Interações entre floresta, chuva e solo em áreas com lençol freático superficial na Amazônia Central

A central issue in ecology is the relationship between environmental gradients, species composition and forest structure. However, there is large environmental variability in Amazonia and these relationships have been little studied, especially in areas where the water table is shallow. I investigated the role of rainfall, water-table depth and soil physical properties on the variation in floristic composition, forest structure and biomass stocks in Central Amazonia. I evaluated if a new proxy for water table depth derived from remote sensing can be used as a predictor of floristic composition in different life forms (chapter 1), how forest structure components (stem density and the average individual mass) and biomass stocks are affected by rainfall gradients and soil properties (chapter 2), and if environmental gradients linked to soil water supply are limiting factors to canopy height (chapter 3). The first study was conducted in Reserva Ducke, north of Manaus, where the relief is dissected and the areas close to the streams have shallow water tables and sandy soils. The studies presented in chapters 2 and 3 were conducted in the Purus-Madeira interfluve, where the relief is relatively flat, the soil is predominately silty, and the water table is shallow even far from streams. Plant-species composition was strongly related to the proxy for water-table depth in the terra-firme forest north of Manaus, suggesting that water-table access differentially affects species establishment. Forests over shallow water tables had larger variation in species composition. This pattern may be associated with more dynamic forests in areas where the aerated soil volume for root development is limited by the shallow water table, anchorage is low due to sandy soils and individuals are more susceptible to death by uprooting. The areas where with most variation in species composition extend to hundreds of meters from the streams. Brazilian environmental law does not fully protect these areas of shallow water table because it considers only short horizontal distances from streams (30 m for small streams). Water table fluctuations are correlated with soil physical properties, such as the effective depth to which roots develop, and anoxic conditions. Shallower and more impeditive soils sustained forests with lower mean individual mass and higher stem density, supporting the hypothesis of a more dynamic forest over more restrictive soils. Shallow silty soils and superficial water table were also associated with lower canopy heights, suggesting that water excess and reduced space for root development limit forest growth. The positive effect of longer dry seasons on mean individual mass also indicates limitations to biomass accumulation related to water excess in areas of shallow water table. The results of the three studies suggest that forests over shallow water table and impeditive soils to root development are more rachitic in structure, and probably are more dynamic, with larger variation in species composition. Growth limitation by water excess seems to be an underappreciated mechanism affecting the structure and functioning of forests over shallow water table in central Amazonia, implying that current expectations of forest responses to droughts should be reconsidered.A relação entre distribuição de espécies, estrutura da floresta e gradientes ambientais é um tema central em ecologia. No entanto, as relações de funcionamento da floresta considerando a grande variabilidade ambiental na Amazônia ainda são pouco conhecidas, especialmente em áreas onde o lençol freático é superficial. Nesta tese, investiguei o papel de gradientes de chuva, profundidade do lençol freático e características físicas do solo nas variações da composição florística, estrutura da floresta e estoques de biomassa na Amazônia Central. Avaliei se um novo indicador de profundidade de lençol freático obtido de sensoriamento remoto pode ser usado como preditor de variações na composição florística de diferentes formas de vida (capítulo 1), como componentes estruturais da floresta (densidade de indivíduos e massa média individual) e estoques de biomassa são influenciados por gradientes de precipitação e características do solo (capítulo 2), e se gradientes ambientais ligados ao suprimento de água no solo são fatores limitantes para a altura do dossel (capítulo 3). O primeiro estudo foi realizado na Reserva Ducke ao norte de Manaus, onde o relevo é dissecado e as áreas próximas dos cursos d’água tem lençol freático raso e são arenosas. Os estudos relatados nos capítulos 2 e 3 foram desenvolvidos ao longo do interflúvio Purus-Madeira, onde o relevo é relativamente plano, o lençol freático é raso, mesmo distante dos cursos d’água, e o solo é predominantemente siltoso. A composição de espécies de plantas teve uma forte relação com o índice de profundidade do lençol freático na floresta de terra-firme ao norte de Manaus, sugerindo que o acesso ao lençol freático tem um papel importante para o estabelecimento de espécies. As florestas em áreas com lençol freático raso apresentaram maior variação na composição de espécies. Esse padrão pode estar associado ao maior dinamismo da vegetação nessas áreas, onde o volume de solo aerado para o desenvolvimento de raízes é limitado, a ancoragem é baixa devido ao solo arenoso e os indivíduos estão mais suscetíveis a morte por desenraizamento. As áreas onde há maior variação na composição de espécies podem se estender por centenas de metros de distância do curso d’água e não são protegidas pelos critérios atuais da legislação ambiental brasileira, que leva em conta distâncias horizontais da drenagem (30 m para o caso do porte dos cursos d’água estudados). Os níveis de flutuação do lençol freático estão correlacionados com as características físicas do solo, como profundidade efetiva para o desenvolvimento de raízes, e condições anóxicas. Solos mais rasos e impeditivos sustentam florestas com indivíduos de menor massa e em maior adensamento, o que suporta a hipótese de que solos mais restritivos estão associados a florestas mais dinâmicas. Solos rasos, siltosos e com lençol freático superficial também estiveram associados a florestas com dossel mais baixo, sugerindo que o excesso de água e o espaço reduzido para o desenvolvimento de raízes são limitantes para o crescimento da floresta. O efeito positivo de estações secas mais prolongadas sobre a massa média dos indivíduos também indica limitações ao acúmulo de biomassa relacionadas ao excesso de água em áreas de lençol freático superficial. Os resultados dos três estudos sugerem que florestas sobre lençol freático raso e solos com características físicas impeditivas têm estrutura mais raquítica e provavelmente são mais dinâmicas e com maior variação na composição de espécies. A limitação de crescimento por excesso de água no solo parece ser um mecanismo subestimado para entender a estrutura e funcionamento das florestas sobre lençol freático superficial na Amazônia Central, e isso implica que as expectativas atuais de repostas da floresta à mudanças climáticas devem ser revistas

Influência da disponibilidade de luz na dinâmica do mercúrio em pequenos tributários do sistema fluvial do rio Jaú, Amazônia Central

Amazortian soils have accumulated naturally relatively high concentrations of mercury (Hg), which is slowly exported to tlie fluvial system and may bioaccumulate in aquatic food chains. The solar radiation can reduce Hg+2 to Hg^, a highly volatile form of the element, and its formation favors the removal of Hg from the aquatic system. This mechanism is called photoreduction and can diminish Hg concentrations on the aquatic system. This work investigated the influence of light availability on the leveis of dissolved gaseous mercury(DGM) and total Hg in water and scdimcnts of 30 small black water tributaries of the Jaú River, central Amazônia. Light intcnsity was asscsscd by using the proportion of canopy opening(% CO) above the sampled tributary, in addition to the light intensity relativo to the hour of sampling. The effects of dissolved organic carbon (DOC)leveis and water pH were also evaluated. Multiple regressions were used for data analysis. Results showed that tributaries with a higher% CO had lower total Hg concentrations in water and sediments, suggesting the occurrence of photoreduction. There may exist a bottleneck effect on total Hg leveis in water that occurs when CO above tributaries ícaches 20 %.The light availability may bc cnough to reduce Hg to its volatile form. A relationship between%CO and DGM leveis was not observed because (i) highcst Hg"production in water only occurs at ccrtain pcriods ofthe day,when hght is less intenso,(ii) outflow in this system is quick and thus, avoids OGM accumulation on superficial waters, and (iii) there may be is a limitation of substrate available to photoreductif)n, as indicated by positively correlations between DGM with the possiblc water and sedimcnt substratcs. DOC and pH corrclatcd positively with Hg leveis in water. Results indicated that the common black water high DOC and low pH values may increase the residence time ofHg in the water column in detriment ofthe photoreduction and HgO outflow.Os solos amazônicos apresentam acúmulo natural e concentrações relativamente elevadas de mercúrio(Hg),o qual é lentamente exportado para o sistema fluvial e pode se acumular na cadeia trófica,causando danos à saúde dos organismos. A radiação solar pode reduzir o Hg"'"^ para Hg^,forma altamente volátil e passível de ser liberada para atmosfera. Este processo é chamado de foto-redução e pode diminuir as concentrações de Hg no sistema aquático. O presente trabalho investigou a influência da disponibilidade de luz, através da% de abertura de dossel(% AD)acima do tributário, e da intensidade luminosa relativa à hora da coleta (ILr) sobre os níveis de mercúrio dissolvido gasoso(MDG)e Hg total na água e sedimentos de 30 pequenos tributários de águas pretas da bacia do rio Jaú, na Amazônia central. Também foram avaliados os efeitos dos níveis de carbono orgânico dissolvido (COD) e pH da água. Regressões múltiplas foram empregadas para análise dos dados,e os resultados mostraram que em tributários com maior% AD as concentrações de Hg total na água e sedimentos são menores, sugerindo a ocorrência de foto-redução no sistema fluvial. Para os níveis de Hg total da água parece existir um efeito de gargalo que ocorre quando as águas passam por tributários com AD de 20 %,nos quais a disponibilidade de luz provavelmente é suficiente para reduzir o mercúrio à sua forma volátil. Não foi observado um efeito da %AD sobre os níveis de MDG provavelmente porque(i)as maiores produçõesde Hg® na água acontecem apenas em alguns períodos do dia, quando a luminosidade é menos intensa,(ü) a evasão neste sistema é rápida e impede o acúmulo de MDG nas águas superficiais e também,(iü) há uma provável limitação de substrato disponível para fotoredução,indicada pelas correlações positivas do MDG com os possíveis substratos da água e sedimentos. O COD e pH tiveram influência principalmente sobre os níveis de Hg da água. A interação,comum nas águas pretas, entre altos teores de COD e baixos valores de pH parece favorecer a permanência do Hg na coluna d'água em detrimento da foto-redução e evasão dó Hg® do sistema aquático

Trait divergence and habitat specialization in tropical floodplain forests trees

Habitat heterogeneity of tropical forests is thought to lead to specialization in plants and contribute to the high diversity of tree species in Amazonia. One prediction of habitat specialization is that species specialized for resource-rich habitats will have traits associated with high resource acquisition and fast growth while species specialized for resource-poor habitats will have traits associated with high resource conservation and persistence but slow growth. We tested this idea for seven genera and for twelve families from nutrient-rich white-water floodplain forest (várzea) and nutrient-poor black-water (igapó) floodplain forest. We measured 11 traits that are important for the carbon and nutrient balance of the trees, and compared trait variation between habitat types (white- and black-water forests), and the effect of habitat and genus/family on trait divergence. Functional traits of congeneric species differed between habitat types, where white-water forest species invested in resource acquisition and productive tissues, whereas black-water forest species invested in resource conservation and persistent tissues. Habitat specialization is leading to the differentiation of floodplain tree species of white-water and black-water forests, thus contributing to a high diversity of plant species in floodplain forests

Higher rates of liana regeneration after canopy fall drives species abundance patterns in central Amazonia

In tropical rainforest, most vascular plants have some capacity to resprout, and lianas are often effective resprouters after canopy fall. However, the diversity of resprouting responses of liana species and the consequence for plant persistence are poorly understood. We hypothesized that variation in regeneration among liana species causes differences in liana species abundance in tropical rainforest through differential resprouting capacity, such that liana species with higher densities produce more resprouts after canopy falls.We applied a manipulative field experiment investigating the effect of different levels of disturbance on the production of resprouts and adventitious roots in 10 liana species of the tribe Bignonieae (Bignoniaceae) with contrasting abundances in central Amazonia. We selected 15 individuals of each species and assigned the lianas to three distinct conditions: (a) total canopy fall with lianas severely damaged and detached from trees; (b) partial fall of lianas, without visible damage; and (c) intact lianas (control). We tested whether liana species regeneration patterns were related to species density. Liana species density was calculated using previous research on liana species distribution in 30 1‐ha plots systematically distributed in a 6 × 6 km2 grid at the Ducke Reserve.The number of aerial resprouts produced by lianas under the total canopy fall treatment was twice that of plants under lower levels of disturbance, while the production of adventitious roots did not differ among treatments. Liana species showed different intensities of resprouting, and species with higher average densities on the forest landscape had more resprouts after the total canopy fall treatment.Synthesis. Our results shed new light on the factors that influence liana species abundance, highlighting the role of resprouting after canopy fall and its variation among liana species. Resprouting mitigates the negative effects of canopy damage, suggesting that the impact of increased tree fall disturbances over time, which has been attributed to Amazonian forests in the literature, may increase already abundant liana species with effective resprouting capacity. We identify liana species that are more resilient to disturbance and may alter forest dynamics during climatic change.Our results shed new light on the factors that influence liana species abundance, highlighting the role of resprouting after canopy fall and its variation among liana species. Resprouting mitigates the negative effects of canopy damage, suggesting that the impact of increased tree fall disturbances over time, which has been attributed to Amazonian forests in the literature, may increase already abundant liana species with effective resprouting capacity. We identify liana species that are more resilient to disturbance and may alter forest dynamics during climatic change.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155931/1/jec13345_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155931/2/jec13345.pd

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

The importance of hydraulic architecture to the distribution patterns of trees in a central Amazonian forest

Species distributions and assemblage composition may be the result of trait selection through environmental filters. Here, we ask whether filtering of species at the local scale could be attributed to their hydraulic architectural traits, revealing the basis of hydrological microhabitat partitioning in a Central Amazonian forest. We analyzed the hydraulic characteristics at tissue (anatomical traits, wood specific gravity (WSG)), organ (leaf area, specific leaf area (SLA), leaf area : sapwood area ratio) and whole-plant (height) levels for 28 pairs of congeneric species from 14 genera restricted to either valleys or plateaus of a terra-firme forest in Central Amazonia. On plateaus, species had higher WSG, but lower mean vessel area, mean vessel hydraulic diameter, sapwood area and SLA than in valleys; traits commonly associated with hydraulic safety. Mean vessel hydraulic diameter and mean vessel area increased with height for both habitats, but leaf area and leaf area : sapwood area ratio investments with tree height declined in valley vs plateau species. [Correction added after online publication 29 March 2017: the preceding sentence has been reworded.] Two strategies for either efficiency or safety were detected, based on vessel size or allocation to sapwood. In conclusion, contrasting hydrological conditions act as environmental filters, generating differences in species composition at the local scale. This has important implications for the prediction of species distributions under future climate change scenarios. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trus

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

Correction: Pervasive gaps in Amazonian ecological research

In the original version of the article, the authors incorrectly stated the value of current and projected deforestation in the results: the values should be 23.50% and 27.29%, respectively. This error does not impact the results or conclusions presented in the paper. The error has now been corrected online. The authors apologize for the error and any confusion that may have resulted