The impact of grazing on plant communities,plant populations and soil conditions on salt marshes

Grazing an abandoned salt marsh causes retrogressive succession, since mid salt-marsh communities change into lower salt-marsh communities. Grazing and mowing are compared in detail. Both management practices enhance species diversity in an abandoned salt marsh. This can be attributed to the removal of litter. The finding that lower salt-marsh species appear more with grazing than with mowing or abandoning is not related to a higher soil salinity as compared to mowing or abandoning, but probably to locally baring of the soil by grazing animals. Only species of pioneer or unstable environments seem to have a persistent seed bank, for other species seed dispersal seems to be a limiting factor for their establishment.Nomenclature follows Heukels & van Ooststroom (1977) for species; Westhoff & den Held (1969) for syntaxa.Mrs R. Rusthoven analyzed the soil samples, Mr E. Leeuwinga drawed the figures, and Mrs J. O'Brien corrected the English text.     

Vertical canopy structure of Dutch chalk grasslands in relation to their management

Analysis of leaf canopy overtopping relationships was carried out using a non-destructive point quadrat method followed by a destructive stratified harvest of the above-ground phytomass in Dutch chalk grasslands with different management: summer sheep grazing and annual autumn mowing. The two methods of analysis are compared: e.g. relative leaf overtopping can be recorded by the point quadrat method but it is obscured in vertical vegetation profiles based on stratified phytomass distribution. However the stratified harvest method describes the relationship between canopy phytomass and light microclimate, recorded by measuring Photosynthetically Active Radiation (PAR) at different heights in the vegetation. Plant growth form during peak standing crop is of greater significance than Raunkiaerian life form in determining structure of chalk grassland vegetation. In annually mown grasslands, the tall graminoid growth form, shown by Brachypodium pinnatum, reduces PAR in the lower canopy and suppresses most other growth forms except those which can reach the higher canopy levels, e.g. clumped herbs such as Origanum vulgare. In contrast, grazing can result in a reduction of dominance from the tall graminoids and reduction of the abundance of taller, grazing-sensitive herbs, e.g. clumped and climbing herbs such as Origanum and Lathyrus pratensis, and an increase in grazing-tolerant species, e.g. smaller rosette herb growth forms, e.g. Leontodon hispidus and shorter rhizomatous or stoloniferous graminoids, e.g. Carex flacca and Briza media. Changes in both the overtopping hierarchy at the peak of the growing season and the intensity of overtopping in the course of a growing season are of conclusive importance in determining the relative abundance of species in the vegetation.     

Germination and establishment of Sahelian rangeland species

Summary In order to understand the vegetation dynamics of Sahelian rangelands, the effects of water availability on germination were investigated under controlled conditions in climate rooms. Mixtures of seeds from species that occur in the same habitats but have different seed characteristics were exposed to different watering treatments. Responses to the treatments in the climate room were comparable to those observed in the field situation. However, induction time was generally some-what longer, and in some cases the germination rate was lower. The size, frequency, and timing of showers decisively influenced the ratio between the proportions of the various species among the seedlings that established. In general, conditions were favourable for fast germinating species with rainfall patterns without serious intermittent periods of drought, whereas the conditions became favourable for the slower germinating species after dry periods had eliminated the seedlings of the fast germinating species. Large differences in drought resistance were found among seedlings of different species. This causes more differentiation in establishment of species. Seed losses during the pre-emergence phase were also important. These losses can be very high, especially for the fastest germinating species. The dynamics observed in field situations could be explained on the basis of germination characteristics and drought resistance.     

Germination and establishment of Sahelian rangeland species

Summary In the context of a study on the dynamics of Sahelian rangelands, seed characteristics of about 30 species have been described, with particular attention to germination characteristics. Data on both form and weight of the seeds are presented. Germination was studied under controlled conditions in a climate room. Optimum conditions for germination were established, and the species were characterized by induction time, slope of germination vs. time curve and final germination percentage. The results obtained under climate room conditions appear to be correlated satisfactorily with the behaviour of the different species in the field.     

Morphology and phenology of Scabiosa columbaria from mown and grazed habitats - Results of a simulation experiment

We analysed the morphology and phenology of Scabiosa columbaria in relation to grassland management by mowing and grazing. We selected 12 populations from mown and grazed calcareous grassland in six regions of central Europe. At each population site, we collected seed material to produce plants for a morphological and phenological analysis of the species in a simulation experiment, which comprised three treatments (control, simulated mowing and simulated grazing).The simulation experiment revealed a clear morphological and phenological differentiation of S. columbaria. Plants from the two treatment types differed in size, since individuals from mown sites had longer top peduncles than individuals from grazed sites. Individuals from mown populations flowered earlier than individuals from grazed populations. In the control treatment, individuals from both habitat types produced a similar number of fruiting capitulums. When subjected to simulated mowing, the reproductive success of the individuals was clearly reduced. Plants from mown habitats produced, however, a significantly larger number of fruiting capitulums than plants from grazed habitats. Simulated grazing reduced the reproductive success stronger than simulated mowing but differences between individuals from both habitat types were not significant.The results of our simulation experiment clearly indicate morphological and phenological adaptation of S. columbaria to mowing and grazing. The comparatively young selection pressure of mowing obviously selected early flowering individuals, while the original land use by grazing favoured late flowering plants.     

Aggregative responses of brent geese on salt marsh and their impact on plant community dynamics

The aggregative responses and habitat preferences of a generalist herbivore, the dark-bellied brent goose Branta bernicla bernicla, feeding on salt marshes are examined in relation to vegetation community characteristics and the abundances of individual plant species. In the autumn, feeding was strongly concentrated on the low marsh, which had the highest biomass of the preferred food plant, Salicornia europaea. There was a strong aggregative response of the geese to the abundance of S. europaea. A decline in the availability of S. europaea led to an increase in the pattern of aggregation in relation to the two other major food plants on the low marsh, Aster tripolium and Puccinellia maritima. The availability of these food plants, however, reached critically low levels in mid-winter and the geese abandoned the low marsh for the high marsh. Within the high marsh, the plant communities selected tended to be dominated by the inedible species Limonium vulgare. The food plants selected were P. maritima in the winter and P. maritima and Triglochinmaritimum in the spring. On the high marsh, aggregative responses were shown to both P. maritima and T. maritimum, but in both cases, aggregation increased up to a critical level of biomass, and then declined. The prevention of grazing with exclosures for 3 years led to an increase in the abundance of P. maritima on both high and low marshes. This change was slight on high marsh but pronounced on low marsh, where S. europaea showed a decrease in abundance in the exclosures over this time. The implications of the aggregative responses for the population dynamics of P. maritima and S. europaea are discussed. Received: 11 September 1997 / Accepted: 12 December 1997     

Dispersal by cattle of salt-marsh and dune species into salt-marsh and dune communities

We investigated the spatial cohort structure of Trillium populations in old-growth cove forests in Great Smoky Mountains National Park (TN, USA). We mapped the locations of all Trillium erectum L., Trillium grandiflorum (Michaux) Salisbury, and Trillium vaseyi Harbison occurring within two 10 × 10 m sample plots at each of three old-growth sites—Anthony Creek, Cove Mountain, and Kalanu Prong. The height and life stage of each individual were recorded and a randomly selected subset was excavated for age determination. Our results suggest that Trillium populations in cove forests of the southern Appalachians display a high degree of spatial aggregation and are relatively stable, spatially, over long time periods (i.e., decades). Individual patches (aggregations of plants) within populations were typically multi-aged and no clear spatial cohort structure was observed. Surprisingly, more isolated plants (distal from large aggregations) were among the oldest plants in the population, rather than recent colonists dispersing away from parent populations. Individual species were less mingled than expected given that they share a common dispersal agent (ants). This study provides a double-baseline for Trillium population structure in old, primary forests with low browse pressure.     

Phytosociology and ecology of old hay meadows in Hordaland,western Norway in relation to management

Well-drained mown hay meadows in Hordaland, western Norway, were investigated. The hay meadows are either managed in a traditional or in a semi-traditional way. Traditional management in the area involves little or no use of manure or fertilizer, mowing once or twice a year with a first cut later than June 23, clearing in spring and intensive grazing for short periods in spring and autumn. Semi-traditional management involves use of small to medium quantities of commercial fertilizer, often in addition to manure. Grazing may be irregular, light or lacking.Eight units of hay meadow vegetation are described, all assigned to the class Molinio-Arrhenatheretea, order Arrhenatheretalia; four units to the Atlantic alliance Cardaminion pratensis, association Cardamino pratensis-Conopodietum majoris (with three subassociations); one unit to the alliance Arrhenatherion elatioris, three units are provisionally grouped as Galium uliginosum-Knautia arvensis meadows.Continuous management of these meadows has resulted in characteristic species compositions, which vary along a west-east climatic gradient, and are related to the amount of commercial fertilizer used and the natural mineral-content of the soil.These hay meadows seem to be best maintained by continuing the traditional management regime. Grazing in spring and in autumn reduces fast growing dominants and creates openings for new seedlings of annuals and biennials. A late first cut allows for ripening of the seeds and creates openings for light for the species of the lower field layer. A list of species characteristic of traditionally managed permanent hay meadows is presented, and possible effects of present changes in management on the species composition of the meadows are discussed.The amount of organic matter in the topsoil is small in most stands. The pH values are between 4.0 and 5.6. The highest values were recorded in soil where little or no commercial fertilizer is used, and where the subsoil is naturally rich in minerals. A tendency to Mg impoverishment in the best fertilized stands is demonstrated. Species-rich stands on Ca-rich soils are poor in P.The expected changes in vegetation, future use, and conservation of permanent hay meadows in Hordaland are discussed.     

Review: Prospects and limitations of prescribed burning as a management tool in European grasslands

Grassland managers and scientists are increasingly interested in cost-effective alternative ways of grassland biodiversity conservation. Prescribed burning is a promising management tool which should be integrated in the planning of management efforts. In addition, small-scale prescribed burning is an effective fire suppression strategy to decrease the serious negative impacts of uncontrolled burnings on ecosystems and human life. Prescribed burning forms an integral part of the North-American grassland management practice, while in Europe it is rarely applied, despite the fact that uncontrolled burning occurs frequently in some regions. Our goal was to evaluate the use of prescribed burning as a promising but neglected management tool in European grasslands. We found that European studies on prescribed burning of grasslands are scarce and we conclude that annual burning is usually not an appropriate option for the conservation of species-rich grasslands. We reviewed burning studies from North-America to identify findings which might be adapted to the European grassland conservation strategy. In North-America, contrary to Europe, the application of burning is fine tuned in terms of frequency and timing, and usually combined with other restoration measures (grazing or seed sowing). Thus, we conclude that with the application of carefully designed prescribed burning, multiple conservation goals, e.g. invasion control and enhancing landscape-level heterogeneity, can be linked with an effective fire suppression strategy. We emphasize that for the application of prescribed burning in Europe, the general findings of carefully designed case studies should be combined with the practical knowledge of conservation managers concerning the local application circumstances to reach specific management objectives.     

From protégé to nurse plant: establishment of thorny shrubs in grazed temperate woodlands

Question: Thorny shrubs play keystone roles in grazed ecosystems by defending non‐protected plants against herbivores, but their establishment in grazed ecosystems is poorly understood. Which factors control establishment of recruits of thorny nurse shrubs in grazed temperate woodlands? Location: Ancient grazed temperate woodlands (52°32′N, 6°36′E), The Netherlands. Methods: We surveyed biotic and abiotic factors for saplings of thorny nurse shrubs in plots with and without saplings. To disentangle these factors, we performed a transplantation experiment over two growing seasons with nurse shrub saplings (Prunus spinosa and Crataegus monogyna) planted in two dominant vegetation types – tall unpalatable swards and short grazed lawns – half of them protected from herbivory via exclosures. Results: Plots with shrub saplings had taller surrounding vegetation, higher soil pH and higher soil moisture than plots without saplings. These plots predominantly contained unpalatable sward species, while plots without saplings mainly contained palatable lawn species. After transplantation, sapling survival was higher in exclosures than in the open, and higher in sward exclosures than in lawn exclosures. Sapling growth was higher in swards than in lawns, higher inside than outside exclosures, and higher for Prunus than Crataegus, while browsing on saplings was higher in lawns. Conclusion: Unpalatable swards form essential establishment niches for thorny shrubs in grazed temperate woodlands: they protect against herbivores before thorns fully develop in saplings, and sapling growth is better due to improved micro‐environmental conditions. Once established and thorny, shrub saplings grow out of the protective range of the swards and in turn facilitate tree seedlings, which are essential for long‐term persistence of grazed temperate woodlands. This study shows that nurse plants may start as protégés before becoming facilitators for other plants in a later life stage. This may be common for nurse plants in various ecosystems. We argue that improved understanding of establishment of nurse plants and their constraining factors is crucial for effective conservation and restoration in various ecosystems.     

Effects of light competition and litter on the performance of Viola palustris and on species composition and diversity of an abandoned fen meadow

Theeffects of light competition and litter on seedling recruitment and theperformance of established individuals were examined in Violapalustris. This polycarpic perennial plant was a common component ofspecies-rich fen meadows in northwestern Germany until the middle of thiscentury, but today is considered to be regionally endangered. From summer 1996until summer 1998 a bi-factorial field experiment combining three standing croptreatments (mowing, thinning, control) with two litter layer treatments (litterremoval, no litter removal) was carried out in an abandoned fen meadow toinvestigate the effects of these factors both on V.palustris and on aboveground species composition and diversity.MANOVAs (multivariate analysis of variance) revealed significant treatmenteffects for the performance of V. palustris related toexperimental manipulation. Mowing increased vital attributes including thenumber of rosette leaves, the percentage of individuals with chasmogamous andcleistogamous flowers and the number of rhizomes. In contrast, the length of theleafstalk, mean leaf area and the length of rhizomes were negatively associatedwith mowing. Litter removal significantly increased the number of V.palustris seedlings. The removal of the litter layer already resultedin an increase in aboveground species richness in the first year of theexperiment. After three years of experimental manipulation, both abovegroundspecies richness and diversity were positively associated with mowing.Redundancy Analysis showed that typical wet meadow species (Cardaminepratensis, Lychnis flos-cuculi, Lotuspedunculatus) and species of mesotrophic fens (Violapalustris, Agrostis canina, Potentillapalustris) were positively influenced by mowing. It can be concludedthat V. palustris recruitment and growth is promoted by aregular disturbance regime on fen meadows. The conservation of many typicalspecies of wet meadows and fens in northwestern Germany depends on moderategrazing or cutting. These management types prevent successional changes whichlead to an increase in standing crop and the development of a litter layer, bothof which can cause local extinction.     

Nutrient concentrations and fibre contents of plant community biomass reflect species richness patterns along a broad range of land-use intensities among agricultural grasslands

Understanding changes in biodiversity in agricultural landscapes in relation to land-use type and intensity is a major issue in current ecological research. In this context nutrient enrichment has been identified as a key mechanism inducing species loss in Central European grassland ecosystems. At the same time, insights into the linkage between agricultural land use and plant nutrient status are largely missing. So far, studies on the relationship between chemical composition of plant community biomass and biodiversity have mainly been restricted to wetlands and all these studies neglected the effects of land use. Therefore, we analyzed aboveground biomass of 145 grassland plots covering a gradient of land-use intensities in three regions across Germany. In particular, we explored relationships between vascular plant species richness and nutrient concentrations as well as fibre contents (neutral and acid detergent fibre and lignin) in the aboveground community biomass.We found the concentrations of several nutrients in the biomass to be closely linked to plant species richness and land use. Whereas phosphorus concentrations increased with land-use intensity and decreased with plant species richness, nitrogen and potassium concentrations showed less clear patterns. Fibre fractions were negatively related to nutrient concentrations in biomass, but hardly to land-use measures and species richness. Only high lignin contents were positively associated with species richness of grasslands. The N:P ratio was strongly positively related to species richness and even more so to the number of endangered plant species, indicating a higher persistence of endangered species under P (co-)limited conditions. Therefore, we stress the importance of low P supply for species-rich grasslands and suggest the N:P ratio in community biomass to be a useful proxy of the conservation value of agriculturally used grasslands.     

Bio-available amino acids and mineral nitrogen forms in soil of moderately mown and abandoned mountain meadows

Summary. The abandonment of traditional mowing methods of mountain meadows in the Czech Republic at the end of the last century has resulted in secondary re-colonization of these areas. Altered accumulation of plant biomass resulted in a deceleration of N turnover. A mountain meadow may be regarded as a N-limited ecosystem in which plant nutrition is dependent on direct uptake of soil amino acids. The composition and distribution of ammonium ions, nitrate ions and the 16 bio-available proteinaceuous amino acids were investigated in the top 7 cm of the Ah horizon of a Gleyic Luvisol in a long-term moderately mown meadow and an eleven year old, abandoned or uncut meadow. Ammonium N has a dominant role in both ecosystems. The moderately mown meadow showed accelerated N-turnover and higher net ammonization. The plant community showed a dependence on this form. Plant utilization of nitrates and amino acids appeared to be negligible. The uncut or abandoned meadow showed net ammonization from May (start of the experiment) through August, after which plant N-uptake consisted only of amino acids due to microbial immobilization. The release of bio-available nitrogen from spring until the beginning of summer in the Ah horizon was too low to explain total plant N-uptake. Glutamic acid, arginine and aspartic acids had the highest concentrations of any of the amino acids analyzed. Authors’ address: Pavel Formánek, Department of Geology and Pedology, Mendel University of Agriculture and Forestry, Zemedelska 3, 613 00 Brno, Czech Republic     

The role of landuse and natural determinants for grassland vegetation composition in the Swiss Alps

The Alps provide a high habitat diversity for plant species, structured by broad- and fine-scale abiotic site conditions. In man-made grasslands, vegetation composition is additionally affected by the type of landuse. We recorded vegetation composition in 216 parcels of grassland in 12 municipalities representing an area of 170×70 km in the south-eastern part of the Swiss Alps. Each parcel was characterized by a combination of altitudinal level (valley, intermediate, alp), traditional landuse (mown, grazed), current management (mown, grazed, abandoned), and fertilization (unfertilized, fertilized). For each parcel we also assessed the abiotic factors aspect, slope, pH value, and geographic coordinates, and for each municipality annual precipitation and its cultural tradition. We analysed vegetation composition using (i) variation partitioning in RDA, (ii) cover of graminoids, non-legume forbs, and legumes, and (iii) dominance and frequency of species. Species composition was determined by, in decreasing order of variation explained, landuse, broad-scale abiotic factors, fine-scale abiotic factors, and cultural tradition. Current socio-economically motivated landuse changes, such as grazing of unfertilized former meadows or their abandonment, strongly affect vegetation composition. In our study, the frequency of characteristic meadow species was significantly smaller in grazed and even smaller in abandoned parcels than in still mown ones, suggesting less severe consequences of grazing for vegetation composition than of abandonment. Therefore, low-intensity grazing and mowing every few years should be considered valuable conservation alternatives to abandonment. Furthermore, because each landuse type was characterized by different species, a high variety of landuse types should be promoted to preserve plant species diversity in Alpine grasslands.     

Nitrogen and phosphorus limitation in a coastal barrier salt marsh: the implications for vegetation succession

1 A factorial fertilizer experiment was conducted in a 15-year-old coastal barrier salt marsh with a low soil nitrogen content, and in an older 100-year-old marsh with a higher nitrogen content. Plots were fertilized at high and low marsh elevations in both marshes. Nitrogen and phosphorus were applied at low and high concentrations both separately and in combination in each of 3 successive years.
2 Nitrogen limited above-ground plant growth in both young and old salt marshes in all years. Phosphorus limitation of plant growth was apparent in the first year in the young marsh and in the last year in both marshes. In young marshes with low soil organic matter, phosphorus limitation may occur. In addition, phosphorus limitation occurs at both successional stages when a marsh is saturated with nitrogen.
3 Plant species that are typical of nitrogen-rich habitats and late successional stages significantly increased in biomass after fertilization. Limonium vulgare , a low stature species of early and intermediate successional stages, decreased in biomass, whereas the taller Elymus pycnanthus and Artemisia maritima increased. After 3 years of fertilization, plant species composition in a young marsh was similar to the species composition in an unfertilized older marsh. Fertilization of a 100-year-old marsh, however, still resulted in a change in plant species composition, suggesting that succession was still occurring and that, overall, plants in marshes of different age are similar in their response to fertilization.     

Whole-canopy nitrogen-use efficiency of pioneer species in early secondary forest succession in Vietnam

The size hierarchy among plants during forest succession can be influenced by differences in nitrogen-use efficiency (NUE). During succession, soil nitrogen availability decreases, which increases the importance for species to use nitrogen efficiently. We compare whole-canopy-NUE and its underlying traits among pioneer species in a tropical forest over the first years of succession. At the leaf level, potential photosynthetic NUE (PPNUE: light-saturated photosynthetic rate/leaf N content) was partly positively correlated with species growth rate but not to species height. Canopy-NUE differed two-fold among species. The species with the highest PPNUE and growth rate but with a small stature had a high canopy-NUE and the tallest species had a low canopy-NUE. Differences in canopy-NUE appeared to be largely determined by leaf life span (LLS) and nitrogen resorption. A high LLS or a high resorption resulted in a high mean residence time of nitrogen and thus a high canopy-NUE. Canopy-NUE of a species was different between successional stands that differed in age and thus in height, leaf-area index, and resource availability. Thus, an increase in competitive pressure with succession did cause some changes in the use of nitrogen, except for one species. Species that are generally considered part of the same functional group (pioneer trees) can differ considerably in NUE and its underlying traits.     

Linking small desert mammal distribution to habitat structure in a protected and grazed landscape of the Monte, Argentina

Interpretation of landscape patterns from the perspective of different species allows knowing the way in which they perceive landscape, and how their perception varies with scale. We examined distribution of four small mammal species at different scales over a landscape including protected and grazed areas, and associated species distribution with landscape structure. The study was conducted in the central Monte Desert (Reserve of Ñacuñán). Trap grids were set in both areas at two scales, varying their grain and extent. To determine whether spatial patterns are random, clumped or regular, we used a point pattern analysis. Logistic regressions were performed to relate the presence-absence of small mammals to environmental variables. Intensity of the point pattern was not constant, either in the Reserve or the grazed area. Small mammal abundance exhibited a heterogeneous distribution, and the existence of a first-order effect was detected for all species. No second-order effects were detected, the point pattern was random for all species in both areas. Both areas were differently perceived by rodent species. Habitat structure in both conditions and its variations with scale appear to be important factors affecting distribution patterns.     

Effects of habitat management on vegetation and above-ground nesting bees and wasps of orchard meadows in Central Europe

We studied the vegetation, stand structure and communities of above-ground nesting bees and wasps in 45 orchard meadows that were grazed, mown or abandoned (15 of each) in an agricultural landscape near Göttingen, Germany. Total species richness of plants was significantly lower and the proportion of dead wood was significantly higher on abandoned meadows compared to mown or grazed meadows. Species richness of bees, eumenid wasps and sphecid wasps did not differ between the three management types. Abundance of sphecid wasps was significantly higher on abandoned than on managed orchard meadows. Landscape context did not affect management type. The results suggest that management practises affect vegetation more significantly than the studied insect groups.