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Native Grassland (native + grassland)

Distribution by Scientific Domains

Earth and Environmental Science	52%
Life Sciences	47%

Selected Abstracts

Testing methods for reducing weed loads in preparation for reconstructing species-rich native grassland by direct seeding.

ECOLOGICAL MANAGEMENT & RESTORATION, Issue 2 2010
Paul Gibson-Roy
First page of article [source]

Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable cropping

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2002
W. Amelung
Summary Long-term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse-textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro-ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle-size fractions. Long-term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi-exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt- and clay-sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation. [source]

Argentine rangeland quality influences reproduction of yearling pregnant heifers?

GRASSLAND SCIENCE, Issue 2 2009
Liliana G. Hidalgo
Abstract The Flooding Pampa natural grasslands are gradually being transformed into croplands to increase the economic returns of ranches. It is therefore becoming necessary for stockmen to increase beef cattle efficiency to compete with crops and to maintain the native grassland and its associated fauna. However, natural grasslands during winter have the lowest content of nutrients of the year. We intend to demonstrate that, with breeding weights of over 65% of cow mature weight, low forage quality of rangelands during winter does not have a negative effect on reproduction. These higher breeding weights were obtained by selecting early born female calves and by grazing annual and cultivated pastures. Pregnant Aberdeen Angus yearling heifers (n = 90) were evaluated using a pregnancy test (May 2005) until the second calving (July 2006). At the beginning of the experiment, yearling heifers with live weight ranging 360,514 kg (mean, 425 kg ± 3.5 SE) were used. Cattle grazed native grasslands (humid mesophytic meadows and humid prairie grasslands) and old mixed pastures. The second pregnancy was high (100%), with the same mean calving date as in the first pregnancy (227 Julian days). Heifers which calved later in the first calving year were early calvers in the second year, resulting in the relatively constant average calving dates across the animals. [source]

Grazing exclusion as a conservation measure in a South Australian temperate native grassland

GRASSLAND SCIENCE, Issue 2 2009
Nicholas J. Souter
Abstract Many of South Australia's remnant temperate native grasslands are degraded by introduced livestock grazing. As a conservation measure, grazing was excluded from three 50 × 50 m exclosures in grazed native grassland. After 4 years, grazing removal had a noticeable effect on the grassland structure, increasing basal vegetation cover. Grazing removal had no significant effect on either native or exotic species richness, rather differences in richness changed as a result of interannual differences, such as the amount of rainfall that fell in the growing season. The percent cover of the native tussock grass Austrostipa spp. and the introduced annual grass Avena barbata, whilst fluctuating from year to year, both increased following the removal of grazing. Multivariate analyses showed that whilst only interannual differences affected community taxon richness, changes in structure were affected by the interaction between grazing treatment and year. Excluding livestock from a degraded grassland resulted in limited recovery and restoration of these endangered plant associations will require active rehabilitation efforts. [source]

Phenology of fine roots and leaves in forest and grassland

JOURNAL OF ECOLOGY, Issue 6 2008
Diego F. Steinaker
Summary 1The phenology of temperate vegetation is advancing in association with climate warming. Most phenology data, however, comes from flowers and tree leaves. We tested the generality of results from shoot phenology by expanding data collection in two new directions. We related forest leaf phenology to root phenology, and to phenology in a second habitat, grassland. 2We measured leaf and root phenology simultaneously in aspen forest and adjacent native grassland. Root growth accounts for 80,90% of productivity in these habitats. Seasonal variation in soil moisture and temperature were also measured. 3Forest leaf production was greatest about 45 days before peak root production, resulting in a significant negative correlation between leaf and root production in forest. Grassland leaf production was greatest about 15 days before peak root production, and grassland leaf and root production were significantly positively correlated. The duration of root production was 40% greater than that of shoot production. 4Forest leaf production increased significantly with increasing soil moisture, but not temperature. In contrast, the production of forest roots, grassland roots and grassland leaves increased significantly with soil temperature. 5Synthesis. The most commonly measured aspect of phenology, forest leaves, is out of step with the majority of production in forest, as well as phenology in grassland. The invasion of grassland by woody vegetation is characterized by a decoupling of root and shoot phenology, a result that has not been reported previously. Given the global nature of woody plant encroachment, this decoupling may influence our general understanding of productivity and carbon sequestration in response to warming. [source]

Lack of relationship between below-ground competition and allocation to roots in 10 grassland species

JOURNAL OF ECOLOGY, Issue 4 2003
James F. Cahill Jr
Summary 1A field experiment in a native grassland in Central Alberta, Canada, tested whether plants alter relative allocation to roots vs. shoots in response to below-ground competition, and whether the mass of a species' root system accounts for interspecific differences in below-ground competitive response. 2Seedlings of each of 10 native species were transplanted into the naturally occurring vegetation in the field at the start of the growing season. Root interactions between the target plants and their neighbours were manipulated through the use of PVC root exclusion tubes, with target plants grown with or without potential root interactions with their neighbours. Neighbour shoots were also tied back, forcing any target,neighbour interactions to be below ground. 3Below-ground competition generally reduced plant growth, with its relative magnitude varying among species. 4An allometric analysis indicated that competition below ground did not result in an increase in the relative biomass allocated to roots for any of the 10 target species. This is counter to the growth-balance hypothesis (and optimal foraging theory). Below-ground competition did increase root : shoot ratios, but this was due to reduced plant size (small plants have larger root : shoot ratios), rather than adaptive plasticity. 5A species' below-ground competitive ability was not related to its root system size. Although this finding is counter to commonly made assumptions, it is supported by other work demonstrating below-ground competition to be generally size-symmetric. 6Despite the majority of plant,plant interactions in grasslands being below ground, our understanding of plant competition above ground is significantly more robust. Several wide-spread assumptions regarding below-ground competition are suspect, and more multispecies studies such as this are required to provide a fuller picture of how plants respond to, and compete for, soil resources. [source]

Nitrogen biomarkers and their fate in soil,

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2003
Wulf Amelung
Abstract More than 90,% of the nitrogen (N) in soils can be organically bound, but the mechanisms and rates by which it is cycled have eluded researchers. The objective of this research was to contribute to a better understanding of the origin and transformation of soil organic N (SON) by using amino sugars and the enantiomers of amino acids as markers for microbial residues and/or aging processes. Studied samples presented here comprised (1) soil transects across different climates, (2) arable soils with different duration of cropping, and (3) radiocarbon-dated soil profiles. The results suggested that increased microbial alteration of SON temporarily results in a sequestration of N in microbial residues, which are mineralized at later stages of SON decomposition. Microorganisms increasingly sequestered N within intact cell wall residues as frost periods shortened. At a mean annual temperature above 12,15,°C, these residues were mineralized, probably due to limitations in additional substrates. Breaking the grassland for cropping caused rapid SON losses. Microbial residues were decomposed in preference to total N, this effect being enhanced at higher temperatures. Hence, climate and cultivation interactively affected SON dynamics. Nevertheless, not all SON was available to soil microorganisms. In soil profiles, L-aspartic acid and L-lysine slowly converted into their D-form, for lysine even at a similar rate in soils of different microbial activity. Formation of D-aspartate with time was, therefore, induced by microorganisms while that of D-lysine was not. The racemization of the two amino acids indicates that SON not available to microorganisms ages biotically and abiotically. In native soils, the latter is conserved for centuries, despite N deficiency frequently occurring in living terrestrial environments. Climate was not found to affect the fate of old protein constituents in surface soil. When native grassland was broken for cropping, however, old SON constituents had become available to microorganisms and were degraded. Stickstoff-Biomarker und ihre Dynamik im Boden Über 90,% des Stickstoffs im Boden können organisch gebunden sein. Um zu einem besseren Verständnis der Norg -Dynamik im Boden beitragen zu können, analysierte ich Aminozucker und Aminosäure-Enantiomere als Marker für mikrobielle N-Rückstände und/oder Alterungsprozesse von Norg im Boden. Das hier vorgestellte Untersuchungsmaterial umfasste (1) Bodentransekte entlang unterschiedlicher Klimate, (2) Ackerböden mit verschiedener Nutzungsdauer und (3) 14C-datierte Bodenprofile. Die Ergebnisse zeigten, dass mit fortschreitender Umwandlung des Norg mikrobielle N-Rückstände nur vorübergehend im Boden akkumulieren, da sie in späteren Abbauphasen wieder mineralisiert werden. Mikroorganismen bauten zunehmend N in intakte Zellwandrückstände ein, wenn sich die Frostperioden verkürzten. Bei einer Jahresmitteltemperatur über 12,15,°C sank der Beitrag mikrobieller Rückstände zum N-Gehalt, vermutlich weil Mikroorganismen diese mangels anderer Substrate verstärkt mineralisierten. Umbrüche von Gras- zu Ackerland führten zu raschen N-Verlusten. Mikrobielle N-Rückstände wurden bevorzugt abgebaut, ein Effekt, den höhere Temperaturen verstärkten. Demnach steuerte das Klima die Intensität von Nutzungseffekten auf die Norg -Dynamik. Doch nicht der gesamte Norg war für Mikroorganismen zugänglich. Der D-Gehalt von Asparaginsäure und Lysin nahm mit steigendem Alter der organischen Bodensubstanz zu, Lysin racemisierte in den verschiedenen Böden sogar mit gleicher Geschwindigkeit. Anders als die Bildung von D-Asparaginsäure wurde die von Lysin also nicht durch Mikroorganismen beeinflusst. Die Racemisierung der beiden Aminosäuren deutet deshalb darauf hin, dass nicht-bioverfügbare Norg -Bestandteile biotisch und abiotisch im Boden altern. Klimaeinwirkungen auf den Verbleib alter Proteinrückstände ließen sich nicht feststellen. Mit Umbruch von Gras- zu Ackerland erhielten Mikroorganismen allerdings Zugang zu alten Norg -Verbindungen und bauten diese ab. [source]

Limited effects of above- and belowground insects on community structure and function in a species-rich grassland

JOURNAL OF VEGETATION SCIENCE, Issue 1 2009
Malcolm D. Coupe
Abstract Question: Do above- and belowground insects differentially impact plant community structure and function in a diverse native grassland? Location: Rough fescue prairie in Alberta, Canada. Methods: Above- and belowground insects were suppressed with insecticides for 5 years using a randomised block design. During this experiment, a severe drought began in 2001 and ended in 2003. Aboveground plant growth was measured as cover and biomass from 2001 to 2005. Root demography was measured in 2002 using a minirhizotron. Mixed models and repeated measures ANOVA were used to determine treatment effects on a number of response variables. MRBP were used to test for treatment effects on community composition. Results: Five years of insect suppression had few significant effects on plant growth, species richness or community composition, and were limited primarily to the severe drought in 2002. During the drought, insect attack increased root mortality, reduced plant cover, and altered community composition. Following the drought, plant responses were unaffected by insecticide application for the remainder of the experiment. Conclusions: Five years of insect suppression had only minor effects on community structure and function in this diverse native grassland. There was no indication that these effects increased over time. The results are counter to studies conducted in productive old-field communities that revealed large effects of insects on community structure. We suggest that the unique features of this system, such as high species evenness, abundance of generalist herbivores, and a lack of competition for light among plants, limited the potential for insects to greatly impact community-level processes. [source]

A conceptual model of plant community changes following cessation of cultivation in semi-arid grassland

APPLIED VEGETATION SCIENCE, Issue 4 2010
Nathan K. Wong
Abstract Question: Can vegetation changes that occur following cessation of cultivation for cereal crop production in semi-arid native grasslands be described using a conceptual model that explains plant community dynamics following disturbance? Location: Eighteen native grasslands with varying time-since-last cultivation across northern Victoria, Australia. Methods: We examined recovery of native grasslands after cessation of cultivation along a space for- time chronosequence. By documenting floristic composition and soil properties of grasslands with known cultivation histories, we established a conceptual model of the vegetation states that occur following cessation of cultivation and inferred transition pathways for community recovery. Results: Succession from an exotic-dominated grassland to native grassland followed a linear trajectory. These changes represent an increase in richness and cover of native forbs, a decrease in cover of exotic annual species and little change in native perennial graminoids and exotic perennial forbs. Using a state-and-transition model, two distinct vegetation states were evident: (1) an unstable, recently cultivated state, dominated by exotic annuals, and (2) a more diverse, stable state. The last-mentioned state can be divided into two further states based on species composition: (1) a never-cultivated state dominated by native perennial shrubs and grasses, and (2) a long-uncultivated state dominated by a small number of native perennial and native and exotic annual species that is best described as a subset of the never-cultivated state. Transitions between these states are hypothesized to be dependent upon landscape context, seed availability and soil recovery. Conclusions: Legacies of past land use on soils and vegetation of semi-arid grasslands are not as persistent as in other Australian communities. Recovery appears to follow a linear, directional model of post-disturbance regeneration which may be advanced by overcoming dispersal barriers hypothesised to restrict recovery. [source]

Small-scale spatial dynamics of vegetation in a grazed Uruguayan grassland

AUSTRAL ECOLOGY, Issue 4 2009
MARCOS TEXEIRA
Abstract We explored the small-scale plant species mobility in a subhumid native grassland subjected to grazing by cattle in south-western Uruguay. We established four permanent plots of 40 × 40 cm, divided in 16 × 16 cells. In each cell, the presence of species was seasonally recorded for 2 years and annually recorded for 4 years. By nesting the cells, we studied the mobility at different scales, from 6.25 cm2 to 400 cm2. At each scale we measured species richness, cumulative richness and the turnover rates of the dominant species. We found that the cumulative species richness was an increasing power function, with higher accumulation rates with smaller spatial scale. Although species richness showed seasonal fluctuations, the mean species richness was constant during the study period. We detected significant spatio-temporal variability in mobility patterns among species. Certain species showed a high capacity to colonize new sites, whereas other species rotate among sites that they previously occupied. Grazed communities in Uruguayan Campos are structured as a dense matrix of perennials grasses and forbs, where vegetative propagation is the main form of growth of the species. The small-scale dynamics and the high variability in the mobility characteristics could be linked with the diversity of growth forms and spatial strategies of the species in this community. We believe that a high degree of small-scale spatial dynamics contribute to explain the species coexistence and the apparent stability of communities at local scales. [source]

Accentuation of phosphorus limitation in Geranium dissectum by nitrogen: an ecological genomics study

GLOBAL CHANGE BIOLOGY, Issue 8 2008
SUSAN SUMMERS THAYER
Abstract Global climate change experiments have shown changes in productivity, phenology, species composition, and nutrient acquisition and availability; yet, the underlying mechanisms for these responses, especially in multi-factorial experiments, are poorly understood. Altered nutrient availability is a major consequence of global change, directly due to anthropogenic nitrogen (N) deposition, and indirectly due to shifts in temperature and water availability. In the Jasper Ridge Global Change Experiment, microarrays were used to investigate the transcriptional responses of the dominant dicot, Geranium dissectum, to simulated N deposition. The transcript levels for several photosynthetic genes were elevated in plants exposed to elevated N, as has been reported previously, validating the use of microarrays under field conditions. A coordinated response of a suite of genes previously reported to be induced in response to phosphate (Pi) deficiency was observed, including genes for the glycolytic bypass pathway, which reduces ATP and Pi requirements for sugar degradation, suggesting that the plants were phosphorus (P) limited. Confirming this conclusion, foliar P levels in G. dissectum leaves were reduced to levels that are suboptimal for growth in plants grown in elevated N and elevated CO2 plots. Thus, although plants commonly produce more biomass in response to elevated N in native grasslands, this growth response may be suboptimal due to a P limitation. Foliar P levels in plants from elevated CO2 plots were also suboptimal for growth. However, genes indicative of Pi deficiency were not significantly expressed at higher levels. Transcript levels for genes involved in nitrate uptake and assimilation were unchanged by the elevated N deposition treatment, possibly due to the combined impacts of elevated N deposition and P limitation under field conditions. These observations highlight the complexity of the impact of global climate change factors in the field. [source]

Land-use impact on ecosystem functioning in eastern Colorado, USA

GLOBAL CHANGE BIOLOGY, Issue 6 2001
J. M. Paruelo
Abstract Land-cover change associated with agriculture has had an enormous effect on the structure and functioning of temperate ecosystems. However, the empirical evidence for the impact of land use on ecosystem functioning at the regional scale is scarce. Most of our knowledge on land-use impact has been derived from simulation studies or from small plot experiments. In this article we studied the effects of land use on (i) the seasonal dynamics and (ii) the interannual variability of the Normalized Difference Vegetation Index (NDVI), a variable linearly related to the fraction of the photosynthetically active radiation (PAR) intercepted by the canopy. We also analysed the relative importance of environmental factors and land use on the spatial patterns of NDVI. We compared three cultivated land-cover types against native grasslands. The seasonal dynamics of NDVI was used as a descriptor of ecosystem functioning. In order to reduce the dimensionality of our data we analysed the annual integral (NDVI-I), the date of maximum NDVI (DMAX) and the quarterly average NDVI. These attributes were studied for 7 years and for 346 sites distributed across eastern Colorado (USA). Land use did modify ecosystem functioning at the regional level in eastern Colorado. The seasonal dynamics of NDVI, a surrogate for the fraction of PAR intercepted by the canopy, were significantly altered by agricultural practices. Land use modified both the NDVI integral and the seasonal dynamics of this spectral index. Despite the variability within land-cover categories, land use was the most important factor in explaining regional differences of the NDVI attributes analysed. Within the range of environmental conditions found in eastern Colorado, land use was more important than mean annual precipitation, mean annual temperature and soil texture in determining the seasonal dynamics of NDVI. [source]

Argentine rangeland quality influences reproduction of yearling pregnant heifers?

Grazing exclusion as a conservation measure in a South Australian temperate native grassland

Grasshopper Herbivory Affects Native Plant Diversity and Abundance in a Grassland Dominated by the Exotic Grass Agropyron cristatum

RESTORATION ECOLOGY, Issue 1 2009
David H. Branson
Abstract The indirect effects of native generalist insect herbivores on interactions between exotic and native grassland plants have received limited attention. Crested wheatgrass (Agropyron cristatum) is the most common exotic rangeland grass in western North America. Crested wheatgrass communities are resistant to colonization by native plant species and have strong competitive effects on native species, imposing problems for the restoration of native grasslands. Grasshoppers are generalist herbivores that are often abundant in Crested wheatgrass,dominated sites in the northern Great Plains. We conducted two experiments in a Crested wheatgrass,dominated grassland in western North Dakota to test the hypothesis that grasshopper herbivory influences local Crested wheatgrass community composition by impeding native seedlings. Grasshopper herbivory negatively affected the species richness, abundance, and Shannon diversity of native plants in 3 of 4 years. Although additional research is needed to determine if grasshoppers actively select native plants, the effects of grasshopper herbivory may be an important consideration in the restoration of Crested wheatgrass areas. Our findings illustrate the importance of understanding the impact of native generalist invertebrate herbivores on the relationships between exotic and native plants. [source]

A conceptual model of plant community changes following cessation of cultivation in semi-arid grassland

Flooding and grazing promote germination and seedling establishment in the perennial grass Paspalum dilatatum

AUSTRAL ECOLOGY, Issue 3 2009
PATRICIA S. CORNAGLIA
Abstract Seed germination and seedling emergence are key processes for population recruitment. Flooding and grazing are disturbances forming gaps that may strongly influence recruitment patterns in space and time, but their combined effects and action mechanisms have rarely been addressed. In this study we analysed the effects of microhabitat conditions associated with winter flooding and spring-summer defoliation on seed germination and seedling establishment of Paspalum dilatatum, a dominant perennial C4 grass in native grasslands of the Flooding Pampa, Argentina. The dynamics of seedling emergence from natural seed banks and buried seeds was studied in a factorial experiment with flooding and defoliation treatments applied to soil monoliths (mesocosms) collected from natural grassland. Additional laboratory experiments were applied to investigate seed germination under different combinations of temperature, light quality and simulated flooding. Seed germination and seedling emergence of P. dilatatum were promoted by flooding and high intensity defoliation. Gaps generated by flooding were maintained by high intensity defoliation exercising a synergistic effect on survival seedlings. Flooding resulted in the breaking of seed dormancy and higher germination rates associated with alternating temperature and the activation of the phytochrome system. Our results indicate that microhabitat conditions associated with the disturbances forming gaps, such as flooding and heavy grazing, synergistically promote the recruitment process of this dominant grass species. [source]

Effects of spatial aggregation on competition, complementarity and resource use

AUSTRAL ECOLOGY, Issue 3 2008
KAREL MOKANY
Abstract The spatial distributions of most species are aggregated to varying degrees. A limited number of studies have examined the effects of spatial aggregation on interspecific and intraspecific interactions, generally finding that spatial aggregation can enhance coexistence between species by reducing the capacity for interspecific competition. Less well studied are the effects of spatial aggregation on complementarity (i.e. differences in resource use strategies) and resource use. Our primary hypothesis was that spatial aggregation reduces the complementarity between species owing to: (i) less interspecific interactions as a result of spatial separation; and (ii) less differences between species as a result of phenotypic plasticity. We further postulate that these negative effects of spatial aggregation on complementarity will reduce resource use by the community. Here we test these hypotheses in a pot experiment in which we applied three levels of spatial aggregation to three sets of two-species mixtures of herbaceous perennial plant species from native grasslands of south-eastern Australia. Both root and shoot biomass were significantly affected by spatial aggregation, although the nature of these affects depended upon the species involved, and the relative strengths of interspecific versus intraspecific competition. Complementarity between species in the distribution of their green leaves decreased significantly as spatial aggregation increased for one of the species mixtures, providing some evidence in support of our hypothesis that aggregation reduces complementarity through phenotypic plasticity. Spatial aggregation also altered light interception and use of soil moisture resources, although these effects were dependent on the species involved. We suggest that clear effects of spatial aggregation on complementarity and resource use may be obscured by the idiosyncratic way in which neighbour identity influences plant growth and hence plant size, limiting the ability to generalize, at the community level, any underlying effects of spatial pattern on ecological process. [source]

Grassland invertebrate assemblages in managed landscapes: Effect of host plant and microhabitat architecture

AUSTRAL ECOLOGY, Issue 6 2007
ADELE M. REID
Abstract Grasslands are often considered as two-dimensional habitats rather than complex, multilayered habitats. However, native grasslands are complex habitats, with multiple layers of annual and perennial grasses, sedges, shrubs and mosses. Vegetation complexity, including plant type, quality and three-dimensional structure is important for providing a variety of food and habitat resources for insects. Grazing by domestic livestock can affect these processes through the loss or fragmentation of habitats, as well as altering the vertical and horizontal vegetation structure. This study aimed to investigate the role of host plants and microhabitat architecture for determining foliage invertebrate assemblages. Different plant species supported distinct invertebrate assemblages and less complex host plants supported fewer invertebrate individuals and species. Manipulations of plant architecture changed the species composition of invertebrates, with most species found in more complex vegetation. This study illustrates the importance of host diversity and pasture complexity for invertebrate communities. Management practices that encourage a heterogeneous environment with diverse and structurally complex pastures should also sustain a more diverse and functional invertebrate assemblage. [source]