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.     

Distribution and abundance of tree species in swamp forests of Amazonian Ecuador

Research to date on Amazonian swamps has reinforced the impression that tree communities there are dominated by a small, morphologically specialized subset of the regional flora capable of surviving physiologically challenging conditions. In this paper, using data from a large‐scale tree inventory in upland, floodplain, and mixed palm swamp forests in Amazonian Ecuador, we report that tree communities growing on well‐drained and saturated soils are more similar than previously appreciated. While our data support the traditional view of Amazonian swamp forests as low‐diversity tree communities dominated by palms, they also reveal four patterns that have not been well documented in the literature to date: 1) tree communities in these swamp forests are dominated by a phylogenetically diverse oligarchy of 30 frequent and common species; 2) swamp specialists account for < 10% of species and a minority of stems; 3) most tree species recorded in swamps (> 80%) also occur in adjacent well‐drained forest types; and 4) many tree species present in swamps are common in well‐drained forests (e.g. upland oligarchs account for 34.1% of all swamp stems). These observations imply that, as in the temperate zone, the composition and structure of Amazonian swamp vegetation are determined by a combination of local‐scale environmental filters (e.g. plant survival in permanently saturated soils) and landscape‐scale patterns and processes (e.g. the composition and structure of tree communities in adjacent non‐swamp habitats, the dispersal of propagules from those habitats to swamps). We conclude with suggestions for further research to quantify the relative contributions of these factors in structuring tree communities in Amazonian swamps.     

Insights into regional patterns of Amazonian forest structure,diversity, and dominance from three large terra-firme forest dynamics plots

We analyze forest structure, diversity, and dominance in three large-scale Amazonian forest dynamics plots located in Northwestern (Yasuni and Amacayacu) and central (Manaus) Amazonia, to evaluate their consistency with prevailing wisdom regarding geographic variation and the shape of species abundance distributions, and to assess the robustness of among-site patterns to plot area, minimum tree size, and treatment of morphospecies. We utilized data for 441,088 trees (DBH ≥1 cm) in three 25-ha forest dynamics plots. Manaus had significantly higher biomass and mean wood density than Yasuni and Amacayacu. At the 1-ha scale, species richness averaged 649 for trees ≥1 cm DBH, and was lower in Amacayacu than in Manaus or Yasuni; however, at the 25-ha scale the rankings shifted, with Yasuni < Amacayacu < Manaus. Within each site, Fisher’s alpha initially increased with plot area to 1–10 ha, and then showed divergent patterns at larger areas depending on the site and minimum size. Abundance distributions were better fit by lognormal than by logseries distributions. Results were robust to the treatment of morphospecies. Overall, regional patterns in Amazonian tree species diversity vary with the spatial scale of analysis and the minimum tree size. The minimum area to capture local diversity is 2 ha for trees ≥1 cm DBH, or 10 ha for trees ≥10 cm DBH. The underlying species abundance distribution for Amazonian tree communities is lognormal, consistent with the idea that the rarest species have not yet been sampled. Enhanced sampling intensity is needed to fill the still large voids we have in plant diversity in Amazon forests.     

Fungal disease incidence along tree diversity gradients depends on latitude in European forests

European forests host a diversity of tree species that are increasingly threatened by fungal pathogens, which may have cascading consequences for forest ecosystems and their functioning. Previous experimental studies suggest that foliar and root pathogen abundance and disease severity decrease with increasing tree species diversity, but evidences from natural forests are rare. Here, we tested whether foliar fungal disease incidence was negatively affected by tree species diversity in different forest types across Europe. We measured the foliar fungal disease incidence on 16 different tree species in 209 plots in six European countries, representing a forest‐type gradient from the Mediterranean to boreal forests. Forest plots of single species (monoculture plots) and those with different combinations of two to five tree species (mixed species plots) were compared. Specifically, we analyzed the influence of tree species richness, functional type (conifer vs. broadleaved) and phylogenetic diversity on overall fungal disease incidence. The effect of tree species richness on disease incidence varied with latitude and functional type. Disease incidence tended to increase with tree diversity, in particular in northern latitudes. Disease incidence decreased with tree species richness in conifers, but not in broadleaved trees. However, for specific damage symptoms, no tree species richness effects were observed. Although the patterns were weak, susceptibility of forests to disease appears to depend on the forest site and tree type.     

The potential for harvesting fruits in tropical rainforests: new data from Amazonian Peru

New data shows that edible fruit and nut production in Amazonian forests is substantially lower than most conservationists assume. Direct measures of production in Amazonian Peru show that two terra firma forest types produced significantly less edible fruit than an alluvial soil forest. Swamp forest produced more edible fruit than any other forest type measured. Palms produce 60% of edible fruit productivity, averaged over three forest types, but the most preferred palm fruits are difficult to harvest because they are borne too high for easy access by collectors. Forest fruit collection in Amazonia is less productive in the short-term than all other food-producing activities except for hunting and cattle ranching. Technological, social and political changes are essential so that sustainable but intrinsically low-yielding extractive activities like fruit collecting become more attractive to Amazonians.     

Interactive effects of flooding and forest gap formation on tree composition and abundance in the Peruvian Amazon

In order to better understand how flooding and gap formation affect Amazonian rainforests, I set up plots both in three major forest types that differed by flooding duration (referred to here as dry, wet, very wet) and in their respective gaps. Sampling of those plots after 4 years of regeneration showed: (1) common species exist between wet forests and their gaps and between wet and very wet gaps, (2) tree richness is maximum in dry forest and minimum in very wet gaps except in the wet gaps that show the second highest number of species, (3) there were less stems in gaps compared to forests and less stems in forests as flooding increased, except again in the wet gaps, and (4) dominance-diversity curves have more dominance by single species in the dry gap plots compared to other gaps and in dry forest compared to other forests. In general while some aspects of structure such as tree stem density is largely determined by tree-fall gap dynamics, tree composition is determined by flooding regime. Finally a jump in tree richness in wet forests and wet gaps compared to other plots suggests a “mass effects” hypothesis where species from dry and very wet forest and gaps have overlapping ranges in the wet forest and gap. This effect may help explain the high species diversity seen in this part of the Amazon.     

Determinants of Plant Community Assembly in a Mosaic of Landscape Units in Central Amazonia: Ecological and Phylogenetic Perspectives

The Amazon harbours one of the richest ecosystems on Earth. Such diversity is likely to be promoted by plant specialization, associated with the occurrence of a mosaic of landscape units. Here, we integrate ecological and phylogenetic data at different spatial scales to assess the importance of habitat specialization in driving compositional and phylogenetic variation across the Amazonian forest. To do so, we evaluated patterns of floristic dissimilarity and phylogenetic turnover, habitat association and phylogenetic structure in three different landscape units occurring in terra firme (Hilly and Terrace) and flooded forests (Igapó). We established two 1-ha tree plots in each of these landscape units at the Caparú Biological Station, SW Colombia, and measured edaphic, topographic and light variables. At large spatial scales, terra firme forests exhibited higher levels of species diversity and phylodiversity than flooded forests. These two types of forests showed conspicuous differences in species and phylogenetic composition, suggesting that environmental sorting due to flood is important, and can go beyond the species level. At a local level, landscape units showed floristic divergence, driven both by geographical distance and by edaphic specialization. In terms of phylogenetic structure, Igapó forests showed phylogenetic clustering, whereas Hilly and Terrace forests showed phylogenetic evenness. Within plots, however, local communities did not show any particular trend. Overall, our findings suggest that flooded forests, characterized by stressful environments, impose limits to species occurrence, whereas terra firme forests, more environmentally heterogeneous, are likely to provide a wider range of ecological conditions and therefore to bear higher diversity. Thus, Amazonia should be considered as a mosaic of landscape units, where the strength of habitat association depends upon their environmental properties.     

Tree species composition and rain forest-environment relationships in the middle Caquetá area,Colombia, NW Amazonia

As part of an integrated forest vegetation and soil survey, tree species composition (DBH 10 cm) was recorded in 95 plots of 0.1 ha, distributed over the principal physiographic units in the middle Caquetá area, Colombian Amazonia. A total of 1077 tree species was found, classified into 271 genera and 60 families. Leguminosae and Sapotaceae show high familial importance values in all physiographic units. Lauraceae, Chrysobalanaceae, Moraceae, and Lecythidaceae are more important on well drained (flood plain or upland) soils, while Palmae, Guttiferae, Bombacaceae, and Apocynaceae are more important in swamps and on podzolised (white sand'rs) soils. Plots on well drained soils show a lower degree of dominance than plots in swamps or on podzolised (white sand) soils. The composition of the most dominant species in the plots changes continuously. Most species (59%) are only recorded in one plot. Individual plot pairs generally show a low overlap of about 2–5 tree species, resulting in Jaccard coefficients below 20%.complementary to a previous forest classification based on TWINSPAN analyses, detrended and canonical correspondence analyses were carried out, using CANOCO 3.1. Despite of a low amount of tree species variance explained (only 6.2% by the first two canonical axes), meaningful patterns of tree species composition were recognised. These are most strongly related to drainage, flooding, humus forms, and soil nutrient status. Forest types are well separated in the CCA ordination diagram. The most frequently found tree species are listed according to their preference with respect to drainage, flooding, and soil nutrient status.Tree species composition in the well drained upland forests was analysed separately. In view of the model explaining high NW Amazonian tree species diversity on the basis of dense community packing and high beta diversity along soil gradients, the canonical analysis here focused on the effect of soils. By means of partial canonical ordination it was found that patterns of tree species composition depended significantly on soil properties, even though the edaphic component explains only a small fraction of the tree species variance. The results show that the well drained uplands of the middle Caquetá area are covered by a complex of two intergrading tree species assemblages. The first assemblage (community of Goupia glabra-Clathrotropis macrocarpa) is associated to some-what less poor, clayey soils developed in Andean origin deposits or Tertiary sediments from the Pebas formation. The second assemblage (community of Swartzia schomburgkii-Clathrotropis macrocarpa) shows affinities to very poor, loamy soils developed in parent materials derived from the Guiana shield. This simple dichotomous pattern of geology, soils, and forest types is incompatible with concepts of high soil heterogeneity and associated beta diversity controlling tree species diversity in well drained uplands of NW Amazonia. The gradient length of tree species in the detrended correspondence analysis was low (3.7 SD), also suggesting a low beta diversity.     

Ecosystem state shifts during long‐term development of an Amazonian peatland

The most carbon (C)‐dense ecosystems of Amazonia are areas characterized by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here, we present an investigation into long‐term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation ca. 8.9 ka BP), and developed in three stages: (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since ca. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (ca. 6.6–6.1 and ca. 4.9–3.9 ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland–forest swamp–peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on ca. 1.8–1.1 ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.     

Riqueza y Distribución Ecológica de Especies de Pteridofitas en la Zona del Río Yavarí-Mirín, Amazonía Peruana

We studied the ecological distribution of pteridophytes (ferns and fern allies) along eight 8-km transects covering 12.7 ha in Peruvian Amazonia. Subunits of 200 m² of the transects have previously been classified into four different forest types, and here we document and quantify the floristic differences among these forest types. Pteridophytes have been suggested as an indicator group to classify rain forest habitats, but this requires that the ecological preferences of the species are well documented and consistent across geographic regions. Here we analyzed in detail the distribution and diversity patterns of 130 species across the four rain forest types. Relative species abundance and species diversity were similar among some of the forest types and differed among others, but the species composition differed markedly. Our results largely confirmed the earlier interpretation of the edaphic preferences of the pteridophyte species in western Amazonia. This supports the proposition that deterministic processes have an important role in influencing the floristic composition of Amazonian forests.     

Geographic distribution of tree species occurring in the region of Manaus, Brazil: implications for regional diversity and conservation

The alpha-diversity of trees found in the region of Manaus, Brazil is among the highest recorded for one-hectare plots in Amazonia or any tropical forest. Based on a survey of the distributions of 2541 Neotropical tree species, we analyzed the geographic distribution of 364 species of terra firme forest trees that occur in the region and that are not edaphic specialists. Fifteen distinct distribution patterns were recognized for trees occurring in Manaus. The great majority of species (84.9%) have continuous, somewhat restricted distributions, 35 (9.6%) show broad distributions and 20 species (5.5%) show disjunction between Amazonia and Eastern Brazil. A remarkable 150 (41.2%) of these species showed the region of Manaus as one of their distribution limits. Using the same pool of 2541 species distributions, the percentage of species with a distribution limit in Manaus was compared with that for other localities known to be centers of botanical collection. The null hypothesis that the difference in proportion of species with distribution limits among these localities and Manaus is insignificant was rejected. We conclude that the results are not an artifact of collecting density, that Manaus is indeed a crossroads of distinct phytogeographic regions, and that this explains part of the high species diversity of trees in the region of Manaus. A number of scenarios proposed for the Pleistocene in Amazonia postulate some degree of fragmentation of Amazonian forests or at least populations. As much as these theories may conflict with each other in some respects, they are compatible with the concept of Manaus as a region of re-convergence of isolated or disrupted floras and faunas. The significance of the vicinity of Manaus in the history of the Amazon flora and its current status as a repository for surprisingly high tree diversity highlights the need to make this region a conservation priority.     

Fire-mediated dieback and compositional cascade in an Amazonian forest

The only fully coupled land-atmosphere global climate model predicts a widespread dieback of Amazonian forest cover through reduced precipitation. Although these predictions are controversial, the structural and compositional resilience of Amazonian forests may also have been overestimated, as current vegetation models fail to consider the potential role of fire in the degradation of forest ecosystems. We examine forest structure and composition in the Arapiuns River basin in the central Brazilian Amazon, evaluating post-fire forest recovery and the consequences of recurrent fires for the patterns of dominance of tree species. We surveyed tree plots in unburned and once-burned forests examined 1, 3 and 9 years after an unprecedented fire event, in twice-burned forests examined 3 and 9 years after fire and in thrice-burned forests examined 5 years after the most recent fire event. The number of trees recorded in unburned primary forest control plots was stable over time. However, in both once- and twice-burned forest plots, there was a marked recruitment into the 10-20cm diameter at breast height tree size classes between 3 and 9 years post-fire. Considering tree assemblage composition 9 years after the first fire contact, we observed (i) a clear pattern of community turnover among small trees and the most abundant shrubs and saplings, and (ii) that species that were common in any of the four burn treatments (unburned, once-, twice- and thrice-burned) were often rare or entirely absent in other burn treatments. We conclude that episodic wildfires can lead to drastic changes in forest structure and composition, with cascading shifts in forest composition following each additional fire event. Finally, we use these results to evaluate the validity of the savannization paradigm.     

The legacy of human use in Amazonian palm communities along environmental and accessibility gradients

Aim

Palms are iconic and dominant elements of neotropical forests. In the Amazon region, palms have been used and managed by humans for food, material, medicine and other purposes for millennia. It is, however, debated to what extent the structure of modern palm communities reflects long-term human modification. Here, we investigate the complex interplay of ecological and societal factors that influence the distributions of both human-used and non-used palms in western Amazonia.

Location

Amazonia.

Time period

Present.

Major taxa studied

Palms (Arecaceae).

Methods

We used Bayesian hierarchical joint species distribution models to predict the distributions and environmental niche dimensions of 78 western Amazonian species, and to explore their relationships with their diversity of human uses and with specific uses (food, construction and medicine). The models were parameterized with a comprehensive set of field- and satellite-derived environmental predictors.

Results

Our results suggest that a combination of ecological and anthropogenic factors drive the present-day distributions of Amazonian palms. The modelled ecological niches of the species revealed use-related species-sorting along soil, climatic, accessibility and drainage gradients. We found peaks in the proportions of useful palms and their diversity of uses in fertile soils, close to rivers, and on floodplains. These are habitats favourable for human settlement, although they harbour naturally restricted palm species pools. We also found a negative correlation between predicted palm species richness and number of human uses across western Amazonia.

Main conclusions

Soil characteristics, accessibility, and species pool size all contribute to defining palm–human relationships. At the basin scale, the signature of human use on palm communities was predicted to be stronger in the species-poor south-west than in central-western Amazonia. Overall, we conclude that environmental conditions have influenced modern Amazonian palm distributions both directly and indirectly, by regulating human settlement patterns and natural resource use over extended time periods.     

A novel comparative research platform designed to determine the functional significance of tree species diversity in European forests

One of the current advances in functional biodiversity research is the move away from short-lived test systems towards the exploration of diversity-ecosystem functioning relationships in structurally more complex ecosystems. In forests, assumptions about the functional significance of tree species diversity have only recently produced a new generation of research on ecosystem processes and services. Novel experimental designs have now replaced traditional forestry trials, but these comparatively young experimental plots suffer from specific difficulties that are mainly related to the tree size and longevity. Tree species diversity experiments therefore need to be complemented with comparative observational studies in existing forests. Here we present the design and implementation of a new network of forest plots along tree species diversity gradients in six major European forest types: the FunDivEUROPE Exploratory Platform. Based on a review of the deficiencies of existing observational approaches and of unresolved research questions and hypotheses, we discuss the fundamental criteria that shaped the design of our platform. Key features include the extent of the species diversity gradient with mixtures up to five species, strict avoidance of a dilution gradient, special attention to community evenness and minimal covariation with other environmental factors. The new European research platform permits the most comprehensive assessment of tree species diversity effects on forest ecosystem functioning to date since it offers a common set of research plots to groups of researchers from very different disciplines and uses the same methodological approach in contrasting forest types along an extensive environmental gradient.     

Poor Prospects for Avian Biodiversity in Amazonian Oil Palm

Expansion of oil palm plantations across the humid tropics has precipitated massive loss of tropical forest habitats and their associated speciose biotas. Oil palm plantation monocultures have been identified as an emerging threat to Amazonian biodiversity, but there are no quantitative studies exploring the impact of these plantations on the biome’s biota. Understanding these impacts is extremely important given the rapid projected expansion of oil palm cultivation in the basin. Here we investigate the biodiversity value of oil palm plantations in comparison with other dominant regional land-uses in Eastern Amazonia. We carried out bird surveys in oil palm plantations of varying ages, primary and secondary forests, and cattle pastures. We found that oil palm plantations retained impoverished avian communities with a similar species composition to pastures and agrarian land-uses and did not offer habitat for most forest-associated species, including restricted range species and species of conservation concern. On the other hand, the forests that the oil palm companies are legally obliged to protect hosted a relatively species-rich community including several globally-threatened bird species. We consider oil palm to be no less detrimental to regional biodiversity than other agricultural land-uses and that political pressure exerted by large landowners to allow oil palm to count as a substitute for native forest vegetation in private landholdings with forest restoration deficits would have dire consequences for regional biodiversity.     

What can mixed‐species flock movement tell us about the value of Amazonian secondary forests? Insights from spatial behavior

The value of secondary forest for rain forest species remains an important question for conservation in the 21st century. Here, we describe the spatial behavior of understory mixed‐species flocks in a heterogeneous landscape in central Amazonia. Understory mixed‐species flocks represent a diverse, highly organized component of the rich Amazonian avifauna. We recorded movements within 26 flock home ranges in primary forest, secondary forest, interfaces between forest types, and forest fragments. We describe frequency and movement orientation in relation to forest edges, movement patterns and proportion of use between secondary and primary forest, the relation between home range sizes and vegetation height, and home range configuration. Flocks visited only a small portion of forest edges, and showed a tendency for moving parallel to edges next to less‐developed secondary forest. Movement patterns in secondary forests did not show significant differences compared to primary forests. Time spent in secondary forests increased in proportion to mean canopy height. Flocks were consistently present in secondary forests where vegetation height averaged over 15 m, but home ranges were nearly twice as large compared to primary forest. Home range limits tended to be aligned with disturbed vegetation, essentially rearranging a territorial configuration normally adjusted by topography. The spatial behavior of this important subset of the Amazonian avifauna shows that secondary forests are tolerated above a certain development threshold, but perceived as suboptimal habitat until canopy height closely matches primary forests.     

Effect of Host Tree Traits on Epiphyte Diversity in Natural and Anthropogenic Habitats in Ecuador

Vascular epiphytes represent a highly diverse element of tropical rain forests, but they depend strongly on the structure and taxonomic composition of their tree communities. For conservation planning, it is therefore critical to understand the effect of host tree characteristics on epiphyte species richness in natural and anthropogenically transformed vegetation. Our study compares the effect of human land‐use on epiphyte diversity based on 220 study plots in a lowland rain forest and an Andean cloud forest in western Ecuador. We evaluate the relevance of host tree size and taxonomic identity for epiphyte species richness in contiguous primary forests, forest fragments, isolated remnant trees (IRTs), and secondary forests. At both study sites, epiphyte diversity was highest in primary forests, and it was lowest on IRTs and in secondary forests. Epiphyte species numbers of forest fragments were significantly reduced compared with the contiguous primary forest at the lowland study site, but not in the cloud forest area. Host tree size was a core predictor among secondary forests, but it had less significance within other habitat types. Taxonomic identity of the host trees also explained up to 61 percent of the variation in epiphyte diversity, especially for IRTs. The structural and taxonomic composition of the tree community in anthropogenically transformed habitat types proved to be fundamental to epiphyte diversity. This highlights the importance of deliberate selection of tree species for reforestation in conservation programs and the possible negative effects of selective logging in primary forests. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Plant diversity patterns in subtropical evergreen broad-leaved forests of Yunnan and Taiwan

The subtropical evergreen broad-leaved forests of Yunnan and Taiwan were compared along environmental and successional gradients with the aim of identifying important taxon and species diversity as well as the drivers of mountain biodiversity patterns. A detrended correspondence analysis of an exhaustive set of data collected from 105 and 223 plots for Yunnan and Taiwan, respectively, was applied to classify natural mature forest types. Additional data from 72 and 68 plots for Yunnan and Taiwan, respectively, were used for analyses of secondary succession. The floristic richness and diversity index were calculated for each type of forest. In Yunnan, the monsoon forests in mesic-humid sites had more taxa and tended to show higher species diversity than the other two forest types. In Taiwan, species diversity values were significantly higher in the Machilus–Castanopsis zone in the middle altitudes (500–1500 m) than for the other three forest zones. For both Yunnan and Taiwan, the forests at the middle successional stage showed significantly higher species diversity than those at the early successional stage. Differences in diversity between the middle and late stages were not significant. These findings highlight the high species diversity of the natural mature evergreen broad-leaved forests of both Yunnan and Taiwan. In the secondary forests, as succession proceeds, species diversity comes to resemble that of the natural mature forests. In both ecosystems, the drivers of species diversity patterns are moisture, altitude, and succession/disturbance.     

A Miocene hyperdiverse crocodylian community reveals peculiar trophic dynamics in proto-Amazonian mega-wetlands

Amazonia contains one of the world''s richest biotas, but origins of this diversity remain obscure. Onset of the Amazon River drainage at approximately 10.5 Ma represented a major shift in Neotropical ecosystems, and proto-Amazonian biotas just prior to this pivotal episode are integral to understanding origins of Amazonian biodiversity, yet vertebrate fossil evidence is extraordinarily rare. Two new species-rich bonebeds from late Middle Miocene proto-Amazonian deposits of northeastern Peru document the same hyperdiverse assemblage of seven co-occurring crocodylian species. Besides the large-bodied Purussaurus and Mourasuchus, all other crocodylians are new taxa, including a stem caiman—Gnatusuchus pebasensis—bearing a massive shovel-shaped mandible, procumbent anterior and globular posterior teeth, and a mammal-like diastema. This unusual species is an extreme exemplar of a radiation of small caimans with crushing dentitions recording peculiar feeding strategies correlated with a peak in proto-Amazonian molluscan diversity and abundance. These faunas evolved within dysoxic marshes and swamps of the long-lived Pebas Mega-Wetland System and declined with inception of the transcontinental Amazon drainage, favouring diversification of longirostrine crocodylians and more modern generalist-feeding caimans. The rise and demise of distinctive, highly productive aquatic ecosystems substantially influenced evolution of Amazonian biodiversity hotspots of crocodylians and other organisms throughout the Neogene.     

Palm species richness,abundance and diversity in the Yucatan Peninsula,in a neotropical context

Species richness, abundance and diversity patterns in palm communities in the Yucatan Peninsula were compared at three sites with different forest types (semi‐deciduous, semi‐evergreen and evergreen), as well as different precipitation, geomorphology and soil depth. All individual palms, including seedlings, juveniles and adults, were identified and counted in forty‐five (0.25 ha) transects. A total of 46 000 individual palms belonging to 11 species from nine genera and two subfamilies were recorded. Palm richness, diversity and abundance were highest in the evergreen forest. Species from the subfamily Coryphoideae dominated the semi‐deciduous and semi‐evergreen forests while species from the subfamily Arecoideae dominated the evergreen forest. Seven species were found only in the evergreen forest. Chamaedorea seifrizii and Sabal yapa were found in all three forest types, while Thrinax radiata was found in the semi‐deciduous and semi‐ evergreen forests and Cocothrinax readii only in the semi‐evergreen forest. Compared to other neotropical palm communities, the richness and diversity in the Yucatan Peninsula are lower than in the western Amazon basin. Although palm richness and diversity on the Yucatan Peninsula were positively associated with precipitation, other variables, in particular soil depth and fertility as well as habitat heterogeneity (microtopography and canopy cover), need to be considered to better understand the observed patterns.