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Grass Biomass (grass + biomass)
Selected AbstractsDynamical effects of the statistical structure of annual rainfall on dryland vegetationGLOBAL CHANGE BIOLOGY, Issue 5 2006CHRISTOPHER A. WILLIAMS Abstract In this study, we extend a model of daily dryland dynamics by parameterizing a modified version of a minimalistic annual model to examine how the statistical structure of annual rainfall and grazing intensity interact to influence dryland vegetation. With a Monte Carlo approach, an ensemble outcome provides a statistical description of likely dryland vegetation dynamics responding to variations in rainfall structure and grazing intensity. Results suggest that increased rainfall variability decreases the average and increases the variability of grass cover leading to more frequent degradation of the grass resource. Vegetation of drier regions is found to be more sensitive to interannual variability in rainfall. Concentrating this variability into an organized periodic mode further decreases the mean and increases the variability of grass cover. Hence, a shift toward lower, more variable, or more inter-annually correlated annual rainfall will likely lead to a general decrease in the grass resource and increased dryland vulnerability to degradation. Higher grazing intensity or lower annual rainfall both lead to more frequent and longer duration degradation of the grass condition. We note an interesting interaction in the response of grass biomass to grazing intensity and rainfall variability, where increased rainfall variability leads to longer duration degradation for low grazing, but shorter periods of degradation for high grazing. Once grass reaches a degraded condition, we find that woody vegetation strongly suppresses recovery even if successive rainfall is high. Overall, these findings suggest that the projected increase in interannual rainfall variability will likely decrease grass cover and potentially lead to more frequent, longer lasting degradation of dryland vegetation, particularly if enhanced rainfall variability is concentrated in long period (e.g. decadal) modes. [source] Factors affecting the distribution patterns of zebra and wildebeest in a resource-stressed environmentAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Rosemary Groom Abstract Understanding the spatial dynamics of landscape use by free-ranging herbivores is integral for successful ecosystem management. We used binary logistic regression analyses to determine the relative importance of biotic, abiotic and human factors in influencing the distribution (presence/absence) of wild grazers on two Maasai ranches in Kenya's Amboseli-Tsavo ecosystem. Both ranches had low grass biomass and suffered from regular droughts. We found that grazers consistently located themselves where grass biomass was highest, usually irrespective of grass quality, suggesting that forage quantity may be the limiting factor where grass biomass is generally low. The availability of surface water had no significant effect on the likelihood of grazers being present, even in the dry season. Résumé La bonne compréhension de la dynamique spatiale de l'utilisation du paysage par les herbivores qui paissent en liberté fait partie intégrante de la gestion réussie d'un écosystème. Nous avons employé des analyses de régression logistique binaire pour déterminer l'importance relative des facteurs biotiques, abiotiques et humains dans l'influence sur la distribution (présence/absence) d'herbivores sauvages sur deux ranches masaï de l'écosystème Amboseli-Tsavo, au Kenya. Les deux ranches avaient une faible biomasse herbeuse et souffraient de sécheresses régulières. Nous avons découvert que les herbivores brouteurs se trouvaient de façon constante là où la biomasse herbeuse était la plus grande, sans tenir compte, d'habitude, de la qualité de l'herbe; ceci suggère que la quantité de fourrage pourrait être le facteur imitant là où la biomasse herbeuse est généralement faible. La disponibilité de l'eau de surface n'avait pas d'effet significatif sur la probabilité de la présence des herbivores, même en saison sèche. [source] Year-to-year variation in plant competition in a mountain grasslandJOURNAL OF ECOLOGY, Issue 1 2003Herben Summary 1We used a series of removal experiments to examine how species response to competition and climatic differences varied in three different years. We tested the interaction between removal of the dominant grass species, Festuca rubra, and year-to-year environmental variation in a mown mountain grassland. 2In each year, we quantified shoot frequency and above-ground biomass of all remaining plant species. Above-ground responses were tested both by analysis of covariance and by redundancy analysis with randomization tests of changes in total species composition. 3Analysis of above-ground biomass data showed that other species compensated for the removal of F. rubra biomass within 2 years and that the response in total biomass of the community did not differ among years in which the experiment was started. 4Multivariate tests showed that species composition changed as a result of the removal; grass biomass and frequency increased more than that of dicotyledons. However, response of species composition to removal of F. rubra was significantly different between onset years. Specific conditions in individual years thus affect the competitive ability of individual species in a non-additive way. 5Our results indicate that the year-to-year variation at the site has the potential to affect species coexistence and richness. As a consequence, year-to-year variation of climatic parameters may be an important driving factor in community dynamics and should be taken into account in studies of ecosystem response to climate. [source] Strategic light manipulation as a restoration strategy to reduce alien grasses and encourage native regeneration in Hawaiian mesic forestsAPPLIED VEGETATION SCIENCE, Issue 3 2010S. McDaniel Abstract Question: Is there a light level at which alien grass biomass is reduced while still supporting growth and survival of native woody species, allowing for native species regeneration in abandoned pastures? Location: Island of Hawaii, USA. Methods: In a two-part study we examined the effect of light availability on common native woody and alien grass species found in secondary forests in Hawaii. A field survey was conducted to examine the relationship between light availability and canopy type (open pasture, planted canopy and secondary forest) on understory grass biomass and litter accumulation. We then experimentally manipulated light levels to determine the effect of light availability on growth and survival of six native woody species and three alien grasses. Low-light (5%), medium-light (10%) and high-light (20-30%) treatments were created using shade structures erected beneath the existing secondary koa canopy. Results: In the field survey, alien grass biomass was greatest under the open pasture and lowest in the secondary forest. There was a positive correlation between understory light availability and alien grass biomass. In the experimental study, large reductions in relative growth rates were documented for all of the grass species and four of the six woody species under the lowest light level. Although growth at 5% light is substantially reduced, survival is still high (84-100%), indicating that these species may persist under closed canopy. Conclusion: Low-light conditions result in the greatest reduction in alien grass biomass while creating an environment in which native woody species can grow and survive. [source] Grazing and landscape controls on nitrogen availability across 330 South African savanna sitesAUSTRAL ECOLOGY, Issue 7 2009JOSEPH M. CRAINE Abstract The availability of nitrogen (N) is an important determinant of ecosystem and community dynamics for grasslands and savannas, influencing factors such as biomass productivity, plant and herbivore composition, and losses of N to waters and the atmosphere. To better understand the controls over N availability at landscape to regional scales, we quantified a range of plant and soil characteristics at each of 330 sites in three regions of South Africa: Kruger National Park (KNP), private game reserves adjacent to KNP (private protected areas , PPAs) and Hluhluwe-iMfolozi Park (HiP). In comparing regions and sites within regions, grazing appeared to have a strong influence on N availability. Sites in the PPAs adjacent to KNP as well as sodic and alluvial sites in general typically had the highest N availability. The high N availability of these sites was not generally associated with greater potential N mineralization, but instead with less grass biomass and more forb biomass that indicated greater grazing pressure. Whereas sodic sites had a long history of high N availability as evidenced by their high soil ,15N, the greater N availability in the PPAs over the two parks appeared to be relatively recent. Grazer biomass, average potential mineralization rates and grass biomass for HiP were greater than KNP, yet there were no differences in N availability as indexed by soil and foliar ,15N between sites in the two parks. Although the short-term increase in N availability in PPAs is not necessarily deleterious, it is uncertain whether current productivity levels in those ecosystems is sustainable. With differences in management causing herbivore biomass to be 150% greater in the PPAs than the adjacent KNP, changes in plant communities and nitrogen cycling might lead to long-term degradation of these ecosystems, their ability to sustain herbivore populations, and also serve as an economic resource for the region. [source] Green biorefinery demonstration plant in Havelland (Germany),BIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 3 2010Birgit Kamm Abstract The Green Biorefinery (GBR) is a complex and full-integrated system of environment- and resource-protecting technologies for comprehensive material and energetic use of green biomasses. GBR's are multiproduct systems and perform and produce in accordance with the physiology of the corresponding plant material preserving and using the diversity of the synthesis generated by nature. In addition to the general biorefinery concept, GBR's are based strongly on sustainable principles (sustainable land use, sustainable raw materials, gentle technologies, autarkic energy supply, etc.). Existing agricultural structures of the green crop processing industry, such as green crop drying plants, offer good opportunities for the implementation of biorefinery technologies that will help overcoming energy-intensive and partially obsolete technologies, such as the thermal drying of feedstock. Accordingly, the primary fractionation of green biomasses and the integrated production of proteins, fermentation media, animal feed, and biogas was projected and will be realized in a demonstration facility directly linked to the existing green crop drying plant, Selbelang, in Havelland (Germany, state Brandenburg, 50 km west of Berlin). The primary refinery will have an annual capacity of 20 000 tons alfalfa and grass biomass and can be diversified in modules for the production of platform chemicals and synthesis gas. We discuss the processes, products, operating costs and climate protection effects through examination of the basic engineering of the primary refinery. The production site and planned demonstration facility are also presented. Copyright © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd [source] | ||||||||||