Fuzzy set ordination and classification of Serengeti short grasslands,Tanzania

Abstract. Species abundance data from 32 representative stands are used to evaluate the vegetation in the heavily grazed Serengeti short grasslands. The abundant species are: Kyllinga nervosa, Sporobolus ioclados, S. kentro-phyllus and Eustachys paspaloides, all occurring in elevated areas, and Hypoestes forskalei, which is found in the drainage areas. Numerical classification and fuzzy set ordination revealed four main grassland communities associated with a topographic gradient. The communities are considered distinct since their niches, as computed in the community and environmental fuzzy system space are not overlapping. Leaching, erosion and animal disturbance effects correlated with the topographic gradient are found to determine species composition and overall community structure in the grasslands.     

Spatial and depth-associated distribution patterns of shallow gorgonians in the Algarve coast (Portugal, NE Atlantic)

The ecological role of gorgonians for marine rocky bottoms is worldwide recognized, but the information on the distribution patterns of NE Atlantic temperate species is insufficient, considering current global, regional and local threats. To overcome the lack of information on the spatial distribution patterns of gorgonians in south Portugal, in 2009/2010, the occurrence and abundance of gorgonian species in rocky bottoms were quantified over more than 25 km of coast (37.1°N/8.6°W) down to 30 m depth. Eunicella labiata, Eunicella gazella, Eunicella verrucosa and Leptogorgia sarmentosa were abundant and frequent in the studied area, while Leptogorgia lusitanica was less abundant. All species evidenced a similar depth pattern, that is abundance significantly increased with depth below 15 m. At shallower waters (up to 15 m), the distribution of gorgonians may be constrained by abiotic factors and competition with algae. Indeed, the abundance of gorgonians was negatively correlated with the percentage cover of algae along the depth gradient, but gorgonians and sponges coexist. Competition among gorgonian species also seems to be low in this area because of the similarity in the abundance pattern observed for the most abundant species and also their high association. In NE Atlantic shallow temperate rocky bottoms, the distribution of gorgonians seems to be influenced by environmental factors and biological interactions, namely competition (algae) and coexistence (sponges and other gorgonians).     

Zonation of submerged macrophyte vegetation in Lake Kariba,Zimbabwe and its ecological interpretation

The submerged vegetation of Lake Kariba is described in relation to degree of slope (lake morphometry), depth and light transparency. The direct gradient analysis technique — canonical correspondence analysis and the TWINSPAN classification programs were used to analyse the data set. The western end of the lake with low transparency has a low species diversity (with Vallisneria aethiopica dominating). Species diversity increases with increased transparency in the other parts of the lake. The classification revealed monospecific communities for all species as well as mixed communities with Lagarosiphon as the associate species with the broadest distribution. The ordination revealed a first axis strongly related to depth and transparency gradients and the second axis related to slope. Vallisneria aethiopica has a growth form adapted to grow in shallow areas subjected to wave action. Potamogeton octandrus also growing in shallow areas is restricted to sheltered areas. Lagarosiphon ilicifolius precluded from the shallow exposed areas grows at medium depth but has a growth form adapted to tap light at the surface. Najas pectinata and Ceratophyllum demersum are adapted to grow in deep water.Abbreviations CCA Canonical correspondence analysis     

Distribution and environmental control of coral assemblages in northern Safaga Bay (Red Sea, Egypt)

Summary Coral assemblages in northern Safaga Bay, Red Sea, Egypt, are qualitatively described. Nine distinct assemblages were found, which correspond to quantitatively defined community types previously described from the area off Hurghada, northern Red Sea. Their distribution within northern Safaga Bay was mapped. Strong gradient and/or steep relief assemblages were:Acropora assemblage on windward (exposed) reefs,Porites assemblage on leeward (sheltered) reefs,Millepora assemblage on current exposed reefs,Stylophora assemblage on reef flats. Low gradient and/or low relief assemblages were:Acropora dominated coral patches in areas of good circulation to a depth of 15 m,Stylophora/Acropora coral patch assemblages in shallow sheltered environments, faviid carpet in low relief areas between 10 and 25 m which with increasing turbidity turns into a depauperate faviid carpet,Porites carpet in low relief areas between 5 and 15 m with clearest water,Sarcophyton carpet in low relief areas with high suspension load, platy scleractinian assemblage in deeper water (>25 m) with low light intensity. The distribution of coral assemblages depends basically on 1) topography 2) hydrodynamics 3) light and 4) suspension load.     

Taconic Foreland Basin graptolites: age zonation, depth zonation, and use in ecostratigraphic correlation

Late Middle Ordovician graptoloids are stratigraphically zoned by depth of deposition as well as by age along an 83 km long downslope transect through a roughly four million year long continental-shelf and outer-trench slope sequence in the Mohawk Valley, New York. The distribution of graptoloid assemblages parallels the distribution of sediment types and benthic macroinvertebratc assemblages in showing the general, convergence-related marine transgression, secondary transgressive and regressive pulses, and topographic irregularities related to syndepositional block faulting. The relationship of ordination scores for graptoloid assemblages (which arc based on relative abundances of genera) to the samples' positions on downslope transects along bentonite beds, and to depth-related ordination scores for benthic macroin-vertebrate assemblages in the same samples throughout the sequence, quantitatively demonstrates zonation by depth of deposition. Rather like modern pelagic colonial tunicates, graptoloids were evidently zoned by depth in the water column, with Orthograptus spp. predominating in offshore waters above the oxygen minimum zone, Climacograptus spp. near the top of the minimum zone at 300 to 500 m depths, and Corynoides spp. well within the minimum zone. Destruction of sinking rhabdosomes by decomposers evidently accentuated zonation by depth of deposition, and may have contributed to the strong, broad oxygen minimum zone thought to have been characteristic of graptolitic shale basins. Stratigraphic sections' approximate relative sea level curves, calibrated in terms of graptoloid assemblage ordination score, give ecostratigraphic correlations of 2–3 × 10⁵ year average accuracy when statistically cross-correlated between sections, and when cross-correlated with similar curves based on benthic macroinvertebratc assemblage ordination score. □Graptolithina, age zonation, depth zonation, paleoeco-logy, Middle Ordovician, ecostratigraphy, coenocorrelation.     

Geomorphology and benthic cover of mesophotic coral ecosystems of the upper insular slope of southwest Puerto Rico

The upper insular slope of southwest Puerto Rico is defined as extending from the shelf break at ~20 m water depth down to a depth of ~160 m where there is a pronounced change in geomorphic character and the basal slope begins. The upper slope is divided into two geomorphic zones separated by a pronounced break in slope gradient at ~90 m water depth. Descending from the shelf break, these are Zone I (20–90 m) and Zone II (90–160 m). As orientation of the shelf margin changes, geomorphology of Zone I shows systematic variations consistent with changes in exposure to prevailing waves. Within Zone I, exposed southeast-facing slopes have a gentler gradient and lower relief than more sheltered southwest-facing slopes, which are steep and irregular. Mesophotic coral ecosystems (MCEs) are largely restricted to Zone I and concentrated on topographic highs removed from the influence of active downslope sediment transport. Accordingly, MCEs are more abundant, extensive and diverse on southwest-facing slopes where irregular topography funnels downslope sediment transport into steep narrow grooves. MCEs are more sporadic and widely spaced on southeast-facing slopes where topographic highs are more widely spaced and downslope sediment transport is spread over open, low-relief slopes inhibiting coral recruitment and growth. Relict features formed during preexisting sea levels lower than present include deep buttresses at ~45–65 m water depth and a prominent terrace at ~80 m. Based on correlations with existing reef accretion and sea-level records, it is proposed that the 80-m terrace formed during the last deglaciation ~14–15 ka and subsequently drowned during a period of rapid sea-level rise associated with meltwater pulse 1A at ~14 ka and deep buttresses at ~45–65 m formed between ~11.5 and 13.5 ka and then drowned during a period of rapid sea-level rise associated with meltwater pulse 1B at ~11.3 ka.     

Chironomidae (Diptera) larvae assemblages differ along an altitudinal gradient and temporal periods in a subtropical montane stream in Northwest Argentina

The objective of this study was to analyze the spatial and temporal dynamics of Chironomidae larvae assemblages in a subtropical mountain river basin of northwestern Argentina. We hypothesized that they would respond to (1) environmental changes along the altitudinal gradient in the Yungas forests; (2) environmental changes caused by spates (e.g., increased discharge or sediment transportation). We sampled five sites along an altitudinal gradient of ca. 1,500 m (from 680 to 2,170 m) during low-water and high-water period for 2 years. The Chironomidae larvae assemblages varied along the altitudinal gradient and between sampling periods based on an indicator species analyses and an ordination analyses (NMDS). The best indicator for high altitude sites was “Genus X” followed by Onconeura sp.2, “Genus 9”, “Genus 10”, and Rheotanytarsus sp.2; while Rheotanytarsus lamellatus, Oliveiriella sanjavieri, and Thienemanniella sp. were good indicators for low altitude sites. O. sanjavieri and R. lamellatus were the best indicators for high-water period. The most relevant environmental variables influencing their spatial and temporal distribution were altitude, water temperature, conductivity, and pH. This study is the first to analyze and describe in detail the spatial and temporal distribution of Chironomidae larvae assemblages in northwestern Argentina, and most of the taxa reported here are new records for the region.     

Interpretation of the fossil record of Acanthaster planci from the Great Barrier Reef: a reply to criticism

The nature and interpretation of the fossil record of Acanthaster planci from the GBR is reviewed in the light of comments from Keesing et al. (1992) and Pandolfi (1992). Skeletal remains of A. planci in reef-top sediment of many reefs has been derived from very large numbers of individuals, indicating substantial, long-term mortality at reef-top locations. The fossil record provides useful perspective on mortality patterns in the absence of substantive ecological data. The incidence of skeletal elements on reefs where they are abundant cannot be adequately accounted for by the mortality of non-outbreak populations as estimated by recent surveys. Analysis of all available data reaffirms a relationship between the incidence of skeletal elements in surface sediment and observed outbreak history. There is no presently identified taphonomic mechanism by which the accumulation of A. planci skeletal elements released on death might be systematically biased relative to other skeletal components of reefal sediment. Because of skeletal degradation, physical transport and extensive bioturbation that applies in shallow-water reefal sediment, reconstructive taphonomic analysis of A. planci skeletal remains is not achievable. Core sediment, on which interpretation of the longterm fossil record of A. planci is based, is homogeneous, unstratified, and has experienced substantial time averaging due to pervasive bioturbation. Extensive bulk sediment dating has shown that the cores have retained a general age structure but fine-scale stratigraphic detail, required for the recognition of outbreak events from the fossil record available in reefal sediment is unlikely. As required by the principle of simplicity, the proposition that abundant A. planci skeletal elements found in sediment from Green Island, John Brewer and other reefs of the GBR represent the time-averaged product of outbreaking populations should be adopted as the favoured working hypothesis. Other alternative explantions have been advanced but all require patterns or processes that have yet to be substantiated.     

Understorey vegetation change in a Picea mariana chronosequence

Eighteen black spruce (Picea mariana) stands, representing postfire ages of 26 to 120 yr, were surveyed for understorey vegetation and site/microsite characteristics at two spatial scales. This enabled comparison of within- versus among-stand compositional variation.Detrended correspondence analysis (DCA) ordination among the 18 stands revealed a complex age/moisture gradient. DCA ordination among 1 800 quadrats within the stands indicated a similar gradient with much compositional overlap. Quadrats were grouped, using two-way indicator species analysis (TWINSPAN), into 9 classes each representing a phase in understorey vegetation composition. These phases shifted in abundance from young to old stands with a high degree of concordance among replicates in the same age class. Understorey succession is strongly linked to the stages in tree growth, mortality and thinning coupled with the accumulation of site moisture.Abbreviations DCA Detrended Corrospondence Analysis     

How does coarse gravel augmentation affect early‐stage Chinook salmon Oncorhynchus tshawytscha embryonic survivorship?

Early‐stage Chinook salmon Oncorhynchus tshawytscha embryos were incubated in artificial redds that mimicked hyporheic conditions in gravel‐augmented habitat to assess survivorship. Two complementary experiments were conducted where units varied along gradients of (1) increasing interstitial flow velocity (0·05–2·50 cm s^?1) in a uniformly coarse (particles ≥22 mm) sediment mixture and (2) increasing sediment porosity with interstitial flow velocity held constant. Embryonic survivorship increased moderately along a gradient of interstitial flow velocity, while survivorship among units with varying sediment porosities was consistent. No evidence for flow‐induced agitation and mortality was observed. Results suggest that high interstitial flow velocities may confer a moderate advantage for incubating salmonid embryos when conditions that typically reduce embryonic mortality (i.e. low concentrations of fine particles) are ideal.     

Bacterial communities reflect the spatial variation in pollutant levels in Brazilian mangrove sediment

The majority of oil from oceanic oil spills converges on coastal ecosystems such as mangrove forests. A major challenge to mangrove bioremediation is defining the mangrove’s pollution levels and measuring its recuperation from pollution. Bioindicators can provide a welcome tool for defining such recovery. To determine if the microbial profiles reflected variation in the pollutants, samples from different locations within a single mangrove with a history of exposure to oil were chemically characterised, and the microbial populations were evaluated by a comprehensive range of conventional and molecular methods. Multivariate ordination of denaturing gradient gel electrophoresis (DGGE) microbial community fingerprints revealed a pronounced separation between the sediment and rhizosphere samples for all analysed bacterial communities (Bacteria, Betaproteobacteria, Alphaproteobacteria, Actinobacteria and Pseudomonas). A Mantel test revealed significant relationships between the sediment chemical fertility and oil-derived pollutants, most of the bacterial community fingerprints from sediment samples, and the counts by different cultivation strategies. The level of total petroleum hydrocarbons was significantly associated with the Bacteria and Betaproteobacteria fingerprints, whereas anthracene and the total level of polycyclic aromatic hydrocarbons were associated with the Actinobacteria. These results show that microbial communities from the studied mangrove reflect the spatial variation of the chemicals in the sediment, demonstrating the specific influences of oil-derived pollutants.     

藏北高原草地群落的数量分类与排序

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。     

Toxicity of Santander Bay Sediments to the Euryhaline Freshwater Oligochaete Limnodrilus hoffmeisteri

The freshwater euryhaline oligochaete Limnodrilus hoffmeisteri was selected for use in bioassays with polluted sediment from Santander Bay. It is easy to culture; is tolerant of low to moderate, up to 15‰, salinity; and is common in oligohaline conditions in European and North American estuaries. Worms were collected from an estuarine population and kept in unpolluted sediment for between 2 and 4 weeks, under laboratory conditions, at 7–8.5‰ salinity and 22.5 °C. Sediment from different sites in Santander Bay were sieved through 250 μm mesh and adjusted to a salinity of approx. 7‰ prior to the bioassays, either by adding sea water or dechlorinated tap water to the overlying water. High levels of ammonia in some sediment, which may confound results in ecotoxicity bioassays, were reduced by oxidation of the sediments in shallow trays. Sediment bioassays were performed with sexually mature Limnodrilus hoffmeisteri worms in 250-ml beakers, with a 1:3 ratio of sediment:water and 4 worms per baker. Endpoints in the 14-day bioassay were % mortality, adult final biomass, % adults that have shown resorption of the clitellum, number of cocoons, and burrowing behaviour. It was possible to rank the sites according to their toxicity using both mortality rates and sublethal effects. The control site had the following values for the endpoints: 5% mortality, ( ) 2.40 ± 1.52 cocoons per beaker and 1.271 ± 0.470 mg dw adult final biomass. The most toxic sediment resulted in 65% mortality, resorption of the clitellum in 67% of the adults, no production of cocoons and a low final biomass ( =0.681 ± 0.489 mg dw per adult). A second site had high mortality (60%) and no reproduction, although resorption of the clitellum did not occur in surviving animals. The remaining sites showed similar mortality (35–42%), and at only one of them was low reproduction observed (0.8 ± 0.447 cocoons per beaker). Behavioural effects, measured as length of galleries in a fixed area of the test-vessel at the end of the bioassay, were significant compared with control at only one site. Multivariate analysis showed the mortality gradient to be the strongest, with a second unassociated gradient representing clitellum resorption. The mortality gradient was associated with Cu and Zn concentration, and PAH and Pb possibly with resorption.     

祁连山东段高寒植被群落特征及其与地形气候因子关系研究

地形气候因子与物种分布的关系影响着高寒植被群落的演替,同时对山地水源涵养林功能和结构的维持具有重要的意义。以祁连山东段水源涵养林为研究对象,基于野外植物群落物种组成及地形气候因子调查数据,运用数量分类与排序等方法,探究了高寒植物群落特征及其与地形气候因子的关系。结果表明:65个调查样方中出现181个植物种,隶属40科,124属。科的物种组成及占总物种数比例分别为菊科30个种,占16.57%;蔷薇科17个,占9.44%;禾本科13个种,占7.22%;豆科11个种,占6.11%。毛茛科10个种,占5.56%。单属种82个,占总属数的66.13%。群落层片由乔木层、灌木层和草本层组成,乔木8种,灌木25种,草本148种。乔木层优势种有青海云杉、祁连圆柏、红桦。灌木层优势种有金露梅、山生柳、匙叶小檗、高山绣线菊。草本层优势种有甘肃薹草、珠芽蓼、早熟禾、唐松草、甘青蒿。TWINSPAN将高寒植被群落划分为7个群丛类型:群丛I红桦-红花蔷薇-甘肃薹草B.albosinensis-Rosa moyesii-C.kansuensis,群丛II青海云杉-匙叶小檗-甘肃薹草P.crassifolia-B.vernae-C.kansuensis,群丛III祁连圆柏-高山绣线菊-珠芽蓼Sabina chinensis-Spiraea alpine-P.viviparum,群丛IV高山绣线菊+鬼箭锦鸡儿-珠芽蓼S.alpine+Caragana jubata-P.viviparum,群丛V沙棘+甘青蒿+鼠掌老鹳草Hippophae rhamnoides+A.tangutica+Geranium sibiricum,群丛VI沙棘+苦荬菜+苦荞麦H.rhamnoides+Ixeris polycephala+Fagopyrum tataricum,群丛VII沙棘-冰草+西北沼委陵菜H.rhamnoides-Agropyron cristatum+Comarum salesovianum。7个群丛在DCA排序图上聚集分布,反映了较好的环境梯度。CCA排序结果表明,海拔是祁连山高寒植被群落植物种分布的最重要环境因子,其次是降水、温度、坡向、坡度。     

Upper Eocene larger foraminiferal–coralline algal facies from the Klokova Mountain (southern continental Greece)

Within the Gavrovo–Tripolitza area (southern continental Greece), marine carbonate platforms existed from the Late Triassic to the Late Eocene. The Middle–Upper Eocene marine shallow-water carbonates of the Klokova Mountain represent remnants of the large volumes of sediment that were produced on a middle ramp sedimentary system which culminated in the Lower Oligocene terrigenous deposits. Facies analysis of Bartonian–Priabonian shallow-water carbonate successions and the integration with palaeoecological analysis are used to produce a detailed palaeoenvironmental model. In the proximal middle ramp, porcelaneous foraminiferal packstone facies is characterised by larger foraminifera such as Praturlonella and Spirolina. These forms thrived in a shallow-water setting with low turbidity, high-light intensity and low-substrate stability. The foraminiferal packstone facies, the thin coralline wacke–packstone facies and the rhodolith packstone facies deposited approximately in the same depth range adjacent to one another in the middle-ramp. Nummulitids (Nummulites, Assilina, Pellatispira, Heterostegina and Spiroclypeus) increase in abundance in the middle to distal mid-ramp together with the orthophragminids. Coralline algae, represented by six genera, are present in all facies. Rhodoliths occur in all facies but they show different shapes and growth forms. They develop laminar sub-ellipsoidal shapes in higher turbulence conditions on mobile sand substrates (foraminiferal packstones and rhodolith rudstones), whilst sub-discoidal shapes often bound by thin encrusting coralline plants in lower hydrodynamic settings. The distinctive characteristics of the palaeoecological middle-ramp gradient are an increase in dominance of melobesioids, a thinning of the encrusting coralline plants and a flattening of the larger benthic foraminiferal shells.     

Resuspension created by bedload transport of macroalgae: implications for ecosystem functioning

Previous studies suggest that current-driven plant transport in shallow lagoons and estuaries is associated with increased turbidity. Our hypothesis is therefore that macroalgae erode surface sediment while drifting as bedload. This ballistic effect of moving plants on surface sediment was tested in a series of controlled annular flume experiments, where simultaneous measurements of macrophytes transport and turbidity were conducted at increasing current velocities. Sediment erosion always started earlier in experiments with plants than in control experiments without plants. Turbidity increased immediately when plants started to move at current velocities of 2–4 cm s⁻¹. From a background concentration of 7–10 mg SPM l⁻¹, turbidity increased to 30–50 mg SPM l⁻¹ for Ceramium sp., Ulva lactuca and Chaetomorpha linum, while the more rigid Gracilaria sp., caused much higher turbidities (50–180 mg SPM l⁻¹). Such plant induced sediment erosion at low current velocity can explain the observed appearance of turbid waters in estuaries and lagoons in the absence of strong wind and wave action. Based on 3-D hydrodynamic modelling, it was determined that plant driven erosion occurs during most of the growth season in a shallow eutrophic estuary (Odense Fjord, Denmark).     

基于地形梯度的甘肃白龙江流域典型生态系统服务分布特征

白龙江流域是长江上游重要的水源涵养区和生态屏障,同时也是国家级贫困县集中连片区(秦巴山区)。基于ArcGIS软件和InVEST模型,从高程、坡度、地形起伏度、地形位指数等方面分析了甘肃白龙江流域典型生态系统服务的地形梯度特征。结果表明:(1)甘肃白龙江流域碳储量、水源涵养、生境质量、土壤保持服务功能的空间分异明显,其高值区主要分布在自然保护区、林区,低值区则在河谷、城镇、农耕地区。(2)碳储量、水源涵养和生境质量随着坡度和地形起伏度的增加而增加,土壤保持则呈先增加后降低的趋势,随地形位指数增加呈现波动变化;(3)流域综合生态系统服务供给重要区域逐渐向两极分化,多种生态系统供给服务的重要区域主要在中高梯度片区,而一般区主要分布在低梯度片。地形特征是影响流域生态系统服务梯度差异的重要因素。通过分析流域不同地形因子下分析碳储量、水源涵养、生境质量、土壤保持的空间分异特征,可为中国西部山地流域生态系统格局优化管控和生态文明建设提供科学依据。     

Transgression, regression and fossil community succession

Recent paleoecological studies have emphasized the recognition of successional stages of level-bottom communities, but have neglected to point out techniques for distinguishing succession within a fossil community from the temporal and spatial replacement of one fossil community by another. The physical integrity of a marine level-bottom community is discernible, in most instances, through careful temporal and spatial study, and one community can be distinguished from another by judicious application of the 'end-member' concept. Community boundaries are only as distinct as the associated environmental stress gradient. Of first-order significance in understanding fossil community succession and replacement is appreciation of the basic asymmetry of the community dynamics involved in transgression-regression events. Of second-order importance is appreciation of the nature of the onshore-offshore environmental stress gradient, which, in turn, is controlled by the physical setting of transgression-regression (e.g. progradation versus eustatic control; high topographic relief versus low topographic relief, etc.). The application of the preceding concepts is shown by detailed study of community succession and replacement in the Cambridge Limestone (Upper Pennsylvanian), Guernsey County, Ohio.     

秦岭山地天然次生林群落MRT数量分类、CCA排序及多样性垂直格局

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。