Ecosystem response to removal of exotic riparian shrubs and a transition to upland vegetation

Understanding plant community change over time is essential for managing important ecosystems such as riparian areas. This study analyzed historic vegetation using soil seed banks and the effects of riparian shrub removal treatments and channel incision on ecosystem and plant community dynamics in Canyon de Chelly National Monument, Arizona. We focused on how seeds, nutrients, and ground water influence the floristic composition of post-treatment vegetation and addressed three questions: (1) How does pre-treatment soil seed bank composition reflect post-treatment vegetation composition? (2) How does shrub removal affect post-treatment riparian vegetation composition, seed rain inputs, and ground water dynamics? and (3) Is available soil nitrogen increased near dead Russian olive plants following removal and does this influence post-treatment vegetation? We analyzed seed bank composition across the study area, analyzed differences in vegetation, ground water levels, and seed rain between control, cut-stump and whole-plant removal areas, and compared soil nitrogen and vegetation near removed Russian olive to areas lacking Russian olive. The soil seed bank contained more riparian plants, more native and fewer exotic plants than the extant vegetation. Both shrub removal methods decreased exotic plant cover, decreased tamarisk and Russian olive seed inputs, and increased native plant cover after 2 years. Neither method increased ground water levels. Soil near dead Russian olive trees indicated a short-term increase in soil nitrogen following plant removal but did not influence vegetation composition compared to areas without Russian olive. Following tamarisk and Russian olive removal, our study sites were colonized by upland plant species. Many western North American rivers have tamarisk and Russian olive on floodplains abandoned by channel incision, river regulation or both. Our results are widely applicable to sites where drying has occurred and vegetation establishment following shrub removal is likely to be by upland species.     

Vegetation dynamics of Mediterranean shrublands in former cultural landscape at Grazalema Mountains,South Spain

Plant community dynamics in Mediterranean basin ecosystems are mainly driven by an alternation of episodes of human intervention and land abandonment. As a result, a mosaic of plant communities has evolved following different stages of degradation and regeneration. Some authors has relate secondary succession to abandoned culture lands and regeneration to natural systems with abandonment of livestock or forestry exploitation. In this paper, the dynamics of shrublands in mid-mountain areas in the South of Spain after disturbance and land abandonment has been studied. The plant cover and 13 environmental variables of 137 selected sites on the Grazalema mountains was analysed to determine the vegetation pattern in relation to environmental factors and the succession types, either regenerative or secondary succession. The results show that today the Grazalema mountains have a heterogeneous vegetation pattern. Besides physical factors such as altitude or soil , human disturbance has modulated current vegetation patterns and dynamics. Two main types of vegetation dynamics can be distinguished in the study area. In areas affected by cutting, regeneration results in rich and dense shrub land, with resprouters as dominant species. In areas affected by recurrent wildfires or agriculture, secondary succession became dominant, resulting in less diverse shrubland, due to the dominance of seeders and decrease in resprouter species richness and cover.     

Are plant functional types relevant to describe degradation in arid,southern Tunisian steppes?

Abstract. In the Tunisian arid zone disturbances (e.g. overgrazing and agriculture) and stresses (e.g. aridity, low fertility) drive changes in the structure and functioning of rangelands, with a decrease in perennial plant cover, changes in floristic composition and erosion. Long‐term monitoring requires (1) an understanding of the dynamics of vegetation change and associated ecological processes and (2) identification of relevant indicators. Using data from the arid zone of southern Tunisia we tested the hypothesis that plant functional response types could be used to address these two goals. We identified plant functional response types in response to a gradient of soil and vegetation types characterized by changes in perennial plant cover, dominant species and associated soil types. Vegetation samples were stratified by contrasted vegetation patch types with varying perennial plant cover (1.6 to 22%). We focused our analysis of trait responses within dwarf–shrubs, which are the dominants in typical steppe ecosystems of south Tunisia. Available trait data concerned morphology (plant height, leaf type), regeneration (dispersal mode, phenology and regeneration mode) and grazing value. Although we found it difficult to recognize ‘indicator response types’ that could be used directly to monitor changes in community composition, we were able to identify plant response syndromes that are relevant to long‐term vegetation changes, and in particular degradation processes, in the region. Two main response types were identified: the decreaser type, made up of small or medium chamaephytes with high grazing palatability and the increaser type with medium to tall chamaephytes and low grazing palatability. These response types are proposed as key elements in a state‐and‐transition model of vegetation dynamics in the context of agropastoral disturbances and climatic and edaphic stresses.     

General and specific responses of understory vegetation to cervid herbivory across a range of boreal forests

Understanding the responses of ecological communities to perturbation is a key challenge within contemporary ecology research. In this study we seek to separate specific community responses from general community responses of plant communities to exclusion of large cervid herbivores. Cervid herbivory and forestry are the main drivers of vegetation structure and diversity in boreal forests. While many studies focus on the impact of cervids on trees, a high proportion of the biodiversity and ecosystem services in boreal forests is found in the field layer. However, experimental approaches investigating the influence of herbivory on understory vegetation are highly localised. In this study we use a regional‐scale design with 51 sites in four boreal forest regions of Norway, to investigate the influence of cervid herbivory on the physical and ecological structure of field layer vegetation. Our study sites cover a range of forest types differing in productivity, management and dominant cervid species, allowing us to identify generic responses and those that are specific to particular conditions. We found that the height of the field layer and the abundances of individual species were most susceptible to change following short‐term cervid exclusion across different forest types and cervid species. Total vegetation density and vascular plant diversity did not respond to cervid exclusion on the same time scale. We also found that the field‐layer vegetation in clear‐cut forests used by moose was more susceptible to change following cervid exclusion than mature forests used by red deer, but no strong evidence that the response of vegetation to herbivore exclusion varied with productivity. Our study suggests that the parameters that respond to cervid exclusion are consistent across forest types, but that the responsiveness of different forest types is idiosyncratic and hard to predict.     

Analysis of macrofungal communities reveals a complex reciprocal influence between Mediterranean montane calcareous grassland and surrounding forest habitats

Fungi are essential components of all terrestrial ecosystems. Despite the crucial ecological role of soil fungi in grasslands, knowledge about fungal community diversity and structure in Mediterranean meadow habitats is still fragmentary. We analyzed macrofungal communities in three geographically distinct Mediterranean montane calcareous grasslands and surrounding forests, by means of fruit body surveys. We investigated a number of biotic and abiotic factors influencing the studied fungal communities, including plant species composition. Out of 6365 fruit bodies, a total of 268 species belonging to 84 genera were found. In general, there was a significant correlation between plant species richness and fungal richness. Variation in vegetation and plant community structure accounted for approximately 20% of variance in fungal community structure. Tree and shrub vegetation played a dominant role in shaping the analyzed fungal communities, both in meadows and surrounding forests, with particular influence on ectomycorrhizal, litter, and lignicolous saprotrophic fungi. Fungal biodiversity in the studied meadows was increased by the presence of tree and shrub species from the adjacent forests, but was reduced by the increasing vegetation cover.     

Diversity, ecological structure, and conservation of the landbird community of Dadia reserve, Greece

Birds are integral to many environmental monitoring schemes. However, there has been little research on the ecological basis of utilizing bird species as indicators of their respective communities and habitats. We used point counts to survey 72 landbird species, 16 of conservation concern, in the Dadia Nature Reserve, Greece, in order to understand the ecology of bird diversity patterns, analyse community composition, identify species characteristic of major vegetation types, and improve long-term management and monitoring protocols. We sampled 36 sites representing 21 vegetation types. Highly heterogeneous sites were the most species rich and rural mosaics (small fields and pastures of low intensity land use, separated by thick hedgerows and tree lines) were twice as rich as intensified crop monocultures. Using multivariate analysis, we found that vegetation cover and height affected the composition of the avifauna. Twenty-one predefined vegetation categories clustered into eight distinct bird habitat types: field crops, rural mosaics, mosaic sites, poplar trees, broadleaved woods, pinewoods, shrubs, and heaths. Ten bird species were highly characteristic of the main bird habitat types in the study area. Our results emphasize the importance of conserving rural mosaics, hedgerows, and openings within forests for landbird conservation in the Mediterranean countryside. We also provide evidence in support of maintaining horizontal heterogeneity at a local scale. Finally, we suggest that monitoring populations of certain indicator bird species can be a cost-effective and efficient way to monitor the state and habitat quality of the entire landbird community, thereby integrating the knowledge of community structure into conservation decision-making.     

Remotely sensed vegetation phenology and productivity along a climatic gradient: on the value of incorporating the dimension of woody plant cover

Aim Woody plants affect vegetation–environment interactions by modifying microclimate, soil moisture dynamics and carbon cycling. In examining broad‐scale patterns in terrestrial vegetation dynamics, explicit consideration of variation in the amount of woody plant cover could provide additional explanatory power that might not be available when only considering landscape‐scale climate patterns or specific vegetation assemblages. Here we evaluate the interactive influence of woody plant cover on remotely sensed vegetation dynamics across a climatic gradient along a sky island. Location The Santa Rita Mountains, Arizona, USA. Methods Using a satellite‐measured normalized difference vegetation index (NDVI) from 2000 to 2008, we conducted time‐series and regression analyses to explain the variation in functional attributes of vegetation (productivity, seasonality and phenology) related to: (1) vegetation community, (2) elevation as a proxy for climate, and (3) woody plant cover, given the effects of the other environmental variables, as an additional ecological dimension that reflects potential vegetation–environment feedbacks at the local scale. Results NDVI metrics were well explained by interactions among elevation, vegetation community and woody plant cover. After accounting for elevation and vegetation community, woody plant cover explained up to 67% of variation in NDVI metrics and, notably, clarified elevation‐ and community‐specific patterns of vegetation dynamics across the gradient. Main conclusions In addition to the environmental factors usually considered – climate, reflecting resources and constraints, and vegetation community, reflecting species composition and relative dominance – woody plant cover, a broad‐scale proxy of many vegetation–environment interactions, represents an ecological dimension that provides additional process‐related understanding of landscape‐scale patterns of vegetation function.     

Effects of cover soil stockpiling on plant community development following reclamation of oil sands sites in Alberta

Stockpiling of cover soil can influence vegetation development following reclamation. Cover soil, comprising the upper 15–30 cm of the surface material on sites scheduled for mining, is commonly salvaged prior to mining and used directly or stockpiled for various lengths of time until it is needed. Salvaging and stockpiling causes physical, chemical, and biological changes in cover soils. In particular, stockpiling reduces the availability and vigor of vegetative propagules and seed, and can lead to increases in the abundance of some weedy species. This study uses data from monitoring plots to assess how stockpiling of cover soil impacts plant community development on reclaimed oil sands mine sites in northern Alberta. Development of plant communities differed distinctly between directly placed and stockpiled cover soil treatments even 18 years after reclamation. Direct placement of cover soil resulted in higher percent cover, species richness, and diversity. Nonmetric multidimensional scaling and multiresponse permutation procedure revealed compositional differentiation between the treatments. Indicator species analysis showed that direct placement treatment was dominated by perennial species while grasses and annual forb species dominated sites where stockpiled soil was used. Results indicate that stockpiling leads to slower vegetation recovery while direct placement of cover soil supports more rapid succession (from ruderal and annual communities to perennial communities). In addition, direct placement may be less costly than stockpiling. However, scheduling of salvage and placement remains a challenge.     

Regional productivity mediates the effects of grazing disturbance on plant cover and patch‐size distribution in arid and semi‐arid communities

Patch‐size distribution and plant cover are strongly associated to arid ecosystem functioning and may be a warning signal for the onset of desertification under changes in disturbance regimes. However, the interaction between regional productivity level and human‐induced disturbance regime as drivers for vegetation structure and dynamics remain poorly studied. We studied grazing disturbance effects on plant cover and patchiness in three plant communities located along a regional productivity gradient in Patagonia (Argentina): a semi‐desert (low‐productivity community), a shrub‐grass steppe (intermediate‐productivity community) and a grass steppe (high‐productivity community). We sampled paddocks with different sheep grazing pressure (continuous disturbance gradients) in all three communities. In each paddock, the presence or absence of perennial vegetation was recorded every 10 cm along a 50 m transect. Grazing effects on vegetation structure depended on the community and its association to the regional productivity. Grazing decreased total plant cover while increasing both the frequency of small patches and the inter‐patch distance in all communities. However, the size of these effects was the greatest in the high‐productivity community. Dominant species responses to grazing explained vegetation patch‐ and inter‐patch‐size distribution patterns. As productivity decreases, dominant species showed a higher degree of grazing resistance, probably because traits of species adapted to high aridity allow them to resist herbivore disturbance. In conclusion, our findings suggest that regional productivity mediates grazing disturbance impacts on vegetation mosaic. The changes within the same range of grazing pressure have higher effects on communities found in environments with higher productivity, markedly promoting their desertification. Understanding the complex interactions between environmental aridity and human‐induced disturbances is a key aspect for maintaining patchiness structure and dynamics, which has important implications for drylands management.     

Understory Plant Community Composition Is Associated with Fine-Scale Above- and Below-Ground Resource Heterogeneity in Mature Lodgepole Pine (Pinus contorta) Forests

Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species.     

Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra

An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above‐ and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.     

Acridid communities (Orthoptera: Acrididae,pyrgomorphidae, pamphagidae,tetrigidae) of dominant plant associations in the Kopet Dagh foothills and plain

Acridid communities of the dominant plant associations on the Kopet Dagh northern foothills and foothill plain are described for the first time. The structure of the communities is determined by the plant cover and soil conditions. Acridid communities of natural plant associations are characterized by high species and ecological diversity (at least 13 species and subspecies, 11 types of life forms), high abundance (about 1000 ind./h), and polydominant structure.     

Long-term effects of climate and phosphorus fertilisation on serpentine vegetation

The long-term effects of phosphorus fertilisation and climate on serpentine plant communities in Tuscany, central Italy have been investigated by using data from a 12 year before-after control-impact (BACI) experiment. Using the point quadrat method, data on plant communities were collected in June of each year from 1994 to 2005 in eight 2 × 2 m plots, four fertilised with phosphorus and four used as controls. Climatic data were obtained from a nearby meteorological station and summarised in 24 variables. Phosphorus addition significantly affected vegetation cover of both vascular and cryptogamic vegetation but did not influence species richness. The effects on species composition were clear but not marked, and consisted in promoting the abundance of some species already present in the community but not leading to the colonisation of other species. Interannual climate differences affected vegetation cover in the fertilised plots but not in the control ones, while climate affected the species richness values of different/various life-forms in both groups of plots, with more evident effects in the fertilised one. The effects of climate on plant community composition were weak once both the variability among individual plots and the successional dynamics were subtracted from the variance in species composition.     

Plant community resilience in the face of fire: experimental evidence from a semi‐arid shrubland

The ability of communities or ecosystems to recover their structure and function after a disturbance is known as resilience. According to different views, resilience can be influenced by the resource‐use strategies of the plant functional types that dominate the community or by the existence of functional redundancy within plant functional types. We investigated how the dominance of different plant functional types and species affected the resilience of a mountain shrubland after an intense fire. We took advantage from a pre‐existing long‐term removal experiment in which either whole plant functional types (deciduous shrubs, graminoids, perennial forbs and annual forbs) or the dominant species within each plant functional type were removed for 10 years. We sampled species and plant functional types cover during the first growing season after the fire. First, to test whether functional redundancy increased resilience, we analyzed the existence of functional compensation inside plant functional types. Second, to test whether the dominance of plant functional types with different resource‐use strategies affected recovery, we compared resilience at the levels of species, plant functional types and total cover, estimated on the basis of a change index and multivariate Euclidean distances. No compensation was observed in any of the plant functional types. At the level of species, we found that the assemblages dominated by conservative resource‐use strategies were the ones showing higher resilience. This was due to the high recovery of the dominant species of shrubs plant functional type. The opposite (lowest recovery of conservative resource‐use strategies) was found at the plant functional type and total cover‐levels. Our study did not support the hypothesis of resilience by functional redundancy. Instead, regeneration by buried meristems from the pre‐fire stage appeared to be the factor that most influenced recovery. Resource‐use strategies explained resilience of vegetation cover, but not of floristic composition. Regeneration traits, rather than vegetative traits or mechanism of functional compensation, appeared as the most relevant to explain the response of this system after fire.     

Habitat structure and neighbor linear features influence more carabid functional diversity in olive groves than the farming system

The effects of land-use management and environmental features at different scales on carabid beetle diversity and trait structure were assessed across olive groves in northeastern Portugal. We selected organic and integrated olive groves that were distinct in terms of specific management practices, local linear features and landscape configurations. Besides the management intensification levels, differences in carabid diversity and community traits were mainly due to local habitat and ecological linear structures at a finer spatial scale. Carabid community traits related to disturbance, namely traits of body size and species dispersal ability, responded to land-use intensity and particular olive grove features were influencing diversity patterns. Within the olive grove patches, larger and brachypterous species were associated to plots with more dense vegetation cover while macropterous and small-sized species were more associated to open areas. Also, larger carabid species benefitted from higher patch size heterogeneity within the landscape mosaics. Our findings indicate that the effects of farming system is contingent on the specific management practices, local and linear features present in agroecosystems such as olive groves. Particularly, the influence of local features on carabid diversity patterns and community traits linked to dispersal and movement may be crucial in maintaining pest control at a landscape scale.     

Multi-Scale Associations between Vegetation Cover and Woodland Bird Communities across a Large Agricultural Region

Improving biodiversity conservation in fragmented agricultural landscapes has become an important global issue. Vegetation at the patch and landscape-scale is important for species occupancy and diversity, yet few previous studies have explored multi-scale associations between vegetation and community assemblages. Here, we investigated how patch and landscape-scale vegetation cover structure woodland bird communities. We asked: (1) How is the bird community associated with the vegetation structure of woodland patches and the amount of vegetation cover in the surrounding landscape? (2) Do species of conservation concern respond to woodland vegetation structure and surrounding vegetation cover differently to other species in the community? And (3) Can the relationships between the bird community and the woodland vegetation structure and surrounding vegetation cover be explained by the ecological traits of the species comprising the bird community? We studied 103 woodland patches (0.5 - 53.8 ha) over two time periods across a large (6,800 km²) agricultural region in southeastern Australia. We found that both patch vegetation and surrounding woody vegetation cover were important for structuring the bird community, and that these relationships were consistent over time. In particular, the occurrence of mistletoe within the patches and high values of woody vegetation cover within 1,000 ha and 10,000 ha were important, especially for bird species of conservation concern. We found that the majority of these species displayed similar, positive responses to patch and landscape vegetation attributes. We also found that these relationships were related to the foraging and nesting traits of the bird community. Our findings suggest that management strategies to increase both remnant vegetation quality and the cover of surrounding woody vegetation in fragmented agricultural landscapes may lead to improved conservation of bird communities.     

Plant communities preferences of terrestrial crustaceans (Isopoda: Oniscidea) in a protected coastal area of southeastern Sicily (Italy)

We studied the plant communities preferences of oniscidean isopods in a protected coastal area in southeastern Sicily that is characterized by ponds, dunes and rocky coast. In total, five sites were sampled between March 2003 and February 2004 using pitfall traps. A total of 7,326 specimens were found, belonging to 23 species. The vegetation analysis, using the phytosociological method, recognized a total of 11 types of plant communities, with specific ecological features. Measuring the species richness, diversity and annual activity density (aAD) values of the terrestrial isopod communities from each sampling site revealed differences among the various plant communities. PCA analysis confirmed the correlation between isopods species and specific plant communities. Moreover our results show that the high species richness is associated with a high vegetation cover and number of plants.     

Browsing‐mediated shrub canopy changes drive composition and species richness in forest‐tundra ecosystems

Changes in climate and in browsing pressure are expected to alter the abundance of tundra shrubs thereby influencing the composition and species richness of plant communities. We investigated the associations between browsing, tundra shrub canopies and their understory vegetation by utilizing a long‐term (10–13 seasons) experiment controlling reindeer and ptarmigan herbivory in the subarctic forest tundra ecotone in northwestern Fennoscandia. In this area, there has also been a consistent increase in the yearly thermal sum and precipitation during the study period. The cover of shrubs increased 2.8–7.8 fold in exclosures and these contrasted with browsed control areas creating a sharp gradient of canopy cover of tundra shrubs across a variety of vegetation types. Browsing exclusions caused significant shifts in more productive vegetation types, whereas little or no shift occurred in low‐productive tundra communities. The increased deciduous shrub cover was associated with significant losses of understory plant species and shifts in functional composition, the latter being clearest in the most productive plant community types. The total cover of understory vegetation decreased along with increasing shrub cover, while the cover of litter showed the opposite response. The cover of cryptogams decreased along with increasing shrub cover, while the cover of forbs was favoured by a shrub cover. Increasing shrub cover decreased species richness of understory vegetation, which was mainly due to the decrease in the cryptogam species. The effects were consistent across different types of forest tundra vegetation indicating that shrub increase may have broad impacts on arctic vegetation diversity. Deciduous shrub cover is strongly regulated by reindeer browsing pressure and altered browsing pressure may result in a profound shrub expansion over the next one or two decades. Results suggest that the impact of an increase in shrubs on tundra plant richness is strong and browsing pressure effectively counteracts the effects of climate warming‐driven shrub expansion and hence maintains species richness.     

金沙江干旱河谷植物群落的数量分类及其结构分异的环境解释

植物群落的空间分异格局是异质生境条件下物种性状、种间相互作用等生态学过程共同作用的结果, 对其分析有助于深入理解群落构建进程。本文基于金沙江流域干旱河谷116个样点562个样方的植物群落调查数据, 采用自适应仿射传播聚类的方法进行群落数量分类, 运用莫兰特征向量地图, 和方差分解的方法对影响群落结构的空间和环境因子进行分析。结果表明: (1)自适应仿射传播聚类将金沙江干旱河谷的植物群落分为30组, 可归为7个植被型, 23个群系, 以稀树草原(30.0%)、暖性落叶阔叶灌丛(55.7%)为最主要的植被类型。(2)年均温和干燥指数是限制金沙江干旱河谷植物群落分布的主要环境因子。稀树草原、肉质灌丛、常绿阔叶灌丛是典型的干热河谷植被类型; 暖性落叶阔叶灌丛、常绿硬叶林是干暖河谷植被的优势类型; 暖性针叶林、落叶阔叶林则主要在干温河谷环境占优势。(3)纯环境因子可以解释群落物种组成变化的5.5%, 纯空间因子可以解释的物种组成变化为22.5%, 有空间结构的环境因子部分为6.6%, 未解释的部分为65.4%。在诸多环境因子中, 年均温及干燥指数的不同显示了不同群落生境的重要差异, 并显著影响到群落的分布格局。大尺度的空间因子则主要通过地理隔离对群落结构的差异产生影响。     

茂县土地岭植被恢复过程中物种多样性动态特征

植被恢复是退化生态系统重建的重要途径,植被恢复过程物种多样性的变化反映了植被的恢复程度.通过群落调查和多样性分析,研究了岷江上游土地岭植被恢复过程中群落物种多样性特征.结果表明： 恢复过程中6类不同类型群落分别表现其对于不同环境特征、干扰及更新方式等的响应;森林是较灌丛更适合当地环境状况的植被类型;人工恢复无干扰和轻度干扰群落的多样性相对较高,是较好的恢复模式.重度干扰使得1年生植物与地下芽植物比例增加,其它口食性较好的多年生草本减少.较强的干扰是群落无法更新、长期处于灌丛阶段且多样性较低的重要原因.本地区人工恢复群落在更新进程和多样性维持上优于自然更新群落,种植华山松加速了本地区植被演替进程.建议以适合恢复区域的多种恢复配置方式进行造林,并避免较强干扰,可以加速群落演替进程并保持恢复群落较高的物种丰富度与多样性.