Gerhard E. Overbeck

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.

Toward an old‐growth concept for grasslands, savannas, and woodlands

We expand the concept of “old growth” to encompass the distinct ecologies and conservation values of the worlds ancient grass-dominated biomes. Biologically rich grasslands, savannas, and open-canopy woodlands suffer from an image problem among scientists, policy makers, land managers, and the general public, that fosters alarming rates of ecosystem destruction and degradation. These biomes have for too long been misrepresented as the result of deforestation followed by arrested succession. We now know that grassy biomes originated millions of years ago, long before humans began deforesting. We present a consensus view from diverse geographic regions on the ecological characteristics needed to identify old-growth grasslands and to distinguish them from recently formed anthropogenic vegetation. If widely adopted, the old-growth grassland concept has the potential to improve scientific understanding, conservation policies, and ecosystem management.

Fine‐scale post‐fire dynamics in southern Brazilian subtropical grassland

Abstract Question: How does fire influence species richness and diversity in subtropical grassland in southern Brazil? Location: Recurrently burned grassland in Porto Alegre, Brazil (30°03′ S, 51°07′ W; max. altitude 311 m a.s.l.) and abandoned grassland near São Francisco de Paula, Brazil (29°47′ S, 50°22′ W; ca. 900 m a.s.l.). Methods: In the burned grassland, between-year changes in community composition and single-plot diversity, species number and vegetation structure were analysed in two consecutive years for plots with different time since last fire. Responses to fire of individual species were analysed. At the abandoned site, diversity, species number and vegetation structure were examined. Results: Species number and small-scale species turnover were highest ca. one year after the burn, and decreased as caespitose grasses increased in cover with time since fire until reaching a stable, but less diverse state three to four years after a fire. The abandoned grassland showed higher dominance of caespitose grasses and lower richness and diversity. Conclusions: Fire clearly leads to a short-term increase in species richness and diversity at the plot scale, as competitive interactions are being reduced and recruitment possibilities are high in early post-fire vegetation development. Overall community composition does not change after a fire. While small herbs seem to be slightly favoured in the early post-fire environment, no clear group of fire following species (absent in vegetation unburned for longer) was observed. The results indicate that the community is adapted to the current fire regime and is being maintained under the influence of fire.

Tyranny of trees in grassy biomes.

![Figure][1] Highland grassland in Brazil is considered a forest landscape restoration opportunity PHOTO: G. W. FERNANDES Tree planting, fire suppression, and exclusion of megafaunal herbivores (native or domestic) are ecologically reasonable restoration strategies in deforested landscapes

Floristic composition, environmental variation and species distribution patterns in burned grassland in southern Brazil

In regularly burned grassland on Morro Santana, Porto Alegre, RS, Brazil, we investigated differences in the floristic composition and their relation to soil properties, aspect and distance from the forest border. In 48 plots of 0.75 m2, we identified a total of 201 species from a local species pool of approximately 450 to 500 species. Most species occurred in low frequencies, showing clumpy distribution patterns in the studied area. Multivariate analysis showed that plots close to the forest edge clearly differed from plots in the open grassland concerning composition and structure. Plots exposed to the north differed from plots on the top of the hill both in the composition of species as well as in soil variables, mainly due to shallower soil in the former. No strong relation between soil properties and variation in vegetation composition could be detected at a finer scale. The studied grassland, as all grassland vegetation in southern Brazil, is very rich in species compared to other grassland formations worldwide. However, this high biodiversity and conservational value of Campos vegetation in general has so far not been recognized properly. Disturbance is essential to maintain this open vegetation type and its species richness. Fire should be considered as a management option in the absence of grazing.

Late-Holocene fire history in a forest-grassland mosaic in southern Brasil: Implications for conservation

ABSTRACT Question: Is the diverse mosaic of forest/grassland (Campos) vegetation on the hills in the Porto Alegre region natural or of anthropogenic origin? What are the best approaches to management and conservation of forest/grassland mosaics in southern Brazil? Location: 280 m a.s.l., Rio Grande do Sul State (30°04′32″S; 51°06′05″W, southern Brazil. Methods: A 50-cm long radiocarbon dated sediment core from a swamp on Morro Santana was analysed for pollen and charcoal, and multivariate data analysis was used to reconstruct past vegetation and fire dynamics. Results: The formation of swamp deposits is related to a change to wetter climatic conditions since 1230 cal yr BP. The diverse forest/grassland mosaic existed already at that time and can be seen as natural in origin as it has been also shown from other studies in southern Brazil. Since 580 cal yr BP, forests expanded continuously. The marked higher occurrence of the pioneer Myrsine during the last 70 years, indicates a change in the disturbance regime. In the past, vegetation has been influenced by mostly anthropogenic fire, set first by Amerindians and later by European settlers. Conclusions: Management for conservation of forest/grassland mosaics should take into account, first, that grasslands are remnants of earlier drier Holocene periods and not a result of deforestation and, second, the history of disturbance by grazing and fire. Suppression of grazing and burning has likely resulted in a trend towards more woody vegetation under modern wet climatic conditions. If management for conservation excludes fire, the present grassland patches will tend to disappear due to forest expansion under the modern humid climate. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire. Abbreviations AD = Anno Domini; AMS = Accelerator mass spectrometry; Cal yr BP = calibrated years before 1950; PCoA= Principal Coordinates Analysis

Seedling recruitment of Succisella inflexa in fen meadows: Importance of seed and microsite availability

Abstract The effects of different forms of land use on germination and establishment of the rare fen species Succisella inflexa were investigated in seed introduction experiments in a mown and an abandoned fen meadow in SE Germany. Treatments included abandonment, mowing in fall and mowing with creation of gaps in the moss and litter layer. Floating capacity of seeds was tested in order to estimate potential dispersal by water. On the mown meadow, gaps had a slightly positive effect on germination rates, while greatly increasing seedling survival until the next spring. At the abandoned site, litter inhibited germination, whereas mosses had a negative effect on germination and a positive effect on survival rates during the first year after germination. Both germination and seedling establishment were negatively affected by the presence of slug herbivores. On the abandoned site, no seedlings at all survived until the next spring. Even though seeds of Succisella inflexa were capable to float for several weeks and to germinate thereafter, the situation at the field sites indicates that long-distance dispersal is highly unlikely. Our results showed that not only direct effects of abandonment, such as accumulation of litter, may have led to poor germination and poor seedling establishment of the species. Additionally, indirect consequences of changes in land use, such as higher seedling herbivory by slugs and successional vegetation changes due to abandonment, were important in determining habitat quality and availability of microsites for seedling recruitment. Furthermore, early mowing imposed seed limitation on plant populations. Nomenclature: Oberdorfer (1994) for vascular plants; Frahm & Frey (1992) for mosses.

How much do we know about distribution and ecology of naturalized and invasive alien plant species? A case study from subtropical southern Brazil

AbstractMegadiverse tropical and subtropical countries may be especially at risk from exotic species invasions. However, for these regions, the number of studies on invasive species is low. This paper aims at synthesizing knowledge on the alien herbaceous and shrub flora in the state of Rio Grande do Sul, southern Brazil, considering both presence of alien species in different vegetation types and availability of trait data. Our database is an extensive list of different studies that present vegetation data or species lists in the state. Trait data was gathered from a large number of sources. Only a small portion of alien plants was found with higher frequency in the analyzed studies, some of them species considered to be invasive. However, the data set available for our study clearly is biased towards well-conserved vegetation, and vegetation types that likely contain larger proportions of alien species have been poorly studied. On the basis of the existing data, it is impossible to assess impact of the large majority of the species considered to be invasive. Ordination analysis of alien species described by traits revealed no clear set of traits associated to species that are considered to be invasive, even though some broad patterns became obvious: C4 grasses of African origin, a group that includes several invasive species, were separated from the large majority of species, and very few invasives are among the large group of European forbs. Overall, we conclude that lack of data is a serious impediment to an evaluation of the risk posed by invasive species for the study region.

Ecological literacy and beyond: Problem-based learning for future professionals

Ecological science contributes to solving a broad range of environmental problems. However, lack of ecological literacy in practice often limits application of this knowledge. In this paper, we highlight a critical but often overlooked demand on ecological literacy: to enable professionals of various careers to apply scientific knowledge when faced with environmental problems. Current university courses on ecology often fail to persuade students that ecological science provides important tools for environmental problem solving. We propose problem-based learning to improve the understanding of ecological science and its usefulness for real-world environmental issues that professionals in careers as diverse as engineering, public health, architecture, social sciences, or management will address. Courses should set clear learning objectives for cognitive skills they expect students to acquire. Thus, professionals in different fields will be enabled to improve environmental decision-making processes and to participate effectively in multidisciplinary work groups charged with tackling environmental issues.

South Brazilian Forest-Grassland Ecotones: Dynamics Affected by Climate, Disturbance, and Woody Species Traits

The southernmost part of Brazil is characterized by extended grasslands—the southern Campos. In some parts of the region, these grasslands occur in close contact with different forest types of the Atlantic forest biome or riparian forests, forming mosaics. Otherwise, they form large and continuous areas toward south and southwest, where they reach the Pampa grassland of Uruguay and Argentina. Throughout this region, forest expansion and/or shrub encroachment can be observed and have been related both to site conditions (abiotic variables and disturbance regimes) and climatic changes. We know today, based on studies of pollen records from peat profiles, that expansion of woody vegetation throughout the past centuries was driven by changes in the climatic conditions towards a climate increasingly favorable for forest development, and evidence exists that this process is halted or at least slowed down as consequence of land use and disturbances. Current vegetation dynamics in forest-grassland ecotones thus likely are linked both to climatic changes (on the regional scale) and vegetation management and/or disturbance regime (on the local scale).