Effect of Quadrat Shape on Spatial Point Pattern Performance of Haloxylon ammodendron

In this study, we investigated the natural growth of Haloxylon ammodendron forest in Moso Bay, southwest of Gurbantunggut Desert. Random sample analysis was used to analyze the spatial point pattern performance of Haloxylon ammodendron population. ArcGIS software was used to summarize and analyze the spatial point pattern response of Haloxylon ammodendron population. The results showed that: 1) There were significant differences in the performance of point pattern analysis among different random quadrants. The paired t-test for variance mean ratio showed that the P values were 0.048, 0.004 and 0.301 respectively, indicating that the influence of quadrat shape on the performance of point pattern analysis was significant under the condition of the same optimal quadrat area. 2) The comparative analysis of square shapes shows that circular square is the best, square and regular hexagonal square are the second, and there is no significant difference between square and regular hexagonal square. 3) The number of samples plays a decisive role in spatial point pattern analysis. Insufficient sample size will lead to unstable results. With the increase of the number of samples to more than 120, the V value and P value curves will eventually stabilize. That is, stable spatial point pattern analysis results are closely related to the increase of the number of samples in random sample square analysis.

Spatial Pattern and Influencing Factor Analysis of Attended Collection and Delivery Points in Changsha City, China

Attended collection and delivery points are vital components of ‘last-mile logistics’.Based on point of interest(POI) data for Cainiao Stations and China Post stations in Changsha City, China, this paper provides a detailed exploration of the basic features, spatial distribution, and location influencing factors of attended collection and delivery points.Specifically, analyses of the types, service objects and location distributions of the attended collection and delivery points alongside a discussion of their spatial pattern and influencing factors provides a reference for their general geographic layout and characteristics.The findings of this study indicate that: 1) The main mode of operation of attended collection and delivery points is franchises, with other modes of operation rely on supermarkets and other individual shop types.2) The main service targets of attended collection and delivery points are communities, schools, and businesses, followed by townships, enterprises, scenic spots, and administrative units.3) Approximately 77.44% of the attended collection and delivery points are located near the exits of service areas;others are situated in the centre of the service areas.For the Cainiao Stations, 80% are located within 125 m of the exit;for the China Post stations, 80% are located within 175 m of the exit.4) The spatial distribution of the attended collection and delivery points in Changsha is unbalanced, with ‘more centre and fewer surrounding’.The centre is an ‘inverted triangle’, and the edge is an ‘orphan’, showing a northwest-southeast orientation and symmetrical along the axis.The layout of the attended collection and delivery points forms three core areas, and the number of sites decreases with the distance from the core.5) The number and distribution of the attended collection and delivery points are strongly consistent with the regional economic development level, population, and roadway system traffic convenience.Most attended collection and delivery points are on residential, scientific and educational, and commercial and financial land.

Spatial patterns of Picea crassifolia driven by environmental heterogeneity and intraspecifi c interactions

Research on the spatial patterns of tree populations is critical for understanding the structure and dynamic processes of forests.However,little is known about how the underlying drivers shape these patterns and species interactions in forest systems.In this study,spatial point pattern analysis investigated the combined eff ects of intraspecifi c interactions and environmental heterogeneity on the spatial structure and internal maintenance mechanisms of Picea crassifolia in the Qilian Mountain National Nature Reserve,China.Data were obtained from a 10.2-ha dynamic monitoring plot(DMP)and sixteen 0.04-ha elevation gradient plots(EGPs).Under complete spatial randomness,both mature trees and saplings in the DMP demonstratedlarge-scale aggregation with negative correlations.In EGPs,saplings were clustered in small mesoscales,mature trees were randomly distributed,and the interactions of saplingstrees at all elevations were not correlated.By eliminating the interference of environmental heterogeneity through the inhomogeneous Poisson process,saplings in the DMP and EGPs were clustered in small scales and trees randomly distributed.Intraspecifi c associations were negatively correlated,in the DMP and at low elevations,and no correlations in high elevations of EGPs.In the vertical scale,saplings showed a small-scale aggregation pattern with increase in elevation,and the aggregation degree fi rst decreased and then increased.The interactions of saplings-trees and saplings–saplings showed inhibitions at small scales,with the degree of inhibition gradually decreasing.Spatial patterns and associations of adults–adults did not change signifi-cantly.The results revealed that intraspecifi c interactions and environmental heterogeneity regulated the spatial patterns of P.crassifolia at small and large scales,respectively.Environmental heterogeneity might be the most decisive factor aff ecting the spatial patterns of saplings,while trees were more aff ected by intraspecifi c interactions.Moreover,competition between trees in this area could be more common than facilitation for the growth and development of individuals.

Canopy gap characteristics and spatial patterns in a subtropical forest of South China after ice storm damage

The divergent gap characteristics and spatial patterns of canopy gaps created by natural or artificial disturbances can exert a dominant influence on forest structure and composition.However,little research has been conducted on the effects of ice storm damage on canopy gaps in subtropical mature forests of South China.In this study,one semi-natural site was dominated by a broad-leaf forest and two managed sites were representative of plantations with coniferous forests.Based on airborne laser scanning data and field evidence across sites,statistical analyses were used to examine gap characteristics following ice storms of moderate severity.Generalized Ripley’s K-function analysis was applied to test gap spatial patterns at a range of scales,and spatial point pattern analysis was used to quantitate the relative importance of specific influences on patterns of gap occurrence.The results revealed that the average gap size was 75.7 m^2 and that 12.2 gaps occurred per hectare.Most gaps were single-tree fall events.In addition to more gaps,the mean gap size was smaller and the shape was more complex in the semi-natural site than in two managed sites.Large differences in gap characteristics were observed among snapped,uprooted,snag,and artificial gap damage types.Gaps generally showed a clustered distribution at large scales(e.g.70 m),whereas spatial patterns varied with gap damage types at different sites.The occurrence of gaps was strongly related to slope and topographic position at the semi-natural site,whereas slope,stem density,and human accessibility(proximity to pathways)were the most important factors affecting gap occurrence at the managed sites.We suggest that gap-based silvicultural treatments and natural disturbances regimes conjoin,highlighting interactions with other factors such as microsite conditions,non-tree vegetation and more.

Spatio-temporal point pattern analysis on Wenchuan strong earthquake

For exploring the aftershock occurrence process of the 2008 Wenchuan strong earthquake, the spatio-temporal point pattern analysis method is employed to study the sequences of aflershocks with magnitude M≥4.0, M≥4.5, and M≥5.0. It is found that these data exhibit the spatio-temporal clustering on a certain distance scale and on a certain time scale. In particular, the space-time interaction obviously strengthens when the distance is less than 60 km and the time is less than 260 h for the first two aftershock sequences; however, it becomes strong when the distance scale is less than 80 km and the time scale is less than 150 h for the last aftershock sequence. The completely spatial randomness analysis on the data regardless of time component shows that the spatial clustering of the aftershocks gradually strengthens on the condition that the distance is less than 60 km. The results are valuable for exploring the occurrence rules of the Wenchuan strong earthquake and for predicting the aftershocks.

Spatial pattern analysis and associations of different growth stages of populations of Abies georgei var.smithii in Southeast Tibet,China

Abies georgei var.smithii is an important plant species in Southeast Tibet,China.It has high ecological value in terms of biodiversity protection,as well as soil and water conservation.We analyzed the spatial pattern and associations of A.georgei var.smithii populations at different growth stages by using Ripley's L function for point pattern analysis.The diameter structure was a nearly reverse 'J' shape.The amount of saplings and medium-sized trees accounts for a large part of the entire population,suggesting a high regeneration rate and an expanding population.In the transition from saplings to medium trees or to large trees,saplings show a significant aggregation distribution at small scales,while medium trees and large trees show a random distribution.There are significant inverse associations between saplings and medium trees and large trees at small scales,while there are no obvious associations between medium trees and large trees.The natural regeneration was affected by interspecific competition,and it was also affected by intraspecific competition.The joint effects of biological characteristics and environmental factors contribute to the spatial distribution pattern and associations of this A.georgei var.sm ithii population.

Population structure and spatial pattern analysis of Quercus aquifolioides on Sejila Mountain,Tibet,China

Understanding population structure provides basic ecological data related to species and ecosystems.Our objective was to understand the mechanisms involved in the maintenance of Quercus aquifolioides populations.Using a 1 ha permanent sample plot data for Q.aquifolioides on Sejila Mountain,Tibet Autonomous Region(Tibet),China,we analyzed the population structure of Q.aquifolioides by combining data for diameter class,static life table and survival curve.Simultaneously,the spatial distribution of Q.aquifolioides was studied using Ripley’s L Function in point pattern analysis.The results showed:(1) Individuals in Q.aquifolioides populations were mainly aggregated in the youngest age classes,that accounted for94.3% of the individuals; the older age classes had much smaller populations.Although the youngest age classes(ClassesⅠ and Ⅱ) had fewer individuals than Class Ⅲ,the total number of individuals in classes Ⅰ and Ⅱ was also greater than in classes Ⅳ to Ⅸ.In terms of tree height,fewsaplings,more medium-sized saplings and few large-sized trees were found.The diameter class structure of Q.aquifolioides populations formed an atypical ‘pyramid’type; the population was expanding,but growth was limited,tending toward a stable population.(2) Mortality of Q.aquifolioides increased continuously with age; life expectancy decreased over time,and the survivorship curve was close to a Deevey I curve.(3) The spatial distribution pattern of Q.aquifolioides varied widely across different developmental stages.Saplings and medium-sized tree showed aggregated distributions at the scales of 0–33 m and 0–29 m,respectively.The aggregation intensities of saplings and medium-sized trees at small scales were significantly stronger than that of large-sized trees.However,large-sized trees showed a random distribution at most scales.(4) No correlation was observed among saplings,medium-and large-sized trees at small scales,while a significant and negative association was observed as the scale increased.Strong competition was found among saplings,medium-and large-sized trees,while no significant association was observed between medium-and largesized trees at all scales.Biotic interactions and local ecological characteristics influenced the spatial distribution pattern of Q.aquifolioides populations most strongly.

The Spatial Patterns of Road Traffic Crash Black Spots and Emergency Facilities in Federal Capital City

This study aimed at determining the spatial patterns of Road Traffic Crash (RTC) black spots, Federal Road Safety Commission (FRSC) zebra points and emergency health care facilities in Federal Capital City (FCC). The aim was to provide stakeholders with information that will aid their understanding of accident prone locations and accessible rescue possibilities for accident victims on the roads in FCT. GPS Map 76S Mark (GARMIN) was used to locate and pick coordinates of data in the study area. A total of 16 possible emergency health care facilities, seventy (70) RTC black spots and Five Zebra point locations were obtained from FRSC. ArcGIS 10.0 was used to compute the data by plotting the coordinates to produce maps of the spatial relationship and to carry out Nearest Neighbour Analysis (NNA). The result was further used to determine the spatial patterns of RTC black spots as well as patterns of the emergency facilities. Generally, the result shows that the spatial trend is turning towards dispersion. However, there is less than 1% likelihood that the dispersed patterns could be the result of random chance. It was recommended that, the Federal Road Safety Commission should be staffed with trained professionals that can be responsible for accident data surveillance and analysis using geospatial techniques.

Spatiotemporal patterns of non-point source nitrogen loss in an agricultural catchment

Non-point source nitrogen loss poses a risk to sustainable aquatic ecosystems. However, non-point sources, as well as impaired river segments with high nitrogen concentrations, are difficult to monitor and regulate because of their diffusive nature, budget constraints, and resource deficiencies. For the purpose of catchment management, the Bayesian maximum entropy approach and spatial regression models have been used to explore the spatiotemporal patterns of non-point source nitrogen loss. In this study, a total of 18 sampling sites were selected along the river network in the Hujiashan Catchment. Over the time period of 2008e2012, water samples were collected 116 times at each site and analyzed for non-point source nitrogen loss. The morphometric variables and soil drainage of different land cover types were studied and considered potential factors affecting nitrogen loss. The results revealed that, compared with the approach using the Euclidean distance, the Bayesian maximum entropy approach using the river distance led to an appreciable 10.1% reduction in the estimation error, and more than 53.3% and 44.7% of the river network in the dry and wet seasons, respectively, had a probability of non-point source nitrogen impairment. The proportion of the impaired river segments exhibited an overall decreasing trend in the study catchment from 2008 to 2012, and the reduction in the wet seasons was greater than that in the dry seasons. High nitrogen concentrations were primarily found in the downstream reaches and river segments close to the residential lands. Croplands and residential lands were the dominant factors affecting non-point source nitrogen loss, and explained up to 70.7%of total nitrogen in the dry seasons and 54.7% in the wet seasons. A thorough understanding of the location of impaired river segments and the dominant factors affecting total nitrogen concentration would have considerable importance for catchment management.

Spatial distributions of tropical tree species in northern Vietnam under environmentally variable site conditions

Ecological interactions of species and thus their spatial pat- terns may differ between homogeneous and heterogeneous forests. To account for this, techniques of point pattern analysis were implemented on mapped locations of tree individuals from two 1-ha tropicalforest plots in Vietnam. We analyzed the effect of environmental heterogeneity on tree distributions; spatial distribution patterns of dominant species; inter-specific associations; and conspecific associations between life stages. Our analyses showed that： environmental conditions were homo- geneous at plot 1 but heterogeneous at plot 2; in both plots, all six domi- nant species were aggregated at various scales up to 30 m, and tree spe- cies were aggregated at larger scales in the homogeneous site than in the heterogeneous site; attraction between pairs of species was remarkably higher at the homogeneous site while negative associations were more frequent in the heterogeneous site; some species, H. kurzii, T. ilicifolia （homogeneous plot） and D. sylvatica, S. wightianum （heterogeneous plot） showed a lack of early life-stage individuals near conspecific adults. Moreover, additional clustering of young individuals was independent from conspecific adults, except D. sylvatica in both sites. These findings are consistent with the Janzen-ConneU hypothesis. Overall, habitat het- erogeneity influences spatial patterns and inter-specific associations of the tree species and evidences of self-thinning are shown in most species.

Statistical functions used for spatial modelling due to assessment of landslide distribution and landscape-interaction factors in Iran

Landslides influence the capacity for safe and sustainable development of mountainous environments.This study explores the spatial distribution of and the interactions between landslides that are mapped using global positioning system(GPS) and extensive field surveys in Mazandaran Province,Iran.Point-pattern assessment is undertaken using several univariate summary statistical functions,including pair correlation,spherical-contact distribution,nearest-neighbor analysis,and O-ring analysis,as well as bivariate summary statistics,and a markcorrelation function.The maximum entropy method was applied to prioritize the factors controlling the incidence of landslides and the landslides susceptibility map.The validation processes were considered for separated 30%data applying the ROC curves,fourfold plot,and Cohen’s kappa index.The results show that pair correlation and O-ring analyses satisfactorily predicted landslides at scales from 1 to 150 m.At smaller scales,from 150 to 400 m,landslides were randomly distributed.The nearest-neighbor distribution function show that the highest distance to the nearest landslide occurred in the 355 m.The spherical-contact distribution revealed that the patterns were random up to a spatial scale of 80 m.The bivariate correlation functions revealed that landslides were positively linked to several linear features(including faults,roads,and rivers) at all spatial scales.The mark-correlation function showed that aggregated fields of landslides were positively correlated with measures of land use,lithology,drainage density,plan curvature,and aspect,when the numbers of landslides in the groups were greater than the overall average aggregation.The results of analysis of factor importance have showed that elevation(topography map scale:1:25,000),distance to roads,and distance to rivers are the most important factors in the occurrence of landslides.The susceptibility model of landslides indicates an excellent accuracy,i.e.,the AUC value of landslides was 0.860.The susceptibility map of landslides analyzed has shown that 35% of the area is low susceptible to landslides.

上海数字文化产业空间集聚特征及空间分异格局研究

基于上海数字文化产业兴趣点(POI)数据,运用ArcGIS软件,结合核密度分析、空间自相关分析、标准差椭圆分析等方法,分析上海数字文化产业空间集聚特征与空间分异格局,探讨上海数字文化产业空间分异的影响因素及其交互机制。研究发现:(1)上海数字文化产业总体集聚水平较高,区域集聚程度差异化明显;(2)上海数字文化产业在空间上呈非随机性分布,具有明显的空间自相关性,由南向北呈现出阶梯式分异格局;(3)上海数字文化产业门类集聚程度存在差异,其中应用软件开发类集聚程度最高,创意内容制造服务类类集聚程度最低。

不同空间尺度的内蒙古森林火点及面积分布格局研究

通过选用空间变异性分析(变异系数)、全局空间自相关分析、热点分析和尺度方差分析等方法,研究1981—2020年内蒙古森林火点及面积在盟市和旗县2个空间尺度上分布的变异性、关联性及尺度效应。结果表明:盟市尺度林火面积变异系数总体呈上升趋势;旗县尺度林火面积变异系数总体呈下降趋势,旗县尺度空间变异性更大。40 a全局森林火点Moran's I指数为0.99,双空间尺度Moran's I指数均呈下降趋势。其中,盟市级别最大值在1991—1995年,为0.46;旗县级别最大值在1986—1990年,为0.61。双尺度森林火点在空间上均呈现高度聚集性。旗县级尺度更显著地展示了森林火灾的空间分布差异及较小区域的森林火灾热点类型;盟市级尺度揭示了森林火灾的总体空间分布规律,热点类型明显缺乏多样性。盟市尺度热点区主要分布在呼伦贝尔市、兴安盟,冷点区不明显。旗县尺度均存在热点聚集区,林火发生水平较高。不同空间尺度的尺度方差表现为旗县>盟市,旗县级尺度林火面积差异对全内蒙古自治区的总体差异贡献率远超过盟市尺度。1981—2020年林火面积在双空间尺度呈现一定的分布规律,火点空间聚集性呈减弱趋势,森林火点与林火面积之间不完全呈正相关关系。内蒙古东部地区由于自然因素和人为因素造成火灾发生次数高于中西部,相关部门应继续加大防火力度。随着尺度的减小,林火空间分布模式愈加明显、聚集度增强,未来需进一步缩小研究范围。

基于Voronoi图的空间点事件统计聚类方法

挖掘地理空间数据中点事件聚集模式对于揭示流行疾病、犯罪分布热点区域及城市基础设施空间分布格局等具有重要意义。针对不同形状、密度和大小的显著空间点聚集模式的识别,目前以空间扫描统计为代表的方法虽然可以对空间点聚类的显著性进行统计推断,减少虚假聚类结果,但其主要用于识别球形或椭圆形状的聚簇,对于沿着街道或河道分布的任意形状、不同密度的显著空间点聚簇识别还存在局限。因此,本研究提出一种基于Voronoi图的空间点聚集模式统计挖掘方法。首先,采用Voronoi图来度量空间点分布的聚集性,将空间点聚类问题转化为热点区域探测问题;其次,结合局部Gi*统计量探测统计上显著的空间点聚簇;最后,通过模拟数据和真实犯罪事件数据进行实验与对比分析。结果表明:本方法能够有效探测任意形状的空间点聚类,并对空间点簇的显著性进行统计判别,识别显著的空间点簇,减少随机噪声点的干扰;聚类识别结果优于现有代表性方法,如DBSCAN算法、空间扫描统计方法等。

城市休闲产业聚类模式APM算法模型开发与校验

城市休闲相关产业的高质量发展对当前我国城市消费升级以及人居环境质量提升具有重要现实意义。但是,现有研究未能精准地捕捉海量广域分布的城市休闲产业的基本空间分布规律与结构,而已有的空间聚类算法较多适用于城市用地分析,未能很好地适用于离散分布的城市休闲产业研究。为此,文章基于空间兴趣点数据,开发距离通达值及空间集群中心点等算法,构建城市休闲旅游产业聚类模式空间算法模型(APM)。在以广州为例的研究中,APM模型捕捉出3170个以500 m步行生活圈为范围的城市休闲产业集群,校验了APM模型的科学性与应用价值。整体上,APM算法可以较好地捕捉城市休闲业态集群的空间结构,清晰识别城市休闲产业空间冷、热点分布的基本结构,由其捕捉行程的聚类边界与实际道路和建筑走向、水系边界、区域范围等重合度高,聚类集群符合实际情况,具备可信度与有效性。该研究是休闲产业集聚机制研究的一次方法创新,在算法精度、实际应用、可视化效率上均做出了创新性推进。与Fishnet方法相比,可以更科学精准地识别城市内部多个休闲消费商圈的边界,实现了高效率的城市休闲产业集群捕捉;与同位模型相比,可以呈现多类别的城市休闲业态结构,突破了现有研究只能捕捉两类业态组团的局限。

林窗对黄檗幼树空间分布及生长发育的影响

【目的】林窗增加了林分空间结构的复杂性和林下生境的异质性,对林下幼树的更新具有重要影响。黄檗是我国国家重点保护野生植物,研究黄檗幼树的生长状况、空间分布与林窗空间结构的关系,有助于了解其对林下生境的适应性,对促进黄檗种群的更新具有重要意义。【方法】本文以2014年在北京百花山自然保护区内林下栽种的黄檗幼树为研究对象,于2021年对黄檗的生长及存活状况进行了调查,并使用背包式激光雷达获取了样地的林窗空间结构数据。采用空间点格局、生境关联性检验和方差分析等方法研究了林窗对黄檗幼树空间分布及生长状况的影响。【结果】(1)自然生长条件下,7年后黄檗幼树存活率为19.25%,在排除扩散限制后,存活黄檗幼树的空间分布表现为聚集分布。(2)林窗空间结构是黄檗幼树空间分布格局形成的重要原因,黄檗幼树分布与林窗边缘呈显著正关联,而与林冠区呈显著负关联。(3)黄檗幼树的基径在林窗边缘显著高于林冠区和林窗中心(P<0.01),在林冠区与林窗中心之间没有显著差异;黄檗幼树的冠幅和树高则呈现显著的梯度变化(P<0.05),即林窗边缘>林冠区>林窗中心。【结论】研究表明林窗对黄檗幼树的空间分布格局和生长状况具有重要的影响。林窗边缘的生境条件更有利于黄檗幼树的存活和生长,而林窗中心和林冠区则会对黄檗幼树的生长发育产生一定的抑制作用。

荒漠草原蒙古冰草种群分布格局及种内关联性

空间格局是植物种群受生物和非生物因素影响综合形成的结果。为了解荒漠草原蒙古冰草种群空间分布格局对外部环境变化的适应策略,分别在宁夏盐池县大水坑镇、青山乡、花马池镇和高沙窝镇选取以蒙古冰草为优势种的群落为研究样地(分别以D、Q、H和G样地表示),在每个样地,将蒙古冰草个体按丛径划分为Ⅰ级(0─5cm)、Ⅱ级(5.1─10cm)、Ⅲ级(10.1─15cm)、Ⅳ级(>15cm)4个株丛级,并基于点格局分析探讨了蒙古冰草的株丛结构、空间分布格局及种内关联。结果表明:(1)4个研究样地蒙古冰草和牛枝子的重要值、生态位宽度均较大,其间生态位重叠指数较高,其他物种的重要值及生态位特征值在不同样地之间变异较大。(2)蒙古冰草的株丛密度和平均丛径在不同样地之间均存在显著差异(P<0.05)。在Q、G和H样地中,蒙古冰草以Ⅰ级株丛为主;在D样地中,蒙古冰草以Ⅱ级株丛占比最高,为43.98%,株丛密度较小。(3)在本研究尺度范围内,蒙古冰草种群在Q和G样地中主要呈聚集分布,在D和H样地中表现为聚集和随机交替分布。其中,各样地中Ⅰ级株丛在小尺度范围内主要呈聚集分布,Ⅱ级株丛随尺度的增大逐渐由聚集分布过渡到随机分布和均匀分布,Ⅲ、Ⅳ级株丛主要表现为随机分布。(4)在本研究尺度范围内,蒙古冰草Ⅰ级株丛分别与Ⅱ、Ⅲ、Ⅳ级株丛呈负关联或无关联;Ⅱ、Ⅲ、Ⅳ级各株丛级之间主要呈无关联。综上,随荒漠草原环境条件的变化,蒙古冰草可以通过调节种群结构、密度及整体分布格局以维持种群的更新和稳定。

雅鲁藏布江巨柏种群分布格局及其对环境变化的响应

利用点格局分析、相关分析、逐步回归的方法研究巨柏(Cupressus gigantea)种群的空间分布格局,分析不同尺度上巨柏种群分布格局的差异及其影响因子.结果表明巨柏种群的空间分布格局总体上以随机分布或集群分布为主,随着海拔、土壤养分、土壤质地等条件变化而变化.半阴坡低海拔种群分布格局在0.9~10.0 m尺度呈随机分布(P<0.05),在其他尺度呈集群或随机分布;中等海拔种群在2.8~10.0 m尺度呈集群分布(P<0.05),在其他尺度呈随机分布.阳坡低海拔种群在0.6~10.0 m尺度呈集群分布(P<0.05),在其他尺度呈随机分布.阴坡低海拔种群在0~10.0 m尺度均呈随机分布(P<0.05).半阳坡中等海拔种群在0~10.0 m尺度上均呈随机分布(P<0.05).尺度<5.0 m时,随着海拔梯度的升高,巨柏种群的聚集程度逐渐减弱;尺度>5.0 m时,海拔对巨柏种群分布的影响逐渐降低,土壤养分、土壤质地等因素的影响逐渐占据主导地位.不同尺度上巨柏种群分布格局受多种环境因子的影响,海拔和地形改变导致的小环境变化会显著影响巨柏种群的分布格局.在未来的巨柏保护中,应综合考虑环境因子的影响.

胜山阔叶红松林粗木质残体空间分布格局

为探究胜山阔叶红松(Pinus koraiensis)林粗木质残体(Coarse woody debris,CWD)的形成过程及机制,采用点格局分析法对10.4 hm^(2)大型样地内不同分类的CWD的空间格局、空间关联性进行了研究。结果表明:(1)总CWD在0—7 m尺度聚集分布,7—50 m尺度随机分布。(2)腐烂等级5级CWD、倒木、伐根在所有尺度随机分布;其他CWD随尺度增大由聚集分布转为随机分布,但格局尺度不同(在2—10 m之间)。(3)大、中径级与小径级CWD在0—4 m、0—6 m尺度正相关;高腐烂等级与低腐烂等级CWD在0—5 m尺度以内正相关;枯立木与倒木在0—4 m尺度正相关;落叶松(Larix gmelinii)CWD与小径级、腐烂等级2级的红皮云杉(Picea koraiensis)CWD在0—3 m尺度正相关,与中径级、腐烂等级1、2级在13—16 m尺度负相关。胜山阔叶红松林CWD的形成是由树种特性、小尺度的个体竞争、大尺度的自然衰老、外界干扰、生境异质性等共同决定的;大、中径级对小径级CWD、先形成对后形成CWD、枯立木对倒木具有一定的正向影响,落叶松对红皮云杉CWD在小尺度有正向影响,而在稍大尺度有负面影响;在一定程度上揭示了该林型CWD的形成过程和机制。

不同间伐强度对华北落叶松人工林天然更新的影响

研究塞罕坝30年生华北落叶松(Larix principis-rupprechtii)人工林抚育间伐强度对天然更新空间点格局及种间关联性的影响规律,对于塞罕坝人工林空间结构调整和天然更新保护具有重要意义。以塞罕坝地区华北落叶松人工纯林为研究对象,设置高(60%~65%)、中(45%~50%)、低(35%~40%)3种间伐强度及对照固定样地各3块,每块样地面积均为900 m^(2),间伐前平均密度为2611株/hm^(2)。运用g(r)和g_(12)(r)函数,研究不同间伐强度下天然更新个体特征变化、主林层大树与天然更新格局及种间关联性变化。其中,林下乔木更新物种数在不同间伐强度之间没有显著差异,中度间伐强度的平均高度、平均基径和平均冠幅均为最大值,分别达到了52.68、5.18 cm和34.49 cm,只有平均密度在中间伐强度下为最小值,为93株/hm^(2)。主林层空间点格局以随机分布为主;天然更新空间点格局以聚集分布为主;天然更新和主林层种间关联性以不相关为主。研究结果表明,中等间伐强度(45%~50%)有利于调整塞罕坝地区华北落叶松人工纯林空间结构和保护天然更新。