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The aim of this thesis was to investigate offsetting conventional nitrogen (N) inputs with more sustainable options in order to maintain or increase production. This was examined through four separate investigations, namely, 1) a retrospective analysis of the incorporation of the legume white clover (Trifolium repens L.; WC) into PRG swards within a high N input grazing dairy system (Chapter 4), 2) a systems experiment investigating PRG-only and PRG-WC swards at two levels of N fertiliser (150 and 250 kg N/ha; Chapter 5), 3) supplementing PRG diets with a rumen protected protein source compared to a rumen degradable protein source within a low CP concentrate supplement (Chapter 6) and 4) comparing herbage production of different N fertiliser types and rates (Chapter 7). Chapter 4 interrogated an existing database, comprised of results from a larger, overall systems experiment, that showed fluctuations in WC content in PRG swards within a high N input (250 kg N/ha, annually) grazing dairy system. In Chapter 5, a separate grazing experiment was established that compared both herbage and milk production of PRG-only and PRG-WC swards at 150 and 250 kg N/ha. Chapter 6 investigated the impact of supplementation of differing protein sources at low amounts on milk production and N use efficiency. Finally, Chapter 7 investigated N fertiliser type and rate on PRG herbage production in a rotational temperate grazing system through a comparison of calcium ammonium nitrate (CAN), urea + N-(n-butyl) thiophosphoric triamide (urea + NBPT) and urea at 150 and 250 kg N/ha per year. In summary, this thesis explored varying options within intensively grazed temperate dairy systems to offset and protect the N inputs while maintaining or perhaps increasing milk production.

The transmission of Mycobacterium bovis between and among cattle and badgers represents an area of research which continues to pose many questions in the pursuit to eradicate the disease from cattle herds within the UK and Ireland. Predominant queries remain over when and where both species become infected, how likely infection is to occur, and how can transmission events be minimised. This thesis aimed to assess 1) the number of indirect contacts between the species, 2) locations where indirect contacts can occur, 3) the behaviour of badgers in relation to cattle related pastures and 4) management of cattle at pasture in relation to bTB risks. Data was collected using three different methods; camera traps, GPS collars deployed on badgers and cattle grazing locations recorded by farmers. The results found that setts and latrines were focal points for indirect contact between badgers and cattle throughout the studies. Not only did camera traps find cattle investigating these locations but farmers were not actively avoiding the locations when designating grazing fields for cattle use. Since M. bovis can survive in the environment it is pertinent to ensure cattle cannot access these locations, ideally by avoiding the fields but if this is not possible then by erecting barricades i.e. fencing to prevent cattle access. Badgers avoided fields with cattle present, this was confirmed by both camera traps and collared badgers. Forage and rough pasture fields were preferred by badgers, and cattle grazing in these fields should be avoided to help reduce co-occurrence. Implementing changes to cattle management at grass could reduce contact between local herds therefore reducing transmission between herds. This study suggests that 18% of grazing days were spent adjacent to neighbouring herds, land fragments of farms overlapped with multiple other farms and animals in herds moved approximately 27.5km during the grazing season. Recommendations to reduce neighbour contacts include; avoid grazing boundary fields, double fencing if not possible, minimise the number of land fragments used by grazing cattle and moving cattle between spatially close fields. Recommendations are made that are low cost, low tech and could be achievable by farmers on most farms. The recommendations should be communicated to farmers to help raise awareness.

Palaeoecological studies have proven to make significant contributions to two large ongoing debates that include the influential power of climate and the impact of human land management on the vegetation patterns in certain areas in the UK and Northwest Europe. The need and importance for higher resolution vegetation reconstructions has long been recognised in the wider literature. The main focus of this research is to further understand the relationship between human behaviour, climate and land cover change on Exmoor, of which the upland areas are comparable with others found in Britain and Northwest Europe. High resolution records of pollen, NPP and charcoal data are presented, stemming from three upland sites on Exmoor: Great Buscombe, Spooners and Codsend Moors. Sequences are dated with the use of radiocarbon dates and recently identified tephra layers, enabling a better comparison between sequences from different sites on Exmoor. Additionally, a long-term climate reconstruction from a fourth site, The Chains, is presented and was produced through peat humification analysis. Vegetation reconstructions were produced through pollen analysis, whereas archives of past grazing intensities and fire histories were created with the use of NPP (non-pollen palynomorph) and charcoal data. Statistical analyses of pollen, NPP, charcoal and climate data was conducted in order to test the relative importance of grazing, climate and burning on identified changes in the vegetation compositions. Palaeoecological data from Exmoor shows a general trend of woodland clearance from the late Neolithic onwards, which was largely completed by the late Iron Age. This trend has been associated with an increase in the charcoal data and a coinciding decrease of pastoralism. Results further suggest that climatic changes did not necessarily directly affect the vegetation patterns on a larger, regional scale, but may have played a key role in societal changes. Finally, changes in vegetation patterns and land use on Exmoor did not occur simultaneously across all sites, resulting in a dynamic and heterogeneous landscape from the late Neolithic until the late Iron Age.

Parrotfish are a diverse and ubiquitous group found on coral reefs worldwide. They are categorised into three main feeding modes; the browsers, scrapers and excavators, which together perform a number of important functional roles on coral reefs. Scraper and excavator parrotfish are common on most Indo-Pacific coral reefs where their roles in bioerosion, sediment production, grazing pressure and sediment reworking have been shown to influence benthic community composition, reef growth potential and sediment supply to reef habitats and reef associated sedimentary landforms. However, despite the widely known importance of parrotfish on coral reefs, our understanding of how their roles in carbonate cycling vary among species and among whole parrotfish communities in different reef habitats remains limited. This thesis produces original contributions to knowledge in the areas of species specific bioerosion estimates for the central Indian Ocean, bottom-up controls of habitat type on parrotfish assemblages and how variations in parrotfish assemblages translate to contributions to carbonate cycling processes among different reef habitats. The study was carried out across eight habitats on an atoll-edge reef platform in the central Maldives, where it was found that parrotfish community composition was driven by reef structural complexity and substrate type. Parrotfish occurred in six of the eight habitats, comprising ~44% of the platform area. Among these habitats, overall grazing pressure, bioerosion rates, sediment reworking and sediment production varied markedly. These processes were also found to have different spatial patterns over the reef platform, showing that they are not necessarily tightly coupled. In addition, reef habitats can vary in their importance for both sediment supply, and the relative importance of reworked sediment. Parrotfish produced a wide range of sediment size fractions, from < 32 to 2000 μm and produced predominantly coral sands (>80%) between 125 and 1000 μm in diameter. This is comparable to the grain types found on local reef islands, and it is likely that the most significant supply of this material is from habitats on the atoll-edge side of the platform (which make up ~20% of the total platform area). Quantifying parrotfish functional roles and understanding the drivers behind these processes is important for informing future empirical and modelling studies, particularly as coral reefs undergo a time of dramatic environmental change.

Excessive ammonia (NH3) emission, originating largely from agriculture, can affect water, air and soil quality, and through these, endanger ecosystem and human health. Since NH3 emission is strongly dependent on temperature and also influenced by other meteorological variables, the question arises: how will NH3 emission alter in a changing climate? A way to address this question and predict the subsequent environmental consequences is to construct meteorology-driven models of NH3 emission from every agricultural source. Furthermore, NH3 emission is a highly localised and dynamic process. The focus of this thesis is NH3 emission from grazing. In the first stage a new process-based model for NH3 emission from a urine patch was developed. The GAG model (Generation of Ammonia from Grazing) is capable of simulating the TAN (total ammoniacal nitrogen) and the water content of the soil under a urine patch and also soil pH dynamics. In the second stage, GAG was applied to the scale of a grazed field, combining multiple simulations of the patch-scale model including both urine-affected and unaffected (“clean”) areas. The modelled NH3 fluxes were found to be in good agreement with the observations for both model types. The sensitivity of NH3 flux was assessed to various soil physical and chemical parameters for both the patch and the field scale models. It was found that ammonia volatilization from a urine patch could be influenced by the possible restart of urea hydrolysis after a rain event as well as carbon-dioxide emissions from the soil. Over the field scale, it was shown that the temporal evolution of the NH3 exchange flux was dominated by the NH3 emission from the patches within the field. The results also suggested that NH3 fluxes over the field in a given day could be considerably affected by the NH3 emission from urine patches deposited several days earlier. In the last stage of the work, a comprehensive sensitivity analysis was carried out with a special focus on temperature, for both versions of the GAG model. It was shown that due to the different governing dynamics over the patch and the field scale, the temperature-dependence of NH3 exchange is stronger over the field scale. It was also concluded that the temperature-dependence of NH3 exchange is stronger if the sinks of NH3 are stronger within the system. Finally, it was found, that Q10, a widely-used metric to express the relative increase of trace gas emissions over a range of 10 °C, is influenced by the length of the period of investigation and the initial value of the temperature range.

Tropical coral reefs are among the most diverse ecosystems of the world but facing increasing threats to their health. Over the last thirty years, many Caribbean coral reefs have undergone dramatic changes and experienced large losses in coral cover, due to direct and indirect anthropogenic disturbances. The results of which are reefs with low rugosity, changed trophic dynamics and low fish diversity. In recent times reefs have failed to recover from disturbances due to an increase in frequency and severity of disturbances and stresses. In the Caribbean on many coral reefs this has resulted in a shift towards macroalgal dominance by species of the phylum Phaeophyta. The processes and factors affecting the standing crop of macroalgae are many and complex. Two main hypotheses are identified in the literature as being the driving forces of algal dynamics: nutrient dynamics (availability, supply and uptake) and herbivory. However, many studies have been found to be inconclusive because of the complexity of the coral reef ecosystem, which makes it difficult if not impossible to control for all factors and processes influencing the standing crop of macroalgae such as light, water flow and sedimentation. The inherent characteristics of macroalgae, like morphology and life history, make them behave differently. Whilst herbivore characteristics, like size of mouth parts, feeding modes and preferences, will influence the amount of algal biomass removed. The spatial context (i.e. coral fore reef vs. back reef) will influence the effects of both bottom-up and top-down controls. Besides these inter-habitat differences, macroalgae within similar habitats but differing geographical locations may respond differently, for example, a forereef exposed to the open ocean or a forereef located in a sheltered bay. This thesis attempts to provide insight into the dynamics of two dominant brown macroalgae on Caribbean coral reefs, Dictyota spp. and Lobophora variegata. This aim was addressed by developing a model for the macroalga species Dictyota to model the various processes and factors on a coral forereef affecting percentage cover. Further, the patch dynamics of both Lobophora variegata and Dictyota were investigated to gain an insight into their dynamics under varying environmental conditions: the windward and leeward sides of an atoll. Finally, herbivory is identified as one of the key process affecting macroalgal cover. I investigated this process by deploying cages on both the windward and leeward side of the atoll to investigate the effects of grazing pressure under varying environmental conditions. A Bayesian Belief Network model was developed for Dictyota spp. to model the bottom-up and top-down processes on a coral forereef determining the percentage cover. The model was quantified using relationships identified in the scientific literature and from field data collected over a nine moth period in Belize. This is the first BBN model developed for brown macroalgae. The fully parameterized model identified areas of limited knowledge and because of its probabilistic nature it can explicitly communicate the uncertainties associated with the processes and interactions on standing crop. As such the model may be used as a framework for scientific research or monitoring programmes and it is expected that the model performance to predict macroalgal percentage cover will improve once new information becomes available. Size-based transition matrices were developed for both Dictyota spp. and Lobophora variegata to investigate the patch dynamics under varying environmental conditions: the windward and leeward sides of an atoll. The matrices reveal that standard measures of algal percent cover might provide a misleading insight into the underlying dynamics of the species. Modelling the patch dynamics with matrices provided insight into the temporal behaviour of macroalgae. This is an important process to understand because patch dynamics are determining competitive interactions with other coral reef benthic organisms. The outcome of competitive interactions will differ with macroalgal species. This study indicate that Dictyota spp. responded strongly to differing environmental conditions in that it has reduced growth rates and lower percent cover on the leeward side of the atoll, whilst Lobophora variegata showed far less sensitivity to environmental conditions. The patch dynamics of Dictyota spp. also showed a higher temporal variation than Lobophora variegata but only on the exposed forereef. A caging experiment was set up to investigate the response of both macroalgal species to different grazing pressure scenarios, under varying environmental conditions. Dictyota spp. had a significant response to environmental conditions in that a higher percentage cover was found on the exposed side of the atoll, whilst for Lobophora variegata the response was far less obvious. The less clear response of Lobophora variegata was very likely caused by competition of Dictyota with Lobophora due to the very high cover Dictyota obtained in the cages where all herbivores were excluded. The low grazing pressure treatments also showed an increase in cover of Dictyota, whilst for Lobophora, only a reduction in the rate of increase could be observed. The results indicate that on the leeward side of the atoll, fish grazing alone seems sufficient to control the standing crop of Dictyota and Lobophora variegata. Retrospective analysis of the experimental design showed that the limited size of the experimental set up could have confounded the results for Lobophora as well. In future experiments it is recommended to increase number replicates. Management of coral reef habitats is frequently constrained by a lack of funds and resources. The BBN Model once fully parameterized can provide a useful tool for coral reef management, because the model allows exploration of different reef scenario’s, which in turn can aid in prioritizing management strategies. Furthermore, the thesis provided an insight into the complexities of macroalgal dynamics. The responses of macroalgae to physiological factors and ecological processes are species specific and dependent on the location, and caution against generalizing on what controls the standing crop of macroalgae. Therefore it is argued that future investigations into algal ecology should clearly define the species, habitat and location. This can help to make informed management decisions.

The decline of many altricial species in temperate areas on land managed for agriculture is thought to be linked to changes in summer food availability, impacting on chick survival. This study specifically investigates the impacts of livestock grazing on the breeding performance of an insectivorous species, the meadow pipit (Anthus pratensis), through the assessment of chick diet. Using conventional methods, adults are found to feed chicks a wide range of prey taxa. The significance of this diversity is shown by improved chick growth, emphasising an important link between diet and chick survival. Changes in the diets fed to chicks, as measured by conventional dietary methods, were observed in association with different intensities of grazing management. High stocking densities and also no livestock grazing resulted in a reduced biomass of invertebrates being fed to chicks. Conventional dietary analysis methods have a number of biases associated with them. Examining diet using three methods produced significantly different diet descriptions for meadow pipit chicks. The concept of using dietary markers was examined, which is increasingly becoming popular in ecological dietary studies. Lipids, namely hydrocarbons have been successfully established as faecal dietary markers in the examination of herbivore diet compositions. A range of hydrocarbons were extracted, identified and quantified from both invertebrate prey and bird faeces indicating the potential for this technique to assess bird diets, also highlighting areas of focus for future research. Hydrocarbon analysis was successfully used to show dietary changes occurring as result of grazing managements; therefore, this approach shows great potential as an ecological tool for assessing ecosystem changes as a result of human activities.

Consistent individual differences (CIDs) in animal behavior can be measured in assays that target specific behaviors which are assumed to represent underlying stable traits. These are linked to various outcome measures, such as how animals use space and/or forage in natural environments. Consistent individual behavioral variation in beef cattle has been previously studied, however, traditional assays involve stressful contexts, subjective rating scales, and short-term assessments. CIDs measured in multidimensional behavior assays with extensively managed beef cattle have not yet been linked to grazing patterns by previous studies. The grazing patterns of beef cattle that forage on extensive rangeland landscapes have implications for the environmental sustainability of cattle production and conservation of rangeland ecosystems. The objectives of this dissertation were to measure CIDs in behavior in cattle using broad scope, yet practical, assays and investigate how these relate to relevant feeding behaviors (Chapter 1), identify consistent grazing patterns of cattle on rangeland (Chapter 2), and examine the relationship between CIDs measured in assays and grazing patterns (Chapter 3). I found that cattle showed consistency in behaviors observed across short-term and long-term time frames in a management context (handling cows through an open chute) without using physical restraint (Chapter 1). Behaviors measured in distinct locations of the assay loaded onto different principal components (e.g. time to traverse the concrete chute while isolated and time to traverse the hydraulic squeeze chute while isolated), which may indicate different mechanisms from which these behaviors arise. Less active and less excitable cows during the assay chose to feed from supplement rather than be in proximity to groupmates in a social-feed tradeoff task (Chapter 1). Individual cows were consistent in grazing patterns across two summers despite cattle having access to a new, high-elevation watering site during the second summer of grazing the same rangeland pasture (Chapter 2). This provides evidence that consistent individual differences in grazing are robust and persist between two years and despite a management tool (off-stream water) added to the rangeland environment, which is a commonly used method to achieve better distribution of cows. Cows that were using higher elevation and were further from water were also more variable in their elevation and distance from water, thus behavioral flexibility coincides with overall rangeland use patterns in cattle (Chapter 2). Ultimately, cattle that appeared more cautious and passive in the narrow cement chute while isolated were those that were grazing higher elevation areas, further from water, and closer to upland supplement sites (Chapter 3). This could signify that cows that have a reactive (also called a passive) response when coping with mildly stressful contexts (i.e. isolation and handling) also notice environmental fluctuations over the grazing season and respond by grazing wider and higher, less utilized areas of the pasture. These passive cows are thought to be using the rangeland more sustainably (or optimally) because they are not clumping near water resources or preferred grazing areas, but rather grazing vegetation that is more difficult to travel to and may otherwise go under-grazed. Altogether, temperature was the most influential animal or environmental factor on grazing patterns; cows conserved energy by not traveling as far or on high elevation and prioritized being closer to water and resting sites on hotter days or weeks (Chapter 2 and 3). Neither grazing patterns nor behaviors exhibited during the management context assay related to cows’ approach to a novel feeding opportunity (Chapters 1 and 3). This dissertation (a) informs the design and utilization of behavior assays for identifying CIDs in beef cattle (Chapter 1), (b) fills literature gaps in how management tools used to optimize cattle distribution alter grazing patterns of individual cows (Chapter 2), and (c) demonstrates the potential to select cattle that exhibit certain behaviors (i.e. more passive cows) to shape a herd with more desirable grazing patterns (i.e. use higher elevation areas further from water; Chapter 3).

In my thesis, I examined impacts of nesting and floral resources on ground-nesting bee assemblages at nine ranch sites with differing grazing histories. Because ecological disturbances can strongly affect the availability of foraging and nesting resources over time, I also examined the impacts of grazing history on nesting and floral resources for ground-nesting bees. I sampled bee assemblages, a comprehensive array of vegetation and soil measures, and floral abundance and richness. I used these data to determine (1) the importance of different nesting habitat resources and livestock grazing history for ground-nesting bees and (2) how livestock grazing history influenced the availability of nesting and floral resources. I found that sites with sandier soils had greater abundance and richness of ground-nesting bees, and sites with less compacted soils had greater bee abundance. Contrary to many other studies, the availability of bare ground was not important for ground-nesting bee abundance or richness. Grazing history did not affect any measures of nesting or floral habitat, and had negligible effects on ground-nesting bee abundance, richness, and community composition. My results suggest that the availability of sandier or less compacted soils may be limiting for ground-nesting bee abundance or richness, especially in areas with predominately clay soil types. In this context, the availability of such nesting resources may be more limiting than floral resource availability. More research is necessary to tease apart the effects of different nesting and floral resources for bees, and how different grassland management types affect bees through those resources. My findings highlight the importance of considering nesting habitat resources in bee conservation and restoration efforts.

Two experiments were conducted to determine the correlation of corn residue feed value and utilization on cow performance and potential grazing strategies. A qualitative observation of corn residue grazing by 13 cattle herds across Nebraska was conducted over two years. Based on producer reported grain yields and stocking rates, it was found that these producers were generally not as aggressive as the recommended 1.2 animal unit months (AUM) for each 6,280 kg/ha (100 U.S. bushels/acre) of harvested grain. They stocked 17 to 101% of the recommendation and on average used 63% of the carrying capacity. Across herds, average body condition score did not change throughout the grazing season, but a wide range in cow body condition score changes from -0.4 to + 0.6 was observed. On average, the utilization of husk was 71% compared to just 42% of residue as a whole. A corn hybrid experiment evaluated the effects of corn grain yield on resulting quantity and quality of corn residue. As corn grain yield increased, the amount of grain relative to whole plant biomass (harvest index) increased, indicating less total residue produced per kilogram of corn grain produced. Additionally, the quality of husk and leaf declined as grain yield increased. The average amount of digestible organic matter (DOM) from leaf plus husk was 3.6 kg/25.4 kg of grain (1 U.S. bushel) and ranged from 2.5 to 5.8 kg. Therefore, the concentration of nutrients in corn residue declined as grain yield increased, meaning higher yielding corn had lower quality residue. Impacts of this decline in diet quality on cow performance should be further evaluated. Advisor: Mary E. Drewnoski

Abstract: Defoliation is a globally ubiquitous driver of plant community structure and function. However, plant community responses to defoliation remain challenging to predict as they are highly context-dependent. Following defoliation, plant community diversity and production may increase, decrease, or display no change depending on climate, plant neighbors, and the disturbance’s timing, frequency, and location. In this thesis, I disentangle the role of these three core contingencies in mediating the plant community–defoliation relationship across a broad spectrum of scales in time and space. First, I test the assumption that defoliation instigates higher plant production and diversity when applied using high-intensity, short-duration holistic grazing management across the northern great plains. I find holistic grazing management supports fewer vascular plant species at both local and landscape scales despite no difference in plant community composition and variability. However, holistically managed ranches showed markedly higher plant community production than their regionally typical counterparts, with 20% higher aboveground biomass, 26% higher litter mass, and equivalent amounts of surface root biomass. Second, I examined how varying the proportion and patchiness of defoliation disturbances impacted community-wide competition and production using experimental mesocosms. I found that defoliation intensity strongly interacted with the proportion of the plant community disturbed to influence whole-community production and competition. Increased defoliation intensity negatively affected mesocosm production (aboveground, belowground, and total biomass) when all individuals were defoliated but positively affected production where half the mesocosm was defoliated. Finally, I used a meta-analysis of grazing studies across North America to examine how the consequences of grazing exclusion on plant community production and richness vary depending on the weather at the sampling time, climate, year, and study location. Study location and sampling time mediated the effects of grazing exclusion on plant community production and richness. Plant richness, not plant abundance, responded to grazing exclusion differently depending on mean annual precipitation, with less positive effects of exclusion found when precipitation was higher. Data collection within an unusually wet year detected less positive effects of grazing exclusion. Our results demonstrate that climate and weather drive the effects of grazing exclusion on plant communities and that these effects are growing more deleterious toward plant abundance over time. Overall, the results of this thesis promote a new understanding of how grazing management, plant-plant interactions, and study location in time and space modify the plant community–defoliation relationship.

Abstract: Grassland ecosystems cover more than 40% of the global land area and provide many ecological goods and services, therefore, it is important to sustain these terrestrial ecosystems. One of the ecological services they provide is their potential to act as a carbon (C) sink. However, northern temperate grasslands, which are arid/semi-arid in nature, are specifically vulnerable to climate change (e.g. drought) and natural as well as anthropogenic disturbances such as overgrazing. This study was conducted, at seven different locations across a climate gradient, to test the effects of drought (45% rainfall reduction using rainout shelters) and defoliation on different grassland soil components to understand how these disturbances affect C and nutrient cycling. Defoliation was applied by clipping experimental plots either once or twice a year at two variable heights (3 and 7 cm). A combination of five defoliation treatments was applied including control (no-defoliation). In the first study, I tested the effect of drought and defoliation on soil extracellular enzyme activity. Five enzymes were selected based on their role in C (β-glucosidase, β-cellobiosidase and β-xylosidase), N (N-acetyl-β-glucosaminidase) and P (Acid phosphatase) cycling. I found that the activity of all enzymes decreased with drought, except that β-xylosidase increased with drought conditions, suggesting a shift in biogeochemical processes of these soils under future drought. Furthermore, β-glucosidase activity was reduced under intermediate defoliation. In the second study, I tested the effects of drought and defoliation on greenhouse gas (CO2, N2O and CH4) emissions over two growing seasons (April to September in 2017 and 2018). I found that intermediate defoliation (i.e., defoliation once a year) reduced CO2 emissions as compared to heavy defoliation (i.e. defoliation twice a year). No treatment effects were observed on N2O and CH4 fluxes. Furthermore, I found that defoliation frequency, not timing, was the driving factor for CO2 emissions. Soil temperature and extracellular enzyme activity were the best predictors for greenhouse gas emission rates. Findings suggest that annual single-event defoliation could reduce CO2 emissions in future drought conditions in northern temperate grasslands. In the third study, I tested the effects of drought and defoliation on soil microbial communities in two contrasting grasslands (Kinsella vs Mattheis). I found that drought affected beta diversity at Kinsella (wetter site) where there was a significant effect of drought on beta diversity between as well as within groups (ambient vs drought). Soil bacterial communities were affected by drought; however, soil fungi showed resistant and/or even favored drought conditions. At Kinsella, xylanolytic bacteria (involved in breakdown of xylan) were increased under drought conditions. Overall, the findings of this thesis imply that drought effects were more consistent on enzymes, greenhouse gas emissions and soil microbial communities, while defoliation effects were limited and dependent upon drought treatment and local climate. Results from this thesis suggest that single annual defoliation (specifically in early season) have the potential to reduce CO2 emissions and increase C stocks in northern temperate grassland soils under future drought conditions.

Grazing by domestic livestock is one of the primary ways by which humans have modified landscapes. At low stocking rates livestock grazing can modify vegetation community composition, but at high stocking rates grazing can also reduce vegetation productivity and initiate soil erosion, leading to land degradation. The country of Iceland has undergone severe land degradation over the past 1100 years, with over half of the former vegetation cover being lost, and the remainder having depleted productivity. This work focuses upon the role that grazing by domestic livestock played in this degradation, and how the interactions between farm management, vegetation cover and climate affected grazing patterns in space and time. The aims of the research were achieved by constructing an environmental simulation model, called Búmodel, which allowed a cross-disciplinary approach that integrated landscape ecology, environmental archaeology and historical analysis. Búmodel was loosely coupled with GIS so that spatially based model inputs and outputs could be displayed and analysed in map form. The purpose of Búmodel was to predict spatial and temporal patterns of vegetation biomass production and utilisation (through grazing and hay-making) with a view to commenting on vegetation degradation in the pre-modern period (pre-1900 AD). The model was parameterised using contemporary and historical Icelandic agricultural data. Model validation was undertaken using sensitivity tests and comparison with data from an independent grazing experiment in the north of Iceland. Búmodel was then applied to two contrasting study areas: Vestur- Eyjafjallahreppur, a farming community on the south coast of Iceland, and Hofstaðir, a farm estate in the north east of the country, situated inland by Lake Mývatn. These applications demonstrated the importance of farm management in avoiding land degradation and in ameliorating the impact of climate. They also established the usefulness of Búmodel as a tool for the investigation of human and environmental interactions in Iceland.

This thesis addresses the effects of seasonality of grazing on vegetation dynamics. Background to the thesis is provided by the Hill Sheep and Native Woodland (HSNW) project, a system-scale experiment with the long-term aim of integrating upland sheep husbandry within native woodlands. Sheep husbandry in the HSNW project has involved a change from year-round grazing to off-wintering (grazing on upland areas from April to October only). The potential impact of this change on individual plants, plant communities and the landscape is evaluated. A cutting experiment was run to simulate herbivory in different seasons at the level of the individual plant. In grassland communities, where most species are wintergreen graminoids, interaction between species and seasons in response to cutting was minimal. In mire communities, where species with a range of life-forms and phenologies are present, there was considerable interaction between species and lifeform in response to cutting in different seasons. Non-wintergreen graminoid species recovered more rapidly than wintergreen graminoid species following cutting in spring, but the reverse occurred following cutting in autumn. Dwarf shrubs and forbs were slow to recover from cutting in all seasons in both mires and grasslands. The impacts of three grazing treatments in the HSNW project (unchanged year-round grazing, change to off-wintering, and change to zero grazing) on sward structure and species abundance were monitored. Sward height increased in the ungrazed treatment, but changes in species relative abundance were minimal in the short time-scale of the study. Literature suggests that change in plant species abundance in grazed systems is driven by herbivore selection preference for (or avoidance of) plant species and plant responses to grazing. Experts were interviewed to generate a set of seasonal data on herbivore selection preferences and plant responses, and levels of agreement between experts were assessed. Information was also collated on plant response to herbivory from the cutting experiment (above) and plant trait information from the literature. A qualitative model was developed to predict change in species abundance. It was used to: i) explore patterns of interaction between herbivore preferences and plant responses to grazing; ii) compare short-term predictions of change in abundance made using each of the information sources available; iii) make longer-term predictions using plant trait information. The short-term predictions were tested against the small changes in species abundance that had occurred in the HSNW project. Predictions made with the plant trait information were more accurate than those made with other information. A study of levels of browsing on regeneration was carried out in mature sheep-grazed birch woodlands. It was rare to find regeneration at sites grazed only by sheep, but tree regeneration did occur in the presence of sheep. Seasonal variation in browsing was found to be more related to the presence of cattle than to the presence of sheep. Finally, the findings are collated to make management recommendations for the HSNW project and other systems where seasonal grazing regimes could be beneficial.

The effects of three biotic factors (a new species, grazing, and plant-plant interactions) were considered on the spatial patterns and temporal changes observed on coastal methods and manipulative field experiments were conducted at several locations in the Solent region. The Solent has a rich resource of saltmarsh habitats, which are of high scientific value and are of national conservation importance. Palaeoecological saltmarshes. Palaeoecological investigations were carried out on three sites (Beaulieu, Hythe and Marchwood) to investigate the long term effects of the appearance of the hybrid grass Spartina anglica C.E. Hubbard (common cord grass). Historical records were researched to complement the data obtained from the analysis of sediment cores, to characterise the saltmarsh environments before the appearance of the new species. The evidence suggests that before S. anglica appeared in the region (in the second half of the nineteenth century), mudflat and pioneer marsh were much more significant features of the Solent coast than they are at present. Manipulative experiments were carried out at two locations on the Beaulieu Estuary. The effects of excluding large wild grazing animals (principally geese, rabbits and deer) on the plant communities were investigated by constructing experimental exclosures. These were monitored for three years, after which above ground biomass was harvested from randomly selected parts. Excluding grazing animals produced rapid structural changes in the plant canopy. Palatable species, which had previously been suppressed by grazing (e.g. Plantaeo maritima L.), proliferated rapidly. Some low-growing species, which had previously been conspicuous in the community (e.g. Armeria maritima (Mill.)), declined significantly, possibly due to shading by the increased growth of other species. The importance of competition and facilitation in setting the positions of two plant species within the zonation of a saltmarsh was investigated by transplanting them to different vertical zones. When the lower marsh grass S. anglica was transplanted to the upper marsh it was outcompeted by more competitive plant species. When the surrounding above ground vegetation was removed, it grew successfully. The upper marsh rush Juncus gerardii Loisel was transplanted to the lower marsh. This species could not tolerate the harsher physical conditions at a lower level, but that the presence of neighbouring plant growth increased its success.

Commercial sheep farming in the Highlands of Scotland has had a considerable influence on the landscape, ecology and economy of the region. The hill sheep industry developed in the Highlands in the mid 18th Century and remains the dominant form of agriculture in the hills and uplands. The hill grazings used by these sheep are dominated by unimproved semi-natural grassland, heather moorland and blanket bog. There is considerable concern from conservationists over the impact that sheep grazing is having on these semi-natural habitats, in particular the loss of heather moorland and the expansion of Nardus stricta-dominated grasslands. The government response to this has revolved around encouraging hill farmers to reduce sheep numbers (i.e. extensify). The semi-natural hill grasslands are of considerable economic importance to the sheep industry. Nardus stricta and Juncus squarrosus dominate a large proportion of these grasslands. The production and grazing utilisation of these semi-natural hill grasslands, and their response to extensification are therefore of considerable interest. This study investigated the effect that changes in grazing management had on species composition, vegetation structure, above-ground biomass, production and utilisation of a range of hill grassland and mire communities. The data collected from the study was then used to test and evaluate the vegetation component of the Hill Grazing Management Model (HGMM). The HGMM is a computer model designed to assist grazing management decision-making on British hill farms. The HGMM has a number of weaknesses, the main one being the limited range of vegetation types. The model does not include communities dominated by Juncus squarrosus, and although it does include Nardus stricta grassland it is only considered in terms of the Festuca - Agrostis growing between the Nardus stricta tussocks. One of the main aims of this study was to modify the HGMM to improve its predictive ability for sites with high proportions of Nardus stricta and Juncus squarrosus dominated grassland, using data collected from the study site. The study was carried out at a system scale level, using three large enclosures of approximately 40 hectares each. Two enclosures were grazed by sheep at mean annual stocking rates of 0.074 LU ha-1 and 0.051 LU ha-1, and the third enclosure was grazed by sheep and summer grazing cattle at a mean annual stocking rate of 0.096 LU ha-1. A quadrat survey and a vegetation mapping exercise were carried out to provide detailed information on the floristic composition of the vegetation community types, their areas, and spatial and altitudinal distributions. A detailed vegetation map was produced using a total survey station and a geographic information system. The study site consisted of a complex mosaic of twenty-two NVC vegetation types. Communities dominated by Nardus stricta covered over half the study area. Permanent nested quadrats and monthly sward surface height measurements were used to monitor changes in the composition and structure of the vegetation under the different grazing treatments. Few changes in species composition or the abundance of dominant species were observed, and none of the monitored vegetation types changed their NVC type. A number of ruderal and grazing tolerant species increased in frequency within the sheep and cattle grazed enclosure, as did the area of bare ground. The sward was also significantly shorter in the sheep and cattle grazed enclosure. Monthly above-ground biomass values of four vegetation types were estimated by harvesting strips of vegetation, sub-sampling, sorting, drying and weighing. Biomass varied significantly through the year. Mean summer biomass values varied from year to year. The biomass of both the Nardus stricta grassland and Juncus acutiflorus mire were significantly lower in the enclosure with the sheep and summer grazing cattle. The work presented in this thesis indicates that in the short term, extensification has very little impact on the species composition of hill grasslands and only minor effects on the structure and biomass of these grasslands. Entering into short-term management agreements to reduce sheep numbers is unlikely to result in any major environmental benefits if Nardus stricta and Juncus squarrosus dominate the hill vegetation.

The establishment of native woodland in the moorland areas of upland Britain is increasing. However, there is no clear basis on which to predict either the effect of this on the ecology of the mountain hare, or the effect of mountain hare on woodland establishment. This study investigates the feeding ecology of the mountain hare, a primarily moorland inhabitant in upland Britain, in an upland landscape containing a newly established native woodland and also the potential impact that they may have on regeneration of native woodland species (Pinus sylvestris, Betula pubescens and B. pendula). The mean home range size, determined by radio-tracking, of male mountain hares was 12.1 ha and females 8.9 ha. The native woodland habitat was not preferentially selected by mountain hares in summer or winter. Faecal n-alkane and long-chain fatty alcohol analysis revealed that P. sylvestris and B. pubescens were minor components of the diet in all seasons. The diet of both male and female hares was dominated by Calluna vulgaris in winter and by grasses, sedges and rushes in summer. Annual measurements of browsing by mountain hares on P. sylvestris and B. pendula saplings at eight sites throughout Scotland, showed that on average only 5.8 % of trees sustained browsing each year. Relative hare abundance, tree density, tree species and ground vegetation height did not predict the extent of browsing damage by mountain hares. In contrast, a field-based planting experiment involving nursery grown B. pubescens saplings, had higher local hare densities and revealed that mountain hares do browse saplings extensively and that season, tree density and ground vegetation height are important in determining the extent of browsing. Seasonal habitat utilisation of the experimental plots by mountain hares fluctuated in relation to the frequency of browsing. In general, the results showed that moderate densities of mountain hares are unlikely to inhibit regeneration of native woodlands However, the likelihood of damage will increase if trees occur at high densities and if local hare density is high.

In Scotland, bilberry is well known as a member of the dwarf shrub community on moorlands, which provide valuable habitats for wildlife. Recently it has been envisaged that bilberry populations could play an important role in improving the dwarf shrub vegetation in degraded moorland areas. This study was therefore undertaken to investigate the above-ground growth dynamics of bilberry with emphasis on responses to grazing by sheep and seedling establishment. The leaf production of bilberry was increased by higher nitrogen availability. High nitrogen supply also led to greater activation of dormant buds. Abortion of buds was less when nitrogen was continuously supplied. The reproductive capacity of bilberry was shown to be decreased by herbage removal. In contrast flowering was increased following supply of high nitrogen in glasshouse conditions. Almost all the flowers developed into fruits in the field, but a very low production of fruits was reported from bilberry plants that were grown in the glasshouse. Results of a series of laboratory experiments on seed production, germination, seed storage and evaluation of a moorland seed bank confirmed that the scanty seedling recruitment of bilberry was due to the limited production of 'germinable' seeds in berries and risks imposed by the environment after dispersal particularly when seeds are in the litter layer and/or soil. This could suggest that limited picking of bilberry fruits would not have a detrimental effect on establishment of bilberry populations in moorlands. Therefore, areas could be identified which were suitable for public access and berry exploitation in Scotland. The berry production was estimated approximately to be about 3220-9660 tones per year in this zone.

Increased deposition of nitrogenous compounds from the atmosphere may lead to the competitive dominance of aggressive grass species and reductions in species richness. This thesis aims to investigate the effects of atmospheric deposition of ammonia on species-rich limestone grasslands in the Cotswolds, and the role that management may have in modifying these effects. A field survey investigated species composition and quantified environmental variables including atmospheric ammonia concentration. Species richness and diversity were greatest on the more heavily grazed sites on deeper soils, but these diverse grasslands were composed of a high proportion of nitrophilic, competitive and ruderal species. No relationships between atmospheric ammonia and species composition were detected. The effects of grazmg and nitrogen on species composition were investigated by transferring turves between sites with contrasting atmospheric ammonia concentrations. Although grazed plots at the high ammonia site were of slightly higher diversity than grazed plots at the low ammonia site, these differences were reversed in fenced plots. In ungrazed plots, the development of a grass dominated, species-poor community was less pronounced at the low ammonia site, although the higher level of nitrophilic/competitive species here suggested that soil depth and soil phosphorous may also be important. A controlled greenhouse experiment investigated the effect of nitrogen addition and cutting on the competition between Brachypodium pinnatum and Bromopsis erecta. Above ground growth of both species was limited by nitrogen, although growth of B. erecta appeared to be limited by another resource at high densities. There was significant niche overlap between the two species, though cutting of high density pots reduced this niche overlap. The two grasses were equally matched in competitive ability, and neither treatment had any clear effect on the outcome of competition. The tillering response to cutting was greater in B. pinnatum than in B. erecta, although nitrogen addition increased tiller production by B. erecta. The effects of nitrogen addition and cutting treatments on nine grassland species was investigated in a greenhouse experiment. Nitrogen addition had no significant effects, but cutting reduced the above ground biomass of B. erecta and B. pinnatum and increased the above ground biomass and size of most of the other species. It is concluded that atmospheric ammonia deposition appears relatively unimportant in determining the species composition of species rich grasslands. However, experimental addition of nitrogen may increase grass growth, and grass dominance in the field can lead to reductions in species richness. In grazed grasslands, grasses may become more grazing resistant under conditions of enhanced nitrogen availability. However, phosphorous may be an important factor modifying the effects of enhanced nitrogen deposition.

This study describes and analyses cattle management in Tlokweng Sub District. Two methods were used. The two are households' interviews and a system dynamics STELLA model called the Rain Land Cattle model, which was adapted from the 1990 Braat and Opschoor model. Ninety households, 61% of the 1991 households in the study area, were interviewed. All the households had arable fields and fifty nine percent had cattle. The Rain Land Cattle model uses 52 parameters to predict several cattle management factors, which include rainfall, stocking rate, total grazing area and livestock water availability. The model explored the use of parameters to relate water availability to grazing area and show the seasonality of the water source. Sixty two percent of the household had access to an ideal livestock water source. Cattle graze from the 5000 hectares of arable area for four months after harvesting. This seasonal grazing, optimises the uses of the grazing resource in the small sub - district. The model simulated a S and 20 percent permanent grazing land loss. Such a grazing land loss, increased the stocking rate, decreased the carrying capacity and cast doubt on sustainable cattle production. The model shows that the stocking rate is chronically greater than the carrying capacity. Most households acknowledged that there was land pressure due to the loss of grazing land. A drier climate scenario will lead to a loss of seasonal grazing, reduced livestock water, which will increase cattle emigration and cause cattle management problems. The model is exploratory; it needs to be validated. It is easily understood, adaptable to other communal areas, and identifies the most influential factors in cattle management. The livestock water parameters functioned reliably in the model. Based on the understanding of the cattle management derived from this study, more fenced grazing land is unlikely to improve the cattle management in the area.

A backgrounding experiment (Exp 1) was conducted over two years to determine the interactions of winter rate of gain at a high gain (HIGH) of 0.91 kg and low gain (LOW) 0.45 kg, and implant strategy in the winter and summer phases and subsequent effects in the finishing phases. The first factorial was a 2C2C2 with factor one being high or low gain during the winter period, factor two implant or no implant during the winter, and factor three implant or no implant during the summer phase. The second factorial was also a 2C2C2 utilizing pen-fed steers to achieve similar ADG as the HIGH and LOW steers grazing corn residue. The first factor is a rate of gain at either HIGH or LOW. The second factor was implant strategy in the summer phase receiving an implant or no implant. Steers were penned in experimental units during the summer phase and fed a forage-based diet. In the finishing phase, all steers were placed on a common finishing program. In the winter phase, HIGH and LOW steers gained 0.95 and 0.53 kg/d (P < 0.01). Steers on the HIGH treatment housed on corn residue had greater ADG than those housed in pens, 0.95 and 0.88 kg/d respectively. In the summer, LOW steers gained 0.95 kg/d vs. 0.84 kg/d for HIGH steers (P < 0.01). At the conclusion of finishing, HIGH resulted in 45 kg more final BW than LOW steers (P < 0.01) while the Rev-IS implant during the summer phase resulted in 38 kg of additional final BW over non-implanted steers (P < 0.01). Supplementing at a high rate of gain during the winter backgrounding phase and implanting in the winter and summer results in the greatest total system gain and HCW. A grazing experiment (Exp 2) was conducted to evaluate the performance of steers grazing smooth bromegrass pastures supplemented dried distillers grains plus solubles (DDGS) either daily or three times per week. Treatments consisted of 1) steers supplemented DDGS daily 2) steers supplemented DDGS three times a week and 3) steers that received no supplementation (control). The control calves gained 0.85 kg/d. The supplemented treatments significantly increased (P < 0.01) ADG compared to the control, with daily supplementation gaining 1.25 kg/d and 3x gaining 1.11 kg/d. Ending BW and ADG was decreased (P < 0.01) with 3x a week compared to daily supplementation. For steers grazing smooth bromegrass pastures, daily supplementation of DDGS resulted in greater gains and ending BW when compared to three times a week supplementation, which were both greater than not supplementing. Advisor: James MacDonald

Pasture-based farming systems, as in New Zealand, are susceptible to changes in the climate through feed supply variability. Future climate change will likely alter pasture growth patterns, posing opportunities and risks that farmers will have to respond to and adapt to remain profitable. Due to the heterogeneous nature of farm systems in New Zealand, adaptation strategies must be evaluated on a farm-by-farm basis. The main objectives of this research were to use a case-study methodology to evaluate the impacts of climate change on a dairy farm system, and to investigate a range of farm management strategies aimed to maintain productivity and profitability. The study was based on the Northland Agricultural Research Farm (NARF; 35⁰56’39” S 173⁰50’34”E), using performance and farm management data over three production seasons to set up a baseline farm. Whole farm systems modelling was used to simulate climate change effects on the baseline farm in the middle and end of the 21st century. Two dynamically downscaled climate change scenarios for the baseline farm were provided by the National Institute of Water and Atmospheric Research (NIWA). These were used in the mechanistic model, DairyMod, to simulate the effects of climate change on the pasture growth rates of the baseline farm in the middle and end of the century under two warming pathways. These growth rates were used in the whole-farm systems model, Farmax, to simulate the feasibility of the farm in the middle and end of the century with altered pasture supply as impacted by climate change projections. Tactical system changes were used to match the herd’s energy demand with the altered pasture supply curves in order to re-optimise the farm system impacted by climate change. The findings of this research identified that with the use of systems changes, farms in the Northland region of New Zealand may reduce negative impacts on production and profit associated with climate change. A second round of modelling work was completed using the strategic adaptation strategy of utilising alternative pasture species that may be better suited to the changing climate. Differences in the morphological and physiological characteristics of the baseline and adapted pasture resulted in different pasture supply curves impacted by climate change. These required more extreme system changes compared with the baseline pasture. However, with the use of system changes, production and profitability were maintained or increased compared with the baseline farm. Overall, this study showed that with the use of farm system changes farmers may be able to capitalise on the opportunities associated with climate change to offset the risks.

Evaluation of pasture biomass measurements aids producers in knowing the availability of cool season grass in pasture for cattle grazing. The objective of this study was to compare satellite technology with the rising plate meter and forage biomass clippings as a method of pasture monitoring in the Upper Midwest of the USA. The study was conducted at the University of Minnesota West Central Research and Outreach Center, Morris, MN grazing dairy from May 2021 to October 2021 and May 2022 to September 2022. The pasture system was composed of cool-season perennials and included mixtures of meadow bromegrass (Bromus riparius Rehmann), meadow fescue (Schedonorus pratensis (Huds.) P. Beauv.), orchardgrass (Dactylis glomerata L.), alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and white clover (T. repens L.), and intermediate wheatgrass (Thinopyrum intermedium). Grazing height and forage availability were measured weekly in 9 pastures with a Jenquip pasture plate meter (Jenquip, Feilding, New Zealand). Pastures ranged in size from 2.55 ha to 9.7 ha. Satellite images were from Planet Labs PBC (San Francisco, CA) and average normalized difference vegetation index (NDVI) values were calculated weekly for the area inside each pasture. Pearson correlations were from PROC CORR of SAS 9.4 and determined associations of forage biomass from the plate meter and satellite imagery. Across the summer grazing season, mean forage biomass was 3,267 kg DM/ha (range was 2,864 to 3,622 kg DM/ha) from the plate meter and 2,325 kg DM/ha (range was 985 to 3,321 kg DM/ha) from NDVI satellite images. The correlations for specific pastures of the rising plate meter and the satellite image NDVI ranged from 0.074 to 0.91 and the average correlation was 0.58. Correlations were greater with greater forage availability in the pastures. Alternative methods to calculate the biomass of pastures may provide more advantages for farmers to determine the grazing management of pastures.

Tropical savannas support globally important biological diversity and provide a variety of cultural and economic ecosystem-services to humans. As mosaic landscapes, they are characterized by the coexistence of woody and grassy habitats which are strongly regulated by abiotic gradients (e.g., soils, climate) and local disturbance regimes (e.g., fire, flooding and grazing). Consequentially, savannas are inherently dynamic over a variety of scales and provide an array of temporal and spatial ecological niches for wildlife. However, tropical savannas and their ecological functions have been widely degraded by intensifying human land-use and are threatened by impending climate change. Unfortunately, our scientific understanding of savanna ecology is currently limited, impeding development of appropriate conservation approaches. This is especially true of Neotropical systems. This dissertation provides new research, carried out within the Beni, a seasonally flooded Neotropical savanna in Bolivia, that aims to address critical knowledge gaps in savanna ecology. This research will contribute to developing sustainable land management and restoration initiatives to secure and protect savanna ecosystems for people and wildlife.The overarching aim was to understand how ecological (flooding) and agricultural (managed fire and cattle grazing) disturbance influences habitats and wildlife in Beni. To achieve this, three specific objectives were identified: 1) understand how restoration, through cessation of long-term cattle grazing impacts (i) regeneration, (ii) understory structure and composition, and (iii) abundance and diversity of large mammals and nocturnal birds, within the regions’ naturally patchy gallery forests; 2) examine how compounded disturbance from flooding and fire shapes the distribution of woody plants and habitats across a savanna-grassland mosaic; and 3) determine functional responses of avian biodiversity to livestock removal across a savanna-grassland ecotone.First, comparing grazed and restored gallery forests, I assessed the abundance and composition of tree functional types at different life stages (seedlings, saplings and trees), with focus on Attalea princeps (motacú) a keystone palm species that shapes gallery forest structure, microclimate and ecology in Beni. Additionally, I surveyed habitat structure and composition in the shrub and ground-layer and monitored occurrence and encounter rates of large mammals and nocturnal birds along dusk and evening transects. Livestock grazing resulted in lower recruitment of motacú palms in Beni’s gallery forests. Principal components analysis showed that grazed forests also had simpler, more open shrub-layers and altered ground-layer structure and composition including increased bare ground. Mammal species richness was greater on the restored site, and there were more declining, globally threatened and site-unique species. Species richness was similar for nocturnal birds in both forests, but nearly all species tended to be encountered more frequently on the restored site. Results suggest cattle negatively impact forest regeneration and alter understory structure and composition with consequences for the diversity and abundance of wildlife. However, the alleviation of grazing can promote understory regeneration over relatively short time scales (~10 years) with positive benefits for wildlife.For objective two, I deployed ground-based flooding loggers and completed assessments of woody vegetation at forty-eight plots split evenly across four savanna-grassland habitats. Fifteen-year fire histories were quantified for each plot via fire-scar mapping using remote sensing data from Landsat 7 and 8 missions. Finally, I tested how flooding and fire histories influenced tree abundance using a hurdle model approach. Results demonstrated there is significant landscape-scale variation in environmental gradients and fire histories across habitats in Beni, resulting in variable woody plant communities. Compared to woodier formations, open grassland habitats experience longer flooding and more frequent fires. Congruent with increases in flooding and fires, the abundance of broadleaf woody plants declines between closed and open habitats. At the same time fire-adapted corky-barked broadleaved species become dominant while palms become sparse. Ultimately, the abundance of woody plants, in nearly all life stages, is shaped by compounded disturbances. Fire may be more limiting than flooding for broadleaf trees. Given the contribution of fire and flooding regimes to ecosystem structure and function, alterations to these cycles, (e.g., driven by climatic or land-use change), may have considerable consequences for the future sustainability of savanna-grassland mosaics. For objective three, annual avian point counts were completed over three years at 48 plots distributed evenly across four savanna-grassland habitats. These were equally split over two sites with different management histories, facilitating a space-for-time experimental approach with one site having livestock removed for 0, 1 and 2 years during surveys, the other 8, 9 and 10 years. Vegetation surveys were completed in tandem to track shifts in understory structure and composition, canopy assessments were made in the final year. The breeding and resource-acquisition traits of 162 bird species were classified and used to track shifts in key metrics of functional diversity (functional richness, functional evenness and functional dispersion) and community composition over time. The functional response of bird communities to livestock removal varied across habitats. In woody grasslands, functional richness increased, while functional evenness and variability remained stable. In tandem, habitat-dependent shifts in avian functional composition occurred relating to both resource-acquisition traits, and nesting and breeding traits. Notably, the abundance of more specialized resource-acquisition traits increased, while the occurrence of social breeding strategies declined. Conversely, in open habitats functional richness did not change following livestock removal, but functional evenness and variability declined. This resulted in grassland bird communities becoming more similar and was associated with homogenization of habitat structure. Results suggest that livestock removal positively benefits ecosystem function in woody habitats, at least in the short term. However, continued monitoring is needed to determine if effects remain positive. In contrast, disturbance may be necessary to promote the spatial and temporal heterogeneity in habitats that maintains functionally diverse grassland bird communities. Overall, my research demonstrates that livestock grazing, and frequent managed fire can have negative consequences for habitats and associated wildlife across the forest-grassland ecotone. This includes inhibiting the regeneration of forest understories, eroding savanna-grassland ecotones and degrading ecological function in avian communities associated with woody grasslands. Nonetheless, habitat regeneration and ecological functions can show signs of positive recovery over relatively short timescales. My research also shows that ecological disturbance may be critical to retaining diversity of avian function in open habitats. Thus, in both protected and working landscapes, disturbance management, for example patch burning, rotational grazing or their combination via pyric herbivory schemes could help to retain avian functional integrity in open grassland formations. In contrast, longer-term protection may be needed to support regeneration of forested habitats and woody savannas. However, fire will likely be required to maintain woody grassland structure and associated bird communities here in the long term.

Abstract: Climate models project a greater likelihood of increases in precipitation variability and droughts over the Great Plains of North America. Drought’s interactions with other co-occurring factors, such as grazing, can lead to substantial and long-lasting changes to ecosystem goods and services. In this thesis, I examine variations in precipitation and defoliation to better understand how their interactive effects shape ecosystem structure and function. First, I test the effects of grazing on ecosystem sensitivity to precipitation using spatially extensive long-term records of aboveground net plant productivity (ANPP) and precipitation. I found that grazing increased ANPP sensitivity to interannual variability in precipitation, especially at arid grasslands, suggesting that the explanatory power of the precipitation-ANPP relationship may not hold for ecosystems subjected to two or more global change drivers. Second, I examine the commonly assumed but little tested hypothesis – that drought impacts are progressive through time. I do so using a factorial experiment crossing drought and defoliation that I conducted at seven northern temperate grasslands over four years. I found that multi-year drought led to greater changes to community composition than productivity, and effects did not compound through time. Shifts in species composition were driven by variation in the abundance of dominant species, which also likely resulted in stability in ANPP under drought. Third, I examine the sensitivity of both shoot and root biomass to the combined effects of drought and defoliation. This topic is important because root responses are often overlooked in ecosystem models. I found that ANPP increased under drought relative to the ambient treatment, and the combined effects of drought and defoliation reduced ANPP but had no impacts on root biomass. Moreover, using minirhizotrons, I further examine root length dynamics in response to drought and defoliation at two of my seven field sites. I found root length dynamics were affected by every factor manipulated or measured in this thesis. In general, I found decreases in length, production, and lifespan of roots with drought in the shallow soil depth in the absence of defoliation. Notably, I found that the two sites exhibited general convergence in many aspects of their root length dynamics when exposed to both drought and defoliation, but when differences existed, they occurred under the ambient condition or at the deep soil depth. Further, the mortality and lifespan of roots were the aspects of root length dynamics that caused the observed shifts in total root length resulting from drought and variation in defoliation. In sum, this thesis demonstrates that northern temperate grasslands are highly resistant to a reduction in water availability via stability among dominant species or root responses, particularly root length dynamics, but defoliation, regardless of what regime, makes these systems sensitive to drought. Further, my results emphasize that the combined effects of global change drivers on plant root and shoot responses must be included in ecosystem models and will more accurately project ecosystem sensitivity to future variable weather.

Horses require daily access to forage in order to support their gastrointestinal tract function as well as natural grazing behaviors. Well-managed pasture provides horses with a consistent forage source and diminishes health risks such as colic, ulcers and stereotypies. However, equine grazing behaviors are more intense than other livestock and may be detrimental to plant and soil health. A grazing management technique specifically for horses is necessary to prevent both health and environmental issues. The following dissertation explores both the movement of required maintenance elements, such as feed, shelter, and water, as well as the manipulation of feeding frequency and mechanism to deliberately distribute equine activities within an equine pasture environment. Both considerations were evaluated via Global Positioning System units to determine location within respect to feed, shelter and water and scan-sampling to categorize grazing and non-grazing behaviors. It was determined that frequent movement of the feeding element may also distribute horse activities accordingly and become an efficient pasture management technique. Feeding frequency and mechanism was found to also distribute equine location with the most influential component being manual, twice daily feeding of a concentrated hay balancer.

There is a recognised need to establish more permanent indigenous forest throughout the world to mitigate climate change and enhance declining biodiversity. In New Zealand, the Climate Change Commission He Pou a Rangi has recommended the establishment of 300,000 hectares of new indigenous forest by 2035, with a focus on areas of hill country with marginal productivity for agriculture. A significant barrier to the achievement of this goal is the cost and logistical difficulties of restoration planting and direct seeding in hill country landscapes. Reliance on natural regeneration has the potential to be a more practical and economically viable option, particularly where large areas are involved. However, the rate of natural regeneration and key factors enabling it within pastoral hill country landscapes are not well understood. Based on aerial imagery, object-based image classification was used to detect changes in woody vegetation over a 16-year period on Oashore Station, a 540ha hill country property on Banks Peninsula, Canterbury. The focus was on identifying areas of the property that had changed from grassland to woody shrubland as the first stage in a successional process of natural regeneration from pasture to indigenous forest. Random forest machine learning and logistic regression were then used to evaluate the influence of different variables on the observed natural regeneration, including the impact of environmental factors and grazing regimes. The results for this study indicate that only 3.3% of Oashore Station experienced observed natural regeneration of woody vegetation in pasture between 2003 and 2019. The key factor influencing natural regeneration was the proximity of existing woody vegetation, with areas within 2m of existing woody vegetation being significantly more likely to experience natural regeneration. Cattle grazing was also found to have a significant negative impact on regeneration of woody vegetation, with regeneration most likely to occur in areas that had been free of cattle grazing for at least 10 years. Grazing by sheep and other environmental factors were not found to have a significant impact on natural regeneration. These findings have implications for hill country farmers considering natural regeneration on pastoral land with similar conditions and can help to identify locations where regeneration is most likely to occur. Areas with a higher proportion of existing woody vegetation should be prioritised for natural regeneration, with cattle grazing generally excluded from such areas. However, even in favourable conditions, the establishment of indigenous forest through natural regeneration is likely to be a slow, incremental process. This should be recognised in financial incentive schemes such as the Emissions Trading Scheme and has implications for the achievement of broader goals seeking to increase the amount of permanent indigenous forest on marginal hill country. If significantly faster rates of natural regeneration are desired, additional strategic interventions and support may be necessary.

I evaluated the relationship between saliva urea N (SUN) and plasma urea N (PUN) in red deer calves (n = 23) over five months, with the objective of creating an easy tool to quickly evaluate circulating urea nitrogen concentrations. The experimental design was a 2x2 factorial arrangement different seasonality phenotype (High and Low) and two different forage based diets, a medium-quality diverse treatment (Diverse) or a low-quality perennial ryegrass-white clover treatment (PRG) offered ad libitum. Blood and saliva samples for determination of PUN and SUN were evaluated monthly at civil dawn between April and September of 2022. A moderately strong relationship between PUN and SUN was identified by simple linear regression (R2 = 0.65, P < 0.001). The interaction between diet and date of sampling had a significant effect on the relationship between SUN and PUN (P < 0.001). This interaction is likely explained by the seasonal variation of crude protein (CP) content of the diet. The use of a mixed model procedure improved the model fit increasing the adjust R2 by 0.12 and reducing the root mean square error by 0.341. There was no effect of seasonality on prediction estimates of PUN from SUN although a tendency for sex by seasonality interaction was observed (P = 0.09). Therefore, evaluation of the diet and date of sampling can be used to improve reliability of the prediction estimates of PUN from SUN in red deer calves. Further investigation into the effects of significant factors on this relationship is required to improve the reliability of the model, before SUN can be used to predict PUN.

Agricultural businesses deal with uncertainty of all kinds. Uncertainty arising from variability in resources, markets, human factors, and regulatory policy can be sources of significant risks. Acquiring or building flexibility in an operation is one of the ways suggested to manage risk and uncertainty—reducing the impact of negative outcomes and increasing the benefit of positive outcomes. Although flexibility has been repeatedly encouraged for businesses, the definition of flexibility and its value remains ambiguous after more than 80 years of research. Flexibility is often described as a multi-dimensional ability to effectively deal with change in the business operating environment. Flexibility can also be described as an ability to switch to alternative means that allow the same objectives to be reached. Thus, maintaining flexibility requires active and ongoing management to retain its effectiveness for mitigating risk. The goal of the first chapter is to present a compilation of literature discussing flexibility in general in an attempt to define, measure, and value flexibility in isolation. In the second chapter, flexibility in agricultural systems will be explored as a risk management strategy and, through a series of applied examples, described both in isolation and together with other risk management strategies. The emphasis will be placed on agricultural scenarios, but non-agricultural cases will be visited as well. In the third chapter, the theory of flexibility will be illustrated in depth through a natural resource management example. Building on the framework of real options, different approaches for cross fencing a pasture for grazing will be used to identify the value of flexibility to alter land use. Advisor: Jay Parsons

Fire and grazing are primary sources of natural disturbance in grasslands and savannas worldwide, but they are also shaped by human impacts and decision-making. Appropriate management is therefore an essential goal for biodiversity conservation in disturbance-dependent landscapes. The butterflies which inhabit these ecosystems are reliant on the disturbances necessary for grassland and savanna persistence. Regular fire, herbivory, and drought shape and maintain these ecosystems, keeping woody plants from dominating. How, then, do butterflies persist and respond to disturbance in their chosen habitats? What management regimes are required in human-altered landscapes to conserve grassland and savanna butterfly biodiversity? I examine butterfly responses to management of disturbance-dependent ecosystems in North American and Australian using both taxonomic and functional trait lenses. In Chapter 1, I assess the impacts of current fire and grazing management regimes on butterfly communities in Minnesota tallgrass prairie and compare butterfly and bee responses to management. In Chapter 2, I assess the impacts of these same fire and grazing regimes on monarch butterflies (Danaus plexippus) and their milkweed host plants in Minnesota tallgrass prairie. In Chapter 3, I examine butterfly and butterfly resource responses to fire regimes in Australian tropical savanna, and in Chapter 4, I demonstrate the utility of trait-based ecology to explain global and mechanistic patterns in butterfly responses to fire by presenting and comparing butterfly traits associated with fire regimes in U. S. temperate prairie and Australian tropical savanna. I present findings that butterfly and bee abundances in tallgrass prairie are significantly negatively correlated. Butterfly abundance, but not species richness, is nearly twice as high at tallgrass prairie sites managed with fire compared to grazing, and prairie-associated grass-feeding butterflies are more abundant at sites with higher plant species richness. I find that monarch butterflies are also more abundant at tallgrass prairie sites managed with fire than with grazing, and that this association is not related to milkweed or forb frequencies, which are similar between burned and grazed prairies. In Australian tropical savanna, I find that recent, early dry season burning promotes butterfly diversity and abundance by increasing the supply of nectar resources in tropical savanna fire treatments. In my evaluation of butterfly traits associated with fire, diapause strategy, host plant specificity, wingspan, voltinism, and flight period are all associated with at least one fire treatment, but trait associations are not shared across Australian tropical savanna and U.S. temperate prairie. In tallgrass prairie, land managers and conservation practitioners interested in promoting butterfly abundance and diversity may consider increasing plant species richness and maintaining fire in the landscape. Because species composition differs between sites managed with fire and grazing and among sites managed for different numbers of years, I suggest a variety of management strategies is required to support the entire suite of butterfly species. In tropical savanna, land managers and conservation practitioners can ensure some areas of recent, early-season fire are maintained and focus on additional actions that will promote floral resource abundance and diversity, which will benefit butterflies as well as many other animal taxa. Trait-based ecology methods can help us understand the role of traits such as diapause strategy, host plant specificity, wingspan, voltinism, and flight period in explaining general patterns in butterfly responses to fire. However, to inform good conservation and management, trait-based findings should be tied back to the local species and landscapes being managed. The second chapter of this dissertation is published in Frontiers in Ecology and Evolution (Leone et al. 2019) and the first chapter is currently under review with the Journal of Insect Conservation. As a reflection of the collaborative nature of the work I present, I will use the first-person plural voice “we” throughout the rest of this dissertation.

Cool-season annual (CSA) grass and legume species, as well as warm-season forbs, can enhance established native warm-season grass (NWSG) pastures by extending the grazing season, reducing supplemental feed costs, suppressing weeds, increasing herbage production and overall forage quality, and increasing food and cover resources for pollinators and wildlife. Therefore, two NWSG experiments were conducted near Spring Hill, TN, 2018-2020, to assess three CSA seeding options (cereal rye monoculture, a cereal rye, ‘Purple Top’ turnip, ‘Trophy’ rape, ‘Frosty’ berseem clover, and ‘Dixie’ crimson clover polyculture, or non-planted control) and two warm-season N rates (0 or 67 kg N ha-1) on established switchgrass (SG) and big bluestem/indiangrass (BBIG) pastures. Switchgrass and BBIG plant density were not influenced by CSA seeding but varied by Year (P < 0.001). Plant density for BBIG was lower in 2020 than 2018 (23.6 vs. 29.1 plants m-2, respectively), whereas SG plant density was similar for 2018 and 2020 (15.0 and 14.0 plants m-2, respectively). Hay yield for both SG and BBIG varied among harvests (July 2019, July 2020, and September 2020; P < 0.001) but not by CSA seeding. Additionally, two other NWSG experiments were conducted near Greeneville, TN, 2017-2020, to assess the effect of within-season rest on the persistence of 11 native forbs when interseeded into established SG and BBIG pastures. Within-season rest treatment was not influential for total forb plant density or NWSG tiller density thus indicating persistence of forbs may not require within-season rest. Purple prairie clover never established while Illinois bundleflower was only observed flowering once despite having the greatest seeding rate among the forbs. Of the 11-species in the current mixture, interseeding a 6-species polyculture of black-eyed susan, Dixie ticktrefoil, lanceleaf coreopsis, Maximilian sunflower, oxeye sunflower, and purple coneflower could allow for plant biodiversity while offering floral resources for pollinators during the NWSG grazing season. Because CSA and native forbs did not affect plant density over the course of these experiments, incorporating CSA or native forbs may be a viable option for increasing grazing opportunities and forage production in NWSG pastures.

Re-integrating crop and livestock production through cover crop (CC) and corn residue grazing could efficiently utilize resources and ensure profitability while improving environmental quality, but how this integration affects soils and crops is not well understood. We conducted two studies to address this. In the first study, we evaluated the impact of cattle (1.3-3.7 head ha-1) grazing an oat (Avena sativa L.) CC on soil and crop yields in two adjacent irrigated no-till corn (Zea mays L.)-soybean (Glycine max L.) fields on silt loam soils in eastern Nebraska. Field I was grazed twice, while Field II was grazed thrice during a 5-yr study. Cover crop grazing reduced CC biomass by 47 to 87% without impacting soil penetration resistance, bulk density, aggregate stability, hydraulic properties, organic matter fractions, microbial biomass, and crop yields compared to non-grazed CC. In the second study, we evaluated the impact of cattle grazing of corn residue [717-807 animal unit days (AUD) ha-1] and an oat CC (1354 AUD ha-1) on soil compaction parameters including bulk density, penetration resistance, and initial infiltration under two rainfed no-till systems (I and II) on a silty clay loam in eastern Nebraska. System I had one year of corn residue grazing under soybean-corn without horse manure, while System II had one year of CC grazing and another year of corn residue grazing under soybean-wheat (Triticum aestivum L)-corn with horse manure. Dry horse manure application rate in System II averaged 3.92 Mg ha-1. Oat CC was planted following wheat. Corn residue grazing did not impact bulk density, penetration resistance, and infiltration in both Systems. Cover crop grazing in System II did not impact penetration resistance and infiltration but increased bulk density (1.43±0.04 vs 1.38±0.04 Mg m-3), although the increase was below values that affect root growth. Overall, grazing of CC and corn residue has little to no impact on soil properties and crop production and, thus, it could be a viable practice to re-integrate crop with livestock production. Advisor: Humberto Blanco

Grasslands are one of the most threatened landscapes in North America, and the Northern Great Plains Ecoregion of Montana has been identified as a global priority for grassland conservation. Within this ecoregion, the nonprofit American Prairie Reserve was created to establish a large conservation herd of plains bison (Bison bison bison, hereafter referred to as bison) in an effort to restore the landscape to ecological conditions prior to agriculture in the region. Bison are regarded as a keystone species for their unique behaviors that drastically influence ecosystem structure and function. Among these behaviors is a decreased use of riparian zones compared to cattle, which may lead to the recovery of riparian vegetation communities from overgrazing and trampling. Bison also create patches of disturbed soils on the landscape called wallows, which may provide habitat to plant species that would otherwise be outcompeted on the surrounding prairie, thus increasing landscape plant biodiversity. The Northern Great Plains is experiencing controversy over the bison restoration due to local concerns that year-round bison grazing will negatively impact riparian areas and upland forage more than seasonal cattle grazing, which is the norm. The objective of our first chapter was to compare the riparian vegetation community response to year-round bison grazing versus seasonal cattle grazing. In 2019 and 2020 we surveyed vegetation and soil compaction within riparian zones of pastures exposed to either seasonal cattle grazing or year-round bison grazing. Out of 24 vegetation and soil variables we measured, we found that native species richness and woody height heterogeneity were higher in the bison restored sites than the cattle-grazed sites, while the rest of the variables did not differ between grazer treatments. Collectively, our findings show that bison restoration may be beneficial for some aspects of the riparian zone, and support reviews critiquing the promotion of seasonal grazing as superior to year-round grazing when it is not the case in many ecosystems. The objective of our second chapter was to evaluate whether wallows provided a different vegetation community than the surrounding prairie as described in studies from other systems, and whether these differences increased with time since bison reintroduction. We surveyed wallow vegetation within, at the edge of, and in the surrounding prairie of 30 wallows from 3 sites differing in year since bison reintroduction. We observed half as much perennial species richness and abundance within and at the edge of wallows compared to the surrounding prairie. Time since reintroduction also mattered, and the greatest difference in perennial species abundance between the wallow and prairie occurred 8-15 years since bison reintroduction and the least difference in hydrophyte richness occurred 2 years since bison reintroduction. Bison wallows in this region provided vegetation communities that differed from the surrounding prairie, although not consistently in ways that have been observed in the tallgrass and southern mixed-grass prairies. Collectively, our two chapters provided evidence that bison may be acting as a keystone species in changing the vegetation communities of riparian zones and prairies.

Tall fescue seed crops require post-harvest residue management to prepare the crop for the following season. Previously farmers relied on methods such as burning residue, but due to a change in social license around air quality and public safety concerns, there has been a reduction in this management practice. The objective of this research was to investigate non-thermal post-harvest residue management practices required to maximise seed yield for a tall fescue seed crop with full post-harvest straw load retained. Two experiments were conducted on a crop of tall fescue (cv. Volupta) entering its third year of seed production. Trial 1 showed that in the absence of grazing, the most effective method of residue management was to leave the crop stubble at a post-harvest height of 14 cm, and to mow the crop either under a frequent (monthly) or lax (once at closing) regime. The frequency of the mowing treatments had no effect on seed yield. These treatments produced an average seed yield of 435 kg/ha. Trial 2 showed that under grazing, seed yields were highest in plots left with 14 cm of stubble after harvest, with an average seed yield of 327 kg/ha. Spring nitrogen applications in the grazed trial had no effect on final seed yield. The lower seed yield in the cutting to 7 cm and nil cut treatments, was a result of a lower number of fertile tillers. For the former, cutting removed all of the leaf tissue, while in the latter, plants were shaded. Both reduced the leaf surface area for photosynthesis and therefore the ability to support tiller initiation and growth. This in turn reduced the final seed yield of the crop and showed the most effective management practice is to leave the crop at 14 cm and mow frequently or laxly.

Cattle operations in the Southeastern United States are primarily cow-calf and stocker based and rely heavily on forage. As such, research regarding supplementation strategies that are specific to both the forage cultivars and management strategies that are common in the region are necessary for accurate nutritional recommendations. Additionally, further research is necessary to develop solutions to cope with the negative effects of fescue toxicosis that are common in the region. Therefore, the objectives of this dissertation are to examine supplementation strategies specific to growing cattle as well as to investigate methods of reducing ergot alkaloid intake. Corn gluten feed (CGF) is a common corn co-product that is used to supply supplemental energy and protein. Experiment 1 investigated the effect of supplementing CGF or corn to grazing cattle and found that in grazing situations, growing cattle that are supplemented with CGF have greater average daily gain (ADG) and feed efficiency compared to those supplemented with corn (P  0.03). This improvement in ADG was without changes in subcutaneous fat accretion (P = 0.87), as there were no differences among treatments in fat thickness at the 12th rib (P = 0.54). This improvement in growth and efficiency was thought to be due to differences in the digestibility of fiber in the rumen. Therefore, experiment 2 was designed to investigate the effect of corn or CGF supplementation on apparent total tract nutrient digestibility when cattle are fed a forage-based diet. However, the results from this experiment indicated that there were no changes in neutral detergent fiber digestibility (P > 0.19). In fact, heifers supplemented with corn at 0.25% BW had greater acid detergent fiber digestibility compared with those supplemented with corn at the same level (P = 0.05). Ultimately, this resulted in animals being supplemented with corn tending to have greater organic matter digestibility compared to those supplemented with CGF (P = 0.10). Therefore, the improvement in performance that is observed when grazing cattle are supplemented with CGF compared to corn does not seem to be due to improvements in fiber digestibility. Experiment 3 examined if prolonged storage of ensiled tall fescue would result in the degradation of ergot alkaloids to levels similar to that of hay. Surprisingly, there were no differences among hay or haylage samples for individual or total ergot alkaloids regardless of storage time. Ergovaline concentrations, however, declined after 30 d of storage and were similar throughout the remainder of the storage period. Although no differences were observed among treatments, the reduction of ergovaline concentrations after 30 d of storage indicate that short-term storage may help to reduce the negative effects of fescue toxicosis for the animals consuming it.

Marine protists are important components at the base of the marine food web. The growth and grazing of protistan organisms in response to the toxicity of petroleum hydrocarbons and elevated seawater temperature at the community and species levels were investigated. In exposure to 10 μL L⁻¹ of chemically dispersed crude oil in the mesocosms, the grazing impacts of microzooplankton (20-200 μm) on phytoplankton were reduced. While the microzooplankton grazing accounted for ~50% of the phytoplankton’ population growth in the control treatment, there was a de-coupling between these two parameters in the oil-loaded treatment. The de-coupling could potentially lead to algal blooms in the natural environment under certain conditions. In contrast, in exposure to chemically dispersed crude oil in the microcosms, the grazing impacts of nanoplankton (2-20 μm) on bacteria did not differ among the treatments of control and low (2 μL L⁻¹) and high (8 μL L⁻¹) concentrations. The tight couplings between the nanoplankton grazing and bacterial population growth in the control and oil-loaded treatments could have kept the abundance of bacterial cells steady. The community compositions of bacteria in the low and high dose crude oil treatments became increasing similar and different from those in the control treatment. It is believed to be related to the availability of carbon and inorganic nutrients. The relatively high abundance of hydrocarbon-degrading bacteria Cycloclasticus and Alcanivorax in the oil-loaded treatments indicated the presence of biodegradation. Exposure experiments were conducted to investigate the responses of marine protistan species to the toxicity of soluble petroleum hydrocarbon and elevated seawater temperature. In exposure to increasing concentrations of the water accommodated fraction (WAF) of crude oil, the heterotrophic dinoflagellates Oxyrrhis marina and Protoperidinium sp. and ciliates Euplotes sp. and Metacylis sp. showed species- specific vulnerabilities to oil toxicity, as reflected by their specific growth rates. When compared to the control treatment, their population grazing impacts and per capita ingestion rates were reduced with exposure to the WAF of crude oil alone and the mixture of crude oil and dispersant at the same concentration. In exposure to elevated seawater temperature, the Florida strain of mixotrophic dinoflagellate Fragilidium subglobosum obtained a specific growth rate of ~0.3 d⁻¹ at both 19°C and 23°C in mono-specific culture but zero or negative growth rates in cultures with added prey dinoflagellate Tripos tripos. F. subglobosum grown at 19°C showed higher maximum photosynthetic efficiency than at 23°C but did not differ in cellular chlorophyll-a content or cell size. This strain of F. subglobosum is believed to be non-mixotrophic and therefore the hypothesis that this dinoflagellate species becomes more heterotrophic at elevated temperature was not proved or disapproved

Abstract: Grasslands cover a quarter of the planet’s terrestrial surface and constitute 70% of the world’s agricultural land area. Grasslands provide clean water, facilitate effective nutrient cycling, and provide necessary habitat and forage for livestock and wildlife. In addition, grasslands have the potential to mitigate greenhouse gas emissions by sequestering carbon (C) and nitrogen (N) in soil. Grazing is one of the most common uses of grasslands and may alter C and nutrient mineralisation. Therefore, understanding the impact of different grazing systems (i.e. continuous and rotational) on C and nutrient cycling, as well as past management practices (cultivation), climate and soil properties, is of significant interest. This study examined the role of grazing systems on soil biogeochemical cycling by measuring extracellular enzyme activity (EEA), which is an indicator of soil biological activity. The activities of six soil extracellular enzymes were analysed that are involved in C (xylosidase, β-glucosidase, cellobiosidase), nitrogen (N) (N-acetyl-β glucosaminidase, urease), and phosphorus (phosphatase) cycling. Soil samples were tested from 12 pairs of field sites (i.e., ranches) with varying grazing practices (i.e., AMP or non-AMP grazing, with divergent stocking rates) for at least five years prior. An information theoretic model selection approach was used to determine those independent variables (disturbance regime, climate, soil) that explained the variability of each EEA. Results showed that a long resting period (mainly present in AMP ranches) increased β-glucosidase activity, while a high stocking rate increased urease activity. In contrast, soils with known previous cultivation had lower xylosidase and phosphatase activities, suggesting a legacy effect of previous cropping. The main environmental factors regulating enzyme activity were available soil N and climatic aridity. Overall, grazing practices, as represented by grazing systems, appear capable of altering C and nutrient cycling, with AMP grazing increasing C mineralisation iniiithese Alberta grasslands. This finding highlights the importance of grazing practices that maintain soil biological activity.