Dissertations / Theses on the topic 'Grasslands'

Thesis (M.S. in crop science)--Washington State University, August 2010.
Title from PDF title page (viewed on July 30, 2010). "Department of Crop and Soil Sciences." Includes bibliographical references.

Thesis (M.S.) University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 27, 2007) Includes bibliographical references.

European floodplain grasslands are characterized by periodic flooding and regular management, usually cutting and grazing as part of an agricultural system. Past losses and ecological degradation have been due largely to river regulation and either agricultural intensification or abandonment and have resulted in a substantial reduction in area across Europe. Nevertheless, the remaining resource supports considerable biodiversity and a high level of biological production. A better quantitative understanding of the functioning of these grasslands is required in order to establish effective conservation management within a sustainable land use system. The thesis examines the impact of key management factors on three important functional characteristics of the biodiversity of floodplain plant communities, namely plant diversity (measured by species diversity), cover (%) and primary production (above-ground biomass), on two floodplain grasslands of the River Trent, UK and a third on the the Luznice river, the Czech Republic. Field investigations of the effects of cutting, grazing, cessation of management, the influence of floodborne litter, and the impact of fertilizer nitrogen were undertaken over periods of between one and three seasons. These demonstrated that floodplain grassland plant communities are sensitive to variations in management and that impacts on communities are mediated particularly through effects on plant competition. Productive competitive species were encouraged both by abandonment and fertilizer application whereas cutting and grazing management, and the imposition of litter, favoured stress-tolerating perennials. Species diversity decreased both with high inputs of litter and additions of fertilizer. Plant community responses and competitive strategies of key species are discussed in the context of biodiversity conservation, ecological restoration and management of European floodplain grasslands.

Thesis (Ph.D.) - University of Glasgow, 1996.
Ph.D. thesis submitted to the Environmental Sciences Department, Scottish Agricultural College, 1996. Includes bibliographical references. Print version also available.

The grasslands of South Africa are the foundation of commercial and subsistence agriculture yet they are being degraded at an alanning rate. The coastal grasslands of the Eastern Cape are no exception and they suffer added pressure of coastal resort development because of their proximity to an attractive coastline. In order to determine the degree of conservation necessary for any area it is essential to know what species occur there in order to determine if protection from habitat destruction is required. Four aims were defined for this studv. The initial aim was a phytogeographical classification of the grasslands in the coastal region west of the Kei River. This was done by vegetation sampling followed by computer based analysis with TWINSPAN. This analysis defined ten grassland associations. five being located in the area west of the Keiskamma River and five occurring east of it. The associations in the eastern half are termed mesic while those in the western balf are xeric. The second aim was to determine the presence of any underlying ecological gradients affecting the distribution of tbe associations. Indirect gradient analysis was carried out where samples are analysed irrespective of environmental factors. Direct gradient analysis was then carried out using scores per sample of various environmental factors. Environmental factors whicb migbt produce such gradients are both naturally-ocurring and man-induced. Natural factors which were recorded in the field include depth of soil at sample site, soil family, aspect and distance from the shore. An important factor is the land / sea interface. Natural factors analysed in the laboratory include soil pH. conductivity. percent organic matter, calcium, magnesium, phosphate and potassium. Man-induced factors are land use history e.g. Ploughing and grazing. Both direct and indirect gradient analysis were carried out with the computer based programme CANOCO. The third aim of the study was to determine the presence of any successional trends between the ten defined associations. This was done using several characteristics of the associations. Alpha and beta diversity were the first factors compared between associations. The percentage contribution of the Cyperaceae, Fabaceae, Asteraceae and Poaceae to each association was assessed and compared. The presence of various life forms of the species occurring in each association was determined together with the cover abundance of different classes of grass species. These results were then combined and analysed in the light of the results from CANOCO analvsis. They show that the mesic Themeda Iriandra - Anthospermum herhoceum, association which occurs closest to the shore and with the least disturbance is a depauperate form of the mesic climax Themeda triandra association. The mesic Hyparrhenia hirta - Dtheteropogon amplectens association may be a secondary grassland on account of phosphate and potassiun poor soils and land-use. The mesic Hyparrhenia hirta - Themedo triandra association is a slightly degraded form of the climax association due to grazing. The severely disturbed Stenotaphrum secundatum - C'entella coriacea association, which is located close to the shore, is a secondary grassland. Analysis of the xeric associations indicates a clearly defined ordination of associations on the basis of land-use. The Cynodon daclylon - Helictolrichon hirtulum and Sporobolis africanus - Setaria sphacelata associations which occur where ploughed lands have been left to lie fallow are secondary in nature. The Themeda triandra - Ehrharta calycina association is thought to be the closest representati ve of a climax xeric association but the presence of E. calycina indicates that some disturbance has occurred. The vegetation is subject to moderate grazing. The Cynodon dactylon - Ehrharla calycina and Diheleropogon filifolius - Ehrharla calycina associations are subject to varying intensities of trampling and grazing and are degraded forms of the Themeda triandra - Ehrharla calycina association. Because of tbe overriding influence of the land-use gradient separation along gradients of the remaining eight factors was limited. The effect of fire and temporal change in the mesic Themeda triandra and Hyparrhenia hirta - Themeeia trianda associations was assessed via long-term studies at Potter's Pass outside East London. The results show a quick response to burning with a return to 100% cover within six months by both associations. During spring the two associations could not be separated by either TWINSPAN or DECORANA. indicating a temporal shift from the Hyparrhenia hirta - Themeda triandra association to the Themeda triandra association. The fourth and final aim was to identify plants requiring protection from habitat destruction and to make recommendations for further conservation areas and management of the coastal grasslands. Through the collection and identification of as many plants as possible a species checklist was prepared and the status of each was determined through reference to the Red Data Book of threatened and endangered species. Kniphofia rooperi is vulnerable in the Cape and Euphorbia hupleuroides is considered rare in kwazulu-Natal. Ten species are endemic to the Cape and / or South Africa. The richness of the vegetation lies in the presence of species representative of the four major floras which converge in the eastern Cape. i.e. The Cape, NamaKarroo, Tongoland-Pondolaod floras and the Kalahari Highveld Regional Transitional Zone. Suggestions are made for the conservation of the grassland associations at various sites within the study area based on the present area conserved. Less than 2% of the coastline in the study area is conserved and it is felt that the area under conservation should be increased. Management suggestions based on the available literature are given for both farmed and conserved areas. There is a great potential for further studies on grassland dmamics within the areas surveyed. In terms of management, the grasslands require careful examination to determine the most effective season in which to burn if at all. As with most agricultural systems in South Africa. grazing strategies will benefit from further research. Any additional research on the dynamics of these grasslands can only be of benefit to the sustained utilisation of this vital resource.

Following the surface application of different fertiliser treatments (cattle slurry, cattle manure, and inorganic fertiliser) to grassed hillslopes, the transport of nitrogen (N) and phosphorus (P) was monitored on controlled plots. The plots measured 30 m by 5 m, the lower 10 m acting as an untreated buffer zone, in order to examine the effect of following current codes of practice when applying fertilisers (MAFF and WOAD, 1991). Surface and sub-surface nutrient flow pathways were monitored, by sampling water from the saturated and unsaturated zones of the soil profile, and from surface runoff. Sub-surface flow was dominated by N03--N. However, concentrations of this N species were relatively low (3-6 mg 1-1), and differences between treatments and the control were not significant. Generally, this indicated immobilisation of N species and P fractions, outputs in plant uptake and possibly to atmosphere (denitrification). For surface runoff, concentrations of N and P from treated plots were significantly higher than those from the control. N was largely present as organic-N and NH4+-N for the slurry and manure (15 mg 1-1 and 5 mg 1-1 respectively), and as NH4+-N and N03--N for the inorganic fertiliser (20 mg 1-1 in both cases). P was largely present as P04--P (0.5 mg 1-1 for manure and slurry, 10 mg 1-1 for inorganic fertiliser), except for the manure treatment, where some 75 % of the total was organic-P. The 10 m buffer was effective in reducing the delivery of N and P in surface runoff, differences between the treatments and the control being rendered insignificant. This result was qualified in terms of the ratio of the buffer area to the treated area and the relatively low surface loads of N and P observed. N and P transport was then examined under less controlled conditions at the field to headwater catchment scale (4-18 ha). Sub-surface throughflow was associated with similar concentrations of N03--N (3-8 mg 1-1) and very low concentrations of P04--P (0.03-0.1 mg 1-1). These concentrations appeared to vary more in relation to seasonal changes in the level of discharge from the catchment than to changes in land-use, which implied that N and P in sub-surface throughflow was transport rather than supply limited. This was in broad agreement with observations made at the plot scale. At this larger scale, fluctuations in the concentrations of NH4+-N and P04--P occurred during rainfall events in response to what was probably the short-term occurrence of surface runoff from partial source areas of reduced infiltration capacity or variable source areas of saturation. These short-term fluctuations implied variations in topography and the distribution of surface derived N and P at the catchment scale. There was evidence of the occurrence of preferential flow during field experiments at both scales, which had important implications for the timing and magnitude of N and P transport. Finally, a functional and semi-distributed mathematical model was constructed to operate at the headwater catchment scale, and the effect of spatial variability in the interaction between land-use and topography on the transport of N and P was considered further.

Species assembly into local communities from the surrounding region can be caused either by species failure to reach the site (i.e. seed limitation) or to establish (i.e. establishment limitation). The aim of this thesis was to investigate plant species assembly and to determine the relative importance of different factors in that process. In a cultivated landscape in southeast Sweden, plant community assembly was studied in grazed ex-arable fields. Community assembly from the surrounding region into the local community was explored using trait-based null models and seed sowing and transplanting experiments. The influence of local environmental factors and landscape history and structure on community assembly was also studied. In addition, differences in species assembly between ex-arable fields and semi-natural grasslands were explored. Seed limitation was the strongest filter on local community assembly. Only a fraction (36%) of species in a region dispersed to a local site and adding seeds/transplants increased species establishment. Species abundance at the regional scale, species dispersal method and seed mass strongly influenced which species arrived at the local sites. Establishment limitation also affected the assembly. Of species arriving at a site 78% did establish, seedling survival was low and which species established was influenced by species interactions, local environmental conditions and stochastic events. In addition, landscape structure that determined the species richness in the regional species pool influenced the local assembly. The comparison between assembly in ex-arable fields and semi-natural grasslands indicated that the main cause of difference in species assembly between them was difference in their age. The main conclusion of this thesis is that regional processes are more important than local factors in determining plant community assembly.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Manuscript.

Acocks (1953) suggested that Transkei was once covered in Forest and Scrub-Forest and has possibly been transformed by the Iron Age Farmers to grasslands. Feely (1985) suggested that the grasslands are ancient. I therefore used C isotope analysis to reveal whether there has been any change in the dominant vegetation during the Iron Age period. We measured the δ¹³C value of the soil organic matter taken at various depths These were taken from selected sites throughout Transkei that represented the grasslands, forests and grasslands suspected of once being forest or scrub-forest. The results show that the vegetation has remained stable. Those area that are presently covered in grasslands have remained grasslands for the time period represented by the depth of the samples taken. There is however a small shift in the forest and grassland sites to a lower isotopic value either as a result of changing vegetation or changes in the atmospheric [O₂]. There is also archaeological, ecological and historical evidence supporting these results. There is evidence of settlements scattered along the coast and in river valleys during the Early Iron Age (AD 300 to AD 1000). The earliest evidence of settlements during the Late Iron Age dates to AD 1400. The impact of the farmers appears to be localised and the vegetation type appears to have remained constant although impacted on.

North American grasslands and grassland birds have declined drastically due to habitat degradation by fire suppression (i.e., woody encroachment), fragmentation, and conversion to croplands. A better understanding is needed of the relationships among disturbance regimes (e.g., fire), resultant vegetation changes, and grassland bird communities to effectively manage remaining grasslands and grassland birds. I assessed the relationship between post-fire succession, and mean relative abundance and nesting ecology of breeding grassland birds (i.e., nest-site selection and nest success) in mesquite-dominated rangeland of the Texas Rolling Plains, where prescribed fire is used as a tool to manage shrub encroachment. Brush cover, grass cover, and visual obstruction generally increased with post-fire succession, and bare ground decreased with post-fire succession. Species richness, grasshopper sparrows (Ammodramus savannarum), Cassin’s sparrows (Aimophila cassinii), and dickcissels (Spiza americana) responded positively to post-fire succession, and lark sparrows (Chondestes grammacus) responded negatively to post-fire succession.; abundance of these avian groups was low on the control sites. During 2004–2005, 90 grassland bird nests were monitored. I found conflicting results for vegetation parameters important to nest site selection and probability of nest success. For all species except lark sparrows, nest-site location was positively associated with visual obstruction and with grass or forb cover. However, the probability of nest success increased with lower visual obstruction, bare ground cover, or grass cover. Grassland bird abundance, nest-site location, and nest success had differing associations with vegetation variables. These results suggest that to effectively manage remaining grasslands for sustainable breeding grassland bird populations, managers should engage in practices that keep habitat in multiple vegetative successional stages.

Les graminées (Poaceae) sont une très grande famille cosmopolite de plantes. Dans la thèse présentée ici, j'ai utilisé des méthodes moléculaires pour analyser leur histoire biogéographique. Le premier chapitre s'intéresse aux déterminants de la dispersion dans la sous-tribu tempérée Loliinae. La distance apparaît comme le facteur dominant. Le deuxième chapitre présente une analyse des origines des graminées de Madagascar. Les résultats montrent deux grandes radiations in situ de graminées C3 et une immigration répétée de graminées C4, soutenant l'existence de savanes malgaches avant la présence humaine. Le troisième chapitre résout la position d'une lignée C3 d'Asie à l'aide de la phylogénomique, avec des implications pour l'évolution de la photosynthèse C4 et des savanes tropicales. Le quatrième chapitre présente une méthode de méta-barcoding pour l'analyse des communautés d'endophytes fongiques associées aux graminées à Madagascar, démontrant des limitations méthodologiques
Grasses (Poaceae) are a large, cosmopolitan plant family. In this dissertation, I used molecular methods to study their biogeographic history. The first chapter focuses on determinants of lineage dispersal in the temperate subtribe Loliinae, with distance found to be the dominant factor. The second chapter analyses the origins of Madagascar's grass flora. Two large in situ radiations of C3 grasses were found while C4 grasses immigrated more frequently and support the pre-human presence of grasslands in Madagascar. The third chapter resolves relationships of an Asian C3 lineage using phylogenomic methods, with implications for C4 photosynthesis evolution and the assembly of tropical grasslands. The fourth and final chapter developed a metabarcoding method for the analysis of fungal endophyte communities associated to grasses in Madagascar, with results highlighting methodological limitations

A phytosociological study covering approximately 12 000 km2 was completed within Southeastern Mpumalanga high altitude grasslands. The towns of Belfast, Barberton, Piet Retief and Wakkerstroom represented the four corners of the area. The study formed part of the Grassland Biome Project sponsored by the Department of Environmental Affairs and Tourism. The Braun-Blanquet approach was applied. Grassland research results from the western side of the country, determined that soil patterns and vegetation distribution are significantly correlated. Based on these results, it was hypothesised that the same correlation would exist in the east. The eight soil patterns used during the survey as homogenous units, were Ab, Ac, Ad, Ae, Ea, Fa, Fb and lb. A pro rata, randomly stratified sample size of 405 plots were used. An in-depth literature study of the environmental and other factors related to vegetation distribution, indicated on local scale that a significant correlation exists between landform and plant distribution. Two geographic information systems, Idrisi and Arc-Info/Niew, aided in the modelling and extraction of environmental attributes from existing databases. A TWINSPAN classification of the complete floristic data set falsified the null hypothesis based on the soil patterns but verified the null hypothesis based on landforms. The TWINSPAN dendrogram revealed clusters associated with three landforms (mountains, hills and lowlands, and plains) in two ecosystems, the terrestrial and the wetlands or aquatic. The three landforms represented three mapping units: Southeastern Mpumalanga Mountain Vegetation Type, Southeastern Mpumalanga Hills and Lowland Vegetation Type and Southeastern Mpumalanga Plain Vegetation Type. A second TWINSPAN classification was executed on each of the vegetation types. The resulting clusters were tested for uniqueness and informational value using a set of criteria. Those clusters which qualified were arranged in a Braun-Blanquet table to determine communities, sub-communities and variations using constancy and fidelity values. The plant communities within the vegetation types were described in terms of floristic composition and environmental attributes. The indirect gradient analysis ordination program DECORANA was used to determine environmental trends and was confirmed by using multiple regression. Soil water availability was the most significant environmental trend between the two ecosystems and within the communities of the ecosystems in each vegetation type. Soil water availability is influenced by numerous factors, whose significance differs from one vegetation type to another. lt was concluded from this study that, in high rainfall areas, soil patterns and vegetation distribution are not significantly correlated but that landforms and vegetation distribution are significantly correlated. Landscape slope configuration or landform influences soil water availability through soil characteristics (rockiness, texture and depth) and local climatic conditions (aspect, perpendicular insolation and precipitation). lt is suggested that the current Grassland - Savanna Biome boundary be changed towards the west using the boundary between the covered and exposed shields. This suggestion is supported by the presence of Hyparrhenia hirta/Hyperthelia dissoluta - Acacia sieberiana communities to the east of the study area in the different vegetation types which correlate significantly with the thorntree-tall grass savanna formation on a global scale. AFRIKAANS : 'n Fitososiologiese studie is gedoen van die Suid-oostelike Mpumalanga hoe liggende grasveld tussen die dorpe Belfast, Barberton, Piet Retief en Wakkerstroom. 'n Area van ongeveer 12 000 km2 is bestudeer. Die studie is deel van die Grasveld Bioom Projek gefinansier deur die Departement van Omgewingsake en Toerisme. Die Braun-Blanquet benadering is gebruik. Resultate van grasveldnavorsing in die westelike deel van die grasveld bioom, het aangedui dat 'n betekenisvolle verband tussen grondpatrone en plantegroei verspreiding bestaan. Na aanleiding van hierdie resultate, is die hipotese gemaak dat dieselfde verband in die ooste sal voorkom. Agt grondpatrone, Ab, Ac, Ad, Ae, Fa, Fb, en lb is as homogene eenhede beskou. 'n Eweredige ewekansige steekproefneming van 405 punte is gebruik. 'n Deeglike literatuurstudie van die omgewing en faktore wat verband hou met plantegroei verspreiding, het aangedui op lokale skale, dat 'n verband tussen landvorm en plantegroei verspreiding bestaan. Twee geografiese inligtingstelsels, ldrisi en Arc-lnfo/View, is gebruik in die modelering en verkryging van omgewings data vanuit bestaande databasisse. 'n TWINSPAN klassifikasie gebaseer op die volledige spesiesamestelling, het die nul hipotese oor die grondpatrone ongeldig verklaar maar die nul hipotese oor die landvorme bevestig. Die TWINSPAN dendrogram het groeperings bevat wat verband hou met drie landvorme (berge, heuwels en laaglande en vlaktes) in twee ekosisteme, terrestrieel en vleiland van akwatiese omgewings. Die drie landvorme is beskou as drie karteerbare eenhede: Suid-oostelike Mpumalanga Berg Plantegroeitipe, Suidoostelike Mpumalanga Heuwels en Laagland Plantegroeitipe en Suid-oostelike Mpumalanga Vlakte Plantegroeitipe. 'n Tweede TWINSPAN klassifikasie is op elk van die plantegroeitipes toegepas. Elke plantegroeitipe se groeperings is met behulp van bepaalde voorwaardes vir uniekheid en inligtingswaarde getoets. Die groeperings wat gekwalifiseer het, is met behulp van konstantheids en getrouheids waardes in 'n Braun-Blanquet tabel gerangskik in gemeenskappe, sub-gemeenskappe en variasies. Elke plantegroei tipe se gemeenskappe is beskryf in terme van floristies spesiesamestelling en omgewingsfaktore. 'n indirekte gradientanalise ordeningsprogram DECORANA is gebruik vir die bepaling van omgewings tendense en is bevestig met behulp van veelvuldige regressies. Grondwaterbeskikbaarheid was die mees betekenisvolle omgewingstendens tussen die ekosisteme en die gemeenskappe van die plantegroei tipes. Grondwaterbeskikbaarheid word deur 'n aantal faktore beïnvloed, waarvan die belangrikheid van plantegroei tipe tot plantegroeitipe wissel. 'n Gevolgtrekking van die studie is, dat in hoë reënvalomgewings daar nie 'n betekenisvolle verband is tussen grondpatrone en plantegroei verspreiding nie maar wel tussen landvorme en plantegroeiverspreiding. Landskap hellingsamestelling of landvorme beïnvloed grondwaterbeskikbaarheid deur middel van grondeienskappe (klipperigheid, tekstuur en diepte) en lokale klimaatstoestande (aspek, loodregte bestraling en presipitasie). Daar word voorgestel dat die huidige Grasveld- Savanna Bioom grens weswaarts geskuif word om ooreen te stem met die grens tussen die bedekte en blootgestelde plate. Die voorstel word ondersteun deur die teenwoordigheid van Hyparrhenia hirta/Hyperthelia dissoluta - Acacia sieberana plantgemeenskappe in die ooste van die plantegroeitipes wat betekenisvol ooreenstem met die langgras-doring boom savanna formasie op globale skaal.
Dissertation (MSc)--University of Pretoria, 1999.
Plant Science
unrestricted

Although semi-natural grasslands in Europe are declining there is often a time delay in the local extinction of grassland species due to development of remnant populations, i.e., populations with an extended persistence despite a negative growth rate. The objectives of this study were to examine the occurrence of remnant populations after abandonment of semi-natural grasslands and to examine functional traits of plants associated with the development of remnant populations. We surveyed six managed semi-natural grasslands and 20 former semi-natural grasslands where management ceased 60-100 years ago, and assessed species response to abandonment, assuming a space-for-time substitution. The response of species was related to nine traits representing life cycle, clonality, leaf traits, seed dispersal and seed mass. Of the 67 species for which data allowed analysis, 44 species declined after grassland abandonment but still occurred at the sites, probably as remnant populations. Five traits were associated with the response to abandonment. The declining but still occurring species were characterized by high plant height, a perennial life form, possession of a perennial bud bank, high clonal ability, and lack of dispersal attributes promoting long-distance dispersal. Traits allowing plants to maintain populations by utilizing only a part of their life cycle, such as clonal propagation, are most important for the capacity to develop remnant populations and delay local extinction. A considerable fraction of the species inhabiting semi-natural grasslands maintain what is most likely remnant populations after more than 60 years of spontaneous succession from managed semi-natural grasslands to forest.

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Inner Mongolian grasslands are part of the vast Eurasian steppe belt and were used for nomadic pastoralism for thousands of years. As a result of political and economic changes in China in the last century, this mobile grazing management has been replaced by a sedentary and intensified livestock production. Stocking rates have increased substantially, overshooting the carrying capacity of the grasslands. These land use changes have induced severe grassland degradation. The impact and causes of grassland degradation have been investigated by the Sino-German joint research group MAGIM (Matter fluxes in grasslands of Inner Mongolia as influenced by stocking rate) in the Xilin River catchment of Inner Mongolia since 2004. This work is part of subproject P6, which amongst others pursues the goal of quantifying water balance exchange by micrometeorology and remote sensing. The dominating process of water balance losses in Inner Mongolian grasslands is evapotranspiration (ET), whereby water vapour is released into the lower atmosphere. ET is highly variable in both time and space in this semi-arid environment, as it is coupled with the typically fluctuating amount of precipitation (P). However, despite ET being the key output process of the hydrological cycle of Inner Mongolian grasslands and despite its important role as an indicator for ecosystem functioning, little is known about its spatiotemporal distribution and variability in this remote area. Recent studies on ET have demonstrated variations due to phenology, soil moisture and land use, but these studies have been limited to short periods and have been conducted on a few field sites in close proximity with debatable representativeness for the 2600 km² of grasslands in the Xilin River catchment. The development of a number of remote sensing methods in the last decades has introduced various approaches to determining spatial ET from space, but the application of remotely sensed ET in regional long-term studies is still problematic. Nevertheless, a variety of surface parameters are provided by the sensor MODIS (moderate resolution imaging spectroradiometer) at a resolution of approx. 1km. The aim of this work was (1) to close the gap between the limitations of available local ET measurements and the need for long-term studies on spatial ET in Inner Mongolian grasslands and (2) to analyse the spatiotemporal variability of ET and its implications on livestock management in this area. Therefore, micrometeorological data, remote sensing products and hydrological modelling with BROOK90 were integrated to model spatial ET for the grasslands of the Xilin River catchment over 10 years. The hydrological model BROOK90 calculates ET based on a modified Penman-Monteith approach including the separation of energy into transpiration and soil evaporation. The spatial application of the model was based on a land use classification restricted to the land use unit typical steppe. BROOK90 was parameterised from eddy covariance measurements, soil characteristics and MODIS leaf area index (LAI). Location and canopy parameters were provided individually, as well as the essential daily model input, including P and air temperatures for each pixel. Minimum and maximum air temperatures were calculated based on a relationship between measured air temperatures and MODIS surface temperatures (R²=0.92 and R²=0.87, n=81). Spatial P was estimated from a relationship found between the measured cumulative P of six rain gauges within the grasslands and the increase of MODIS LAI around these measurements (R²=0.80, n=270). Modelled ET is plausible and fits in the range of published results. ET was demonstrated to be highly variable in both time and space: the high spatiotemporal variability of eight-day ET is reflected by the coefficients of variation, which varied between 25% and 40% for the whole study area and were up to 75% for individual pixels. Soil evaporation reacts considerably more sensitively to precipitation pulses than transpiration. Modelled annual ET sums approached or exceeded precipitation sums in general; however, P exceeded ET in 2003, when exceptionally high precipitation occurred. The strong dynamics and the high spatiotemporal variability of ET clearly demonstrate that the current static livestock management is not adapted to the conditions of Inner Mongolian grasslands. New concepts for a sustainable livestock management could be developed in consideration of the intrinsic long-term patterns of spatial ET distribution and spatiotemporal variability identified in this work. Moreover, as this method for modelling spatial ET is not restricted to the grasslands of the Xilin River catchment, livestock management in other semi-arid grasslands could benefit from it as well
Die Grasländer der Inneren Mongolei sind Teil des riesigen eurasischen Steppengürtels und wurden seit Tausenden von Jahren für die nomadische Weidewirtschaft genutzt. Als Folge der politischen und wirtschaftlichen Veränderungen in China im letzten Jahrhundert ist diese mobile Weidewirtschaft durch eine ortsgebundene und intensivierte Tierhaltung ersetzt worden. Besatzdichten wurden erheblich erhöht und die Tragfähigkeit der Grasländer wurde deutlich überschritten. Diese Landnutzungsänderungen haben schwerwiegende Degradationserscheinungen der Grasländer induziert. Die Ursachen und Auswirkungen der Degradation sind von der Deutsch-Chinesischen-Forschungsgruppe MAGIM (Matter fluxes in grasslands of Inner Mongolia as influenced by stocking rate) im Einzugsgebiet des Xilin-Flusses in der Inneren Mongolei seit 2004 untersucht worden. Diese Arbeit wurde im Rahmen des Teilprojektes P6 erstellt, welches unter anderem das Ziel verfolgt, Wasserhaushaltsprozesse mit Mikrometeorologie und Fernerkundung zu quantifizieren. Der dominierende Prozess der Wasserbilanz-Verluste in den Grasländern der Inneren Mongolei ist die Verdunstung (ET), wobei Wasserdampf in die untere Atmosphäre freigesetzt wird. ET ist in diesem semi-ariden Ökosystem in Zeit und Raum sehr variabel, da an die in der Regel schwankenden Niederschläge (P) gekoppelt. Trotz der Schlüsselrolle, die ET im Wasserkreislauf der Inneren Mongolei einnimmt, und der wichtigen Rolle als Indikator für die Funktionsweise des Ökosystems, ist wenig über die raum-zeitliche Verteilung und Variabilität von ET in dieser abgelegenen Region bekannt. Neuere Studien haben ET-Schwankungen aufgrund von Phänologie, Bodenfeuchte und Bodennutzung dargestellt, aber diese Studien sind auf kurze Zeiträume beschränkt und wurden auf nur wenigen Standorten, die sich in unmittelbarer Nähe befinden, durchgeführt. Dies stellt ihre Repräsentativität für die 2600 km² an Grasland im Xilin-Einzugsgebiet in Frage. Die Entwicklung von Fernerkundungsmethoden in den letzten Jahrzehnten hat verschiedene Ansätze zur Bestimmung der räumlichen ET hervorgebracht, jedoch ist die Anwendung von ET aus Fernerkundungsdaten in regionalen Langzeitstudien immer noch problematisch. Dennoch werden eine Vielzahl von Oberflächenparametern durch den Sensor MODIS (Moderate Resolution Imaging Spectroradiometer) bei einer Auflösung von ca. 1km zur Verfügung gestellt. Das Ziel dieser Arbeit war (1) die Lücke zwischen den verfügbaren lokalen ET-Messungen und dem Bedarf an langfristigen Untersuchungen zu räumlicher ET im Grasland der Inneren Mongolei zu schließen und (2) die räumlich-zeitliche Variabilität von ET vor dem Hintergrund des Beweidungsmanagements zu analysieren. Daher wurden mikrometeorologische Daten, Fernerkundungsprodukte und hydrologische Modellierungen mit BROOK90 integriert, um die räumliche ET für die Grasländer des Xilin-Einzugsgebietes über 10 Jahre zu modellieren. Das hydrologische Modell BROOK90 berechnet ET auf Basis eines modifizierten Penman-Monteith-Ansatzes einschließlich der Aufteilung in Transpiration und Bodenverdunstung. Die räumliche Anwendung des Standortmodells basiert auf einer Landnutzungsklassifikation und wurde für die Landnutzungsklasse typical steppe durchgeführt. Eddy-Kovarianz-Messungen, Bodeneigenschaften und MODIS-Blattflächenindex (LAI) wurden zur Parametrisierung von BROOK90 verwendet. Sowohl Lage- und Pflanzenparameter, als auch die notwendigen Modelleingangsdaten (Tageswerte von P und Lufttemperaturen), wurden für jeden Pixel individuell zur Verfügung gestellt. Minimum- und Maximum-Lufttemperaturen wurden mittels einer Beziehung zwischen gemessenen Lufttemperaturen und MODIS-Oberflächentemperaturen berechnet (R²=0.92 und R²=0.87, n=81). Räumliche P wurden aus einem Zusammenhang zwischen gemessenen kumulierten P von sechs Niederschlagsmessern im Untersuchungsgebiet und der Erhöhung des MODIS-LAI im Bereich dieser Messungen abgeleitet (R²=0.80, n=270). Die modellierte räumliche ET ist plausibel und liegt im Wertebereich der publizierten Ergebnisse. Es wurde gezeigt, das ET sehr variabel in Raum und Zeit ist: die raum-zeitlichen Schwankungen der achttägigen ET wurden durch den Variationskoeffizienten dargestellt, welcher zwischen 25% und 40% für das gesamte Untersuchungsgebiet variiert und für einzelne Pixel bis auf 75% ansteigt. Die Bodenverdunstung reagiert wesentlich empfindlicher auf Niederschlagsereignisse als die Transpiration. Modellierte Jahres-ET-Summen erreichen oder überschritten die Niederschlagssummen in der Regel, jedoch übertraf P die ET im Jahre 2003, als außergewöhnlich hohe Niederschläge aufgetreten sind. Die starke Dynamik und die hohe raum-zeitliche Variabilität der ET zeigen deutlich, dass die aktuelle statische Tierhaltung nicht an die Bedingungen in den Innermongolischen Grasländern angepasst ist. Neue Konzepte für eine nachhaltige Viehwirtschaft könnten unter Berücksichtigung der inhärenten langfristigen Muster der räumlichen Verteilung von ET und ihrer raum-zeitlichen Variabilität, die in dieser Arbeit identifiziert wurden, entwickelt werden. Außerdem ist die Anwendung der entwickelten Methode für die Modellierung räumlicher ET nicht auf die Grasländer des Xilin-Einzugsgebietes beschränkt; die Weidewirtschaft in anderen semi-ariden Grasländern könnte ebenfalls davon profitieren

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

Abstract Plants and soil organisms are closely linked. Plants are the sole source of carbon in the soil and soil organisms are responsible for recycling of nutrients, making them available for plant growth. To understand the function of a system, it is important to understand the interactions between the soil and plants. These interactions have mainly been studied in temperate areas, with few studies in the arctic and subarctic. The aim of this thesis was to investigate the effect of ecological disturbances in sub- and low-arctic grasslands on soil organisms and plant-soil feedback relationships. The effect of removal of vegetation, replanting of a local plant species, and different components of grazing (trampling, defoliation and return of nutrients) on soil decomposer organisms were studied. Whether short term effects of defoliation depended on plant species community was also studied, as well as whether defoliation in the field could create changes in the soil system systems that affect the growth of seedlings. Experiments were conducted under both controlled greenhouse conditions and in field sites. The results showed that physical disturbance (removal of vegetation and trampling) reduced the abundance and diversity of soil biota. Defoliation increased soil decomposer abundance in the short term. Plant species composition did not affect soil biota and only in a few cases did it changes their responses to defoliation. In the long-term, effects of fertilization and defoliation on the soil biota were context-dependent. However, defoliation did create changes in the soil that reduced the growth of seedlings planted into the soil. Furthermore, plant species community and spatial heterogeneity (revealed by blocking) had important effects on the soil communities.

This thesis is about the dynamics of eastern grey kangaroo (Macropus giganteus) populations and their food supplies in temperate grasslands of south-eastern Australia. It is based on the study of three populations of eastern grey kangaroos inhabiting �warm dry�, �cold dry�, and �warm wet� sites within the Southern Tablelands climatic region. After a pilot survey and methods trial in early 2001, the main period of study was from August 2001 to July 2003. The study populations were found to have the highest densities of any kangaroo populations, 450 to 510 km-2. Their density was the same at the end of the two year study period as at the beginning, in spite of a strong decline in herbage availability due to drought. The eastern grey kangaroo populations were limited according to the predation-sensitive food hypothesis. Fecundity, as the observed proportion of females with late pouch young in spring, was high, in spite of the high kangaroo density and restricted food availability. Age-specific fecundity of a kangaroo sample shot on one of the sites in 1997 to avert starvation was the highest reported for kangaroos. Thus, limitation acted through mortality rather than fecundity. Population growth rate was most sensitive to adult survival but the demographic rate that had the greatest effect in practice was mortality of juveniles, most likely sub-adults. The combination of high fecundity with high mortality of immatures would provide resilience to low levels of imposed mortality and to fertility control. The normal pattern of spring pasture growth was not observed in the drought conditions and few of the recorded increments of growth were of the magnitude considered typical for sites on the southern and central tablelands. Temperature was necessary to predict pasture growth, as well as rainfall, over the previous two months. The best model of pasture growth (lowest AICc) included negative terms for herbage mass, rainfall over the previous two months, and temperature, and a positive term for the interaction between rainfall and temperature. It accounted for 13% more of the variation in the data than did the simpler model of the type used by Robertson (1987a), Caughley (1987) and Choquenot et al. (1998). However this was only 63% of total variation. Re-evaluation of the model based on measurements of pasture growth in more typical (non-drought) conditions is recommended. Grazing had a powerful influence on the biomass of pasture due to the high density of kangaroos. This is a marked difference to many other studies of the type which have been conducted in semi-arid environments where rainfall dominates. The offtake of pasture by kangaroos, as estimated on the research sites by the cage method, was linear on herbage mass. It was of greater magnitude than the more exact estimate of the (curved) functional response from grazedowns in high�quality and low�quality pastures. The widespread recognition of three forms of functional response is inadequate. Both the theoretical basis, and supporting data, have been published for domed, inaccessible residue, and power forms as well (Holling 1966; Noy-Meir 1975; Hassell et al. 1976, 1977; Short 1986; Sabelis 1992). Eastern grey kangaroos had approximately the same Type 2 functional response when consuming either a high quality artificial pasture (Phalaris aquatica), or dry native pasture (Themeda australis) in autumn. Their functional response rose more gradually than those published for red kangaroos and western grey kangaroos in the semi-arid rangelands, and did not satiate at the levels of pasture available. This gradual behaviour of the functional response contributes to continuous stability of the consumer-resource system, as opposed to discontinuous stability. The numerical response was estimated using the ratio equation, assuming an intrinsic rate of increase for eastern grey kangaroos in temperate grasslands of 0.55. There is indirect evidence of effects of predation in the dynamics of the kangaroo populations. This is demonstrated by the positive relationship between r and kangaroo density. Such a relationship can be generated by predation. A desirable future task is to compile estimates of population growth rate and simultaneous estimates of pasture, in the absence of predation, where kangaroo population density is changing, so that the numerical response can be estimated empirically. The management implications arising from this study are numerous and a full account would require a separate report. As one example, kangaroos in these temperate grasslands are on average smaller, eat less, are more numerous, and are more fecund, than would be predicted from other studies (e.g. Caughley et al. 1987). Thus the benefit of shooting each kangaroo, in terms of grass production, is less, or, in other words, more kangaroos have to be shot to achieve a certain level of impact reduction, and the population will recover more quickly, than would have been predicted prior to this study. Secondly, of much importance to managers, the interactive model which can readily be assembled from the products of Chapters 4, 5 and 8, can be used to test a range of management options, and the effect of variation in weather conditions, such as increased or decreased rainfall. For example, the model indicates that commercial harvesting (currently under trial in the region), at the maximum level allowed, results in a sustainable harvest of kangaroos, but does not increase the herbage mass, and only slightly reduces the frequency of crashes when herbage mass falls to low levels. (To demonstrate this with an ecological experiment would require an extremely large investment of research effort.) However, an alternative �national park damage mitigation� formula, which holds kangaroo density to about 1 ha-1, is predicted to increase herbage mass considerably and to reduce the frequency of crashes in herbage mass, but these effects would be achieved at the cost of having to shoot large numbers of kangaroos. Thus, aside from many specific details of kangaroo ecology, the knowledge gained in this study appears to have useful potential to illustrate to managers the dynamic properties of a resource-consumer system, the probabilistic nature of management outcomes, and the consequences of particular kangaroo management proposals.

During the past century there have been vast changes in land use, which have led to succession processes in outlying lands. As a consequence, species-rich semi-natural grasslands are disappearing and many of their associated species have become threatened with extinction. For targeted and successful conservation of these species, it is important to identify the ecological factors determining their distribution and abundance. The aim of this study was to reveal effects of different management types on the distribution and abundance of rare low-herb species, while controlling for vegetation type, moisture and pH. A case study was performed at Brekken, an upland outlying landscape in Norway. Seven study species were chosen; three Botrychium species (B. lunaria, B. boreale, B. lanceolatum), three gentian species (Gentiana nivalis, Gentianella campestris, Gentianella amarella) and one orchid (Nigritella nigra). Species observations were obtained by distance transect sampling. Within transects, present vegetation was recorded as intervals of distinct types, and moisture and pH was measured and used in characterization of vegetation types. Using generalized linear models and generalized linear mixed models, density and probability of occurrence was modeled in response to management (mowing, grazing and abandonment) and vegetation types. For all species in total, both the density and the probability of occurrence is higher in grazed areas than in mown and abandoned areas, and their habitat ranges are wider in the grazed area. From models fit per species, the gentian species show higher density or probability of occurrence in mown areas. Most of the studied species were shown to be at highest density and/or have highest probability of occurrence in low-grown grassland vegetation. Such grasslands are products of land use, and therefore management effects are in some species analyses assumed to be masked within significant effects of vegetation types. In restoration and conservation, type of management should be determined specifically for each site, based on local land use history and the overall conservation aim.

Thesis (Ph. D. in the Field of Hydrology)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2013.
"February 2012." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 155-172).
This thesis addresses the coupling of hydrologic and biogeochemical processes and, specifically, the organization of ecosystem traits with the water, carbon, and nitrogen cycles. Observations from a factorial irrigation-fertilization experiment in a seasonally dry annual grassland are combined with a simple ecosystem model to identify relationships between vegetation, nitrogen availability, and hydrology. Assuming primary productivity is water-limited, data analysis indicates that soil moisture and canopy conductance are insensitive to nitrogen supply, owing to a trade-off between canopy density and leaf conductance that maximizes efficient use of available water. That is, fertilization-induced increases in leaf area index are offset by reduced leaf area-based stomatal conductance. When primary productivity is assumed to be co-limited by water and nitrogen availability, total surface conductance is estimated to be insensitive to nitrogen supply, but added nitrogen increases the ratio of transpiration to evaporation. This coupled water-carbon-nitrogen model is then extended to predict ecosystem sensitivity across independently varied gradients of water and nitrogen supply rates. This analysis reveals two distinct regimes of plant-resource organization. In arid climates, rooting depths decrease with increasing aridity, while in humid climates, rooting depths increase with aridity. In all climates, rooting depths increase with increased nitrogen supply. Further, relative root-carbon allocation always increases with aridity and decreases with nitrogen supply. These resource use strategies result in an efficient use of available water in arid climates and efficient use of available nitrogen in humid climates. The associated ecosystem process rates indicate that nitrogen supply is an important determinant of surface water and carbon fluxes in humid climates, but only of carbon fluxes in arid climates.
by Anthony Joseph Parolari.
Ph.D.in the Field of Hydrology

Surface application of broiler litter to grasslands can increase concentrations of ammonium (NH₄+-N) and dissolved reactive phosphorus (DRP) in surface runoff. It is not known, however, for how long after broiler litter applications that NH₄+-N and DRP concentrations remain elevated. Five 0.75-ha, fescue-bermudagrass paddlocks received four broiler litter applications in 1995 and 1996, and only inorganic fertilizer N in 1997 and 1998. Runoff from each paddock was measured, sampled, and analyzed for NH₄+-N and DRP. Flow-weighted NH₄+-N and DRP concentrations increased from background values of 0.5 and 0.4 mg L-1, respectively, to values as high as 50.7 mg NH₄+-N L⁻¹ and 18.8 mg DRP L-1 in a runoff event that occurred immediately after the third litter application. Concentrations remained high while broiler litter was being applied but decreased steadily after the last application, reaching values near 1 mg L⁻¹ (for NH₄+-N and DRP) by 19 months after the final application. Among the factors that affected the average concentration of NH₄+-N and DRP in cumulative runoff after a litter application were cumulative runoff, rates of total N and NH₄+-N applied, and cumulative total litter N, total litter P, and water-soluble litter P applied during the four years of the study. Soil test P also affected DRP concentrations, but its effect depended on when the paddocks last received broiler litter. There is a need for tools to identify situations in which the application of broiler litter may enrich surface runoff with P. One such tool is the simulation model Erosion Productivity Impact Calculator (EPIC). EPIC's ability to simulate runoff volume and losses of dissolved reactive P (DRP) was evaluated. Data from the five 0.75-ha, tall fescue-bermudagrass plots that were fertilized with broiler litter during two years, and received only inorganic fertilizer N for the two subsequent years, were compared with EPIC estimates. EPIC simulations of runoff volume in individual events did not show bias in three of the plots but underestimated runoff in one plot and overestimated runoff in another. On an annual basis, the runoff volumes simulated by EPIC were similar to the observed values. A modified version of EPIC yielded better estimates of event DRP losses than the original EPIC and generated estimates of annual DRP loss that were similar to observed values. These results suggest that the modified EPIC may be useful for identifying situations where there is a high risk of large annual P losses from grasslands fertilized with broiler litter.
Ph. D.

There has been a widespread assessment of the capacity of grasslands to restore after several forms of disturbance. In South Africa forestry is a significant habitat disturbance within the Eastern Highveld grasslands where this study was conducted. The study compared ant communities between disturbed grasslands that have been rehabilitated after pine forestry and undisturbed grasslands. Ant sampling was conducted using pitfall traps within rehabilitated sites of age 10 years to 40 years and undisturbed grassland sites. We expected that exposure to pine plantations would result in remarkable differences in ant species richness, assemblages and abundance. A total of 17 genera and 31 morphospecies were collected; 25 species within the rehabilitated and 22 species from the undisturbed grasslands. The sites did not show any significant differences in their species richness, although they had distinctive species assemblages. Ant diversity showed recovery with increasing age after pine with older sites (38 years and 40 years) showing higher diversity compared to the younger sites especially the 10 year old site. Copyright
Dissertation (MSc (Environmental Ecology))--University of Pretoria, 2011.
Zoology and Entomology
Unrestricted

Non-native grasses, originally introduced for pasture improvement, threaten Australia's iconic low-resource grasslands and a thorough understanding of the life-history strategies associated with these species is essential for effective management. Comparing invasive qualities across four congener pairs of native and non-native grasses, it was revealed that non-natives displayed a unique combination of morphological and physiological traits compared to natives. This study applied a novel technique of microdialysis and found that native and non-native grasses use soil nitrogen differently, likely contributing to the competitive advantage shown by non-native grasses across Australia.

Predation by exotic predators (cats Felis catus and foxes Vulpes vulpes) is believed to be one of the factors that has contributed to the decline of medium-sized mammals in arid Australia. Other factors include habitat degradation by introduced herbivores (rabbits Oryctolagus cuniculus and grazing stock) and altered fire regimes after Aboriginal people moved into permanent settlements. In general, the impact of exotic predators on arid zone mammals is believed to be significant only when predator numbers have been elevated by increased food availability from exotic prey species (rabbits, house-mice Mus domesticus, cattle carcasses) or when native prey populations have already been dramatically reduced by competition from introduced herbivores. In much of the spinifex grasslands of the central Australian deserts, pastoralism never occurred, rabbit colonisation was extremely patchy and in some areas, traditional burning was still being practised when the extinctions commenced. None of the current models of mammalian extinctions adequately explain the declines in this environment. In this study I examined predator-prey interactions in two areas of the Tanami Desert to investigate whether predation by exotic predators may be a primary agent of extinction in its own right, capable of causing mass declines even in the absence of other human-induced perturbations. If this were the case then the following would be expected: (i) cats and foxes would eat medium-sized mammals when they are available, but be able to survive on alternative prey when mammals are scarce; (ii) populations of cats and foxes would be buffered against the declines of mammals during droughts, or would be able to recover more quickly than medium-sized mammals after droughts; (iii) medium-sized mammals would be more vulnerable to predation by cats and foxes than by dingoes Canis lupus dingo and other native predators, and (iv) there would be a correlation between the timings of the extinctions and the colonisation (or sudden increase) of cats and foxes. These predictions were investigated by monitoring the diets and relative abundance of cats, foxes and dingoes in relation to fluctuating prey availability in two areas of the Tanami Desert at latitudes separated by approximately 400 km. Mean annual rainfall is higher and more reliable in the northern study area which was situated in the centre of bilby Macrotis lagotis distribution within the Northern Territory, whereas the southern study area was located on the southern edge of the bilby�s range. Within each study area, monitoring occurred at three sites, approximately 20 km apart. Each site contained a sub-plot in each of two habitat types. Field work was conducted between September 1995 and December 1997. When the study began, the southern study area was experiencing drought conditions, however both study areas received significant rainfall in early 1997. The population dynamics of a variety of potential prey groups were monitored to examine their resilience during droughts, patterns of recolonisation after rainfall, and use of two habitat types: the ubiquitous sandplain, and the moister, nutrient enriched palaeodrainage habitat which is believed to have provided a refuge for medium-sized mammals during droughts. Native mammals were uncommon throughout the study period. Bilbies and macropods were significantly more abundant in the northern study area, and tended to occur more frequently in palaeodrainage habitat than sandplain. However, the palaeodrainage habitat did not appear to provide adequate refuge for the medium and large mammals during drought conditions in the southern study area, as they disappeared from the study sites altogether. Small mammals were significantly more abundant in the southern study area but densities remained low (less than 2% trap success) throughout the study, and showed little response to improved seasonal conditions. In contrast, the abundance and species richness of birds showed a marked increase following rainfall in the southern study area. Flocks of nomadic birds arrived within several months of drought-breaking rains, increasing the relative abundance of birds from 9.3 per km of transect in December 1996 to 49/km in July 1997. Reptiles were the most resilient prey group during the drought conditions. Both varanids and smaller reptiles were equally abundant in the wet and dry years and showed no difference in abundance between study areas. However, reptiles showed marked temperature-related patterns in activity, with many species becoming inactive in the winter months. A total of 142 cat scats, 126 fox scats and 75 dingo scats were analysed to investigate predator diets in the two study areas. Unlike cat, fox and dingo diets elsewhere in Australia (and the world), mammalian prey did not dominate. Reptile was the prey category that was most frequently consumed by cats and foxes in �summer� (October-April) and by dingoes throughout the year, and was identified as a �seasonal staple� prey type for all three predators in the Tanami Desert. When biomass of prey was taken into account, the varanids (predominantly the sand goanna Varanus gouldii) were the most important prey sustaining predators in the two study areas. Birds were an important part of the diets of cats and foxes in winter when reptiles were less active. Small mammals were consumed by cats and foxes throughout the study, in proportion to their field abundances. Invertebrates were a major component of the diets of foxes, representing 31% of prey items consumed. There was considerable overlap in the diets of the three predator species, but dingoes ate more medium (100-999 g) and large (greater than 1000 g) prey than cats and foxes did. The scarcity of medium-sized mammals in the study areas provided little opportunity to find evidence of predation events on such prey. However, bilby remains were found in two cat scats and one dingo scat in the northern study area, mulgara Dasycercus cristicauda remains occurred in several cat and fox scats from the southern study area, and there were fourteen occurrences of marsupial mole Notoryctes typhlops in predator scats during the study, primarily in fox scats. Elsewhere in Australia, there is ample evidence that cats and foxes regularly consume medium-sized mammalian prey (e.g. rabbits and ringtail possums Pseudocheirus peregrinus) when it is available. Overall cats were the most abundant eutherian predators in the two study areas, and they were significantly more abundant in the northern study area than the southern study area. Surveys revealed that cats can persist into droughts by feeding on reptilian prey. When the study commenced, cats occurred on five of the six sub-plots in the southern study area, despite six consecutive years of below-average rainfall. However, by the end of the first year, they could only be detected on one sub-plot. Recolonisation of the sites rapidly occurred after significant rainfall (260 mm in 2 months), when nomadic birds colonised the sites and provided a plentiful food source. Foxes also declined to very low densities during drought in the southern study area, but they had recolonised all sites by the winter of 1997. This coincided with the increase in abundance of birds, which became their most frequently consumed prey item. Overall, foxes were equally abundant in the two study areas, but statistical analyses revealed a significant interaction between latitude and habitat because in the southern study area foxes tended to utilise the palaeodrainage habitat more than the sandplain, whereas in the northern study area the majority of fox sign was detected in the sandplain habitat. This may have been due to the abundance of dingoes in the palaeodrainage habitat in the northern study area. Dingoes were significantly more abundant in the northern study area than the southern, where they were usually only present at one of the three sites. The northern study area had higher densities of macropods (supplementary prey for dingoes) and more reliable access to drinking water, which persisted in the palaeodrainage channels for up to 6 months after significant rain events. Dingo numbers were relatively stable throughout the study and did not increase in response to improved seasonal conditions in the southern study area in 1997. This study revealed that the distribution of foxes extends further north into the Tanami Desert than has previously been reported, and is not necessarily tied to the distribution of rabbits in the Northern Territory. Furthermore, discussion with Aboriginal people who lived a traditional lifestyle in the area until the 1940s, revealed that foxes were already present in the northern Tanami desert at that time, before the disappearance of many medium-sized mammal species. The patterns of medium-sized mammalian extinctions in the northern and western deserts between 1940 and 1960 is thus consistent with the colonisation of the fox. Although cats had been present in central Australia for at least 50 years before the mammalian declines occurred, this does not discount them from contributing to the extinction process. It is postulated that during the early decades of their colonisation of the arid interior, cat populations may have been maintained at low levels by predation from dingoes and also Aboriginal people (for whom cats were a favoured food). But between 1920 and 1960 the western deserts were depopulated of Aboriginal people, and human hunting of cats diminished. This coincided with the introduction of the dingo bounty scheme, which encouraged many Aboriginal people to continue making regular excursions into the deserts to collect dingo scalps. In this study, cat remains occurred in 9% of dingo scats, suggesting that dingoes may be an important predator of cats. Thus, there may have been an increase in the cat population between 1930 and 1960, producing a more significant impact on native mammal populations than had previously occurred. Information collected during this study was used to construct a new model of mammalian extinctions in the spinifex grasslands of central Australia that promotes predation by cats and foxes as the primary agent of extinction. The model proposes that cats and foxes will eat medium-sized mammals when they are available, but are capable of subsisting on naturally occurring alternative prey when mammals are scarce. Thus, cats and foxes can persist into drought periods by feeding on reptilian prey, which remains an abundant resource regardless of rainfall (at least during the warmer months). Predator populations eventually decline after a series of dry winters. When the drought breaks, the rapid response of nomadic birds provides a readily available food source for cats and foxes as they recolonise areas and commence breeding. Predation by cats and foxes thereby has the potential to exacerbate the declines of native prey populations during droughts and delay their recovery when seasonal conditions improve. In this way, introduced predators are capable of causing local extinctions of medium-sized mammals when populations contract during drought periods, even in the absence of introduced herbivores and altered fire regimes. Although dingoes also prey upon medium-sized mammals, dingoes did not cause extinctions of medium-sized mammals in the spinifex grasslands because (i) they are more reliant on drinking water than foxes and cats, thus waterless areas would have provided some degree of predation refugia, and (ii) their social structure and territoriality prevent high densities accumulating, even when resources are abundant. If further extinctions of medium-sized mammals (such as the bilby) are to be prevented, it may be necessary for wildlife managers to establish a series of predation refugia where fox and cat populations can be controlled without extinguishing local dingo populations. This could be achieved with a combination of predator-proof enclosures, zones in which foxes are killed through poison baiting and areas where Aboriginal people are employed to utilise traditional hunting methods to control introduced predators.

Hieracium pilosella is an invasive weed of New Zealand's short tussock grasslands. Since the 1960s, the abundance of H. pilosella has dramatically increased; it is now thought to occur in 6 million hectares of New Zealand (Espie, 2001), predominantly in grasslands. It is at least common in 42% of this area (Espie, 2001). Ecology is inherently spatial and as plants closely interact with their direct neighbours, the spatial arrangement of plants is vital to their functioning. A handful of recently published articles have implicated spatial structure of plant communities in theories of plant competition, resource use and the invasion of plant communities. The aims of this thesis were to: 1) determine if there are consistent spatial patterns in New Zealand's short tussock grasslands at relatively small scales (i.e. spatial relationships between individuals); 2) investigate how the invasion of H. pilosella may be altering these spatial patterns; and 3) establish if the spatial patterns of species, life-forms and root systems are being altered in different ways. Spatial patterns of both tussock and inter-tussock species, life-forms and root functional groups were evaluated at a range of short tussock grassland sites across a gradient of H. pilosella invasion levels in Canterbury, using both join-count statistics and Ripley's K-function. A classification system for the root functional groups of vascular species in these communities was developed and applied. It was found that species, life-forms and root functional groups in short tussock grasslands had generally consistent spatial patterns across sites both within and between species. These patterns were variable between significantly different levels of H. pilosella ground cover. The type of spatial pattern exhibited, and the way it was altered differed between species, life-form and root functional groups. For example, tussocks exhibited increased regularity up to scales of 160 cm and increasing aggregation at scales up to 500 cm, with increases in H. pilosella abundance. In contrast, both Agrostis capillaris and herbaceous chamaephytes had increased aggregation across scales up to 160 cm. These differences in spatial patterns along the gradient of invasion are a strong indication that H. pilosella is structurally fragmenting New Zealand's short tussock grasslands. This fragmentation is likely to have far reaching effects including the disturbance of invertebrate communities and the disruption of ecosystem services including pollination, vegetation regeneration, and nutrient cycling.

Global environmental changes, especially land-use changes, have profound effects on both ecosystem functioning and biodiversity, having already altered many ecosystem services. These losses emphasize the need to preserve what remains; however when conservation programs are not sufficient, restoring areas that have been destroyed or disturbed can improve conservation efforts and mitigate damages. This work focuses on campos rupestres, Neotropical grasslands found at altitudes, which are part of the Cerrado (Brazilian savannas). They host a great biodiversity with a high level of endemism and, like other mountain ecosystems, provide valuable ecosystem services, such as water purification and recreational services. They have been and still are being impacted by human activities, such as civil engineering construction, quarrying or mining. The first objective of this thesis was to describe the reference ecosystem in order to aim for a clear restoration target and to monitor progress and success. We show that campos rupestres are composed of at least two distinct plant communities (i.e. sandy and stony grasslands), each having a specific composition and structure, hosting a great biodiversity. Several phenological patterns occur among the herbaceous communities: the majority of species flowers and fruits appear during the rainy season but other patterns can be observed. During our 2-year survey, some dominant species belonging to Poaceae, among others, were not observed reproducing, which implies limited chances to disperse on degraded areas. Campo rupestre vegetation is not resilient following a strong disturbance: several years after the disturbance, almost no native species are encountered on the degraded areas, soils are completely altered and seed bank recomposes only with non-target ruderal species. According to the filter model, a local community is a subset of the regional species pool determined by a set of dispersal, abiotic and biotic filters. Acting on the different filters to influence the plant community was the core of our restoration interventions. We then applied three in-situ restoration protocols (hay transfer, species translocation and turf translocation) to restore both kinds of grassland. Hay transfer does not allow the restoration of campo rupestre vegetation because of soil alteration and mainly because of poor seed quality. Indeed, germination studies show that, while some Xyridaceae and Velloziaceae have a high germinability, some dominant Poaceae, Cyperaceae or Asteraceae species have embryoless, unviable or dormant seeds, which makes seeding less efficient. There is no evidence that fire-related cues enhance germination in campos rupestres. Species translocation is successful for only one species, Paspalum erianthum; for the others, root damages probably impede survival. Finally, turf translocation is the most successful method, since numerous species are re-introduced on degraded areas. However due to the low resilience of pristine campos rupestres where turfs are taken from, turf translocation can only be considered in the case of habitat rescue, in circumstances when complete habitat destruction is otherwise unavoidable. Face to the difficulty to restore these peculiar grasslands, the protection and the conservation of campos rupestres must be made a high priority

The mechanisms underlying the positive relationship between species richness (diversity) and temporal variability in community biomass (stability) are not well understood. Here a model incorporating density dependence and environmental and demographic stochasticity is fit to experimental data from two European and two American experimental grassland sites. The parameterization of this model allows for the calculation of an approximation of community variability which explicitly separates two mechanisms: 1. asynchrony in environmental responses, and 2. overyielding. Analysis shows that this approximation accounts for much of the underlying variation and that both these mechanisms are important in stabilizing systems. Comparison of the estimated parameters highlights differences and similarities between datasets and suggests that this can be explained by species identity, experimental design and protocol, and geographical location. This thesis provides support for the view that different systems are stabilized by different mechanisms and this emphasizes the importance of examining a diversity of large, long-term ecological experiments.
Les mécanismes qui soutiennent la relation positive entre la richesse en espèces (biodiversité) et la variabilité temporelle de la biomasse de la communauté (la stabilité) ne sont pas bien compris. Ici un modèle qui intègre densité dépendance, stochasticité environnementale, et stochasticité démographique est ajusté aux données expérimentales de quatre sites expérimentaux: deux européens et deux américains. Le paramétrage de ce modèle permet le calcul d'une approximation de la variabilité de la communauté qui sépare explicitement deux mécanismes: 1. asynchronie dans les réponses a l'environnement, et 2. surproduction due a la diversité des espèces. L'analyse montre que cette approche explique une grande partie de la variation de la variabilité de la communauté et que ces deux mécanismes sont importants dans la stabilisation des systèmes écologiques. La comparaison des paramètres estimés révèle les différences et les simililarités entre les jeux de données et démontre l'importance des espèces clés dans la médiation des relations entre la stabilité et la diversité. Ce travail soutient la thèse qu'une diversité de facteurs influence les fluctuations écologiques et met l'accent sur l'importance des grands expériences écologiques à grand durée.