油松人工林乔木层结构与林下灌木多样性耦合关系研究

人工林生态系统是森林生态系统的重要组成部分,以陕西省延安市黄龙山林区油松人工林为研究对象,对比了4种不同密度的油松人工林样地内乔木空间结构(角尺度、混交度、密集度和大小比数)和灌木多样性(Simpson指数、Shannon-Wiener指数、Pielon指数、Gleason指数和Margalef指数)的差异,建立了乔木空间结构与灌木多样性的耦合关系,探讨了乔木空间结构和灌木多样性的作用关系。结果显示:1)在不同密度的样地中,株数密度为2 300～2 800株/hm~2的样地空间结构最佳;2)灌木多样性受林分密度影响显著,灌木多样性在不同密度中排序为低密度>较低密度>较高密度>高密度;3)不同密度的林分中,乔木空间结构对灌木多样性的影响不同,其中株数密度为2300～2800株/hm~2的林分中,灌木多样性与乔木空间结构具有较强的相关关系,在该密度下可以通过调整乔木层的结构而改变灌木层的多样性。     

基于物种多样性的杉木-闽楠混交林最适密度及混交比例研究

以金洞林场杉木纯林、杉木-闽楠混交林为研究对象,对不同密度和混交比例的林分进行研究,将物种多样性指数作为衡量林分密度和混交比例是否合理的参考指标,为人工混交林的经营提供理论依据。采用典型抽样法,按其混交比例分为类型Ⅰ(10杉)、类型Ⅱ(9杉1楠)、类型Ⅲ(7杉3楠)、类型Ⅳ(5杉5楠)4种类型设置典型样地,同种类型林分设置3个密度等级,低密度(A:600~1000株/hm^2)、中密度(B:1200~1600株/hm^2)、高密度(C:2000~2400株/hm^2),对比分析其林下植被物种组成及多样性差异。结果表明:从类型Ⅰ至类型Ⅳ随着闽楠比例的增加其林下植被的物种数增加。林下灌木及草本Patrick丰富度指数、Shannon-Wiener多样性指数、Simpson优势度指数表现为类型Ⅳ>类型Ⅲ>类型Ⅱ>类型Ⅰ。林分密度及混交比例与林下灌木及草本层的物种多样性指数呈显著(P<0.05)或极显著相关关系(P<0.01);拟合曲线表明林下植被Shannon-Wiener多样性指数和Patrick丰富度指数达峰值时的闽楠比例为0.465~0.506,即闽楠比例在46.5%~50.6%之间其林下植被物种多样性达到最大值。物种多样性指数与密度及混交比例均具有显著或极显著相关关系,可将物种多样性作为确定杉木-闽楠混交林最适密度和混交比例的因子之一。当前阶段,金洞林场杉木-闽楠混交林最适密度为1200~1600株/hm^2,杉木与闽楠的株数比例控制在0.97~1.10之间。     

不同抚育方式对油松人工林生态效益的影响

为探索抚育方式对油松人工林生长和生态效益的影响,选取经不同程度抚育间伐后的4种林分密度下的油松人工林标准样地,并对样地及样方内的林木生长、林下生物多样性及土壤有机质等进行调查和测定,结果表明:油松人工林油松胸径、树高和冠幅均随着林分密度的增加而减少,以抚育间伐后林分密度为2 280～2 660株·hm~(-2)的油松生长最好,林分密度对高径比无明显影响。林分密度为3 120株·hm~(-2)时,林下物种数量最多,丰富度指数、辛普森指数、香农-威纳指数和均匀度指数均为最大,植被生物多样性稳定,但不利于土壤养分的积累。在林分密度为2 280～2 660株·hm~(-2)时,土壤有机质含量高,利于土壤养分的积累。油松人工林林分密度为2 280～2 660株·hm~(-2)更适合林木的生长及土壤养分蓄积,有助于形成良好的生态效益。     

金沙江流域华山松低效林改造对生物多样性的影响——以会东县为例

低效林改造是周期短、投资小,改善林分结构,提高林地生产力,提升林分质量,充分发挥森林效益的森林经营措施。本次调查针对"长江中上游低效林改造"在会东县设置的10个华山松低效林改造实验示范点为研究对象,对林下植被的生物多样性进行调查研究。采用样地调查法,记录林下植被的种名、高度、胸径、郁闭度、盖度,运用Shannon-Wiener、Simpson、Pielou、丰富度指数S分析林下植被的物种多样性,并对两次调查的结果进行比较。结果表明,乔木的物种数较少,分布不均匀;灌草的群落结构较为稳定,物种数较多,丰富度指数有所上升。     

中亚热带典型林分空间结构对土壤养分含量的影响

【目的】研究林分空间结构对土壤养分含量的影响,揭示影响土壤养分含量的主导空间结构因子,为以改善森林土壤养分含量为目标的森林空间结构优化措施的制定提供理论依据。【方法】以中亚热带人工针叶纯林、人工阔叶纯林、人工阔叶混交林、人工针阔混交林、天然次生林和竹林6种典型林分为研究对象,在比较其空间结构与土壤养分含量差异的基础上,运用Pearson相关系数、多元线性回归分析和典型相关分析法分析林分空间结构对土壤养分含量的影响。【结果】天然次生林的林分空间结构在整体上最优,其土壤有机质和氮磷含量也最高,其他5种人工林分的空间结构和土壤有机质、氮磷钾含量的优劣排序随着指标的改变而改变,没有呈现出规律性;Pearson相关分析表明林分混交度、角尺度和林层指数均与土壤有机质、全氮和有效磷含量显著正相关(P0. 05);多元线性逐步回归结果显示混交度和林层指数是影响土壤有机质和有效磷含量的主导因子,而影响土壤全氮含量的林分空间结构主导因子只有混交度;典型相关分析表明第一组典型变量的相关系数为0. 951,属于强相关(P0. 01),说明林分空间结构与土壤养分整体上相关程度极显著;典型载荷分析进一步表明在对土壤养分的整体影响力上,混交度和林层指数起着决定作用。【结论】从数量有限的样地调查结果来看,研究地点的林分空间结构显著地影响着土壤养分含量,对土壤有机质、有效磷含量及土壤养分整体水平起决定作用的均是混交度和林层指数,而对土壤全氮含量水平起决定作用的只有混交度。因此,欲提高土壤有机质、有效磷含量水平或土壤养分含量整体水平,应采用调整林分树种结构和林层结构的综合经营措施;而要提高土壤全氮含量,只需选择调整树种结构的经营措施。     

林分空间结构对天然林木本植物多样性的影响

为探究不同类型天然林林分空间结构与木本植物多样性的相互作用关系,在星斗山保护区参照CTFS样地标准建立马尾松、杉木和光叶水青冈3种天然林固定监测样地,基于样地调查数据,分析不同类型林分空间结构、木本植物多样性的差异,应用Pearson相关分析检验林分空间结构指标对木本植物多样性的影响作用。结果表明：3种林分的混交度、角尺度整体上无明显差异,杉木林、光叶水青冈林的大小分化程度均值存在一定差异,但3种林分均形成混交、聚集且具有一定竞争力的生长状态。各林分木本植物物种组成丰富,以杉木林乔木层的Shannon-Weiner指数、Simpson指数、物种数量为最高,但3种林分之间差异不显著(P>0.05);光叶水青冈林的Pielou指数值最高,各林分类型间无显著差异(P>0.05);马尾松林灌木层的Shannon-Weiner指数、Simpson指数值最高,光叶水青冈林灌木层ShannonWeiner指数显著低于马尾松林(P <0.05),Simpson指数值也显著低于马尾松林和杉木林(P <0.05),但光叶水青冈林Pielou指数显著高于另外两种林分(P<0.0...     

一面坡林场主要人工林林分空间结构特征分析研究

为提高我国大面积人工的科学经营水平,本文以尚志林管局一面坡林场3种主要人工林(杨树、红松和落叶松)不同生长阶段的固定样地调查数据为例,采用目前常用的林分空间结构参数定量分析各林分的基本空间结构特征,为人工林的健康经营提供基础。研究结果表明:各林型不同生长阶段的林分平均混交度均属典型零度或轻微弱度混交;林分的平均大小比值均接近0.50左右,整体处于中庸状态;林分的平均角尺度则均为典型的均匀分布或轻微聚集分布;林分整体空间结构则显示各林型的空间结构极不合理。为此,必须采取积极的森林经营措施以提高当前森林生态系统结构和功能稳定性。     

小陇山2种典型天然林空间结构参数分布特征

采用林分空间结构参数一元分布、二元分布、林分综合指数和距离分析方法,探讨小陇山林区2种典型天然林空间结构特征。结果显示:(1)油松天然林混交度为0.397,树种隔离程度较低,锐齿栎天然林混交度为0.797,混交良好,油松、锐齿栎天然林胸径大小比数分别为0.507、0.485,林分均处于中庸状态,角尺度分别为0.511、0.508,林木分布格局均属随机分布。(2)油松、锐齿栎天然林中相同混交程度或优劣程度的林木大多处于随机分布,相同混交程度或分布格局的林木处于不同优劣程度的林木大致相等。区别在于油松天然林中同一优劣程度或分布格局的林木大多与同种相邻,而锐齿栎天然林中同一优劣程度或分布格局林木大多处于强度和极强度混交。(3)油松、锐齿栎天然林林分空间结构指数(FSSI)分别为0.526、0.739,林分空间结构距离(FSSD)分别为0.788、0.576,锐齿栎林空间结构明显优于油松林。FSSI和FSSD具有极显著的线性关系,FSSD=-1.481 5×FSSI+1.625 7,R²=0.990 6(P < 0.01),二者在表述林分空间结构方面具有较强的一致性。研究表明:二元分布、林分空间结构指数和距离分别是从林木水平和样地水平研究林分空间结构较为有效的方法,可为小陇山林区林分微观结构分析和精细的结构调整提供新途径。     

基于π值法则的油松人工林稳定性与空间结构关联性研究

【目的】研究林分空间结构与稳定性的关系是开展结构化森林经营的前提,旨在探索空间结构对林分稳定性的影响特征,为结构化森林经营提供支持与理论依据。【方法】以黄龙山油松人工林为研究对象,通过设置典型样地,采用最优林分的π值法则,选取10项稳定性指标进行稳定性评价,利用典型相关分析、逐步线性回归分析等方法研究空间结构(包括混交度M、角尺度W和Hegyi竞争指数CI)与林分稳定性ω的关联机制。【结果】1)林分稳定性ω平均值为0.18,变异系数为36%,总体评价结果偏差;混交度M平均值为0.26,变异系数为79%,研究区油松林分物种入侵差异大。2)典型相关分析显示,空间结构指数(包括混交度M、角尺度W和Hegyi竞争指数CI)与稳定性评价指标体系在整体上存在很强的线性相关,典型相关系数可达0.95。3)Pearson相关性分析中,W、M和CI均与ω强烈相关,相关系数分别为-0.5、0.61和-0.73。W与林分健康状态呈极显著负相关,相关系数为-0.63;M与树种多样性呈极显著正相关,与林分长势呈极显著负相关,相关系数分别为0.86、-0.66;CI与林分健康、林分密度呈极显著负相关,相关系数分别为-0.60、-0.57。4)逐步回归分析显示,混交度和林木竞争是影响稳定性的主要因素;由标准化系数可看出,林木竞争(-0.58)对稳定性的影响比混交度(0.39)大。【结论】空间结构与林分稳定性在整体上显著相关;林分混交程度显著提高林分稳定性,但是会削弱优势林木长势;团状分布格局加大了林木竞争,不利于林分稳定性。在结构调控中应适当提高林分混交程度,对竞争强度进行调整时可以连带调整林分的团状分布格局,从而提高林分稳定性水平。     

“莫兰蒂”强台风对闽南沿海马尾松林下植物多样性的影响

以2016"莫兰蒂"强台风对森林生态系统的破坏为背景,通过对受害当年和第二年马尾松人工林林下植被物种组成的调查,分析台风灾害对林下植物多样性的影响。结果表明:与未受"莫兰蒂"台风影响的马尾松样地相比,在轻度、中度和重度受害的林分,当年马尾松林下草本和灌木植物种类分别增加3种、12种和20种,第二年后分别增加15种、23种和21种,林下植物种类增加较明显。中度和重度受害林分受害后当年和第二年,显著提高了林下草灌植物的Margalef丰富度指数、Simpson和Shannon-Wiener多样性指数;轻度受害林分受害后当年林下草灌植物的丰富度指数、多样性指数变化不大或略有下降,风灾后第二年这3个指数都有明显增加;与对照相比,受害后当年马尾松林下草灌植物Pielou均匀度指数均有明显增加,而第二年增加不明显。强台风改变了林内光热条件,促进林下植物的生长更新,丰富了植物的多样性,中强度风灾影响尤为明显。     

Structure and composition of the understory treelets in a non-dipterocarp forest of tropical Asia

Species richness, floristic composition, and structure of understory treelets were investigated in three 1-ha plots, distributed in the undisturbed tropical seasonal rain forest of Xishuangbanna, SW China. We investigated all the woody species except lianas in these plots, compared the differences of species diversity of trees and treelets in these plots and the differences of understory structure between this forest and the typical dipterocarp forests in SE Asia. We found 5089 individuals belonging to 356 species, 189 genera, and 63 families in the three plots. The five most important families were Rubiaceae, Euphorbiaceae, Lauraceae, Meliaceae, and Annonacae. The treelet layer was much more diverse than the tree layer, indicating that result based only on trees may be not an appropriate representation of the diversity status of a particular tropical forest type. The three plots were more similar when the treelet layer was considered than when tree layer was considered. In contrast with the dipterocarp forests in SE Asia, the understory of tropical seasonal rain forest was mainly composed of the trees with small and middle stature at maturity classes. These results indicate that the structure of tropical forest understory may differ not only among continents but also within continent.     

Effects of multiple factors on plant diversity of forest fragments in intensive farmland of Northern Portugal

The joint and independent effects of dominant tree species, forest patch spatial attributes, and forest structure and management as drivers of plant species richness and composition in small forest patches scattered within an intensive agricultural landscape were addressed.In a landscape with scattered urban and intensive dairy agricultural areas in north-west Portugal, within which small forest patches (dominated by pines, eucalypts, or both) represent semi-natural habitat islands, 50 small forest patches, with areas ranging between 0.3 and 3 ha, were selected and surveyed for vascular plant diversity, within dairy farming landscape mosaics dominated by annual forage crops. Explanatory variables were composed of three datasets derived either from GIS mapping or field observations: forest type (dominant tree species), forest patch spatial attributes (patch area and shape index), and measures of forest management and structure (diameter at breast height, tree density per hectare, and percentage cover of vegetation strata). Variations in these forest patch attributes were assessed across forest types, and related to measures of plant diversity (total, native, alien, woody, and herbaceous species richness). Redundancy analysis with variance partitioning was applied to evaluate the joint and independent effects of the three sets of variables on species assemblages. The recent shift in canopy dominance from pine to eucalypt observed in the region appears to be related to a (nonsignificant) tendency for the increase of patch area and to the decrease of patch complexity, as well as several changes in forest structure and management, expressed as a trend to denser tree canopies and lower cover of understory plants. Dominant tree species and attributes related to forest structure and management were the most important factors determining plant diversity. The joint effect of the dominant tree species and forest structure and management resulted in lower levels of plant species richness in eucalypt plantations. These were also more prone to invasion by alien species, probably due to decreased biotic resistance from unsaturated native plant assemblages. Our results draw attention to the importance of dominant tree species and management practices for the maintenance of plant diversity levels (species richness and composition) in dairy landscape mosaics, highlighting the importance of the remnants of semi-natural forests as refuges for plant diversity in the landscape context. Nonetheless, forest plant diversity could further be fostered by promoting naturalness of pine stands and the regeneration of native oak woodlands in some forest areas. This would also diversify the range of ecosystem services that could be provided by forest areas in these peri-urban farmlands.     

Effects of the overstory on the diversity of the herb and shrub layers of Anatolian black pine forests

Understory plants are important components of forests because they are responsible for the majority of the vascular plant diversity of forest ecosystems. The richness and composition of understory communities are closely related to the tree layer diversity, structure and composition. The aim of this study was to examine the understory diversity of Anatolian black pine (Pinus nigra Arnold subsp. pallasiana (Lamb.) Holmboe)-dominated forests on the Kazda?? Mountains of West Turkey. To describe the overstory structure and composition in a numerically and quantitatively well-defined manner, cumulative abundance profiles (CAPs) of the tree species were used. The resemblance of the sampling plots was classified into five stand types assessing the CAP through the Fuzzy C-Means clustering method. A permutational multivariate analysis of variance (PERMANOVA) was performed to test the variance of the community ecological distance between the five stand types, and the results showed significant differences in these clusters. Many shade-tolerant plants were associated with the mixed stands of Anatolian black pine–Kazda?? fir. The composition of the herb and shrub layer could not be explained by the environmental variables but by differences in the overstory structure of the stands. Pure or nearly pure Anatolian Black pine stands were more diverse than mixed oak–Anatolian black pine and Kazda?? fir–Anatolian black pine stands. However, although dense and young pure Anatolian black pine stands had the most diverse plant species in the shrub layer, they were ranked third in terms of the herb layer diversity. The Anatolian black pine–Kazda?? fir mixed stands had the lowest herb and shrub layer diversity. These results allow us to comprehend the relationship between the overstory structure and composition, and the understory diversity. Understanding this relationship is important for the conservation of understory plant diversity in the management of forest ecosystems.     

皆伐前后油松人工林下植物多样性变化及与土壤水分的关系

【目的】探讨油松人工林皆伐前后林下植物多样性的变化及与土壤水分的关系,为在油松林皆伐后植被恢复和发育阶段维持生物多样性、保持林分结构稳定、发挥更高生态效益等方面提供科学依据和经营措施建议。【方法】采用时序研究法,在河北平泉地区选择立地一致的不同林龄油松人工林(32年中龄林、40年近熟林、53年成熟林)和皆伐后不同时间(5、10、24 a)的天然更新林作为研究对象,分析不同生长发育阶段油松人工林下植物物种组成与多样性的变化规律及与土壤水分间的相关性。【结果】1)皆伐前后6种林分样地共出现灌木植物21种,草本植物65种,不同样地林下植物组成存在差异。胡枝子在各林分样地均有出现,且重要值均> 20%,在灌木层优势地位明显;草本层中菊科植物种类最多,有18种,其次是蔷薇科和禾本科,分别为6种和4种。2)不同林分样地林下植物多样性指数均表现为草本层>灌木层,皆伐前随着林龄增加林下植物多样性逐渐增加;皆伐后灌木层植物多样性表现为先下降后增加再下降,且变化幅度明显,伐后10 a灌木层Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数最大,分别为1.40、0.61、1.24和0.74,与53年样地差异不显著。皆伐后不同时间的天然更新林草本层植物多样性均与伐前53年样地的差异不显著,皆伐对灌木层植物的影响较大。3)不同林地土壤水分变化规律较一致,表现为伐前随林龄增加而逐渐增加,伐后5~10 a仍保持较高水平,伐后24 a出现下降,经相关分析植物多样性指数与土壤水分之间有显著的正相关关系,与草本层的相关性达极显著水平。【结论】伐前林下植物多样性变化主要与林分密度降低、光照条件改善有关,伐后主要与油松天然更新及种间竞争有关。依靠油松天然更新恢复的林地保持了较高的生物多样性,但在皆伐10 a后出现下降的趋势,建议在此时对油松更新苗进行人工抚育、降低密度以维持植物多样性。土壤水分是影响植物多样性的关键生态因子,良好的土壤水分条件和林下植被的恢复和发展可以相互促进。     

林分密度对蒙古栎林下草本植物多样性的影响研究

以内蒙古赤峰市阿鲁科尔沁旗沙日温都栎林自然保护区蒙古栎林为主要研究对象,研究不同林分密度对林下草本植物多样性的影响。结果表明,研究区内共有13科、14属、16种草本植物;Simpson指数、Shannon-Wiener指数、Pielou均匀度指数和物种丰富度指数均随着林分密度的增加呈先增大后减小的趋势,当林分密度为750株/hm²时,林下草本植物多样性指数达到最大值;林分密度与Shannon-Wiener多样性指数、Pielou均匀度指数、Simpson多样性指数、物种丰富度指数、树高、胸径均呈极显著负相关,与郁闭度呈极显著正相关,与枝下高不相关。综上所述,最合理的蒙古栎林密度为750株/hm²,该密度下最有利于蒙古栎林及林下草本植物生长发育。     

Clearance of understory in urban woodlands: Assessing impact on bird abundance and diversity

Clearance of understory to enhance the recreational value of the forest is common in urban woodlands. Open forests are generally perceived as safe and pleasant, but clearance is likely to be negative for woodland birds as the shrub layer is important for foraging and protection. In this 3-year experiment with a before after control impact (BACI) design, the effects from understory clearance on woodland bird abundance and diversity in five suburban broadleaved forests in south-western Sweden were studied. Understory clearance was either made in regular patches, with 50% removal of understory, or as “Complete” (90%) removal. Adjacent stands of equal size were left unmanaged as controls. Woodland birds and understory vegetation were surveyed before and after the management. The total density of breeding forest birds decreased in the plots with “Complete” removal of the understory compared to plots with “Patchy” clearance. “Patchy” clearance had no significant effect on bird density. Bird diversity was not affected by the management. Woodland birds are highly valued animals in urban green areas and the impact on bird fauna should therefore be taken into consideration in the development of management plans for urban woodlands. The present study has demonstrated that clearance of understory can have negative effects on bird abundance if carried out over large areas. Clearance in patches was not found to have negative effects on bird abundance and can promote recreational values by increasing visibility and structural variation of the forest.     

北京西山油松人工林结构特征研究

以西山试验林场近自然经营试点区建立的11块中龄油松人工林样地为依据,对油松林分的结构特点、表达模型和树种多样性格局进行了分析。结果表明：油松人工林林分平均密度为1069株／hm^2,平均胸径为13．7cm,平均高为8．6m,蓄积量为86．36m3／hm^2。应用正态分布、Weibull分布、对数正态分布、Gamma分布和Beta分布拟合直径和树高结构,发现正态分布拟合直径分布和树高分布效果最好,也符合人工林的林分结构规律;油松人工林层次结构简单,物种多样性较低,乔木层、灌木层和草本层的Shannon—wiener指数、均匀度指数分别为0．355、0．726、0．160和0．372、0．651、0．266;幼苗更新各高度级均以构树和栾树为主,他们分别占总体更新树种的72．2％和10．2％。     

Effects of Different Management Practices on Stand Composition and Species Diversity in Subtropical Forests in Nepal: Implications of Community Participation in Biodiversity Conservation

In this article, we compared the structure, composition, and diversity of trees, shrubs and saplings, seedlings and herbaceous species of community- and government-managed forests in the lowlands of eastern Nepal. Results suggest that among the trees, the community forest was dominated by a single species, Shorea robusta. However, Shorea robusta and Terminalia myriocarpa were codominant in the government forest. Tree density and basal area were higher in the government forest, but shrub/sapling density and basal area were higher in the community forest, suggesting a positive effect of community management on tree regeneration. Overstory species assemblages showed an obvious compositional difference between the forests, but understory species assemblages were less obvious. Plot-level tree and shrub/sapling species richness was higher in the government forest than the community forest. However, seedling-herbaceous species richness was higher in the community forest. The dominance of Shorea robusta trees in the community forest suggests that people involved in managing forests may be more interested in a limited number of economically valuable species while removing less important trees. Such preferential management practices may increase resource heterogeneity within a forest and maintain species diversity in the understory. Thus, community participation in forest management should be encouraged, with guided management techniques and exercises, to achieve maximum forest recovery, provide sustainable ecosystem services, and maintain forest diversity.     

Modeling the spatial structure of topical forests

The spatial structure of tropical forest stands under different management conditions was modeled as a series of different spatial point processes. Spatial patterns were first assessed by K-function analyses to help choose a point process appropriate for observed patterns. The homogenous Neyman–Scott process accurately described live tree distribution in clear cut areas, where tree patterns tended to be aggregated. Parameters were estimated by minimizing Diggle's modified least squares criterion, and goodness-of-fit was assessed by comparison to confidence envelopes constructed by Monte Carlo simulation. Parameter estimates can be interpreted to help understand the ecological processes influencing re-colonization of disturbed areas. The inhomogeneous Poisson process was investigated for simulating the spatial pattern of ingrowth trees in lower canopy strata. The intensity function of this process was inversely proportional to variables representing canopy density. As assessed by Monte Carlo generation of confidence envelopes, the inhomogeneous Poisson process successfully portrayed the influence of canopy structure on understory plant distribution in most stands. Tree mortality was modeled as a thinning process in which the probability of individual tree mortality was conditional on subject tree attributes and competitive environment. The thinning function took the form of a generalized linear model with a binomial error distribution and logit link function. In most stands, tree neighborhood variables were powerful predictors of mortality, but they were not important predictors in all plots. This suggests that the surrounding forest structure of a subject tree has considerable influence on its morality, but competition is not the sole cause of tree morality in tropical forests.     

不同发育阶段马尾松人工林经营效果动态分析

为揭示不同发育阶段马尾松人工林经营效果的动态变化特征规律,对青羊湖林场不同发育阶段的马尾松人工林(幼龄林、中龄林、近熟林)林分空间结构、物种多样性、土壤肥力、林木生长等指标进行动态分析,运用主成分分析法,对不同发育阶段的各经营样地的经营效果进行综合评价。结果表明:不同发育阶段的马尾松林在经营改造后,空间结构明显改善,物种多样性指数均明显提高,土壤肥力也有所改善;幼龄林、中龄林和近熟林9块样地抚育间伐补植改造效果综合评价得分依次为0.079,-0.021,-0.241,0.528,0.438,1.028,-0.145,-0.780,-0.886,得分越高说明改造经营效果越好。经营促进了不同发育阶段马尾松人工林林分空间结构的优化、树种多样性的提高、土壤肥力的改善和林木蓄积生长的提高,林分向异龄复层混交林方向发展,为马尾松人工林经营提供理论依据。