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Understanding how species' interactions impact upon the composition and functioning of ecological communities is central to conservation biology. The overarching objective of this thesis is to aid the enhancement of biodiversity and ecosystem services by investigation of bottom-up ecosystem processes in an agricultural context; specifically in conventionally managed grasslands. Grassland for livestock production is a dominant form of land-use throughout Europe. Its intensive management threatens biodiversity in agricultural landscapes. Given its extensive cover, modest increases to conventional grassland biodiversity could have considerable positive impacts on the provision of ecosystem services, such as pollination, to surrounding habitats. The impact of conventional grassland diversity and management on the functional diversity and ecosystem service provision of pollinator communities was investigated. This relationship was assessed using a field-scale experiment in which grassland seed mixes and sward management were manipulated. This was complemented by surveys on ten working farms which possessed a natural gradient of plant diversity within SW England and phytometer experiments (assessing fruit production and seed set of strawberry, broad bean and red campion). The impact of grassland diversity on the ecosystem service of herbivorous pest control was also investigated via a bio-assay experiment on the working farms which assessed parasitism of a surrogate pest; the firethom leaf minor. Increasing plant species richness, by the addition of both legumes and forbs, was associated with significant enhancements in the functional diversity of grassland pollinator communities. This was associated with increased temporal stability of flower-visitor interactions at the community level. Increased sward richness was correlated with an increase in the pollination of the phytometer species strawberry and red campion but not broad bean. Enhanced pollinator functional diversity of more diverse pastures was a potential mechanism for improved pollination of the strawberry phytometers. Increased sward richness under grazing management was associated with increased pollinator biomass and thereby potential resources for insectivores. Visitation networks revealed pasture species Taraxacum sp. and Cirsium arvense to have the highest pollinator visitation frequency and richness, though Cichorium intybus was highlighted as a potential target species for pasture seed mixes due to its agronomic benefits. Finally, increased pasture plant species richness was positively associated with parasitism of the surrogate pest by parasitoids. Results of this study further our understanding of the relationship between plant diversity and invertebrate community functioning, helping us to manage ecosystem services within agro-ecosystems. An additional objective was to assess the importance of different taxa in the pollination process following the observation that non-syrphid Diptera are frequently neglected in the literature. Data from 32 pollen-transport networks and 69 pollinator-visitation networks was analysed to compare the importance of various flower-visiting taxa as pollen-vectors. The non-syrphid Diptera and Syrphidae were compared in detail to determine if neglect of the former in the literature is justified. No significant difference in pollen loads was found between the syrphid and non-syrphid Diptera in terms of pollen count and specialisation. It was estimated that non-syrphid Diptera carry 87% of total pollen carried by farmland Diptera. As important pollinators such as bees and hoverflies have suffered serious declines, it would be prudent to improve our understanding of the role of non-syrphid Diptera as pollinators.

Human-managed grasslands deliver a wide range of ecosystem services including food production and the regulation of nitrogen (N) and carbon (C) cycles between aboveground and belowground compartments. Common management practices, however, such as animal grazing, agricultural liming and nutrient fertilization can greatly influence the functioning of grassland ecosystems and reduce their long-term sustainability. This PhD study has specifically addressed how grazing, liming and nutrient additions might affect soil biogeochemistry and aboveground-belowground interactions in a grassland experiment established in 1991 at Silwood Park, Berkshire, UK. Key findings from this study show how repeated liming applications have significantly (1) increased archaeal and bacterial (B) abundance while reducing fungal (F) abundance, (2) increased the C pool of soil smaller soil aggregate fractions (e.g. micro and silt clay aggregates), and (3) enhanced plant nitrogen use efficiency (NUE). Chronic nutrient fertilization has also significantly increased the abundance of ammonia oxidizing bacteria and decreased plant NUE. A novel result of this study is no change in Fungal and Bacterial gene copies in response to multiple nutrient additions. This suggests that fungal taxa are benefitting from labile resources and not all functional bacterial groups are benefitting from an increase in labile resources returned to the soil. These findings are state of the art and in line with papers that are questioning the classic model of the soil food web where bacteria predominantly metabolise labile detritus and fungi predominantly metabolise recalcitrant detritus. These resources were thought to form part of two distinct basal energy channels, however, the findings in this study support an emerging conceptual framework that understands the food web to have one continuous C pool that can at different times benefit both bacteria and fungi.

Savannahs are globally important but not well understood systems. They consist of the coexistence of trees and grasses. A major challenge in savannah ecosystems studies is the need of maps of vegetation structure over large areas where the field data collection is impractical and time consuming. Active remote sensing such as spaceborne LiDAR and RADAR has experienced limited use in these complex heterogeneously vegetated systems. This thesis examines the ability of spaceborne ICESat-GLAS data to retrieve vegetation parameters from these more structurally and sparsely complex vegetated ecosystems. For this main purpose, two methods of retrieving savannah vegetation heights from GLAS data were explored based on Gaussian decomposition. Results showed that the direct method works well over flat areas (R=0.63 and RMSE=1.32m; R=0.68and RMSE=2.61m; n=12) for GLA01 and GLA14 respectively, while sloped areas need statistical methods to remove the effect of terrain slopes on the waveform extent for better estimation of maximum vegetation height (R²=0.78 and RMSE =14.5m; R²=0.67 and RMSE=17.5m; n=6) for using terrain index and waveform width as a terrain correction factor in regression models. This work has compared the estimation of vegetation parameters derived from airborne LiDAR data and field measured data with results from spaceborne GLAS LiDAR data. GLAS estimated stand density produced R=0.98 with those estimated from airborne LiDAR data. Moreover, GLAS ratio which related to the amount of woody cover in each footprint shows a strong relationship with those extracted from LiDAR airborne data (R=0.93) and also presents a good correlation (R=0.85) when compared with woody cover field observations. In addition, ALOS PALSAR RADAR data was used to evaluate the results of estimating woody cover from GLAS LiDAR waveform parameters in another site at the Kruger National Park. This comparison showed a significant correlation between GLAS estimated woody cover and ALOS L-band HH backscatter (R=0.59). This work provides an important source of knowledge for the South Africa National Parks (SANParks) Authority with a powerful tool for an adequate spatially-consistent monitoring and assessment of the woody vegetation structure of savannah landscapes.

The role of vertebrate herbivores in affecting plant diversity and coexistence in grasslands is well known. What is less clear is the importance of invertebrate herbivores and how different groups of herbivores might interact to affect plant communities. I will present data from a 16 year study which factorially excluded insects, molluscs and rabbits in an acid grassland in South East England. Rabbits play a keystone role in preventing tree invasion and therefore maintaining the community as a grassland. The invertebrate herbivores are also important but have contrasting effects: a specialist insect Diuraphis hold feeds on the competitive dominant Holcus mollis, reducing its competitiveness and allowing the coexistence ofother grasses and of forbs. Molluscs feed on forbs, particularly forb seedlings, and therefore reduce diversity by excluding these species. These resulted are supported by short tenn (three year) exclusions ofthese herbivores.One ofthese experiments also excluded fungi, with foliar fungicides, and it suggests that pathogenic fungi may be important in maintaining grassland diversity as well, by reducing the dominance of, in particular Festuca ruhra. The invertebrate herbivores may also interact with the fungi. As mentioned above mollusc herbivores have their greatest impact at the recruitment stage and my thesis will include data from an experiment with mollusc and rabbit exclusion as well as seed sowing and the use ofselective herbicides, to show what effect molluscs have on seedling recnntment and how this interacts with plant competition

The plant diversity of agricultural grassland field margins in Northern Ireland is assessed to provide an ecological basis for agri-environmental management. Approximately 70 per cent of the land area of Northern Ireland (NI) is used for agriculture, of which grassland, typically with hedged boundaries, comprises most. Improved grasslands are predominant, with less semi- improved grassland and a much smaller area of species-rich semi-natural grassland. The thesis aims were to model: a) the regional ecological influence of agricultural management factors on the plant species composition of grassland field margins and b) vegetation composition along the field boundary, field margin, managed grass field spatial gradient. The methodology was through statistically structured quadrat sampling. Multivariate ordination was carried out by detrended correspondence analysis and canonical correspondence analysis to assess the main regional and spatial explanatory environmental gradients influencing plant species composition. A hierarchical typology of Neutral grassland field margins was created with two-way indicator species analysis, to facilitate the implementation of agri-environment scheme management. A soil fertility gradient inferred from weighted vegetation indicators for nitrogen and pH was the main regional environment gradient influencing the species composition of field margins. This gradient was related to grassland management intensity and field boundary structure. A spatial composition gradient between the field margin, field boundary and grass field was also related to field boundary structure and grassland management intensity. This highlights the spatial and temporal variability of the field margin zone as a habitat to be targeted by agri-environment schemes.

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In grasslands, climate change has the potential to disrupt a range of ecosystem services, including agricultural production, carbon (C) storage and nutrient cycling. In particular, climate change is likely to increase the frequency and severity of extreme climate events, such as drought and the subsequent rewetting event. Yet the effect of drought events will not be consistent across grassland communities, instead likely varying with grassland properties. One such property may be the level of nutrient availability, which brings about changes in plant productivity, plant community composition, and soil microbial composition and function. In this thesis, the effect of reduced precipitation on C cycling in UK species-rich grasslands is investigated in two field experiments, with varying long-term grassland restoration treatments and short-term nutrient addition, and a glasshouse experiment with reduced soil moisture. It was hypothesised that changes in plant and soil microbial communities, brought about by differences in nutrient availability, would modulate above and belowground C cycling responses to drought. This thesis found that the level of nutrient availability was important for modulating how C is cycled in response to drought in plants, soil microbial communities and whole ecosystem CO2 fluxes. For plants, the effect of drought and nutrient availability differed between functional groups, species and due to intraspecific trait variation. For soil microbial communities, the effect of drought on carbon use efficiency was modulated by short-term nutrient addition. Increased nutrient availability and drought therefore interact to determine how C is cycled and stored in plants and soil microbial communities, revealing the importance of agricultural practices in modulating whole community responses to climate change. Overall, this thesis shows the mechanisms by which drought may alter C cycling and its potential feedbacks to climate are complex, but at least in part, depend on the level of nutrient availability.

No description available.