Dendroecologia de Macrolobium acaciifolium (Fabaceae) em florestas alagáveis da Amazônia central

The forest dynamics in the Amazonian floodplains is strongly triggered by the flood pulse. Trees respond to unfavorable growth conditions during the flood period by cambial dormancy, which results in the formation of annual growth rings. We determined tree age and compared the mean annual rates of increase in the diameter of Macrolobium acaciifolium with hydrological and climatic factors in three regions of central Amazonian floodplain forest. A wood sample was obtained from each tree using an increment borer. Ring growth was assessed by marginal parenchyma bands to determine tree age and the mean diameter increment. Ring widths were indexed to construct cross-dating chronologies and correlated with climatic and hydrological variables. The analyses demonstrate that the mean annual diameter increment did not differ between the three study sites. The chronologies correlated significantly with the terrestrial phase. There was no significant difference in the ring-width index between El Niño years and other years, and between La Niña and other years. These results show that the hydrological variables can be considered crucial to the rates of tree growth and diameter increment in floodplains, and El Niño signals were not detected in the tree-ring chronologies.A dinâmica das florestas alagáveis da Amazônia é fortemente influenciada pelo pulso anual de inundação. As árvores respondem às condições de crescimento desfavoráveis durante o período de inundação através da dormência cambial, resultando na formação de anéis de crescimento anuais. Neste estudo, determinamos a idade das árvores e comparamos as taxas anuais médias de incremento em diâmetro de Macrolobium acaciifolium com fatores hidrológicos e climáticos em três regiões de florestas alagáveis na Amazônia central. Para cada árvore, uma amostra de madeira foi obtida usando uma broca dendrocronológica. O crescimento do anel foi avaliado por bandas de parênquima marginal, para determinar a idade da árvore e o incremento médio em diâmetro. As séries de anéis foram indexadas, para construir cronologias, e correlacionadas com variáveis climáticas e hidrológicas. Nossas análises demonstraram que o incremento anual médio em diâmetro não diferiu entre os três locais de estudo. As cronologias correlacionaram-se significativamente com a fase terrestre. Não houve diferença significativa no índice de largura dos anéis entre os anos de El Niño e outros anos, e entre os anos de La Niña e outros anos. Estes resultados mostraram que as variáveis hidrológicas podem ser consideradas cruciais para as taxas de crescimento e de incremento em diâmetro das árvores em florestas alagáveis, e que não foram detectados sinais de El Niño nas cronologias das árvores analisadas

Crecimiento y rasgos funcionales de especies arbóreas en un bosque nublado tropical al sudeste de venezuela

The relationship between growth rates and functional traits of 14 tree species was analyzed using growth modeling of diameter and height (based on growth ring analysis) and functional traits (wood density, maximum size and age, crown illumination, seed weight and natural regeneration). Through cluster analysis and ecological interpretation, six functional groups of species were discriminated: intermediate heliophyte, small and long-lived heliophyte, large and long-lived heliophyte, intermediate partial-shade-tolerant, long-lived and partial-shade tolerant and small shade-tolerant. Among species, growth rates varied with age, identifying three growth patterns: fast, intermediate and slow. There is an evident relationship between growth patterns and functional groups. The absence of pioneer species, the scarcity of shade-tolerant, and the predominance of intermediate functional strategies in most species, suggest a trend of habitat behavior more generalist than specialized. © 2017, Universidad Central de Venezuela. All rights reserved

Incremento diamétrico mensual de especies arbóreas relacionado con variables ambientales y fenología en un bosque nublado al sudeste de Venezuela

Diameter, crown area and crown illumination of 33 trees corresponding to 11 species were recorded in a cloud forest. Tree diameter was measured monthly with dendrometers during 26 months, and phenology was documented for 12 months. Soil moisture, air temperature and soil temperature were measured using thermohygrometers. Variation of Monthly Increase of Diameter (IDM) of all species was mainly controlled by the air temperature. Growth of each species responds in two ways: 1) seven species were correlated with water variables, and 2) four species correlated with thermal variables. The seasonal distribution of growth of some species was determined by the phenology. Three groups of species were identified: 1) species with higher IDM and wide and illuminated crowns, 2) species with lower IDM and small and less illuminated crowns, and 3) intermediate condition species. © 2016, Universidad Central de Venezuela. All rights reserved

New records and range extension of a Brazilian Amazon white-sand endemic species: Roraimaea aurantiaca Struwe, S.Nilsson & V.A.Albert (Gentianaceae)

Roraimaea aurantiaca Struwe, S.Nilsson & V.A.Albert, a white-sand endemic species, was previously known from only two specimens collected in Roraima state, Brazil. Our new field collections and re-identified herbarium specimens expand this species’ distribution and include the first records from the Brazilian state of Amazonas. Based on this effort, we present a distribution map, preliminary conservation status of Endangered, the first photographs of living plants, and an updated morphological description. This study aggregates new information on the flora of the northern Amazon Basin, in addition to discussing conservation of R. aurantiaca

HERBÁCEAS AQUÁTICAS EM SEIS IGAPÓS NA AMAZÔNIA CENTRAL: COMPOSIÇÃO E DIVERSIDADE DE GÊNEROS

As herbáceas aquáticas são componentes estruturais dos corpos de água amazônicos e de suas áreas alagáveis. Elas propiciam abrigo e alimento para organismos da biota aquática, enriquecem nutricionalmente os ambientes e sua ocorrência e abundância estão relacionadas às propriedades físicas e químicas dos diferentes corpos de água da região, que refletem a geologia de suas áreas de captação. Neste estudo foi estabelecida e analisada a riqueza de gêneros de herbáceas aquáticas e sua distribuição em seis igapós de água preta na Amazônia Central; esses resultados foram comparados àqueles disponíveis na literatura para áreas de várzea também da Amazônia Central. Os resultados foram obtidos por meio de inventários realizados entre os anos de 2007 e 2013 nos rios Negro, Jaú, Jufari, Acará, Água Boa do Univiní e Cuiuni. Foram amostradas 106 parcelas retangulares de 100 x1 m distribuídas nos seis pontos amostrais (10 a 29 parcelas por ponto). O levantamento florístico revelou 63 gêneros distribuídos em 25 famílias botânicas, predominando as famílias Cyperaceae, Poaceae e Araceae. A composição de famílias teve apenas 17% de semelhança com o inventário disponível para a várzea próxima a Manaus. As áreas também apresentaram alta dissimilaridade compartilhando apenas três gêneros, Scleria, Montrichardia e Paspalum. As áreas de igapó estudadas, da mesma forma que aquelas de várzea registradas na literatura são reguladas pelo pulso de inundação, entretanto, as águas ácidas e pobres em nutrientes típicas das áreas de igapó inventariadas podem explicar a baixa diversidade do igapó, bem como a baixa similaridade de espécies entre os dois ecossistemas. A presença de uma composição de herbáceas aquáticas diferenciada daquela de outros ecossistemas alagáveis amazônicos pode resultar de uma alta especialização a ambientes extremos

Fires in Amazonian Blackwater Floodplain Forests: Causes, Human Dimension, and Implications for Conservation

The Amazon basin is being increasingly affected by anthropogenic fires, however, most studies focus on the impact of fires on terrestrial upland forests and do not consider the vast, annually inundated floodplains along the large rivers. Among these, the nutrient-poor, blackwater floodplain forests (igapós) have been shown to be particularly susceptible to fires. In this study we analyzed a 35-year time series (1982/1983–2016/2017) of Landsat Thematic Mapper from the Jaú National Park (Central Amazonia) and its surroundings. Our overall objective was to identify and delineate fire scars in the igapó floodplains and relate the resulting time series of annual burned area to the presence of human populations and interannual variability of regional hydroclimatic factors. We estimated hydroclimatic parameters for the study region using ground-based instrumental data (maximum monthly temperature–T$_{max}$, precipitation–P, maximum cumulative water deficit–MCWD, baseflow index–BFI, minimum water level–WL$_{min90}$ of the major rivers) and large-scale climate anomalies (Oceanic Niño Index–ONI), considering the potential dry season of the non-flooded period of the igapó floodplains from September to February. Using a wetland mask, we identified 518,135 ha of igapó floodplains in the study region, out of which 17,524 ha (3.4%) burned within the study period, distributed across 254 fire scars. About 79% of the fires occurred close to human settlements (<10 km distance), suggesting that human activities are the main source of ignition. Over 92.4% of the burned area is associated with El Niño events. Non-linear regression models indicate highly significant relationships (p < 0.001) with hydroclimatic parameters, positive with T$_{max}$ (R$^{2}$adj. = 0.83) and the ONI (R$^{2}$adj. = 0.74) and negative with P (R$^{2}$adj. = 0.88), MCWD (R$^{2}$adj. = 0.90), WL$_{min90}$ (R$^{2}$adj. = 0.61) and BFI (R$^{2}$adj. = 0.80). Hydroclimatic conditions were of outstanding magnitude in particular during the El Niño event in 2015/2016, which was responsible for 42.8% of the total burned floodplain area. We discuss these results under a historical background of El Niño occurrences and a political, demographic, and socioeconomic panorama of the study region considering the past 400 years, suggesting that disturbance of igapós by fires is not a recent phenomenon. Concluding remarks focus on current demands to increase the conservation to prevent and mitigate the impacts of fire in this vulnerable ecosystem

A Review of the Ecological and Biogeographic Differences of Amazonian Floodplain Forests

Amazonian floodplain forests along large rivers consist of two distinct floras that are traced to their differentiated sediment- and nutrient-rich (várzea) or sediment- and nutrient-poor (igapó) environments. While tree species in both ecosystems have adapted to seasonal floods that may last up to 270–300 days year−1, ecosystem fertility, hydrogeomorphic disturbance regimes, water shortage and drought, fire, and even specific microclimates are distinct between both ecosystems and largely explain the differences in forest productivity and taxonomic composition and diversity. Here, we review existing knowledge about the influence of these environmental factors on the tree flora of both ecosystems, compare species composition and diversity between central Amazonian várzeas and igapós, and show that both ecosystems track distinct species life-history traits. The ecosystem-level and taxonomic differences also largely explain the biogeographic connections of várzeas and igapós to other Amazonian and extra-Amazonian ecosystems. We highlight the major evolutionary force of large-river wetlands for Amazonian tree diversity and explore the scenarios by which the large number of Amazonian floodplain specialist tree species might even contribute to the gamma diversity of the Amazon by generating new species. Finally, we call attention to the urgent need of an improved conservation of Amazonian várzea and igapó ecosystems and their tree species