Summary 1.Water is a key resource in tropical savannas. Changes in vegetation structure due to land-use change and increased fire frequency may affect the availability of water and the flux of water through these ecosystems. 2. We compared the seasonal soil moisture dynamics of two adjacent savanna ecosystems with contrasting tree densities in central Brazil. Our goal was to investigate the influence of tree density on deep water uptake, soil water dynamics and evapotranspiration. 3. Soil water was measured using a depth of 7·5 m beneath the tree-dominated cerrado denso ecosystem and to 4 m beneath the grass-dominated campo sujo ecosystem. Plantavailable water (PAW) throughout the cerrado denso soil profile ranged from 293 mm at the end of the dry season to 689 mm during the wet season. In the grass-dominated site, PAW in the profile ranged from 155 to 362 mm. 4. During the dry season, ≈ 82% of the water used in cerrado denso and 67% in campo sujo was extracted from the profile below 1 m. The tree-dominated cerrado denso used 137 mm more water than the grass-dominated campo sujo . Significant deep soil water uptake was also observed during the wet season of 1998, when rainfall was below average. 5. Evapotranspiration (ET) rates (estimated as change in soil moisture over time) were higher in cerrado denso than in campo sujo during both seasons. Estimated ET ranged from 1·4 mm day − 1 during the dry season to 5·8 mm day − 1 for the wet season in cerrado denso , and from 0·9 mm day − 1 in the dry season to 4·5 mm day − 1 in early wet season in campo sujo . The differences in PAW and ET rates between the two ecosystems are associated not only with differences in root distribution, but also with differences in tree densities and the phenology of full-leaf canopies. 6. Our results suggest that deep-rooted plants may contribute significantly to the water balance of cerrado ecosystems, and that the hydrological cycle of this biome could change as woody vegetation is replaced by exotic grasses and agricultural crops.

Around 55% of all Brazilian cattle production is located in the Cerrado biome, which also contains the largest pasture area in Brazil. Previous studies indicated that about 60% of these pastures were degraded by 2010. However, up-to-date and more precise estimates are necessary to access the extent and degree of degradation of the Cerrado pastures, since these areas constitute strategic land reserves for both livestock intensification and soybean expansion. Therefore, in this study, we estimated the area of degraded pastures in the Cerrado by analyzing the trends of cumulative NDVI anomalies over time used as a proxy for pasture degradation. The generated slope surface was segmented into two classes, comprising non-degraded and degraded pastures, which were correlated with socio-economic and biophysical variables. According to our study, around 39% of the Cerrado pastures are currently degraded, encompassing 18.2 million hectares, mostly in areas with a cattle carrying capacity below 1.0 AU ha−1. These areas, distributed in the northwest Cerrado, mostly within the Brazilian states of Maranhão, Piauí, and Bahia (i.e., Matopiba region), tend to be associated with decreasing rainfall patterns and low investments in soil conservation practices. The degraded areas also tend to be concentrated in municipalities with low human development indices (HDI).

The continuous growth of biodiversity databases has led to a search for techniques that can assist researchers. This paper presents a method for the analysis of occurrences of pairs and groups of species that aims to identify patterns in co-occurrences through the application of association rules of data mining. We propose, implement and evaluate a tool to help ecologists formulate and validate hypotheses regarding cooccurrence between two or more species. To validate our approach, we analyzed the occurrence of species with a dataset from the 50-ha Forest Dynamics Project on Barro Colorado Island (BCI). Three case studies were developed based on this tropical forest to evaluate patterns of positive and negative correlation. Our tool can be used to point co-occurrence in a multi-scale form and for multi-species, simultaneously, accelerating the identification process for the Spatial Point Pattern Analysis. This paper demonstrates that data mining, which has been used successfully in applications such as business and consumer profile analysis, can be a useful resource in ecology.

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Aim: To investigate the influence of bioclimatic, productivity and topographic variables on avian diversity patterns in riparian habitats along a savanna/humid forest environmental gradient. We investigate how this gradient affects patterns of taxonomic and phylogenetic alpha and beta diversities, and whether the changes observed along the river are the result of taxonomic (and phylogenetic) replacement or nestednessresultant dissimilarities. We also explore a potential ecological mechanism to account for differences in species richness along the gradient. Location: Basin of the Rio Branco, northern Amazonia, Brazil. Taxa: An avian community of 325 bird species. Methods: We sampled avian communities using standardized avian point counts at 16 localities, systematically distributed along the Rio Branco and two of its major tributaries. We compared patterns of species richness using rarefied numbers of species detected, and patterns of phylogenetic diversity with a community-wide consensus tree. In addition, we partitioned beta diversity in species replacement and nestedness-resultant dissimilarities. We reduced predictor variables using a principal components analysis, correlating locality scores with changes in diversity. We tested the effect of climatic variables on beta diversity with a distance-based redundancy analysis (dbRDA). Results: Patterns of avian composition and species richness were highly correlated with climatic and productivity variables. We found more bird species in less arid localities with higher annual precipitation, and in areas with lower annual temperatures, lower evapotranspiration and less temperature variation throughout the year. Despite differences in species richness, the number of individuals remained relatively similar along the gradient. However, species-rich localities presented lower average species frequency and median avian biomass. Patterns of taxonomic and phylogenetic beta diversity were correlated with the climatic gradient and were due to species replacements. Main conclusions: Climate represents a major player in structuring avian communities along the Rio Branco, affecting distinct levels of avian diversity organization. We found evidence of species packing, a mechanism to fit more species in the communities. Patterns of species replacement highlight the importance of transitional zones | 2329 NAKA et Al.