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1.
In comparison to countries with a tradition of vegetation studies, a comprehensive, hierarchical classification of plant communities in the province of British Columbia has not yet been developed. Such a classification is needed for systematic ecological studies and coordinated conservation of vegetation. As the culmination of fifty years of detailed surveys, tabular and multivariate analyses of 3779 relevés of natural, old-growth, submontane, montane and subalpine forest communities in coastal British Columbia were used to develop a hierarchy of vegetation units according to the Braun-Blanquet approach. At the highest level, we distinguished seven orders: Quercus garryana, Pseudotsuga menziesii-Mahonia nervosa, Tsuga heterophylla-Rhytidiadelphus loreus, Tsuga mertensiana, Thuja plicata-Tiarella trifoliata, Populus trichocarpa, and Pinus contorta-Sphagnum. Diagnostic table, ordination, and elimatic and edaphic regimes were used to show floristic affinities among the orders and to interpret their relationships to regional environmental gradients. Plant communities of each order were briefly characterized by their floristic composition, physiognomy, succession, and environment. The synopsis for all delineated vegetation units (order, suborder, alliance, and association) of coastal British Columbia is included.  相似文献   

2.
The vegetation in a beech forest, Fritzøehusparken, is analysed using one hundred sample plots, each 25 m2, distributed by a restricted random procedure. Percentage cover and frequency in subplots are used for quantification of species amounts, and their relative performance are evaluated. Advantages of choosing frequency in subplots are discussed. Thirteen environmental variables are measured from each of the sample plots. The vegetation is divided into four topographical/ecological types. This classification served as a reference in the further treatment. Ecological gradients corresponding to the most important vegetational gradients in the beech forest are identified by means of DCA ordination followed by statistical interpretation. Two main complex gradients were recognized; (1) the gradient in nutrient conditions, and (2), the gradient inlitter-wind conditions. The advantages of using DCA and statistical interpretation with integration of ecological measurements are emphasized.  相似文献   

3.
Lawesson  Jonas E. 《Plant Ecology》2000,151(2):199-221
In this study, the first comprehensive multivariate statistical analysis of Danish native forest vegetation, based on 1768 sample plots, is presented. Data were composed of data from literature sources and newly collected data. A series of cluster analyses resulted in 24 forest community types, grouped in beech (Fagus sylvatica), oak (Quercus robur-Q. petraea), hornbeam (Carpinus betulus), alder-ash (Alnus-Fraxinus) and lime (Tilia cordata, T. platyphyllos) types, in addition to mixed forest communities with several co-dominant tree species. The described communities are provisionally arranged syntaxonomically, when possible, according to the international phytosociological system. The distribution of ecological indicator values of pH, soil moisture and nitrogen is gradual in relation to the perceived plant communities. Many forest types, such as beech and oak dominated types, obtain indicated values for pH that span most of the indicated gradient. It is suggested that natural Danish forests probably would be composed of a multitude of canopy forming tree species. The present stands with one or a few tree species forming the canopy is the result of long anthropogenic influence and selective logging.  相似文献   

4.
在野外调查基础上,采用TWINSPAN和DCA对小陇山林区次生林群落进行了数量分类和排序,从植物群系组成、植物群落与环境的生态关系方面,研究小陇山植被群落的分布格局,用以确定该区次生林演替,并给予合理的环境解释。结果表明:采用TWINSPAN数量分类方法,将植被划分为12个群落类型;DCA排序图明显反映出排序轴的生态意义,第一轴基本上突出反映了湿度变化,沿第一轴从左到右,湿度逐渐增大;第二轴主要表现了温度梯度,沿第二轴从下到上,温度逐渐降低;次生林的演替序列为山杨林→山杨+白桦林→锐齿栎混交林及锐齿栎纯林,其自然恢复演替以锐齿栎林为顶极群落。  相似文献   

5.
A.K. Cajander's forest site type classification system is based on definition of plant communities typical to certain climatical and edaphical site conditions, but the structure and composition of the tree stands in Finland are considered sensitive to random variation and are therefore not used as primary classification criteria. The system has often received criticism, usually that the effects of the tree stand and successional stage of the stand have been underestimated. Most of the present-day forest stands in Finland represent young successional stages and are subjected to intensive management. This should result in an additional difficulty in the application of the forest site types in the field.The present study is based on three independent data sets representing forests on mineral soil in southern part of Finland. TWINSPAN classification, DCA ordination and canonical correspondence analysis (CCA) techniques were applied in successive stages of the data analysis. It was found that the definition of the intermediately fertile, mesic site types was clearly confused by the effects of the tree species and age of the stand. The analyses also revealed that the succession pathways on mesic forest sites are largely determined by the tree species composition. In stands dominated by Pinus sylvestris, the succession follows the competitive hierarchy model, whereas in stands dominated by Picea abies, severe shading of the tree canopy governs the development of understorey vegetation.Abbreviations CCA Canonical correspondence Analysis - DCA Detrended correspondence Analysis - TWINSPAN Two-way indicator species analysis  相似文献   

6.
7.
藏北高原草地群落的数量分类与排序   总被引:1,自引:0,他引:1  
王景升  姚帅臣  普穷  王志凯  冯继广 《生态学报》2016,36(21):6889-6896
采用TWINSPAN数量分类和DCA、CCA排序的方法,对藏北高原草地29个样点进行统计分析。结果显示:(1)TWINSPAN数量分类将藏北高寒草地群落划分成10种类型。(2)样点DCA排序第一轴基本反映了水分环境梯度,第二轴基本反映了热量梯度。(3)TWINSPAN分类所划分的各群落在DCA排序图上都有各自的分布范围和界限,说明DCA排序能较好的反应各优势群落与其环境资源之间的关系。(4)样点CCA排序表明,影响群落分布的首要环境因子是水分因子(年均降水量)和空间因子(经度),其次是热量因子(年均温度),CCA排序进一步阐明了群落分布决定于水分和温度等环境因子,并间接验证了TWINSPAN的分类结果。(5)物种CCA排序和TWINSPAN分类结果表明:植物群落中物种的分布格局与植物群落类型的分布格局存在一定的相似性。  相似文献   

8.
Question: Which are the gradients of floristic differentiation in Greek beech (Fagus sylvatica) forests? Which is the role of geographical and ecological factors in this differentiation? Location: Beech forests of the plant geographical regions Northeast, North Central and East Central Greece. Methods: A total of 1404 published and unpublished phytoso‐ciological relevés were used in the analyses. TWINSPAN and DCA were applied to classify and ordinate the relevés. Altitude, Indicator Values of relevés and their X and Y coordinates were used in a posteriori interpretation of the ordination axes. Kendall's correlation coefficients were calculated between DCA relevé scores and explanatory variables. Multiple linear regression was used to partition the variation explained by the first two DCA axes, between the geographical and the ecological variables. Results: Classification resulted in 14 vegetation units defined by species composition. Two types of gradients, ecological and geographical, were revealed by the DCA of all releves. The partition of the variation accounted for by the first and second DCA axis was attributed mainly to ecological and geographical variables, respectively. Conclusions: Beech forests of northeast and Central Greece show phytogeographical differences, while ecologically similar vegetation units occur in both regions. A west‐east gradient is revealed in Greek beech forest vegetation. The extent of the study area, its position along regional gradients and the comprehensiveness of the data set that is analysed determine the types of the gradients which can be revealed in a vegetation study.  相似文献   

9.
Question: Is the vegetation of meadow and mountain steppes distinct from the ground vegetation of light taiga forests in the transitional zone between these biomes? Location: Western Khentey Mountains, northern Mongolia. Methods: Vegetation was recorded from 100‐m2 plots from all dominant types of light taiga forest and dry grassland. Distinctness of ground vegetation was studied with Detrended Correspondence Analysis (DCA). Results: Ground vegetation in the light taiga was significantly different from the herbal vegetation of meadow and mountain steppes. Clear separation was only absent for the Car ex amgunensis meadow steppes that occur in a narrow strip along the forest edge and are partly shaded by trees. Forest and steppe communities followed a moisture gradient according to the DCA ordination with light taiga forests at the moistest sites and steppe communities at the driest sites. Ulmus pumila open woodlands diverged from this pattern, because of their close spatial and phytosociological relationship to mountain steppes. Conclusions: The present results do not support the assumption that grasslands in Mongolia's transitional zone between forest and steppe would generally resemble the ground vegetation of light taiga forests. This contradicts a published hypothesis stating that the vegetation of meadow and mountain steppes would not clearly differ from ground vegetation of light taiga forests in the forest‐steppe transitional zone of Mongolia.  相似文献   

10.
神农架川金丝猴栖息地森林群落的数量分类与排序   总被引:1,自引:0,他引:1  
在神农架川金丝猴生境典型地段设立样方58块,根据样方资料对神农架川金丝猴栖息地的森林群落用组平均法分类和DCA排序.用组平均法将58块样地分为9个群系,依据《中国植被》的分类原则和系统将研究区植物群落划归为7个植被型.样地的DCA排序较好地揭示了该区森林群落的分布格局与环境梯度的关系;DCA第二轴明显地反映出森林群落的海拔梯度变化,沿DCA第二轴从右到左,海拔逐渐升高;第一轴表现了各植物群落或植物种所在环境的坡度、坡向,即水分和光照因素,沿第一轴从下到上,坡度渐缓、坡向渐向阳.其中海拔梯度是环境因子中对森林群落起决定性作用的因子.研究表明,巴山冷杉+糙皮桦-大齿槭+尾萼蔷薇-高原露珠草+星果草群系发育较好,高大树木占有较大的比例,是神农架川金丝猴最适宜栖息地.7个植被型物种丰富度指数在群落梯度上呈规律性波动.其中针叶林和针叶-阔叶混交林中,物种丰富度指数在群落梯度上的总体趋势表现为灌木层>草木层>乔木层;在常绿阔叶林和常绿-落叶阔叶混交林中,该趋势为灌木层>乔木层>草本层;在落叶阔叶林中,其丰富度指数的趋势为灌木层>草本层和乔木层.不同植被类型川金丝猴食源植物种类在群落梯度上的变化趋势与物种丰富度指数相同,但地衣类植物作为川金丝猴冬季的重要食物只在针叶林和针叶-阔叶混交林中生长.本研究为制定栖息地保护计划,更好地保护神农架川金丝猴提供了科学理论依据.  相似文献   

11.
Mire vegetation of the Muránska planina Mts and adjacent parts of neighbouring orographical units was studied in 1998–2005 using the standard Zürich-Montpellier (Braun-Blanquet) approach. We applied the defined phytosociological species groups and national formal definitions of mire associations in data processing. Within the classes Scheuchzerio-Caricetea fuscae and Oxycocco-Sphagnetea, seven associations (Caricetum davallianae, Carici flavae-Cratoneuretum filicini, Valeriano simplicifoliae-Caricetum flavae, Caricetum goodenowii, Carici echinatae-Sphagnetum, Carici rostratae-Sphagnetum and Pino mugo-Sphagnetum) were classified using formal classification criteria. Two other communities (Sphagno warnstorfii-Caricetum davallianae and Eriophoro vaginati-Sphagnetum recurvi) were not classified due to the lack of sufficient number of diagnostic species from species groups. The first DCA axis followed the mineral richness gradient. Vegetation plots were arranged from rich fens over moderately rich fens towards poor Sphagnum fens and raised bog. This fact was confirmed by a strong and significant correlation of the DCA site scores on the first axis with the measured pH and water conductivity as a surrogate of mineral richness. The second DCA axis correlated with mean Ellenberg’s indicator values for both temperature and soil nutrients. This pattern corresponds to that found in other regions of diversified Central-European landscape. We can therefore conclude that marginal geographical position and climatic specifity of the region under study did not alter gradient structure of the mire vegetation. When diversity of mire vegetation was compared to other regions in Slovakia by applying the same formal definitions to different regions, the study region was found to be conspicuously less diverse than the distribution centres of mire habitats in Slovakia (Orava and Vysoké Tatry regions), but more diverse than most of other marginal regions of mire distribution. Relatively high beta diversity of mires was probably caused by variable bedrock and local climate.  相似文献   

12.
网格化清查方法有助于准确诊断一个地区的植被性质,并为探索植被分类方法提供支持。该研究以上海大金山岛为对象,借助航拍影像等间距地将其划分为140个清查网格(40 m × 40 m),按照统计样方法逐网格调查植物群落特征,综合运用列表法和双向指示种法,进行植被分类并绘制现状植被图。按照新修订的植被三级分类系统进行分类:一级单位根据植被型,大金山岛植被划分为落叶阔叶林、常绿落叶阔叶混交林、常绿阔叶林、落叶阔叶灌丛、常绿落叶阔叶混交灌丛、常绿阔叶灌丛和草丛; 二级单位根据优势种和植物区系特征,可划分出15种群丛或群落类型; 三级单位根据群落年龄和外貌可划分为22种群落类型。以上结果表明,大金山岛不仅是上海市物种多样性最高的区域,也拥有华东海岛最典型、最多样的自然半自然森林群落。就植被状态而言,地带性森林群落处于演替中后期,但少数次生植被处于演替前期,且面临着猴群干扰导致的植被发育停滞不前等生态问题。关于植被分类方法,网格化清查方法可充分揭示植物群丛连续性中包含间断性和过渡性群落的现象。  相似文献   

13.
Abstract. Sirén (1955) studied understorey species composition, tree stand properties and humus‐layer thickness in 64 unlogged forest stands on topographically and pedologically comparable sites. The stands were of even age (6 – 300 yr), stocked with the first or second tree generation after wildfire. The view of Sirén and several authors after him, that the vegetation of old‐growth boreal Picea forests is homogeneous on a broad scale, was examined by applying, in parallel, the partial variants of two ordination methods (DCA and PCA) to Sirén's vegetation data. Two main vegetation gradients were found: a major gradient running from recently burnt plots with prominence of pioneer species to plots with stand age > 100 yr, a well stocked tree layer and a thick humus layer, dominance of feather‐mosses and ample occurrence of shade‐tolerant as well as light‐preferring vascular plant species, and a second gradient along which first‐ and second‐generation plots segregate. The more prominent element of Betula trees in first‐ than in second‐generation stands < 100 yr contributed to the latter. A minor third gradient related to humus‐layer thickness was recovered by partial DCA only. The main vegetation gradient reappeared in separate ordinations of data from 47 mature forest stands (> 100 yr), but without being correlated with forest age. Variation among mature‐forest stands in the importance of pioneer species is considered mainly to be brought about by fine‐scale disturbance processes such as tree uprooting. Increasing importance of factors operating on within‐stand scales [development of a varied gap structure and stronger gradients in tree influence (radiation at ground level), soil moisture, soil depth and nutrient availability] with time is also reflected in the second and third mature‐forest ordination axes. Possible implications of the results for conservation of biological diversity and monitoring of changes in boreal forests are discussed.  相似文献   

14.
The response of an ecosystem to disturbance reflects its stability, which is determined by two components: resistance and resilience. We addressed both components in a study of early post-fire response of natural broadleaved forest (Quercus robur, Ilex aquifolium) and pine plantation (Pinus pinaster, Pinus sylvestris) to a wildfire that burned over 6000 ha in NW Portugal. Fire resistance was assessed from fire severity, tree mortality and sapling persistence. Understory fire resistance was similar between forests: fire severity at the surface level was moderate to low, and sapling persistence was low. At the canopy level, fire severity was generally low in broadleaved forest but heterogeneous in pine forest, and mean tree mortality was significantly higher in pine forest. Forest resilience was assessed by the comparison of the understory composition, species diversity and seedling abundance in unburned and burned plots in each forest type. Unburned broadleaved communities were dominated by perennial herbs (e.g., Arrhenatherum elatius) and woody species (e.g., Hedera hibernica, Erica arborea), all able to regenerate vegetatively. Unburned pine communities presented a higher abundance of shrubs, and most dominant species relied on post-fire seeding, with some species also being able to regenerate vegetatively (e.g., Ulex minor, Daboecia cantabrica). There were no differences in diversity measures in broadleaved forest, but burned communities in pine forest shared less species and were less rich and diverse than unburned communities. Seedling abundance was similar in burned and unburned plots in both forests. The slower reestablishment of understory pine communities is probably explained by the slower recovery rate of dominant species. These findings are ecologically relevant: the higher resistance and resilience of native broadleaved forest implies a higher stability in the maintenance of forest processes and the delivery of ecosystem services.  相似文献   

15.
本文运用国际较为先进的双向指示种分析(TWINSPAN)多元等级分划分类方法和无趋势对应分析(DCA)排序方法对大兴安岭阿木尔林区1987年特大森林火灾后的植物群落进行了研究。通过排序结果和冻土环境的多元分析,得出:DCA排序轴1代表了土壤岩性与地形的梯度而决定植物群落的分布;DCA排序轴2则反映了森林火烧的程度梯度,并通过冻土融化深度和浅层地温值的变化而影响植物群落的分布,运用相关回归分析方法,定量地找出了它们之间相互关系的回归方程。 据此,进而探讨了该地区森林火灾后冻土环境的变化对植物次生演替方向和进程的影响。  相似文献   

16.
The aim of this study is to classify and describe all plant communities with Quercus coccifera covering the entire eastern Adriatic coast and islands from north Croatia to south Albania, and to relate their species composition, chorotypes and life forms to environmental factors using Pignatti ecological indicator values. From total 70 phytosociological relevés, we identified and described four floristically and ecologically distinctive vegetation communities (two new proposed subassociations, one association and stand each) using TWINSPAN and the Braun-Blanquet classification scheme. In Croatia and Montenegro, Q. coccifera is forming macchia within the Fraxino orni–Quercetum cocciferae pistacietosum lentisci. Quercus coccifera occurs only sparsely in south Croatia as a shrubland within Fraxino orni–Quercetum cocciferae nerietosum oleandri subassociation or macchia within the Erico arboreae–Arbutetum unedonis association. Despite the difference in biogeographic position and bioclimates, low shrubby Albanian Q. coccifera stands are more closely related to the Q. coccifera communities from the western Mediterranean. Eastern Adriatic communities appear exclusively within the Querceta ilicis vegetation zone and spread within the meso-Mediterranean belt. They nevertheless are an important part of the region's natural heritage and management plans must ensure that all forms of land are used in a sustainable way.  相似文献   

17.
In the highlands of northern Ethiopia, remnants of the original Afromontane forest vegetation are largely restricted to church yards and other sacred groves in a matrix of cropland and semiarid degraded savanna. To assess the potential for natural forest regeneration, species composition and diversity of all forest fragments (10) in a study area of 13,000 ha were analyzed in relation to environmental and soil variables. Using a random design and a density of approximately one plot per 2 ha in all fragments, 31 20×20 m plots were sampled. Indicator species analysis and MRPP tests yielded five communities representing two forest types and one degraded savanna habitat. The forest fragments had a species-poor tree and shrub community in which plots were rather homogeneous and most species abundant. NMDS and analysis of variance indicated that a topographical gradient correlated to soil phosphorus, soil depth, stoniness and the proximity to the river system explained the major differences in species composition and separated moist and dry Afromontane forest communities. The grazing intensity further partitioned the habitats. Present communities and their environmental correlates indicate that the secondary climax forest in the area probably consisted of dry Afromontane forest interlaced by broad strips of moist Afromontane forest along rivers and streams and not a continuous, mono-dominant Juniperus forest as is often presumed. Negative effects of the degraded matrix on forest fragments increased with decreasing patch area and increasing shape irregularity. Nevertheless, all remaining fragments are important for their role in the landscape ecology of the region as refuges and species pools and should be protected and managed accordingly. If seed dispersal from forest fragments into exclosures and subsequent tree recruitment are both successful, the vegetation type most likely to establish is Afromontane savanna woodland, and if managed properly, eventually dry Afromontane forest may arise. Increasing the size of small patches and placing forest plantations and exclosures in the vicinity of small forest fragments is expected to yield the most immediate results. This approach may increase the likelihood of patch colonisation by frugivorous forest birds and thus foster the regeneration of native woody species.  相似文献   

18.
The concept of Megamexico as a phytogeographic unit has been introduced by Rzedowski (1991) on the basis of distribution patterns of genera. Until now precise information on the resemblance between plant communities in the proposed Megamexico was scarce. This phytosociological study documents the affinities between plant communities within Megamexico, based on studies from mountain ranges in Mexico (Sierra Chichinautzin, Sierra Nevada) and Guatemalan mountain ranges (Sierra de los Cuchumatanes, Cadena Volcánica). Data, collected in the style of Braun-Blanquet during extensive fieldwork, were pooled into a single data set, and analyzed by using (1) TWINSPAN, for plant community classification, (2) ordination (DCA), (3) alpha log series biodiversity-index to measure intergroup diversity, and (4) information on the altitudinal distribution of the vegetation belts. Classification showed that four communities were common to the two groups of mountain ranges, namely, alpine bunchgrass-land, pine forest, fir forest and mixed forest. Along the altitudinal gradient Mexican communities are distributed 200 m higher than their Guatemalan equivalents. This appears to be an illustration of the Massenerhebungseffekt. DCA showed that the first axis represents a set of minor differences of closely related ecological factors (e.g., temperature, precipitation) and the second a humidity gradient. The biodiversity index showed that the Mexican mixed forest was significantly more diverse than the Guatemalan mixed forest. From the present results, ecological conditions among mountain ranges in Megamexico differed significantly. To conclude, phytogeographical units in Megamexico can better be defined on basis of both historical and ecological characteristics of the communities.Abbreviations: community refers to plant community throughout the paper.  相似文献   

19.
钟娇娇  陈杰  陈倩  姬柳婷  康冰 《生态学报》2019,39(1):277-285
采用多元回归树(MRT)对秦岭山地天然次生林群落进行数量分类,采用典范对应分析(CCA)进行排序,分析了秦岭山地天然次生林群落物种多样性沿海拔梯度的变化规律。结果表明:(1) 275个样方共有种子植物195种,隶属61科128属。乔、灌、草3个层次物种多样性变化沿海拔梯度的变化趋势基本一致,呈单峰模型;(2)经交叉验证认为秦岭山地天然次生林群落可分为2类,Ⅰ冬瓜杨(Populus purdomii)+陇东海棠(Malus kansuensis)+蛇莓(Duchesnea indica)群落,Ⅱ锐齿槲栎(Quercus aliena var. acuteserrata)+黄栌(Cotinus coggygria)+茜草(Rubia cordifolia)群落;(3) CCA排序结果揭示了群落生境的分布范围,反映出生态轴的排序意义,较好地反映秦岭山地天然次生林群落与环境因子的关系,其结果表明,海拔、坡向、凋落层厚度和干扰情况4个变量对该地区次生林群落的分布有较大的影响。  相似文献   

20.
Changes in composition and structure of plant communities in relation tothe soil and snow cover variation were analyzed along an altitudinal transect(1150–1750 m) from the mountain-temperate forests to a woodyshrub community and alpine meadows on Mt Velký Gápel', Slovakia.The soils below the treeline (1510 m) had a more developedorganic layer above the mineral substratum. Generally, soil depth decreased asthe altitude increased, although the maximum values were recognized at a middlealtitude in a beech stand. Snow was redistributed by westerly winds from theridgeline down to the upper forest margin. Mean snow depth decreased withaltitude up to almost snow-free sites around the summit. In the 48 plots at 16sites we recorded 118 taxa including 6 tree, 7 shrub, 18 grass, 42 herb, 5fern,25 moss and 15 lichen species. The species diversity showed no distinctrelationship to altitude but declined with canopy consolidation. The TWINSPANfloristic classification distinguished five groups of community typescharacterised by different dominants, and a further three clusters of samplesfrom transition zones. Horizontal compositional heterogeneity increased inareaswhere trees were aggregated and tree basal area was smaller. Vegetationcomposition became more patchy at open-canopy Acerpseudoplatanus–Abies alba mixed forest at 1150 m,in Picea abies forest limit 1470 m, andin Pinus mugo krummholz at 1590 m. Speciesturnover of the entire transect was 6.1 half-changes as estimated by DCA.Despite this heterogeneity, none of the 15 elevational bands had significantaggregation of species' limits. Vegetation varied continuously, with individualspecies overlapping in transition zones delimited by dominant taxa. Thecoincident aggregation of up-slope and down-slope boundaries was found at abelt1430–1510 m. This discrete ecotone corresponds to a shiftfrom the closed coniferous forest to P. mugo krummholz.Thesecond inherent up-slope boundary aggregation indicated the P.mugo krummholz – alpine meadow vegetation transition at1700 m. Spatial analysis (K-function) of eight forest plots(0.12 ha each) showed that at lower elevation, adult trees of thebroad-leaf forest were closer to a random arrangement while at higherelevation,trees of evergreen coniferous stands became aggregated toward the forest limitwith the highest intensity from 2 to 4 m. Altitudinal gradient andrelated factors explained 35% of the variance in vegetation data.Canonical correspondence analysis also showed that main vegetation changesabovethe treeline area were associated with the topographic pattern of pine shrubsand snow cover.  相似文献   

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