Relationships between bird species and tree species assemblages in forested habitats of eastern North America

Aim We examined the relative influence of geographical location, habitat structure (physiognomy), and dominant plant species composition (floristics) on avian habitat relationships over a large spatial extent. Although it has been predicted that avian distributions are more likely to covary with physiognomy than with floristics at coarse scales, we sought to determine, more specifically, whether there remained a significant association between gradients in assemblages of bird species and dominant plant species within a general biome type, after statistically controlling for structural variation and geographical location of sampling sites. Location Our sample consisted of a subset of North American Breeding Bird Census survey sites that covered most of the range of eastern forests, from Florida to Nova Scotia, and west to Minnesota and North Dakota (up to c. 2500 km between sites). Methods We restricted our analyses to the single year (1981) that provided the largest sample of sites (47) for which vegetation data were available within ± 2 years of the avian surveys. We examined the relationship between avian community composition and tree species composition over this series of forested plots. Data were divided into four sets: (1) bird species abundances, (2) tree species abundances, (3) physiognomic or structural variables and (4) geographical location (latitude and longitude). We performed separate detrended correspondence analysis ordinations of birds and trees, before and after statistically partialling out covariation associated with structural variables and geographical location. To gauge the relationship between the two sets of species we correlated site scores resulting from separate ordinations. We also compared continental‐scale patterns of variation in bird and tree assemblages to understand possible mechanisms controlling species distribution at that scale. Results Both bird and tree communities yielded strong gradients, with first‐axis eigenvalues from 0.75 to 0.97. All gradients were relatively long (> 4.0), implying complete turnover in species composition. However, geographical location accounted for < 10% of the total variation associated with any ordination. Prior to partialling out covariation resulting from location and physiognomy, bird species ordinations were strongly correlated with tree species ordinations. The strength of association was reduced after partialling, but one bird and one tree axis remained significantly correlated. There was a significant species–area effect for birds, but not for trees. Main conclusions There was a significant relationship between bird species assemblages and tree species assemblages in the eastern forests of North America. Even after partialling out covariation associated with spatial location and forest physiognomy, there remained a significant correlation between major axes from bird and tree ordinations, consistent with the hypothesis that floristic variation is likely to be important in organizing assemblages of birds within a general biome type, albeit over a much larger spatial extent than originally predicted. Forest tree species ordinations differed from bird species ordinations in several ways: trees had a higher rate of turnover along underlying environmental gradients; trees appeared more patchily distributed than birds at this scale; and tree species were more spaced out along the underlying ecological gradients, with less overlap. By understanding the relationship between bird assemblages and forest floristics, we might better understand how avian communities are likely to change if tree species distributions are altered as a result of climatic changes.     

Tree diversity,tree height and environmental harshness in eastern and western North America

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co‐varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.     

Vascular plant diversity in eastern Asia and North America: historical and ecological explanations

Taxonomic diversity of vascular plants (ferns, gymnosperms and angiosperms) was compared between eastern Asia and North America. Eastern Asia has significantly higher species richness in all three classes but the difference was greatest in ferns and least in angiosperms. Differences in taxonomic treatments between the two continents are not likely contributors to these patterns. The relationship of regional to global species richness across the three plant classes suggested that diversity patterns were relatively homogeneous at three taxonomic levels. Thus, differences in species richness are established at the family level and are therefore relatively old. The previously noted fact that eastern Asia has a higher proportion of primitive taxa was shown by analyses both among and within plant classes. Diversity patterns across three taxonomic levels (i.e. family, genus and species) of the three classes may reflect the relative historical positions of the two continents (following continental drift) to the centre(s) of their origin, neighbouring land masses, differential speciation/extinction rates, and switches in dominance levels associated with climate change (including glaciation), as well as reproductive/dispersal mechanisms of the three plant classes.     

Distributions of exotic plants in eastern Asia and North America

Although some plant traits have been linked to invasion success, the possible effects of regional factors, such as diversity, habitat suitability, and human activity are not well understood. Each of these mechanisms predicts a different pattern of distribution at the regional scale. Thus, where climate and soils are similar, predictions based on regional hypotheses for invasion success can be tested by comparisons of distributions in the source and receiving regions. Here, we analyse the native and alien geographic ranges of all 1567 plant species that have been introduced between eastern Asia and North America or have been introduced to both regions from elsewhere. The results reveal correlations between the spread of exotics and both the native species richness and transportation networks of recipient regions. This suggests that both species interactions and human-aided dispersal influence exotic distributions, although further work on the relative importance of these processes is needed.     

Trends in seedling growth and carbon‐use efficiency vary among broadleaf tree species along a latitudinal transect in eastern North America

Factors constraining the geographic ranges of broadleaf tree species in eastern North America were examined in common gardens along a ~1500 km latitudinal transect travers in grange boundaries of four target species: trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera) to the north vs. eastern cottonwood (Populus deltoides) and sweet gum (Liquidambar styraciflua) to the south. In 2006 and 2007, carbon‐use efficiency (CUE), the proportion of assimilated carbon retained in biomass, was estimated for seedlings of the four species as the quotient of relative growth rate (RGR) and photosynthesis per unit tree mass (A_tree). In aspen and birch, CUE and RGR declined significantly with increasing growth temperature, which spanned 9 °C across gardens and years. The 37% (relative) CUE decrease from coolest to warmest garden correlated with increases in leaf nighttime respiration (R_leaf) and the ratio of R_leaf to leaf photosynthesis (R_%A). For cottonwood and sweet gum, however, similar increases in R_leaf and R_%A accompanied modest CUE declines, implying that processes other than R_leaf were responsible for species differences in CUE's temperature response. Our findings illustrate marked taxonomic variation, at least among young trees, in the thermal sensitivity of CUE, and point to potentially negative consequences of climate warming for the carbon balance, competitive ability, and persistence of two foundation species in northern temperate and boreal forests.     

沈阳市行道树树种的选择与配置

采取典型抽样的方法对沈阳市行道树进行了全面的群落调查。结果表明 ,研究区内行道树共 13科 ,2 4属 ,2 2 91株 ,森林覆盖率为 15 13%。胸径 <0 2 5m(1级胸径 )和 0 2 5～ 0 5m(2级胸径 )的树木分别占 4 3 0 %、17 9% ;树高 <4 6m (1级 )的树木占 4 9 8% ,介于 4 6～10 7m(2级 )为 4 3 3% ;健康状况为中等以上 ,沈阳市行道树处于种群稳定时期 ,但树种多样性指数不高 ,结构单一。根据城市的自然条件和行道树的选择标准 ,提出了沈阳市行道树树种选择与配置的对策与建议。     

The number of species occurring in a sample of a biotic community and its connections with species-abundance relationship and spatial distribution

Connections among species-abundance (i-m _i ), species-frequency (i-F _i ), and species-sample size (S _n -n) relationships were examined on the basis of the mapping data of a natural forest in Thailand. The spatial distribution of individual trees without any discrimination of species was nearly random. Provided that the spatial distribution of each species was random, thei-m _i and thei-F _i relationship was reconstructed from each other in terms of the total number of species (S) and the total number of individuals (N) in the data. The number of species (S _n ) in a subsample consisting ofn individuals was then obtained from thei-F _i relationship. Logarithm ofS _n increased with logn and showed a convex curve through the origin. The values of diversity indices based onN andS(orn andS _n ) were affected by sample size. These trends were further examined on the basis of 944 data sets of biotic communities and three mathematical models of anS-N relationship. The properties of species-area relation were discussed in the light of these results.     

元谋干热河谷生态恢复区昆虫多样性研究

以元谋退化生态系统初始生态恢复中人工构建植被为研究对象,在样地调查的基础上,对比分析了退化生态系统和恢复生态系统昆虫群落多样性组成与结构的恢复状况及其对人工群落类型的生态响应。结果表明,植物群落组成是影响昆虫群落多样性的关键因子。与天然植被相比,混交林促进了昆虫在退化地的扩散和定居,物种多样性明显增加。主成分分析排序将6种生境分为两大类:第Ⅰ类为赤桉纯林,代表物种单一、林下空旷、环境干燥为特点的植被;第Ⅱ类为扭黄茅草坡、车桑子灌丛及赤桉 银合欢、赤桉 相思、相思 银合欢3种混交林,代表物种相对复杂,生境偏向湿润的植被。不同生境的特有昆虫和优势昆虫种类和数量分析表明,在3种混交林中,相思 合欢恢复的效果较赤桉 相思与赤桉 合欢显著,是最好的先锋群落植物混交模式,能够较快改良生境,提高其物种多样性。但由于造林面积较小,植被恢复时间短,受人为干扰较大,昆虫多样性恢复的效果还不明显。     

Beta diversity of angiosperms in temperate floras of eastern Asia and eastern North America

The diversity of a region reflects both local diversity and the turnover of species (beta diversity) between areas. The angiosperm flora of eastern Asia (EAS) is roughly twice as rich as that of eastern North America (ENA), in spite of similar area and climate. Using province/state‐level angiosperm species floras, we calculated beta diversity as the slope of the relationship between the log of species similarity (S ) and either geographic distance or difference in climate. Distance‐based beta diversity was 2.6 times greater in the north–south direction in EAS than in ENA and 3.3 times greater in the east–west direction. When ln S was related to distance and climate difference in multiple regressions, both distance and climate PC1 were significant effects in the north–south direction, but only geographic distance had a significant, unique influence in the east–west direction. The general predominance of distance over environment in beta diversity suggests that history and geography have had a strong influence on the regional diversity of these temperate floras.     

Phylogeography of white spruce (Picea glauca) in eastern North America reveals contrasting ecological trajectories

Aim The main objective of this study was to investigate the origin of white spruce (Picea glauca) range discontinuities in eastern North America. A first analysis aimed at uncovering the glacial origin and post-glacial migration route of white spruce in the eastern part of the range. A second analysis aimed at evaluating whether disjunct white spruce populations in central Québec result from a recent expansion or are remnant stands following a northern range contraction. Location The first analysis covered the North American transcontinental boreal distribution of white spruce, and the second focused on the eastern part of its range. Methods A total of 589 P. glauca individuals from 51 populations, 24 of which were from a previous published source, were analysed for variation in three chloroplast DNA regions (trnT/L, trnL/F and ndhK/C). At the continental scale, haplotypic diversity, zones of genetic discontinuities, clustering analysis and analysis of molecular variance (AMOVA) were employed. In the eastern part of the range, haplotypic diversity was assessed with a permutation procedure, demographic history with mismatch analyses, and genetic structure with AMOVA. Results At the continental scale, various lines of evidence (genetic-diversity hotspots, endemic haplotypes, zones of genetic discontinuities, and pattern of molecular variation) show that different lineages migrated from three glacial refugia (Beringian, Mississippian, east Appalachian). Strong genetic discontinuities, low diversity and lack of evidence for demographic expansion were found among stands from isolated high hills in central Québec. Main conclusions White spruce in the eastern part of its range has an east Appalachian origin, a lineage genetically distinct from populations west of the Great Lakes. Previous studies have shown that the northward migration of white spruce is still ongoing as the northernmost populations expand into the tundra. In contrast, mixed white spruce and balsam fir (Abies balsamea) stands from isolated high hills in central Québec have already reached their Holocene maxima and are currently declining. This range contraction is probably a result of increased wildfire disturbance, which gradually creates a pattern of regional white spruce isolation and replacement by fire-prone black spruce (Picea mariana) forest.     

浙江省生态公益林植被恢复过程中物种组成及多样性的变化

在浙江省生态公益林区域的现状植被中分析了6种主要群落类型的物种组成和多样性的变化格局,包括演替系列中的2种灌丛、松优势林、2种混交林和常绿阔叶林。结果表明含松较多的灌丛和松优势林常分布在环境退化较严重(土层瘠薄)的生境中,其中灌木层主要由阳性的映山红、木、白栎等组成,常绿阔叶林优势种木荷、青冈、苦槠、甜槠等在其中偶见,因此推断其自然恢复为常绿林的速度慢;含常绿阔叶树较多的灌丛及含松较少的混交林分布在土层较厚处,木荷、青冈、苦槠、甜槠等的频度和重要值都较大,较容易自然恢复为常绿阔叶林。各种群落中物种多样性指数——Gleason、Shannon-Wiener、Simpson指数基本上以常绿阔叶林为最高,其次是含松较少的混交林,含松较多的灌丛和松优势林各种多样性指数最低。本研究显示我国中亚热带东部森林植被恢复途径有3条:(1)灌草丛→针叶林(松)→针(松)阔混交林→常绿阔叶林;(2)灌草丛→针(松)阔混交林→常绿阔叶林;(3)灌草丛→常绿阔叶林。这意味着本区域的常绿阔叶林恢复可以不必经历松林阶段,在生境条件较好的地方通过人工干预、补种常绿阔叶树可以加速常绿阔叶林恢复。     

兰科火烧兰属分布于北美西部和喜马拉雅-中亚的一对替代种

对间断地分布于北美西部和喜马拉雅-中亚的一对替代种———北美火烧兰Epipactis gigantea和卵叶火烧兰E.royleana进行了分类学与植物地理学方面的讨论。提供了一幅形态图、一份地理分布图以及它们之间形态区别的表。     

南岭东西段植物群落物种组成及其树种多样性垂直格局的比较

根据沿海拔梯度设置的样地的调查资料,对南岭东段的莽山和西段的猫儿山植物群落乔木层物种多样性的垂直分布格局进行了比较研究。莽山和猫儿山的植被类型差异不大,但相同植被类型的物种组成有比较明显的差异。随海拔的上升,两山体乔木的最大树高均呈现显著下降趋势。猫儿山乔木的最大胸径、胸高断面积之和以及立木密度在海拔梯度上呈单峰曲线变化趋势。莽山乔木的最大胸径、胸高断面积之和与海拔呈明显的负相关性,而立木密度的变化规律不明显。这种单峰曲线格局或负相关关系与中尺度上的海拔高度以及小尺度上的土壤特性、小地形以及人为干扰强度等因素有关。在海拔1000m以下的常绿阔叶林群落和1700m以上的山顶矮林群落,莽山乔木的物种丰富度均明显高于猫儿山。两山体的乔木种数与海拔之间都显示出负相关性,但莽山由于高海拔群落受人为干扰的影响,这种相关性不显著。乔木层α多样性沿海拔梯度没有表现出明显的变化规律,并且在两山体之间也看不出明显的差别。本文最后还对两山脉低海拔区段的常绿阔叶林群落的物种组成和多样性进行了对比分析,结果表明人为干扰导致猫儿山常绿阔叶林的物种丰富度(S)和α多样性(H’)明显低于莽山的原生性常绿阔叶林群落,而且落叶阔叶树种和毛竹(Phyllostachys pubescens)开始入侵到群落中。     

Predicting the distribution of Sasquatch in western North America: anything goes with ecological niche modelling

The availability of user-friendly software and publicly available biodiversity databases has led to a rapid increase in the use of ecological niche modelling to predict species distributions. A potential source of error in publicly available data that may affect the accuracy of ecological niche models (ENMs), and one that is difficult to correct for, is incorrect (or incomplete) taxonomy. Here we remind researchers of the need for careful evaluation of database records prior to use in modelling, especially when the presence of cryptic species is suspected or many records are based on indirect evidence. To draw attention to this potential problem, we construct ENMs for the North American Sasquatch (i.e. Bigfoot). Specifically, we use a large database of georeferenced putative sightings and footprints for Sasquatch in western North America, demonstrating how convincing environmentally predicted distributions of a taxon's potential range can be generated from questionable site-occurrence data. We compare the distribution of Bigfoot with an ENM for the black bear, Ursus americanus , and suggest that many sightings of this cryptozoid may be cases of mistaken identity.     

The relative roles of environment and history as controls of tree species composition and richness in Europe

Aim This study investigates the determinants of European‐scale patterns in tree species composition and richness, addressing the following questions: (1) What is the relative importance of environment and history? History refers to lasting effects of past large‐scale events and time‐dependent cumulative effects of ongoing processes, notably dispersal limited range dynamics. (2) Among the environmental determinants, what is the relative importance of climate, soils, and forest cover? (3) Do the answers to questions 1 and 2 differ between conifers and Fagales, the two major monophyletic groups of European trees? Location The study area comprises most of Europe (34° N–72° N and 11° W–32° E). Methods Atlas data on native distributions of 54 large tree species at 50 × 50 km resolution were linked with climatic, edaphic, and forest cover maps in a geographical information system. Unconstrained (principal components analysis using Hellinger distance transformation and detrended correspondence analysis) and constrained ordinations (redundancy analysis using Hellinger distance transformation and canonical correspondence analysis) and multiple linear regressions were used to investigate the determinants of species composition and species richness, respectively. History is expected to leave its mark as broad spatial patterns and was represented by the nine spatial terms of a cubic trend surface polynomial. Results The main floristic pattern identified by all ordinations was a latitude‐temperature gradient, while the lower axes corresponded mostly to spatial variables. Partitioning the floristic variation using constrained ordinations showed the mixed spatial‐environmental and pure spatial fractions to be much greater than the pure environmental fraction. Biplots, forward variable selection, and partial analyses all suggested climatic variables as more important floristic determinants than forest cover or soil variables. Tree species richness peaked in the mountainous regions of East‐Central and Southern Europe, except the Far West. Variation partitioning of species richness found the mixed spatial‐environmental and pure spatial fractions to be much greater than the pure environmental fraction for all species combined and Fagales, but not for conifers. The scaled regression coefficients indicated climate as a stronger determinant of richness than soils or forest cover. While the dominant patterns were similar for conifers and Fagales, conifers exhibited less predictable patterns overall, a smaller pure spatial variation fraction relative to pure environmental fraction, and a greater relative importance of climate; all differences being more pronounced for species richness than for species composition. Main conclusions The analyses suggest that history is at least as important as current environment in controlling species composition and richness of European trees, with the exception of conifer species richness. Strong support for interpreting the spatial patterns as outcomes of historical processes, notably dispersal limitation, came from the observation that many European tree species naturalize extensively outside their native ranges. Furthermore, it was confirmed that climate predominates among environmental determinants of distribution and diversity patterns at large spatial scales. Finally, the particular patterns exhibited by conifers probably reflect greater environmental specialization and greater human impact. These findings warn against expecting the European tree flora to be able track fast future climate changes on its own.     

热带森林中的斑块动态与物种多样性维持

斑块作为景观要素之一,直接到景观结构的空间格局及其内部各要素之间的相互关系,其动态也将导致景观格局的变化。异质性的斑块在自然森林中是普遍存在的,这就是说,顶极森林中仍然存在着由不同种类或不同生长时期的植物种群组成的森林斑块。由自然或人为干扰所驱动的森林生长循环导致敢这些斑块在空间上的镶嵌,对于持定的地域片段,也导致了不同生长时期的森林斑块的周期性循环。在热带森林中,森林的生长循环由林窗期（ｇａｐ     

辽东山区次生林物种多样性的空间分布及尺度效应

以辽东山区次生林为研究对象,分析4 hm²样地Gleason丰富度指数、Simpson优势度指数、Shannon多样性指数和Pielou均匀度指数的空间分布特征及其与尺度的关系.结果表明: 4个多样性指数的空间分布均表现出较高的空间异质性;4个多样性指数的方差随尺度的增加其变化趋势有所差异;4个多样性指数的变异系数随尺度的增加呈下降趋势;乔木层的4个多样性指数值高于灌木层,且随尺度增加其变化趋势有所差异.在分析辽东山区次生林物种多样性时应考虑尺度效应.