Grassland Community Composition Research Articles

Responses of a California annual grassland to litter manipulation

AbstractQuestion:What are the physical and chemical effects of plant litter on annual grassland community composition, above‐ground net primary production (ANPP), and density?Location:California annual grassland.Methods:We manipulated litter and light levels independently and in concert. Litter removal and litter addition treatments tested both the physical and chemical impacts of litter's presence. We additionally simulated the effect of litter physical shading by using shade cloth, and added powdered litter to test for the chemical impacts of decomposing litter.Results:Increased whole litter and shading decreased grass germination and establishment, but not that of forbs or legumes. Species shifts occurred within all groups across treatments, including a transition from small‐seeded to large‐seeded grass and legume species with increased shading. ANPP was highest in control plots (473 ± 59 g/m2), and species richness was highest in litter removal plots. While the physical effects of litter via shading were significant, the chemical effects of adding powdered litter were negligible.Conclusions:This work suggests that over one growing season, the physical impacts of litter are more important than chemical impacts in shaping community structure and ANPP in annual grasslands. Changes in light availability with altered litter inputs drive shifts in species and functional group composition. Litter feedbacks to ANPP and species composition of local patches may help maintain diversity and stabilize ANPP in this grassland.

The significance of small herbivores in structuring annual grassland

Abstract Question: Herbivores can play a fundamental role in regulating the composition and structure of terrestrial plant communities. Relatively inconspicuous but nevertheless ubiquitous gastropods and small mammals are usually considered to influence grassland communities through distinct modes. 1. Do terrestrial gastropods and small mammals, either alone or in combination, influence plant community composition of an intact annual grassland? 2. Do these herbivores influence the plant size structure of the dominant grass Avena? Location: Jasper Ridge Biological Preserve (37°24′ N, 122°13′ W, elevation 150 m) in northern California. Methods: Animal exclosures were used to examine the single and combined influences of these herbivores on annual grassland production, community composition, and plant size structure during the growing season of an intact annual grassland. Results: The removal and exclusion of the herbivores increased the prevalence of grasses relative to legumes and non-legume forbs; increas...

Effect of Sheep Urine Deposition on the Bacterial Community Structure in an Acidic Upland Grassland Soil

The effect of the addition of synthetic sheep urine (SSU) and plant species on the bacterial community composition of upland acidic grasslands was studied using a microcosm approach. Low, medium, and high concentrations of SSU were applied to pots containing plant species typical of both unimproved (Agrostis capillaris) and agriculturally improved (Lolium perenne) grasslands, and harvests were carried out 10 days and 50 days after the addition of SSU. SSU application significantly increased both soil pH (P < 0.005), with pH values ranging from pH 5.4 (zero SSU) to pH 6.4 (high SSU), and microbial activity (P < 0.005), with treatment with medium and high levels of SSU displaying significantly higher microbial activity (triphenylformazan dehydrogenase activity) than treatment of soil with zero or low concentrations of SSU. Microbial biomass, however, was not significantly altered by any of the SSU applications. Plant species alone had no effect on microbial biomass or activity. Bacterial community structure was profiled using bacterial automated ribosomal intergenic spacer analysis. Multidimensional scaling plots indicated that applications of high concentrations of SSU significantly altered the bacterial community composition in the presence of plant species but at different times: 10 days after application of high concentrations of SSU, the bacterial community composition of L. perenne-planted soils differed significantly from those of any other soils, whereas in the case of A. capillaris-planted soils, the bacterial community composition was different 50 days after treatment with high concentrations of SSU. Canonical correspondence analysis also highlighted the importance of interactions between SSU addition, plant species, and time in the bacterial community structure. This study has shown that the response of plants and bacterial communities to sheep urine deposition in grasslands is dependent on both the grass species present and the concentration of SSU applied, which may have important ecological consequences for agricultural grasslands.

Herbivore control of annual grassland composition in current and future environments

Selective consumption by herbivores influences the composition and structure of a range of plant communities. Anthropogenically driven global environmental changes, including increased atmospheric carbon dioxide (CO(2)), warming, increased precipitation, and increased N deposition, directly alter plant physiological properties, which may in turn modify herbivore consumption patterns. In this study, we tested the hypothesis that responses of annual grassland composition to global changes can be predicted exclusively from environmentally induced changes in the consumption patterns of a group of widespread herbivores, the terrestrial gastropods. This was done by: (1) assessing gastropod impacts on grassland composition under ambient conditions; (2) quantifying environmentally induced changes in gastropod feeding behaviour; (3) predicting how grassland composition would respond to global-change manipulations if influenced only by herbivore consumption preferences; and (4) comparing these predictions to observed responses of grassland community composition to simulated global changes. Gastropod herbivores consume nearly half of aboveground production in this system. Global changes induced species-specific changes in plant leaf characteristics, leading gastropods to alter the relative amounts of different plant types consumed. These changes in gastropod feeding preferences consistently explained global-change-induced responses of functional group abundance in an intact annual grassland exposed to simulated future environments. For four of the five global change scenarios, gastropod impacts explained > 50% of the quantitative changes, indicating that herbivore preferences can be a major driver of plant community responses to global changes.

Influence of land use on plant community composition and diversity in Highland Sourveld grassland in the southern Drakensberg, South Africa

Summary Biodiversity conservation of grasslands in the face of transformation and global climate change will depend mainly on rangelands because of insufficient conservation areas in regions suited to agriculture. Transformed vegetation (pastures, crops and plantations) is not expected to conserve much biodiversity. This study examined the impact of land use on the plant diversity and community composition of the southern Drakensberg grasslands in South Africa, which are threatened with complete transformation to pastures, crops and plantations. The main land uses in this high rainfall region are: ranching or dairy production under private tenure using indigenous grassland, pastures (Eragrostis curvula, kikuyu and ryegrass) and maize; plantation forestry; communal tenure (maize and rangelands); and conservation. Plant diversity and composition were assessed using Whittaker plots. Transformed cover types were depauperate in species and ranged from kikuyu (1·4 species m−2) and ryegrass (2·9), to pine plantation (3·1), E. curvula pasture (3·1), commercial maize (3·2) and communal maize (7·8). With the exception of pine plantations, these communities supported mostly exotic (50 of 70 species) or ruderal indigenous species and made little contribution to plant species conservation. Abandoned communal cropland reverted to an indigenous grassland almost devoid of exotic species within c. 20 years. It was predicted that frequently cultivated sites (maize and ryegrass) would support less diversity than long‐lived pastures (kikuyu and E. curvula). This was contradicted by the relatively high species diversity of communal maize fields, which was attributed to a lack of herbicides, and the depauperate communities of kikuyu and of E. curvula pasture, which were attributed, respectively, to a dense growth form and a severe mowing regime. Pine plantations harboured fourfold more indigenous species per plot (27) than other transformed types. Species were mostly shade‐tolerant grassland relics that had persisted for 12 years since planting, and some forest colonizers. Indigenous species were unlikely to be maintained because of aggressive invasion by the exotic Rubus cuneifolius and severe disturbance associated with tree harvest and replanting. The richness of indigenous grasslands was expected to differ in response to grazing pressure but they differed only in composition. Grasslands were dominated by grasses, despite the richness of herbaceous species. The dominance of Themeda triandra was reduced under livestock grazing in favour of more grazing‐tolerant species. Exotic species were inconspicuous except for the dicotyledon Richardia brasiliensis, a subdominant under communal grazing. Southern Drakensberg grasslands are probably now stocked with livestock six‐ to 35‐fold higher than during pre‐settlement times. A grassland protected for c. 50 years supported twofold greater richness (101 species plot−1) than grazed grasslands, suggesting that a 150‐year history of increased mammalian grazing had already reduced plant diversity. Synthesis and applications. Land acquisition is costly, thus conservation of plant diversity in the southern Drakensberg requires a policy that inhibits transformation of rangelands. This can be achieved by enhancing their economic viability without changing the vegetation composition. Their inherent value must be recognized, such as for water production. The viability of commercial ranches can be improved by increasing their size. Conservation efforts need to be focused on plant taxa that only occur on unprotected rangelands.

Virus infection in remnant native bunchgrasses from invaded California grasslands

This study examined the effects of infection with barley and cereal yellow dwarf viruses (BYDVs) on wild grass species in California, a region in which native perennial bunchgrasses have been largely replaced by exotic annual grasses. We sought to determine whether these widespread viruses compromise the fitness of wild hosts and thus have the potential to influence grassland dynamics. Plant viruses have been long overlooked in ecological studies, and their influence on wild hosts has often been assumed to be minimal. We examined the short-term and long-term consequences of infection on field-grown individuals from 18 different populations of wild California grasses (from seven native and one exotic species). Barley yellow dwarf virus infection was aggressive in most hosts and markedly impaired host fitness by reducing growth, survivorship, and fecundity. Previous work indicates that the presence of exotic grasses can more than double BYDV incidence in natives. Given the ubiquity of BYDVs, our results suggest that apparent competition and other virus-mediated processes may influence interactions among native and exotic grasses and potentially contribute to shifts in grassland community composition.

Effects of charring on the carbon isotopic composition of grass (Poaceae) epidermis

Charred modern grass epidermis preserves the carbon isotopic composition of the parent plant photosynthetic pathway. Fifty-nine modern grasses and sedges were collected in lowland western Uganda. All charred epidermal samples from C 4 grasses or sedges preserve a carbon isotopic value within the range typical for C 4 plants (−17 to −10‰), and charred epidermal fragments from C 3 plants have carbon isotopic values between −30 and −26‰. The process of charring results in a slightly enriched carbon isotopic signature (−11.9‰ mean charred value as compared to −12.8‰ mean unaltered grass tissue value). δ 13C measurements of replicate samples from the same plant vary within 1–2‰, yet all values for the same plant stay within the expected values for the photosynthetic pathway of the plant. δ 13C measurements on >180-μm charred grass epidermal fragments extracted from surface sediment samples from three lakes on the lowland western Ugandan landscape confirm the predominant lowland C 4 grass input (δ 13C=−16 to −19‰). These results demonstrate the utility of using carbon isotopic analysis of charred grass epidermis to reconstruct C 3 vs. C 4 grassland assemblages on the landscape. Furthermore, such downcore δ 13C profiles can be used to highlight key zones of C 3 vs. C 4 grass change for which taxonomic analysis of fossil grass epidermis could provide more detailed information regarding grassland community composition.

Effect of AM symbiosis exclusion on grassland community composition

Experimental data on grassland community response to exclusion of arbuscular mycorrhizal (AM) symbiosis using fungicide benomyl and to phosphate addition were evaluated after four years of continued manipulation using multivariate direct gradient analysis. While the community responded only to phosphate application in the third year (phosphate application suppressing forbs in favour of graminoids), the data from the fourth season indicate relative suppression of some forbs (includingPlantago lanceolata, Cerastium holosteoides) with both phosphate and fungicide applications. Positive response of graminoids to phosphate addition seems to interact with fungicide application, while an important community constituent —Achillea millefolium — seems to profit primarily from fungicide applications. The effect of the fungicide on the AM symbiosis was confirmed on roots ofPlantago lanceolata. The direct evaluation of frequency of AM fungal structures in plant roots also revealed a diverse response of different plant species to phosphate application. Nevertheless, in all species (except non-mycorrhizalLuzula campestris), phosphate decreased the frequency of arbuscules and increased the frequency of non-infected root segments.

Functional interpretation of archaeobotanical data: Making hay in the archaeological record

Hay malting and hay meadows have long been of fundamental ecological, economic and social importance in temperate Europe. A variety of archaeological sources suggests that hay making may date back to the Iron Age, but direct archaeobotanical evidence for this practice is problematic. Past grassland communities are imperfectly represented and preserved in archaeobotanical assemblages, and ancient meadow and pasture communities may not resemble present-day communities in terms of management practices or botanical composition. This paper explores the potential of ‘FIBS’ (Functional Interpretation of Botanical Surveys) in the archaeobotanical investigation of ancient grassland management. The botanical composition of present-day grassland communities was analysed in terms of functional attributes (e.g. canopy height) relevant to cutting, grazing and habitat productivity. The utility of these attributes for distinguishing between present-day meadow, pasture and unmanaged grassland communities has been evaluated. Similar analyses were performed on archaeobotanical data from Neolithic to post-Medieval northwestern and central Europe. Functional shifts over time, interpreted in the light of the functional analysis of modern grassland, suggest that hay-making was well established by the Iron Age. Avenues are suggested for the refinement and further development of the FIBS methodology in the archaeobotanical investigation of grassland management.

Elevated CO 2and water supply interactions in grasslands: a pastures and rangelands management perspective

Water is a key variable driving the composition and productivity of pastures and rangelands, and many of the ecosystems in these grasslands are highly sensitive to changes in water supply. The possibility that elevated CO2 concentrations may alter plant water relations is therefore particularly relevant to pastures and rangelands, and may have important consequences for grassland ecosystem function, water use, carbon storage and nutrient cycling. The planning of effective research to better understand these changes requires attention to both: (i) gaps in knowledge about CO2 and water interactions, and (ii) knowledge of how precisely the effects of CO2 must be understood in relation to other factors, in order to predict changes in grassland structure and production. A recent microcosm experiment illustrates that non‐linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosystems remain to be precisely determined through ecosystem‐level experiments. A simplified simulation of the impact of different levels of productivity change in a water‐limited Australian rangeland system was conducted by varying effects of CO2 on radiation and water use efficiency. The results indicate that direct effects of CO2 may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO2 on water supply to grassland ecosystems.

The contributions of Dr Raymond Wilkie Brougham to grassland science and management

The contributions to grasslands research and practice of the internationally notable New Zealand Scientist, Dr Raymond Wilkie Brougham are reviewed. He made significant contributions to the fundamental understanding of processes in pasture establishment, pasture growth particularly its relationship with leaf area and light interception, and to grazing management effects on the botanical and genetic composition of grassland communities.

The Effects of Ozone and Cutting on the Species Composition of Artificial Grassland Communities

1. Pots containing a mixture of the grasses Agrostis capillaris and Festuca rubra and the forbs Trifolium repens and Veronica chamaedrys were exposed to ozone in open-top chambers ventilated with charcoal-filtered air. Total ozone exposure ranged from 800 nl l -1 h above 40 nl l -1 to 15 000 nl l -1 h above 40 nl l -1 . 2. Half of the pots in each chamber were cut fortnightly. Linear relationships were fitted between biomass or proportion of each species and ozone exposure. 3. In uncut pots T. repens biomass decreased with increasing ozone but biomass of F. rubra increased, so that total biomass was unaffected. 4. Trifolium repens also declined in cut pots, in which the proportional reduction of its biomass was much greater. Agrostis capillaris biomass increased with ozone in cut pots, so that again total biomass did not decline significantly. The response of proportion of forbs to ozone was significantly greater in cut pots. 5. It is concluded that ozone exposures experienced in the UK may potentially affect the species composition of semi-natural grasslands, that cumulative exposure above a threshold of 40 nl l -1 may be used to express critical levels of ozone for such communities, and that cutting or grazing may influence community responses to ozone.

Effects of ozone on calcareous grassland communities

A system of 16 open-top chambers was used to investigate the effects of a range of ozone concentrations typical of those found in southern Britain on the species composition of calcareous grassland communities. Two experimental approaches were adopted: the first involved the use of artificial communities of species typical of calcareous grasslands, whilst the second involved semi-natural chalk grassland swards transplanted from the field. Elevated ozone had little effect on total biomass of the artificial communities, but did significantly alter the species composition. The proportion of forbs decreased linearly with increased ozone exposure above 40ppb. Species composition was stable in the transplanted swards receiving filtered air, whilst there was a shift towards what appeared to be a more calcareous grassland community in the swards treated with higher ozone exposures. Thus, both experiments provide evidence that ambient levels of ozone in southern Britain can cause changes in species composition of semi-natural calcareous grassland communities.

Palynological data on a holocene peat deposit in tropical Brasil: preliminary paleoclimatic and paleoecological interpretations

A evolução das vertentes do planalto de Campos do Jordão durante o Pleistoceno é documentada por três gerações de anfiteatros de erosão, que refletem uma seqüência de importantes movimentos de massa relacionados a fases de incisão de caráter tectônico e a flutuações climáticas - provavelmente na transição para os climas mais secos contemporâneos das duas últimas glaciações do hemisfério norte. No Holoceno, processos com menor ação erosiva teriam depositado os colúvios das vertentes, evidenciando diminuição do ritmo de levantamento do planalto e da intensidade das flutuações do clima de montanha. O acentuado contraste ambiental criado pelo aparecimento dos anfiteatros teria condicionado a distribuição da vegetação e a organização do mosaico mata-campo. O estudo palinológico de um depósito turfoso de base de anfiteatro permitiu detectar mudanças na cobertura vegetal do planalto durante o Holoceno Superior. Variações das associações vegetais das matas e dos campos seriam explicadas pelo ajustamento das formações vegetais a variações das condições de temperatura e umidade. Estas modificações refletiriam a transição dos climas mais quentes e provavelmente mais secos do Holoceno Médio para o clima atual do planalto, caracterizado por temperaturas mais baixas e por distribuição mais homogênea das chuvas.

The composition, structure and distribution of heathland and grassland communities in the subalpine tract of the Bogong High Plains, Victoria

Abstract In the subalpine tract of the Bogong High Plains (37°S, 147°E; altitude 1600–1800 m a.s.l.) the vegetation consists of a mosaic of snow gum (Eucalyptus pauciflora) woodland, heathland, grassland and wetland communities. Classification (polythetic‐agglomerative) and ordination (principal co‐ordinates analysis) of quadrat data from heathlands and grasslands on relatively well drained sites allowed the identification of four main heathland and grassland vegetation units. These units may be ranked in a structural and floristic continuum, from closed heath variously dominated by Prostanthera cuneata, Orites lancifolia and Phebalium squamulosum to closed heath dominated by P. squamulosum and Grevillea australis, open grassy heath of G. australis and Poa hiemata. and grassland of P. hiemata. The transition from Prostanthera closed heath to Poa grassland is correlated with gradients of decreasing steepness and rockiness of terrain, and increasing exposure and frost.