			Home About us Contact

Annual Grassland (annual + grassland)

Distribution by Scientific Domains

Life Sciences	50%
Earth and Environmental Science	50%

Distribution within Life Sciences

Conservation Science	66%
Ecology & Organismal Biology	32%

Kinds of Annual Grassland

california annual grassland

Selected Abstracts

Herbivore control of annual grassland composition in current and future environments

ECOLOGY LETTERS, Issue 1 2006
Halton A. Peters
Abstract 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 (CO2), 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. [source]

Several components of global change alter nitrifying and denitrifying activities in an annual grassland

FUNCTIONAL ECOLOGY, Issue 4 2006
R. BARNARD
Summary 1The effects of global change on below-ground processes of the nitrogen (N) cycle have repercussions for plant communities, productivity and trace gas effluxes. However, the interacting effects of different components of global change on nitrification or denitrification have rarely been studied in situ. 2We measured responses of nitrifying enzyme activity (NEA) and denitrifying enzyme activity (DEA) to over 4 years of exposure to several components of global change and their interaction (increased atmospheric CO2 concentration, temperature, precipitation and N addition) at peak biomass period in an annual grassland ecosystem. In order to provide insight into the mechanisms controlling the response of NEA and DEA to global change, we examined the relationships between these activities and soil moisture, microbial biomass C and N, and soil extractable N. 3Across all treatment combinations, NEA was decreased by elevated CO2 and increased by N addition. While elevated CO2 had no effect on NEA when not combined with other treatments, it suppressed the positive effect of N addition on NEA in all the treatments that included N addition. We found a significant CO2,N interaction for DEA, with a positive effect of elevated CO2 on DEA only in the treatments that included N addition, suggesting that N limitation of denitrifiers may have occurred in our system. Soil water content, extractable N concentrations and their interaction explained 74% of the variation in DEA. 4Our results show that the potentially large and interacting effects of different components of global change should be considered in predicting below-ground N responses of Mediterranean grasslands to future climate changes. [source]

Interactive effects of elevated CO2, N deposition and climate change on extracellular enzyme activity and soil density fractionation in a California annual grassland

GLOBAL CHANGE BIOLOGY, Issue 10 2005
Hugh A. L. Henry
Abstract Elevated CO2, N deposition and climate change can alter ecosystem-level nutrient cycling both directly and indirectly. We explored the interactive effects of these environmental changes on extracellular enzyme activity and organic matter fractionation in soils of a California annual grassland. The activities of hydrolases (polysaccharide-degrading enzymes and phosphatase) increased significantly in response to nitrate addition, which coincided with an increase in soluble C concentrations under ambient CO2. Water addition and elevated CO2 had negative but nonadditive effects on the activities of these enzymes. In contrast, water addition resulted in an increase in the activities of lignin-degrading enzymes (phenol oxidase and peroxidase), and a decrease in the free light fraction (FLF) of soil organic matter. Independent of treatment effects, lignin content in the FLF was negatively correlated with the quantity of FLF across all samples. Lignin concentrations were lower in the aggregate-occluded light fraction (OLF) than the FLF, and there was no correlation between percent lignin and OLF quantity, which was consistent with the protection of soil organic matter in aggregates. Elevated CO2 decreased the quantity of OLF and increased the OLF lignin concentration, however, which is consistent with increased degradation resulting from increased turnover of soil aggregates. Overall, these results suggest that the effects of N addition on hydrolase activity are offset by the interactive effects of water addition and elevated CO2, whereas water and elevated CO2 may cause an increase in the breakdown of soil organic matter as a result of their effects on lignin-degrading enzymes and soil aggregation, respectively. [source]

Root production and demography in a california annual grassland under elevated atmospheric carbon dioxide

GLOBAL CHANGE BIOLOGY, Issue 9 2002
Paul A. T. Higgins
Abstract This study examined root production and turnover in a California grassland during the third year of a long-term experiment with ambient (LO) and twice-ambient atmospheric CO2 (HI), using harvests, ingrowth cores, and minirhizotrons. Based on one-time harvest data, root biomass was 32% greater in the HI treatment, comparable to the stimulation of aboveground production during the study year. However, the 30,70% increase in photosynthesis under elevated CO2 for the dominant species in our system is considerably larger than the combined increase in above and belowground biomass. One possible explanation is, increased root turnover, which could be a sink for the additional fixed carbon. Cumulative root production in ingrowth cores from both treatments harvested at four dates was 2,3 times that in the single harvested cores, suggesting substantial root turnover within the growing season. Minirhizotron data confirmed this result, demonstrating that production and mortality occurred simultaneously through much of the season. As a result, cumulative root production was 54%, 47% and 44% greater than peak standing root length for the no chamber (X), LO, and HI plots, respectively. Elevated CO2, however, had little effect on rates of turnover (i.e. rates of turnover were equal in the LO and HI plots throughout most of the year) and cumulative root production was unaffected by treatment. Elevated CO2 increased monthly production of new root length (59%) only at the end of the season (April,June) when root growth had largely ceased in the LO plots but continued in the HI plots. This end-of-season increase in production coincided with an 18% greater soil moisture content in the HI plots previously described. Total standing root length was not affected by CO2 treatment. Root mortality was unaffected by elevated CO2 in all months except April, in which plants grown in the HI plots had higher mortality rates. Together, these results demonstrate that root turnover is considerable in the grassland community and easily missed by destructive soil coring. However, increased fine root turnover under elevated CO2 is apparently not a major sink for extra photosynthate in this system. [source]

The effect of small gaps in California annual grassland on above-ground biomass production

GRASS & FORAGE SCIENCE, Issue 4 2001
J. S. Fehmi
Small gaps and clumped species distributions are common in grasslands. In California annual grasslands, patches of Lolium multiflorum Lam. and Bromus hordeaceus L. are often separated by gaps. These gaps potentially limit the productivity and associated resource use of these grasslands. The effect that differences in spatial aggregation, gap distribution and species mixing on 20-cm-diameter plots has on overall forage production by these two grasses was tested. There were three levels of aggregation: whole plots planted; half planted/half empty; two opposing quarters planted/two empty. Each species was planted in each distribution, and they were combined as mixed, half L. multiflorum/half B. hordeaceus and two quarters L. multiflorum/two quarters B. hordeaceus (nine treatments). Plant aggregation had no significant effect on above-ground production of whole plots, but individual tillers near gaps were significantly larger than others. Plasticity in the growth of individual annual grasses effectively buffered against variation in average productivity resulting from variations in plant distribution. There were significant (P < 0·001) differences in forage production as a result of the species the plots contained. Plots containing only L. multiflorum produced 4053 kg of dry matter (DM) ha,1, B. hordeaceus plots produced 2448 kg of DM ha,1, and plots containing both species produced 4712 kg of DM ha,1. At small scales, spatial distribution was less important than species composition in determining annual grassland productivity. [source]

Landscape monitoring of semi-arid rangelands in the Kenyan Rift Valley

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2000
A. D. Q. Agnew
A sampling system was devised and used from 1992 to 1996 in annual grassland and open woodland of the south-west Kenyan Rift Valley. The monitoring was designed to detect vegetation changes consequent on the attempted removal of the tsetse vectors of trypanosomiasis in cattle during a simultaneous trapping programme. The sampled sites covered most vegetation-landscape types, and have led to a better understanding of processes within some. Although fluctuations in pastoralist use and occupancy have been observed, no change in vegetation can be attributed to increased grazing or browsing. Although there is high climatic variability some vegetation types seemed stable over the period studied, and some trends appear to be predictable. Resume On a conçu un système d'échantillonnage qui fut utilisé de 1992 à 1996 dans les prairies annuelles et dans les forêts ouvertes du sud-ouest de la Rift Valley, au Kenya. La surveillance était conçue de façon à détecter les changements de végétation qui résultaient des tentatives d'éradication des mouches tsé-tsé, vecteurs de la trypanosomiase chez le bétail, au cours d'un programme de piégeage. Les sites d'échantillonnages couvraient des paysages correspondant à la plupart des types de végétation et ont conduit à une meilleure compréhension du processus dans certains d'entre eux. Bien qu'on ait observé des fluctuations dans l'occupation et l'utilisation pastorales, on ne peut attribuer aucun changement de végétation à une augmentation du pâturage. Bien que le climat soit très variable, certains types de végétations semblent être restés stables pendant la durée de l'étude et l'on semble pouvoir prédire certaines tendances. [source]

Responses of a California annual grassland to litter manipulation

JOURNAL OF VEGETATION SCIENCE, Issue 5 2008
Kathryn L. Amatangelo
Abstract Question: 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. [source]

The significance of small herbivores in structuring annual grassland

JOURNAL OF VEGETATION SCIENCE, Issue 2 2007
Halton A. Peters
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; increased total production of above-ground plant biomass; and increased mean plant size and exacerbated size hierarchies in populations of Avena. The effect of both gastropods and small mammals, alone and in combination, was characterized by temporal oscillations in the relative dominance of grasses in plots with vs. without herbivores. Conclusions: Both groups of herbivores are important controllers of California annual grassland that exert similar influences on production and composition. While other factors appear to determine the absolute number of individuals in this plant community, selective consumption of grasses by gastropods and small mammals partially offsets the competitive advantages associated with their early germination. [source]

Conversion of sagebrush shrublands to exotic annual grasslands negatively impacts small mammal communities

DIVERSITY AND DISTRIBUTIONS, Issue 5 2009
Steven M. Ostoja
Abstract Aim, The exotic annual cheatgrass (Bromus tectorum) is fast replacing sagebrush (Artemisia tridentata) communities throughout the Great Basin Desert and nearby regions in the Western United States, impacting native plant communities and altering fire regimes, which contributes to the long-term persistence of this weedy species. The effect of this conversion on native faunal communities remains largely unexamined. We assess the impact of conversion from native perennial to exotic annual plant communities on desert rodent communities. Location, Wyoming big sagebrush shrublands and nearby sites previously converted to cheatgrass-dominated annual grasslands in the Great Basin Desert, Utah, USA. Methods, At two sites in Tooele County, Utah, USA, we investigated with Sherman live trapping whether intact sagebrush vegetation and nearby converted Bromus tectorum -dominated vegetation differed in rodent abundance, diversity and community composition. Results, Rodent abundance and species richness were considerably greater in sagebrush plots than in cheatgrass-dominated plots. Nine species were captured in sagebrush plots; five of these were also trapped in cheatgrass plots, all at lower abundances than in the sagebrush. In contrast, cheatgrass-dominated plots had no species that were not found in sagebrush. In addition, the site that had been converted to cheatgrass longer had lower abundances of rodents than the site more recently converted to cheatgrass-dominated plots. Despite large differences in abundances and species richness, Simpson's D diversity and Shannon-Wiener diversity and Brillouin evenness indices did not differ between sagebrush and cheatgrass-dominated plots. Main conclusions, This survey of rodent communities in native sagebrush and in converted cheatgrass-dominated vegetation suggests that the abundances and community composition of rodents may be shifting, potentially at the larger spatial scale of the entire Great Basin, where cheatgrass continues to invade and dominate more landscape at a rapid rate. [source]

The sensitivity of annual grassland carbon cycling to the quantity and timing of rainfall

GLOBAL CHANGE BIOLOGY, Issue 6 2008
WENDY W. CHOU
Abstract Global climate models predict significant changes to the rainfall regimes of the grassland biome, where C cycling is particularly sensitive to the amount and timing of precipitation. We explored the effects of both natural interannual rainfall variability and experimental rainfall additions on net C storage and loss in annual grasslands. Soil respiration and net primary productivity (NPP) were measured in treatment and control plots over four growing seasons (water years, or WYs) that varied in wet-season length and the quantity of rainfall. In treatment plots, we increased total rainfall by 50% above ambient levels and simulated one early- and one late-season storm. The early- and late-season rain events significantly increased soil respiration for 2,4 weeks after wetting, while augmentation of wet-season rainfall had no significant effect. Interannual variability in precipitation had large and significant effects on C cycling. We observed a significant positive relationship between annual rainfall and aboveground NPP across the study (P=0.01, r2=0.69). Changes in the seasonal timing of rainfall significantly affected soil respiration. Abundant rainfall late in the wet season in WY 2004, a year with average total rainfall, led to greater net ecosystem C losses due to a ,50% increase in soil respiration relative to other years. Our results suggest that C cycling in annual grasslands will be less sensitive to changes in rainfall quantity and more affected by altered seasonal timing of rainfall, with a longer or later wet season resulting in significant C losses from annual grasslands. [source]

The effect of small gaps in California annual grassland on above-ground biomass production

Seed size and response to rainfall patterns in annual grasslands: 16 years of permanent plot data

JOURNAL OF VEGETATION SCIENCE, Issue 1 2009
B. Peco
Abstract Question: Are seed size and plant size linked to species responses to inter-annual variations in rainfall and rainfall distribution during the growing season in annual grasslands? Location: A 16-year data set on species abundance in permanent plots 15 km north of Madrid in a Quercus ilex subsp. ballota dehesa. Methods: At species level, a GLM was used to analyse the effects of various rainfall indices (total autumn rainfall, early autumn rainfall and spring drought) on species abundance residuals with respect to time and topography. We also assessed the importance of seed size and plant size in the species responses at community level using species as data points. Seed mass and maximum stem length were used as surrogates for seed size and plant size, respectively. Results: Seed mass and plant size may explain some of the fluctuations in the floristic composition of annual species associated with autumn rainfall patterns. Species that are more abundant in dry autumns have greater seed mass than those species that are more abundant in wet autumns. Early autumn rainfall seems to favour larger plants. Conclusions: Our empirical results support the hypothesis that autumn rainfall patterns affect the relative establishment capacity of small and large seedlings in annual species. [source]