Species Diversity In Grasslands Research Articles

Conservation management of calcareous grasslands. Changes in plant species composition and response of functional traits during 25 years

Five management treatments have been applied to a calcareous grassland since 1974 to study their efficiency in maintaining high diversity of grassland species. The treatments were: continuing sheep grazing, mowing, mulching, burning and leaving fallow (unmanaged). After 25 years of management, the treatments mowing and mulching resulted in a species composition similar to that from grazing by sheep. Thus, mowing and mulching can be useful management alternatives to grazing. In contrast, both burning and leaving fallow considerably changed the species composition. The changes were similar in both treatments and neither can be recommended for management purposes. We also evaluated eight traits with assumed sensitivity to the treatments (life form, life cycle, growth form, runners, lateral spread, fecundity, seed mass, germination season). In 1999, all traits except life cycle were found to respond to the different treatments. Trait response is discussed in detail.

Soil acidity and nutrient supply ratio as possible factors determining changes in plant species diversity in grassland and heathland communities

To elucidate the causes of the sharp decline in plant species diversity in heathland and nutrient-poor grasslands in The Netherlands, we investigated the spatial variation in plant species richness and the abundance of threatened plant species in relation to soil acidity and soil nutrient supply ratio. We selected 68 plots divided equally between species-rich and species-poor parts of the study area, and collected data on soil characteristics, above-ground biomass and vegetation composition in each plot. In addition, we used phytometers planted with Molinia caerulea tillers to measure the nutrient supply in the soil. Soil acidity was the variable most strongly correlated with plant species diversity in heathland and grassland communities. We found that increased N:P and N:K ratios in plant biomass had additional negative effects. The Red List species in the data set and all other species that had been declining sharply in the Netherlands since 1950 were growing in soils with pH >5 and most were growing in soils with balanced nutrient supply ratios.

The resource balance hypothesis of plant species diversity in grassland

Abstract: We hypothesize that plant species diversity is favoured when actual resource supply ratios are balanced according to the optimum resource supply ratios for the vegetation as a whole. This ‘resource balance hypothesis of plant species diversity’ (RBH) follows from two different mechanisms of plant species coexistence, namely: ‘differential resource limitation’, which allows species to coexist in a competitive equilibrium in a homogeneous environment and ‘micro‐habitat differentiation’, which builds on spatial heterogeneity. Both mechanisms require that resource supply ratios are intermediate between the optimum supply ratios of the species present in the species pool. Additional conditions, concerning the resource acquisition and requirement ratios of the species, are easier to meet for the second mechanism than for the first. To test the RBH we measured species diversity parameters in 74 grassland plots, as well as the N, P and K concentrations in the above‐ground biomass. We used a new ceiling detection algorithm to examine the relationship between maximum observed diversity and the N/P‐, P/K‐ and K/N‐ratios in the biomass. Most of these ceiling relationsips could be described by parabolic curves with significant quadratic terms. This indicates that high diversity does not occur at the extremes of the observed ranges of nutrient ratios. This supports the RBH.

Restoration of species diversity in grasslands: The effect of grassland management and changes in ground water level

Summary Results are presented of a grassland restoration experiment on a humic sandy soil and on a nutrient rich humic clay. The effect of cutting time and frequency, sod stripping and a rise in ground water level is studied on the decrease in dry matter and nutrient yield and changes in botanical composition. When the annual production is lower than 6 tonnes a second cut hardly contributes to a faster soil impoverishment. But a second cut creates a favourable vegetation structure for seedling establishment. Sod stripping to 5 cm caused only for a short period a lower production, but it stimulates the establishment of species from the soil seedbank. The yield of N and P is lower in the longer run, that of K is very low with and without sod stripping. The changes in yield and concentration of K in the biomass show that the availability of K is very low and possibly limits the further decrease in the dry matter production. Establishment and generative spread of plant species in the undisturbed sward are low...

Species Diversity in Grasslands of Stable and Eroded Biancana Domes in the Orcia Valley, Central Italy

Species Diversity in Grasslands of Stable and Eroded Biancana Domes in the Orcia Valley, Central Italy

Productivity of Loessal Grasslands in the Kluane Lake Region, Yukon Territory, and the Beringian "Production Paradox"

The Beringian "Production Paradox" is posed by abundant evidence that large ungulates populated unglaciated portions of northwestern North America and adjacent northeast Asia during the late Pleistocene, while botanical data from the same period suggest a poorly productive tundra environment. It is not clear how the large animals sustained themselves, but portions of Beringia, locally in receipt of loess, may have harbored sufficient forage-producing plants to nourish these animals. Loessal soils in the region today are warm and dry in summer, and are often used as rangelands. The loessal hypothesis was examined on grasslands in the Kluane Lake area, southwest Yukon Territory, at sites which have recently received loess blown from the Slims River delta. The biomass and species diversity of grasslands around the lake increase with the quantity of silt in the soil. Likewise, soil fertility indices, including total nitrogen, available nitrogen (NH4), and total carbon, increase with silt content, particularly at sites where the soil surface has been stable for some time, and a "humified" loess (Ahk) horizon has developed. These results support the hypothesis that sites in receipt of loess may have played a significant role in the vegetative productivity of the Beringian ecosystem.

Effects of Urine Deposition on Small‐Scale Patch Structure in Prairie Vegetation

Large grazing mammals contribute to the species diversity of grasslands via direct and indirect effects of defoliation and urine deposition. We examined the influence of one and two applications of simulated bovine urine on vegetation structure on (1) tallgrass prairie burned either every 2 or 4 yr at Konza Prairie Research Natural Area (KPRNA), Kansas, and (2) unburned sandhills prairie at the Niobrara Valley Preserve, Nebraska. We also examined the influence of urine and the clipping of graminoids on an annually burned site at KPRNA. Plant abundance in general increased on urine patches but the response appeared dependent on litter accumulation. C4 grasses increased at the annual burn and Niobrara sites where litter levels were low. C3 forbs increased at the 2— and 4—yr burn sites where litter levels were high. Urine treatment significantly affected community composition at all but the 2—yr burn site. Alpha—diversity decreased on urine patches at the annual and 4—yr burn sites but increased on urine patches at the Niobrara site. Beta—diversity increased on urine patches at the annual burn and Niobrara site but decreased on urine patches at the 4—yr burn site. The clipping of graminoids at the annual burn site reduced both α— and β—diversity and graminoid abundance while forb abundance was not affected.

Stability May Decrease with Diversity in Grassland Communities: Empirical Evidence from the 1986 Cantabrian Mountains (Spain) Drought

Frank and McNaughton reported that community stability, measured by the resistance to change in species composition when perturbed by drought, increased with species diversity in grasslands of Yellowstone, USA. They also found that species diversity increased with spatial heterogeneity of the community, pattern diversity. In a similar study of grasslands in the Cantabrian Mountains, we found exactly the opposite; when affected by drought, the resistance of these communities to change in species composition decreased as diversity increased, and diversity was not related to spatial heterogeneity. The contrasted results in Yellowstone and Cantabrian grasslands match theoretical predictions derived from model systems and suggest the existence of complex relationships between diversity and community stability.

Abundance, vegetation, and environment of four patch types in a northern mixed prairie

The importance of concurrent disturbances to the maintenance of plant species diversity in grasslands has been emphasized by several authors, but there are few studies comparing different disturbances at the same site. In this study the size, abundance, vegetation, and environment of thatching ant mounds, earthen mammal mounds, bison wallows, and openings in dry marshes are compared in a northern mixed prairie in north central South Dakota. Patch size and abundance varied considerably between patch types. Ant and earthen mammal mounds were the smallest but most abundant patch types. Bison wallows and dry marshes were larger and occurred less frequently than ant and earthen mounds. Different patch types occupied a similar amount of area. Ordination of patch vegetation revealed marked between-type compositional differences; ant and earthen mounds were dominated by vegetatively reproducing perennials, while annuals occurred more abundantly in bison wallows and dry marshes. Many species were restricted to either wallows or marshes. Levels of nitrate, phosphorus, soil organic matter, and other environmental factors varied significantly between patch types. Different patch types supported different groups of species, and patch vegetation was a product of mechanism of patch creation, patch environment, and location. Key words: ant mounds, disturbance, earthen mounds, northern mixed prairie, patches, potholes, wallows.

MICRO‐SPATIAL HETEROGENEITY AND SEEDLING DEMOGRAPHY IN SPECIES‐RICH GRASSLAND

It is suggested that spatial niche‐separation between grassland species occurs in the regeneration phase and that the differential response of species to micro‐variations in leaf cover may allow coexistence at high density. A technique for measuring heterogeneity in leaf‐cover on a scale of 1‐cm2 units (micro‐cover) and the demography of seedling cohorts of Reseda lutea and Anthyllis vulneraria in relation to this heterogeneity is described. Densities of seedlings were significantly higher in micro‐sites of low micro‐cover for R. lutea and for one of the three cohorts of A. vulneraria studied. No relationship was found between mortality and density of seedlings or micro‐cover. The ultimate causes of these distribution patterns of seedlings and their consequences for the maintenance of species diversity in grassland are discussed.