Floristic variation in ecotonal areas: Patterns,determinants and biogeographic origins of subtropical forests in South America

We present the first quantification of forest community composition and its relationship with environmental factors in South American subtropical Atlantic Forests. In this region, rain, seasonally dry and mixed forests form an ecotonal zone near the parallel of latitude 30°S. To investigate how well current knowledge on climatic effects and biogeographic distribution apply to subtropical ecotones, we tested the following expectations: (i) there is a floristic longitudinal gradient correlated to altitudinal and climatic gradients; (ii) climatic variables are more important than soil factors in shaping floristic composition; and (iii) there are three floristic regions in the southernmost limit of the Atlantic Forest biome that are expected to be distinct in composition, structure and biogeographical origin. We examined floristic composition and its relationship with environmental factors across 52 1‐ha permanent study areas in subtropical Brazil, containing in total 269 tree species ≥ 9.5 dbh (diameter at breast height). Climatic data, related to rainfall seasonality and temperature, as well as soil properties, were compiled from published sources or global data banks. Expectations one and two were confirmed, but expectation three was only partially met. Hierarchical cluster analysis divided the southernmost Atlantic Forests into four major groups (Rain, Seasonally Dry, Western Mixed and Eastern Mixed Forests). Overall, the tested environmental variables differed significantly among the four regions. Using indicator species analysis, we distinguished 46 indicator species, which had significant environmental preferences for one floristic region. These species can be used as indicators of environmental conditions or to determine to which floristic region a certain forest belongs. Biogeographic distributions differed between floristic groups, supporting the interpretation that Eastern Mixed Forests are relict forests of a temperate forest of Andean origin that occurred during colder palaeoclimates. Western Mixed Forests represent the main floristic ecotone between Seasonally dry and Eastern Mixed Forests.     

Correspondence between Scientific and Traditional Ecological Knowledge: Rain Forest Classification by the Non-Indigenous Ribereños in Peruvian Amazonia

Traditional ecological knowledge (TEK) is a potential source of ecological information. Typically TEK has been documented at the species level, but habitat data would be equally valuable for conservation applications. We compared the TEK forest type classification of ribereños, the non-indigenous rural peasantry of Peruvian Amazonia, to a floristic classification produced using systematically collected botanical data. Indicator species analysis of pteridophytes in 300 plots detected two forest types on non-flooded tierra firme, each associated with distinct soil texture and fertility, and one forest type in areas subject to flooding. Nine TEK forest types were represented in the same set of plots. Each TEK forest type was consistently (>82%) associated with one of the three floristic classes and there were also clear parallels in the ecological characterizations of the forest types. Ribereños demonstrated clear preferences for certain forest types when selecting sites for slash-and-burn agriculture and hunting. Our results indicate that the non-tribal inhabitants of Amazonia possess valuable TEK that could be used in biodiversity inventories and wildlife management and conservation for characterizing primary rain forest habitats in Amazonia.     

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and α diversity in the Amazonian white‐water (várzea) forest, looking particularly at: (1) the flood‐level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods The data originate from 16 permanent várzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 várzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, α diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood‐level gradient. Results More than 900 flood‐tolerant tree species were recorded, which indicates that Amazonian várzea forests are the most species‐rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood‐level gradient, with a distinct separation between low‐várzea forests and high‐várzea forests, (2) in relation to natural forest succession, with species‐poor forests in early stages of succession and species‐rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing α diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions The east‐to‐west gradient of increasing species diversity in várzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine‐scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, várzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high‐várzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low‐várzea forests can exhibit high floristic similarity over large geographical distances. The high várzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long‐distance dispersal of many low‐várzea trees contributes to comparatively low species richness in highly flooded low várzea.     

Pteridophyte diversity and species composition in four Amazonian rain forests

Abstract. Local variation in individual density, species composition, species richness and species diversity of terrestrial pteridophytes were studied at four sites in the tropical lowland rain forest of western Amazonia. 15 568 pteridophyte individuals representing 40 species were recorded in four plots. The variability among subplots within the same plot was considerable in all the characteristics measured (number of individuals, number of species, species diversity); the square 1‐ha plot was more homogeneous in these respects than any of the three 5 m by 1300 m transects. Species richness was affected by the density of individuals both within and among plots. Density of individuals was not affected by topographical position within any of the plots, whereas in some of the plots both species richness and species diversity were. Clustering and ordination analyses showed that floristically similar subplots could be found in different plots: although there was a tendency for subplots from the same plot to be floristically similar and therefore to group together, many recognized groups included subplots from two or more plots. Both within and among plots, the floristic differences corresponded to topographic position and were probably related to soil drainage. This was also evident in that the abundance patterns of many species followed the topography.     

Floristic composition and diversity of mixed primary and secondary forests in northwest Guyana

The adequate protection and sustainable management of a tropical rain forest requires a good knowledge of its biodiversity. Although considerable parts of Guyana's North-West District have been allocated as logging concessions, little has been published on the forest types present in this region. The present paper reviews the floristic composition, vegetation structure, and diversity of well-drained mixed and secondary forests in northwest Guyana. Trees, shrubs, lianas, herbs and hemi-epiphytes were inventoried in four hectare plots: two in primary forests, one in a 20-year-old secondary forest and one in a 60-year-old secondary forest. The primary forests largely corresponded with the Eschweilera–Licania association described by Fanshawe, although there were substantial variations in the floristic composition and densities of dominant species. The late-succession forest contained the highest number species and was not yet dominated by Lecythidaceae and Chrysobalanaceae. There is a need for updating the existing vegetation maps of northwest Guyana, as they were based on limited information. Large-scale forest inventories may provide a fair indication of species dominance and forest composition, but do not give a reliable insight in floristic diversity. Although previous reports predicted a general low diversity for the North-West District, the forests plots of this research were among the most diverse studied in Guyana so far. These results will hopefully influence the planning of protected areas in Guyana.     

滇南热带雨林物种多样性的取样面积探讨

通过不同面积样方种数的比较、物种多样性指数等的计算和逐步扩大样地面积的调查, 本文研究了滇南热带雨林种数/面积关系、个体/种数关系、物种多样性及树种的频度分布规律, 认为滇南热带雨林群落学调查的最适取样(样方)面积是0.25 hm², 这个面积接近该类型热带雨林理论上的群落最小表现面积。 为能体现一个具体森林(群落)类型的基本的植物区系组成, 需设置4～5个这样的样方(总面积累计1 hm²以上)。从与世界不同地区热带雨林的比较亦可见,云南热带雨林有类似的树种频度分布规律,单位面积上的物种多样性比典型的东南亚低地热带雨林稍低,但比非洲的热带雨林要高。     

Variation in species composition, abundance and microhabitat preferences among western Amazonian terra firme palm communities

Western Amazonia harbours one of the richest palm floras of the Neotropics. About 121 palm species and 33 genera occur in this region. Approximately 40% of these species and three monotypic genera ( Aphandra , Itaya and Wendlandiella ) are restricted to western Amazonia. Bactris (23 spp.), Geonoma (20 spp.), Attalea (17 spp.), Astrocaryum (11 spp.) and Oenocarpus (7 spp.) are the most well-represented genera in the region. Palms, however, are not homogeneously distributed across western Amazonia. A major change in palm composition occurs between Yasuní (eastern Ecuador) and Iquitos (eastern Peru). Species that are very abundant on the unflooded forest of Yasuní, such as Iriartea deltoidea or Prestoea shultzeana , are replaced by Socratea exorrhiza , Lepidocaryum tenue var. tenue or Iriartella stenocarpa in the Iquitos–Pebas region. Moreover, the distribution ranges of the majority of eastern Ecuadorean palms reach the Iquitos region, but the converse is not observed. Censuses of palm communities along transects, studies of microhabitat preferences of Oenocarpus bataua and documentation of the distribution limit of Astrocaryum species in the intermediate zone provide new insights on the floristic change that is occurring. Modern ecological constraints and geological history during the Cenozoic may explain the observed variations.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 127–140.     

Forest classification in an Amazonian rainforest landscape using pteridophytes as indicator species

Habitat classification systems are poorly developed for tropical rainforests, where extremely high plant species richness causes numerous methodological difficulties. We used an indicator species approach to classify primary rainforest vegetation for purposes of comparative wildlife habitat studies. We documented species composition of pteridophytes (ferns and fern allies) in 635 plots (2×100 m) along 8 transects within a continuous rainforest landscape in northeastern Peruvian Amazonia. Considerable floristic variation was found when the data were analyzed using multivariate methods. The obtained forest classification was interpreted with the help of indicator value analysis and known soil preferences of the pteridophyte species. The final classification included four forest types: 1) inundated forests, 2) terrace forests, 3) intermediate tierra firme forests and 4) Pebas Formation forests. This rapid and relatively simple vegetation classification technique offers a practical, quantitative method for large-scale vegetation inventory in complex rainforest landscapes.     

Contrasting effects of mosaic structure on alpha and beta diversity of bird assemblages in a human‐modified landscape

Habitat loss and fragmentation are key processes causing biodiversity loss in human‐modified landscapes. Knowledge of these processes has largely been derived from measuring biodiversity at the scale of ‘within‐habitat’ fragments with the surrounding landscape considered as matrix. Yet, the loss of variation in species assemblages ‘among’ habitat fragments (landscape‐scale) may be as important a driver of biodiversity loss as the loss of diversity ‘within’ habitat fragments (local‐scale). We tested the hypothesis that heterogeneity in vegetation cover is important for maintaining alpha and beta diversity in human‐modified landscapes. We surveyed bird assemblages in eighty 300‐m‐long transects nested within twenty 1‐km² vegetation ‘mosaics’, with mosaics assigned to four categories defined by the cover extent and configuration of native eucalypt forest and exotic pine plantation. We examined bird assemblages at two spatial scales: 1) within and among transects, and 2) within and among mosaics. Alpha diversity was the mean species diversity within‐transects or within‐mosaics and beta diversity quantified the effective number of compositionally distinct transects or mosaics. We found that within‐transect alpha diversity was highest in vegetation mosaics defined by continuous eucalypt forest, lowest in mosaics of continuous pine plantation, and at intermediate levels in mosaics containing eucalypt patches in a pine matrix. We found that eucalypt mosaics had lower beta diversity than other mosaic types when ignoring relative abundances, but had similar or higher beta diversity when weighting with species abundances. Mosaics containing both pine and eucalypt forest differed in their bird compositional variation among transects, despite sharing a similar suite of species. This configuration effect at the mosaic scale reflected differences in vegetation composition among transects. Maintaining heterogeneity in vegetation cover could help to maintain variation among bird assemblages across landscapes, thus partially offsetting local‐scale diversity losses due to fragmentation. Critical to this is the retention of remnant native vegetation.     

Avian Composition Co‐varies with Floristic Composition and Soil Nutrient Concentration in Amazonian Upland Forests

Spatial heterogeneity in the plant species composition of tropical forests is expected to influence animal species abundance and composition because vegetation constitutes the primary habitat feature for forest animals. Floristic variation is tied to variation in soils, so edaphic properties should ultimately influence animal species composition as well. The study of covariation in floristic and faunistic turnover has been hindered by the difficulty of completing coordinated surveys in hyperdiverse tropical communities, but this can be overcome with the use of a few plant taxa that function as surrogates for general floristic turnover. We used avian and plant transect surveys and soil sampling in a western Amazonian upland (terra firme) forest landscape to test whether spatial variation in bird community composition is associated with floristic turnover and corresponding edaphic gradients. Partial Mantel tests and Non‐metric Multidimensional Scaling showed floristic distinctiveness between two forest types closely associated with differences in soil cation concentrations, and differences in both floristic composition and cation concentrations were further linked to compositional differences in avian species, independent of geographic distances among sites. Ten percent of bird species included in Indicator Species Analyses showed significant associations with one of the two forest types. The upland forest types that we sampled, each corresponding to a different geological formation, are intermediate relative to edaphically extreme environments in the region. Models of avian diversification should take into account this environmental heterogeneity, as should conservation planning approaches that aim to represent faunal diversity. Abstract in Spanish is available in the online version of this article.     

西南桦人工林与山地雨林的群落学特征比较

人类活动对生态系统的影响是当今生态学的研究热点之一, 但对在退化生态系统上进行人工造林对地带性植被群落学特征的影响研究尚较欠缺。本文根据组成群落的植物生态学特征能对其生态环境做出准确的反应这一规则, 通过样地调查法分析了林龄为12年的西南桦(Betula alnoides)人工群落的区系组成和基本的群落学特征, 并与当地的地带性植被——山地雨林的区系组成和群落学特征进行了比较, 从而探讨人工造林对当地天然生态系统的影响。结果发现, 与天然群落相比, 人类活动(人工种植西南桦林)对生态系统的植物物种的生活型谱、物种叶型谱、区系成分、物种多样性等方面的群落学特征影响不大;即使在这些方面有或多或少的差异, 可能也是小环境的异质性造成的。但是人工种植西南桦林对群落的季相外貌、群落的结构、物种组成、物种丰富度以及生物量等方面有较大的影响。进行综合分析后得出结论: 虽然人工造林可以缩短植被自然恢复的时间以及具有显著的经济价值, 但与地带性植被相比, 还是有较大的生态学差异。建议为了当地经济的发展, 有必要适当发展一定面积的人工林, 但规模应适度。     

Peatland forests are the least diverse tree communities documented in Amazonia,but contribute to high regional beta‐diversity

Western Amazonia is known to harbour some of Earth's most diverse forests, but previous floristic analyses have excluded peatland forests which are extensive in northern Peru and are among the most environmentally extreme ecosystems in the lowland tropics. Understanding patterns of tree species diversity in these ecosystems is important both for quantifying beta‐diversity in this region, and for understanding determinants of diversity more generally in tropical forests. Here we explore patterns of tree diversity and composition in two peatland forest types – palm swamps and peatland pole forests – using 26 forest plots distributed over a large area of northern Peru. We place our results in a regional context by making comparisons with three other major forest types: terra firme forests (29 plots), white‐sand forests (23 plots) and seasonally‐flooded forests (11 plots). Peatland forests had extremely low (within‐plot) alpha‐diversity compared with the other forest types that were sampled. In particular, peatland pole forests had the lowest levels of tree diversity yet recorded in Amazonia (20 species per 500 stems, Fisher's alpha 4.57). However, peatland pole forests and palm swamps were compositionally different from each other as well as from other forest types in the region. Few species appeared to be peatland endemics. Instead, peatland forests were largely characterised by a distinctive combination of generalist species and species previously thought to be specialists of other habitats, especially white‐sand forests. We suggest that the transient nature and extreme environmental conditions of Amazonian peatland ecosystems have shaped their current patterns of tree composition and diversity. Despite their low alpha‐diversity, the unique combination of species found in tree communities in Amazonian peatlands augment regional beta‐diversity. This contribution, alongside their extremely high carbon storage capacity and lack of protection at national level, strengthens their status as a conservation priority.     

Distribution of Pteridophyta and Melastomataceae along an edaphic gradient in an Amazonian rain forest

Abstract. Pteridophyta and Melastomataceae were studied in an area of non-flooded (tierra firme) rain forest in Peruvian Amazonia, close to the village of Mishana (River Nanay, in the vicinity of Iquitos City). The general objective of the study was to establish a method for rapidly documenting changes in the floristic composition among and within rain forests in geologically different areas. More specifically, the changes in the plant communities were documented along an edaphic and topographic gradient from clay soil on level ground to quartzitic sand on a hill top. Two 5-m-wide, parallel transects were established 50 m apart. A total of 40 species of pteridophytes were found; 18 of these were confined to clayey soil and 11 to sandy soil. The total number of Melastomataceae on the transects was 22, and 14 of these were confined to clayey soil while only two were confined to sandy soil. Further differences in the abundance of many species correlated with drainage conditions and the accumulation of organic matter on the soil surface. Cluster analyses were made using both edaphic and floristic criteria, and in all cases the transects could be divided into distinct sections. Both transects gave rather similar results, and therefore it was concluded that the chosen transect width was sufficient to document the prevalent floristic patterns.     

Beta‐Diversity of Termite Assemblages Among Primary French Guiana Rain Forests

Termites are an important component of tropical rain forests, and have been included in many studies focusing on the influence of human disturbance. Their distribution among primary rain forest has, however, rarely been investigated. Here we studied the termite fauna in seven mostly undisturbed forest sites, representing several rain forest types. Overall, approximately 70 percent of species were soil‐feeders and 25 percent were wood‐feeders, the remaining 5 percent being classified here as litter‐feeders. Termite species richness did not differ significantly among sites, but sites differed in termite abundance. The palm swamp and the low forest situated on the foothills of an inselberg, hosted different termite communities to the other sites. These two sites presented a singular physiognomy suggesting that forest type is an important factor influencing species composition. We found no correlation between termite species composition and distance between sites, highlighting that at the scale of our study (about 100 km), forest sites share a similar species pool.     

Biodiversity assessment in incomplete inventories: leaf litter ant communities in several types of Bornean rain forest

Biodiversity assessment of tropical taxa is hampered by their tremendous richness, which leads to large numbers of singletons and incomplete inventories in survey studies. Species estimators can be used for assessment of alpha diversity, but calculation of beta diversity is hampered by pseudo-turnover of species in undersampled plots. To assess the impact of unseen species, we investigated different methods, including an unbiased estimator of Shannon beta diversity that was compared to biased calculations. We studied alpha and beta diversity of a diverse ground ant assemblage from the Southeast Asian island of Borneo in different types of tropical forest: diperocarp forest, alluvial forest, limestone forest and heath forests. Forests varied in plant composition, geology, flooding regimes and other environmental parameters. We tested whether forest types differed in species composition and if species turnover was a function of the distance between plots at different spatial scales. As pseudo-turnover may bias beta diversity we hypothesized a large effect of unseen species reducing beta diversity. We sampled 206 ant species (25% singletons) from ten subfamilies and 55 genera. Diversity partitioning among the four forest types revealed that whereas alpha species richness and alpha Shannon diversity were significantly smaller than expected, beta-diversity for both measurements was significantly higher than expected by chance. This result was confirmed when we used the unbiased estimation of Shannon diversity: while alpha diversity was much higher, beta diversity differed only slightly from biased calculations. Beta diversity as measured with the Chao-Sørensen or Morisita-Horn Index correlated with distance between transects and between sample points, indicating a distance decay of similarity between communities. We conclude that habitat heterogeneity has a high influence on ant diversity and species turnover in tropical sites and that unseen species may have only little impact on calculation of Shannon beta diversity when sampling effort has been high.     

Spatial distribution and floristic composition of trees and lianas in different forest types of an Amazonian rainforest

A quantitative inventory of trees and lianas was conducted (1) to compare floristic composition, diversity and stem density variation between three different forest types (tierra firme, floodplain and swamp), and (2) to analyse the relationships between floristic similarity and forest structure in two regions ~60 km apart in Yasuní National Park, Amazonian Ecuador. A total of 1,087 species with a diameter at breast height ≥ 2.5 cm were recorded in 25 0.1-ha plots. Tierra firme was the habitat with the highest number of species and stem density for trees and lianas, followed by floodplain and swamp in both regions. Two hypotheses that have been independently proposed to describe plant distribution in tropical rain forests, together explain species spatial distribution in this study. The fact that the 30 most important species per forest type (totalling 119 species) accounted for 48.2% of total individuals supports the oligarchy hypothesis. Likewise, 28 out of these 119 species are reported as restricted to a single forest type, which supports the environmental-determinism hypothesis. In general, both canopy and understorey trees and lianas showed rather similar floristic patterns across different forest types and regions.     

Distribution and Diversity of Pteridophytes and Melastomataceae along Edaphic Gradients in Yasuní National Park, Ecuadorian Amazonia1

We documented the floristic composition of pteridophytes (ferns and fern allies) and Melastomataceae in Yasuní National Park, Amazonian Ecuador. Our main questions were: (1) Are the density of individuals, species richness, and/or species diversity (measured with Shannon's H′) of the two plant groups related to edaphic differences? and (2) How many of the pteridophyte and Melastomataceae species are non–randomly distributed in relation to a soil base content gradient within terra firme (non–inundated forest). To answer these questions, we sampled 27 line transects of 500 × 5 m distributed in an area of ca 20 × 25 km. The study area included a permanent 50 ha plot established to monitor forest dynamics; thus, our results also provide information on landscape–scale floristic variability to which results from within the plot can be compared. A total of 45,608 individuals and 140 species of pteridophytes, and 4893 individuals and 89 species of the Melastomataceae, were counted in the transects. Both with pteridophytes and with Melastomataceae, a clear negative correlation was found between the amount of extractable bases in the soil and the number of plant individuals encountered in a transect. With Melastomataceae, species richness and species diversity also were negatively correlated with soil base content, but with pteridophytes they were not. More than 50 percent of the common species of both pteridophytes and Melastomataceae were nonrandomly distributed along the soil cation content gradient within terra firme. We conclude that while the species richness patterns observed in one plant group are not indicative of similar patterns in other plant groups, it seems likely that a substantial (but unknown) proportion of species belonging to other plant groups will be found to show distribution patterns that reflect edaphic preferences within terra firme forests.     

Patterns and Determinants of Floristic Variation across Lowland Forests of Bolivia

Floristic variation is high in the Neotropics, but little is known about the factors shaping this variation at the mesoscale. We examined floristic composition and its relationship with environmental factors across 220 1‐ha permanent plots in tropical lowland Bolivia. For each plot, abundance of 100 species (93 tree and 7 palm species ≥10 cm diam) was obtained. Climatic data, related to rainfall seasonality and temperature, were interpolated from all available weather stations in the region, and soil properties, related to texture and fertility, were obtained for each plot. Floristic variation was strongly associated with differences in water availability and temperature, and therefore the climatic gradient shaped floristic variation more strongly than the edaphic gradient. Detrended correspondence analysis ordination divided lowland Bolivia primarily into two major groups (Southern Chiquitano region vs. the Amazon region) and a multiple response permutation procedure distinguished five floristic regions. Overall, the tested environmental variables differed significantly among the five regions. Using indicator species analysis, we distinguished 82 strong indicator species, which had significant environmental preferences for one floristic region. These species can be used as indicators of environmental conditions or to determine which floristic region a certain forest belongs. Given the predicted decreases in rainfall and increases in temperature for tropical lowland forests, our gradient approach suggests that species composition may shift drastically with climate change. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Beta diversity and oligarchic dominance in the tropical forests of Southern Costa Rica

Recent studies have reported a consistent pattern of strong dominance of a small subset of tree species in neotropical forests. These species have been called “hyperdominant” at large geographical scales and “oligarchs” at regional‐landscape scales when being abundant and frequent. Forest community assembly is shaped by environmental factors and stochastic processes, but so far the contribution of oligarchic species to the variation of community composition (i.e., beta diversity) remains poorly known. To that end, we established 20.1‐ha plots, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) investigate how community composition responds to differences in topography, successional stage, and distance among plots for different groups of species (all, oligarch, common and rare/very rare species) and (b) identify oligarch species characterizing changes in community composition among forest types. From a total of 485 species of trees, lianas and palms recorded in this study only 27 species (i.e., 6%) were nominated as oligarch species. Oligarch species accounted for 37% of all recorded individuals and were present in at least half of the plots. Plant community composition significantly differed among forest types, thus contributing to beta diversity at the landscape scale. Oligarch species was the component best explained by geographical and topographic variables, allowing a confident characterization of the beta diversity among tropical lowland forest stands. Abstract in Spanish is available with online material.     

Ecological and biogeographical studies on the tropical rain forest of south Yunnan,SW China with a special reference to its relation with rain forests of tropical Asia

Abstract. Ecological and biogeographic analyses of the tropical rain forest in south Yunnan were made using data from seventeen sample plots and floristic inventories of about 1000 species of seed plants. The rain forest is shown to be a type of true tropical rain forest because it has almost the same profile, physiognomic characteristics, species richness per unit area, numbers of individuals in each tree species and diameter classes of trees as classic lowland tropical rain forests. As the area is at the northern margin of monsoonal tropics, the rain forest differs from equatorial lowland rain forests in having some deciduous trees in the canopy layer, fewer megaphanaerophytes and epiphytes but more species of lianas as well as more species of microphylls. In its floristic composition, about 80% of total families. 94% of total genera and more than 90% of total species are tropical, of which about 38% of genera and 74% of species are tropical Asian. Furthermore, the rain forest has not only almost the same families and genera, but also the same families rank in the top ten both in species richness and in dominance of stems, as lowland forests in southeast Asia. It is indisputable that the flora of the rain forest is part of the tropical Asian flora. However, most of the tropical families and genera have their northern limits in south Yunnan and most have their centre of species diversity in Malesia. More strictly tropical families and genera have relatively lower species richness and importance compared with lowland rain forests in tropical southeast Asia. Thus, the flora also shows characteristics of being at the margin of the tropics. Based mainly on physiognomy and floristic composition the tropical rain forest of Yunnan is classified into two types, i.e. seasonal rain forest and wet seasonal rain forest, the latter is further divided into two subtypes, i.e. mixed rain forest and dipterocarp rain forest. From analysis of geographic elements it is also shown that the tropical rain forest of Yunnan occurs at a geographical nexus with its flora coming mainly from four sources, i.e. Malesia, south Himalayas, Indochina and China.