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Herb Groups (herb + groups)

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Life Sciences100%

Selected Abstracts

Mesoscale Gradients of Herb Richness and Abundance in Central Amazonia,

BIOTROPICA, Issue 6 2006
Flávia R. C. Costa
ABSTRACT There are few hypotheses to explain local understory diversity patterns. There is a consensus that climate and soil fertility affect understory density and diversity at large scales, but few studies addressed the mechanisms controlling density and diversity locally. Here, I examine patterns of abundance and diversity of three understory herb groups along gradients of soil nutrients and topography at the mesoscale (64 km2) in a wet tropical forest, and possible factors causing them. Herb richness, diversity, density, and cover were measured in fifty-nine 250 × 2 m plots systematically distributed over Reserva Ducke, Manaus. Herb groups responded differently to environmental gradients. Whereas density and cover of pteridophytes increased with altitude and slope, Marantaceae density and cover decreased. Density of sedges increased with altitude, but did not vary with slope. Density and cover of Marantaceae and sedges but not pteridophytes increased with the soil cation content. Pteridophyte richness increased with slope whereas Marantaceae richness decreased, richness of both groups increased with cation content. Diversity increased with altitude for Marantaceae and decreased for pteridophytes. Some of these patterns agree with what is expected from herbs, such as the greater abundance of Marantaceae and sedges in flat and low altitude plots, where water availability is higher and probably also light, and the greater richness of Marantaceae and pteridophytes in higher nutrient plots. The unexpected results of higher abundance and richness of pteridophytes in slopes, instead of in bottomlands, suggest that biotic or litter-mediated controls may be important to set these patterns. RESUMO Existem poucas hipóteses para explicar os padrões locais de diversidade do sub-bosque. Existe consenso de que clima e fertilidade do solo afetam a densidade e diversidade do sub-bosque em macro-escala, mas poucos estudos procuraram os mecanismos que controlam a densidade e diversidade em escala local. Neste estudo, eu examino os padrões de abundância e diversidade de 3 grupos de ervas de sub-bosque ao longo de gradients de nutrientes e topografia em uma floresta tropical úmida, e os possíveis fatores causais. A riqueza, diversidade, cobertura e densidade das ervas foram medidas em 59 parcelas de 250 × 2 m, distribuídas sobre 64 km2 na Reserva Ducke, Manaus. Os grupos de ervas responderam de forma diferente aos gradientes ambientais. Enquanto a densidade e cobertura das samambaias aumentaram com a altitude e a inclinação do terreno, a densidade e cobertura de Marantaceae diminuíram. A densidade de capins aumentou coma altitude, mas não variou com a inclinação. A densidade e cobertura de Marantaceae e capins aumentou com o conteúdo de nutrientes do solo, mas não para as pteridófitas. A riqueza de samambaias aumentou com a inclinação do terreno enquanto a riqueza de Marantaceae decresceu, e a riqueza dos dois grupos aumentou com o conteúdo de nutrientes. A diversidade aumentou com a altitude para Marantaceae e diminuiu para as samambaias. Alguns destes padrões concordam com o esperado para ervas, tais como a maior abundância de Marantaceae e capins nas parcelas planas e baixas, onde a disponibilidade de água e provavelmente de luz são maiores. Entretanto, os resultados inesperados de maior abundância e riqueza de pteridófitas nos terrenos mais inclinados, ao invés de nos baixios, sugerem que controles bióticos ou mediados pela liteira podem ser mais importantes para o estabelecimento destes padrões. [source]

Mesoscale distribution patterns of Amazonian understorey herbs in relation to topography, soil and watersheds

JOURNAL OF ECOLOGY, Issue 5 2005
FLÁVIA R. C. COSTA
Summary 1Many authors have suggested that topography and soils are the major determinants of species distributions and community patterns at small or regional scales, but few studies addressed the patterns at mesoscales. We used Reserva Ducke (100 km2) as a model to analyse the effects of soil, topography and watersheds on the variation of the herb community composition, and to determine the relative importance of the environmental factors on species composition. 2Taxonomic groups are frequently used as surrogates in studies of biodiversity distribution and complementarity, but their efficacy is controversial. We therefore studied the correlations between the distributional patterns of three different herb groups (Marantaceae, pteridophytes and ,others') and their responses to environmental predictors. 3Terrestrial herbs were sampled in 59 plots of 250 × 2 m, systematically distributed over the reserve. Plots followed isoclines of altitude, to minimize the internal variation of soil. Composition of the total herb community and of the three herb groups was summarized with PCoA. 4Soil structure, represented by PCA axes, was the main determinant of the variation in herb composition for all groups, but slope affected only pteridophytes. Soil and topography explained less than one-third of the variance in community data. Herb composition was significantly different between watersheds, but watersheds differ only slightly in soil parameters. Our results indicate high turnover in species composition, on spatial scales of 5,10 km in central Amazonia, which is not necessarily associated with soil change. 5Compositional patterns of the three groups analysed were significantly correlated, but with low values for the correlation coefficient. Although composition was correlated, the responses to environmental predictors differed among groups, and the use of one group as a surrogate will miss around 50% of the variation in other groups. 6Although important, soil and topography alone cannot predict herb community structure. Knowledge of geographical, historical or other landscape features, such as watershed morphology, may therefore be necessary to predict the turnover patterns over mesoscales. Moreover, the same factors may not have the same effectiveness as predictors of the structure of seemingly similar biological groups. [source]

Mesoscale Gradients of Herb Richness and Abundance in Central Amazonia,

BIOTROPICA, Issue 6 2006
Flávia R. C. Costa
ABSTRACT There are few hypotheses to explain local understory diversity patterns. There is a consensus that climate and soil fertility affect understory density and diversity at large scales, but few studies addressed the mechanisms controlling density and diversity locally. Here, I examine patterns of abundance and diversity of three understory herb groups along gradients of soil nutrients and topography at the mesoscale (64 km2) in a wet tropical forest, and possible factors causing them. Herb richness, diversity, density, and cover were measured in fifty-nine 250 × 2 m plots systematically distributed over Reserva Ducke, Manaus. Herb groups responded differently to environmental gradients. Whereas density and cover of pteridophytes increased with altitude and slope, Marantaceae density and cover decreased. Density of sedges increased with altitude, but did not vary with slope. Density and cover of Marantaceae and sedges but not pteridophytes increased with the soil cation content. Pteridophyte richness increased with slope whereas Marantaceae richness decreased, richness of both groups increased with cation content. Diversity increased with altitude for Marantaceae and decreased for pteridophytes. Some of these patterns agree with what is expected from herbs, such as the greater abundance of Marantaceae and sedges in flat and low altitude plots, where water availability is higher and probably also light, and the greater richness of Marantaceae and pteridophytes in higher nutrient plots. The unexpected results of higher abundance and richness of pteridophytes in slopes, instead of in bottomlands, suggest that biotic or litter-mediated controls may be important to set these patterns. RESUMO Existem poucas hipóteses para explicar os padrões locais de diversidade do sub-bosque. Existe consenso de que clima e fertilidade do solo afetam a densidade e diversidade do sub-bosque em macro-escala, mas poucos estudos procuraram os mecanismos que controlam a densidade e diversidade em escala local. Neste estudo, eu examino os padrões de abundância e diversidade de 3 grupos de ervas de sub-bosque ao longo de gradients de nutrientes e topografia em uma floresta tropical úmida, e os possíveis fatores causais. A riqueza, diversidade, cobertura e densidade das ervas foram medidas em 59 parcelas de 250 × 2 m, distribuídas sobre 64 km2 na Reserva Ducke, Manaus. Os grupos de ervas responderam de forma diferente aos gradientes ambientais. Enquanto a densidade e cobertura das samambaias aumentaram com a altitude e a inclinação do terreno, a densidade e cobertura de Marantaceae diminuíram. A densidade de capins aumentou coma altitude, mas não variou com a inclinação. A densidade e cobertura de Marantaceae e capins aumentou com o conteúdo de nutrientes do solo, mas não para as pteridófitas. A riqueza de samambaias aumentou com a inclinação do terreno enquanto a riqueza de Marantaceae decresceu, e a riqueza dos dois grupos aumentou com o conteúdo de nutrientes. A diversidade aumentou com a altitude para Marantaceae e diminuiu para as samambaias. Alguns destes padrões concordam com o esperado para ervas, tais como a maior abundância de Marantaceae e capins nas parcelas planas e baixas, onde a disponibilidade de água e provavelmente de luz são maiores. Entretanto, os resultados inesperados de maior abundância e riqueza de pteridófitas nos terrenos mais inclinados, ao invés de nos baixios, sugerem que controles bióticos ou mediados pela liteira podem ser mais importantes para o estabelecimento destes padrões. [source]