Plant Species Richness In Grasslands Research Articles

Effects of fragmentation on grassland plant diversity depend on the habitat specialization of species

Evaluating the impacts of habitat loss and fragmentation is essential for biodiversity conservation. However, an understanding of how habitat loss and fragmentation interact and affect biodiversity is limited. Based on 134 landscapes in the agro-pastoral ecotone of northern China selected by a stratified random sampling approach, we used a structural equation model to evaluate the direct effects of habitat loss and its indirect effects (via habitat fragmentation, including edge density, patch density, mean patch area, and mean nearest-neighbor distance) on grassland plant species richness (including specialists and weeds) at the landscape scale. Our results show that habitat loss had a direct negative effect on overall species richness and grassland specialist richness but a positive effect on weed richness. Meanwhile, the increase in patch density caused by habitat loss had a positive effect on overall species richness and grassland specialist richness. These results indicate that the effects of habitat loss and fragmentation can differ for habitat specialists and generalists. Increasing the number of habitat patches in the landscape could increase the species richness of habitat specialists. Our findings emphasize the importance of the management of adding habitat patches in fragmented landscapes for conserving habitat specialists.

Geographical divergence of species richness and local homogenization of plant assemblages due to climate change in grasslands

In arid and semi-arid regions worldwide, grassland plant species richness is highly sensitive to climate change. Studies assessing local grassland richness patterns have yielded inconsistent trends toward climate change, partly due to differences in recording approaches, environmental conditions, and local flora. Remote sensing presents a valuable opportunity to investigate plant richness–climate change relationships in grasslands across large environmental gradients. Based on spectral diversity indices extracted from Landsat satellite imagery, we explore how plant diversity responds to climate change and aim to determine the major climatic drivers of plant diversity patterns in ten grassland nature reserves worldwide. Plot‐level plant richness was correlated with 19 bioclimatic variables through stepwise linear regression for each climate change scenario in every nature reserve. The performance of the models was assessed according to the model accuracy. We used the fitted models between climatic variables and plant richness from 1990 to 2000 to predict plant richness in 2050 and 2070 under 33 climatic change scenarios for 1120 plots in each reserve. A general tendency toward a decrease in the plot-level plant richness and beta (β)-diversity in the future decades were observed in most cases, although there also were some opposite trends in plant richness. The dominant bioclimatic predictors involved in predictive models varied across sites. Spectral plant richness responses diverge geographically, while β-diversity generally declines under climate change scenarios. Over the next decades, the expected homogeneities in plant species across grasslands encountered on different continents will likely lead to the dominance of climate generalist species. Policy-makers and conservationists therefore need to urgently develop strategies to ensure plant survival, particularly that of locally endemic species under predicted climatic scenarios; human assistance may be required when adjusting their distribution ranges.

Effect of Grazing System on Grassland Plant Species Richness and Vegetation Characteristics: Comparing Horse and Cattle Grazing

Horses are of increasing relevance in agriculturally managed grasslands across Europe. There is concern to what extent grazing with horses is a sustainable grassland management practice. The effect of longer-term horse grazing on the vegetation characteristics of grasslands has received little attention, especially in comparison to grazing cattle. Our study analyses the relative importance of grazing system (grazer species and regime) and grassland management for vegetation characteristics in grasslands as indicator for sustainable management. We monitored grassland vegetation in western central Germany and compared paddocks grazed by horses under two different regimes, continuous (HC) vs. rotational (HR), to paddocks grazed by cattle (C) under similar trophic site conditions. We observed more plant species and more High Nature Value indicator species on HC compared to C. The vegetation of C was more grazing tolerant and had higher forage value than HC. Regardless of the grazing regime, the competitive component was lower, the stress-tolerant component higher and the floristic contrast between patch-types stronger on HC and HR paddocks compared to C. Species richness was strongly influenced by the extent of the floristic contrast. Our results emphasize the potential of horse grazing for biodiversity in agriculturally managed grasslands.

Increasing amount and quality of green infrastructures at different scales promotes biological control in agricultural landscapes

Green infrastructures are key elements for the delivery of ecosystem services in agricultural landscapes. However, how to combine quality and quantity of green infrastructures at multiple spatial scales to optimize the delivery of ecosystem services remains largely unknown. In this study, we investigated how hedgerow amount in the landscape modulated the local effect of grassland quality (plant species richness) on the spillover of biological pest control services in adjacent sunflower fields. We quantified biological pest control and predator communities in 23 adjacent sunflower-grassland field couples selected along two uncorrelated gradients: a gradient of plant species richness in grassland and a gradient of hedge length in the landscape. Our study shows that increasing the amount or the quality of green infrastructures can enhance biological pest control in adjacent crops but that the effects depend on the pest considered. We found that weed seed predation depends only on hedge length in the large scale landscape, while aphid predation depends on plant species richness in the adjacent grassland and on the hedge length in the immediate landscape. Also, the abundance of spiders affects aphid predation suggesting a key role of this functional group for controlling aphids in sunflower fields. This study suggests that management options based on increasing local plant species richness should be prioritized in landscapes with low amount of hedgerows, and confirms the fact that increasing hedgerow networks should promote pest control services.

Mediterranean cork oak wooded grasslands: synergies and trade-offs between plant diversity, pasture production and soil carbon

Mediterranean wooded grasslands that emerge from silvopastoral activities are multifunctional systems that result in high biodiversity and offer ecosystem services such as forage production and soil carbon sequestration. During 3 years, ten grazed wooded grassland fields were studied in the Berchidda–Monti long-term observatory, located in NE Sardinia, Italy, with the aim of exploring the synergies and trade-offs between biodiversity and selected ecosystem services. Positions below and outside the canopy of three cork oak trees in each field were randomly selected to compare seasonal pasture production, pasture utilization rate by animals, botanical composition, biodiversity indicators (Shannon index and plant species richness) and soil organic carbon. In autumn, dry matter production of pasture was similar in the two positions; in two winters out of three it was greater below the trees than outside, and in spring it was greater outside than below the trees. While plant species richness and Shannon index were not significantly influenced by the position, the overall wooded grassland plant species richness was 31% higher than that outside of the tree crown. The soil organic carbon content in the 0–40-cm soil layer was also higher below the trees. Our findings highlight that if the main purpose of the wooded grasslands is to provide forage for grazing animals rather than conserving and/or enhancing plant diversity and soil fertility, the presence of trees constrains the overall forage productivity, although the greater forage availability in winter under the trees can contribute to improve the seasonal distribution of forage production.

Interpreting the effects of landscape connectivity on community diversity

Landscape connectivity is considered a key factor regulating species diversity of natural and managed landscapes, yet the influence of connectivity relative to other factors remains poorly resolved. In this issue of Journal of Vegetation Science, Jakobsson and colleagues illustrate how grassland plant species richness is more strongly affected by the age and management of grassland patches than by connectivity.

Height and clonality traits determine plant community responses to fertilization

Fertilization via agricultural inputs and nutrient deposition is one of the major threats to global terrestrial plant richness, yet we still do not fully understand the mechanisms by which fertilization decreases plant richness. Tall clonal species have recently been proposed to cause declines in plant species richness by increasing in abundance in response to fertilization and competing strongly with other species. We tested this hypothesis in a fertilization experiment in a low productivity grassland by using a novel experimental manipulation of the presence vs. absence of clonal species and by examining the role of height within these treatments. We found that fertilization decreased species richness more in the presence than absence of clonal species. We also found that only tall species increased in biomass in response to fertilization. In the absence of clonal species, fertilization increased biomass of tall nonclonal species. However, in the presence of clonal species, fertilization decreased tall nonclonal biomass and only tall clonal biomass increased. Fertilization caused almost all short species to be lost in the presence, but not the absence, of clonal species and caused greater declines in the mean and variance of light levels in the presence of clonal species. These results show that the traits of species in a community can determine the magnitude of species loss due to fertilization. The strongly negative effect of tall clonals on species richness in fertilized plots is likely a result of their capacity to decrease light levels to a greater extent and more uniformly than nonclonal species, and thereby drive the exclusion of short species. These results help clarify the mechanisms whereby fertilization decreases grassland plant species richness and suggest that efforts to prevent the loss of species under fertilized conditions may be most effective when they focus on controlling the biomass of tall clonal species.

Equivalence of grasslands in an ecological network and a World Heritage Site

Ecological networks (ENs) of indigenous vegetation among commercial forestry plantations have been implemented to offset the negative effects of the alien plantation trees on local biodiversity. However, it is not known whether these ENs are equivalent to protected areas (PAs) in terms of their grassland biodiversity. To address this knowledge gap, we investigated how well grassland plant species richness and composition in an EN corresponds to similar habitats in an adjacent PA. This took place in grasslands on the east coast of South Africa, and was done at four paired sites using ten replicates at each of the eight sites. Pairwise comparisons (EN vs. PA) of plant species composition yielded statistically smaller differences than comparisons between different pairs of sites within either the EN or PA, illustrating considerable turnover of species whether or not they were in an EN or PA. Overall, there were fewer plant species in the EN for three of the four pairs of sites. Nevertheless, plant species composition was similar in each pair of sites. The grassland EN was also characterized by greater maximum vegetation height and less green vegetation cover. When differences between the EN and a PA were viewed against the natural variation of abiotic and biotic conditions across the landscape, they were small. We conclude that ENs of natural habitat contribute substantially to biodiversity conservation in transformed, commercially-productive landscapes, are almost as good as PAs for maintaining grassland plant diversity.

Plant diversity is associated with the amount and spatial structure of soil heterogeneity in meadow steppe of China

The link between environmental heterogeneity and diversity is a major tenet of plant ecology. Previous studies designed to test the heterogeneity–diversity hypothesis largely have only included measures characterizing the overall variation in habitat (e.g., CV of soil parameters). Rarely has the spatial structure of that variation been considered in relation to diversity. Here we examined the spatial variability (CV) and spatial structure of that variation (i.e. spatial scale of patchiness) of several main soil variables (C, N, P, pH, and conductivity) in relation to grassland plant species richness and diversity (H′). We determined the relationships of plant species richness and diversity at two spatial scales (50 × 50 m plot scale, 1 × 1 m quadrat scale) with the whole-plot soil heterogeneity within an ~750 ha natural area of Kerqin grasslands in northeastern China. We found that the best models describing species richness at the 0.25 ha and 1 m2 scales included patch size of soil conductivity and N, respectively. For each of the two spatial scales, pairs of models best described H′; a simple regression with CV of soil N and a multiple regression including soil N patch size and CV at the 0.25 ha scale, and, at the 1 m2 scale, a simple regression with soil conductivity CV and multiple regression including CV and patch size of soil N. Soil N was negatively associated with conductivity, likely due to sodium, the primary determinant of conductivity in this meadow steppe system, inhibiting plant growth and the capacity of soils to accumulate N. Consequently our results indicated that the heterogeneity of soil N was the principal control of plant species richness and H′. Moreover, our findings indicate that spatial structure (the average size of a patch), in addition to CV, was important in determining grassland species richness and diversity. Our results indicate that both components of environmental heterogeneity need to be included in future tests of the heterogeneity–diversity hypothesis.

Contrasting impacts of different-sized herbivores on species richness of Mediterranean annual pastures differing in primary productivity

Vertebrate herbivores can be key determinants of grassland plant species richness, although the magnitude of their effects can largely depend on ecosystem and herbivore characteristics. It has been demonstrated that the combined effect of primary productivity and body size is critical when assessing the impact of herbivores on plant richness of perennial-dominated grasslands; however, the interaction of site productivity and herbivore size as determinants of plant richness in annual-dominated pastures remains unknown. We experimentally partitioned primary productivity and herbivore body size (sheep and wild rabbits) to study the effect of herbivores on the plant species richness of a Mediterranean semiarid annual plant community in central Spain over six years. We also analyzed the effect of grazing and productivity on the evenness and species composition of the plant community, and green cover, litter, and plant height. We found that plant richness was higher where the large herbivore was present at high-productivity sites but barely changed at low productivity. The small herbivore did not affect species richness at either productivity site despite its large effects on species composition. We propose that adaptations to resource scarcity and herbivory prevented plant richness changes at low-productivity sites, whereas litter accumulation in the absence of herbivores decreased plant richness at high productivity. Our results are consistent with predictions arising from a long history of grazing and highlight the importance of both large and small herbivores to the maintenance of plant diversity of Mediterranean annual-dominated pastures.

Grazing and an invasive grass confound spatial pattern of exotic and native grassland plant species richness

Previous work has shown exotic and native plant species richness are negatively correlated at fine spatial scales and positively correlated at broad spatial scales. Grazing and invasive plant species can influence plant species richness, but the effects of these disturbances across spatial scales remain untested. We collected species richness data for both native and exotic plants from five spatial scales (0.5–3000m2) in a nested, modified Whittaker plot design from severely grazed and ungrazed North American tallgrass prairie. We also recorded the abundance of an abundant invasive grass, tall fescue (Schedonorus phoenix (Scop.) Holub), at the 0.5-m2 scale. We used linear mixed-effect regression to test relationships between plant species richness, tall fescue abundance, and grazing history at five spatial scales. At no scale was exotic and native species richness linearly related, but exotic species richness at all scales was greater in grazed tracts than ungrazed tracts. Native species richness declined with increasing tall fescue abundance at all five spatial scales, but exotic species richness increased with tall fescue abundance at all but the broadest spatial scales. Severe grazing did not reduce native species richness at any spatial scale. We posit that invasion of tall fescue in this working landscape of originally native grassland plants modifies species richness-spatial scale relationships observed in less disturbed systems. Tall fescue invasion constitutes a unique biotic effect on plant species richness at broad spatial scales.

The relative importance of the species pool, productivity and disturbance in regulating grassland plant species richness: a field experiment

Summary Ecologists have generally focused on how species interactions and available niches control species richness. However, the number of species in the regional species pool may also control richness. Moreover, the relative influence of the species pool and species interactions on plant richness may change along productivity and disturbance gradients. We test the hypothesis that many species from the propagule pool will colonize into habitats of moderate productivity and moderate disturbance, and the number of species in the pool will, therefore, primarily control plant species richness in such habitats. The hypothesis also states that few species from the propagule pool will colonize into habitats of high productivity and minimal disturbance because competitive species interactions primarily control plant richness in such habitats. To test this hypothesis, we experimentally varied resource availability via fertilization and irrigation, the size of the available propagule pool via sowing the seeds of 49 species and disturbance via vegetation clipping. A larger propagule pool increased species richness 80% in the absence of fertilization and the presence of clipping but had no significant effect on richness in the presence of fertilization and the absence of clipping (significant fertilization × clipping × seed addition interaction). Irrigation increased species richness primarily in the absence of fertilization and the presence or clipping (significant fertilization × clipping × irrigation interaction). Synthesis. These results support the assertion that the control of plant species richness shifts from the number of species in the propagule pool to the intensity of species interactions as productivity due to soil fertility increases and disturbance decreases. However, increases in productivity due to irrigation caused an increase in species richness, probably because of reduced seedling desiccation. Other studies have found similar outcomes along natural productivity gradients where productivity is confounded with other variables, but this study is the first to find such an outcome along an experimental productivity gradient. These results suggest habitats with moderate soil fertility and disturbance may be more open to colonization from the propagule pool than other habitats, a finding that has implications for plant restoration and invasive species management.

Evaluation of PCR primers for universal nifH gene targeting and for assessment of transcribed nifH pools in roots of Oryza longistaminata with and without low nitrogen input

The bias of widely used degenerate nifH-specific primer sets was first tested using denaturing gradient gel electrophoresis (DGGE), and their application for profiling of complex communities assessed for roots of Oryza longistaminata. When primers (P) with mismatches at nondegenerate positions were used on genomic DNA of Azotobacter vinelandii, which harbors three single divergent nifH genes, template-to-product ratios were highly skewed. In contrast, we obtained no evidence for a large PCR bias when we used highly degenerate primers with no mismatches (Z). Similar results were obtained for reverse transcription (RT)-PCR amplifications from root RNA from O. longistaminata grown at the river bed of the Okavango, where Z-primers detected a more complex nifH pool, corroborating that the P-primers are quite biased in the nifH sequences they amplify. In microcosms of O. longistaminata grown in the phytotron in the presence or absence of constant low nitrogen input (25 kg NH4NO3 ha(-1) year(-1)), roots of nitrogen-treated plants showed similar, slightly higher levels of nifH-mRNA. However, nitrogen treatment had a strong effect on the composition and diversity of expressed nifH pools that shifted towards methylotroph-related nitrogenases. Thus the active population of diazotrophs was not resistant towards low rates of nitrogen input and decreased significantly in richness, as also observed for plant species richness in grasslands by others.

Role of Soil Organisms in the Maintenance of Species-Rich Seminatural Grasslands through Mowing

To preserve species-rich grasslands, management practices such as mowing are often required. Mowing is known to promote aboveground conditions that help to maintain plant species richness, but whether belowground effects are important as well is not known. We hypothesized that if mowing decreases belowground carbon transfer by reducing root mass, this will reduce the abundance and activity of soil decomposers and lead to diminished nutrient availability in soil. In grasslands, this would provide a means to mitigate the negative effects of nitrogen enrichment on plant species richness. We established experimental plots on grassland with one-third of plots growing untouched, one-third mowed once a summer, and one-third mowed twice a summer for three growing seasons. Root and soil attributes were measured at each plot 1 month after each mowing. Mowing decreased root mass but had few effects on belowground biota and soil NH4-N, NO3-N, and PO4-P concentrations. Mowing did not affect root N concentrations. Our results show that despite reducing root mass, mowing may have few effects on those soil biota that control nutrient supply and, as a result, have no clear-cut effects on nutrient availability in soil. This suggests that the effects of mowing on soil decomposers and soil nutrient availability may not provide an effective means to mitigate N enrichment and enhance plant species richness in grasslands in a timescale of a few years. Whether such effects could, however, be achieved with longer lasting mowing remains open.

Mountain grassland biodiversity: Impact of site conditions versus management type

Summary Grasslands of the Swiss Alps provide agricultural goods, ecological services, disaster protection, and scenic beauty. We identified influences of site conditions and management type on grassland biodiversity, and specifically evaluated the effectiveness of the agri-environmental programme in the Alps. Vascular plants and grasshoppers were mapped in conventionally managed cut meadows, cut meadows of the ecological compensation programme (ECA meadows), and conventionally managed pastures ( n =324). We determined climatic and topographic site conditions, quantified the degree of remoteness of all plots in GIS, and estimated the habitat diversity in the vicinity of the sampling sites. The data were analysed by discriminant analysis, rank-correlation analysis, non-parametric ANOVA, general linear models, and ANCOVA. Plant biodiversity hot spots were in economically unattractive, remote sites. These were the typical site conditions of ECA meadows. Hence we concluded that the ecological compensation programme was effectively ensuring management at these sites, and thus protecting mountain grassland plant species richness. Grasshoppers seemed not to benefit from mountain ECA meadows, which were probably often situated at the climatic limit of several species. Pastures were the most species rich management type (plants and grasshoppers), but conversion from cut grassland to pastures should be limited, as negative economic and ecological effects have been reported. We propose that the co-existence of well-managed pastures and long-term ECA meadows might best conserve mountain grassland biodiversity.

From plant neighbourhood to landscape scales: how grazing modifies native and exotic plant species richness in grassland

The interactive effect of grazing and soil resources on plant species richness and coexistence has been predicted to vary across spatial scales. When resources are not limiting, grazing should reduce competitive effects and increase colonisation and richness at fine scales. However, at broad scales richness is predicted to decline due to loss of grazing intolerant species. We examined these hypotheses in grasslands of southern Australia that varied in resources and ungulate grazing intensity since farming commenced 170 years ago. Fine-scale species richness was slightly greater in more intensively grazed upper slope sites with high nutrients but low water supply compared to those that were moderately grazed, largely due to a greater abundance of exotic species. At broader scales, exotic species richness declined with increasing grazing intensity whether nutrients or water supply were low or high. Native species richness declined at all scales in response to increasing grazing intensity and greater resource supply. Grazing also reduced fine-scale heterogeneity in native species richness and although exotics were also characterised by greater heterogeneity at fine scales, grazing effects varied across scales. In these grasslands patterns of plant species richness did not match predictions at all scales and this is likely to be due to differing responses of native and exotic species and their relative abundance in the regional species pool. Over the past 170 years intolerant native species have been eliminated from areas that are continually and heavily grazed, whereas transient, light grazing increases richness of both exotics and natives. The results support the observation that the processes and scales at which they operate differ between coevolved ungulate—grassland systems and those in transition due to recent invasion of herbivores and associated plant species.

The interactive effects of grazing ungulates and aboveground production on grassland diversity

The variable and nonlinear relationships between plant species richness (SR) and aboveground production (NAP) among terrestrial ecosystems indicate that the energetic capacity of ecosystems interacts with other environmental factors to control diversity. One contributing factor determining plant diversity is herbivory; but few studies have effectively examined the interaction of herbivores and NAP on SR. The objective of this study was to investigate how NAP and herds of native migrating ungulates determine plant SR in grasslands of Yellowstone National Park. Plant SR at peak aboveground biomass was compared inside and outside ungulate exclosures at two spatial scales, 1.0 m2 ("local") and 100 m2 ("community"), in ten variable grasslands. NAP also was determined inside and outside exclosures. The relationship between SR and NAP was unimodal for grazed and ungrazed grassland at both spatial scales. Grazers increased local SR, independent of NAP. In contrast, herbivore effects on community SR ranged from no effect among low-productive grassland to an increasingly positive influence as NAP increased. In addition, ungulates reduced beta diversity (the contribution to community SR attributed to variability among local patches) at dry, low-productive and wet, high-productive sites. These results suggest that the size of the pool of species available to colonize grassland is an important factor controlling the response of grassland SR to herbivory, particularly from low- to intermediate-productive grassland.

Does resource availability, resource heterogeneity or species turnover mediate changes in plant species richness in grazed grasslands?

Grazing by large ungulates often increases plant species richness in grasslands of moderate to high productivity. In a mesic North American grassland with and without the presence of bison ( Bos bison), a native ungulate grazer, three non-exclusive hypotheses for increased plant species richness in grazed grasslands were evaluated: (1) bison grazing enhances levels of resource (light and N) availability, enabling species that depend on higher resource availability to co-occur; (2) spatial heterogeneity in resource availability is enhanced by bison, enabling coexistence of a greater number of plant species; (3) increased species turnover (i.e. increased species colonization and establishment) in grazed grassland is associated with enhanced plant species richness. We measured availability and spatial heterogeneity in light, water and N, and calculated species turnover from long-term data in grazed and ungrazed sites in a North American tallgrass prairie. Both regression and path analyses were performed to evaluate the potential of the three hypothesized mechanisms to explain observed patterns of plant species richness under field conditions. Experimental grazing by bison increased plant species richness by 25% over an 8-year period. Neither heterogeneity nor absolute levels of soil water or available N were related to patterns of species richness in grazed and ungrazed sites. However, high spatial heterogeneity in light and higher rates of species turnover were both strongly related to increases in plant species richness in grazed areas. This suggests that creation of a mosaic of patches with high and low biomass (the primary determinant of light availability in mesic grasslands) and promotion of a dynamic species pool are the most important mechanisms by which grazers affect species richness in high productivity grasslands.

Impact of different‐sized herbivores on recruitment opportunities for subordinate herbs in grasslands

Abstract. Potential effects of herbivores on plant species diversity depend on herbivore size, species and density. In this study we examine the effect of different‐sized herbivores (cattle and rabbits) on recruitment of subordinate herbs in grasslands. We show that in a grazed floodplain, grassland plant species richness is mainly determined by the presence of many species of subordinate herbs. These herbs experience high colonization and extinction rates. We conclude that the creation of colonization opportunities for subordinate herbs plays a crucial role in maintaining plant species richness in productive grasslands. We found that cattle disperse large amounts of seeds via their dung, over ten times more than rabbits. Rabbits create more and on average larger bare soil patches than cattle. In a field experiment artificial disturbances improved germination success tremendously for four tested herb species. We found that bare soil is the best regeneration site, while cattle dung gave a too strong nutrient stimulus, resulting in tall vegetation and therefore light limitation. These results can be confirmed with results from field monitoring plots where plant species richness was positively related to the occurrence of bare soil patches. Therefore both large and small herbivores have a major impact on dispersal and colonization, but for different reasons. Cattle are identified as most important for seed dispersal whereas rabbits have a main effect as creators of disturbances. These results emphasize the importance of distinguishing between herbivore species in assessing their (potential) effects.

Impact of different-sized herbivores on recruitment opportunities for subordinate herbs in grasslands

Abstract. Potential effects of herbivores on plant species diversity depend on herbivore size, species and density. In this study we examine the effect of different-sized herbivores (cattle and rabbits) on recruitment of subordinate herbs in grasslands. We show that in a grazed floodplain, grassland plant species richness is mainly determined by the presence of many species of subordinate herbs. These herbs experience high colonization and extinction rates. We conclude that the creation of colonization opportunities for subordinate herbs plays a crucial role in maintaining plant species richness in productive grasslands. We found that cattle disperse large amounts of seeds via their dung, over ten times more than rabbits. Rabbits create more and on average larger bare soil patches than cattle. In a field experiment artificial disturbances improved germination success tremendously for four tested herb species. We found that bare soil is the best regeneration site, while cattle dung gave a too strong nutrient stimulus, resulting in tall vegetation and therefore light limitation. These results can be confirmed with results from field monitoring plots where plant species richness was positively related to the occurrence of bare soil patches. Therefore both large and small herbivores have a major impact on dispersal and colonization, but for different reasons. Cattle are identified as most important for seed dispersal whereas rabbits have a main effect as creators of disturbances. These results emphasize the importance of distinguishing between herbivore species in assessing their (potential) effects.