Richness and diversity of Leguminosae in an altitudinal gradient in the tropical semi‐arid zone of Brazil

Abstract Many studies are based on the premise that, on a local scale, diversity is the result of ecological processes, whereas on a regional scale factors such as the topography, geology, hydrology, and historical and evolutionary events would influence this control. The Baturité Mountain Range (Ceará state), located in the Brazilian semi‐arid zone, is considered an area of extreme importance for conservation with its vegetation varying with the altitude and slope (windward vs. leeward). On the windward (wet) slope, rainforest dominates, whereas the leeward (dry) slope is dominated by seasonal forests and thorny woodland. The aim of this study was to contribute to the knowledge of the patterns of richness and diversity of the family Leguminosae on a local scale (Baturité Mountain Range) as well as a regional scale (northeastern Brazil). The two slopes present quite distinct floras. The dry slope presents higher richness and diversity indices for Leguminosae than the wet slope. The highest diversity of Leguminosae in the dry areas did not corroborate the ideas of other studies carried out in neotropical forests (total flora) that the higher species richness was predicted for wet areas. The present study indicates that the historical and evolutionary processes influence the diversity patterns on a local scale (Baturité Mountain Range), as well as on a regional scale (Brazilian semi‐arid). Our results reinforce the uniqueness of each portion of this area and its importance for conservation.     

Biogeographical relationships among tropical forests in north-eastern Brazil

Aim To use parsimony analysis of endemicity and cladistic analysis of distributions and endemism to evaluate two hypotheses addressing biogeographical relationships among Amazonia, the Caatinga forest enclaves, Pernambuco Centre and the southern Atlantic Forest. Location North‐eastern Brazil, South America. Methods To find the most parsimonious areagram we analysed a matrix composed of the presence (1) or absence (0) of 745 taxa (i.e. 293 genera and 452 species of woody plants) within 16 localities belonging to the four large regions addressed in this study. Results One most parsimonious areagram was found and it shows a basal separation between the southern Atlantic Forest and all other regions. This break is followed by a separation between all Caatinga forest enclaves (except Baturité) from a cluster composed of Baturité, the Pernambuco Centre and Amazonia. In this cluster, the most basal separation isolates Baturité from the cluster formed by localities from Amazonia and the Pernambuco Centre. The biogeographical relationships among sites could not be explained by either a random distribution of species among sites or by the geographical distance between sites. Main conclusions We found strong cladistic signal within the raw distribution and phylogenetic data used in our analysis, indicating structured species assemblages in the surveyed localities. They have resulted from the fragmentation of an ancestral biota that was once widely distributed in the region. Our results also support the hypothesis that Atlantic Forest is not a biogeographically natural area, because the Pernambuco Centre is more closely related to Amazonia than to the southern Atlantic Forest. Finally, our data do not support the notion that Caatinga forest enclaves comprise a single biogeographical region, because one Caatinga forest enclave (Baturité) is much more closely related to the cluster formed by Amazonia and the Pernambuco Centre than to other sites. These relationships suggest the occurrence of forest connections between Amazonia and the Atlantic Forests across Caatinga during several periods of the Tertiary and Quaternary. However, palaeoecological data currently available for the Caatinga region are still scarce and do not have either the spatial or temporal resolution required to reconstruct the history of connections among the forests in north‐eastern Brazil.     

Contrasting effects of wildfire and climate on radial growth of Pinus canariensis on windward and leeward slopes on Tenerife, Canary Islands

Little is known concerning the effects of wildfires on tree radial growth and their climatic response under contrasting regimes of fog water inputs on oceanic islands. On Tenerife, Canary Islands, windward slopes are humid with high-fog frequency due to influence of wet trade winds, while climate on leeward slopes is more arid. We used tree-ring records of Pinus canariensis Sweet ex Spreng. to quantify the effects of a fire of known date on radial growth and determine the main limiting climatic factors for growth. Radial growth patterns and their responsiveness to fire severity and climatic variation differed between windward and leeward slopes. Surface fire did not significantly impact growth, while crown fire caused short-term growth reduction, and even cessation, more pronounced on the windward slope. Growth rates, tree-ring common signal, and climate sensitivity were smaller on the windward slope, with cold winters, and summer water stress limiting growth. On the leeward slope, climate explained a greater amount of growth variation mainly due to negative effects of high October–December sea-level pressures causing dry winter conditions. Contrasting growth dynamics on both slopes may result from diverging physiological effects of water inputs and reduced radiation caused by fog drip. Our findings suggest that dating growth suppressions and absent rings are useful to date past high-severity crown fires in P. canariensis forests, in addition to ordinary fire scars dating indicative of low-severity surface fires.     

Changing ecological communities along an elevation gradient in seasonally dry tropical forest on Hispaniola (Sierra Martín García,Dominican Republic)

We report the results of systematic vascular plant and bird surveys in Seasonally Dry Tropical Forest (SDTF) across leeward and windward elevation gradients (31–884 masl) in the Sierra Martín García (SMG), Dominican Republic. We expected to see gradual, systematic changes in plant distributions with elevation owing to the strong effect of topoclimate. In contrast, we predicted bird community composition to be related only weakly to elevation, because we expected bird distributions to be more strongly related to vegetation structure than composition. Based on 48 vegetation transects, we identified seven groups that differed in their species composition, which was correlated with elevation and precipitation. The most distinctive vegetation community occurs in dry, warm, and low elevations on the leeward slope, featuring large numbers of non‐woody indicator species (those species found frequently within one group but not in other groups) even though most of its trees and shrubs represent species that are widespread. Low rainfall and shale bedrock (rather than limestone) may be the primary drivers of distinctiveness in the low‐elevation leeward plots. On the leeward slope, where we also surveyed the birds, the vegetation community changes gradually with elevation at mid‐ to high elevations. The most distinctive bird community also was associated with the low‐elevation forest on shale bedrock and was dominated by widespread species. At higher elevations, but still within leeward SDTF, the bird communities had a stronger component of species endemic either to Hispaniola or to Caribbean islands, and species turnover did not correspond to the elevation gradient. Abstract in Spanish is available with online material.     

Distribution patterns of páramo plants in Ecuador

We will analyse the geographical and vertical distributions of Ecuadorian high páramo plants. Lists of species were prepared for six Ecuadorian mountains, and floristic relationships among them were expressed by means of Sørensen's index of similarity. A mantel test was employed to analyse the pattern of geographical distribution of the species to see if the distance between the mountains was sufficient to explain the differences discovered. Altitudinal range and mean altitude of species occurrence were tested against the number of mountains from which the species were recorded using a Kruskal–Wallis nonparametric test. We found that distance as a single factor can not fully explain the pattern of floristic similarity shared by the mountains. Other important factors are involved. Altitudinal range of the species examined was positively correlated with their distribution in Ecuador. Species with a broad altitudinal occurrence were found on several mountains, whereas species with narrow altitudinal distribution were found on fewer mountains.     

浑善达克沙地不同微地形的土壤物理性质和草本群落分布及其相关性分析

采用样方调查和室内检测相结合法对内蒙古浑善达克沙地迎风坡、坡顶、背风坡和丘间地不同土层(0~10、10~20和20~40 cm)的土壤物理性质(包括含水量、田间持水量、容重、总孔隙度和毛管孔隙度)及草本群落的生产力(包括盖度和地上部生物量)和物种多样性(包括Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数)进行比较分析;在此基础上,采用Pearson相关性分析法对不同微地形的土壤物理性质与草本群落各指标间以及草本群落生产力与物种多样性各指标间的相关性进行分析.结果表明:4种微地形的土壤物理性质总体上差异显著,但不同土层的土壤物理性质总体上无明显差异;从丘间地、背风坡、坡顶到迎风坡,土壤的含水量、田间持水量、总孔隙度和毛管孔隙度依次递减,而土壤容重则依次递增,说明迎风坡的土壤结构较差且水分散失较多,而丘间地的土壤结构和水分状况均相对较好.不同微地形间草本群落生产力和物种多样性总体上也存在明显差异,从背风坡、丘间地、坡顶到迎风坡,草本群落的生产力和物种多样性依次递减,仅Margalef丰富度指数表现为在丘间地最高、在迎风坡最低,说明迎风坡的草本群落物种多样性较低,群落稳定性差,而背风坡和丘间地的草本群落物种多样性和生产力水平均较高,群落稳定性较好.相关性分析结果表明:该区域的草本群落生产力和物种多样性与土壤容重呈负相关,与土壤的其他物理性状呈正相关,但仅部分指标间有显著或极显著相关性;草本群落生产力与物种多样性各指标间呈正相关,但多数指标间的相关性并不显著.研究结果显示:微地形能够显著影响浑善达克沙地的土壤物理性质和草本群落的分布特征,气候和人为干扰使该沙地的土壤物理性质受到严重破坏,导致草本群落生产力降低并处于不稳定状态.     

中国西南地区珍稀濒危及国家保护植物区系地理

根据《中国植物红皮书》(第一册)和1999年《国家重点保护野生植物名录(第一批)》,对分布于中国西南地区的珍稀濒危及国家保护植物进行了调查和统计分析,并探讨了其区系成分特点及地理分布特征,结果表明:西南地区有珍稀濒危及国家保护植物共计95科195属275种;其植物区系具有明显的热带亚热带性质,种子植物热带分布型的属数占总数的48.57%,热带分布型的科数占总数的46.91%;特有性强,共有52种中国特有植物;起源古老,有41种古老孑遗植物;此外,这些种的地理分布不均匀,主要集中分布在省与省或国与国交界的边境地区以及中、低山地区。     

Are long‐unburnt eucalypt forest patches important for the conservation of plant species diversity?

Question: Are long‐unburnt patches of eucalypt forest important for maintaining floristic diversity? Location: Eucalyptus forests of southeastern New South Wales, Australia. Methods: Data from 976 sites representing a range of fire history from three major vegetation formations – shrubby dry sclerophyll forest (SF), grassy dry SF and wet SF – were analysed. Generalized linear models were used to examine changes in species richness with increasing time since wildfire and analysis of similarities to examine changes in community composition. Chi‐squared tests were conducted to examine the distribution of individual species across four time since fire categories. Results: Plant species relationships to fire varied between the three formations. Shrubby dry SF supported lower plant species richness with increasing time since wildfire and this was associated with shifts in community composition. Grassy dry SF showed significant shifts in community composition and species richness in relation to time, with a peak in plant species richness 20–30 yr post fire (either prescribed fire or wildfire). Wet SF increased in species richness until 10–20 yr post wildfire then displayed a general declining trend. Species richness in each vegetation type was not related to the fire frequencies and fire intervals observed in this study. Conclusions: Long‐unburnt (30–50 yr post wildfire) forests appeared to play a minor role in the maintenance of plant species diversity in dry forest systems, although this was more significant in wet forests. Maintenance of a range of fire ages within each vegetation formation will assist in maintaining floristic diversity within regions.     

海岸带迎风坡环境干扰对造林植物叶片解剖、气孔和水分利用效率的影响

海岸迎风坡植被恢复是海岸带破坏生态系统修复的重要内容。本试验在广东中山市五桂山海岸带迎风坡（海拔300 m）选择了3种用于植被恢复的人工造林植物,红锥（Castanopsis hystrix）、米老排（Mytilaria laosensis）、云南石梓（Gmelina arborea）和2个同地点的野生种降真香（Acronychia pedunculata）与鸭脚木（Schefflera octophylla）作为实验材料,研究4年后3种造林树种对海岸迎风坡环境的适应。测定5种植物叶片的解剖特征、气孔形态、气孔密度（SD）和大小（SL）、光合作用和水分利用效率（WUE）等生理特性。结果表明,（1）5种植物的叶片解剖特征在迎风坡和背风坡都没有明显差异,除红锥外,SD和SL在两坡面也未表现出显著变化;（2）红锥和云南石梓在迎风坡显示出低的WUE,野生种降真香和鸭脚木有潜在的高的WUE,而米老排在迎风坡显示出对迎风坡造林环境有一定的适应能力;（3）5种植物叶片解剖特征和光合行为对潜在的水分胁迫响应的表型可塑性变化存在明显的种间差异。     

藏南布丹拉山南坡种子植物区系海拔格局分析

生态群落交错区通常因物种丰富、区系成分复杂而被视为关键带.藏南布丹拉山处在半湿润向半干旱的生态环境过渡带上,因其特殊的自然地理环境而有着丰富的山地植物多样性,但这一重要生态过渡区的种子植物组成和区系成分海拔分布格局目前尚缺乏了解.为了理清布丹拉山南坡种子植物区系成分及其垂直分布变化格局,该文通过野外植物群落的样方调查、...     

Diversity of the ground-dwelling ant fauna (Hymenoptera: Formicidae) of a moist, Montane forest of the semi-arid Brazilian "Nordeste"

Although the so called "green islands" of the semi-arid Brazilian "Nordeste" are economically, socially, and ecologically important. relatively little is known about their biodiversity. We present the results of the first survey of the ground-dwelling ant fauna of a secondary forest in the Serra de Baturité (4 degrees 05'-4 degrees 40' S / 38 degrees 30'-39 degrees 10' W), among the biggest of the moist, montane forests of the state of Ceará, Brazil. From February to March 2001, samples were taken every 50 m along twelve 200 m transects, each separated from the others by at least 50 m and cut on either side of a recreational trail. Where possible, two transects were cut from the same starting point on the trail, one on either side. At each sample site two methods were used, as recommended in the ALL. protocol: a pitfall trap and the treatment of 1 m2 of leaf litter with the Winkler extractor. The myrmecofauna of the Serra de Baturité is quite diverse: individuals from 72 species, 23 genera, and six subfamilies were collected. The observed patterns of specific richness show the same tendencies noted in other tropical regions, particularly the frequency of capture distribution with many rare and few abundant species. Differences with the Atlantic and Amazonian forests were also observed, especially the relative importance of the Ponerinac and Formicinae subfamilies, indicating a possible influence of the surrounding "caatinga" (savanna-like ecosystem) on the myrmecofauna of the moist, montane forest.     

Altitudinal pattern of vegetation variation on Tenerife

Abstract. The variation in structure and floristic composition of the vegetation of Tenerife is related to different environmental factors. 200 sample plots, stratified according to altitude, exposure to wind, kind and age of parent rock, inclination and degree of disturbance were analysed throughout the island. The resulting data were analysed using univariate statistics (altitudinal distribution profiles of the more frequent species) and multivariate methods (Correspondence, Cluster and Pattern Analysis). Altitude, exposure to wind and, to a lesser extent, disturbance were found to be the major determinants of vegetational variation, whereas parent rock and inclination were less important. Ordination results show a continuum in structural and floristic variation of the vegetation with species distributions varying continually along the altitudinal gradient. Nevertheless, altitudinally bound plant community types were recognized with Cluster Analysis. Vegetational discontinuities, which were also detected by pattern analysis, are more evident on the windward slope of the island; they have been attributed to the existence of a major underlying environmental discontinuity the ‘cloud sea’-which is associated with a climatic inversion. On the leeward slope, beyond the influence of the cloud sea, discontinuities are less evident and vegetational variation seems to be closer to a coenocline, i.e. a vegetational continuum.     

A biogeographic delineation of the European Alpine System based on a cluster analysis of Carex curvula-dominated grasslands

Biogeographic delineations within the European temperate mountains remain poorly understood, as there has been little effort to assemble and analyze vegetation relevés covering Pyrenees, Alps, Carpathians and Balkans altogether. Our study tackles this issue by focusing on the widely distributed alpine acidic grasslands dominated by Carex curvula. Cluster analysis of more than 800 vegetation relevés revealed the European-scale spatial patterns of vascular plant diversity in these alpine grasslands. The geographical distribution of floristic clusters was partly congruent with the physiography of European mountains. Southern European ranges (Southern Balkans and Pyrenees) exhibit a high level of endemism and corresponding floristic clusters are well separated from the others. Marked floristic similarities between the Easternmost Alps, the Carpathians, and the Northern Balkans (Stara Planina) supported a major floristic boundary that runs through the Austrian Alps and that is likely the legacy of a shared Quaternary history. Within the Alps, floristic clustering was mainly driven by ecological drivers and not geography. This paper presents the first detailed study of spatial patterns of species distribution within the European Alpine System, based on a comprehensive analysis of within- and between-community species diversity. It shows that the quantitative analysis of large and consistent data sets may question the traditional delineations of biogeographic regions within European mountains.     

Phytogeographical relations of the Andean dry valleys of Bolivia

Aim The objective of this study is to examine the phytogeographical affinities of the Andean dry valleys of Bolivia in order to contribute to a better understanding of the Andean dry flora's distribution, origin and diversity. Particular emphasis is given to the analysis of the floristic connections of this flora with more austral parts of South America. Location The dry valleys of Bolivia are located in the Andes of the southern half of the country, at elevations between 1300 and 3200 m. Methods An extensive floristic list compiled by the author to evaluate plant diversity in these Andean regions was used as the base for this study. To accomplish this, all recorded genera and species were assigned, respectively, to 11 and 12 phytogeographical elements established previously by the author. Two phytogeographical spectra were thus obtained and analysed. Results At the genus level, the Andean dry valleys of Bolivia are clearly dominated by genera that have widespread distributions (cosmoplitan and subtropical genera). Many of these reached the Andes from the lowland region of the Chaco. At species level, Andean elements constitute more than 60% of the species total, most of which are restricted to the central‐southern Andes. This suggests that Chaco‐related and Andean genera had considerable levels of speciation in these valleys. Many genera and more than half the species have their northernmost distribution in the dry valleys of Bolivia, thereby underlining strong relationships with central‐southern South America (mainly Argentina, Paraguay and southern Brazil). The data supports the belief of the existence, in central‐southern Peru, of a floristic disjunction in dry to arid environments that separates a tropical dry flora north of this limit from a dry subtropical/warm temperate flora south of it. Main conclusions The Andean dry valleys of Bolivia are diverse plant communities with high levels of endemism (c. 18% of the species). The species of this region are more related to those present in central‐southern South America than to the flora of northern South America that ranges southwards to Peru. Many of the species have restricted distributions in the dry Andes of Bolivia and Argentina, and many genera of these dry valleys have their northernmost distribution in Bolivia/southern Peru, too. The data point to high levels of speciation also in the central Andes.     

海岸不同坡向滨麦光合特性与风速异质环境的关系

在自然条件下,测定分析了夏季和秋季静风天及秋季大风天,海岸沙丘不同坡向环境因子及滨麦株高、叶片叶绿素含量、土壤含水量和光合日变化特性,以期明晰滨麦响应不同风速环境的生理调控机理。结果表明,不同坡向环境异质性明显,滨麦形态可塑性强。海岸迎风坡风大、温度低、湿度大,滨麦植株低矮、叶绿素含量较高;背风坡温度高、土壤干旱、空气流动差,滨麦植株高大,叶绿素含量低。在夏秋季静风天,迎风坡和背风坡滨麦叶片Pn出现光合"午休"现象,但迎风坡滨麦日均Gs、Tr、Pn均显著高于背风坡;而在秋季大风天,迎风坡和背风坡滨麦叶片Pn"午休"现象消失,并且背风坡滨麦日均Pn、Tr、Gs均显著高于迎风坡滨麦。同坡向相比,秋季大风天迎风坡滨麦日均Pn、Tr、Gs明显较秋季静风天低,而背风坡滨麦日均叶片Pn、Tr、Gs却较静风天分别增高126%、66.3%、134%。强海风吹袭引发迎风坡温度降低、滨麦叶片摇摆、气孔导度降低导致Pn下降,而强海风使背风坡空气流动加快、温度降低、气孔导度增大、"午休"消失使Pn增高。不同坡向滨麦对不同海风风速的适应表现出明显的光合生理可塑性,它在滨麦适应不同风力、提高其光合速率和增加物质积累上具有重要作用。而滨麦的形态和光合生理可塑性可能是其在不同海风强度下生存、生长、实现种群扩张的重要生理调控机理,这一特性在未来作物、牧草和树木抗风、抗盐育种中具有重要应用价值。     

Plant coexistence in coastal heaths: Floristic patterns and species attributes

Abstract An investigation was made of plant coexistence in coastal heaths. A 4 km stretch of Pleistocene beach sand was selected, and patterns of variation in heath vegetation on ridges and slopes in the beach system were studied. The sampling design covered variation with geographic distance among transects, plots within transects and quadrats within plots which were orthogonal to the alignment of ridges and slopes. Cover of vascular plant species was scored within each quadrat and both multivariate and univariate analyses tested the hypothesis that variation in the data was associated with environmental difference and geographic distance. There was a strong flohstic variation between the ridge and slope habitats. However, within these habitats there was no significant variation with distance at scales of kilometres, nor at hundreds of metres within transects nor at tens of metres within plots in floristic composition, in numbers of species, and in cover. Though differing floristically, the vegetation of the slopes and ridges had similar curves of importance values and fairly similar spectra of life forms and forms of post-fire regeneration in their constituent species, although the ridges had slightly more obligate-seeding species and fewer species of sedges and herbs than the slopes. The two habitats shared several genera, however, within such genera, species with similar attributes mostly occurred in different habitats. Hypotheses were suggested to explain segregation of species between the two habitats and the coexistence of species within habitats. Since patterns of variation among habitats were consistent over both smaller and larger scales of distance examined, experiments to test hypotheses may be designed so that their findings might be applied generally to the whole system studied.     

Gradients in field-layer vegetation on an arid misty mountain plateau in the Sudan

Abstract. Earlier studies have described how moist, on-shore winds cause meso-scale vegetation patterns on arid mountains near the sea. However, all protruding objects such as trees, micro-relief, and hill slopes influence the distribution of sea-mist. The influence of the tree-canopy, aspect, and distance to the sea on the field-layer vegetation in montane savanna was investigated on 16 hills in the Red Sea Hills, at 34 - 38 km from the sea. At 32 sites, total field-layer cover, species cover, and species number were estimated in a sub-canopy plot and in a nearby open plot on seaward and leeward slopes. Cover and species number in the understorey are significantly higher than in the open. The difference is highest on seaward slopes. Detrended correspondence analysis reveals short species-axes of ca. 2 SD-units. Differences between plots are mainly in species cover. This fits a principal components ordination model. PCA and its constrained version RDA give concordant results. The explanatory variables, Tree-cover and Relative Radiation Index (aspect), have similar indirect influences on plants, and are significantly correlated with axis 1, which is interpreted as a moisture and temperature gradient. The moist seaward plots show an independent trend in species composition along axis 2, which correlates with distance to the sea. On a presence basis the variables, all representing different spatial separation, correlate on the first axis. Presumably, the species composition, at all spatial scales, is directly or indirectly related to the variation in temperature and moisture.     

Drought tolerance and water use by plants along an alpine topographic gradient

Summary In the alpine zones of western North American mountains, topographic-moisture gradients are the results of winter winds blowing snow from the upper windward slopes and ridgetops into snowdrifts on the lee slopes. Wet meadows at the foot of the lee slope are the result of summer snowmelt. Such gradients are repeated many times in a single mountain range. They are useful units for studies of the effects of drought and water use on patterning of alpine vegetation.The research was done through an entire growing season along a topographic gradient at 3,300 m in the Medicine Bow Mountains, Wyoming. Plant water potentials were measured on 29 species (pre-dawn to sunset) at weekly intervals. Simultaneously, leaf conductances were measured on 16 species of these; the remainder had leaves too small for the porometer. Leaf water potentials were generally lowest on the ridgetop and highest in the wet meadow. Highest mean leaf conductances were in the wet meadow plants; the lowest occurred on plants on the upper windward slope. None of the plants on the ridgetop had leaves large enough for the porometer. Plants of most species at all sites but the wet meadow showed sharply reduced leaf conductance or leaf death at plant water potentials below-1.5 MPa. Deep-rooted species such as Trifolium parryi showed maximal conductance at water potentials as low as-1.7 MPa and little reduction in conductance even at lower water potentials. Plant water potentials and leaf conductances showed close relationships with rooting depth, length of dry periods, and position on the gradient.On the occasion of the publication of Volume 50 of OECOLOGIA, the authors respectfully dedicate this paper to Dr. Konrad F. Springer and Dr. M. Evenari for their years of encouragement to the science of physiological ecology. We appreciate their efforts     

中国喀喇昆仑山离瓣花类植物区系特征

中国喀喇昆仑山地区离瓣花类植物有24科114属310种及11变种。分布种数大于60种的科有十字花科(66种)和豆科(63种),20～39种的有3科,10～19种的有4科,这9个科占该地区离瓣花类植物总属数的78.95%和总种数的88.39%,在本植物区系中占较大优势。单种属与寡种属有103属,在属级水平占绝对优势,但多种属与寡种属共含245种,在种级水平优势明显。对其地理成分分析包括8个分布区类型和14个变型,其中,温带或含温带分布的有67属194种,占该区总属数、种数的66.34%和79.18%,区系温带性质明显,且与地中海、西亚、中亚交流相对较多,而与东亚交流很少,缺乏热带分布型及中国特有分布型。与邻近区域相比,本区系与中国帕米尔高原的关系最为密切,相似系数最高,科级、属级与种级水平上,分别达82.14%、63.69%及33.86%;其次,在属级水平与阿富汗、东喜马拉雅及青藏高原相似性也分别达到17.92%、15.36%、16.26%,但种级相似性系数较低,仅为1.76%～5.69%,有一定联系。     

Forest fragmentation drives Atlantic forest of northeastern Brazil to biotic homogenization

Aim To examine whether the tree flora of the Atlantic forest of northeastern Brazil has experienced detectable taxonomic homogenization via the proliferation of native pioneer species in response to habitat loss and fragmentation. Location Biotic homogenization (BH) was examined across the Atlantic forest of northeast Brazil, i.e. a 56,000 km² piece of tropical forest and a distinct centre of species endemism in South America. Methods We assessed a dataset consisting of 5122 tree records and compared the similarity of tree floras from 12 semi‐natural sub‐regions of the Atlantic forest between two time periods: pre‐1980 (plant records between 1902 and 1980), and post‐1980 (between 1981 and 2006). To understand the mechanisms leading to BH (1) tree floras were ordered (via non‐metric multidimensional scaling – NMDS) by date (pre/post 1980) based on species occurrence and frequency, (2) NMDS axes were regressed against the proportion of those species that increased their occurrence post‐1980 (i.e. the winner species), and (3) patterns of geographic distribution and frequency of particular life‐history traits were examined across winner species and a control group. Results Tree floras across the Atlantic forest became c. 20–40% more similar to each other post‐1980, but patterns of species similarity were also influenced by between‐plot geographical distance. NMDS ordination clearly segregated pre‐ and post‐1980 floras with a clear signal of floristic convergence. Furthermore, winner tree species were largely composed of short‐lived and small‐seeded pioneer species that exhibit wide geographic distributions. Main conclusions Our results suggest that tropical forest biotas are susceptible to taxonomic homogenization (i.e. increasing levels of similarity) in the context of severe human‐disturbance via the proliferation of particular groups of native species comprised mainly by ecologically‐plastic, generalist species. We are thus extending the concept of homogenization to address and highlight a pervasive biological shift in the structure of tropical forest communities currently taking place across hyper‐fragmented landscapes.