川西北甘南云冷杉林的DCA排序、环境解释和地理分布模型的研究

 本文应用DCA排序的方法进行了四川西北部和甘肃南部云冷杉林的梯度分析,建立了植物群落梯度环境解释的数学模型和植物群落地理分布的数学模型。研究结果表明：影响川西北甘南云冷杉林植物群落地理分布的生态梯度中最显著并起主导作用的是温度梯度和水分梯度。在水分梯度上,大致有这样的植被序列,由较湿的藓类和杜鹃冷杉及云杉林,中生性的箭竹冷杉林和云杉林,偏旱的高山栎冷杉林和云杉林;处于恢复中期的桦木林的生境也偏旱,但一般不如高山栎林。冷杉林比云杉林更趋于阴湿的生境。 在温度梯度上,呈现出灌木云杉林—桦木林—落阔冷杉林—高山栎云杉林—箭竹云杉林—箭竹红桦林—高山栎冷杉林—藓类红桦林—藓类云杉林—箭竹冷杉林—藓类云冷杉林—藓类冷杉林—小叶章云杉林—杜鹃冷杉林的排序。基本特征是：川西北和甘南的云杉林的温度需求高于冷杉林。川西北云冷杉林与甘南云冷杉林在DCA排序轴上没有明显的区别。虽然川西北地区云冷杉林的海拔分布高于甘南地区,但是其纬度也低于甘南,故在温度条件上基本一致。在水分梯度上,川西北云冷杉林的湿度要稍大于甘南云冷杉林。利用植物地理分布的数学模型和有关的图、表,详细地分析了植物群落的空间分布,进行了环境解释,并找出了主导的环境因子。     

The impact of forest transformation on stand structure and ground vegetation in the southern Black Forest, Germany

The goal of this study was to investigate the effects of 'ecologically orientated' forest transformation on forest floor vegetation. Forest transformation, as defined by the BMBF southern Black Forest project group, is the process which converts even-aged spruce forest into structured continuous-cover forest, consisting principally of spruce (Picea abies), fir (Abies alba) and beech (Fagus sylvatica). In order to analyse the transformation process, four transformation stages were defined as part of a 'conceptual forest development model' (pure even-aged, species enrichment, structuring and continuous cover forest stage). Four forest districts representative of the southern Black Forest were selected for the study. The analysis included the separate classification of structures, sites, and ground vegetation. In a second step, the relationships between the three complexes were analysed. The influence of forest structure on ground vegetation was investigated by examining the relationships between so-called substructure types and ground vegetation types. The substructure types associated with the pure spruce stand, species enrichment and continuous cover forest stages exhibited a ground vegetation resembling that of the Luzulo-Fagetum and Luzulo-Abietetum, whereas the structuring stages exhibited a ground vegetation of the Galio-Fagetum type. Transformation of pure, even-aged spruce forest into mixed, uneven-aged continuous cover forest is considered an important silvicultural tool to combine the demands of sustainable timber production and nature conservation. Transformation brings about greater diversity in stand structure and tree species composition. The frequencies of acidophytic mosses and vascular plants in spruce forest decrease during the transformation process. The species requiring moderate base supply increase over the transitional stages. The continuous cover forest, the final stage of transformation, increasingly contains ground species of both, i.e., species normally associated with both conifer and deciduous forest.     

Vegetation patterns at the alpine treeline ecotone: the influence of tree cover on abrupt change in species composition of alpine communities

Aims: The upper elevation limit of forest vegetation in mountain ranges (the alpine treeline ecotone) is expected to be highly sensitive to global change. Treeline shifts and/or ecotone afforestation could cause fragmentation and loss of alpine habitat, and are expected to trigger considerable alterations in alpine vegetation. We performed an analysis of vegetation structure at the treeline ecotone to evaluate whether distribution of the tree population determines the spatial pattern of vegetation (species composition and diversity) across the transition from subalpine forest to alpine vegetation. Location: Iberian eastern range of the Pyrenees. Methods: We studied 12 alpine Pinus uncinata treeline ecotones. Rectangular plots ranging from 940 to 1900 m² were placed along the forest‐alpine vegetation transition, from closed forest to the treeless alpine area. To determine community structure and species distribution in the treeline ecotone, species variation along the forest‐alpine vegetation transition was sampled using relevés of 0.5 m² set every 2 m along the length of each plot. Fuzzy C‐means clustering was performed to assess the transitional status of the relevés in terms of species composition. The relation of P. uncinata canopy cover to spatial pattern of vegetation was evaluated using continuous wavelet transform analysis. Results: Vegetation analyses revealed a large degree of uniformity of the subalpine forest between all treeline ecotone areas studied. In contrast, the vegetation mosaic found upslope displayed great variation between sites and was characterized by abrupt changes in plant community across the treeline ecotone. Plant richness and diversity significantly increased across the ecotone, but tree cover and diversity boundaries were not spatially coincident. Conclusions: Our results revealed that no intermediate communities, in terms of species composition, are present in the treeline ecotone. Ecotone vegetation reflected both bedrock type and fine‐scale heterogeneity at ground level, thereby reinforcing the importance of microenvironmental conditions for alpine community composition. Tree cover did not appear to be the principal driver of alpine community changes across the treeline ecotone. Microenvironmental heterogeneity, together with effects of past climatic and land‐use changes on ecotone vegetation, may weaken the expected correlation between species distribution and vegetation structure.     

How does forest landscape structure explain tree species richness in a Mediterranean context?

Although the strong relationship between vegetation and climatic factors is widely accepted, other landscape composition and configuration characteristics could be significantly related with vegetation diversity patterns at different scales. Variation partitioning was conducted in order to analyse to what degree forest landscape structure, compared to other spatial and environmental factors, explained forest tree species richness in 278 UTM 10 × 10 km cells in the Mediterranean region of Catalonia (NE Spain). Tree species richness variation was decomposed through linear regression into three groups of explanatory variables: forest landscape (composition and configuration), environmental (topography and climate) and spatial variables. Additionally, the forest landscape characteristics which significantly contributed to explain richness variation were identified through a multiple regression model. About 60% of tree species richness variation was explained by the whole set of variables, while their joint effects explained nearly 28%. Forest landscape variables were those with a greater pure explanatory power for tree species richness (about 15% of total variation), much larger than the pure effect of environmental or spatial variables (about 2% each). Forest canopy cover, forest area and land cover diversity were the most significant composition variables in the regression model. Landscape configuration metrics had a minor effect on forest tree species richness, with the exception of some shape complexity indices, as indicators of land use intensity and edge effects. Our results highlight the importance of considering the forest landscape structure in order to understand the distribution of vegetation diversity in strongly human-modified regions like the Mediterranean.     

Spatial patterns of ground vegetation, soil microbial biomass and activity in a mixed spruce-birch stand

Trees directly and indirectly influence the above- and below-ground environment, and can be expected to modify the spatial patterns of organisms associated with the forest floor. This study aimed to examine the effects of a coniferous (Picea abies) and a broad-leaved (Betula pubescens) tree species on the spatial pattern of ground vegetation and soil microbial properties in a mixed stand in central Sweden. I have characterised the species composition of ground vegetation, soil microbial biomass and activity, photosynthetic active radiation (PAR), soil water content and soil pH in the stand, and tested whether the spatial patterns of these variables were related to the positioning of trees. Geostatistics were used to describe the spatial variation in ground vegetation, soil mirobiological properties and the soil surface environment. PAR, soil water content and the cover of the moss Brachytecium reflexum and associated herb species decreased with the influence of spruce trees. Microbial biomass, measured as the amount of phospholipid fatty acids, decreased with spruce influence but increased with the influence of birch trees. Microbial respiration was not affected by spruce but increased with the influence of birch. Ground vegetation and microbial respiration, which were influenced by one tree species only, aggregate on a scale of 4-5 m, corresponding fairly well with patches of a single tree species. Soil microbial biomass, which was affected by both tree species, aggregated on a scale of 7-8 m. roughly corresponding to the distance between patches of spruce and birch trees respectively. I suggest that spruce trees influenced vegetation mainly through shading, and that a difference in the availability of organic matter under birch and spruce trees caused spatial variation in microbial biomass and activity. Thus, spatial patterns in ground vegetation and soil microbial properties may develop in a mixed forest of coniferous-broad leaved trees, as a result of the difference in influence of tree species and nested variation associated with the arrangement of the trees.     

Presence of bark influences the succession of cryptogamic wood-inhabiting communities on conifer fallen logs

Predictors of cryptogamic wood-inhabiting communities need to be examined to understand the drivers of forest biodiversity. We estimated the influence of bark cover on the wood-inhabiting vegetation on conifer logs in early stages of epixylic succession in mature European boreal and hemi-boreal forests. Abundance of substrate groups with respect to log attributes was estimated with generalized linear and generalized linear mixed models. The structure and composition of epixylic communities was analysed using non-metric multidimensional scaling with subsequent environmental fitting. The abundance of true epixylics was inversely related to bark cover. In the first stage, bark cover did not influence the abundance of epiphytes and epigeous species; positively influenced the abundance of facultative epixylics on spruce logs and negatively influenced it on pine logs. In the second stage, the effect of bark cover was positive for epiphytes and epigeous species on spruce logs and for facultative epixylics independent of log species identity and negative for epigeous species on pine logs. Generalist species did not depend on bark cover. Total cover of wood-inhabiting vegetation was marginally influenced by bark cover. The effect of bark cover on epixylic vegetation at community level was negligible. In general, bark cover favours the establishment and growth of species with low substrate specificity. This preference may lead to either burial of logs by epigeous bryophytes, or facilitation of succession towards the dominance of ground vegetation.     

Recovery of pristine boreal forest floor community after selective removal of understorey, ground and humus layers

In boreal spruce forests that rarely experience extensive disturbances, fine-scale vegetation gaps are important for succession dynamics and species diversity. We examined the community implications of fine-scale gap disturbances by selective removal of vegetation layers in a pristine boreal spruce forest in Northern Finland. The aim was to investigate how the speed of recovery depends on the type of disturbance and the species growth form. We also wanted to know if there appeared changes in species composition after disturbance. Five different treatments were applied in the study: Control, removal of the ground layer (bryophytes and lichens), removal of the understorey layer (dwarf shrubs, herbs and graminoids), removal of both the ground and understorey layers, and complete removal of the vegetation and humus layers above the mineral soil. The vegetation recovery was monitored in terms of cover and species numbers over a 5-year period. Understorey layer cover, composed mainly of clonal dwarf shrubs, recovered completely in 4 years in treatments where the humus layer remained intact, whereas ground layer cover did not reach the control level in plots from where bryophytes and lichens were removed. Recovery was faster in terms of species number than species cover. Bryophytes, graminoids and dominant dwarf shrubs appeared in all disturbed plots quickly after disturbance. Seedlings of trees appeared exclusively in disturbed plots. Graminoids dominated after the removal of humus layer. The results indicate that the regeneration of forest floor after small gap disturbance occurs mainly by re-establishment of the dominant species. Although destruction of the humus layer leaves a long-lasting scar to the forest floor, exposing of mineral soil may enhance the sexual reproduction of dominant species and the colonization of weaker competitors.     

Spectral analysis discerns pattern and feedback in natural‐ and anthropogenic‐disturbed boreal black spruce forests

The two major disturbance types of boreal black spruce forest in north–central Quebec, Canada – natural disturbance by wildfire and anthropogenic disturbance by harvest – may affect processes of recovery differently and leave distinct post‐disturbance soil and vegetation spatial patterns. We tested whether 1) spatial patterns of physico‐chemical soil organic layer properties, black spruce diameter and density, and understory ericaceous shrub cover, differ between these two principal disturbance types; 2) operations associated with forest harvest result in distinct, regular spatial patterns of these same variables related to presence of machine trails; and 3) ericaceous shrub presence is a potential factor contributing to the legacy of spatial patterns after harvest. We explored these patterns on black spruce‐feathermoss forest stands, including fire‐origin stands (18 and 98 years) and stands originating from harvest (16 and 62 years) in central Quebec, Canada. We used two spatial analysis methods, spectral analysis and principal component analysis in the frequency domain, to characterize and relate spatial patterns of these soil and vegetation variables, measured along 50‐m transects on each site. Spatial patterns of distribution of soil and vegetation variables were different on the burned and the harvested forest sites. Wildfire gave rise to spatial patterns in soil and vegetation variables at multiple scales, reflecting the complexity generated by variable burn intensity. Patterns following forest harvest were mainly related to the regular structure defined by trails created by logging operations. In contrast to burned sites, ericaceous shrub patterns on harvested sites were strongly associated with spatial arrangements of spruce diameter and density, promoting absence of canopy closure and persistence of trails. Moreover, different spatial signatures did not converge in the long‐term (62–98 years) between the two disturbance types. The divergence in spatial structure between natural and anthropogenic disturbances has implications for ecosystem structure and function in the longer term.     

Oribatid Mites (Acariformes, Oribatei) as an Index of Postpyrogenous Changes in Podzol and Peat Soils of Boreal Forests

Population changes of oribatid mites were studied in a bilberry-moss spruce stand and shrub-peat moss pine stand caused by ground fire. The fire resulted in a drop of population density and changes in the species composition of mites in both forest types. In the case of the spruce stand, the restoration of species composition proceeded parallel to the formation of a bilberry-moss cover and litter and became distinct four years after the fire. In the case of pine stand, the fire enveloped only the peripheral region. After the sphagnum cover burned out, the moor dehydration began and the mineralized organogenic substrate emerged. Here, the oribatid complex was significantly rearranged and the previously dominating moisture-loving species were replaced by the mesophilous-xerophilous species typical predominantly for mineralized soils. This explains why the oribatid species composition in the burned pine stand is more similar to that in the control spruce stand than to that in the control pine stand.     

Microhabitat nest‐site selection by ducks in the boreal forest

The boreal forest is one of the North America’s most important breeding areas for ducks, but information about the nesting ecology of ducks in the region is limited. We collected microhabitat data related to vegetation structure and composition at 157 duck nests and paired random locations in Alberta’s boreal forest region from 2016 to 2018. We identified fine‐scale vegetation features selected by ducks for all nests, between nesting guilds, and among five species using conditional logistic regression. Ducks in the boreal forest selected nest sites with greater overhead and graminoid cover, but less forb cover than random sites. Characteristics of the nest sites of upland‐ and overwater‐nesting guilds differed, with species nesting in upland habitat selecting nests that provided greater shrub cover and less lateral concealment and species nesting over water selecting nests with less shrub cover. We examined the characteristics of nest sites of American Wigeon (Mareca americana), Blue‐winged Teal (Spatula discors), Green‐winged Teal (Anas crecca), Mallards (Anas platyrhynchos), and Ring‐necked Ducks (Aythya collaris), and found differences among species that may facilitate species coexistence at a regional scale. Our results suggest that females of species nesting in upland habitat selected nest sites that optimized concealment from aerial predators while also allowing detection of and escape from terrestrial predators. Consequently, alteration in the composition and heterogeneity of vegetation and predator communities caused by climate change and industrial development in the boreal forest of Canada may affect the nest‐site selection strategies of boreal ducks.     

Susceptibility of burned black spruce (Picea mariana) forests to non-native plant invasions in interior Alaska

As climate rapidly warms at high-latitudes, the boreal forest faces the simultaneous threats of increasing invasive plant abundances and increasing area burned by wildfire. Highly flammable and widespread black spruce (Picea mariana) forest represents a boreal habitat that may be increasingly susceptible to non-native plant invasion. This study assess the role of burn severity, site moisture and time elapsed since burning in determining the invisibility of black spruce forests. We conducted field surveys for presence of non-native plants at 99 burned black spruce forest sites burned in 2004 in three regions of interior Alaska that spanned a gradient of burn severities and site moisture levels, and a chronosequence of sites in a single region that had burned in 1987, 1994, and 1999. We also conducted a greenhouse experiment where we grew invasive plants in vegetation and soil cores taken from a subset of these sites. In both our field survey and the greenhouse experiment, regional differences in soils and vegetation between burn complexes outweighed local burn severity or site moisture in determining the invasibility of burned black spruce sites. In the greenhouse experiments using cores from the 2004 burns, we found that the invasive focal species grew better in cores with soil and vegetation properties characteristic of low severity burns. Invasive plant growth in the greenhouse was greater in cores from the chronosequence burns with higher soil water holding capacity or lower native vascular biomass. We concluded that there are differences in susceptibility to non-native plant invasions between different regions of boreal Alaska based on native species regeneration. Re-establishment of native ground cover vegetation, including rapidly colonizing bryophytes, appear to offer burned areas a level of resistance to invasive plant establishment.     

Relationships between seed banks and spatial heterogeneity of North American alvar vegetation

Abstract. This is the first quantitative study of seed bank characteristics in North American alvar habitats. We assessed seed bank density, species richness, and species composition in 75 plots distributed among five alvar sites in Bruce Peninsula National Park, Ontario, Canada, each of which displayed areas of high and low vegetation cover within the alvar and a fully forested perimeter area. Forested habitats immediately adjacent to alvar patches contained minimal seed banks for species restricted to the alvar patches. Open alvars contained less than 1% seeds from woody forest species. This suggests that forest is not invading adjacent alvar habitat via seeds and that adjacent forest does not contain a reservoir of alvar seeds. When compared to areas on the alvar with high vascular plant cover, areas with low cover contained a slightly smaller viable seed bank, but seed banks from high and low vegetation cover plots had similar species composition and species richness. High vegetation cover plots had slightly higher mean and maximum soil depths compared with low cover plots, but no differences in other physical and chemical parameters. Thus, spatial heterogeneity in plant cover is associated only weakly with heterogeneity in below‐ground factors. Despite the availability of seed and soil resources, vegetation dynamics are constrained in areas with low plant cover, and thus alvar community development seems to respond non‐linearly to resource availability.     

Estimation of forest-ecosystem site index using remote-sensed data

The estimation of site index and site quality forms the fundamental theory and basic tools in forest-ecosystem management and silviculture practice. The study on the spatial pattern and temporal dynamics of site index and site quality of forest ecosystem still lacks technological advancement. It is a novel approach for estimating forest productivity in large areas using satellite remote-sensed data. The site-index spatial distribution pattern of spruce (Picea asperata) forest in Songpan-Zhengjiangguan watershed, northwestern Sichuan Province, China, was described using the remote-sensing vegetation index application and the established inverse models. The application potential of the methodology in broad regions and forests using the accuracy assessment was evaluated. The results show that the site index of the spruce forest is in linear correlation with the remote-sensed vegetation indices (normalized difference vegetation index (NDVI) and soil adjust NDVI (TNDVI)), as well as with these inverse models with high accuracy. This study demonstrated that this approach can be used in similar estimation of different forest ecosystems.     

Estimation of forest-ecosystem site index using remote-sensed data

The estimation of site index and site quality forms the fundamental theory and basic tools in forest-ecosystem management and silviculture practice. The study on the spatial pattern and temporal dynamics of site index and site quality of forest ecosystem still lacks technological advancement. It is a novel approach for estimating forest productivity in large areas using satellite remote-sensed data. The site-index spatial distribution pattern of spruce (Picea asperata) forest in Songpan-Zhengjiangguan watershed, northwestern Sichuan Province, China, was described using the remote-sensing vegetation index application and the established inverse models. The application potential of the methodology in broad regions and forests using the accuracy assessment was evaluated. The results show that the site index of the spruce forest is in linear correlation with the remote-sensed vegetation indices (normalized difference vegetation index (NDVI) and soil adjust NDVI (TNDVI)), as well as with these inverse models with high accuracy. This study demonstrated that this approach can be used in similar estimation of different forest ecosystems.     

Species composition and invasion in NW Argentinian secondary forests: Effects of land use history,environment and landscape

Abstract. Successional patches are a large component of forest ecosystems throughout the world and their vegetation composition is conditioned by multiple factors such as land use history, disturbances, environmental conditions and landscape context. We investigated the relative contribution of historical, environmental, biotic and spatial factors in determining vegetation composition and invasion by exotic species in secondary forest patches of Sierra de San Javier, Tucumán, Argentina. We estimated canopy cover for shrub, vine and tree species distributed over 51 patches with known land use history. We also recorded environmental, historical and spatial variables and used multivariate techniques to explore the relationship between forest composition and explanatory variables. Land use, time since abandonment, altitude, slope and cover of different strata were related to the vegetation pattern in the study site, and they were all significantly structured over space. Exotic species appeared to differ from natives in their response to explanatory variables. Overall, exotic species were dominant on the edges of young patches originated from herbaceous crops, but the total number of exotic species was related to the distance to urban areas and small farms identified as potential sources of exotic propagules. Vegetation composition of secondary forests in NW Argentina was related to historical and environmental factors, but spatial variables strongly influenced vegetation composition as well as the variation in explanatory variables.     

Analysis of vegetation distribution in Interior Alaska and sensitivity to climate change using a logistic regression approach

Aim To understand drivers of vegetation type distribution and sensitivity to climate change. Location Interior Alaska. Methods A logistic regression model was developed that predicts the potential equilibrium distribution of four major vegetation types: tundra, deciduous forest, black spruce forest and white spruce forest based on elevation, aspect, slope, drainage type, fire interval, average growing season temperature and total growing season precipitation. The model was run in three consecutive steps. The hierarchical logistic regression model was used to evaluate how scenarios of changes in temperature, precipitation and fire interval may influence the distribution of the four major vegetation types found in this region. Results At the first step, tundra was distinguished from forest, which was mostly driven by elevation, precipitation and south to north aspect. At the second step, forest was separated into deciduous and spruce forest, a distinction that was primarily driven by fire interval and elevation. At the third step, the identification of black vs. white spruce was driven mainly by fire interval and elevation. The model was verified for Interior Alaska, the region used to develop the model, where it predicted vegetation distribution among the steps with an accuracy of 60–83%. When the model was independently validated for north‐west Canada, it predicted vegetation distribution among the steps with an accuracy of 53–85%. Black spruce remains the dominant vegetation type under all scenarios, potentially expanding most under warming coupled with increasing fire interval. White spruce is clearly limited by moisture once average growing season temperatures exceeded a critical limit (+2 °C). Deciduous forests expand their range the most when any two of the following scenarios are combined: decreasing fire interval, warming and increasing precipitation. Tundra can be replaced by forest under warming but expands under precipitation increase. Main conclusion The model analyses agree with current knowledge of the responses of vegetation types to climate change and provide further insight into drivers of vegetation change.     

Can Saturniidae moths be bioindicators? Spatial and temporal distribution in the Brazilian savannah

Some moths species are considered good indicators of habitat quality because they are very responsive to human disturbance, vegetation type, and successional processes. However, Saturniidae moths have not yet been considered as indicators of environmental quality. Little is known on the distribution of moth species in different vegetation types and the moths’ seasonal variations in the Brazilian savannah. Therefore, this study aims to describe the spatial distribution and temporal patterns of moths belonging to the Saturniidae family in two vegetation types—Cerrado sensu stricto on rocky outcrops and semi-deciduous forest—in both the rainy and dry seasons. It addresses the influence of the climatic seasons and vegetation types on abundance, richness, and species composition to describe the temporal and spatial distribution patterns and the relationship between the ecological aspects and the life history of these moths. This study was conducted in the Cerrado phytogeographical domain, in Pireneus State Park, Goiás, Brazil. The results revealed that most Saturniidae species sampled are present during the rainy season and typically found in forest habitats. Furthermore, a clear positive connection was found between the abundance pattern and rainfall seasonality and humid habitats; this is apparently related to the physiological tolerance of these moths, due to rudimentary mouthparts during their adulthood. Thus, rainfall and a forest habitat are important to and fundamental requirements for the persistence of the Saturniidae species in the Cerrado domain. Based on the results of this study, we suggest the use of saturniid species as indicators of changes in vegetation and climatic conditions.     

俄罗斯北部平原(VYCHEGDA河盆地)全新世植物群和植被

对Vychegda河流域靠近Baika村(61°16'N,46°44'E)洪积平原的一个剖面进行了孢粉学研究.化石点位于泰加林带中部,靠近欧洲云杉林和亚乌拉尔-西伯利亚云、冷杉-西伯利亚松林界限附近.该河流盆地森林覆盖率高达98%.根据放射性碳年代测定,沉积涵盖了全新世大约自9000 yrs B.P.以来的大部分地层.主要运用化石植物群组成来恢复这一地区全新世以来的植被和气候变化,通过某些化石植物群的全部植物种类的现代地理分布的分析,可以发现与过去植被最接近的现代对应植被类型的位置,通过确定所有植物种现代生长地区的景观和气候来推测与古环境最接近的景观和气候.整个孢粉组合序列中云杉、松和桦占统治地位,但是植物群的成分和植被有变化.暖温带树种,如椴、榆及栎等在森林中的含量有变化,在全新世最暖期,相当于中晚大西洋期(6000-4500 yrs B.P.)达到最高.这些变化通过对应的现代植物群在俄罗斯平原的"迁移"反映出来,从中、南乌拉尔向西至Sukhona河盆地然后再返回到研究区的Vychegda河下游.运用古植物群的方法定量恢复的主要气候指标表明在大西洋期7月份月均温比现代高2.5℃,1月份月均温比现在高出1℃,年降雨量和现在接近.这段时间可以认为是本地区全新世的气候最适宜期.     

Species’ thermal preferences affect forest bird communities along landscape and local scale habitat gradients

The spatial distributions of species, and the resulting composition of local communities, are shaped by a complex interplay between species’ climatic and habitat preferences. We investigated this interaction by analyzing how the climatic niches of bird species within given communities (measured as a community thermal index, CTI) are related to vegetation structure. Using 3129 bird communities from the French Breeding Bird Survey and an information theoretic multimodel inference framework, we assessed patterns of CTI variation along landscape scale gradients of forest cover and configuration. We then tested whether the CTI varies along local scale gradients of forest structure and composition using a detailed data set of 659 communities from six forests located in northwestern France. At landscape scale, CTI values decreased with increasing forest cover, indicating that bird communities were increasingly dominated by cold‐dwelling species. This tendency was strongest at low latitudes and in landscapes dominated by unfragmented forest. At local scale, CTI values were higher in mature deciduous stands than in conifer or early stage deciduous stands, and they decreased consistently with distance from the edge of forest. These trends underpin the assertion that species’ habitat use along forest gradients is linked with their climatic niche, although it remains unclear to what extent it is a direct consequence of microclimatic variation among habitats, or a reflection of macroscale correlations between species’ thermal preferences and their habitat choice. Moreover, our results highlight the need to address issues of scale in determining how habitat and climate interact to drive the spatial distribution of species. This will be a crucial step towards accurate predictions of changes in the composition and dynamics of bird communities under global warming.     

A study on the vegetation in the east side of Helan Mountain

This paper analyzed the vegetation data obtained from a field survey conducted in the East Side of Helan Mountain, China, to reveal the features of mountainous vegetation growing in a transitional zone between the steppe and desert regions. Detrended correspondence analysis (DCA) was applied to the process of analysis, to clarify the spatial variation of floristic composition of the vegetation in the lower mountain range.The preliminary results obtained from the analysis are: (1) There are 53 vegetation formations existing in the area, following the China's criteria of vegetation classification system. (2) Those vegetation types compose a vertical vegetation spectrum in the East Side of Helan Mountain due to the climatic gradient caused by elevation variation. The spectrum consists of 4 zones. They are, from the foot up to the peak in turn, mountain steppe zone, mountain open forest and steppe zone, mountain coniferous forest zone, and alpine bush and meadow zone. The mountain coniferous forest zone can be further divided into two subzones: Pine forest subzone and Spruce forest subzone. (3) Most of the vegetation types show clear xeromorphic features due to the base zone of the vertical vegetation spectrum lying in the arid region of China. (4) The distribution of vegetation types and flora is sensitive and susceptible to the moisture condition that the vertical vegetation spectrum has quite different expressions between northern and southern exposures. (5) Floristic composition of the vegetation shows a northern temperate feature. The families that are rich in species in the area include Gramineae, Compositae, Leguminosae, Chenopodiaceae, Rosaceae and others, most of which are abundant in herbaceous species. (6) The variation of the ecological conditions from the north to the south also leads to the differentiation of vegetation and its floristic composition in the area. (7) The broad-leaved forest can not form a forest zone in the vertical vegetation spectrum. This may be a special characteristic of the spectrum sitting on a transitional zone between the steppe and desert regions.