联结种对数占比最大;AC、PC和Ф值也均表明,紫椴-红松间虽然存在一定联结但联结程度较弱,其他主要树种种间关系多数处于松散的独立状态。总体而言,紫椴红松林群落主要乔木树种已建立了良好的种间关系,可相对稳定地共同利用林地资源。

一种基于地面特征与树木位置关系的无人机和地基LiDAR点云配准方法

【目的】无人机激光雷达与地基激光雷达的工作方式不同,导致无人机点云缺乏林内信息,地基点云缺乏林冠信息,单一平台的LiDAR点云难以完整描述森林三维垂直结构,将这两者点云融合有利于消除各自的扫描盲区,估测更为准确的森林结构参数。基于此,提出了一种基于地面特征与树木位置关系的无标识自动化配准方法。【方法】选取哈尔滨城市林业示范基地内的蒙古栎和樟子松作为研究对象,采用大疆禅思L1激光雷达设备与FARO Focus3D X330三维激光扫描仪分别获取样地内的无人机和地基LiDAR点云。首先,利用改进的渐进式加密三角网滤波算法分别从无人机点云和地基点云中提取地面点云,基于两者相似的快速点特征直方图(FPFH)特征,使用随机采样一致性算法得到初始配准参数,完成初始配准。然后,从初始配准后的无人机点云和地基点云中提取相同高度处的树干点云的水平投影位置作为配准基元,分别构建不规则三角网,并基于三角形的角度相似性原理寻找同名三角形对。最后,使用奇异值分解法得到旋转平移参数,从而完成精细配准。【结果】蒙古栎样地内对应树木水平偏移距离的平均值为0.173 m,樟子松样地内对应树木水平偏移距离的平均值为0.283 m,2个样地的树木点云均取得了较高的配准精度。【结论】提出的点云配准方法有效实现了林区无人机点云数据和地基点云数据的配准,二者的融合可为快速完整地获取林木构型信息提供数据基础,从而推动多源激光雷达技术联合应用于林木三维重建和森林资源精细调查等方面。