A relação entre a usina hidroelétrica de Balbina e a morte de árvores de Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) nas florestas alagáveis a jusante do Rio Uatumã, Amazônia Central

The monomodal flood pulse is the principal driving force in the Amazonian river floodplain systems, triggering productivity and interactions of the ecological processes of its species-rich biota. Trees respond to the long-term and predictable annual flooding by morpho-anatomical and physiological adaptations leading to cambial dormancy and the formation of annual tree rings in the wood. Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) occurs over a wide geographical range of the Amazonian floodplains especially at the lower topographies. This species reaches ages of up to 500 years and forms regular and annual tree rings. At the lower topographies of the black-water floodplains (igapó) of the Uatumã River in Central Amazonia, downstream of the hydroelectric power plant of Balbina, huge populations of dead trees from this and other species have been observed. In this study, dendrochronological methods and radiocarbon dating (14C) were applied to date the year of death of trees from Macrolobium and relate the mortality to changes in the hydrological regime. Comparing the hydrological data of the Uatumã River downstream the Balbina dam, before and after its implementation, we observed a significant increase of the mean water level and a pronounced decrease of the duration of the terrestrial phase for the lower topographies. A chronology spanning the period 1638-2012 from living trees of M. acaciifolium (n = 37) of the Uatumã River floodplains was established comprising the period from 1638 to 2012 which is significantly correlated with the duration of the terrestrial phase calculated by water level data from the Port of Manaus comprising the period 1903-2012 (r = 0.49, p<0.0001). We sampled entire cross sections of 17 dead trees of M. acaciifolium, which still had the presence of the bark in the Uatumã River floodplains with a mean diameter of 71.56 ± 29.83 cm. The ring width of the carefully prepared stem disks was measured and the individual tree-ring series were cross-dated with the exactly dated tree-ring chronology (reference curve). To validate the dating of the trees we isolated the outermost ring to perform radiocarbon dating. The dendrocronological and 14C dating matched in 87.5% of the cases, and in 12.5%, the deviation in the dating was about only one year. All trees died in periods of inundations during consecutive years, up to two decades after the implementation of the hydroelectric dam. Possibly those impacts may be similar among other hydroelectric projects in the Amazonian floodplains. The application of dendrochronology used in this study is unique for tropical forests and may be a useful tool to study the impact of natural and anthropogenic disturbances in tropical forests affecting its structure, dynamic and functioning.Na Amazônia, ao longo de seus grandes rios e tributários, o pulso de inundação monomodal é o principal fator responsável pela produtividade e condução dos processos ecológicos. As árvores respondem a condições desfavoráveis de crescimento durante a fase de inundação através da dormência cambial, resultando na formação de anéis de crescimento. A espécie arbórea Macrolobium acaciifolium é adaptada a prolongados períodos de inundação, possui ampla ocorrência nas áreas alagáveis da Amazônia e é comprovadamente apta para estudos dendrocronológicos. Observa-se uma grande quantidade de indivíduos mortos de M. acaciifolium e de diversas outras espécies nas cotas topográficas baixas a jusante da barragem da Usina Hidrelétrica (UHE) de Balbina, localizada no Rio Uatumã na Amazônia Central. O presente estudo buscou relacionar mudanças no regime de inundação desencadeadas pela UHE com o ano da morte dos indivíduos de M. acaciifolium, o que foi feito através de estudos dendrocronológicos, datação por radiocarbono (14C) e dados hidrológicos (séries históricas de inundação). Após a implementação da UHE, foi verificado a diminuição do pulso de inundação, o aumento do nível médio do rio, o aumento nas variações diárias do nível do rio e a supressão da fase terrestre por anos seguidos. Para a datação do ano da morte foi realizada a interdatação entre cada indivíduo morto (n = 17) e uma cronologia (referência) com indivíduos vivos (n = 37), que estendeu-se de 1638 a 2012 e mostrou-se significativamente datada ao ser comparada com séries temporais de medições instrumentalizadas do Porto de Manaus (r = 0,49; p<0,0001). Ao longo de 100 km a jusante da barragem, foram coletados 17 indivíduos mortos, apresentando em média de 123,35 ± 57,64 anéis, diâmetro à altura do peito (DAP) médio de 71,56 ± 29,83 cm (mínimo: 35,1 - máximo: 127,7) e taxa de incremento radial (TIR) médio de 1,9 ± 1,1 cm. As datações através da dendrocronologia coincidiram com 87,5% dos resultados obtidos por 14C, e quando não houve coincidência o desvio foi de apenas 1 ano. As mortes ocorreram até duas décadas após a implementação da UHE e ocorreram no período em que houve anos consecutivos de supressão da fase terrestre. Esses impactos ao longo do tempo devem ter grandes implicações em toda a floresta de igapó, e possivelmente são semelhantes em outras hidrelétricas em áreas alagáveis tropicais. A aplicação da dendrocronologia utilizada no estudo é inédita nas florestas tropicais, podendo se estender para outros distúrbios ambientais que afetam o desenvolvimento de espécies arbóreas

The shadow of the Balbina dam: A synthesis of over 35 years of downstream impacts on floodplain forests in Central Amazonia

1. The Balbina hydropower dam in the Central Amazon basin, established in the Uatumã River in the 1980s, is emblematic for its socio‐environmental disaster. Its environmental impacts go far beyond the reservoir and dam, however, affecting the floodplain forests (igapó) in the downstream area (dam shadow), which have been assessed using a transdisciplinary research approach, synthesized in this review. 2. Floodplain tree species are adapted to a regular and predictable flood pulse, with high‐ and low‐water periods occurring during the year. This was severely affected by the operation of the Balbina dam, which caused the suppression of both the aquatic phase at higher floodplain elevations and the terrestrial phase at lower floodplain elevations (termed the ‘sandwich effect’). 3. During the period of construction and reservoir fill, large‐scale mortality already occurred in the floodplains of the dam shadow as a result of reduced stream flow, in synergy with severe drought conditions induced by El Niño events, causing hydraulic failure and making floodplains vulnerable to wildfires. 4. During the operational period of the dam, permanent flooding conditions at low topographical elevations resulted in massive tree mortality. So far, 12% of the igapó forests have died along a downstream river stretch of more than 125 km. As a result of flood suppression at the highest elevations, an encroachment of secondary tree species from upland (terra firme) forests occurred. 5. More than 35 years after the implementation of the Balbina dam, the downstream impacts caused massive losses of macrohabitats, ecosystem services, and diversity of flood‐adapted tree species, probably cascading down to the entire food web, which must be considered in conservation management. 6. These findings are discussed critically, emphasizing the urgent need for the Brazilian environmental regulatory agencies to incorporate downstream impacts in the environmental assessments of several dam projects planned for the Amazon region.Additional co-authors: Flávia Machado Durgante, Aline Lopes, Susan E. Trumbore, Hans ter Steege, Adalberto Luis Val, Wolfgang J. Junk, Maria Teresa Fernandez Piedad

Contrasting controls on tree ring isotope variation for Amazon floodplain and terra firme trees

Isotopes in tropical trees rings can improve our understanding of tree responses to climate. We assessed how climate and growing conditions affect tree-ring oxygen and carbon isotopes (δ18OTR and δ13CTR) in four Amazon trees. We analysed within-ring isotope variation for two terra firme (non-flooded) and two floodplain trees growing at sites with varying seasonality. We find distinct intra-annual patterns of δ18OTR and δ13CTR driven mostly by seasonal variation in weather and source water δ18O. Seasonal variation in isotopes was lowest for the tree growing under the wettest conditions. Tree ring cellulose isotope models based on existing theory reproduced well observed within-ring variation with possible contributions of both stomatal and mesophyll conductance to variation in δ13CTR. Climate analysis reveal that terra firme δ18OTR signals were related to basin-wide precipitation, indicating a source water δ18O influence, while floodplain trees recorded leaf enrichment effects related to local climate. Thus, intrinsically different processes (source water vs leaf enrichment) affect δ18OTR in the two different species analysed. These differences are likely a result of both species-specific traits and of the contrasting growing conditions in the floodplains and terra firme environments. Simultaneous analysis of δ13CTR and δ18OTR supports this interpretation as it shows strongly similar intra-annual patterns for both isotopes in the floodplain trees arising from a common control by leaf stomatal conductance, while terra firme trees showed less covariation between the two isotopes. Our results are interesting from a plant physiological perspective and have implications for climate reconstructions as trees record intrinsically different processes

Data-driven competitive facilitative tree interactions and their implications on nature-based solutions

Spatio-temporal data are more ubiquitous and richer than even before and the availability of such data poses great challenges in data analytics. Ecological facilitation, the positive effect of density of individuals on the individual's survival across a stress gradient, is a complex phenomenon. A large number of tree individuals coupled with soil moisture, temperature, and water stress data across a long temporal period were followed. Data-driven analysis in the absence of hypothesis was performed. Information theoretic analysis of multiple statistical models was employed in order to quantify the best data-driven index of vegetation density and spatial scale of interactions. Sequentially, tree survival was quantified as a function of the size of the individual, vegetation density, and time at the optimal spatial interaction scale. Land surface temperature and soil moisture were also statistically explained by tree size, density, and time. Results indicated that in space both facilitation and competition co-exist in the same ecosystem and the sign and magnitude of this depend on the spatial scale. Overall, within the optimal data-driven spatial scale, tree survival was best explained by the interaction between density and year, sifting overall from facilitation to competition through time. However, small sized trees were always facilitated by increased densities, while large sized trees had either negative or no density effects. Tree size was more important predictor than density in survival and this has implications for nature-based solutions: maintaining large tree individuals or planting species that can become large-sized can safeguard against tree-less areas by promoting survival at long time periods through harsh environmental conditions. Large trees had also a significant effect in moderating land surface temperature and this effect was higher than the one of vegetation density on temperature

The nexus between democracy and environment: the crisis of democracy in Brazil and the Amazon degradation

Com a relativa consolidação de um arcabouço teórico em torno da democracia, diversos estudos foram elaborados com o intuito de compreender a conexão da democracia com a dimensão ambiental. A formalização da democracia do Brasil ocorre com a promulgação da Constituição Federal de 1988, acontecimento que resulta na implementação de um arranjo institucional democrático híbrido, em que as formas de participação social indireta coexistem com modalidades de participação social direta. A Amazônia se encontra no cerne dos debates políticos e socioambientais do país, assim, cada momento político tem implicado em diferentes dinâmicas. É possível assumir que desde o início do processo de democratização até os primeiros anos da década de 2010, ocorre um processo contínuo e incremental de avanços institucionais e conceituais nas políticas ambientais. De forma sintomática, entre os anos de 2004 e 2015 foi consolidada a tendência histórica de queda nas taxas de desmatamento na Amazônia. Este horizonte foi interrompido no ano de 2016 quando a democracia entra em uma condição de impasse. Em 2019, com o início da gestão de Jair Bolsonaro, os retrocessos democráticos passaram a ocorrer por diversas frentes, evidenciando um processo de crise democrática. Esta pesquisa tem como objetivo principal: revelar evidências do nexo entre a democracia e o meio ambiente no contexto da Amazônia brasileira. Adotamos a perspectiva interdisciplinar como eixo organizador, interconectando análises conceituais e dados empíricos. A pesquisa se desenvolveu em três momentos. Primeiro, foram realizados debates teóricos sobre o conceito hegemônico de democracia, a democracia na América Latina e a democracia no Brasil, acessando componentes conceituais que conectam a dimensão democrática com a ambiental. Segundo, com a associação de debates teóricos e dados quantitativos da qualidade democrática, foi elaborado um modelo para acessar as conjunturas democráticas do Brasil entre os anos de 1988 e 2022. Terceiro, para cada conjuntura democrática, comparamos e analisamos estatisticamente a correlação entre a qualidade da democracia e as taxas anuais de desmatamento na Amazônia. Identificamos três principais conjunturas, com a crise da democracia se evidenciando no decorrer de duas fases (2016-2018 e 2019-2022). Nossas análises indicam que na crise da democracia, os desmatamentos na Amazônia avançaram a cada retrocesso democrático. Os resultados corroboram com a perspectiva de que o desmatamento da Amazônia é uma proeminente característica da crise da democracia no Brasil. Poucos estudos investigaram a importância da democracia na Amazônia e não existem estudos que traçaram o nexo quantitativo da democracia e o meio ambiente na conjuntura de crise da democracia. As discussões desenvolvidas nesta pesquisa indicam a condição democrática como um novo fator explicativo a ser considerado no desmatamento da Amazônia.With the relative consolidation of a theoretical framework around the meaning of democracy, several studies were elaborated with the intention of understanding the connection of democracy and the environmental dimension, resulting in a multidimensional research field, which has presented different points of view according to the analytical framework adopted. The formalization of democracy in Brazil occurs with the promulgation of the Federal Constitution of 1988, an event that triggered the implementation of a hybrid democratic institutional arrangement, in which the forms of indirect social participation, focused on the choice of political representatives, coexist with modalities of direct social participation. The Amazon is at the core of the political and socio-environmental debates of the country; thus, each political moment of the country has implied in different socio-environmental dynamics for the region, with notable differences in the positioning of the State during the authoritarian and democratic period. It is possible to assume that from the beginning of the democratization process until the first years of the 2010s, institutional and conceptual advances occurred in environmental policy, generating favorable actions for environmental governance in the Amazon. Symptomatically, between 2004 and 2015, the historical threshold of falling deforestation rates in the Amazon was consolidated. This horizon was interrupted in 2016 when democracy enters a period of rupture. In 2019, with the beginning of Jair Bolsonaro\'s presidential mandate, democratic setbacks began to occur on several fronts, evidencing a process of democratic crisis. This research aims to reveal evidence of the nexus between democracy and the environment in the context of the Brazilian Amazon. We adopt the interdisciplinary perspective as an organizing axis, interconnecting conceptual analyses and empirical data. The research was conducted in three moments. First, we analyzed theoretical debates about the hegemonic models of democracy, democracy in Latin America, and democracy in Brazil, accessing conceptual components that connect the democratic and environmental dimensions. Second, with the association of theoretical debates and quantitative data on the quality of democracy, we developed a model to access the democratic conjunctures of Brazil between the years 1988 and 2022. Third, for each democratic conjuncture, we statistically analyzed the correlation between the quality of democracy and annual deforestation rates in the Brazilian Amazon. We identified three main conjunctures, with the crisis of democracy being evident during two phases (2016-2018 and 2019-2022). Our results indicate that in the crisis of democracy, deforestation in the Amazon advances with each democratic setback. The results corroborate the perspective that the degradation of the Amazon is one of the most prominent features of the crisis of democracy in Brazil. Few studies have teased apart the importance of democracy in the Amazon, and no such study investigated the quantitative nexus of democracy and environment in a conjuncture of democracy crisis. The discussions developed in this research suggest the democratic condition as a new explanatory factor in the Brazilian Amazon deforestation

Tree mortality of a flood-adapted species in response of hydrographic changes caused by an Amazonian river dam

The annual and regular flood pulse is the main hydrologic feature found in the large floodplains along Amazonian rivers triggering nutrient cycles, growth rhythms and life cycles of the biota as well as primary and secondary productivity. The construction of hydroelectric dams in the Amazon basin substantially alters the hydrologic regime resulting in severe social, ecological and environmental impacts. While the majority of studies evaluate these impacts in the area of the reservoir and the surroundings of the dam, we focus on disturbances in floodplain forests downstream of the hydroelectric power plant, in this case the Balbina dam, constructed in the 1980s damming the Uatumã River (Central Amazonia). The lowest topographies in the floodplain forests downstream of the dam are dominated by dead trees of Macrolobium acaciifolium (Benth.) Benth. (Fabaceae), a flood-tolerant species forming annual tree rings in consequence of the flood pulse. In this study we evidence alterations in the magnitude and frequency of the hydrologic conditions of the Uatumã River downstream of the hydroelectric power plant comparing the pre-dam (1973–1982) and post-dam (1991–2012) period analyzing a set of biologically relevant hydrologic indicators. To investigate the relationship between the hydrologic changes caused by the dam and the year of death of individuals of M. acaciifolium we use cross-dating techniques (dendrochronology) and radiocarbon dating (14C) as two independent methods. Cross sections of 17 dead individuals were analyzed and individual tree-ring series cross-dated with a well-replicated living trees’ chronology of the same species and region (1804–2012). The outermost tree ring was isolated to perform radiocarbon dating. The dendrochronological and 14C proxies matched in 88% of the cases, while in the 12% mismatched maximum deviation at least one year. Trees died during periods of consecutive years of inundation, up to two decades after the implementation of the hydroelectric dam. Considering the planning of construction of several dozen dams in the Amazon region there is a critical need to include the downstream impacts in all discussions of hydroelectric implementation. © 201