Prostrate juniper heath (H15 <I>Calluna vulgaris-Juniperus communis </I>subspecies <I>nana </I>heath) is of considerable conservation importance. Its infrequent distribution in northwest Scotland is often attributed to historical burning. The intraspecific taxonomy of <I>Juniperus communis </I>L (Cupressaceae) is unclear. This thesis seeks to understand the history and current status of the community, and to clarify the taxonomy of juniper in Scotland. The impact of current levels of land use on extant HI5 was found to be low. A study of the environmental conditions associated with HI5 revealed that the community was absent from large areas of north-west Scotland with suitable conditions. Other communities with only infrequent juniper exist in many such areas. Sites with environmental conditions suitable for HI5 were investigated using palaeoecological methods. Fire had occurred in both HI5and non-H15 sites, but there was a prolonged recent absence in HI5. A study of annual growth rings showed juniper in HI5 to be twice as old as in other communities, emphasising the lack of recent disturbance. Evidence of greater past juniper cover was not found on non-H15 sites. It is argued that the history of prostrate juniper heath is more dynamic and complex than previously believed. Comparative morphological, genetic marker, and reciprocal transplant studies of juniper populations showed that <I>Juniperus communis </I>ssp. <I>nana </I>is characterised by genotypic prostrateness, imbricate leaf arrangement, and abrupt leaf tips. It is argued that the conservation importance of HI5 and juniper are increased by the findings of this study. Implications for conservation practice, and future research, are considered.

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Microscopic charcoal analyses of sediment cores are used widely by palaeoecologists for reconstructing proxy records of past fire activity. Few studies, however, have reconstructed fire histories from UK and Irish moorland environments, a rather surprising situation considering the fact that much of the heather-dominated moorland in the UK and Ireland has been managed and maintained using fire for many centuries, and in some instances millennia. This thesis addresses the main issues regarding the use and applicability of microscopic charcoal analyses in moorland contexts. The literature pertaining to the theory and practical application of microscopic charcoal analyses is comprehensively reviewed, and all aspects of microscopic charcoal analysis, from charcoal production through to the interpretation of sediment charcoal profiles, are discussed and wherever possible related to their applicability in moorland contexts. An investigation of the taphonomy of microscopic charcoal around small moorland fires was conducted in order to provide an appreciation of the processes of charcoal production and the extent of charcoal particle dispersal. The results suggest that small moorland fires produce differential quantities of charcoal particles of different size ranges, smaller particles are produced in significantly greater quantities than progressively larger ones. The majority of charcoal particles produced by small muirburns are deposited locally, within approximately 70-100 m of parent fires, and the wind direction at the time of the fire may be a key factor determining the dispersal of microscopic charcoal particles, the majority being deposited down-wind of fires, few are dispersed laterally or into the wind. A microscopic charcoal quantification technique was developed to reconstruct extended (>50 year) fire histories from moorland soil profiles. A number of fire histories from mor humus-rich moorland soil cores of approximately several centuries duration were reconstructed. Fossil charcoal assemblages produced by in situ fires were distinguished from those produced by nearby ex situ fires on the basis of differences in gross charcoal abundance and charcoal size class distributions. Charcoal assemblages produced by in situ fires are determinable from those produced by ex situ fires because they generally contain a greater total abundance of charcoal particles and higher proportions of medium to large particles. Microscopic charcoal analyses of lake sediment cores from seven UK and Irish moorland catchments were used to reconstruct long-term (>100 year) fire histories. The reconstructed fire histories were used to assess whether changes in fire activity in the catchments may have been responsible for initiating past -episodes of peat erosion, inferred from loss on ignition measurements, and declines in Calluna cover, inferred from pollen analyses, evident at all of the sites. The results suggest that moorland burning may have been an influential factor contributing to the initiation of peat erosion at only one of the seven sites studied. Similarly, fire activity was only significantly related to the loss of Calluna at two of the seven sites studied.

Calluna vulgaris L.Hull readily colonises arsenate contaminated mine spoil soils in south-west(SW)England.At these sites, it forms mycorrhizal association with the ericoid ascomycete fungus Hymenoscyphus ericae. The initial aim of this study was to investigate the physiological response of H.ericae populations to arsenate.Mine site populations were found to have evolved arsenate resistance in comparison to the heathland population.This research demonstrates the evolution of arsenate resistance through an enhanced arsenite efflux in populations of H.ericae from As contaminated mine spoil soils. H.ericae also confers arsenate resistance to C.vulgaris. The ecological significance of these findings is discussed. / Doctor of Philosophy (PhD)

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Avec l'augmentation des sécheresses dans les forêts tempérées, la gestion sylvicole envisage de réduire la densité des peuplements adultes pour limiter le déficit hydrique. Cependant, la réduction de la canopée arborée augmente le rayonnement dans le sous-bois et permet le développement de la strate herbacée monopoliste. Nos objectifs étaient de caractériser l'évapotranspiration (ETu) de 4 herbacées monopolistes (Molinia caerulea, Calluna vulgaris, Pteridium aquilinum and Rubus sp.) et de quantifier leur impact sur la teneur en eau du sol (SWC) dans des peuplements de Quercus petraea. L’ETu des quatre herbacées cultivées en pot a été quantifiée en conditions semi-contrôlées caractérisées par deux niveaux d’éclairement relatif et 3 niveaux de SWC. In situ, le SWC, le microclimat et l’ETu de P. aquilinum et M. caerulea ont été mesurés sur 20 dispositifs dans les peuplements forestiers de Q. petraea présentant un gradient croissant de LAI. Chaque dispositif était subdivisé en 2 placettes, l’une était désherbée et l'autre enherbée. M. caerulea et C. vulgaris ont une faible régulation de leur ETu alors que P. aquilinum et Rubus sp. ont une stratégie conservatrice face au stress hydrique. SWC diminue plus rapidement quand le LAI de la strate herbacée augmente, ce qui est directement lié à l’ouverture du couvert arboré avec une valeur seuil de LAI de la strate arborée à 2-3, sous laquelle la contribution de la strate herbacée à l’évapotranspiration du peuplement pourrait compenser la diminution de celle de la strate arborée.Ces résultats montrent la nécessité de considérer la végétation du sous-bois dans la gestion sylvicole notamment lorsque la ressource hydrique est limitante. Ainsi, la réduction de la densité de la strate arborée doit être un compromis entre la réduction de la surface foliaire des arbres pour réduire l’ET, et le maintien d’une densité suffisante de la strate arborée pour limiter la croissance et l'ETu de la végétation du sous-bois. / In the context of ongoing increase of drought in temperate forests, forest managers consider the reduction of stand density to limit soil water depletion. The reduction of tree canopy density increases light below canopy and allows the development of monopolistic understorey vegetation. Our objectives were to characterize the evapotranspiration (ETu) of common understorey plants (Molinia caerulea, Calluna vulgaris, Pteridium aquilinum and Rubus sp.) and to quantify their impacts on soil water content (SWC) in mature oak stands (Quercus petraea).A first experiment was set up in a greenhouse where the 4 understorey species were potted and subjected to 2 levels of light transmittance and 3 levels of SWC. Microclimate and ETu were monitored. A second experiment was carried out on 20 plots (10 with M. caerulea and 10 with P. aquilinum) in oak stands with contrasted LAI. On each plot, two circular areas were set up, one weeded and the other untouched. SWC, microclimate and ETu were monitored.M. caerulea and C. vulgaris are more water spenders, whereas P. aquilinum and Rubus sp. are more water savers under water stress. Soil water depletion was faster with increasing understorey vegetation LAI, which was directly linked to tree canopy opening with a threshold of tree LAI of 2-3 below which the understorey contribution could offset the reduction of tree ET. The experimentations showed that the relative contribution of understory vegetation in the ecosystem water balance is significant, and depends on SWC and on the understorey species identity. These results show the necessity to consider understorey vegetation in forest management when water availability is an issue. Lower tree canopy density could increase the understorey ETu and soil water stress for trees. From a management perspective, thinning should be designed as a compromise between the reduction of tree leaf area to reduce ET, and maintaining sufficient tree canopy to restrict the growth and ETu of understorey vegetation.

Boreal peatlands store carbon sequestered from the atmosphere over millennia and the importance of this and the other ecosystem services these areas provide is now widely recognised. However, a changing climate will affect these environments and, consequently, the services they provide to the global population. The rate and direction of environmental change to peatlands is currently unclear and they have not yet been included in many climate models. This may in part be due to the ecological heterogeneity and spatial extent of these areas and the sparse sampling survey methods currently adopted. Hyperspectral remote sensing from satellite platforms may in future offer an approach to surveying and do so at the high spectral and spatial resolutions necessary to infer ecological change in these peatlands. However, work is required to develop methods of analysis to determine if hyperspectral data can be used to measure the overstorey vegetation of these areas. This will require an understanding of how annual and inter-annual cyclical changes affect the peatland plant canopy reflectances that would be recorded by hyperspectral sensors and how these reflectances can be related to state variable of interest to climate scientists, ecologists and peatland managers. There are significant areas of peatland within Scotland and, as it is towards the southern extreme of the boreal peatlands, these may be an early indicator of environment change to the wider boreal region. Calluna vulgaris, a hardy dwarf shrub, is the dominant overstorey species over much of these peatlands and could serve as a proxy for ecological, and consequently, environmental change. However, little has been done to understand how variations in leaf pigments or canopy structural parameters influence the spectral reflectance of Calluna through annual and inter-annual growth and senescence cycles. Nor has much work been done to develop methods of analysis to enable images acquired by hyperspectral remote sensing to be utilised to monitor change to these Calluna dominated peatlands over time. To advance understanding of the optical properties of Calluna leaves and canopies and develop methods to analyse hyperspectral images laboratory, field and modelling studies have been carried out in time series over a number of years. The leaf and canopy parameters significantly affecting reflectance have been identified and quantified. Differences between published Chlorophyll(a+b) in vivo absorption spectra and those determined were found. Carotenoids and Anthocyanins were also identified and quantified. The absorption spectra of these pigments were incorporated into a canopy reflectance model and this was coupled to a Calluna growth model. This combined model enabled the reflectance of Calluna canopies to be modelled in daily increments through annual and inter-annual growth and senescence cycles. Reasonable results were achieved in spectral regions where reflectance changed systematically but only for homogeneous Calluna stands. However, it was noted during this research that the area of support for the spectral measurements appeared to differ from that assumed from the specification provided by the spectroradiometer manufacturers. The directional response functions (DRFs) of two spectroradiometers were investigated and wavelength, or wavelength region, specific spatial dependences were noted. The effect that the DRFs of the spectroradiometers would have on reflectances recorded from Calluna canopies was investigated through a modelling study. Errors and inaccuracies in the spectra that would be recorded from these canopies, and commonly used biochemical indices derived from them, have been quantified.

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