Questions
Plant communities in transitional zones between ecosystem types have potentially a large range of ecological strategies, even along short gradients. Exploring these regional differences and ...the drivers of variation is important to understand plant adaptations and changes in ecological processes between distinct ecosystems. Here, we ask whether distinct forest types in the subtropical region present plant communities with distinct ecological strategies and, if so, if these differences are driven by climatic variables.
Location
Subtropical forests in southern Brazil.
Methods
We compiled species lists from 112 sites distributed across rainforests, seasonal forests, Araucaria forests and Pampean forests. We used Grime's CSR scheme and calculated, for each species, CSR values based on information of three leaf traits: leaf area, specific leaf area and leaf dry matter content. Species CSR values were used to calculate the mean value for each community. We selected four climatic variables related to temperate and precipitation and analyzed their influence on plant strategies by linear mixed models.
Results
Our results showed a strong CS component for all subtropical forests studied, with a small contribution from component R. We found clear differences in ecological strategies between forest types: rainforest showed the highest values of component C, and Araucaria and Pampean forests presented the highest values of component S. We found a strong influence of temperature variables on ecological strategies.
Conclusions
Even along a short latitudinal gradient, we found differences in ecological strategies across forest types. Araucaria and Pampean forests were strongly associated with the stress‐tolerant strategy, as they face lower minimum temperatures and/or a larger temperature range, whereas rainforests, which face warmer temperatures and a lower range of variation, presented a strategy where competition is of higher importance. This highlights that regional environmental conditions in this transitional zone influence ecological strategies of tree communities.
Our study shows that CSR ecological strategies (for trees) differ among forest types in subtropical Brazil and that temperature is the main environmental factor affecting these strategies. Araucaria and Pampean forests were more associated with the stress‐tolerant strategy, whereas rainforests showed a higher competition strategy. Even along short gradients, regional environmental conditions can determine species distributions and their ecological strategies.
Seed dispersal influences plant community dynamics and regeneration. Zoochory by cattle is a particularly important type of dispersal in grasslands, but still poorly understood in subtropical ...grasslands. We studied endozoochory in a native grassland area with different grazing intensities, defined by distinct forage allowance levels. On one day in each of the four seasons of the year, dung samples were collected and kept in a greenhouse for germination over one full year. At each dung collection date, a survey of reproducing plants was conducted to relate the species composition of seed within dung to the community in dispersal phase. We used randomisation tests to compare grazing intensities and seasons in terms of dung community richness, abundance and composition. We recorded 93 species in the dung samples, with 65 species in the spring samples, 61 in summer samples, 45 in the autumn samples and 37 in the winter samples. Of the 90 species identified in the vegetation, almost 50% (43 species) also occurred in dung samples. Graminoid herbs presented the largest number of species in all samples. Grazing had no effect on overall seed and species number, but was related to compositional differences in the cattle dung communities. Grazing also influenced the species composition in relation to life cycle, by the increase of annual species at the extremes of our grazing gradient (very high or very low grazing intensities). We conclude that endozoochory by cattle is an important process for the dispersal of native species in the studied system, with potential applications in grassland management and restoration. A better understanding of the strategies involved in seed dispersal is essential to improve knowledge about grassland vegetation regeneration and maintenance.
We studied endozoochory in a native subtropical grassland area with different grazing intensities, in the four seasons of the year. In the dung samples, we found viable seeds from a large number of plant species that represent the typical botanical families of the subtropical grassland system here studied. These results indicate that cattle endozoochory can contribute to grassland vegetation dynamics.
The soil seed bank can be an important source for vegetation regeneration, and data on the similarity between aboveground vegetation and the seed bank can provide information about successional ...pathways after disturbances or land‐use change. We conducted this study in natural grasslands in the subtropical highland region in southern Brazil. We evaluated the effect of silviculture on richness, density, and composition of the seed bank at former grassland sites converted to pine plantations 25 years ago. We worked at six grassland sites and three pine plantation sites and used the seedling emergence method. Seed bank density and richness in grasslands were lower than those reported in similar environments in other regions. Species richness and density varied considerably within each vegetation type; therefore, richness and density were not statistically significant, while composition varied among vegetation types. In terms of species, the pine plantation seed bank was a small subset of the grassland seed bank. Seeds of typical grassland species were missing in the pine plantation, but also had only low abundances in the grassland, and similarity of seed bank and vegetation were low (less than 20%). The low seed density found in this study, including in grasslands areas, indicates that regeneration of species from the soil seed bank likely is of a limited role for the maintenance of plant populations after disturbances in this system. Our data further suggest that natural regeneration after tree planting in grasslands is reduced due to seed limitation.
in Portuguese is available with online material
Resumen
O banco de sementes do solo pode ser uma importante fonte para a recuperação vegetal e dados sobre a similaridade entre vegetação estabelecida e banco de sementes podem prover informações sobre trajetórias de sucessão após distúrbios ou uso do solo. Nós conduzimos este estudo em campos naturais subtropicais de altitude no sul do Brasil. Nós avaliamos o efeito da silvicultura na riqueza, densidade e composição do banco de sementes em locais originalmente campestres convertidos para silvicultura há 25 anos. Nós trabalhamos em seis áreas de campo e três áreas de plantações de pinus e usamos o método de emergência de plântulas. Riqueza e densidade de espécies variaram consideravelmente dentro de cada tipo de vegetação, portanto, riqueza e densidade não foram estatisticamente significativas, enquanto a composição variou entre os tipos de vegetação. O banco de sementes das plantações de pinus foi pequeno subconjunto de espécies do banco de sementes dos campos. Sementes de espécies tipicamente campestres estavam ausentes nas plantações de pinus, mas também apresentaram baixa abundância nos campos, e a similaridade do banco de sementes e da vegetação foi baixa (menos de 20%). A baixa densidade de sementes registrada, inclusive em áreas campestres, indica que a regeneração de espécies do banco de sementes provavelmente tem um papel limitado na manutenção de populações de plantas após distúrbios neste sistema. Nossos dados sugerem que a regeneração natural após silvicultura nos campos é reduzida devido à limitação de sementes.
Understanding how disturbances influence interaction networks is a central but still poorly explored issue in ecology and management. The goal of this study was to test how the structure of ...plant–pollinator networks and the structuring processes are influenced by grazing in a subtropical grassland community on the southern hemisphere. Twelve sampling plots were allocated in order to cover a grazing gradient ranging from overgrazed to ungrazed sites. For each plot, we created a quantitative matrix containing all observed pairwise insect–plant interactions and described morphology, phenology and abundances of each species. We fitted a series of models to test the influence of grazing intensity on metrics describing networks structure. We finally used probabilistic matrices, maximum likelihood and model selection to investigate the processes influencing frequencies of interactions across the gradient of disturbance. Grazing intensity influenced connectance, specialization and interaction evenness, while the number of species and links, nestedness and modularity were less variable. Species abundance was the most important determinant of interaction frequencies regardless of grazing intensity. In contrast to northern hemisphere pollination networks studied so far, these subtropical plant–pollinator networks and their structuring processes were remarkably consistent along the grazing gradient. We argue that this results from the dominance of generalist Asteraceae species, which are selectively avoided by cattle and play a core role in attracting a wide range of pollinators and thereby structuring plant–pollinator interactions, providing therefore stability.
For subtropical Brazilian grasslands, few restoration techniques are established, and seeds of native grassland species are not available on the market. Here, we evaluated the effect of physical ...barriers (PB) on vegetation recovery in a degraded grassland. We considered species that exhibit attributes in their diaspores that facilitate dispersal as well‐dispersed species (WDS) and compared the proportion of WDS at our site to their proportion in the regional species pool. To analyze plots near and distant from the PB, we calculated the extrapolated metrics by an asymptotic estimator (double sample size of each distance). We found 74 species in the degraded area, with higher richness and Shannon diversity values closer to logs, but higher Simpson values with larger distance from logs. Almost half of the species in the degraded area are WDS, more than in the regional species pool. While effects of logs on microsite conditions may also play a role (e.g. logs accumulating organic material or increasing soil moisture, providing shade), our data indicates that the PB works as a seed trap favoring the occurrence of WDS. It seems promising to develop applications in restoration, especially when associating PB with other restoration techniques to increase availability of adequate germination and establishment conditions.
Throughout the world, plantations of tree species (native and exotic) for production purposes make up an important part of tree cover, often at the expense of natural forests. Monocultures of exotic ...and native species generally show a very distinct vegetation physiognomy when compared to natural forests. In the case of abandoned plantations, existing tree regeneration may provide a high potential for restoration of these areas. In this study, we evaluated composition and structure of the adult (upper layer) and regenerative (lower layer) tree component of natural
Araucaria
forest and of monoculture plantations of
Araucaria angustifolia
(Bertol.) Kuntze and
Pinus sp
., and their relationship with edaphic variables and sunshade discontinuity. We aimed to answer the following questions: To which extent do regeneration patterns of native species in the plantations resemble those in natural forests? Does natural regeneration provide a potential for transformation of plantations into natural forests? Does the exotic species regenerate in high abundances, and do other exotic/invasive species establish? Which environmental factors influence regeneration of native species? We expected to find differences in the species composition of the planted areas in relation to the native forest, and more pronounced in the regenerative component. Therefore, the soil parameters and the canopy discontinuity should also be distinct in the distinct vegetation formations. Density of species and tree individuals of the regenerative layer was significantly lower in the plantations, especially in the pine plantation, at the plot level. However, overall species richness was quite similar between vegetation types, with a total of 98 species distributed into 38 families. While light availability did not differ significantly, the soil parameters organic matter, pH, phosphorus and potassium showed significant differences among the vegetation types (in general, lower fertility in plantations). These variables were related to the specific composition of areas, indicating influence of the vegetation on soil conditions and regeneration patterns. Overall, we conclude that restoration of plantations into natural forest based on the existing forest regeneration seems possible, but should be done with caution and under monitoring.
Aims
To identify environmental and anthropogenic drivers of alpha‐ and beta‐diversity for native and alien plant species.
Location
Río de la Plata grasslands, South America (Argentina, Brazil and ...Uruguay; 27.3–39.1°S, 50.1–66.5°W).
Methods
We assembled a data set of 597 vegetation plots distributed across the Río de la Plata grasslands. To assess the drivers of native and alien alpha‐diversity (species richness), we performed a generalized least‐squares regression using environmental and anthropogenic predictors. We evaluated differences in beta‐diversity using Simpson's pairwise dissimilarity between pairs of plots and used multiple regression on distance matrixes to investigate environmental and anthropogenic drivers on compositional dissimilarity for both native and alien plant species.
Results
Native species richness was higher in sites with less demanding environmental conditions, such as lower precipitation seasonality and soils with higher cation exchange capacity. Numbers of alien species were positively related to soil pH, cropland density and road density and negatively to precipitation seasonality, mean temperatures and soil cation exchange capacity. The compositional dissimilarity was similar for native and alien species assemblages (mean ± SD: 0.64 ± 0.16 and 0.64 ± 0.35 respectively). Areas having similar climates and being geographically close shared more taxonomically similar assemblages, for both native and alien assemblages, while soil had disparate effects. Compositional dissimilarity of alien plants decreased with increasing road density.
Conclusions
Our results highlight a grassland ecosystem where native species richness is still shaped only by environmental factors, but both sets of factors influence its composition. On the other hand, alien plants carry a strong signal of both environmental and human factors. As time progresses the number of alien species tend to increase, eroding the patterns of native biodiversity. To avoid this, efforts should be made to reduce road encroachment and the conversion of natural grasslands into croplands.
In the Río de la Plata grasslands, native species richness is still shaped only by environmental factors, but human activities influence its composition. On the other hand, alien plants carry a strong signal of both environmental and human factors.
Allelopathy may be a relevant phenomenon in the dynamics of grasslands, a biome that presents high biodiversity and provides unique ecosystem services. Research on allelopathy in grasslands has been ...conducted worldwide and important suggestions to improve studies have been made in the recent past. However, few general patterns have been established so far. In this review, we report and discuss allelopathy research conducted in grassland ecosystems. We carried out a systematic search for allelopathy studies in grasslands and assessed descriptive, methodological and conceptual aspects of each article. We also evaluated if research quality has improved in recent years. We found that the studies investigated interactions mostly involving herbaceous species in many types of grasslands around the world. The studies have assessed the potential of allelopathy in structuring natural grasslands and artificial pastures and of applying allelopathy to bioherbicide development and to restoration of natural ecosystems. We observed inconsistency in terminology and discussed allelopathy definition. Moreover, we found that in recent years, allelopathy research has improved in some experimental design issues, but not in others. This shows that not all recommendations in literature have been taken into account. Otherwise, innovative methods and analytical tools have emerged. In spite of slow progress, allelopathy has shown potential relevance in dynamics and restoration of grasslands, as well as in weed management in cultivated systems. Thus, a better knowledge about allelopathy can lead to advances in science and in applied fields.
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