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1. Maracá, Brazil, is a large riverine island which is at the boundary between lowland evergreen rain forest and savanna. The island is now uninhabited but there is evidence that much of its forest (including the plots described in this paper) is secondary, dating from before 1880. 2. The mean annual rainfall is about 2300mm and there is a dry season from October to March. 3. Six replicate plots of 0.25 ha each were set up in the rain forest. Three of these were later felled, as part of a long-term study on forest regeneration, and three left undisturbed. 4. Soils were described from a profile pit and for surface samples (0-10cm) in the three undisturbed plots. The soils were a Grossarenic Plinthic Paleudult (USDA). They were acid, had exceptionally low concentrations of total phosphorus, low concentrations of exchangeable cations but a fairly high base saturation, and a sandy texture. There was no surface root mat, no surface accumulation of organic matter, and no sign of podzolization. 5. All trees and lianas ≥10cm d.b.h. in the forest plots were enumerated, and structural features of the trees (including fine-root biomass) and smaller plants were quantified. The plots had a mean tree basal area of 23.8m[Sup2] and the emergents were up to 40m tall. 6. The mean tree species richness for the plots was forty per 0.25 ha and overall the Moraccae were the most important family in terms of basal area. 7. Analyses of leaves of 38 tree species showed wide interspecific variations but, in general. leaf nutrient concentrations were moderate or high. 8. It is concluded that although the Maracá forest occurs on very nutrient-poor soils it shows neither physiognomic nor foliar chemical features which are held to be characteristic of rain forests on such soils. Moreover, even though the soils are dry and sandy, the Maracá forest shows no features of heath forests. [ABSTRACT FROM AUTHOR]

1. The Maracã rain forest occurs on sandy soils which have very low concentrations of nutrients, but it has none of the structural features which are often held to be associated with forests on nutrient-poor soils. 2. The present paper reports tests of three hypotheses which were proposed to account for these unexpected features of the Maracá forest: (a) that the forest is unproductive and has a low nutrient demand: (b) that the trees are particularly efficient at withdrawing foliar nutrients before leaf abscission: and (c) that decomposition is rapid and the nutrients are quickly recycled. 3. Small litterfall (leaves, wood ≤2cm in diameter, reproductive parts. and trash) was measured for 12 months in three replicate 0-25-ha plots for quantity. seasonal distribution and concentrations of nitrogen. phosphorus. potassium, calcium and magnesium. 4. The mean total small litterfall was relatively high with a mean value for the three plots of 9.28tha[Sup-1] year[Sup-1] (range 885-9-52). 5. The nitrogen concentrations in the Maracá small litterfall were at the lower end of the range reported for other tropical forests whilst the concentrations of phosphorus. potassium, calcium and magnesium were relatively high. 6. Small-litter layer mass was measured in the plots on four occasions over a year. It showed changes with season and the mean values for total small-litter for the three plots were least (4.00tha[Sup-1]) in the wet season and highest (5.14tha[Sup-1]) in the dry season. 7. The concentrations of nitrogen, magnesium and potassium were lower in the small-litter layer than those of the litterfall. whilst phosphorus and calcium con- centrations were similar. 8. Mean large-wood (≥2cm in diameter) litter (including standing dead trees) had a mean value of 5-80tha[Sup-1](range 354-7.37) for the three plots. 9. Decomposition quotient (kL) values were relatively high with mean value of 2.94 for the leaf fraction and 2.01 for total small litterfall. [ABSTRACT FROM AUTHOR]

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A correction is presented to the article "Defaunation increases the spatial clustering of lowland Western Amazonian tree communities" which appeared in the issue.

This article provides a summary of the paper "The Role of Caimans in the Nutrient Regime in the Mouth-Lakes of Amazon Affluents" presented by E.-J. Fittkau at the Spring Meeting of the Tropical Group of the British Ecological Society held in London, England, on April 24, 1969. According to the paper, the formerly abundant caimans of the central Amazon region have nearly become extinct because of the demand for their hides. It highlights the existence of close interdependence between caimans and the fish in the Amazonian water-bodies.

This article provides a summary of the paper "Limnological Conditions in Central Amazonia" presented by H. Sioli at the Spring Meeting of the Tropical Group of the British Ecological Society held in London, England, on April 24, 1969. The paper claims that limnological studies give insights into Amazonian landscape-ecology. It discusses the average annual rainfall in the region. It also describes the topography of the valleys and courses of the lower Amazon and the Central Amazonian affluents and the chemistry of Amazonian waters.

Understanding the responses of individual plant species along different edaphic gradients is a key question in ecology, with implications to community assembly, functioning of forest ecosystems, niche theory and conservation planning. In tropical rain forests, responses to soil nutrients have been described only for a handful of species. Even abundant and conspicuous components of the forest, such as the palms (Arecaceae), remain largely unknown in this respect., We inventoried all palm species and analysed soil chemistry in 96 sites across western Amazonia to (i) assess the relative importance of some micronutrients vs. macronutrients as drivers of patterns in palm species composition, (ii) model the response shapes of 61 palm taxa and of canopy vs. understorey palms along gradients of selected soil nutrients, (iii) determine if the response shapes of conspecific palm varieties differ in relation to the most important observed soil nutrient and (iv) assess if the rank order of the most abundant canopy species changes along edaphic gradients., Patterns in palm species composition were best explained by Mehlich-III extractable exchangeable bases (Ca, K, Mg) and phosphorus (P), with the different palm species clearly separating along the soil cation concentration gradient. All 61 palm taxa exhibited statistical responses along soil nutrient gradients. Response shapes in relation to exchangeable bases varied among bimodal skewed (51% of species), unimodal skewed (47%) and monotonic (2%)., There were no significant differences between canopy vs. understorey species in their mean response shapes to the exchangeable bases, but canopy species had significantly higher mean optimum value for soil P and greater mean niche width along the Ca, K, Mg, P and boron (B) gradients. Varieties of the same species of Bactris, Desmoncus and Geonoma generally had different response shapes and different optima for the exchangeable bases., Synthesis. Among the soil variables we studied, macronutrients (especially exchangeable bases and P) emerged as more important than micronutrients in predicting species abundances in palm communities of western Amazonian non-inundated forests. Non-Gaussian responses were predominant, conspecific palm varieties exhibited different response types, and the rank order of dominance of canopy palms varied along the gradients of exchangeable bases and P. Together, these findings advance niche theory about palms and may be used for generating better predictive models of palm species distributions and for experimental studies that search for the physiological mechanisms underlying inter- and infra-specific trade-offs along edaphic gradients. [ABSTRACT FROM AUTHOR]

Classic theory in plant-insect interactions has linked herbivore pressure with diversification in plant species. We hypothesize that herbivores may exert divergent selection on defences, such that closely related plant species will be more different in defensive than in non-defensive traits., We evaluated this hypothesis by investigating two clades of closely related plant species coexisting at a single site in the Peruvian Amazon: Inga capitata Desv. and Inga heterophylla Willd. species complexes. We compared how these lineages differ in the suite of chemical, biotic, phenological and developmental defences as compared to non-defensive traits that are related to habitat use and resource acquisition. We also collected insect herbivores feeding on the plants., Our data show that sister lineages within both species complexes are more divergent in antiherbivore defences than in other non-defensive, functional traits. Moreover, the assemblages of herbivore communities are dissimilar between the populations of coexisting I. capitata lineages., Synthesis. Our results are consistent with the idea that for the I. capitata and I. heterophylla species complexes, interactions with their natural enemies may have played a significant role in their phenotypic divergence and potentially in their diversification and coexistence. It also suggests that defensive traits are evolutionary labile. [ABSTRACT FROM AUTHOR]

1. Climate change predictions in the Amazon have largely focused on carbon-water relations, while the impacts of increased air temperature and reduced precipitation on host-pathogen relationships have not been extensively explored. These relationships are known to affect recruitment of many Amazonian plant species. 2. Host-pathogen relationships are well suited to a dynamical analysis of the effects of climate change due to the direct linkages between pathogen behaviour and abiotic factors such as temperature and rainfall. 3. Seedlings of the palm Iriartea deltoidea experience significant mortality due to infection by the fungus Diplodia mutila. This host-pathogen interaction was examined by combining a semi-analytical model with field data illustrating the temperature sensitivity of D. mutila reproductive rates and I. deltoidea seedling mortality in response to infection. 4. The data-model combination shows that projected climatic shifts in rainfall and temperature for the Amazon region will tend to reduce recruitment by altering pathogen activity and reducing palm fecundity. The magnitude of the reduction is sensitive to the details of the epidemiology of the D. mutila-I. deltoidea host-pathogen system, and ranges from 10% to 56% under plausible scenarios. 5. Although considerable uncertainty remains, the proposed model provides a blueprint for research on one aspect of ecosystem change in future climate models. 6. Synthesis. The study illustrates the potential for ecosystem responses to climate change, which can be investigated through tractable models simple enough to assimilate into climate modelling frameworks. Particular environmental sensitivities in fungal dynamics are identified. The implications of combined plant physiological stress and enhanced pathogenic activity under future climate scenarios are highlighted as critical issues for projecting forest response. [ABSTRACT FROM AUTHOR]

1. Comparative analyses of diversity variation among and between regions allow testing of alternative explanatory models and ideas. Here, we explore the relationships between the tree α-diversity of small rain forest plots in Africa and in Amazonia and climatic variables, to test the explanatory power of climate and the consistency of relationships between the two continents. 2. Our analysis included 1003 African plots and 512 Amazonian plots. All are located in old-growth primary non-flooded forest under 900 m altitude. Tree α-diversity is estimated using Fisher's alpha calculated for trees with diameter at breast height ≥ 10 cm. Mean diversity values are lower in Africa by a factor of two. 3. Climate-diversity analyses are based on data aggregated for grid cells of 2.5 × 2.5 km. The highest Fisher's alpha values are found in Amazonian forests with no climatic analogue in our African data set. When the analysis is restricted to pixels of directly comparable climate, the mean diversity of African forests is still much lower than that in Amazonia. Only in regions of low mean annual rainfall and temperature is mean diversity in African forests comparable with, or superior to, the diversity in Amazonia. 4. The climatic variables best correlated with the tree α-diversity are largely different in the African and Amazonian data, or correlate with African and Amazonian diversity in opposite directions. 5. These differences in the relationship between local/landscape-scale α-diversity and climate variables between the two continents point to the possible significance of an array of factors including: macro-scale climate differences between the two regions, overall size of the respective species pools, past climate variation, other forms of long-term and short-term environmental variation, and edaphics. We speculate that the lower α-diversity of African lowland rain forests reported here may be in part a function of the smaller regional species pool of tree species adapted to warm, wet conditions. 6. Our results point to the importance of controlling for variation in plot size and for gross differences in regional climates when undertaking comparative analyses between regions of how local diversity of forest varies in relation to other putative controlling factors. [ABSTRACT FROM AUTHOR]

Evaluates the effects of proximity to an exposed forest edge on plants in Amazonian lowland forest. Examination of carbon isotopic composition of canopy leaves and of understorey leaves and air; Collection of leaves of Duguetia flagellaris from young gaps, gap edges and old gaps; Estimation of the proportion of the transect area occupied by gaps.

Investigates the fluviodynamic character of the sites colonized by plants along with different river types in the western Amazon forest. Focus on the distribution and survival of colonizing plants in relation to the abiotic environment; Recognition of four frequently occurring landforms in relation to the colonizing process; Effect of fluvial landform evolution on the persistence of the initial plant assemblages.

Characterizes the nutrient stocks in the soil and vegetation in abandoned pastures in Eastern Amazonia. Soil nutrient content in relation to vegetation development in the area; Factors related to nutrient depletion in the pastural area.

(1) Vegetation dynamics during five years of succession following slash-and-burn agriculture in the upper Rio Negro region of the Amazon Basin were elucidated by combining (i) permanent plot studies of plant-replacement dynamics and productivity (ii) field analyses of the resource-procurement strategies of successional species and (iii) field experiments on the role of regeneration strategies, establishment microhabitats and nutrient availability in controlling succession. (2) The main study plot was dominated by grasses and forbs during the first year of succession and then by pioneer trees particularly Vismia spp. Pioneer trees exhibit greatest establishment m protected farm-site microhabitats, such as under fruit trees and among slash. By five years, Vismia mortality exceeded establishment and pioneer trees of the Melastomataceae were growing in the spaces vacated by Vismia. Primary forest species represented only 7% of all stems at this time. (3) The number of tree species (≥ 2 m tall) increased from seventeen (year 1) to thirtyfive (year 5). The number of pioneer species remained constant (about twelve) while the primary forest species increased slowly. Nevertheless most primary forest species were represented by only one individual after five years. (4) A key factor retarding succession is the slow rate at which primary forest species become established on abandoned farms. Diaspores of forest species that were artificially dispersed to a farm site had high rates of removal by animals. However, the probability that the diaspore of a species would escape removal and germinate increased as diaspore size increased. If these diaspores do germinate, they stand a high chance of surviving seedlings of five forest species transplanted to an abandoned farm showed over 90% survival after 4-5 years. (5) Due to burning and to decomposition of forest wood and root residues, there is a dramatic decline in carbon stocks during slash-and-burn agriculture. After five... [ABSTRACT FROM AUTHOR]