Drivers of spatial structure in thinned forests

Background:As is widely known,an increasing number of forest areas were managed to preserve and enhance the health of forest ecosystems.However,previous research on forest management has often overlooked the importance of structure-based.Aims:Our objectives were to define the direction of structure-based forest management.Subsequently,we investigated the relationships between forest structure and the regeneration,growth,and mortality of trees under different thinning treatments.Ultimately,the drivers of forest structural change were explored.Methods:On the basis of 92 sites selected from northeastern China,with different recovery time (from 1 to 15years) and different thinning intensities (0–59.9%) since the last thinning.Principal component analysis (PCA)identified relationships among factors determining forest spatial structure.The structural equation model (SEM)was used to analyze the driving factors behind the changes in forest spatial structure after thinning.Results:Light thinning (0–20%trees removed) promoted forest regeneration,and heavy thinning (over 35% of trees removed) facilitated forest growth.However,only moderate thinning (20%–35%trees removed) created a reasonable spatial structure.While dead trees were clustered,and they were hardly affected by thinning intensity.Additionally,thinning intensity,recovery time,and altitude indirectly improve the spatial structure of the forest by influencing diameter at breast height (DBH) and canopy area.Conclusion:Creating larger DBH and canopy area through thinning will promote the formation of complex forest structures,which cultivates healthy and stable forests.

A novel model to evaluate spatial structure in thinned conifer-broadleaved mixed natural forests

In order to ensure the effective analysis and reconstruction of forests,it is key to ensure the quantitative description of their spatial structure.In this paper,a distance model for the optimal stand spatial structure based on weighted Voronoi diagrams is proposed.In particular,we provide a novel methodological model for the comprehensive evaluation of the spatial structure of forest stands in natural mixed conifer-broadleaved forests and the formulation of management decision plans.The applicability of the rank evaluation and the optimal solution distance model are compared and assessed for different standard sample plots of natural mixed conifer-broadleaved forests.The effect of crown width on the spatial structure unit of the trees is observed to be higher than that of the diameter at breast height.Moreover,the influence of crown length is greater than that of tree height.There are nine possible spatial structure units determined by the weighted Voronoi diagram for the number of neighboring trees in the central tree,with an average intersection of neighboring crowns reaching 80%.The rank rating of natural forest sample plots is correlated with the optimal solution distance model,and their results are generally consistent for natural forests.However,the rank rating is not able to provide a quantitative assessment.The optimal solution distance model is observed to be more comprehensive than traditional methods for the evaluation of the spatial structure of forest stands.It can effectively reflect the trends in realistic stand spatial structure factors close to or far from the ideal structure point,and accurately assesses the forest spatial structure.The proposed optimal solution distance model improves the integrated evaluation of the spatial structure of forest stands and provides solid theoretical and technical support for sustainable forest management.

Spatial pattern and compositive structure of forests in Guizhou

Remote-sensing and field data of Guizhou forest resources in 2000 are processed using ArcGIS, with the production of forest resource distribution map, forest age class structure map, and forest canopy distribution map. Analysis of these data shows that: (1) though there are multiple types of forest resources, forest coverage is low (only 25.27%, excluding sparse woodland, shrub and underage-forest); (2) the geographical distribution of forests is quite uneven, mainly in the southeast of the province and in Zunyi prefecture; (3) the zonal evergreen broad-leaved forests have been seriously destroyed, with striking secondary features, i.e., coniferous forest and shrubbery account for the greatest proportion of Guizhou forests; (4) the timber-forest is much larger in area than shelter-forest and economic forest; (5) young-and-middle aged forests are more widely distributed than near-and-over matured forest; and (6) the forest of Guizhou is not enough to effectively protect the environment of karst mountain areas of the province.

AGE STRUCTURE AND SPATIAL PATTERN OF OLD-GROWTH KOREAN PINE FOREST IN XIAOXING'ANLING MOUNTAIN

Spatial pattern of trees, basal stem increment and height were examined in a 5.0 ha mixed deciduous/ Pinus koraiensis forest from October in 1984 to May in 1987. Conclusions arc as following: 1. Analysis of the age-structure of the korcan pine forest shows that it is different from general steady-state forest type. The lack of saplings and individuals in small-diameter class clearly indicates that regeneration is not continuous. Continuous regeneration depends on thinning of the canopy to form a gap. Similar-aged korcan pine seedings grow in these gaps. 2. The horizontal structure of the korcan pine is a mosaic of more or less even-aged groups of trees. The mosaic is a result of korcan pine by regeneration strategy. The aggregations of korcan pine of different ages overlaps to form a continuous population generation. As a results, the population is maintained in steady state.

Structure and regeneration dynamics of three forest types at different succession stages of spruce – fir mixed forest in Changbai Mountain, northeastern China

Analyzing and understanding the structure and growth dynamics of forests at different stages is helpful to promote forest succession, restoration and management. Three spots representing three succession stages of spruce-fir mixed forest(SF: polar-birch secondary forest, MF: spruce-fir mixed forest and PF: spruce-fir near primary forest) were established. Structure, growth dynamics during two growth seasons for dominant tree species, regeneration were examined, and a univariate O-ring function statistic was used to analyze the spatial patterns of main regeneration tree species. Results showed that,(1) composition of tree species, periodic annual increment(PAI) of the diameter at breast height(DBH), basal area for overstory trees and of ground diameter(DGH) for saplings, were significantly different with the succession;(2) the current species composition and regeneration dynamics of SF suggested a development towards spruce-fir mixed forests. Pioneer species like Betula platyphyllaa will gradually disappear while climax species, such as Abies nephrolepis, Pinus koraiensis, Picea koraiensis and Tilia amurensis will dominate forest stands;(3) Despite the highest volume occurring in PF, and saplings in it grew better than in the others, this forest type is unstable because of its unsustainable structure of DBH class and insufficient regeneration; and(4) MF had the most reasonable distribution of DBH class for adult trees(DBH > 5.0 cm) and DGH class for saplings(H ≥30 cm and DBH ≤5 cm), as well as an optimal volume increment. Limiting canopy opening size can lessen the physiological stress and promote the growth and competitive status of regeneration. Management implications for increasing the gaps and thus creating better growth conditions for understory saplings and facilitating forest succession were discussed.

Small-area estimation of forest stand structure in Jalisco, Mexico

Natural resource statistics are often unavailable for small ecological or economic regions and policymakers have to rely on state-level datasets to evaluate the status of their resources （i.e., forests, rangelands, grasslands, agriculture, etc.） at the regional or local level. These resources can be evaluated using small-area estimation techniques. However, it is unknown which small area technique produces the most valid and precise results. The reliability and accuracy of two methods, synthetic and regression estimators, used in smallarea analyses, were examined in this study. The two small-area analysis methods were applied to data from Jalisco＇s state-wide natural resource inventory to examine how well each technique predicted selected characteristics of forest stand structure. The regression method produced the most valid and precise estimates of forest stand characteristics at multiple geographical scales. Therefore, state and local resource managers should utilize the regression method unless appropriate auxiliary information is not available.

Characterizing stand structure in a spruce forests:effects of sampling protocols

Spatial heterogeneity is an inherent characteristic of natural forest landscapes, therefore estimation of structural variability, including the collection and analyzing of field measurements, is a growing challenge for monitoring wildlife habitat di- versity and ecosystem sustainability. In this study, we investigated the combined influence of plot shape and size on the accuracy of assessment of conventional and rare structural features in two young-growth spruce-dominated forests in northwestern China. We used a series of inventory schemes and analytical approaches. Our data showed that options for sampling protocols, especially the selection of plot size considered in structural attributes measurement, dramatically af- fect the minimum number of plots required to meet a certain accuracy criteria. The degree of influence of plot shape is related to survey objectives; thus, effects of plot shape differ for evaluations of the ＂mean＂ or ＂representative＂ stand structural conditions from that for the range of habitat （in extreme values）. Results of Monte Carlo simulations suggested that plot sizes 〈0.1 ha could be the most efficient way to sample for conventional characteristics （features with relative constancy within a site, such as stem density）. Also, 0.25 ha or even larger plots may have a greater likelihood of capturing rare structural attributes （features possessing high randomness and spatial heterogeneity, such as volume of coarse woody debris） in our forest type. These findings have important implications for advisable sampling protocol （plot size and shape） to adequately capture information on forest habitat structure and diversity; such efforts must be based on a clear definition of which types are structural attributes to measure.

Spatial-temporal variability of throughfall in a subtropical deciduous forest from the hilly regions of eastern China

Throughfall variability plays a crucial role in regulating hydrological and biogeochemical processes in forest ecosystems. However, throughfall variability and its potential influencing factors remain unclear in the subtropical deciduous forest because of its complex canopy and meteorological conditions. Here, the spatial variability and temporal stability of throughfall were investigated from October 2016 to December 2017 within a deciduous forest in the subtropical hilly regions of eastern China, and the effects of meteorological variables and distance from nearest tree trunk on throughfall variability were systematically evaluated. Throughfall variability during the leafed period was slightly higher than that during the leafless period inferred from the coefficient of variation of throughfall amounts(CVTF), with 13.2%-40.9% and 18.7%-31.9%, respectively. The multiple regression model analysis suggested that the controlling factors of throughfall variability were different in studied periods: Maximum 10-min rainfall intensity, wind speed and air temperature were the dominant influencing factors on throughfall variability during the leafed period, with the relative contribution ratio(RCR) of 25.9%, 18.7% and 8.9%, respectively. By contrast, throughfall variability was affected mainly by the mean rainfall intensity(RCR=40.8%) during the leafless period. The temporal stability plots and geostatistical analysis indicated that spatial patterns of throughfall were stable and similar among rainfall events. Our findings highlight the important role of various meteorological factors in throughfall variability and are expected to contribute to the accurate assessment of throughfall, soil water and runoff within the subtropical forests.

Spatial distributions of intra-community tree species under topographically variable conditions

Growing public awareness of the importance of protecting biodiversity requires the development of forest practices that increase the complexity of stand structure.Understanding the ecological processes of different forest vegetation provide insights into community coexistence mechanisms.In this paper,the spatial patterns of three different communities,evergreen broadleaf forest,deciduous broadleaf forest,and mixed needleleaf and broadleaf forest at Mt.Huangshan,China,were quantified with four structural parameters,the mingling index,the uniform angle index,the diameter dominance index and the crowdedness index.All trees with a diameter at breast height of more than 5 cm were measured.Our analyses highlighted that most trees in the three communities were extremely dense and slightly clumped,with a moderate size differentiation and high mixed structure.In mixed needleleaf and broadleaf forest,the distribution pattern of tree species was better than the other two forests.Overall,spatial patterns in mixed needleleaf and broadleaf forest exhibited a strong stability-effect,that is,the stand had a suitable environment for the stable survival of the forest.With the increasing of elevation,the degree of the mingling index and the crowdedness index increased,however,there was no influence on the uniform angle index and the diameter dominance index.Further,at the same elevation,four structural parameters of shady slope were larger than that of sunny slope.Then we found the relationship between stand spatial structure and environment factors had important influence on forest structure.Our work contributes to the knowledge of population structure,and further provide theoretical basis for the sustainable development of forest resources and protecting biodiversity of Huangshan Mountain.In future studies,it is necessary to explore the limiting factors of community spatial distribution by combining species diversity and functional traits.

闽楠-木荷混交林空间结构及其养分利用

【目的】为探讨混交林中闽楠和木荷的种间关系,确定木荷能否作为闽楠的伴生树种营建健康高效的闽楠-木荷混交林。【方法】以金洞林场16年生的闽楠-木荷混交林以及闽楠纯林、木荷纯林为研究对象,通过分析闽楠-木荷混交林的根系分布特性与林分空间结构特性来探讨闽楠-木荷混交林地上与地下部分的种间关系;通过分析不同物候期下3种林分的闽楠与木荷叶片养分的动态规律来阐明闽楠与木荷之间的养分利用关系。【结果】1)在16年生闽楠-木荷混交林中,在闽楠周围1.5 m内闽楠和木荷的根系分布虽有部分重叠,但闽楠仍占据优势地位,闽楠和木荷在地下生长空间和养分吸收利用方面存在竞争但竞争不激烈;2)整体林分空间结构上,闽楠、木荷纯林略优于闽楠-木荷混交林,说明混交林的树种不同,树种之间的生长特性和生态特性不一样,林分的均一性会差一些,对其调整结构的难度要大于纯林。混交林中,木荷已对闽楠形成了一定的竞争优势;3)闽楠-木荷混交林中,对养分吸收利用在物候期上部分不同步,存在相对有利的互补关系;从所有的物候期来看,闽楠叶片的N、P、K含量在大部分时期都高于木荷,表明闽楠-木荷混交更有利于闽楠对养分的吸收利用,木荷对养分的需求更低;4)16年生混交林中闽楠、木荷的生长速度要优于相应的纯林,表明前期竞争促进了林分的生长。【结论】闽楠与木荷混交有利于闽楠获得更多的养分,适度竞争促进了林木的生长,木荷是闽楠较好的伴生树种。

黔中地区马尾松-甜槠针阔混交林群落结构特征与林木空间分布格局及其关联性

为探究黔中地区天然次生马尾松针阔混交林群落结构及其空间分布格局特征,选取典型的马尾松-甜槠针阔混交林和马尾松纯林为调查对象,采用成对相关函数分析环境异质性对主要树种空间分布的影响、主要树种及径级空间格局和空间关联性研究。调查共记录91种植物,其中马尾松-甜槠针阔混交林和马尾松纯林分别为42种和68种。2个森林群落中乔木总径级整体均呈倒“J”形结构,结构稳定,自然更新良好。结果表明,生境异质性对2种群落类型在小距离上空间分布格局的影响作用明显。2块样地幼树、中树及总体分布格局相似,均为点距离在0~10 m内呈聚集分布、在10~25 m内呈随机分布,而大树在整个观察尺度内均为随机分布。马尾松纯林中马尾松-甜槠、甜槠-槲栎的空间关联性均以不相关为主,马尾松-槲栎以负相关为主;而马尾松-甜槠针阔混交林中马尾松与甜槠在10~20 m以负相关为主。2种群落类型不同径级的空间关联性总体为不相关。黔中山地天然次生马尾松-甜槠针阔混交林、马尾松纯林群落结构存在差异,环境异质性、径级结构和空间尺度对两者空间分布格局及其关联性影响明显。

杉木萌芽林结构多样性研究

[目的]多角度分析杉木萌芽林的结构特征,为优化调整林分结构,精准提升杉木萌芽林林分质量提供依据。[方法]以亚热带林业实验中心的山下林场杉木萌芽林为对象,采用3参数Weibull分布拟合直径分布,用林分空间结构量化分析方法分析林分空间结构参数一元和二元分布特征、树种优势度及林分结构多样性,并用遗传绝对距离法进行差异显著性检验。[结果]3个林分的树种组成均为以杉木萌生株为主,混有少量阔叶树,其Shannon-Winner指数在0.933~1.039之间,Simpson多样性指数都小于0.5,说明树种多样性较低;林分直径分布呈现左偏单峰山状曲线,有向倒“J”型发展的趋势;三板桥、七里坑上坡和下坡林分的平均角尺度分别为0.503、0.486和0.500,均属于随机分布的范畴,林分平均混交度分别为0.345、0.404和0.409,林分整体上处于弱度混交向中度混交过渡的状态;3个林分的结构多样性指数值较低,分别为1.423、1.349和1.649,角尺度-混交度、大小比数-角尺度二元分布表现出一定的规律性,但混交度-大小比数二元分布变化相对复杂,规律不明显。[结论]杉木萌芽林树种组成相对简单,树种多样性和林分结构多样性低,胸高直径分布和林木分布格局初步具有天然林的特征,需要通过林分结构优化调整提升林分质量。

栎类次生林自稀疏条件下的林分空间结构单元划分方法

【目的】划分栎类次生林自稀疏结构单元,是应用林分自稀疏发生规律开展栎类次生林经营的基础性工作。【方法】以湖南省2009年和2014年两期森林资源连续清查数据中6块栎类次生林样地为数据源,使用3种林分空间结构单元划分方法,分别得到若干个结构单元,计算各结构单元内林木的株数密度和平均胸径,建立Reineke密度指数模型,比较模型的拟合效果和检验效果。【结果】方法1、方法2和方法3所得样本拟合的自稀疏边界线R^(2)分别为0.882、0.780、0.893;RMSE分别为0.180、0.229、0.169;方法3的拟合效果最好。3种方法的检验结果中,方法3对自稀疏判断的正确率为72%,检验效果较好;其余2种方法均低于50%。【结论】3种结构单元划分方法中,方法1忽略了距离死亡木较远的样木;方法2没有考虑位置不同的样木对死亡木影响的差异;方法3(Voronoi图+样圆权重法)更为完整地统计了对自稀疏有影响的样木,并区分为Ⅰ类样木和Ⅱ类样木,分别计算权重,分析其对死亡木影响的差异。方法3是一种考虑了林木空间分布差异,同时还依据对死亡木影响大小区分样木类别的林分空间结构单元划分方法。

十万大山山地常绿阔叶林群落物种组成与结构特征

十万大山是广西生物多样性热点区域之一,其主要植被类型是山地常绿阔叶林。为了解区域内山地常绿阔叶林的群落现状及优势种群结构的发展现状,该文以十万大山山地常绿阔叶林1 hm^(2)固定监测样地中胸径(DBH)≥1 cm的木本植物为研究对象,分析其物种组成、径级结构、树高结构并用g(r)函数分析优势种的空间分布格局。结果表明:(1)群落中DBH≥1 cm的木本植物共计7517株,隶属52科108属153种;群落的优势种有云南桤叶树(Clethra delavayi)、银木荷(Schima argentea)、毛折柄茶(Hartia villosa)、红锥(Castanopsis hystrix)、黄杞(Engelhardtia roxburghiana)、罗伞树(Ardisia quinquegona)、鼠刺(Itea chinensis)、腺叶山矾(Symplocos adenophylla)、假杨桐(Eurya subintegra)、毛冬青(Ilex pubescens),但优势种的优势地位不明显。(2)群落整体平均DBH为5.51 cm,径级、树高分布呈近似倒“J”型;优势种的径级分布多呈倒“J”型或“L”型,群落有较强的更新能力。(3)群落优势种稳定共存;优势种在样地中呈聚集分布,但优势种间聚集分布的位置有差异。总体而言,群落目前更新状态良好,群落中已有顶极群落优势种的存在,但群落具有一定的次生性特征,还未到达稳定的顶极群落状态,优势种间能稳定共存,有向稳定顶极群落演替的潜力,应继续加强管护,促进十万大山山地常绿阔叶林群落的更新与生存。

小兴安岭阔叶红松林次生演替不同阶段空间结构特征研究

选取小兴安岭凉水自然保护区内阔叶红松林次生演替序列中的天然枫桦次生林、次生阔叶林、次生针阔混交林以及原始阔叶红松林为研究对象,采用空间结构参数(角尺度、大小比数、混交度)的一元和二元分布,分析林木的空间结构特征。结果表明:一元二元分布中,林分角尺度均呈现相对正态分布,在W=0.5时频率最高,4个阶段的平均角尺度分别为0.577、0.557、0.634、0.589,均以轻度聚集分布为主;并随着演替进行,聚集趋势上升,到原始阔叶红松林后聚集程度又下降;4个演替阶段林木之间呈现混交状态为极强混交,强度和极强度混交的比例依次为69.94%、70.08%、65.56%、63.64%,混交林木的比例随着演替序列呈现先上升后下降的趋势。从不同演替阶段的优势种空间分布来看,前5位优势树种呈集聚分布,树种混交程度都较高,但阳性先锋树种和耐阴树种林木的大小分化差异较大。可见,阔叶红松林4个演替阶段的变化说明演替前期林木的角尺度和混交度较大,后期尤其是原始阔叶红松林中聚集程度降低,随机分布比例上升,有利于群落长久稳定发展。

城市三维空间结构对碳排放影响的尺度效应

城市是碳排放最集中的区域,全面厘清城市空间结构对碳排放的影响对碳减排规划具有重要意义。以往研究主要关注城市二维结构与碳排放的关系,表明城市扩张是碳排放剧增的主要原因。虽然城市三维空间结构也会显著影响碳排放,然而其影响的尺度效应依然缺少深入分析。为此以广州市为例,结合相关性分析、随机森林探究三维空间结构与碳排放的关系,并揭示三维空间结构影响的尺度效应。研究结果表明:(1)(高层)建筑物密度、建筑覆盖率、容积率与人口密度是碳排放的关键影响因素,主要通过直接增加人类活动或加剧热岛效应使得能源消耗和碳排放增多;(2)三维空间结构对碳排放的影响具有明显的尺度效应。随着分析尺度的变化,碳排放受三维空间结构的不同方面主导;(3)广州作为紧凑型城市的代表,如果片面追求城市三维空间的紧凑布局将不利于低碳城市的发展。因此,相关部门应重视宏观尺度下的三维空间结构的合理布局,合理开发城市边缘地区,降低城市中心建筑物的紧凑布局,构建多中心的城市格局,以有效降低碳排放水平,促进低碳城市的构建与可持续发展。研究所得成果可为城市建筑三维空间布局的合理优化提供参考依据,助力“双碳”目标的实现。

油松天然林林分空间结构特征

【目的】分析灵空山自然保护区典型森林类型即油松天然林的空间结构并对其进行评价,旨在为油松天然林空间结构优化措施的制定提供理论支撑。【方法】以灵空山自然保护区的油松天然林为研究对象,采用角尺度、大小比数、混交度、林层指数和开敞度5个指数分析油松天然林的空间结构特征,并利用熵权法确定权重进而构建空间结构综合指数,对其空间结构进行分级评价。【结果】油松天然林林分角尺度均值为0.54~0.66,林分空间分布格局总体上呈聚集分布;阳坡林分平均混交度为0.20,属弱度混交,其他立地林分混交程度介于中度与强度混交之间;林分大小比数均值为0.35~0.50,大小分化程度为中庸或近中庸状态;林分平均林层指数为0.29~0.41,且阴坡林层指数高于阳坡,林层结构总体较为简单,但阴坡林层结构较阳坡丰富;林分平均开敞度为0.37~0.52,林分内光照条件总体均达到了基本充足及以上,但半阴坡和阳坡半数以上油松光照条件受限;油松天然林林分空间结构综合指数为0.313 5~0.543 5,评价等级分属2、3级,半阴坡油松和阴坡辽东栎的空间结构综合指数分别为0.283 6和0.253 3,均属2级。【结论】灵空山油松天然林林分结构整体状况较差或一般,需进行结构优化调整,半阴坡油松和阴坡辽东栎的结构调整需求更为迫切,空间结构综合指数可作为优化调整油松天然林林分空间结构的依据。

湘西石漠化区湿地松-马褂木人工混交林林分结构及土壤理化性质研究

为探究湘西石漠化区湿地松-马褂木人工混交林林分结构及土壤理化性质,该研究以湘西石漠化地区湿地松-马褂木人工针阔混交林为对象,利用植物群落学分析和野外取样检测的方法,分析林分结构和土壤理化性质,运用Winklemass 1.0计算林分空间结构参数,并用三维离散随机变量分析了优势种的空间分布格局。结果表明:(1)林分内胸径(DBH)≥2 cm的林木株数为897 plants·hm^(-2),隶属于15科16属。主林层为湿地松,平均DBH为32.3 cm,重要值为44.2%;次林层为阔叶树,中幼龄林木居多,其中樟树、马褂木为优势树种,重要值分别为17.1%和13.2%。此外,还存在较多处于劣势生态位的天然更新种。(2)林木的水平分布格局偏向于随机分布(W=0.503);林分整体趋向于中庸偏劣势过渡的态势(U=0.505);种间隔离程度较高(M=0.689),林木混交状况良好。空间结构参数的三维离散随机变量表明,湿地松87.3%为优势和亚优势,马褂木41.7%为亚优势、26.9%为中庸态势,樟树23.5%为中庸态势、56.8%为劣势和绝对劣势。(3)林分土壤pH值趋于中性;与撂荒地相比,林分土壤的容重、持水量、孔隙度、有机碳、全钾、全氮、全磷等因子均明显改善,但整体而言,林分土壤仍然较为贫瘠,局部土壤紧实,保水能力差。综上表明,湿地松、马褂木作为先锋树种生长43年后,林分有向异龄林、强度混交林演替的趋势;林分内中幼龄阔叶树株数占比较大,近熟林出现断层,老龄针叶树占据优势生态区位,需抽针补阔、间针育阔,择伐劣势木,促使林分向阳生性阔叶树为主、中生性和耐阴性阔叶树为次的林分结构演替。该研究结果为湘西石漠化区的植被恢复、人工林结构优化和土壤改良提供了理论依据。

基于结构方程模型的城郊森林公园林分空间结构评价

为探索优化林分空间结构的有效措施,以太原森林公园为研究对象,以水平空间结构、垂直空间结构和竞争空间结构为一阶因子,以林分空间结构为二阶因子,依据传导机制建立结构方程模型,对指标赋权,并基于样地实测数据,对太原森林公园林分空间结构进行综合评价。结果表明,林分空间结构评价结构方程模型的平均适配度指数(χ^(2)/df)为1.285,近似误差均方根(RMSEA)为0.046,增值适配度指数CFI、TLI和NFI分别为0.986、0.973和0.941,各拟合指数均符合适配度参考值,可满足研究需要。林分空间结构评价体系中,3个准则层因子,即水平、垂直和竞争空间结构的权重分别为0.352、0.347和0.301,水平和垂直空间结构为影响林分空间结构的关键因素。研究区各样地林分空间结构综合得分为0.31~0.78,集中在Ⅱ、Ⅲ和Ⅳ等级;处于不同等级的样地数量表现为Ⅳ等级(7块)>Ⅲ等级(6块)>Ⅱ等级(1块)。林分空间结构主要受水平和垂直空间结构影响;为改善整体林分空间结构,应采取单株采伐抚育、抚育间伐和多树种补植等措施。

大同山杉木人工林林分空间结构与种内竞争关系

为了解大同山国有林场不同龄组杉木人工林林分空结构特征与种内竞争强度的相关性,以大同山国有林场杉木人工林为研究对象,根据幼龄、中龄、近熟、成熟4个龄组共设置8块标准地,应用样地数据,通过计算林分空间结构参数,分析林分的空间结构特征和林分竞争关系。结果表明:(1)杉木人工林在水平维度上普遍处于密集状态,除幼龄林外,其他龄组的林木密集度指数较高,各个龄组杉木人工林的林分密度集分布在0.436 3~0.863 6,各龄组林分内对象木的密集程度处于密集状态。(2)杉木人工林的林分垂直结构较为简单,垂直空间的利用率较低,各龄组样地的林层指数随林龄增加而呈现减小-增大-减小的趋势,且各龄组大部分对象木的林层指数为0~0.33。(3)杉木人工林的密度集和竞争指数的相关性比林层指数和竞争指数的相关性相对较强,林分密集度和竞争指数的相关系数随林龄的增加呈规律性变化;林层指数和竞争指数也存在较强的相关性,但随林龄变化不明显。