Grassland is an important part of the ecosystem in the Canadian prairies and its loss and fragmentation affect biodiversity, as well as water and carbon fluxes at local and regional levels. Over the years, native grasslands have been lost to agricultural activities, urban development and oil and gas exploration. This research reports on new methodologies developed for mapping the spatial extent of native grasslands to an unprecedented level of detail and assessing how the grasslands are fragmented. The test site is in the Newell County region of Alberta (NCRA). 72 Landsat and 34 SPOT images from 1985 to 2008 were considered for the analysis. With an airport runway used as a pseudo-invariant feature (PIF), relative radiometric correction was applied to 17 Landsat and 8 SPOT images that included the same airport runway. All the images were classified using the Support Vector Machine (SVM) classification algorithm into grassland, crop, water and road infrastructure classes. The classification results showed an average of 98.2 % overall accuracy for Landsat images and SPOT images. Spatial extents and their temporal change were estimated for all the land cover classes after classifying the images. Fragmentation statistics were obtained using FRAGSTATS 3.3 software that calculated land cover pattern metrics (patch, class and landscape). Based on the available satellite image data, it is found that in Newell County there is almost no significant change found in the grassland and road infrastructure land cover in over two decades. Also, the fragmentation results suggest that fragmentation of grassland was not due to the result of road infrastructure. / x, 105 leaves : ill., ; 29 cm

No description available.

No description available.

A predictive understanding of plant community response to various environmental influences (e.g. type, timing and frequency of disturbance, site productivity, fertilization, etc.) is a general goal of plant ecology. This study sought to further understanding of mesic grassland dynamics in KwaZulu-Natal using long-term field experiments (> 50 years) and short-term pot and plot competition experiments. The specific objectives were to: 1) examine the effects of long-term burning of grassland on soil organic matter content because of its potential impact on nitrogen cycling and community composition, 2) examine patterns of community composition and species richness in response to different type, timing and frequency of disturbance (burning and mowing) in a long-term grassland burning and mowing experiment and to different type and amounts of fertilizer application in a long-term grassland fertilization experiment, 3) develop hypotheses concerning the response of different species to disturbance and fertilization, and test these hypotheses using pot and plot competition experiments, and 4) provide a general synthesis of the results of the various field, pot and plot experiments that may be used to develop a predictive theoretical framework for mesic grassland dynamics. Total soil nitrogen was lowest in sites burnt annually, intermediate in sites burnt triennially and highest in sites protected from disturbance and sites mown annually in the dormant-period (spring or winter). Winter burning reduced soil organic carbon and total soil nitrogen more than spring burning. Mineralizable nitrogen was reduced by burning. The different effects of type, timing and frequency of disturbance on total soil nitrogen appeared to be an important determinant of community composition and species richness. Short-grass species (Themeda triandra, Eragrostis capensis, Heteropogon contortus, Diheteropogon amplectens and Eragrostis racemosa) were most abundant in annually burnt sites (especially winter burnt sites), whereas medium and tall-grass species (Eragrostis curvula, Cymbopogon spp., Hyparrhenia hirta and Aristida junciformis) were most abundant in triennially burnt sites, sites protected from disturbance and sites mown annually in the dormant-period, all of which had higher total soil nitrogen than annually or biennially burnt sites. Species richness and short-grass species declined with increasing levels of nitrogen fertilization in the fertilizer experiment and declined with increasing productivity and nitrogen availability in both the fertilizer and burning and mowing experiments. Thus, it was hypothesized that the type, timing and frequency of disturbance resulted in different compositional states through different effects on soil resources (especially nitrogen), which affected the competitive balance between short and tall species. The hypothesis that composition was determined by disturbance-mediated soil nitrogen availability was supported by competition experiments, which revealed that shortgrass species were most competitive in low-nutrient/low-productivity treatments and tall-grass species most competitive in high-nutrient/high-productivity treatments. The fertilizer experiment and a competition experiment revealed that tall broad-leaved species were most competitive in sites of highest productivity, fertilized with both nitrogen and phosphorus, whereas tall narrow-leaved species were most competitive in sites of intermediate productivity, fertilized with nitrogen only. It was hypothesized that summer mowing increased the abundance of short-grass species and decreased the abundance of tall-grass species in the burning and mowing experiment by increasing the competitive ability of short-grass relative to tall-grass species, rather than the tall-grass species being less tolerant of mowing. A competition experiment revealed that tall-grass species (Hyparrhenia hirta and Panicum maximum) were as tolerant of cutting as a short-grass species (Themeda triandra). Themeda triandra was shown to become extremely competitive in cutting treatments, reducing the biomass of most other species relative to their monoculture biomass, showing that its dominance of mown sites in the burning and mowing experiment was a result of its superior competitive ability rather than greater tolerance of mowing. However, many tall erect herbaceous dicots appeared to be intolerant of summer mowing, probably because their meristems are aerial and easily removed by mowing, whereas short creeping herbaceous dicots were increased by summer mowing probably because their meristems were below the mowing height. Further, these short species would be vulnerable to shading in unmown sites. Thus, species with basal meristems (hemicryptophytes) or meristems near the soil surface (geophytes) appear to be more tolerant of mowing than species with aerial meristems (phanerophytes), but the tradeoff is that a low meristem height renders them vulnerable to shading in unmown sites. Very high litter accumulation in the sites protected from disturbance appeared to have a direct influence on community composition and species richness. Species that dominated these sites (e.g. Tristachya leucothrix & Aristida junciformis) initiated tillers below-ground and had sharp erect shoots that appeared to be an adaptation for penetrating litter. Species that initiate tillers below-ground are probably less vulnerable to the effects of shading by litter because their tiller initiation is not dependent on high light availability. The fact that Aristida junciformis was shown to have very low competitive ability in two competition experiments, suggests its dominance of protected sites was through tolerance of high litter levels rather than competitive exclusion of other species. Low grass species richness in these sites was probably a result of an inability of many species to tolerate these high litter levels. This study has revealed that inherent site productivity and its interaction with the effect of disturbance on soil resources and litter levels is a major determinant of community composition and species richness. The effect of type, timing and frequency of disturbance on soil nitrogen was able to account for the principal changes in community composition. Thus, the influence of disturbance on soil nitrogen is a unifying principle in plant ecological theory that enables greater understanding of disturbance-composition relationships. However, intolerance of certain forms of disturbance (e.g. mowing) by species with aerial meristems, or intolerance of accumulating litter in the absence of disturbance by species without sharp erect shoots, may also have important influences on composition. In addition, this study has revealed that plant traits (height, leaf width, position of tiller initiation, shoot morphology and position of meristems) were well correlated with the various effects of disturbance and fertilization on community composition, indicating that a plant trait-productivity-disturbance framework has great potential for understanding and predicting species response to disturbance and multiple limiting nutrients. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2003.

Die Futterpflanzen Kaukasischer Klee und Futterchicorée wurden als Reinsaat und in Gemenge mit einer Grünlandmischung auf zwei Standorten in Sachsen auf ihre Anbaueignung und ihren Futterwert untersucht. Der Kaukasische Klee überdauert Trockenstressphasen sehr gut, ist absolut winterfest und weist einen teilweise überdurchschnittlichen Gehalt an wertgebenden Inhaltstoffen auf. Dem stehen eine niedrige Keimfähigkeit und schwierige Etablierung eines Pflanzenbestandes mit geringem Ertrag entgegen. Der Kaukasische Klee ist in seiner Anbaueignung stark eingeschränkt und für sächsische Standortbedingungen wenig geeignet. Der Futterchicorée lässt sich leicht etablieren, zeichnet sich durch rasches Massenwachstum aus und überdauert Trockenstress ebenfalls gut. Er ist gekennzeichnet durch einen teilweise überdurchschnittlichen Gehalt an wertgebenden Inhaltsstoffen, seine Nutzungsmöglichkeiten sind aber durch den geringen Trockensubstanzgehalt eingeschränkt. Der Futterchicorée ist zum Anbau als Futterpflanze in Sachsen geeignet, es deuten sich insbesondere Möglichkeiten der Nutzung als Gemengepartner von Grünlandmischungen an.

The focus of the research is on investigations of various methods for obtaining sensible heat flux (H) for estimating evaporation. The key for this approach is the application of the shortened energy balance equation, and in the case of methods based on the Monin-Obukhov similarity theory (MOST), such as surface-layer scintillometrv and temperature variance with adjusted for stability using air temperature skewness, and surface renewal (SR), die iterative procedures. The application of the shortened energy balance requires that errors associated with measurement of net irradiance (Rnet) and soil heat flux (S) are kept to a minimum To this end. methodology for the calibration of net radiometers for both the infrared and short wave irradiances receive attention. A field study attempts to quantify the error in soil heat flux measurement for a mesic grassland. A standard, convenient and accurate method for calibrating net radiometers would assist in unravelling reasons for the perplexing lack of surface energy balance closure when employing the eddy covariance (EC) flux estimation method as well as improve on the accuracy of the energy balance residual method for estimating evaporation. A relatively inexpensive, accurate and quick laboratory method, based on physical theory, for non-steady radiative conditions above a large water-heated or water-cooled radiator containing circulated water, with surface-embedded thermocouples is used to obtain reproducible net radiometer calibration factor's for the infrared waveband for a wide range in net irradiance. When applied, the method would reduce error m the most important term of the shortened energy balance and assist in energy balance closure aspects of EC measurements. The SLS method, reliant on MOST, is used for estimating a really-averaged H for a mesic grassland for a 30-month period. Comparisons with EC measurements feature prominently in this unique study. These comparisons include using different MOST procedures and the influence of the Bowen ratio on SLS measurement: of if is investigated. Furthermore, since there are reports in the literature that the EC method may underestimate H and or latent energy flux (LE), resulting in the shortened energy balance not being closed, effort is devoted to this aspect. Other methods used for comparison purposes are the traditional Bowen ratio energy balance (BREB), SR, TV and ETo (grass reference) methods. The TV and SLS and/or EC measurements of H are compared above three contrasting canopy surfaces. It is shown that other high frequency air temperature-based methods, for example, for the first time the TV method with adjustment for skewness, may pave the way for evaporation stations from which real-time and sub-hourly estimates may be obtained relatively inexpensively. Another area of research that receives attention is the placement height of EC instruments above short-canopy surfaces and a spectral analysis of the vertical wind speed and some temperature measurement: for close-canopv placement heights. The SR method is used to estimate, for the first time, open-water evaporation. The ideal SR method applied above canopies is the most inexpensive micrometeorological method for estimating H, but the SR weighting factor a needs to be determined using EC and for this reason, the TV method with adjustment for skewness was investigated. Finally, a unique implementation of SR uses an iterative method for calculating H. A similar iterative procedure is applied for MOST and ETo calculations. / Thesis (DScAgric)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Patch grazing may be an important factor providing the focus from which wide-scale veld degradation has occurred in the humid grasslands of KwaZulu-Natal. A number of discrete studies were therefore initiated to examine the patch grazing patterns and selected factors which may influence patch grazing at two sites in the humid grasslands of KwaZulu-Natal. The sites were located at Ukulinga Research Farm, situated in the Southern Tall Grassveld, and Kokstad Research Station in the Highland Sourveld. An investigation into the frequency and intensity of gazing patches and non-patches at Ukulinga Research Farm indicated that patch grazing was most evident and most extensive during summer and autumn. As forage in the patches became limiting during winter animals were forced to forage in areas not frequently grazed during the season. The patch grazing pattern was further modified by the time of grazing commencement after a burn in early spring. Early grazing significantly reduced the extent of patch grazing. With early stocking animals were forced to graze less selectively while with increased delay in the commencement of grazing, animals became increasingly patch-selective. Early grazing in conjunction with an autumn rest and heavy grazing during winter could significantly reduce patch grazing. Urine and dung significantly influenced the patch grazing pattern. The sward surrounding a urine deposit was preferentially grazed by both cattle and sheep for a period of at least six months after deposition. Cattle rejected the sward surrounding cattle and sheep dung immediately after deposition and for a period of up to six months. Sheep also rejected cattle and sheep dung patches immediately after deposition. As dung deposits aged, sheep tended to increase their grazing around both cattle and sheep dung pats, and after six months dung did not seem to influence sheep grazing. Urine may be an important factor influencing patch initiation and consequent patch development. A study to examine the characteristics of patches and non-patches in the Highland Sourveld revealed that patches were characterised by lower soil moisture, soil depth and hydraulic conductivity, but by a higher soil nutrient status. Patches and non-patches could also be distinguished in terms of species composition and basal cover. Patches were characterised by Increaser II species, especially Microchloa caffra and, non-patches by Increaser I species such as Trachypogon spicatus, Alioteropsis semialata and Eulalia villosa. Three seasons of patch grazing at Kokstad Research Station negatively influenced the vigour of Themeda triandra in patches relative to the non-patches. The vigour of T. triandra in patches was consistently low throughout a full season's rest. The vigour of T. triandra in non-patches was initially significantly higher than the vigour in the patches and remained so for c. 24 weeks. Vigour measurements at the start of the following season showed that photosynthate accumulation had taken place and a full seasons rest proved to be sufficient in restoring the vigour of T. triandra in patches to the same level as that in non-patches. A full seasons rest did, however, not prevent animals from regrazing the same previously grazed patches the following season. Growth in patches also started c. six weeks later than in nonpatches and above-ground herbage production in patches was significantly lower than nonpatches for at least 20 weeks after a bum. At the end of a full season's rest above-ground herbage production in patches was still slightly lower than that in non-patches possibly due to a difference in species composition between patches and non-patches. Some implications of patch grazing are discussed together with an evaluation of some management recommendations for the humid grasslands with the aim of reducing the potential for patch degradation. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

La invasió de pastures per arbustos és un fenomen global. Als Pirineus, el bàlec (Cytisus balansae ssp europaeus) és un dels arbustos que més freqüentment envaeix pastures de muntanya. La presència de bàlec comporta alguns efectes negatius, com poden ser la reducció de la productivitat de pastures, homogeneïtat d’hàbitats, pèrdua d’hàbitat per a algunes espècies animals amb interès de conservació o increment del risc d’incendis. Degut als efectes negatius, la invasió de pastures per bàlec s’ha gestionat freqüentment amb foc prescrit o desbrossament mecànic, juntament amb pasturatge per reduir la capacitat de colonització de les pastures per bàlec. Tot i que es creu que la disminució de l’activitat agrària ha afavorit la invasió de pastures per bàlec, les causes d’aquesta invasió són incertes i podrien ser degudes a la combinació de múltiples factors que interaccionen i que per tant, són difícils de considerar de forma aïllada. A escala regional, el canvi climàtic podria contribuir a la invasió de pastures per bàlec. A escala local, les pertorbacions (com el pasturatge i el foc) podrien ser claus per entendre la dinàmica de la vegetació en aquests sistemes. A la mateixa escala, també les interaccions entre plantes (competència i facilitació) podrien determinar la dinàmica de la vegetació en les pastures. A la tesi, s’intenten analitzar les causes de la invasió de pastures per bàlec a escala local, considerant les pertorbacions amb foc, el pasturatge i les interaccions entre plantes en diferents comunitats de pastures com a determinants de la invasibilitat d’aquestes. Entre els efectes de la invasió de pastures per arbustos, s’ha observat una reducció en la capacitat de segrest de carboni dels sòls que podria contribuir de forma decisiva al canvi climàtic, tenint en compte la gran superfície de pastures del planeta que estan sent envaïdes per arbustos. A la tesis s’intenten detectar els efectes de la invasió de pastures per bàlec sobre el segrest de carboni, així com detectar els principals mecanismes que explicarien aquests canvis. Sobre les causes de la invasió de pastures per bàlec es conclou que els processos a petita escala com la competència i la facilitació poden ser claus per entendre la dinàmica de la invasió de pastures per arbustos. Pastures amb diferent palatabilitat van mostrar diferent invasibilitat. Així, el bàlec apareixia amb més freqüència en pastures amb espècies palatables, i en menor freqüència en pastures no palatables, malgrat que en aquestes últimes podria existir una menor mortalitat dels arbusts juvenils degut a una menor pressió de pasturatge. Diferents pertorbacions amb foc també van demostrar tenir efectes diferents sobre la cobertura de bàlec després de la pertorbació, amb els focs prescrits repetits mostrant un efecte similar al dels incendis. Sobre els efectes de la invasió de pastures per arbustos sobre el segrest de carboni, es va observar que no disminuïa el contingut de carboni del sòl. Fins i tot, en els primers centímetres de sòl existia un lleuger increment del carboni sota els arbustos, respecte del carboni sota les pastures. La baixa qualitat de la fullaraca dels arbustos s’apunta com la causa de l’augment de carboni en els primers centímetres de sòl sota els arbustos. Un increment de temperatura com a conseqüència del canvi climàtic podria causar una pèrdua de carboni del sòl tant en les pastures com en els arbustos. Tot i així, la fracció més recalcitrant del carboni dels sòls sota bàlec semblava ser més sensible a increments de temperatura que la fracció de carboni total. / Land use changes are one of the main components of the global change and they have important effects on ecosystems. Woody plant encroachment into grasslands is a worldwide phenomenon. In the Pyrenees, the most abundant shrubs encroaching into mountain grasslands are a legume shrub (Cytisus balansae ssp europaeus) and a conifer shrub (Juniperus communis ssp alpina). This thesis focuses on the understanding of the causes and consequences of shrub encroachment into mountain grasslands in the Pyrenees. The main objectives of the thesis are: (i) understanding the role of different grassland communities and different fire disturbances on grassland invasibility by shrubs, and thus on shrub proliferation dynamics; (ii) understanding how shrub encroachment into grasslands affects carbon (C) sequestration, in order to know if shrub encroachment may contribute to increase global warming. Our results show that fine-scale spatial heterogeneity in grasslands is crucial to understand shrub encroachment into grasslands. Shrubs established more often close to palatable grasses, but the associational resistance mechanism may contribute to decrease shrub mortality rates close to unpalatable grasses. The effects of repeated prescribed burning were similar to those of wildfire on reducing shrub cover and shrub patch size. Contrary to previous works, our results show that shrub encroachment into mesic grasslands increased sequestered C between 4 and 5 kg m-2 with respect to grasslands, mainly due aboveground and belowground biomass and litter. In addition, shrub encroachment increased soil organic C in the top 15 cm of soil with an accretion rate of 28-42 g C m-2 year-1. Shrub encroachment caused changes in the quantity and quality of organic matter and microclimate, although changes in aboveground quality may be the main mechanism to increase soil organic C after shrub encroachment. Increases in temperature, as a consequence of climate change, may reduce C stored in soils both under grasslands and shrublands. However, plant functional type (legume vs. conifer shrub) may have a different effect on C sequestration, and soil C under legume shrubs may be more vulnerable to climate change than soil C under conifer shrubs or grasslands.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.