Dominância, distribuição e diversidade de palmeiras ao longo de gradientes ambientais na Amazônia

The aim of this thesis was to study the patterns of dominance, diversity and species distribution in Amazonian palms. In the first chapter we explored the continental patterns of variation in palm species dominance by relating palm and tree basal area with soil physical properties. In this chapter, we showed that soil physical properties establish the upper limit for palm and tree basal area and that the direction of this relationship differs between them. As soil resistance to root penetration heightens, tree basal area decreases and palm basal area increases. The mechanism of forest partitioning by palms as trees is related to forest structure at the local scale and with forest physiognomy at the basin scale. In the second chapter we explored the regional patterns of palm species abundance variation in relation to environmental gradients and their effect on dominance and floristic composition patterns. In this chapter we demonstrate that subtle and abrupt differences in floristic composition may be caused by changes in species abundance in relation to environmental conditions. We also showed that dominance patterns are linked with the patterns of floristic variation and suggest a mechanism to explain the occurrence of dominance in tropical forests. In the third chapter, we tested the hypothesis that species segregation along subtle environmental gradients will explain species coexistence in local and regional scale. In this chapter, we showed that palm species are segregated along a hydrological axis of soil moisture and that the hydrological niche affiliation of the species is a character that evolved through palm evolution andO objetivo desta tese foi estudar os padrões de dominância, diversidade e distribuição de palmeiras na Amazônia. No primeiro capítulo, exploramos os padrões continentais de variação na dominância de palmeiras relacionando a área basal de palmeiras e árvores com propriedades físicas do solo. Neste capitulo, mostramos que a área basal de árvores e palmeiras é limitada pelas condições físicas do solo e que a direção desta relação varia entre os grupos. Quanto maior a resistência dos solos a penetração de raízes, menor a área basal de árvores e maior a de palmeiras. Este mecanismo de partição da floresta por árvores e palmeiras está relacionado com a estrutura da floresta em escala local e com a fisionomia da floresta na escala da bacia. No segundo capitulo, exploramos os padrões regionais de variação da abundância das espécies de palmeiras em relação a gradientes ambientais e seus efeitos sobre os padrões de dominância e composição florística. Neste capítulo, evidenciamos que tanto diferenças sutis, quanto diferenças abruptas na composição florística podem ser causadas por variações na abundância das espécies em resposta a condições ambientais. Mostramos ainda que os padrões de dominância estão relacionados com os padrões de variação florística e sugerimos um possível mecanismo para explicar a ocorrência de dominância em florestas tropicais. No terceiro capítulo, testamos a hipótese de que a segregação de espécies em gradientes ambientais sutis poderia explicar a coexistência de espécies em escala local e regional. Neste capítulo, mostramos que espécies de palmeiras estão segregadas em eixos hidrológicos de saturação e seca do solo, que a afiliação das espécies a nichos hidrológicos é um caractere lábil ao longo da evolução das palmeiras e que a segregação de espécies nestes eixos de nich

Dispersal limitation induces long-term biomass collapse in overhunted Amazonian forests

Tropical forests are the global cornerstone of biological diversity, and store 55% of the forest carbon stock globally, yet sustained provisioning of these forest ecosystem services may be threatened by hunting-induced extinctions of plant-animal mutualisms that maintain long-term forest dynamics. Large-bodied Atelinae primates and tapirs in particular offer nonredundant seed-dispersal services for many large-seeded Neotropical tree species, which on average have higher wood density than smaller-seeded and wind-dispersed trees. We used field data and models to project the spatial impact of hunting on large primates by ∼1 million rural households throughout the Brazilian Amazon. We then used a unique baseline dataset on 2,345 1-ha tree plots arrayed across the Brazilian Amazon to model changes in aboveground forest biomass under different scenarios of hunting-induced large-bodied frugivore extirpation. We project that defaunation of the most harvest-sensitive species will lead to losses in aboveground biomass of between 2.5-5.8% on average, with some losses as high as 26.5-37.8%. These findings highlight an urgent need to manage the sustainability of game hunting in both protected and unprotected tropical forests, and place full biodiversity integrity, including populations of large frugivorous vertebrates, firmly in the agenda of reducing emissions from deforestation and forest degradation (REDD+) programs

Predicting environmental gradients with fern species composition in Brazilian Amazonia

Conclusions: Fern species composition can be used as an indicator of soil cation concentration, which can be expected to be relevant also for other components of rain forests. Presence-absence data are adequate for this purpose, which makes the collecting of additional data potentially very rapid. Comparison with earlier studies suggests that edaphic preferences of fern species have good transferability across geographical regions within lowland Amazonia. Therefore, species and environmental data sets already available in the Amazon region represent a good starting point for generating better environmental and floristic maps for conservation planning.</p

Revealing floristic variation and map uncertainties for different plant groups in western Amazonia

Questions: Understanding spatial variation in floristic composition is crucial to quantify the extent, patchiness and connectivity of distinct habitats and their spatial relationships. Broad-scale variation in floristic composition and the degree of uniqueness of different regions remains poorly mapped and understood in several areas across the globe. We here aim to map vegetation heterogeneity in Amazonia. Location Middle Jurua river region, Amazonas State, Brazil.Methods: We mapped four plant groups by applying machine learning to scale up locally observed community composition and using environmental and remotely sensed variables as predictors, which were obtained as GIS layers. To quantify how reliable our predictions were, we made an assessment of model transferability and spatial applicability. We also compared our floristic composition map to the official Brazilian national-level vegetation classification.Results: The overall performance of our floristic models was high for all four plant groups, especially ferns, and the predictions were found to be spatially congruent and highly transferable in space. For some areas, the models were assessed not to be applicable, as the field sampling did not cover the spectral or environmental characteristics of those regions. Our maps show extensive habitat heterogeneity across the region. When compared to the Brazilian vegetation classification, floristic composition was relatively homogeneous within dense forests, while floristic heterogeneity in rainforests classified as open was high. Conclusion: Our maps provide geoecological characterization of the regions and can be used to test biogeographical hypotheses, develop species distribution models and, ultimately, aid science-based conservation and land-use planning.</p

The role of topographic-derived hydrological variables in explaining plant species distributions in Amazonia

In Amazonian terra-firme non inundated forests, local floristic composition and species occurrence are explained by water availability as determined by topographic conditions. Topographic complexity can render these conditions quite variable across the landscape and the effects on plant ecological responses are difficult to document. We used a set of topographically defined hydrological metrics to evaluate community composition and single-species responses of four plant groups [pteridophytes (ferns and lycophytes), Melastomataceae, palms (Arecaceae) and Zingiberales] to topographic conditions in the middle Jurui River region, in western Brazilian Amazonia. The area spans two geological formations (Ica and Solimoes) with contrasting topography. River terraces are also found along the main rivers in the area. Local topographic conditions were approximated by height above the nearest drainage (HAND), slope, and Strahler's drainage order, all obtained from a SRTM digital elevation model (DEM). Data were analyzed using linear and generalized linear mixed models and regression trees. HAND was most successful in explaining floristic composition for all plant groups, except for Melastomataceae, and was more important in the hilly Ica formation than in the Solimoes. Individual occurrences of 57% species were predicted by at least one of the topographic variables, suggesting a marked habitat specialization along topographic gradients. For these species, response models using SRTM-DEM-derived variables gave similar results than models using field-measured topography only. Our results suggest that topographical variables estimated from remote sensing can be used to predict local variation in the structure of plant communities in tropical forests

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 thatmost 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

The role of environmental filtering, geographic distance and dispersal barriers in shaping the turnover of plant and animal species in Amazonia

To determine the effect of rivers, environmental conditions, and isolation by distance on the distribution of species in Amazonia. Location: Brazilian Amazonia. Time period: Current. Major taxa studied: Birds, fishes, bats, ants, termites, butterflies, ferns + lycophytes, gingers and palms. We compiled a unique dataset of biotic and abiotic information from 822 plots spread over the Brazilian Amazon. We evaluated the effects of environment, geographic distance and dispersal barriers (rivers) on assemblage composition of animal and plant taxa using multivariate techniques and distance- and raw-data-based regression approaches. Environmental variables (soil/water), geographic distance, and rivers were associated with the distribution of most taxa. The wide and relatively old Amazon River tended to determine differences in community composition for most biological groups. Despite this association, environment and geographic distance were generally more important than rivers in explaining the changes in species composition. The results from multi-taxa comparisons suggest that variation in community composition in Amazonia reflects both dispersal limitation (isolation by distance or by large rivers) and the adaptation of species to local environmental conditions. Larger and older river barriers influenced the distribution of species. However, in general this effect is weaker than the effects of environmental gradients or geographical distance at broad scales in Amazonia, but the relative importance of each of these processes varies among biological groups

The global abundance of tree palms

Aim Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location Tropical and subtropical moist forests. Time period Current. Major taxa studied Palms (Arecaceae). Methods We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work. Conclusions Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests