Limestone Grassland Community Research Articles

The seed bank in soil from the nests of grassland ants in a unique limestone grassland community in Ireland

The seed content of nest soil of four species of ants Myrmica sabuleti, Lasius flavus, L. niger and Formica lemani was investigated in the semi-natural limestone grassland of the Burren, western Ireland. On-nest and off-nest soil samples were compared to determine whether ants promote plant species richness. Samples were collected, monthly, from May to September 2006 from the top 50mm of soil from 10 nests of each species, and from adjacent off-nest grassland soil (total 400 samples). After collection a total of 42 seed species were germinated and identified. L. flavus (both on-nest and off-nest samples) had the highest seed species richness of which 10 species had a high seedling representation (% affinity) for the nest of this species. Persicaria maculosa and Viola tricolour had a high percent affinity for the nests of L. niger, and these were significantly higher on the nest compared to the off-nest samples. Anagallis arvensis and Cerastium holosteoides also had significantly higher percent affinity for the nests of F. lemani. No species was associated with M. sabuleti. The high richness of seedling species associated with Lasius nests may be due to the specialised vegetation on the nest or ant activity. Since L. niger, F. lemani and M. sabuleti nest under stones it is likely that the seeds may be collected by ant activity. Although previously reported for L. flavus, the unique seed banks of the ant nests can account for localised mosaic patches of different vegetation.

Community and ecosystem effects of intraspecific genetic diversity in grassland microcosms of varying species diversity

Studies of whether plant community structure and ecosystem properties depend on the genetic diversity of component populations have been largely restricted to species monocultures and have involved levels of genetic differentiation that do not necessarily correspond to that exhibited by neighboring mature individuals in the field. We established experimental communities of varying intraspecific genetic diversity, using genotypes of eight species propagated from clonal material of individuals derived from a small (100-m2) limestone grassland community, and tested whether genetic diversity (one, four, and eight genotypes per species) influenced community composition and annual aboveground productivity across communities of one, four, and eight species. Eight-species communities were represented by common grass, sedge, and forb species, and four- and one-species communities were represented by four graminoids and the dominant grass Festuca ovina, respectively. After three years of community development, there was a marginal increase of species diversity with increased genetic diversity in four- and eight-species communities, and genetic diversity altered the performance of genotypes in monospecific communities of F. ovina. However, shifts in composition from genetic diversity were not sufficient to alter patterns of community productivity. Neighborhood models describing pairwise interactions between species indicated that genetic diversity decreased the intensity of competition between species in four-species mixtures, thereby promoting competitive equivalency and enhancing species equitability. In F. ovina monocultures, neighborhood models revealed both synergistic and antagonistic interactions between genotypes that were reduced in intensity on more stressful shallow soils. Although the dependence of F. ovina genotype performance on neighborhood genetic composition did not influence total productivity, such dependence was sufficient to uncouple genotype performance in genetic mixtures and monocultures. Our results point to an important connection between local genetic diversity and species diversity in this species-rich ecosystem but suggest that such community-level dependence on genetic diversity may not feedback to ecosystem productivity.

Plant species turnover in an alvar grassland under different environmental conditions and at different scales

Nutrient and water supply, light availability and removal of biomass were manipulated in a limestone grassland community on the Swedish island of Oland from 1990 to 1993 in order to investigate how these factors influence species richness and year-to-year turnover at fine scales. Turnover, broken down into disappearance (‘extinction’) and appearance (‘immigration’) of vascular plant species, was measured at different spatial scales in plots ranging from 4 cm2 to 0.25 m2. For most treatments, turnover was highest at the finest scale, both measured as absolute and relative numbers. Turnover rate increased at all scales when the treatment implied such a change in the environment, where application of fertilizer was combined with shading. In these cases, disappearance of species largely exceeded appearance in a predictable manner, and resulted in species-poor assemblages at all scales. In plots treated with either fertilizer or shade, there were large differences in the direction of the turnover (i.e. whether immigration or extinction dominated) between years, apparently depending on the weather conditions in the respective year. After drought spells total turnover was also high for such treatments, whereas plots regularly receiving additional water supplies had rather similar turnover rates during the whole experiment.

Effects of simulated long‐term climatic change on the bryophytes of a limestone grassland community

AbstractThe bryophyte vegetation of upland limestone grassland at Buxton in the southern Pennine Hills (UK) was studied following seven years' continuous simulated climate change treatments. The experimental design involved two temperature regimes (ambient, winter warming by 3°C) in factorial combination with three moisture regimes (normal, summer drought, supplemented summer rainfall) and with five replicate blocks. Percentage cover of the bryophytes was estimated visually using 15 randomly positioned quadrats (30 cm × 30 cm) within each of the 30 3 m × 3 m plots. Significant treatment effects were found but these were relatively modest. Total bryophyte cover and cover of Calliergonella cuspidata and Rhytidiadelphus squarrosus responded negatively to drought, whereas Fissidens dubius increased in the droughted plots. Campyliadelphus chrysophyllus increased with winter warming, while R. squarrosus, Lophocolea bidentata and species richness all decreased. The effects on the total bryophyte flora were further studied by canonical correspondence analysis, which yielded a first axis reflecting the combined effects of the moisture and temperature treatments. However, this analysis and a detrended correspondence analysis of the plot data also revealed that natural factors were more important causes of variation in the grassland community than the simulated climate treatments. It was concluded that dewfall may be an important source of moisture for grassland bryophytes and that this factor may have reduced the impact of the moisture treatments. The absence of some thermophilous species such as Homalothecium lutescens in the plots initially may also have reduced their scope for major vegetational change.

Restoration of Magnesian Limestone Grassland: Optimizing the Time for Seed Collection by Vacuum Harvesting

Abstract Magnesian limestone grassland is the rarest limestone grassland community in the United Kingdom, with many sites having been lost to quarrying and urban development. Its reestablishment, and that of many other semi‐natural grassland habitats, can be enhanced using seed collected from established communities. However, few studies have evaluated the effectiveness of methods of seed harvesting. The objectives of this study were to (1) test the effectiveness of a hand‐held vacuum harvester in the collection of an adequate quantity of seed, and range of species, to revegetate former quarries and (2) determine the optimum time for seed collection based on a phenological study of the plants at the donor site. Germination tests of harvested seed were used to identify species, based on the germinating seedlings. Thirty‐six species were identified, with Briza media (quaking grass) and Festuca sp. (red and sheep's fescue) being the dominant species and accounting for 74% of germinating seedlings. Species composition of vacuum‐harvested seed was compared with species composition of the vegetation found in the principal donor site. The most common species in the collected seed were also common at the donor site, but some characteristic species of the grassland were absent or did not germinate. Most species reached a peak in ripe seed production between mid‐August and early September. Although having several advantages, vacuum harvesting will not, by itself, provide either sufficient quantity of seed or the wide range of species often required. Suggestions are given for combining this technique with other methods.

Bryophytes, lichens and phanerogams in an alvar grassland: relationships at different scales and contributions to plant community pattern

The relationship between bryophytes and lichens versus phanerogams has been investigated in three stands of a limestone grassland community, along three transects of 500 10 X 10 cm plots. Ordination axes resulting from Detrended Correspondence Analysis for bryophytes and lichens versus phanerogams were correlated using Spearman rank correlation coefficient. The effect of grain (sample plot) size on relationships between species along the gradient and on the correlation between the layers formed by bryophytes and lichens (cryptogams) and phanerogams, and with environmental variables has been as well examined. Values for light, moisture, pH and nitrogen have been derived from the vegetation itself with the help of Ellenberg indicator values. The relative position of species in the ordination space is more or less the same until grain size 3 (10 x 40 cm) for cryptogams and phanerogams and until grain size 2 (10 × 20 cm) for all‐species together. Therefore, it is suggested that sample plot sizes of 10 × 10 cm to 10×20 cm are appropriate as units for field experiments testing interactions between cryptogams and phanerogams. The respective layers were weakly correlated and the correlation between them increased with increase in grain size. The correlation of DCA axis 1 from the ordination of cryptogams, phanerogams and all‐species with the environmental factors was weak and similar in order of magnitude. Only the environmental variables which were strongly correlated with the DCA axis 1 increased in correlation at larger grain sizes. The ordinations of cryptogams, phanerogams and all‐species were correlated along DCA axis 1 with pH in all investigated stands and at almost all grain sizes. Multi‐species patches have been detected by pattern analysis (PASFRAN) on DCA sample scores from ordinations of cryptogams, phanerogams and combined matrices. Multi‐species patterns with sizes between 20‐240 cm. composed by bryophytes and lichens and by phanerogams have been found. Complex patterns formed by cryptogams and phanerogams together, which are different in size than those in the separate layers, suggest that bryophytes + lichens and phanerogams may interact with each other.

Field survey of a monogynous leptothoracine ant (Hymenoptera, Formicidae) evidence of seasonal polydomy ?

484 nests of Leptothorax tuberointerruptus were collected from a coastal limestone grassland community in Dorset, England, over a 16 month period from February 1992 to May 1993. Behavioural observations and dissections of females strongly suggested that the nests were obligately monogynous. Electrophoretic data also suggested that within most nests all the workers shared the same mother and father. Counts of nest contents revealed temporary but dramatic drops in both worker and queen numbers per nest in May—June 1992. Seasonal polydomy is postulated to be the cause of this variation. Such dramatic variation highlights the importance of sampling over as much space and time as possible if premature conclusions about colony demography are to be avoided.

A functional analysis of a limestone grassland community

Abstract. We examine the potential of standardised data, mainly collected in the laboratory, to elucidate mechanisms of species coexistence, using a south‐facing, infertile, species‐ rich limestone grassland at Miller's Dale, Derbyshire, England as a model system. Standardised autecological data for 15 of the more important Miller's Dale species were obtained from the Integrated Screening Programme (ISP), and their functional attributes were reviewed in the context of a larger database, broadly representative of the British flora. Ordination of adult plant attributes demonstrated that the Miller's Dale species are strategically relatively uniform; most are slow‐growing, evergreen and tolerant of mineral nutrient deficiency. Ordination of seed attributes revealed more variety among the Miller's Dale species; the main axis of variation was from species with large, transient seeds (mostly grasses) to species with small, persistent seeds (mostly dicots). From the ordination we derive the predictions that germination of the latter species will be more temporally opportunistic and more inhibited by the presence of vegetation than the former. These predictions are consistent with data collected in experimental studies of seed persistence and germination at the site. These data suggest that spatial and temporal variation in opportunities for regeneration is an important mechanism contributing to the high species richness of dry limestone grasslands.

Species Turnover and Seedling Recruitment in Limestone Grasslands

Species turnover and germination were analysed in the Veronica spicata-Avenula pratensis limestone grassland community. Species turnover was estimated on the basis of presence/absence of species in fifty 10×10 cm permanent plots during the period 1986 to 1989. The contribution made by reproduction by seeds to turnover was evaluated by recording newly-germinated seedlings on thirty-five 10×10 cm plots on three occasions during the growing season in each year from 1986 to 1989. Turnover, expressed as the sum of increase and decrease of individual species (when comparing subsequent years), varied much between species and remarkably much between years. Seedling recruitment varied widely amongst and within years, indicating the occurrence of non-synchronized regeneration occasions for different species (...)

Large Niche Overlaps Among Coexisting Plant Species in a Limestone Grassland Community

In the present study measurements were made on six niche axes, including phenology of above-ground growth over a five-month growing season, together with sol depth, pH, and the levels of available nitrogen, phosphorus and potassium in soil samples taken at the end of the growing season. Analysis of separation in this niche space indicates that it is insufficient to account for the coexistence of all eight species. The possibility that inappropriate or insufficient niche axes may have been chosen is recognized and discussed

On the Spatial Organization of Plant Species in a Limestone Grassland Community

SUMMARY (1) Studies of the spatial organization of plant communities have been based on samples of the physical space occupied by communities. To determine the spatial organization of a community as the plant species themselves experience it (the 'plant's-eye-view'), it is necessary to use a sampling method in which the individual plant is the sample unit. The method of cluster sampling makes this possible in the absence of a census list from which to sample. (2) Cluster sampling is used to estimate the structure of a limestone grassland community as it 'appears' to seven common plant species ('target species') in the community. (3) The mean distances from the target species to the nearest neighbour of each target species indicate that, qualitatively, each experiences the other species in proportion to their abundance in the community, although there is evidence of within-species aggregation in several cases. (4) A similar picture emerges from the mean densities of species in the immediate neighbourhood of each target species. Although spatial patterns within certain species are highly non-random, the spatial patterns of different species are interlocked in such a way that there is little indication of interspecific associations. (5) The amount of neighbour-free space differs between target species. In most cases, this is not correlated with plant size. (6) Spatial organization of the community as exemplified by this study is most likely to be a result of the patterns of clonal growth, although the possibility of fine-scale niche differentiation is not excluded. Such organization could play an important role in shaping future interactions in the community, causing interspecific interactions to be weaker than intraspecific ones.

NUCLEAR DNA CONTENTS, SHOOT PHENOLOGY AND SPECIES CO‐EXISTENCE IN A LIMESTONE GRASSLAND COMMUNITY

SummaryWithin a species‐rich limestone grassland community in Northern England a correlation has been established between nuclear DNA content and the timing and rate of leaf extension in the spring. The data support the hypothesis that natural selection has operated upon nuclear DNA content through the differential sensitivity of cell division and cell expansion to low temperature. It is suggested that measurements of nuclear DNA content may provide an index of temporal niche differentiation in plant communities.

Effects of Fire on a Derbyshire Grassland Community

An experiment is reported in which the effects of fire (heat, litter removal, nutrient redistribution) were separated by a combination of burning and clipping treatments in a limestone grassland community dominated by the tussock grasses Festuca ovina L. and Helictorichon pratense (L.) Pilger and with a light covering of litter. Burning, but not clipping, stimulated the production of inflorescenses of H. pratense and killed many plants of F. ovina. Denudation, whether caused by burning or clipping (with or without the return of plant ash), resulted in hig her soil temperatures and increased frequency of annual and biennial species. Soil moisture tensions were not affected by the treatments. No effects of fire could be attributed to the deposition of ash. The result of the experiment are compared with studies of fire in prairie and other grassland communities.

Multivariate Approaches to a Limestone Grassland Community: III. A Comparative Study of Ordination and Association-Analysis

Multivariate Approaches to a Limestone Grassland Community: III. A Comparative Study of Ordination and Association-Analysis

Multivariate Approaches to a Limestone Grassland Community: I. A Stand Ordination

Multivariate Approaches to a Limestone Grassland Community: I. A Stand Ordination