Common Grassland Research Articles

Assessment of provenance delineation by genetic differentiation patterns and estimates of gene flow in the common grassland plant Geranium pratense

The use of local provenances in restoration, agriculture and forestry has been identified and widely implemented as a measure for species and community conservation. In practice, provenances are often delineated based on climate, geomorphology and correlated spatial descriptors following the boundaries of larger natural regions. They are thought to comprise genetically homogenous plant material. Here we investigate genetic variation at AFLP loci in 26 natural populations of the regionally common grassland species Geranium pratense, which is often used in seed mixtures. Most studied populations are located in one previously delineated provenance in Germany. We assess within- and among provenance differentiation patterns and aspects of gene flow by investigating the mating system, the genetic structure at regional and local scale, gene dispersal and potential selective mechanisms that may have contributed to differentiation patterns found. Compared to other herbaceous, insect-pollinated grassland species and despite being outcrossed (mean t m = 0.88), G. pratense showed low genetic diversity (mean H E = 0.15), considerable genetic differentiation among populations within provenances (mean pairwise F ST = 0.20) and a pronounced within-population spatial genetic structure (mean Sp = 0.064). A genome scan approach identified three potentially adaptive loci. However, their allelic frequencies were only weakly related to climatic parameters thus providing little evidence for adaptive divergence. Nevertheless, the distribution of genetic diversity and derived gene dispersal estimates indicate limited dispersal ability, suggesting that gene flow at distances larger than 10 km is negligible. Our findings may question the approach of delineating provenances by general criteria, and highlight the importance of species-specific studies on differentiation and adaptation patterns.

Are richness patterns of common and rare species equally well explained by environmental variables?

We investigated relationships between richness patterns of rare and common grassland species and environmental factors, focussing on comparing the degree to which the richness patterns of rare and common species are determined by simple environmental variables. Using data collected in the Machair grassland of the Outer Hebrides of Scotland, we fitted spatial regression models using a suite of grazing, soil physicochemical and microtopographic covariates, to nested sub-assemblages of vascular and non-vascular species ranked according to rarity. As expected, we found that common species drive richness patterns, but rare vascular species had significantly stronger affinity for high richness areas. After correcting for the prevalence of individual species distributions, we found differences between common and rare species in 1) the amount of variation explained: richness patterns of common species were better summarised by simple environmental variables, 2) the associations of environmental variables with richness showed systematic trends between common and rare species with coefficient sign reversal for several factors, and 3) richness associations with rare environments: richness patterns of rare vascular species significantly matched rare environments but those of non-vascular species did not. Richness patterns of rare species, at least in this system, may be intrinsically less predictable than those of common species.

Enhanced nitrogen deposition exacerbates the negative effect of increasing background ozone in Dactylis glomerata, but not Ranunculus acris

The combined impacts of simulated increased nitrogen (N) deposition (75kgNha−1yr−1) and increasing background ozone (O3) were studied using two mesotrophic grassland species (Dactylis glomerata and Ranunculus acris) in solardomes, by means of eight O3 treatments ranging from 15.5ppb to 92.7ppb (24h average mean). A–Ci curves were constructed for each species to gauge effects on photosynthetic efficiency and capacity, and effects on biomass partitioning were determined after 14 weeks. Increasing the background concentration of O3 reduced the healthy above ground and root biomass of both species, and increased senesced biomass. N fertilisation increased biomass production in D. glomerata, and a significantly greater than additive effect of O3 and N on root biomass was evident. In contrast, R. acris biomass was not affected by high N. The study shows the combined effects of these pollutants have differential implications for carbon allocation patterns in common grassland species.

Land-use effects on genetic structure of a common grassland herb: A matter of scale

The most common management practices in European grasslands are grazing by livestock and mowing for silage and hay. Grazing and mowing differ in their potential effects on plant gene flow and resulting population–genetic structure. After assessing its breeding system, we investigated the effect of land use on the population–genetic structure in the common grassland plant Veronica chamaedrys using 63 study populations on meadows, mown pastures and pastures in three regions in Germany, the so-called Biodiversity Exploratories. We determined plant density and analysed the genetic diversity, differentiation and small-scale genetic structure using amplified fragment length polymorphism (AFLP) markers. The breeding system of V. chamaedrys turned out as self-incompatible and outcrossing. Its genetic diversity did not differ among land-use types. This may be attributed to large population sizes and the strong dispersal ability of the species, which maintains genetically diverse populations not prone to genetic drift. Genetic differentiation among populations was low (overall F ST = 0.075) but significant among the three regions. Land use had only weak effects on population differentiation in only one region. However, land use affected small-scale genetic structure suggesting that gene flow within plots was more restricted on meadows than on mown and unmown pastures. Our study shows that land use influences genetic structure mainly at the small scale within populations, despite high gene flow.

The conservation value of restored landfill sites in the East Midlands, UK for supporting bird communities

There has been a rapid decline of grassland bird species in the UK over the last four decades. In order to stem declines in biodiversity such as this, mitigation in the form of newly created habitat and restoration of degraded habitats is advocated in the UK biodiversity action plan. One potential restored habitat that could support a number of bird species is re-created grassland on restored landfill sites. However, this potential largely remains unexplored. In this study, birds were counted using point sampling on nine restored landfill sites in the East Midlands region of the UK during 2007 and 2008. The effects of restoration were investigated by examining bird species composition, richness, and abundance in relation to habitat and landscape structure on the landfill sites in comparison to paired reference sites of existing wildlife value. Twelve bird species were found in total and species richness and abundance on restored landfill sites was found to be higher than that of reference sites. Restored landfill sites support both common grassland bird species and also UK Red List bird species such as skylark Alauda arvensis, grey partridge Perdix perdix, lapwing Vanellus vanellus, tree sparrow, Passer montanus, and starling Sturnus vulgaris. Size of the site, percentage of bare soil and amount of adjacent hedgerow were found to be the most influential habitat quality factors for the distribution of most bird species. Presence of open habitat and crop land in the surrounding landscape were also found to have an effect on bird species composition. Management of restored landfill sites should be targeted towards UK Red List bird species since such sites could potentially play a significant role in biodiversity action planning.

How to increase the value of urban areas for butterfly conservation? A lesson from Prague nature reserves and parks

Cities contain only a low representation of natural and semi-natural habitats, existing in fragments surrounded by built-up areas. In 2003-2004, we surveyed butterflies and Zygaenidae moths in 21 reserves and 4 parks within the city of Prague, Czech Republic, situated from the periphery to city centre. A total of 85 species (47% of the Czech fauna of the study groups) was detected, 22 of them being of conservation concern. Ordination analyses of the local assemblages revealed that the richest sites were large, situated far from the city centre, on alkaline bedrocks, south- to southwest oriented, and hosting high numbers of vegetation types and vascular plant species. We then used generalised linear models to fit responses of individual species to the main ordination gra- dient, corresponding to increasing urbanisation. Out of 60 species that met criteria for the modelling, none responded positively to urbanisation. Twenty displayed negative linear response; these urban avoiders contained a surplus of mesophilous species pre- sumably preferring rural landscapes. Further 29 species (suburban adaptable) responded in domed manners, peaking at the city periphery. Prevailing among them were xerophilous specialists inhabiting large grassland reserves at the Prague outskirts. Finally, eleven urban tolerant species did not respond to urbanisation at all, containing three highly mobile species, three xerothermophilous specialists, and five species utilising shrubs or trees and finding suitable conditions even in urban parks. Suburban adaptable butter- flies apparently benefit from such suburban environments as gardens, road or railway verges, collectively increasing the connectivity of remnants of seminatural habitats. The fact that arboreal species persist even in urban parks, whereas common grassland species are absent there, implies that the quality of urban habitats might be increased by a more sensitive management of urban green spaces, such as leaving aside small temporary fallows or adapting lawns mowing schemes.

Distribution of gastropods in floodplain compartments and feeding preferences for river corridor plant species: Is there an effect of gastropod herbivory on the distribution of river corridor plants?

Herbivory through gastropods has among others been proposed as a potential factor responsible for the river corridor distribution of plant species, which is a well known but poorly understood ecological pattern. Since floodplains are characterised by seasonally changing abiotic conditions, viz. floods during winter and spring and severe summer drought that are unsuitable for gastropods they may present safe habitats for highly palatable plant species. In the present study we compared species composition of gastropods and vegetation of twelve grassland sites situated within three floodplain compartments along the Upper Rhine. Additionally, we studied the palatability of 7 days and 25 days old seedlings of five typical floodplain plant species and five mesic grassland species to the slug Deroceras reticulatum in laboratory experiments. Our results showed that both vegetation and gastropod community composition but not gastropod diversity and abundance differed between floodplain compartments. Owing to omnivory of most gastropods the similarity structure of sites based on plants and gastropods was not significantly correlated. In general, slug herbivory significantly reduced survival and biomass of 7 days old seedlings, but responses were species-specific. In contrast, with the exception of Arabis nemorensis, Viola pumila and Taraxacum sect. Ruderalia biomass of 25 days old seedlings was not significantly affected by slug herbivory. Although the response of floodplain plant species as a group to slug herbivory did not differ from common grassland species, our results suggest that gastropods may potentially influence the distribution pattern of the highly palatable river corridor species Arabis nemorensis and Viola pumila. However, further research is needed to estimate the damage to river corridor plants through gastropod herbivory and its effect on competitive relationships under natural conditions.

Temporal dynamics of soil nematode communities in a grassland plant diversity experiment

We report here on an 8-year study examining links between plant and nematode communities in a grassland plant diversity experiment, located in the north of Sweden on previous agricultural soil. The examined plots contained 1, 4 and 12 common grassland plant species from three functional groups; grasses, legumes and forbs. The same plant species composition was maintained in the plots through weeding and resowing during the experimental period. The hypotheses were (i) that the nematode community would shift towards a more diverse and mature fauna over time and (ii) that the effects of both plant species identity and plant species richness would increase over time. As hypothesized, the Bongers’ Maturity Index (a measure of nematode responses to disturbance) increased over time, but not nematode diversity. Instead, the nematode community development in the present grassland experiment seemed to be more characterized by shifts in dominance patterns than by colonization of new taxa. Clear temporal trends were found for plant-feeders and Adenophorea bacterial-feeders which increased in abundance over time in almost all plant treatments. Rhabditidae bacterial-feeders decreased in abundance over time, in particular in plots with legumes. Fungal-feeders, omnivores/predators and the two nematode indices PPI (Bongers’ Plant Parasitic Index) and NCR (Nematode Channel Ratio) had significant interactions between plant composition and time giving some support to our second hypothesis. Our results highlight the need for long-term experiments to examine plant species effects on soil fauna, especially on taxa belonging to higher trophic levels. The results also stress the importance of plant composition for belowground soil faunal communities. ► Nematode community development was more characterized by shifts in dominance patterns than by colonization of new taxa. ► Bongers’ Maturity Index (a measure of nematode responses to disturbance) increased over time. ► A divergence in the nematode community composition among the plant treatments in year 8. ► A significant effect of plant species composition on omnivorous/predacious nematodes, as well as an interaction effect with time.

New fears over bee declines

Summary Around the world, losses of bee colonies and wild pollinators continue. Emerging explanations are complex and call for more research, but the case against systemic pesticides is gaining strength. Michael Gross investigates.

Geographic variation in the response to drought in nine grassland species

Summer precipitation is expected to decrease in Europe due to climate change, which in turn will increase the risk for plants to suffer from drought. To maintain ecosystem functions in grasslands under the conditions of climate change, drought adapted varieties of plant species may be needed. With our experiment, we bridge the gap between single species experiments and field experiments with whole plant communities under proposed scenarios of climate change. In a greenhouse experiment, we investigated the drought response of nine common grassland species which are normally utilized for restoration of mesic grasslands. We chose five European provenances of each species to test for a consistent, provenance-specific drought response. Plants of all nine species were negatively affected by drought with respect to their biomass production, and consistently allocated less resources to roots than control plants. On the other hand, reproductive allocation increased under drought conditions in some species whereas no response to drought could be detected in specific leaf area. In contrast to our expectation, we found little evidence for intraspecific variation in response to simulated drought. However, we found a clear correlation between responsiveness in root allocation, and climatic conditions at the provenance's origin. This pattern became evident only when all species were analysed together, highlighting the advantage of multi-species experiments.

Problem of Applying Sodium Selenate to Increase Selenium Concentration in Grassland Plants in Southern Belgium

In a survey of grasslands, mean selenium (Se) concentration in Holcus lanatus was 83 μg kg−1 (less than 100 μg kg−1, the minimal concentration protecting mammals from deficiency disorders). Despite rather high levels of soil extractable Se, plant Se availability was supposed to be low because of high soil humus concentration. A pot experiment with common grassland species showed contrasting responses to selenate addition (9 g Se ha−1 yr−1). Lolium perenne leaves reached 470 μg kg−1, and Trifolium pratense reached 292 μg kg−1. The controls were less than 100 μg kg−1. Leaves of others species showed greater values both in control and treated series and no significant difference. In a second pot experiment, Melilotus albus, a supposed secondary accumulator, and Lolium perenne as a control were submitted to moderate increased selenate additions (up to 45 g Se ha−1 yr−1). The results confirmed that Melilotus albus was a better accumulator with a leaf concentration that could reach the toxicity level of 2 mg kg−1.

Gene flow from foreign provenances into local plant populations: Fitness consequences and implications for biodiversity restoration

Long-distance transplantation of seed material as done in restoration programs has raised concerns about the risks associated with the introduction of maladapted genotypes that may hybridize with neighboring native conspecifics and decrease local population fitness (outbreeding depression). We studied the consequences of gene flow from foreign provenances into local populations in the common grassland species Plantago lanceolata (Plantaginaceae). Three generations of intraspecific hybrids (F(1), F(2), and backcross to the local plants) were produced by controlled crossings between local plants and plants from geographically or environmentally distant populations. Their performance was compared to that of within-population crosses in a field experiment. Early growth in some interpopulation hybrids was significantly reduced, and this decrease in performance was higher in progeny of crosses with the local population from a different habitat than with geographically distant populations. At the end of the growing season, most fitness-related traits of the interpopulation hybrids were close to the average of their parents. Crosses with low-performing foreign parents therefore resulted in reduced fitness of the hybrids compared to the local plants and dilution of local adaptation. We conclude that the introduction of maladapted populations from distant or ecologically distinct environments might, at least temporarily, decrease the fitness of neighboring local plants.

Despite high uptake efficiency, non‐mycorrhizal Rumex acetosella increases available phosphorous in the rhizosphere soil, whereas Viscaria vulgaris, Plantago lanceolata and Achillea millefolium does not

The phosphorous (P) uptake efficiency, reduction of the soil extractable P, and the root morphology was determined for the four common grassland species Rumex acetosella, Viscaria vulgaris, Plantago lanceolata and Achillea millefolium in one pot cultivation and one microcosm experiment. Rumex acetosella produced more than tree times as much biomass as each of V. vulgaris, P. lanceolata and A. millefolium, and could maintain a P concentration in the tissue that was twice as high as in the other species. R. acetosella was able to take up 10 times more phosphorous than the other species but the high uptake was not reflected in reduced Olsen P levels in the root affected soil. Calculating the uptake efficiency of the roots with a diameter less than 0.5 mm showed that the P uptake, calculated per root area, had been more efficient in R. acetosella than in the other species. The calculated rhizosphere volume (explored by the plant) seemed to correlate with the higher uptake efficiency of R. acetosella. We can conclude that R. acetosella have mechanisms to maintain a high P availability in the soil and may sustain a high uptake without any mycorrhizal interactions.

Real‐time vision‐based detection of Rumex obtusifolius in grassland

van Evert FK, Polder G, van der Heijden GWAM, Kempenaar C & Lotz LAP (2009). Real‐time vision‐based detection of Rumex obtusifolius in grassland. Weed Research49, 164–174.Summary Rumex obtusifolius is a common grassland weed that is hard to control in a non‐chemical way. The objective of our research was to automate the detection of R. obtusifolius as a step towards fully automated mechanical control of the weed. We have developed a vision‐based system that uses textural analysis to detect R. obtusifolius against a grass background. Image sections are classified as grass or weed using 2‐D Fourier analysis. We conducted two experiments. In the first (laboratory) experiment, we collected 28 images containing R. obtusifolius and 28 images containing only grass. Between 23 and 25 of 28 images were correctly classified (82–89%) as showing R. obtusifolius; all grass images were correctly classified as such. In the second (field) experiment, a self‐propelled platform was used to obtain five sequences of images of R. obtusifolius plants. We used the parameters that gave the best classification results in the first experiment. We found, after changing one of the algorithm’s parameters in response to prevailing light conditions, that we were able to detect R. obtusifolius in each image of each sequence. The algorithm scans a ground area of 1.5 m2 in 30 ms. We conclude that the algorithm developed is sufficiently fast and robust to eventually serve as a basis for a practical robot to detect and control R. obtusifolius in grassland.

Habitat Change and Plant Demography: Assessing the Extinction Risk of a Formerly Common Grassland Perennial

An important aim of conservation biology is to understand how habitat change affects the dynamics and extinction risk of populations. We used matrix models to analyze the effect of habitat degradation on the demography of the declining perennial plant Trifolium montanum in 9 calcareous grasslands in Germany over 4 years and experimentally tested the effect of grassland management. Finite population growth rates (lambda) decreased with light competition, measured as leaf-area index above T. montanum plants. At unmanaged sites lambda was <1 due to lower recruitment and lower survival and flowering probability of large plants. Nevertheless, in stochastic simulations, extinction of unmanaged populations of 100 flowering plants was delayed for several decades. Clipping as a management technique rapidly increased population growth because of higher survival and flowering probability of large plants in managed than in unmanaged plots. Transition-matrix simulations from these plots indicated grazing or mowing every second year would be sufficient to ensure a growth rate > or =1 if conditions stayed the same. At frequently grazed sites, the finite growth rate was approximately 1 in most populations of T. montanum. In stochastic simulations, the extinction risk of even relatively small grazed populations was low, but about half the extant populations of T. montanum in central Germany are smaller than would be sufficient for a probability of survival of >95% over 100 years. We conclude that habitat change after cessation of management strongly reduces recruitment and survival of established individuals of this perennial plant. Nevertheless, our results suggest extinction processes may take a long time in perennial plants, resulting in an extinction debt. Even if management is frequent, many remnant populations of T. montanum may be at risk because of their small size, but even a slight increase in size could considerably reduce their extinction risk.

Regional population viability of grassland songbirds: Effects of agricultural management

Although population declines of grassland songbirds in North America and Europe are well-documented, the effect of local processes on regional population persistence is unclear. To assess population viability of grassland songbirds at a regional scale (∼150,000 ha), we quantified Savannah Sparrow Passerculus sandwichensis and Bobolink Dolichonyx oryzivorus annual productivity, adult apparent survival, habitat selection, and density in the four most (regionally) common grassland treatments. We applied these data to a female-based, stochastic, pre-breeding population model to examine whether current grassland management practices can sustain viable populations of breeding songbirds. Additionally, we evaluated six conservation strategies to determine which would most effectively increase population trends. Given baseline conditions, over 10 years, simulations showed a slightly declining or stable Savannah Sparrow population (mean bootstrap λ = 0.99; 95% CI = 1.00–0.989) and severely declining Bobolink population (mean bootstrap λ = 0.75; 95% CI = 0.753–0.747). Savannah Sparrow populations were sensitive to increases in all demographic parameters, particularly adult survival. However for Bobolinks, increasing adult apparent survival, juvenile apparent survival, or preference by changing habitat selection cues for late-hayed fields (highest quality) only slightly decreased the rate of decline. For both species, increasing the amount of high-quality habitat (late- and middle-hayed) marginally slowed population declines; increasing the amount of low-quality habitat (early-hayed and grazed) marginally increased population declines. Both species were most sensitive to low productivity and survival on early-hayed fields, despite the fact that this habitat comprised only 18% of the landscape. Management plans for all agricultural regions should increase quality on both low- and high-quality fields by balancing habitat needs, nesting phenology, and species’ response to management.

Long term grassland vegetation changes: Case study Nature Park Stara Planina (Serbia)

Changes in grassland flora and vegetation caused by inadequate management, primarily under-grazing and grasslands abandonment were studied in the south-east region of Serbia — Mt. Stara Planina, the largest mountain massif of the country. This mountain is one of the major centres of tertiary and endemic-relict plant species that remains in ravines, and glacial relics and mountain endemic species. The paper presents an analysis and comparison of previous (about 30 years ago) and current biodiversity of the most common grasslands, such as: ass. Festuco-Agrostietum vulgaris, Agrostio-Asphodeletum albae, Koelerietum montanae, Agrostietum vulgaris, Festucetum spadiceae, Nardetum strictae, Poetum molinerii-Plantaginetum carinatae, Poetum violaceae and Seslerietum coerulantis . Both environmental and human impacts on grassland vegetation were discussed and a proposal of sustainable grassland use and management is given.

Avian community response to vegetation and structural features in grasslands managed with fire and grazing

This study examined the importance of natural and manmade structural features on the avian community relative to management-induced vegetation dynamics. The study was conducted within the context of two alternative vegetation management treatments applied to pastures on a tallgrass prairie site in northcentral Oklahoma from 2001 to 2003. The brown-headed cowbird, a brood parasite, and the grasshopper sparrow, a common grassland obligate species, were most abundant in areas managed under a traditional treatment in which entire pastures were annually burned. Conversely, Henslow’s sparrow, a grassland obligate of conservation concern, was completely absent from traditional treatment pastures. Total bird species diversity and grassland obligate richness was highest in the patch-burn treatment, in which only discrete portions of each pasture were burned each year to create a mosaic of vegetation ‘patches’ in various stages of recovery from disturbance. Models of bird abundance reflected not only species-specific vegetation preferences, but also the often negative influence of structural features such as woody edges, roads, and ponds on breeding bird use of grasslands. Our study demonstrated that both disturbance-derived vegetation attributes and structural features contribute to heterogeneity and influence subsequent use by and composition of grassland bird communities.

Complementarity among species in horizontal versus vertical rooting space

Aims: Many experiments have shown a positive effect of species richness on productivity in grassland plant communities. However, it is poorly understood how environmental conditions affect this relationship. We aimed to test whether deep soil and limiting nutrient conditions increase the complementarity effect (CE) of species richness due to enhanced potential for resource partitioning. Methods: We grew monocultures and mixtures of four common grassland species in pots on shallow and deep soil, factorially combined with two nutrient levels. Soil volume was kept constant to avoid confounding soil depth and volume. Using an additive partitioning method, we separated biodiversity effects on plant productivity into components due to species complementarity and dominance. Important findings: Net biodiversity and complementarity effects were consistently higher in shallow pots, which was unexpected, and at the low nutrient level. These two results suggest that although belowground partitioning of resources was important, especially under low nutrient conditions, it was not due to differences in rooting depths. We conclude that in our experiment (i) horizontal root segregation might have been more important than the partitioning of rooting depths and (ii) that the positive effects of deep soil found in other studies were due to the combination of deeper soil with larger soil volume.

The influence of below‐ground herbivory and defoliation of a legume on nitrogen transfer to neighbouring plants

Summary Both foliar and root herbivory can alter the exudation of carbon from plant roots, which in turn can affect nitrogen availability in the soil. However, few studies have investigated the effects of herbivory on N fluxes from roots, which can directly increase N availability in the soil and uptake by neighbouring plants. Moreover, the combined effects of foliar and root herbivory on N fluxes remains unexplored. We subjected the legume white clover (Trifolium repens L.) to defoliation (through clipping) and root herbivory (by an obligate root‐feeding nematode, Heterodera trifolii Goggart) to examine how these stresses individually, and simultaneously, affected the transfer of T. repens‐derived N to neighbouring perennial ryegrass (Lolium perenne L.) plants using 15N stable‐isotope techniques. We also examined the effects of defoliation and root herbivory on the size of the soil microbial community and the growth response of L. perenne. Neither defoliation nor root herbivory negatively affected T. repens biomass. On the contrary, defoliation increased root biomass (34%) and total shoot production by T. repens (100%). Furthermore, defoliation resulted in a fivefold increase in T. repens‐derived 15N recovered in L. perenne roots, and increased the size of the soil microbial biomass (77%). In contrast, root herbivory by H. trifolii slightly reduced 15N transfer from T. repens to L. perenne when T. repens root 15N concentration was included as a covariate, and root herbivory did not affect microbial biomass. Growth of L. perenne was not affected by any of the treatments. Our findings demonstrate that defoliation of a common grassland legume can substantially increase the transfer of its N to neighbouring plants by directly affecting below‐ground N fluxes. These finding require further examination under field conditions but, given the prevalence of N‐limitation of plant productivity in terrestrial ecosystems, increased transfer of N from legumes to non‐N‐fixing species could alter competitive interactions, with implications for plant community structure.