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Estrutura de comunidades de arvores em florestas tropicais depende de filtros ambientais e interacoes abioticas, como competicao e facilitacao. Muitas florestas de ecotono no norte da Amazonia sao intrigantemente povoadas por assembleias de arvores, caracterizadas por abundâncias distintas de uma unica especie, Peltogyne gracilipes (Leguminosae). Nao esta claro se este padrao isoladamente reflete filtros ambientais ou tambem interacoes antagonicas entre especies com requisitos de habitats semelhantes. O objetivo deste estudo foi determinar a resposta da riqueza e composicao de especies aos filtros ambientais, analisando o papel de P. gracilipes na estruturacao de comunidades arboreas em areas de floresta de ecotono do norte da Amazonia brasileira. Amostramos 129 parcelas permanentes ao longo de um gradiente hidro-edafico. Todos os individuos arboreos com diâmetro do caule ≥ 10 cm foram medidos e identificados. Regressoes multiplas foram realizadas para testar os efeitos dos filtros ambientais, e da abundância de P. gracilipes na riqueza e composicao das arvores. Riqueza e composicao de especies responderam aos mesmos filtros, os quais, por sua vez, afetaram a composicao das especies direta e indiretamente, por meio da abundância de P. gracilipes. Nossos resultados indicam que tanto os filtros abioticos quanto as interacoes bioticas moldam as comunidades arboreas estudadas. P. gracilipes pode ser considerada uma especie indicadora de condicoes hidroedaficas, mas tambem e ela propria uma impulsionadora da estrutura da comunidade arborea.

The degree of herbivory in plants can be related to leaf traits, which are, in turn, determined by phylogeny and environment. The objective of our study was to determine the level of trait conserva...

The Brazilian Amazonia is a region covered by an extensive mosaic of tropical forests conditioned by different topographical and hydro-edaphic features. Although studies relating environmental determinants of structure and floristic composition are systematically evolving in the region, there is no doubt that there are still information gaps due to the lack of research in peripheric areas of the Amazonia. The seasonally flooded areas of the state of Roraima situated on rio Branco-rio Negro basin, northern Brazilian Amazonia, still are deprived of such information. In this way, this work had as objective determine the physical and soil chemical attributes, and the flooding periodicity that characterize different forest types dispersed in a topographic gradient located in an area on the north of rio Branco-rio Negro basin. Soil samples (0-60 cm) were collected along a 2.7 km transect (31.1-64.8 m a.s.l.) crossing three different forest types: (i) mosaic between treed and forested shade-loving (La+Ld), (ii) area of ecological tension between forested shade-loving and open ombrophilous forest (LO) and (iii) open ombrophilous forest (Ab+As). The results indicated different soil classes and flooding periodicity for each forest type observed: Entisols Fluvents (La+Ld, 3-4 months flooded), Entisols Quartzipsamments (LO, 1-2 months) and Yellow Ultisols (Ab+As, no flooding). All analyzed soils were defined as nutrient-poor areas, especially those located on low altitude, characterized for higher hydrological restrictions (seasonal flooding) aggregating forest types of lower structural patterns (e.g. La+Ld). Soils on low altitude were also characterized as those with the highest percentage of fine sand and silt, while soil free of seasonal flooding (Yellow Ultisols) presented the highest levels of clay and coarse sand, always associated with the ombrophilous forests (higher structural patterns). These results improve our understanding of the environmental factors conditioning different forest types in this peripheral region of Amazonia, suggesting that ecosystems with higher hydro-edaphic restrictions are a strong indicator of forest types with lower structural patterns.

During extreme drought events, aboveground biomass (AGB) dynamics in Amazonian forests are altered through reduced productivity and increased tree mortality and carbon loss. Tree adaptations developed in response to historical drought may reduce the severity of carbon loss. Past droughts were likely associated with fire, which produced Pyrogenic Carbon (PyC), a form of carbon formed by the incomplete combustion of biomass burn and fossil fuel. PyC has specific properties that improve soil fertility and water holding capacity and decrease aluminium toxicity, among others. PyC can be found in different concentrations across the Amazon Basin, since it can be produced by local fires and aerosol deposition. It is unknown whether PyC could explain tree adaptations or contributes to Amazon forest dynamics, especially for extreme drought events. We hypothesize that PyC in soil can serve as a proxy of fire history and fire/drought adaptations and also support the forest during drought events because of its properties, decreasing mortality rates and maintaining rates of AGB gain equivalent to a non-extreme drought year. To evaluate this hypothesis, we used a dataset with more than 70 plots with repeat censuses distributed across the Amazon Basin and classified extreme drought events using maximum cumulative water deficit (MCWD) analysis. Soil samples were collected from the same plots during an intensive fieldwork campaign and PyC was quantified by hydrogen pyrolysis (HyPy). Forest plots were classified into high and low PyC based on the median across the whole dataset. Our preliminary results show that during extreme drought events, plots that have a greater concentration of PyC had significantly higher rates of AGB gain when compared with plots with lower concentrations of PyC (t-test, p < 0.05). During non-extreme drought years there was no significant difference in rates of AGB gain between plots with different concentrations of PyC. When we focus on plots with lower concentrations of PyC there is a significant decrease in rates of AGB gain during drought years compared to non-extreme drought years (t-test, p < 0.05). However, in plots with high concentrations of PyC there is no significant difference in rates of AGB gain, showing trees are able to maintain normal forest dynamics during extreme drought years. We conclude that PyC has an important role in mediating drought resistance and productivity in Amazonian forests.

Wood density is expressed by the ratio between dry weight and fresh volume of a sample piece. The value of this measure is an important variable for assessing wood functional properties, successional stages and biomass/carbon stock estimates in different terrestrial ecosystems. Wood density data were collected for tree species from ecotone forests of the northern Brazilian Amazonia. We sampled 680 individuals with stem diameter ≥10 cm. For each sampled individual measurements were taken for three stem variables: bark thickness (mm), bark density (g cm−3) and wood density (g cm−3). This dataset is intended to improve biomass and carbon estimates of forests in the northern ecotone region of Brazilian Amazonia, an area poorly known in terms of ecosystem dynamics.

Pyrogenic carbon (PyC) derived from charcoal particles (paleo + modern) deposited in the soil column has been little studied in the Amazon, and our understanding of the factors that control the spatial and vertical distribution of these materials in the region's forest soils is still unclear. The objective of this study was to test the effect of forest type and distance from the ignition source on the PyC stocks contained in macroscopic particles of soil charcoal (≥2 mm; 1 m depth) dispersed in ecotone forests of the northern Brazilian Amazon. Thirty permanent plots were set up near a site that had been occupied by pre-Columbian and by modern populations until the late 1970s. The sampled plots represent seasonal and ombrophilous forests that occur under different hydro-edaphic restrictions. Our results indicate that the largest PyC stock was spatially dependent on distance to the ignition source (3 km), occurring mainly in flood-free ombrophilous forests (3.46 ± 5.22 Mg PyC/ha). The vertical distribution of PyC in the deeper layers of the soil (50 cm) in seasonal forests was limited by hydro-edaphic impediments that restricted the occurrence of charcoal. These results suggest that PyC stocks derived from macroscopic charcoal particles in the soil of this Brazilian Amazon ecotone region are controlled by the distance from the ignition source of the fire, and that forest types with higher hydro-edaphic restrictions can inhibit formation and accumulation of charcoal. Making use of these distinctions reduces uncertainty and improves our ability to understand the variability of PyC stocks in forests with a history of fire in the Amazon.

Ecotone has been defined as “a multi-dimensional environmentally stochastic interaction zone between ecological systems with characteristics defined in space and time, and by the strength of the interaction” (Hufkens et al. 2009). This is a known concept to define transitional zones between two or more ecological communities, ecosystems or biotic regions. Ecotone forests, dispersed in northern Brazilian Amazonia, are natural formations which have been largely affected by anthropogenic impacts, such as deforestation and fire. Maracá Ecological Station, State of Roraima, Brazil, is a protected area with extensive representations of ecotone forests in this region of the Amazonia. Forest inventories and floristic surveys are important as they extend our knowledge (1) of forest structure and tree species composition and (2) of tree and palm species ecology in this region of the Amazonia. Both improve our ability to predict changes in plant diversity, considering the future scenarios of climate change in comparison with previous surveys performed in Maracá. We present a forest inventory carried out in 129 plots (10 m x 50 m; 6.45 ha in total) dispersed in a grid (5 km x 5 km) located in a forest zone ecotone in the eastern part of Maracá Ecological Station. All stems (tree + palm) with diameter at breast height ≥ 10 cm were recorded, identified and measured. A total of 3040 stems were recorded (tree = 2815; palm = 225), corresponding to 42 botanic families and 140 identified species. Seven families and 20 genera contained unidentified taxa (12.2%). Sapotaceae (735 stems; 10 species), Leguminosae (409; 24) and Rubiaceae (289; 12) were the most abundant families. Peltogyne gracilipes Ducke (Leguminosae), Pradosia surinamensis (Eyma) T.D.Penn. (Sapotaceae) and Ecclinusa guianensis Eyma (Sapotaceae) were the species with the highest importance value index (~ 25%). The dominance (m2 ha-1) of these species corresponds to > 36% of the total value observed in the forest inventory. Our dataset provides complementary floristic and structure information on tree and palm in Maracá, improving our knowledge of this Amazonian ecotone forest.

Various explanations have been put forward for monodominance in otherwise diverse tropical forests. This study assesses if the monodominance of Peltogyne gracilipes on Maraca Island in the northern Amazon can be related to edaphic factors. The basal area of P. gracilipes and the five other most common tree species on Maraca Island (Astrocaryum aculeatum, Attalea maripa, Ecclinusa guianensis, Licania kunthiana and Pradosia surinamensis) were recorded in 30 regularly-spaced 0.5 ha plots distributed over an area of 25 km2, for which data on topography and concentration of mineral elements in the soil were also obtained. Stems of P. gracilipes accounted for ≥50% of the basal area in five of the plots, which we consider indicative of monodominance, whilst the highest relative basal area that any of the other species achieved in any plot was 31%. The soils data explained more of the variation in the basal area of P. gracilipes than it did for the other five species. The presence vs. absence and basal area of P. gracilipes was positively related to concentrations of magnesium (Mg), aluminium (Al), iron (Fe), phosphorus (P) and silt in the soil and to Mg:Ca ratios. These soils were found in the plots at the lowest elevations, which suggests that drainage factors may also be important. Overall, our results suggest that edaphic factors may explain, at least partially, monodominance in this Amazonian forest.

(Germinação de sementes e estabelecimento de plântulas de Solanum lycocarpum St. Hill submetidas a escarificação mecânica, quí­mica e térmica). Este trabalho testou a influência dos métodos de escarificação mecânica, quí­mica e térmica, na germinação e no estabelecimento de plântulas de Solanum Lycocarpum. Na germinação, a primeira semana foi o perí­odo com maior número de sementes germinadas e o tratamento Lixa diferiu significativamente dos demais, com maior média (66,99%). No estabelecimento, a variável altura, apresentou diferença entre os tratamentos e intervalos avaliados. Exceto nos tratamentos corte e ácido sulfúrico, os maiores crescimentos ocorreram no último intervalo, e o tratamento Lixa apresentou maior média. Já para o número de folhas e o diâmetro, s médias foram semelhantes entre os tratamentos, contudo, entre os intervalos foram encontradas diferenças com maior crescimento no primeiro intervalo, em todos os tratamentos. Para o tratamento Lixa, foram observadas diferenças para o número de folhas e no tratamentoácido sulfúrico para o diâmetro, Assim, a escarificação com lixa é o método mais adequado para tratamento das sementes de S.Lycocarpum.

Background: Previous work has shown that Amazonian tropical forests have experienced two widespread changes in dynamics over recent decades, increases in both tree stem turnover and above-ground biomass. However, data from an Amazonian monodominant forest dominated by Peltogyne gracilipes have shown that the above-ground biomass of this forest type has declined slightly (

This study aimed to compare the spatial and the height distribution of three plant species between two rupestrian field communities, one preserved (A) and the other cultivated (B). One 50 × 100 m plot was delimited in each community and the populations of Eremanthus incanus, Lychnophora pinaster and Vellozia caruncularis were assessed for height and spatial distribution (using the Ripleys’s L-function). In community A, 4,098 individuals were counted, mostly L. pinaster, against 220 individuals in community B, prevailing E. incanus. An inverted-J pattern was observed for height distribution in both communities, however, with lower frequencies in B. Regular spatial distribution was found for E. incanus and V. caruncularis in community A, whereas the pattern for L. pinaster depended on the scale of analysis. The spatial distribution of all species differed between communities. The Ecological Park Quedas do Rio Bonito contributes to the conservation of these rupestrian field species.

Neste estudo, objetivou-se a avaliação da dinâmica estrutural de uma comunidade arbórea, com históricos de incêndios, em uma floresta estacional semidecidual altimontana, entre os anos de 2002 e 2008, na Serra da Mantiqueira. Foram calculadas taxas de dinâmica em função do número de indivíduos sobreviventes, recrutas e mortos e, taxas de dinâmica relativas ao ganho e perda de área basal. Foi verificado se existem diferenças espaciais entre as taxas ao longo de gradiente vegetacional paralelo à elevação do terreno e se há correlações entre as taxas de dinâmicas com as variáveis bióticas (número inicial de indivíduos, área basal inicial) e abiótica (cota altimétrica). Foram encontradas taxas de recrutamento superiores às taxas de mortalidade, havendo também maiores taxas de ganho em relação à perda em área basal. Esse resultado indica que a floresta se encontra em expansão, com ganho em números de indivíduos e em área basal. Quando a comunidade foi analisada em setores (base, meio e topo da encosta), verificou-se que não houve diferenças entre as taxas de dinâmicas para os setores. De maneira geral, obtiveram-se poucas correlações significativas entre as variáveis bióticas e abióticas e as taxas de dinâmicas. O ganho em número de indivíduos e área basal, a não diferenciação das taxas de dinâmica entre os setores e as baixas correlações entre as variáveis com dinâmica da estrutura da floresta são evidências que eventos históricos, como incêndio ocorrido na década de 90, podem estar afetando diretamente as taxas de dinâmica da floresta como um todo. The aim of this study was to evaluate the structural dynamic rates of an shrubs-tree component of a seasonal semideciduous upper montane forest, in Mantiqueira Mountain between 2002 and 2008. We calculated the rates of dynamic according to the number of surviving, dead individuals and recruits, as well as the rates of dynamic for gain and loss of basal area. We verified the spatial differences among the rates along the vegetation gradient parallel to ground elevation. We also studied the correlations between the rates and biotic (initial numbers of trees and initial basal area) and abiotic parameters (altimetric quota). We verified that recruitment was higher than mortality, and the gain of basal area was higher than the loses. This result suggests that the forest is expanding, with gain in number of individuals and in basal area. Normally, this result characterizes forests in recuperation after some disturbance. The community sectors (basis, middle and top of hillside) didn't show any differences in terms of dynamic rates. In general, there were few significant correlations between biotic and abiotic parameters and the dynamic rates. The increase of density and basal area, the similarity of dynamic rates among the sectors and the low correlation between parameters and the dynamic of forest's structure point out that the forest burning occurred in 90's could be, nowadays, interfering directly in dynamic rates of forest.

The aim of this study was to evaluate the structural dynamic rates of an shrubs-tree component of a seasonal semideciduous upper montane forest, in Mantiqueira Mountain between 2002 and 2008. We calculated the rates of dynamic according to the number of surviving, dead individuals and recruits, as well as the rates of dynamic for gain and loss of basal area. We verified the spatial differences among the rates along the vegetation gradient parallel to ground elevation. We also studied the correlations between the rates and biotic (initial numbers of trees and initial basal area) and abiotic parameters (altimetric quota). We verified that recruitment was higher than mortality, and the gain of basal area was higher than the loses. This result suggests that the forest is expanding, with gain in number of individuals and in basal area. Normally, this result characterizes forests in recuperation after some disturbance. The community sectors (basis, middle and top of hillside) didn’t show any differences in terms of dynamic rates. In general, there were few significant correlations between biotic and abiotic parameters and the dynamic rates. The increase of density and basal area, the similarity of dynamic rates among the sectors and the low correlation between parameters and the dynamic of forest’s structure point out that the forest burning occurred in 90’s could be, nowadays, interfering directly in dynamic rates of forest.

The study evaluated variations in the dynamics of seven arboreal populations (Copaifera langsdorffii, Cupaniavernalis, Sebastiania commersoniana, Luehea grandiflora, Machaerium stipitatum, Machaerium villosum and Tapirira obtuse),in three fragments located in the municipal districts of Ibituruna, Ingaí and Luminárias. The populations were chosen with 15 ormore individuals (including dead and recruited), in the surveys carried out in 2000 and 2005 through permanent plots. Allindividuals with DBH > 5cm were sampled. The analyses were made using the results of the two surveys (number of individuals,basal area and diametric distribution). No pattern was found with relation to the behavior of the populations in the three areasstudied. In Ingaí, C. langsdorffii and C. vernalis increased in number of individuals, S. commersoniana and M. villosum reducedin density and in basal area, T. obtuse in number, and L. glandiflora and M. stiptatum remained the same. All species concentratedmost of the individuals in the smaller diameter classes I and II (from 5 to 10cm and from 10 to 20cm). In Ibituruna, all thepopulations, except C. langsdoffii, reduced in number of individuals and were predominant in diameter class II. There was anincrease in basal area for C. vernalis and L. grandiflora. In Luminárias, S. commersoniana presented gain in density, and M. stiptatum remained the same. The other populations of individuals reduced in density. With respect to basal area, all species, exceptM. villosum, presented an increase with respect to diametric distribution, it was verified that for most of the populations, aconcentration of individuals in class I prevailed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Ecossistemas florestais dispersos em matrizes de savana da Amazônia vêm sofrendo vários tipos de impactos antropogênicos, em especial fogo recorrente e extração seletiva. O estoque de carbono na biomassa destes sistemas e a sua contribuição como mitigador dos impactos gerados pelo aquecimento global são pobremente conhecidos. O objetivo deste estudo foi estimar a biomassa arbórea viva acima do solo em ilhas de mata (fragmentos florestais) antropizadas da savana de Roraima, norte da Amazônia Brasileira. Foram avaliados os seguintes fatores: dimensão do fragmento, estrutura florestal (tomando como base a posição no gradiente: borda e interior) e as características físicas e químicas do solo. Foi realizado um inventário florestal em 12 ilhas de mata escolhidas aletoriamente, levando em consideração três categorias dimensionais (k = 3): ilhas grandes (20-60 ha), médias (10-20 ha) e pequenas (< 10 ha). Em cada categoria foram estudadas quatro ilhas (n = 4) e, em cada ilha foram estabelecidas subparcelas (76 no total). Todos os indivíduos arbóreos com diâmetro à altura do peito (DAP) ≥ 10 cm foram inventariados. A altura total de cada indivíduo foi estimada visualmente. O cálculo da biomassa arbórea viva acima do solo (AGB) para todos os indivíduos inventariados foi realizado pelo método indireto a partir de uma equação alométrica. Foram observados 1087 indivíduos de 112 espécies arbóreas (incluindo morfoespécies) pertencentes a 29 famílias botânicas. Pouteria surumuensis Baehni (Sapotaceae) foi a espécie mais abundante em todas as categorias dimensionais. Ilhas de maior dimensão possuem maior abundância de espécies de crescimento tardio e clímax, enquanto espécies pioneiras predominam em ilhas de menor dimensão. A biomassa arbórea não diferiu entre a borda e o interior dos fragmentos, independente da dimensão. Contudo, a biomassa arbórea para fragmentos grandes (469,9 Mg ha-1), médios (357,1 Mg ha-1) e pequenos (206,4 Mg ha-1) diferiu significativamente (ANOVA; Tukey0,05), indicando que fragmentos maiores possuem maior AGB. A biomassa arbórea viva não apresentou relação com as características físicas e químicas do solo. A conclusão deste estudo é que biomassa arbórea viva acima do solo das ilhas de mata da savana de Roraima varia em função da dimensão do fragmento, mas independe da posição no gradiente (borda interior), não indicando relação significativa com estrutura física ou fertilidade do solo. Forest ecosystems dispersed in matrices of Amazonian savannas have been suffering many types of anthropogenic impacts, in particular recurrent fire and selective logging. The carbon stock in the biomass of these systems and its contribution to mitigation of impacts generated by global warming are poorly known. The aim of this study was to estimate the living above ground biomass in anthropized forest islands (forest fragments) in the Savanna of Roraima, Northern Brazilian Amazon. Environmental factors were evaluated: the fragment dimension, forest structure (based on the position in the gradient: edge and interior) and the physical and chemical soil characteristics. A forest inventory was carried out in 12 forest fragments randomly chosen, taking into account three-dimensional categories (k = 3): large islands (20-60 ha), medium (10-20 ha) and small (< 10 ha). In each category were studied four fragments (n = 4) and in each fragment subplots were established (76 in total). All individuals with tree diameter at breast height (DBH) ≥ 10 cm were inventoried. The total height of each individual was estimated visually. Living above ground biomass was calculated for all individuals inventoried using indirect method (allometric equation). One thousand and eight seven (1087) individuals were observed of 112 tree species (including morphospecies) belonging to 29 botanical families. Pouteria surumuensis Baehni (Sapotaceae) was the most abundant species in all dimensional categories. Forest islands with larger dimensions have higher abundance for both late-growing and climax species, while smaller islands were dominated by pioneer species. The living above ground biomass did not differ between the edge and the interior of fragments regardless of dimension. However, the forest biomass of large (469.9 Mg ha-1), medium (357.1 Mg ha-1) and small (206.4 Mg ha-1) fragments differed significantly (ANOVA; Tukey0.05), indicating that larger fragments have higher living above ground biomass. The living above ground biomass did not present any relationship with the physical and chemical soil characteristics. The conclusion of this study is that living above ground biomass of forest islands in the Savanna of Roraima varies depending on the fragment size, but is independent of the position in the gradient (edge-interior), indicating no significant relationship with the structure or soil fertility.