Environmental factors related to the vegetational variation of a natural grassland

Neste trabalho estudam-se as relações entre estrutura da vegetação e fatores de ambiente. Em 30 ha de campo, 60 quadrados de 0,25 m2, locados ao longo de gradientes topográficos a cada mudanca notada na vegetação, foram avaliados quanto a fatores de ambiente e abundância-cobertura de espécies. Através de técnicas de classificação e ordenação foram identificados tipos de comunidades e grupos de espécies. O tipo de comunidade Eleocharis-Centella ocorre em campo uliginoso; Desmodium-Axonopus-Paspalum e Baccharis Andropogon ocorrem em umidade intermediária, e Facelis-Paspalum, Eryngium e Aristida-Borreria-Paspalum, em locais mais secos. As análises foram complementadas pelo estudo de perfis de dispersão de espécies e grupos de espécies em relação a variáveis de ambiente. Foram elaboradas hipóteses de sucessão decorrente de variação de ambiente, com base nos resultados.In this work the relationships between vegetation structure and environmental factors were studied. In a 30-ha natural grassland, 60 quadrats (0,25 m2) located on topographic gradients at each change in vegetation, were evaluated in terms of environmental factors and cover-abundance of species. Identification of community and species groups were done by using classification and ordination techniques. The community type Eleocharis-Centella occurs at lower and moister sites, Desmodium Axonopus-Paspalum and Baccharis-Andropogon occur at medium moisture, and Facelis-Paspalum, Eryngium and Arista-Borreria-Paspalum occur at dryer sites. In addition, dispersion profiles of species in relation to environmental factors were analysed. Hypotheses on vegetation succession due to changes in the environmental conditions were generated

Long-term ecological research in southern Brazil grasslands: Effects of grazing exclusion and deferred grazing on plant and arthropod communities

Grazing exclusion may lead to biodiversity loss and homogenization of naturally heterogeneous and species-rich grassland ecosystems, and these effects may cascade to higher trophic levels and ecosystem properties. Although grazing exclusion has been studied elsewhere, the consequences of alleviating the disturbance regime in grassland ecosystems remain unclear. In this paper, we present results of the first five years of an experiment in native grasslands of southern Brazil. Using a randomized block experimental design, we examined the effects of three grazing treatments on plant and arthropod communities: (i) deferred grazing (i.e., intermittent grazing), (ii) grazing exclusion and (iii) a control under traditional continuous grazing, which were applied to 70 x 70 m experimental plots, in six regionally distributed blocks. We evaluated plant community responses regarding taxonomic and functional diversity (life-forms) in separate spatial components: alpha (1 x 1 m subplots), beta, and gamma (70 x 70 m plots), as well as the cascading effects on arthropod high-taxa. By estimating effect sizes (treatments vs. control) by bootstrap resampling, both deferred grazing and grazing exclusion mostly increased vegetation height, plant biomass and standing dead biomass. The effect of grazing exclusion on plant taxonomic diversity was negative. Conversely, deferred grazing increased plant taxonomic diversity, but both treatments reduced plant functional diversity. Reduced grazing pressure in both treatments promoted the break of dominance by prostrate species, followed by fast homogenization of vegetation structure towards dominance of ligneous and erect species. These changes in the plant community led to increases in high-taxa richness and abundance of vegetationdwelling arthropod groups under both treatments, but had no detectable effects on epigeic arthropods. Our results indicate that decision-making regarding the conservation of southern Brazil grasslands should include both intensive and alleviated levels of grazing management, but not complete grazing exclusion, to maximize conservation results when considering plant and arthropod communities

Data from: Local biodiversity erosion in South Brazilian grasslands under moderate levels of landscape habitat loss

1.Habitat loss is one of the greatest threats to biodiversity, exerting negative effects on the ecological viability of natural vegetation remnants. The South Brazilian grasslands belong to one of the largest temperate grassland regions in the world, but have lost 50% of their natural extent in the past 35 years. To date, there is no empirical evidence for the effects of habitat loss on these grasslands’ biological diversity, undermining their conservation. 2.Using data from a large-scale biodiversity survey, we asked if local plant communities respond to levels of habitat loss representative of the entire region (≤50%). Vegetation in grassland remnants was sampled in 24 landscapes at three localities each, using 9 plots per locality. To investigate whether species losses were a consequence of stochastic or nonrandom local extinctions and whether plant communities became more homogenized, we evaluated species richness, beta-diversity components (spatial turnover and nestedness), and phylogenetic diversity, in respect to landscape change. In part of the landscapes, arthropods were sampled to investigate if loss of plant diversity had a cascading effect on other trophic levels. We evaluated generic richness of ants, an omnivore group with high levels of plant associations, in respect to a plant community's phylogenetic diversity. 3.Local plant communities in landscapes with less grassland cover had fewer species, less spatial turnover, increased nestedness and lower phylogenetic diversity. Our results suggest that the observed species loss can be linked to taxonomic homogenization and is nonrandom, decreasing evolutionary diversity within the community. Furthermore, ant richness declined by 50% in plant communities with the lowest phylogenetic diversity, suggesting that effects of habitat loss propagate to higher trophic levels. 4.Policy implications. We conclude that the biological diversity of South Brazilian grasslands, at the producer and consumer level, is at risk under the current rate of land use conversion, even at habitat losses below 50%. To avoid substantial biodiversity loss, conservation and more restrictive policies for conversion of native grasslands to different land uses in South Brazil are urgent

Vegetação campestre do sul do Brasil: dinâmica de espécies à exclusão do gado Grassland vegetation in Southern Brazil: dynamics of species in cattle excluded areas

O presente estudo objetivou avaliar modificações ocorridas na vegetação em uma área de campo natural, após oito anos sem influência de pastoreio. A área situa-se na Estação Experimental Agronômica da UFRGS, no município de Eldorado do Sul, RS, onde foram realizadas amostragens em 1984 e 1992. Dezesseis unidades amostrais permanentes de 0,25 m² foram utilizadas para verificar a presença e o valor de cobertura das espécies, pela escala de Daubenmire. São apresentados os valores de freqüência e cobertura absolutas (FA e CA, respectivamente) das espécies de Gramineae, Compositae, Rubiaceae, Leguminosae, Umbelliferae e Cyperaceae nos levantamentos de 1984 e 1992. O trabalho evidenciou a relação entre a forma biológica das espécies predominantes e os estados pastejado ou excluído. Em Gramineae, espécies rasteiras, estoloníferas ou rizomatosas (Paspalum notatum, Axonopus affinis e outras), características da área pastejada, foram substituídas por plantas de hábito cespitoso (Andropogon lateralis, Elyonurus candidus e outras), capazes de sombrear e sobrepujar as de baixo porte. Espécies de compostas e rubiáceas, de um modo geral, apresentaram uma redução em FA e pouca alteração em CA. As leguminosas apresentaram principalmente um aumento em FA, mantendo a CA praticamente constante. As umbelíferas destacaram-se pelo aumento da CA em metade de suas espécies. Ocorreu o surgimento de 25 e o desaparecimento de 42 espécies em 1992.<br>The aim of this study was to evaluate modifications after eight years without grazing in a native grassland area, located at the Estação Experimental Agronômica - UFRGS, in Eldorado do Sul, RS. Vegetation surveys were done in 1984 and 1992. Sixteen permanent sample quadrats (0.25 m²) were established and presence of species and cover-abundance values according to the Daubenmire scale were recorded. Absolute frequencies and cover values (AF and AC, respectively) in 1984 and 1992 are presented for Gramineae, Compositae, Rubiaceae, Leguminosae, Umbelliferae and Cyperaceae species. The study showed the relation between the growth forms of the most abundant species and the grazed and ungrazed situations. Creeping, stoloniferous and rhizomatous species of Gramineae (Paspalum notatum, Axonopus affinis and others) were conspicuous when the area was under grazing, being replaced by tussock-type plants (Andropogon lateralis, Elyonurus candidus and others) able to dominate and shade out small understory herbs, when excluded. Compositae and Rubiaceae species showed a reduction in AF and few changes in AC. Leguminosae species had an increase in AF, presenting almost constant values for AC. Half of the Umbelliferae species presented an increase in AC in the second survey. Twenty five species appeared and 42 vanished in 1992

Plant and ant communities along a habitat loss gradient

The file consists of three sheets: "Plants", "Ants" and "Gradient". Plants and Ants are sites x species matrices. Sites are structured as following: "Landscape" is the landscape sampling region (2 x 2 km), in which 3 local sampling units (70 x 70 m), "Unit", are allocated. For Plants each "Unit" is sampled with 9 plots, "Plot". Gradient contains the percentage of grassland remnants, "percent_remGrassland", and the "Latitude" and "Longituted" of each "Landscape"