One sixth of Amazonian tree diversity is dependent on river floodplains

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Evaluation of the management potential of timber resources in clearwater floodplain forests in the Amazon using growth models

The Amazonian clearwater igapós are poorly studied floodplain ecosystems that are mainly covered by forests and are undergoing massive threats due to changes in land use and climate. Their hydrochemical characteristics and edaphic conditions fall between those of the eutrophic várzea floodplains on whitewater rivers and those of the oligotrophic igapós on blackwater rivers. Previous studies have indicated the management potential of timber species in the highly dynamic várzea floodplains due to the fast tree growth and high forest productivity. Timber resource management, however, is not recommended for the blackwater ecosystem because of its slow dynamics and high vulnerability to disturbances. For clearwater igapós, information on the potential for sustainable management of timber resources is lacking. In this study, we modeled the growth in diameter, height, and volume to derive species-specific minimum logging diameters (MLD) and felling cycles (FC) for eight merchantable species in the clearwater igapós of the Branco and Tapajós rivers in the northern and southern Amazon Basin, respectively. Diameter growth was modeled by analyzing the tree rings that are annually formed in the Amazonian floodplains as a consequence of the regular and predicable long-term flooding. Growth modeling followed the guidelines of the Growth-Oriented Logging (GOL) concept, with the adjustment of diameter growth improved by applying nonlinear mixed-effects regression. MLDs varied from 36 to 90 cm and FCs ranged from 6 to 21 years, which diverges from the standards of Brazilian logging regulations (MLD: 50 cm; FC: 25-35 years). This indicates the potential for timber resource management, which should be tested and introduced at small scales, integrated in protected areas to stepwise promote the sustainable management of these natural resources by traditional communities to increase their income and the conservation of this ecosystem.

Consistent patterns of common species across tropical tree communities

Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.

Integrated global assessment of the natural forest carbon potential

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2-5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151-363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution.

The global biogeography of tree leaf form and habit

Understanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, evergreen and deciduous trees. To address these gaps, we conducted a global, ground-sourced assessment of forest leaf-type variation by integrating forest inventory data with comprehensive leaf form (broadleaf vs needle-leaf) and habit (evergreen vs deciduous) records. We found that global variation in leaf habit is primarily driven by isothermality and soil characteristics, while leaf form is predominantly driven by temperature. Given these relationships, we estimate that 38% of global tree individuals are needle-leaved evergreen, 29% are broadleaved evergreen, 27% are broadleaved deciduous and 5% are needle-leaved deciduous. The aboveground biomass distribution among these tree types is approximately 21% (126.4 Gt), 54% (335.7 Gt), 22% (136.2 Gt) and 3% (18.7 Gt), respectively. We further project that, depending on future emissions pathways, 17-34% of forested areas will experience climate conditions by the end of the century that currently support a different forest type, highlighting the intensification of climatic stress on existing forests. By quantifying the distribution of tree leaf types and their corresponding biomass, and identifying regions where climate change will exert greatest pressure on current leaf types, our results can help improve predictions of future terrestrial ecosystem functioning and carbon cycling.

More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia

Indigenous societies are known to have occupied the Amazon basin for more than 12,000 years, but the scale of their influence on Amazonian forests remains uncertain. We report the discovery, using LIDAR (light detection and ranging) information from across the basin, of 24 previously undetected pre-Columbian earthworks beneath the forest canopy. Modeled distribution and abundance of large-scale archaeological sites across Amazonia suggest that between 10,272 and 23,648 sites remain to be discovered and that most will be found in the southwest. We also identified 53 domesticated tree species significantly associated with earthwork occurrence probability, likely suggesting past management practices. Closed-canopy forests across Amazonia are likely to contain thousands of undiscovered archaeological sites around which pre-Columbian societies actively modified forests, a discovery that opens opportunities for better understanding the magnitude of ancient human influence on Amazonia and its current state.

Native diversity buffers against severity of non-native tree invasions

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5-7, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions.

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers.

Seasonal shifts in isoprenoid emission composition from three hyperdominant tree species in central Amazonia

Volatile isoprenoids regulate plant performance and atmospheric processes, and Amazon forests comprise the dominant source to the global atmosphere. Still, there is a poor understanding of how isoprenoid emission capacities vary in response to ecophysiological and environmental controls in Amazonian ecosystems. We measured isoprenoid emission capacities of three Amazonian hyperdominant tree species - Protium hebetatum, Eschweilera grandiflora, Eschweilera coriacea - across seasons and along a topographic and edaphic environmental gradient in the central Amazon. From wet to dry season, both photosynthesis and isoprene emission capacities strongly declined, while emissions increased among the heavier isoprenoids: monoterpenes and sesquiterpenes. Plasticity across habitats was most evident in P. hebetatum, which emitted sesquiterpenes only in the dry season, at rates that significantly increased along the hydro-topographic gradient from white sands (shallow root water access) to uplands (deep water table). We suggest that emission composition shifts are part of a plastic response to increasing abiotic stress (e.g. heat and drought) and reduced photosynthetic supply of substrates for isoprenoid synthesis. Our comprehensive measurements suggest that more emphasis should be placed on other isoprenoids, besides isoprene, in the context of abiotic stress responses. Shifting emission compositions have implications for atmospheric responses because of the strong variation in reactivity among isoprenoid compounds.

The specialized white-sand flora of the Uatumã Sustainable Development Reserve, central Amazon, Brazil

The consensus is that Amazonian white-sand ecosystems (campinaranas) shelter several endemic plant species. However, recent studies have shown that most species are generalists, and they also occur in other Neotropical ecosystems. To investigate this issue, we analyzed the proportion of endemic/specialist species in a checklist of trees, palms, and shrubs sampled between 2014 and 2020 in campinarana patches of the Uatumã Sustainable Development Reserve (USDR), central Amazon. We also provide a description of phytophysiognomies, habitats, distribution, and phenology. We found 167 species belonging to 117 genera and 50 families. Fabaceae was the most representative (21 spp.), followed by Rubiaceae (16 spp.) and Chrysobalanaceae (10 spp.). We found that 30.5% of the species were exclusive to campinaranas, confirming that although there are many endemics, proportionally most species are generalists. The USDR has a rich flora specialized in oligotrophic habitats, which must be considered in the management and conservation strategies of these complex and fragile Amazonian ecosystems. 

Gender-Specific Design and Effectiveness of Non-Pharmacological Interventions against Cognitive Decline - Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

The number of people living with dementia worldwide is increasing rapidly. Preventive approaches constitute a promising strategy to counter the dementia epidemic, and growing numbers of lifestyle interventions are conducted around the globe. Gender differences with respect to modifiable risk factors for dementia have been reported, however, little is known about gender-specific effectiveness of lifestyle trials against cognitive decline and dementia. A systematic review and meta-analysis was conducted to assess evidence on gender-specific design and effectiveness of randomized controlled trials against cognitive decline.

METHODS

Systematic literature searches were conducted in MEDLINE, PsycINFO, Web of Science, Cochrane Central and ALOIS. Studies assessing global and/or domain-specific cognitive function in older adults free from dementia were eligible for the systematic review. We assessed between-group effect sizes using random-effects meta-analysis. Methodological quality of included studies was assessed using the Scottish Intercollegiate Guidelines Network (SIGN)-checklist.

RESULTS

The systematic review and meta-analysis included 34 and 31 studies, respectively. Effects of lifestyle-interventions on global cognition were non-significant overall (g = .27; 95% CI: -.01; .56) and in male subsamples (g = -.05; 95% CI: -.55; .45), and small for female subsamples (g = .38; 95% CI: .05; .72). Small beneficial effects were found for memory (overall: g = .38; 95% CI = .17; .59). Stratified by gender, significant effects were observed only in women (g = .39; 95% CI = .13; .65; men: g = .37; 95% CI: .00; .73). Aspects of gender in study design and conduct were discussed in a small minority of studies. Comparable results were observed for executive function and verbal fluency. Methodological quality was deemed high in 17.6% of studies, acceptable and low quality in 52.9% and 29.4%, respectively.

DISCUSSION

We found evidence for small differences in the effectiveness of lifestyle interventions on global cognition and memory in favor of women. However, small numbers of trials 1) targeting men and 2) reporting gender-specific results for older adults with mild cognitive impairment warrant further attention. Assessing differences in modifiable risk factors for dementia in men and women and systematically addressing aspects of gender in trial conduction and recruitment in future studies might increase knowledge on gender-specific effectiveness of lifestyle trials against cognitive decline.

Modeling the Ecological Responses of Tree Species to the Flood Pulse of the Amazon Negro River Floodplains

The large flood pulse of the Amazon basin is a principal driver of environmental heterogeneity with important implications for ecosystem function and the assembly of natural communities. Understanding species ecological response to the flood pulse is thus a key question with implications for theories of species coexistence, resource management, and conservation. Yet these remain largely undescribed for most species, and in particular for trees. The large flood pulse and high tree diversity of the Negro River floodplain makes it an ideal system to begin filling this knowledge gap. We merged historical hydrologic data with 41 forest inventories under variable flooding conditions distributed across the Negro River basin, comprising a total area of 34 ha, to (i) assess the importance of flood duration as a driver of compositional variation, (ii) model the response curve shapes of 111 of the most frequent tree species in function of flood duration, and (iii) derive their niche properties (optima and tolerance). We found that flood duration is a strong driver of compositional turnover, although the majority site-to-site variation in forest composition still remains unexplained. About 73% of species responded to the flood duration gradient, exhibiting a diversity of shapes, but most frequently skewed. About 29% of species were clearly favored by flood durations >120 days year–1, and 44% of species favored by shorter floods. The median niche breadth was 85 flood days year–1, corresponding to approximately 30% of the flood duration gradient. A significant subset of species (27%) did not respond to flooding, but rather exhibited wide tolerance to the flood gradient. The response models provided here offer valuable information regarding tree species differential capacity to grow, survive, and regenerate along an ecologically important gradient and are spatially valid for the Amazon Negro basin. These attributes make them an appealing tool with wide applicability for field and experimental studies in the region, as well as for vegetation monitoring and simulation models of floodplain forest change in the face of hydrologic alteration.

Convergent evolution of tree hydraulic traits in Amazonian habitats: implications for community assemblage and vulnerability to drought

Amazonian droughts are increasing in frequency and severity. However, little is known about how this may influence species-specific vulnerability to drought across different ecosystem types. We measured 16 functional traits for 16 congeneric species from six families and eight genera restricted to floodplain, swamp, white-sand or plateau forests of Central Amazonia. We investigated whether habitat distributions can be explained by species hydraulic strategies, and if habitat specialists differ in their vulnerability to embolism that would make water transport difficult during drought periods. We found strong functional differences among species. Nonflooded species had higher wood specific gravity and lower stomatal density, whereas flooded species had wider vessels, and higher leaf and xylem hydraulic conductivity. The P₅₀ values (water potential at 50% loss of hydraulic conductivity) of nonflooded species were significantly more negative than flooded species. However, we found no differences in hydraulic safety margin among species, suggesting that all trees may be equally likely to experience hydraulic failure during severe droughts. Water availability imposes a strong selection leading to differentiation of plant hydraulic strategies among species and may underlie patterns of adaptive radiation in many tropical tree genera. Our results have important implications for modeling species distribution and resilience under future climate scenarios.

Biased-corrected richness estimates for the Amazonian tree flora

Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come.

Rarity of monodominance in hyperdiverse Amazonian forests

Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.

Species Distribution Modelling: Contrasting presence-only models with plot abundance data

Species distribution models (SDMs) are widely used in ecology and conservation. Presence-only SDMs such as MaxEnt frequently use natural history collections (NHCs) as occurrence data, given their huge numbers and accessibility. NHCs are often spatially biased which may generate inaccuracies in SDMs. Here, we test how the distribution of NHCs and MaxEnt predictions relates to a spatial abundance model, based on a large plot dataset for Amazonian tree species, using inverse distance weighting (IDW). We also propose a new pipeline to deal with inconsistencies in NHCs and to limit the area of occupancy of the species. We found a significant but weak positive relationship between the distribution of NHCs and IDW for 66% of the species. The relationship between SDMs and IDW was also significant but weakly positive for 95% of the species, and sensitivity for both analyses was high. Furthermore, the pipeline removed half of the NHCs records. Presence-only SDM applications should consider this limitation, especially for large biodiversity assessments projects, when they are automatically generated without subsequent checking. Our pipeline provides a conservative estimate of a species’ area of occupancy, within an area slightly larger than its extent of occurrence, compatible to e.g. IUCN red list assessments.

An expert system model for mapping tropical wetlands and peatlands reveals South America as the largest contributor

Wetlands are important providers of ecosystem services and key regulators of climate change. They positively contribute to global warming through their greenhouse gas emissions, and negatively through the accumulation of organic material in histosols, particularly in peatlands. Our understanding of wetlands' services is currently constrained by limited knowledge on their distribution, extent, volume, interannual flood variability and disturbance levels. We present an expert system approach to estimate wetland and peatland areas, depths and volumes, which relies on three biophysical indices related to wetland and peat formation: (1) long-term water supply exceeding atmospheric water demand; (2) annually or seasonally water-logged soils; and (3) a geomorphological position where water is supplied and retained. Tropical and subtropical wetlands estimates reach 4.7 million km² (Mkm² ). In line with current understanding, the American continent is the major contributor (45%), and Brazil, with its Amazonian interfluvial region, contains the largest tropical wetland area (800,720 km² ). Our model suggests, however, unprecedented extents and volumes of peatland in the tropics (1.7 Mkm² and 7,268 (6,076-7,368) km³ ), which more than threefold current estimates. Unlike current understanding, our estimates suggest that South America and not Asia contributes the most to tropical peatland area and volume (ca. 44% for both) partly related to some yet unaccounted extended deep deposits but mainly to extended but shallow peat in the Amazon Basin. Brazil leads the peatland area and volume contribution. Asia hosts 38% of both tropical peat area and volume with Indonesia as the main regional contributor and still the holder of the deepest and most extended peat areas in the tropics. Africa hosts more peat than previously reported but climatic and topographic contexts leave it as the least peat-forming continent. Our results suggest large biases in our current understanding of the distribution, area and volumes of tropical peat and their continental contributions.

The Brazilian freshwater wetscape: Changes in tree community diversity and composition on climatic and geographic gradients

Wetlands harbor an important compliment of regional plant diversity, but in many regions data on wetland diversity and composition is still lacking, thus hindering our understanding of the processes that control it. While patterns of broad-scale terrestrial diversity and composition typically correlate with contemporary climate it is not clear to what extent patterns in wetlands are complimentary, or conflicting. To elucidate this, we consolidate data from wetland forest inventories in Brazil and examine patterns of diversity and composition along temperature and rainfall gradients spanning five biomes. We collated 196 floristic inventories covering an area >220 ha and including >260,000 woody individuals. We detected a total of 2,453 tree species, with the Amazon alone accounting for nearly half. Compositional patterns indicated differences in freshwater wetland floras among Brazilian biomes, although biomes with drier, more seasonal climates tended to have a larger proportion of more widely distributed species. Maximal alpha diversity increased with annual temperature, rainfall, and decreasing seasonality, patterns broadly consistent with upland vegetation communities. However, alpha diversity-climate relationships were only revealed at higher diversity values associated with the uppermost quantiles, and in most sites diversity varied irrespective of climate. Likewise, mean biome-level differences in alpha-diversity were unexpectedly modest, even in comparisons of savanna-area wetlands to those of nearby forested regions. We describe attenuated wetland climate-diversity relationships as a shifting balance of local and regional effects on species recruitment. Locally, excessive waterlogging strongly filters species able to colonize from regional pools. On the other hand, increased water availability can accommodate a rich community of drought-sensitive immigrant species that are able to track buffered wetland microclimates. We argue that environmental conditions in many wetlands are not homogeneous with respect to regional climate, and that responses of wetland tree communities to future climate change may lag behind that of non-wetland, terrestrial habitat.

Estimating the global conservation status of more than 15,000 Amazonian tree species

Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict that most of the world's >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century.

Hyperdominance in the Amazonian tree flora

The vast extent of the Amazon Basin has historically restricted the study of its tree communities to the local and regional scales. Here, we provide empirical data on the commonness, rarity, and richness of lowland tree species across the entire Amazon Basin and Guiana Shield (Amazonia), collected in 1170 tree plots in all major forest types. Extrapolations suggest that Amazonia harbors roughly 16,000 tree species, of which just 227 (1.4%) account for half of all trees. Most of these are habitat specialists and only dominant in one or two regions of the basin. We discuss some implications of the finding that a small group of species--less diverse than the North American tree flora--accounts for half of the world's most diverse tree community.

Struggle in the flood: tree responses to flooding stress in four tropical floodplain systems

BACKGROUND AND AIMS

In the context of the 200th anniversary of Charles Darwin's birth in 1809, this study discusses the variation in structure and adaptation associated with survival and reproductive success in the face of environmental stresses in the trees of tropical floodplains.

SCOPE

We provide a comparative review on the responses to flooding stress in the trees of freshwater wetlands in tropical environments. The four large wetlands we evaluate are: (i) Central Amazonian floodplains in South America, (ii) the Okavango Delta in Africa, (iii) the Mekong floodplains of Asia and (iv) the floodplains of Northern Australia. They each have a predictable 'flood pulse'. Although flooding height varies between the ecosystems, the annual pulse is a major driving force influencing all living organisms and a source of stress for which specialized adaptations for survival are required.

MAIN POINTS

The need for trees to survive an annual flood pulse has given rise to a large variety of adaptations. However, phenological responses to the flood are similar in the four ecosystems. Deciduous and evergreen species respond with leaf shedding, although sap flow remains active for most of the year. Growth depends on adequate carbohydrate supply. Physiological adaptations (anaerobic metabolism, starch accumulation) are also required.

CONCLUSIONS

Data concerning the ecophysiology and adaptations of trees in floodplain forests worldwide are extremely scarce. For successful floodplain conservation, more information is needed, ideally through a globally co-ordinated study using reproducible comparative methods. In the light of climatic change, with increasing drought, decreased groundwater availability and flooding periodicities, this knowledge is needed ever more urgently to facilitate fast and appropriate management responses to large-scale environmental change.

Drought responses of flood-tolerant trees in Amazonian floodplains

BACKGROUND

Flood-tolerant tree species of the Amazonian floodplain forests are subjected to an annual dry period of variable severity imposed when low river-water levels coincide with minimal precipitation. Although the responses of these species to flooding have been examined extensively, their responses to drought, in terms of phenology, growth and physiology, have been neglected hitherto, although some information is found in publications that focus on flooding.

SCOPE

The present review examines the dry phase of the annual flooding cycle. It consolidates existing knowledge regarding responses to drought among adult trees and seedlings of many Amazonian floodplain species.

MAIN FINDINGS

Flood-tolerant species display variable physiological responses to dry periods and drought that indicate desiccation avoidance, such as reduced photosynthetic activity and reduced root respiration. However, tolerance and avoidance strategies for drought vary markedly among species. Drought can substantially decrease growth, biomass and photosynthetic activity among seedlings in field and laboratory studies. When compared with the responses to flooding, drought can impose higher seedling mortality and slower growth rates, especially among evergreen species. Results indicate that tolerance and avoidance strategies for drought vary markedly between species. Both seedling recruitment and photosynthetic activity are affected by drought,

CONCLUSIONS

For many species, the effects of drought can be as important as flooding for survival and growth, particularly at the seedling phase of establishment, ultimately influencing species composition. In the context of climate change and predicted decreases in precipitation in the Amazon Basin, the effects of drought on plant physiology and species distribution in tropical floodplain forest ecosystems should not be overlooked.

[Titanium-coated silicone is not effective for preventing graft infection]

AIM

Titanium-coated grafts for breast augmentation are available since 2001 and are used clinically. The titan surface is supposed to improve the tissue compatibility and to lower the infection rate. It was the aim of the present study to validate the antibacterial efficiency of titanium-coated silicone.

MATERIAL AND METHODS

C3H/HcN mice were assigned to four different groups (n=6/group). Silicone without (group I and III) or with (group II and IV) titanium were implanted subcutaneously. Following this in groups III and IV a local contamination was induced with 2 x 10 (7) CFU/0.1 ml Staphylococcus aureus ATCC 25923. Groups I and II were not infected. 14 days after primary operation all animals were euthanized and the grafts harvested. Specimens were examined for signs of infections by macroscopy, histology and microbiology.

RESULTS

In group I none of the grafts were infected (0/5). In group II (silicone, + titanium, no contamination) one infection was evident due to biting of the animal (1/6). In group III (silicone, no titanium, contamination) an infection was detected in all mice (6/6). The use of titanium, however, did not significantly reduce the infection rate in contaminated animals (group IV, 5/6). Interestingly, tissue integration of titanium-coated grafts was macroscopically reduced compared to non- titanium-coated grafts (group II vs. I).

CONCLUSION

The titanium-coated silicone grafts were not effective in protecting infection in vivo. The decreased tissue integration of titanium-coated grafts, however, might reduce the rate of capsular contracture. This potential advantage of titanium needs to be validated in controlled clinical trials.

Wood growth patterns of Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) in Amazonian black-water and white-water floodplain forests

Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) is a dominant legume tree species occurring at low elevations of nutrient-poor black-water (igapó) and nutrient-rich white-water floodplain forests (várzea) of Amazonia. As a consequence of the annual long-term flooding this species forms distinct annual tree rings allowing dendrochronological analyses. From both floodplain types in Central Amazonia we sampled cores from 20 large canopy trees growing at identical elevations with a flood-height up to 7 m. We determined tree age, wood density (WD) and mean radial increment (MRI) and synchronized ring-width patterns of single trees to construct tree-ring chronologies for every study site. Maximum tree age found in the igapó was more than 500 years, contrary to the várzea with ages not older than 200 years. MRI and WD were significantly lower in the igapó (MRI=1.52+/-0.38 mm year(-1), WD=0.39+/-0.05 g cm(-3)) than in the várzea (MRI=2.66+/-0.67 mm year(-1), WD=0.45+/-0.03 g cm(-3)). In both floodplain forests we developed tree-ring chronologies comprising the period 1857-2003 (n=7 trees) in the várzea and 1606-2003 (n=13 trees) in the igapó. The ring-width in both floodplain forests was significantly correlated with the length of the terrestrial phase (vegetation period) derived from the daily recorded water level in the port of Manaus since 1903. In both chronologies we found increased wood growth during El Niño events causing negative precipitation anomalies and a lower water discharge in Amazonian rivers, which leads to an extension of the terrestrial phase. The climate signal of La Niña was not evident in the dendroclimatic proxies.

l-Arginine Improves Wound Healing after Trauma-Hemorrhage by Increasing Collagen Synthesis

BACKGROUND

Several studies indicate impaired wound healing after trauma and shock. Wound immune cell dysfunction seems to be responsible for altered wound healing after trauma-hemorrhage (T-H). In this respect, administration of the amino acid L-arginine normalized wound immune cell function under those conditions. It remains unknown, however, whether L-arginine improves impaired wound healing after T-H.

METHODS

To study this, male C3H/HeN mice were subjected to a midline laparotomy (i.e., soft tissue trauma induced), and polyvinyl sponges were implanted subcutaneously at the wound site before hemorrhage (35 +/- 5 mm Hg for 90 minutes) or were subjected to sham operation. During resuscitation, mice received 300 mg/kg body weight L-arginine or saline (vehicle). Seven days thereafter, hydroxyproline (OHP), a metabolite of collagen synthesis, was measured in the wound fluid using high-performance liquid chromatography. Collagen types I and III were determined in the wound by Western blot analysis. In addition, wound breaking strength was measured 10 days after T-H or sham operation.

RESULTS

The results indicate that OHP was significantly decreased in T-H mice. L-arginine, however, restored depressed OHP in the wound fluid in the T-H animals. Similarly, L-arginine treatment prevented a significant depression of collagen I synthesis after T-H. Collagen III was not significantly affected by T-H or L-arginine. Most important, L-arginine increased maximal wound breaking strength after severe blood loss. Therefore, L-arginine improves wound healing after T-H by increasing collagen synthesis.

CONCLUSION

Because L-arginine improves wound healing, the results suggest that L-arginine might represent a novel and useful adjunct to fluid resuscitation for decreasing wound complications after trauma and severe blood loss.

Physiological Levels of 5α-Dihydrotestosterone Depress Wound Immune Function and Impair Wound Healing Following Trauma-Hemorrhage

HYPOTHESIS

Studies indicate that a depressed wound immune function contributes to an increased rate of wound complications and impaired wound healing following trauma-hemorrhage (T-H). Androgen, ie, 5 alpha-dihydrotestosterone, is responsible for producing the depressed systemic cell-mediated immune responses following T-H in males. The aim of the present study was to determine whether depletion of 5 alpha-dihydrotestosterone in males before T-H has any salutary effects on wound immune cell function and wound healing in male mice following T-H.

DESIGN

Mice were castrated or sham castrated 14 days before midline laparotomy (ie, tissue trauma) and subcutaneous polyvinyl sponge implantation, followed by hemorrhage (mean +/- SEM blood pressure, 35 +/- 5 mm Hg for 90 minutes and resuscitation) or sham operation. At 24 hours thereafter, wound immune cells from the sponges were harvested and cultured with lipopolysaccharide A. Release of interleukin 1 beta (IL-1 beta) and IL-6 (in picograms per milliliter) was determined in the supernatants by enzyme-linked immunosorbent assay. In addition, IL-6 was assessed at the wound site by immunohistochemistry. Ten days after T-H, wound-breaking strength was measured.

RESULTS

Precastration prevented the significantly suppressed capacity of wound immune cells to release IL-1 beta and IL-6. In addition, precastration normalized the elevated IL-6 expression at the wound site in the T-H mice. Moreover, wound-breaking strength was improved in castrated mice 10 days after T-H.

CONCLUSIONS

Male sex steroids appear to be responsible for wound immune cell dysfunction following trauma and severe blood loss. Because decreasing androgen levels resulted in improved wound healing, our results suggest that the use of androgen receptor-blocking agents, eg, flutamide, following T-H might represent a novel adjunct for decreasing the rate of wound complications under those conditions.

Rifampin and Triclosan but not silver is effective in preventing bacterial infection of vascular dacron graft material

OBJECTIVES

To evaluate the efficacy of silver- or Triclosan-coated prosthetic material compared to Rifampin bonded Dacron concerning their resistance to infection following subcutaneous implantation and contamination with Staphylococcus aureus.

DESIGN

Animal experimental study in mice.

MATERIAL AND METHODS

Thirty-six C3H/HcN mice (Charles River Lab., Sulzfeld, Germany) with a weight between 24 and 27 g were randomised into six groups counting six animals each. Group I: control, gel-sealed dacron graft, group II: gel-sealed dacron graft and local contamination, group III: Intergard-Silver-prosthesis and contamination, group IV: silver/gel-sealed dacron prosthesis (test graft) and contamination, group V: Rifampin-bonded gel-sealed graft and contamination, group VI: Triclosan/collagen-coated dacron graft and contamination. Dacron graft material 0.8x1 cm was subcutaneously implanted in mice. Local contamination with 2x10(7)/0.2 ml S. aureus ATCC 25923 was carried out in groups II to VI. On day 14 the animals were killed and the grafts were explanted. The microscopic, histologic and microbiological evaluation of the graft material and the perigraft tissue was performed.

RESULTS

In control group I no case of infection was detected. In group II, 6 of 6 animals showed infection. In group III (Intergard-Silver) and group IV (silver/gel-test graft) were 6 of 6, in group V (Rifampin) only 1 of 6 grafts and in group VI (Triclosan) 4 of 6 grafts were infected. The difference between the low rate of infection in group V (Rifampin) in comparison to the completely infected groups III and IV (Silver) as well as the control group II was significant. Treatment of grafts with Triclosan could prevent infection only in 1/3 of the cases in group IV.

CONCLUSION

Silver coating failed to prevent graft infection material. A potential antimicrobial property was evident for Triclosan whereas Rifampin-bonded grafts exhibit a significantly reduced infection rate. Thus, silver-coated vascular grafts cannot ensure protection from vascular graft infection.

[Experimental examination concerning the efficacy of silver-coated Dacron prostheses in vascular graft infections following subcutaneous implantation in a standardized infection model]

It was the aim of the study to examine the efficacy of silver coated prostheses in comparison to Rifampin in impregnated prostheses in the prevention of vascular graft infections.

MATERIAL AND METHODS

24 C3H/HcN mice with a bodyweight between 24 and 27 grams were assigned to four different groups. GROUP I: control gel-sealed Dacron graft (Uni-Graft DV) (6), GROUP II: gel-sealed Dacron graft (Uni-Graft DV) contaminated locally with 2 x 10(7) CFU/1.2 ml Staphylococcus aureus ATCC 25923 (6), GROUP III: silver prosthesis (Intergard Silver) contaminated locally with 2 x 10(7) CFU/0.2 ml Staphylococcus aureus ATCC 25923 (6), GROUP IV: Rifampin impregnated prosthesis contaminated locally with 2 x 10(7) CFU/0.2 ml Staphylococcus aureus ATCC 25923 (6). 14 days after primary operation all animals were euthanized and the grafts harvested. Specimens were examined for signs of infections by histology and microbiology.

RESULTS

At termination of the trial on day 14 none of the grafts of group I were contaminated. 6 out of 6 grafts in group II, 6 out of 6 grafts in group III and 1 out of 6 grafts in group IV presented with infected grafts. The use of antimicrobial Rifampin could significantly prevent infection after bacterial challenge in group IV.

CONCLUSION

The silver protected prosthesis (Intergard Silver) seems to be not effective in protecting vascular infection in vivo. However, the Rifampin group showed excellent results. In conclusion Rifampin bonded gelatin-sealed Dacron grafts are significantly more resistant to bacteremic infection than are silver/collagen-coated Dacron grafts.