No abstract

The objective of this study was to determine the species richness and abundance of the seed bank and the influence of soil attributes along an elevation gradient (800–1400 m a.s.l.). We examined the floristic similarity among areas and determined the regional diversity along this gradient in Serra do Cipó (Minas Gerais, Brazil). A total of 1975 individuals from 149 species were germinated. Richness and abundance were not linearly related to elevation, and exhibited a threshold at 1200 m. The low degree of similarity among the areas reflects environmental heterogeneity, resulting from a rich mosaic of habitats, distinguished by the substrate configuration, continuity of vegetation, floristic composition, and proportion of exposed rock. The diversity between plots of different areas (β2) contributed to regional diversity, and species turnover was the most important factor. The physical variables and base saturation, which had high spatial heterogeneity, may be the most important factors with which to determine species turnover and β diversity. The studied seed bank is strongly influenced by edaphic variables, with a gradient of increasing acidity and proportion of fine sand, and decreasing proportion of clay and organic matter, with elevation. In addition, species richness was influenced by cation exchange capacity, organic matter, and clay; and abundance was influenced by cation exchange capacity, H + Al, organic matter, and base saturation.

-In order to produce useful knowledge to the initiatives of protection and management of forest fragments, more specifically for tropical dry forests which suffer with frequent anthropic activities, and due to the lack of specific studies, this article aimed describe the structure and the floristic similarity among three areas of dry forest with different management histories. The study was developed in Capitão Enéas municipality, Northern Minas Gerais, Brazil, where three fragments were evaluated, being one in regeneration for 30 years, another submitted to occasional fire and the third with selective cut in small scale. The sampling was developed through the point quarter method considering all the alive phanerophyte individuals with circumference at breast height (CBH) > 15 cm. In the three fragments, 512 individuals, distributed in 60 species, 47 genera, and 23 families were sampled. The most representative families were Fabaceae (26), Anacardiaceae (4), Bignoniaceae (3) and Combretaceae (3). However, fourteen families were represented by only one species. Only eight species were common to all fragments -Myracrodruon urundeuva standed out with 26.9% of all sampled individuals -while a great number of species were exclusive of each fragment. The floristic and structural differences between the fragments are possibly related to the history and intensity of management in each area besides the topography variations and the presence or absence of limestone outcrops. These results show the importance of each fragment, indicating that the loss of anyone would cause negative impacts on the regional flora and consequently to the associated biodiversity. ASPECTOS ESTRUTURAIS E SIMILARIDADE FLORÍSTICA ENTRE FRAGMENTOS DE FLORESTA TROPICAL SECA COM DIFERENTES HISTÓRICOS DE MANEJO NO NORTE DE MINAS GERAIS, BRASIL

Th e Cerrado is the largest savanna of South America and its physiognomy varies from savanna to woodlands. Th ere are two main types of woodlands in the Cerrado: dystrophic woodlands, dominated by N-fi xing leguminous trees (LEG), and mesotrophic woodlands dominated by non-leguminous drought-tolerant trees (DRY), which are calcicoles and sensitive to Al . Th e working hypothesis is that LEG and DRY are functional antagonists in terms of the acidifi cation/alkalization processes involving diff erent forms of inorganic nitrogen and pH, Ca 2+ and Al 3+ in soil. Tree species basal area and soil properties were used to investigate the antagonism between LEG and DRY using generalized linear models. Th e results suggest that LEG and DRY are antagonists. Th e LEG were positively associated with Al 3+ , NO 3-and NH 4+ content and negatively related to increasing Ca 2+ content, whereas the DRY were negatively associated with Al 3+ , NO 3-and NH 4+ and positively associated with increasing Ca 2+ content. Th e upper soil layer in plots dominated by LEG species became more acidic and the upper soil layer in plots dominated by DRY species became more alkaline. Th e results suggest that LEG and DRY are functional antagonists and their preferences for NH 4+ or NO 3-might infl uence the way the Cerrado woodland changes.

The soils developed under High Altitude Rocky Complexes in Brazil are generally of very low chemical fertility, with low base saturation and high exchangeable aluminium concentration. This stressful condition imposes evolutionary pressures that lead to ecological success of plant species that are able to tolerate or accumulate high amounts of aluminium. Several analytical methods are currently available for elemental mapping of biological structures, such as micro-X-ray fluorescence (µ-EDX) and histochemical tests. The aim of this study was to combine µ-EDX analysis and histochemical tests to quantify aluminium in plants from High Altitude Rocky Complexes, identifying the main sites for Al-accumulation. Among the studied species, five showed total Al concentration higher than 1000 mg kg -1 . The main Al-hyperaccumulator plants, Lavoisiera pectinata, Lycopodium clavatum and Trembleya parviflora presented positive reactions in the histochemical tests using Chrome Azurol and Aluminon. Strong positive correlations were observed between the total Al concentrations and data obtained by µ-EDX analysis. The µ-EDX analysis is a potential tool to map and quantify Al in hyperaccumulator species, and a valuable technique due to its non-destructive capacity. Histochemical tests can be helpful to indicate the accumulation pattern of samples before they are submitted for further µ-EDX scrutiny.