The aim of the thesis is to assess an influence on a grassland composition and grassland condition with different grazing method, frequency of grazing and animal composition. A basis is a literature review which contains a brief description of productive and nonproductive function of a permanent grassland, an grazing importance of grassland maintenance, a way and intensity of grazing and The experiment was performed in Carlsbad region (Czech republic), near Fojtov township. The experiment contains botanical images of three different grazings, cattle, horse and sheep. At these grazings where made two two-year cycle observations (2013, 2014), on the 15th of June and on the 13th of September. At these grazings where three different observation areas with different water regime and with different agro-botanical composition. Gained data were used to calculate diversity species indices (Simpsons and Hills), site water regime and a grazing forage value. Data were also statistically processed. A part of this experiment was also to calculate grazing load for a whole grazing period and for one grazing cycle.

No description available.

Master of Science / Department of Biology / Jesse B. Nippert / Jesse B. Nippert / Anthropogenic climate change is likely to alter the function and composition of ecosystems worldwide through increased precipitation variability and temperatures. To predict ecosystem responses, a greater understanding of the physiological and growth responses of plants is required. Dominant species drive ecosystem responses, and it is essential to understand how they respond to understand potential ecosystem changes. Dominant species, such as switchgrass (Panicum virgatum L.), posses large genotypic and phenotypic variability, which will impact the degree of responses to projected climate changes. I studied the physiological and growth responses of switchgrass, a common perennial warm-season C4 grass that is native to the tallgrass prairie, to alterations in precipitation amount and temperature. The first experiment I conducted focused on the responses of three ecotypes of P. virgatum to three precipitation regimes (average, 25% below, 25% above). I concluded that the physiological responses of photosynthesis, stomatal conductance, transpiration, dark-adapted fluorescence, and mid-day water potential in P. virgatum were explained by ecotypic differences. Robust responses to altered precipitation were seen in the water use efficiency, mid-day water potential, and aboveground biomass. Ecotypic differences were also seen in several aboveground biomass variables, and most strikingly in flowering times and rates. There were few interactions between ecotype and precipitation, suggesting precipitation is a strong driver of biomass production, whereas adaption of ecotypes to their local environment affects physiological processes. A second experiment studied the response of local populations of P. virgatum to nocturnal warming. Results showed significant differences in daytime E, daytime gs, and flowering phenology between treatments. Differences in aboveground biomass were between topographic positions. I concluded that water availability, based on topographic position, is a strong driver of P. virgatum aboveground biomass production, but nocturnal warming has the potential to impact flowering phenology, physiological responses, and exacerbate plant water stress. I also reviewed the literature on the ecological effects of implementing switchgrass cultivation for biofuel. From the literature review, I concluded that large-scale switchgrass cultivation will have widespread ecological impacts. If landscape heterogeneity is maintained through harvest rotations, no till farming, and mixed species composition, ecosystem services can be maintained while providing economic value.

Master of Arts / Department of Geography / Kendra K. McLauchlan / The quantitative relationship between pollen assemblages in sediment and vegetation cover is largely unknown because many factors influence this relationship. This lack of quantitative relationship is particularly acute in grassland regions, where both past and future climate change have the potential to determine grassland composition and cover. The tool used to reconstruct past grassland cover is the relative abundance of distinct fossil pollen types preserved in sediment. However, the interpretation of grassland pollen assemblages as grassland vegetation types needs to be refined to improve these reconstructions. Using pollen found in the surface sediments from 24 artificially-constructed ponds in the Flint Hills ecoregion of Kansas, USA, I examined relationships between pollen and vegetation in the tallgrass prairie biome, which includes woody components. By comparing the pollen data to field-surveyed vegetation data and land cover classifications taken from Kansas Gap Analysis Program data, I correlated pollen and vegetation in this ecoregion. Pollen productivity estimates for Artemisia, Ambrosia, Asteraceae, Chenopodiaceae, Cornus, Fabaceae, Juniperus, Maclura, Poaceae, Populus, Quercus, and Salix were calculated via the Extended R-Value Model. Common pollen types identified in sediments are mostly herbaceous grassland plant species such as Poaceae, Artemisia, and Ambrosia, but woody plants such as Populus, Quercus, and Juniperus are also represented. PPEs have been calculated for four of these taxa in Europe, and values from the Flint Hills are higher. These are the first PPEs reported for eight of these taxa. This research will further advance quantitative vegetation reconstructions in the Great Plains of North America and refine interpretations of how climate change affects grasslands.

Leaf traits have long been used to classify and characterise species in natural ecosystems. In addition, leaf traits provide important information about plants’ strategies for the use of resources and can be used to improve our understanding of ecosystem level processes such as nutrient cycling and carbon allocation. To explore the linkages between leaf traits and productivity, we worked in two resource-limited ecosystems (a grassland and a forest), and used leaf traits to understand how species respond to changes in available resources and their relationship to ecosystem processes. We worked in a species rich limestone-grassland located in central England, which has been subjected to long-term climatic manipulation (winter warming, summer drought and extra summer rainfall). We characterised species composition in terms of their identity, abundance and leaf structural properties (nitrogen content and leaf mass per area (LMA)) in the main treatments and the control. We found that change in species abundance was the most important factor to understand the differences in productivity (above ground biomass and total foliar nitrogen). We then measured CO2 exchange at ecosystem level, using a chamber technique, and assessed the treatments’ effect on the gross primary productivity (GPP) and ecosystem respiration (Reco). GPP and Reco were controlled by soil moisture and above ground biomass but also influenced by the conditions experienced during the growing season prior to the measuring period. Our second location was a post-disturbance chronosequence in a seasonally dry tropical forest in Costa Rica and we used leaf level gas exchange measurements to explore the role of nitrogen (N) and phosphorus (P) on the temporal-spatial variation of photosynthesis of dominant species. We found that photosynthetic efficiency was strongly linked to leaf N and P content, but that there was an important seasonal pattern on this relationship likely associated to P remobilization. Additionally we found seasonal changes in resources (water, nutrients) had a larger impact on the photosynthetic parameters than changes along the chronosequence. The two ecosystems studied for this thesis are contrasting in their physiognomy, species composition and climate, but are also characterised by species whose structural traits (high LMA and high C:N ratio) are likely to have a significant impact on the nutrient cycling processes. We learned that leaf traits provide important information about species strategies and their usage of resources and they can also aid to address questions at ecosystem level in time and space, either through simple aggregation or as emergent properties. Additionally, the traits explored are important input information to up-scale processes from leaf to the ecosystem level, a step needed to address the effect changes in resources will have on the seasonally dry tropical forest and grasslands, which represent a significant fraction of the total global carbon storage.

No description available.

Dryland ecosystems provide a unique opportunity to study the effects of water limitation on ecosystem activity. The sensitivity of these systems to small inputs of moisture is well-documented, but the expression of water limitation in terms of carbon dioxide flux between the ecosystem and atmosphere remains unclear. Applying a simple conceptual approach to soil moisture dynamics, patterns in carbon flux become clear. Release of carbon dioxide via respiration is primarily driven by moisture in the shallow soil, and differences in respiration rates among plant functional types are only evident after controlling for soil moisture. Alternatively, carbon uptake by a semiarid shrubs ecosystem is largely driven by the availability of deep soil moisture. This link to deep soil moisture improves spatial scaling of gross and net carbon uptake using remote sensing data. Lateral redistribution of moisture on the landscape connects readily observed physical features, namely topography, to ecosystem function, but redistribution is generally not considered in carbon models. A simple runoff scheme coupled to a conceptual model for carbon flux demonstrates the high degree of spatial heterogeneity in carbon dioxide flux resulting from moisture redistribution. The importance of redistribution in carbon modeling is highlighted by interannual variability in modeled carbon fluxes under different rainfall characteristics (event size, event duration, interstorm duration). The links between hydrology and ecology across spatial scales become clearer when topographically-based moisture distribution is used as an organizing variable. In all, this research identifies new avenues for research where moisture dynamics are of central interest in dryland ecohydrology.

Abstract can be viewed in PDF document. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

<p>Rising atmospheric CO2 concentration, currently about 390 ppm, causes climate change and is expected to reach 500 ppm or higher this century due to human activities. Soils are the largest terrestrial pool of carbon, and changes in soil carbon storage due to plant and microbial activities could affect atmospheric CO2 levels. This dissertation studies soil carbon and microbial responses to an experimental preindustrial-to-future CO2 gradient (250-515 ppm) in a grassland ecosystem. Two contrasting soil types are studied in the gradient, providing insight on how natural ecosystem variation modifies CO2 effects.</p><p>Although total soil organic carbon (SOC) did not change with CO2 treatment after four growing seasons, fast-cycling SOC pools did respond to CO2, particularly in the black clay soil. Microbial biomass increased 18% and microbial activity increased 30% across the CO2 gradient in the black clay, but neither factor changed with CO2 in the sandy loam. Similarly a one-year laboratory soil incubation showed that a fast-cycling SOC pool increased 75% across the CO2 gradient in the black clay. Size fractionation of SOC showed that coarse POM-C, the youngest and most labile fraction, increased four-fold across the CO2 gradient in the black clay, while it increased 50% across the gradient in the sandy loam. CO2 enrichment in this grassland increased the fast-cycling soil organic carbon pool as in other elevated CO2 studies, but only in the black clay soil.</p><p>CO2 also induced changes in microbial community composition, and we explored the functional consequences in a microcosm experiment. Soil collected in the third growing season of CO2 treatment was used to inoculate Indiangrass seedlings grown in the lab. The elevated CO2 soil inoculum had higher microbial biomass C/N (C/N = 21) than the subambient CO2 soil inoculum (C/N = 16), suggesting a difference in community composition. Mean plant height in elevated CO2 soil inoculum (475 ppm) was 57% greater than in subambient CO2 soil inoculum (300 ppm), but the difference was not statistically significant. Similarly, total leaf N from plants in elevated CO2 soil was 28% greater on average than in subambient CO2 soil, but not significantly different. CO2-induced microbial effects on plant growth were either negligible or occurred at finer microbial taxonomic levels, making them difficult to resolve at the whole-community level.</p><p>Soil fungi decompose soil organic matter, and studying fungal community responses to CO2 could improve our understanding of soil carbon responses. We studied fungal communities in the CO2 gradient using Sanger sequencing and pyrosequencing of rDNA. As in our soil C study, fungal community responses to CO2 were mostly linear, and occurred mostly in the black clay soil. Fungal species richness increased linearly with CO2 treatment in the black clay. The relative abundance of Chytridiomycota (chytrids) increased linearly with CO2 in the black clay, while the relative abundance of Glomeromycota (arbuscular mycorrhizal fungi) increased linearly with CO2 in the sandy loam. Increased labile C availability at elevated CO2 and/or decreased inorganic N may explain the increase in fungal species richness and Chytridiomycota abundance in the black clay, while increased P limitation may explain the stimulation of Glomeromycota at elevated CO2 in the sandy loam. Across both soils, fungal species richness increased linearly with soil respiration, an index of decomposition rate (p = 0.01, R2 = 0.46). Adding fungal species may have improved decomposition efficiency, but it is also possible that species richness and decomposition increased due to another factor such as C quantity. Soil type strongly structured both fungal community and arbuscular mycorrhizal fungal community composition.</p><p>Together, these studies suggest that soil C and fungal community responses to CO2 were mostly linear, and were most apparent in the black clay soil. Soil type strongly influenced fungal community composition as well as which phyla responded to CO2. Therefore, soil type could be a useful addition to predictions of soil carbon and microbial responses to future CO2 levels.</p> / Dissertation

The Lewisville Lake Environmental Learning Area (LLELA) is a wildlife management area with tallgrass prairie, an endangered ecosystem. Essential ecosystem processes, especially fire, are part of restoration. To support fire management efforts at LLELA and surrounding areas, this project evaluated and developed tools for fire restoration. The four primary prairie grasses respond favorably to burning. Fuel loads and fuel models vary by scale and survey method. One- and 10-hour fuel moisture can be predicted using a statistical model; 100- and 1,000-hour fuel moisture cannot. Historic weather data suggests that burning can occur when it is most effective. The production of ozone precursors produced by burning is comparable to those emitted every six minutes by regional automobiles.