Ilsi Iob Boldrini

Worldwide evidence of a unimodal relationship between productivity and plant species richness

Grassland diversity and ecosystem productivity The relationship between plant species diversity and ecosystem productivity is controversial. The debate concerns whether diversity peaks at intermediate levels of productivity—the so-called humped-back model—or whether there is no clear predictable relationship. Fraser et al. used a large, standardized, and geographically diverse sample of grasslands from six continents to confirm the validity and generality of the humped-back model. Their findings pave the way for a more mechanistic understanding of the factors controlling species diversity. Science, this issue p. 302 The humped-back model of plant species diversity is confirmed by a global grassland survey. The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.

VEGETAÇÃO CAMPESTRE DO SUL DO BRASIL: DINÂMICA DE ESPÉCIES À EXCLUSÃO DO GADO

O presente estudo objetivou avaliar modificacoes ocorridas na vegetacao em uma area de campo natural, apos oito anos sem influencia de pastoreio. A area situa-se na Estacao Experimental Agronomica da UFRGS, no municipio 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 presenca e o valor de cobertura das especies, pela escala de Daubenmire. Sao apresentados os valores de frequencia e cobertura absolutas (FA e CA, respectivamente) das especies de Gramineae, Compositae, Rubiaceae, Leguminosae, Umbelliferae e Cyperaceae nos levantamentos de 1984 e 1992. O trabalho evidenciou a relacao entre a forma biologica das especies predominantes e os estados pastejado ou excluido. Em Gramineae, especies rasteiras, estoloniferas ou rizomatosas (Paspalum notatum, Axonopus affinis e outras), caracteristicas da area pastejada, foram substituidas por plantas de habito cespitoso (Andropogon lateralis, Elyonurus candidus e outras), capazes de sombrear e sobrepujar as de baixo porte. Especies de compostas e rubiaceas, de um modo geral, apresentaram uma reducao em FA e pouca alteracao em CA. As leguminosas apresentaram principalmente um aumento em FA, mantendo a CA praticamente constante. As umbeliferas destacaram-se pelo aumento da CA em metade de suas especies. Ocorreu o surgimento de 25 e o desaparecimento de 42 especies em 1992.

Potential reflection of distinct ecological units in plant endemism categories.

The level of endemism at a site may indicate species richness of the site. Nevertheless, assessing endemism levels in taxonomic groups such as plants may be difficult because the species richness of plants is high relative to species richness of other taxonomic groups (e.g., vertebrates). A major problem in determining whether plant species are endemic is the lack of standardization of the geographic extent of endemism: species are considered endemic to, for example, countries, continents, or states. We compiled a history of the concept of endemism as it applies to plants. The application of the concept to geographic distribution dates from the 19th century, when European explorers discovered many taxa exclusive to regions outside Europe. Two types of endemism, paleoendemism and neoendemism, were then acknowledged, according to evolutionary age, and these categories are still in use. In the 20th century, most of the research on endemism focused on explaining range restriction on the basis of cytological data, edaphic and geological factors, and phylogeny. This research led to a vast number of concepts, of which only edaphic endemism remains relatively well accepted. More recently, researchers suggest that competition may determine endemism in some cases. We suggest that plants be labeled as endemic only if their distribution occurs in a distinct ecological unit, such as a biome. On the basis of a literature review of the factors that cause range restriction, we categorized endemic taxa as paleoendemic, neoendemic, edaphically endemic, or suppressed endemic. For example, Schlechtendalia luzulifolia, is a rare forb that is a paleoendemic species of the granite and sandstone-based grasslands of the Pampa. Levels of endemism in southern Brazilian grasslands are poorly known. We emphasize the importance of recognizing these grasslands as a single transnational biome so that levels of endemism of species therein can be assessed correctly.

Phyllochron of Paspalum notatum Fl. and Coelorhachis selloana(Hack.) Camus in natural pasture

Leaf appearance rate and phyllochron are related variables which play a central role in forage production. Phyllochron is the time interval between the appearance of successive leaves and varies according to a number of environmental factors, among which temperature is the most important. The experiment was conducted in natural pasture with the aim of testing phyllochron variation under different seasons, herbage allowances, and topographic positions. Marked tillers were used to define the phyllochron, establishing a relationship between the number of leaves produced against thermal time during the sampling period. The time (expressed in °C) needed for the emergence of a leaf is equal to 1/b, where b is the slope coefficient of the regression. The lines for the season combinations, herbage allowances and topographic positions sampled were compared. Under Spring and Summer conditions, the phyllochrons for P. notatum and C. selloana were 156°C and 238°C respectively, regardless of treatment.

A new species of Eleocharis R. Brown (Cyperaceae) from southern Brazil

ABSTRACT Eleocharis laeviglumis is a new species from the Brazilian flora. This species belongs to Eleocharis subg. Limnochloa (P. Beauvois ex T. Lestiboudois) Torrey and is very similar to Eleocharis elongata Chapman. The new species differs from all species of Eleocharis R. Brown by culms terete, not septate; lower scale fertile; upper scales cartilaginous, smooth, without prominent veins, with submarginal band vinaceous to brown, hyaline margin conspicuous and abruptly differentiated from the rest of scale; slender bristles; achenes trigonous, reticulate, and without a short neck on the apex. Morphological description, illustration, data on habitat, and comparison with the similar species are presented.

Floristic and vegetation structure of a granitic grassland in Southern Brazil

A floristic and structural survey of a natural grassland community was conducted on Morro do Osso, a granitic hill in Porto Alegre, RS, Brazil. Structural data were surveyed in 39 one square meter plots placed over two major grassland areas. An accidental fire has occurred in one of the areas approximately one year prior to our survey, leading to further analysis of parameters differences between sites. The floristic list contains 282 species, whereas the structural survey has found 161 species. Families with highest accumulated importance values were Poaceae, Asteraceae and Fabaceae. The diversity and evenness indexes were 4.51 nats ind-1 and 0.86, respectively. Cluster analysis denoted two groups coinciding with the areas distinguished by the fire disturbance. A similarity analysis between our data and two other data sets from nearby granitic hills resulted in 28% to 35% similarity, with equivalent species-family distribution and many common dominant species, corroborating the concept of a continuous flora along the South Brazilian granitic hills.

Aspectos florísticos e ecológicos da vegetação campestre do Morro da Polícia, Porto Alegre, RS, Brasil

Estudou-se a variacao da composicao floristica da vegetacao campestre e suas relacoes com altitude e exposicao no Morro da Policia, de origem granitica, em Porto Alegre, Rio Grande do Sul, a 30oS e 51 oW. O levantamento foi realizado de novembro de 1992 a novembro de 1994. A presenca e frequencia de especies foi avaliada usando o metodo de pontos sobre transeccoes em 19 unidades de vegetacao, as quais foram delimitadas com base na exposicao da encosta (N, S, L, O) e altitude (160 a 280m). Os dados foram submetidos a analise multivariada de agrupamentos e ordenacao. Nas transeccoes foram observadas 189 especies, sendo Poaceae, Asteraceae e Apiaceae as familias mais frequentes e Trachypogon montufari e Schizachyrium tenerum as especies dominantes. A analise de agrupamentos e de ordenacao revelou conexoes entre variacao da vegetacao e fatores altitude e exposicao solar. Aristida laevis e Sorghastrum albescens sao caracteristicas de comunidades mais expostas a radiacao solar, enquanto Agenium villosum e Eryngium eriophorum o sao de comunidades menos expostas. Vernonia nudiflora e Axonopus suffultus caracterizam as areas mais elevadas do morro, enquanto Eupatoriitm ligulifolium e Sorghastrum albescens as mais baixas.

Florística e fitossociologia da vegetação de um campo sujeito à arenização no sudoeste do Estado do Rio Grande do Sul, Brasil

Extensas areas de campo nativo do sudoeste do Rio Grande do Sul sao suscetiveis ao processo de arenizacao, que ocorre em areas de fragilidade pedologica, tendo influencia de interferencia antropica e fatores abioticos. Com o objetivo de testar a variacao da cobertura vegetal e a dinâmica da arenizacao no tempo e conforme a influencia da distância da encosta, foi desenvolvido um estudo floristico e fitossociologico em areas de campo nativo sob pastejo. Duas subareas, diferentes quanto ao processo da arenizacao, foram selecionadas no municipio de Sao Francisco de Assis, RS. O levantamento floristico apontou a ocorrencia de 102 especies, distribuidas em 25 familias. No estudo fitossociologico, 35 quadros permanentes de 0,25 m2 em cada subarea foram dispostos em diferentes distâncias da encosta do morro. Foram registradas as coberturas das especies vegetais, do mantilho e do solo exposto em tres periodos. Dados sobre riqueza e diversidade de especies e formas de vida foram avaliados por analise de variância, via testes de aleatorizacao, considerando o fator temporal e o espacial (distância da encosta). Houve maior reducao da diversidade especifica e da cobertura vegetal na subarea 1 (com menor cobertura vegetal) conforme a variacao temporal. Na subarea 2 (com maior cobertura vegetal), o aumento do solo exposto e a consequente reducao da cobertura vegetal tiveram maior influencia da distância da encosta. A alteracao da cobertura vegetal e a expansao da arenizacao observadas ao longo do tempo sao resultado da influencia conjunta da dinâmica pluviometrica, do tipo solo, da presenca de encostas dos relevos tabulares com pouca vegetacao e da continua pressao de pastejo.

HIGHLAND GRASSLANDS AT THE SOUTHERN TIP OF THE ATLANTIC FOREST BIOME: MANAGEMENT OPTIONS AND CONSERVATION CHALLENGES

The natural vegetation in the highlands of the southernmost state of Brazil, Rio Grande do Sul, is characterized by extensive grasslands in mosaics with Araucaria forests, usually under cattle grazing. Plant species diversity and endemism in these grasslands is high, though poorly recognized in conservation policy and the general public, and conversion rates into other land uses are high. In this paper, we give an overview of principal biological features of grassland vegetation in the South Brazilian highland region (plant species richness and diversity) and initiate a debate on conservation possibilities and challenges. We use data from four sites of the Long-Term Ecological Research program (LTER/PELD) Campos Sulinos situated in the highland region of the state, where we explore the effects of different types of grassland management (grazing and grazing exclusion) on vegetation structure and composition. Our data give insight into high species richness on both the plot and site scale. Overall, the results indicate the importance of adequate management for the maintenance of grassland vegetation and its characteristic biological features. In theory, grazing or fire can be employed in grassland management, but specific effects of these two types of management need to be considered, as each type of management has distinct effects. We discuss the question of active nature management in conservation units and highlight the importance of research on restoration of degraded grassland areas. Even though grasslands make up the smaller portion of the South Brazilian Atlantic Forest region, their ecological uniqueness calls for specific conservation policy.

Phytosociology and natural subtropical grassland communities on a granitic hill in southern Brazil

A phytosociological survey was carried out in a study area located at Serra do Sudeste, southern Brazil, where forests and grasslands are distributed in a mosaic, seeking to unravel diversity patterns in four different grassland communities. Grassland management traditionally adopted by the local population is characterized by burning practices that aim to eliminate woody species, delaying the forest expansion process that is favored by the extant climate. The number of plots distributed per community was as follows: rocky grasslands (17), dry grasslands (33), moist grasslands (15) and marshy grasslands (5). Different numbers of plots were used due to the natural conditions of these communities, with highest cover for dry grasslands, followed by rocky, moist and marshy grasslands. Data analyses consisted of calculating community indexes and parameters and exploratory multivariate analysis. We verified that c. 15% of species among the 177 registered taxa were highly dominant in the constitution of the vegetation matrix in all communities, whereas most of the species showed low frequency and cover values. Rocky and dry grasslands showed higher similarity and diversity indexes than moist and marshy grasslands. We concluded that the large number of rare or intermediate-frequency species is decisive for the high