Dissertations / Theses on the topic 'Heather moorland'

For roughly the past 200 years land-managers have used the practice of “muirburning” to manipulate the structure of heather (Calluna vulgaris) to create a patchwork of habitat structures able to provide forage and nesting sites for red grouse (Lagopus lagopus scoticus) as well as grazing for sheep (Ovis aries) and red deer (Cervus elaphus). This thesis investigates both the behaviour and impact of management fires in recognition of the need to develop multi-aim land management practices that ensure both continued productivity and protection of biodiversity in the face of climatic and environmental change. Fuel structure and loading are crucial controlling factors on both fire behaviour and impact governing both rate of spread and heat release to the ground surface. A visual obstruction method is developed that estimates total and fine fuel loading as well as the structure of the heather canopy. In order to adequately understand fire impact a dimensional analysis approach is taken to estimating the mass of burnt heather stems. Experiments at a number of spatial and temporal scales relate variation in heather fuel moisture content to stand structure and variation in weather conditions. Monitoring shows moisture contents to be relatively stable temporally, but spatially variable. Periods of extreme low moisture contents in early spring are associated with frozen ground, winter cuticle damage and physiological drought. Such conditions may have contributed to the large number of wildfires in 2003. A replicated plot design was used to investigate the effect of weather conditions and fuel loading on fire behaviour. An empirical approach is taken to fire behaviour modelling with equations describing rate of spread and fireline intensity being developed on the basis of fuel structure descriptors and windspeed. The theoretical negative correlation between fuel bed density and rate of spread is demonstrated to hold true for heather stands, while the impact of heterogeneity in fuel bed structure is also investigated. Redundancy Analysis is used to investigate the influence of multiple predictors on a number of aspects of fire behaviour including: rate of spread, fireline intensity, flame length and ground surface heating. Data from this and previous studies are used to ground-truth a number of fire behaviour prediction systems including BehavePlus and the Canadian Fire Behaviour Prediction System. Finally linkages between fire behaviour, fire severity and heather regeneration are investigated. A number of proxy measures of ‘Immediate Severity’ are tested and used to examine the influence of fires on plant regeneration. The post-fire development of stands is shown to relate primarily to stand age and structure before burning, and to post-fire substrates rather than variation in fire behaviour and severity.

Heather moorlands are of great ecological value and as such are recognised as internationally important habitats. A large proportion of European heather moorland is concentrated within the UK, covering approximately 2-3 million ha" of the UK upland environment. Enhanced levels of N pollution have led to concerns about the eutrophication of many natural and semi-natural ecosystems in the UK, including heather moorland. This study aimed to investigate the response of a moorland ecosystem to artificially enhanced N deposition and the interaction of P with increasing N input. A further aim was to investigate the potential for moorland ecosystem recovery from enhanced N deposition. The research presented within this thesis was part of an ongoing long-term N manipulation experiment established in 1989 on a heather moorland in Wales. This study focussed on a N manipulation experiment established at the site in 1998, where N was added at treatment levels of 0, 10,20,40 and 120kg ha" yr". In addition to this there were Nand P combination treatments, with P added at a rate of 20kg ha" yr". A N recovery experiment was established on the 1998 experimental plots, whereby treatment with N to one half of each plot ceased in 2003, in order to investigate potential for recovery from enhanced N deposition. Cal/una vulgaris growth was stimulated by increasing total N input as was the foliar N concentration. The stimulation of C. vulgaris growth indicates that this species was N limited at ambient levels of deposition. Bryophyte and lichen frequency and cover and bryophyte species diversity were significantly reduced by artificially enhanced N deposition. The foliar N concentration of the dominant moss species Hypnum jutlandicum was elevated with increasing N input. Peat and litter nutrient levels also responded positively to N input, with significant increases in N concentration and exchangeable N. The increase in exchangeable N with N addition demonstrates the increase in bio-available N with enhanced N deposition in moorland ecosystems. The P acquiring enzyme phosphatase and the lignin degrading enzyme phenol oxidase showed no consistent response to N input. The different components within the moorland ecosystem showed varying levels of N, P or N and P co-limitation. The dominant plant species C. vulgaris was clearly N limited at ambient levels of N deposition, as indicated by significant growth stimulation and foliar N accumulation with increased N input. However, P addition did cause a positive growth response in this species, albeit weaker than the response to N input, suggesting a certain degree of Nand P co-limitation. The bryophyte and lichen community were clearly P limited, with P addition significantly increasing bryophyte and lichen frequency and species diversity. Soil microorganisms also displayed some evidence of P limitation as the addition of P, even at ambient N deposition, significantly reduced the activity of phosphatase. The moorland showed little evidence of recovery 2 years after N treatment had ceased. However, there was a significant reduction in litter exchangeable NH4, C. vulgaris total foliar N concentration and C. vulgaris shoot extension. Liverwort cover had increased in those plots where N treatment had ceased. The data from the N recovery experiment suggests that although there was some evidence of recovery, the legacy of N deposition to the experiment may persist for some time. A regional survey in 2005 of moorland sites in Scotland, Wales and the Peak District, was used to investigate whether any of the responses to artificially enhanced N deposition at the N manipulation experiment could be used as bio-indicators of N deposition at a regional scale. Of the bio-indicators tested, litter exchangeable Nand C. vulgaris N:P ratio showed a significant positive association with modelled N deposition. A significant negative association was observed between litter phenol oxidase activity, bryophyte species richness and N deposition. Litter total N concentration and phosphatase activity and C. vulgaris and H. jutlandicum total foliar N concentration did not have a significant association with N deposition. The potential bio-indicators identified are from varying components of the moorland ecosystem (i.e. soil system, bryophytes and C. vulgaris) and consequently may not only provide an indication of ecosystem N status but also overall moorland health in response to varying levels of N deposition.

The utilisation of heather moorland by red grouse Lagopus lagopus scoticus was studied with particular emphasis on the influences of vegetation structure on grouse behaviour at a series of spatial scales, from the choice of location within individual heather stands up to the composition and alignment of territories on the moor. A novel method of measurement and multivariate statistical analysis was developed for quantifying the structure of vegetation dominated by ling heather Calluna vulgaris. The method was assessed in relation to existing subjective classifications. The method revealed that gaps in the canopy of tall heather were utilised by grouse during the daytime in winter. The manner in which grouse exploit the vegetation types available in their territories was determined by radio-tracking a population on a managed grouse moor in north-east Scotland over the course of two years. During autumn and winter, territorial grouse showed a preference for tall heather relative to its availability. In spring, a greater use was made of heterogeneous mixtures of heather and graminoids during the daytime, and, to some extent, of shorter heather during the intensive feeding periods at dawn and dusk. Hens showed a very strong affinity for edge between heather stands in spring, but spent more time on the side offering the greater cover. Broods tended to range in areas with more old heather and more edge than generally available, but within their ranges, they clearly preferred heterogeneous areas. The relationships between vegetation patterns, the composition of territories and the alignment of territory boundaries were investigated using fifteen years' historical data. The relationships varied considerably between years. When the population was declining, heather edge was distributed evenly between territories, but it was distributed unevenly during population increase. In general, territory alignment showed a greater association with vegetation edges than with particular types of vegetation.

This study contributes to the understanding of spatial aspects of plant-herbivore interactions within a grazed grass-shrub mosaic in heather moorland, an internationally important ecosystem dominating much of the Scottish uplands. A three-year field experiment was conducted to observe plant-herbivore interactions between Scottish Blackface sheep and heather-grass mosaics. Modelling tools were used for virtual experiments, thus complementing and extending the field data. The experiment showed the importance of a spatially explicit approach to understanding the interactions. The pattern of use of the vegetation mosaics by sheep was strongly heterogeneous, with spatially limited areas of intensive use intermixed with large areas of extensive use. Foraging and ruminating behaviour showed distinctively different patterns of impact, indicating that multiple processes determined herbivore of vegetation mosaics and their concomitant impacts on the dynamics of the vegetation. Application of a spatial interaction model, previously used in human geography, to the field data revealed that the amount of grass in an area was a good predictor of the local heather defoliation. Heather defoliation was highest near large grass patches and lowest away from small grass patches. The virtual experiment showed further that cognitive aspects of foraging behaviour could play an important role in determining the pattern of use by herbivores. Performance of foraging strategies was strongly affected by the heterogeneity of the vegetation, suggesting that herbivores could adapt their foraging strategies depending on the pattern of vegetation. This study provides new insights into the spatial aspects of plant-herbivore interactions in grass-shrub mosaics and offers a starting point for more detailed investigations. At the same time the results necessitate the increased use of spatially explicit approaches in the management of grazed ecosystems.

Heather moorland is highly valued for its economic, cultural and biodiversity interest.  Recent declines in moorland extent are largely attributable to intense livestock grazing pressure and atmospheric nitrogen deposition.  Their combined influence leads to a replacement of Calluna vulgaris as the dominant plant by graminoids, especially Molinia caerulea or Nardus stricta.  Recent management has sought to reverse this process and restoration projects utilising either grazing control or more intensive mechanical methods have been initiated at a number of sites.  However the effect of such management on wider aspects of moorland biodiversity is little studied. After characterising differences between plant and invertebrate assemblages of established and degraded heather moor the ability of such populations to reassemble on restored moors was tested.  Moorland restoration was largely successful in re-establishing C. vulgaris but the remainder of the vegetation assemblage was in many cases impoverished.  Moors restored solely by grazing control more closely resembled the original state than those restored by more intensive mechanical means. Restoration aided the reassembly of moorland Lepidoptera and Hemiptera assemblages to a variable extent.  Lepidoptera species reassemble more completely on grazing exclusion sites on which the vegetation assemblage is most complete.  Hemiptera reassemble more successfully on mechanically restored sites, possibly because they are more dependent on a continuous cover of C. vulgaris to disperse freely. The role of habitat isolation in impeding the colonisation of moorland fauna on restored land was studied in a field experiment.  The success of colonisation of habitat patches by moorland Hemiptera declined with increased isolation.  The rate of decline was greatest at up to 20 m though even short distances impeded colonisation.

Concerns have been raised on the deterioration of heather moorland due to management in the UK. A study was therefore conducted on the impacts of moorland management on the soils and hydrology of a catchment on Dartmoor. Soil moisture was measured gridwise using TDR on 19 occasions. At 23 sites within this grid, physical properties of the topsoil were obtained. At three locations, tensiometer nests were installed, recording soil suction at 10 cm depth intervals. At the catchment scale, stream discharge and rainfall were recorded. Grazing densities within the watershed were estimated and the observed patterns were related to vegetation types. Results from the TDR grid showed that in dry conditions, soil moisture patterns are heterogeneous in contrast to a more uniform pattern in wet periods. A threshold soil moisture content of about 0.60 cm3 cm-3 divides the two conditions. The exponential relationship between average hillslope soil moisture content and stream discharge also revealed the division between wet and dry states. A regression analysis showed that during dry conditions, the vegetation plays a significant role in determining the soil water status. During wet conditions, topography becomes more important. In these conditions, the soil water movement is mainly lateral, whereas in the dry state, this is vertical in the soil profile. Tensiometer data showed that most soil water movement is in the topsoil. Analyses suggested that soil moisture under vegetation classes associated with higher grazing pressures is higher in similar topographic conditions. Soil bulk density is higher and the total porosity is lower near the soil surface. This suggests that less rainfall is required to reach the soil moisture threshold and water will be transported laterally down the slope. A heather burning experiment revealed that the direct effect of temperature is shallow. Soil moisture levels do not change over the course of the burn. However, in dry situations during summer, soil moisture contents under burned plots are higher than under unburned vegetation probably due to reduced transpiration. If this effect is similar at the hillslope scale, when the soil is wetting up, the soil moisture threshold value could be reached at an earlier stage and accelerated lateral water movement could be the result. It can be concluded therefore, that moorland management could accelerate water movement on the hillslopes causing higher discharge peaks in wet periods and consequently low flows in summer. However, the effects are subtle and encouraging vegetation heterogeneity could play a role in buffering water to prevent loss to the stream.

This thesis describes a series of laboratory and field experiments that quantify the population dynamics of the heather beetle (Lochmaea suturalis Thomson), in relation to temperature and its host plant heather (Calluna vulgaris (L. ) Hull). The sex ratio, fecundity, egg laying threshold temperature, emergence threshold temperature, life stage development periods, and life stage mortalities were investigated. It was shown that the life stages were significantly dependent on temperature, whilst it was shown that there was no significant relationship between larval growth and Calluna vulgaris plants sourced from the study sites. The results of the population dynamics experiments were incorporated into a temperature driven, cohort based, and daily looped, stochastic population dynamics computer model. The temperature component of the model was derived from temperature data collected from nine moorland sites, at different altitudes, where there was shown to be a significant relationship between temperature and altitude. The population dynamics model was run for a fifty year period with a population of I million beetles at seven temperature regimes and five different altitudes. The model predicted that as daily mean temperatures rose, so there was a greater chance of increasing populations and that as altitude increases, so the chance of increasing populations decreases. At a predicted daily mean temperature rise of 2-3'C there was evidence of considerable population increases at lower altitudes, and with a daily mean temperature rise of 4-6'C the beetle population exhibited persistent, large, fluctuating populations in the region of three to sixty fold increases at all modelled altitudes over a number of years. An uncertainty and sensitivity analysis of the model was undertaken utilising a Latin Hypercube Swnpling regime, where it was shown that fecundity, egg mortality and pupal mortality were the most important life history variables in i contributing to the model output imprecision. The thesis discussesth eser esults in the light of predicted climate change and their use as an aid to moorland and heathland managers.

Grazing is widely used as a tool in conservation management. Many plant communities of conservation importance are dependent on grazing for their existence, maintenance of species diversity and other valued characteristics. Plant community response to grazing depends on many factors, including site productivity and dominant plant species; setting appropriate grazing levels can therefore be challenging. The problems are magnified when more than one species or plant community is the target of conservation goals as they may need different levels of grazing. Where multiple plant communities are present in a mosaic, grazing pressure on the higher productivity community (usually the more attractive to herbivores) can affect the utilisation of the lower productivity communities: grazing on the less productive community is elevated in close proximity (a few metres) to the productive community. This increases the possibility of conflict in managing grazing for the conservation of both communities as low productivity communities can sustain only low levels of grazing. Less well studied are the effect of community layout at larger spatial scales (100s – 1000s of metres) and the effect of vegetation pattern on grazing on the productive community. It is also not well known how the spatial pattern of grazing is affected by changes in herbivore density. I investigated the consequences of the spatial pattern of plant communities and changing herbivore density for grazing patterns on a complex multi-community mosaic and assessed the probable consequence for conservation of these plant communities. The plant mosaic comprised a mixture of species-rich grassland and several less productive communities, primarily heaths and bogs; the main grazers were red deer (Cervus elaphus). The grassland needs higher grazing levels than the others to meet management goals. I used small scale experiments to investigate the effects of reducing grazing on grassland and how the effects varied within the grassland community. Elimination of grazing caused a rapid switch from short, herb-rich grassland towards a graminoid dominated, less diverse sward, as expected. The degree of change in diversity and herb cover was dependent on productivity. Experimental reduction in grazing had mixed consequences for grassland in relation to conservation goals due to pre-existing variation in intensity of grazing on the grassland. The condition of areas of initially heavily grazed and short vegetation improved, whilst taller grasslands deteriorated. Analysis of large-scale datasets was used to investigate the influence of spatial pattern of community types and differences in large scale deer density on the distribution of grazing. There was increased grazing pressure on less productive plant communities where grassland was abundant within 1km and this was fairly consistent across communities and across different grazing indicators. There was an effect on grazing levels on grassland, but the explanatory power was generally lower and the effect less consistently present across indicators of grazing. Sward height and litter depth measures from one dataset indicated heavier grazing with more grassland present nearby (250m); however, lower grazing pressure was indicated by sward height and a combined grazing index when there was more grassland in a more distant zone (500-1000m). Deer density had limited power to explain large scale variation in impacts, probably due to the coarse scale of the information available and correlation with other variables. This limited the ability to thoroughly test the consequences of changes in deer density on the spatial pattern of impacts or investigate whether there was an interaction between deer density and spatial pattern. The inherent conflict in conservation management of grazed communities of different productivities is increased by the influence of the spatial distribution of plant communities on the distribution of grazing; conservation management goals need to account for this and identify a suitable trade-off.

A major component of the vegetation cover in the area chosen for this study consists of heather moorland. This provides an essential habitat for diverse populations of ground-nesting moorland birds. Common heather - Calluna vulgaris (L) Hull - is typically the dominant species of this semi-natural habitat, providing both nutrition and cover for these bird populations. Much heather-dominated vegetation is in a successional stage and management is required to prevent its progressive transformation into rough grassland and woodland scrub. Traditionally management by burning and more recently by mowing has been used to achieve this by encouraging the growth of young heather, through the removal of senescent stands of Calluna vulgaris in the degenerate phase of its life cycle. These forms of management however may also have the effect of creating conditions which favour faster growing, acidophilous grasses which may replace Calluna vulgaris over time as the dominant species. This study investigates the hypothesis that particular management treatments may have specific influences on the composition and nature of the post-management vegetation complex. Particular attention is given to the nutrient status of soils, associated with each of the management treatments chosen for investigation. The influence of this on the long-term floristic composition and vertical stratification of the Callunetum is considered. Stands of vegetation belonging to different management regimes were used as the elements of chronosequences, which were utilised to investigate vegetation change over time in relation to particular management treatments. Vegetation was described from quadrats located within this framework and quadrat-specific soil samples were taken for chemical analysis. Dendrochronology was explored as a method for determining the age of Calluna plants in each treatment category from which the efficiency of different methods of removing the Calluna canopy was assessed. Multivariate methods of classification (TWINSPAN) and indirect gradient analysis (DECORANA) were used to reveal pattern in the vegetation data, which might be attributable to the management treatments defining each of the chronosequence stages. TWINSPAN was successful in identifying homogenous groups of samples on the basis of species associations peculiar to particular treatment categories. DECORANA proved successful in suggesting environmental gradients which might be responsible for these groupings. Data obtained from the chemical analysis of soil samples was used to compare soil nutrient status in each of the treatment categories, representative of the chronosequence stages. The vegetation and soils data-sets were then combined for use in direct gradient analysis (CANOCO), to investigate the combination of management treatments and soil nutrient status as factors influencing the formation of the species associations identified at each of the chronosequence stages. Finally, management goals are discussed in the context of the results of these analyses and the role of these procedures as the basis for an extended investigation into post-management, plant/soil inter-relationships as an influence on successional trends is evaluated.

Outbreaks of winter moth, Operophtera brumata L. (Lepidoptera:Geometridae), have recently become common on moorlands in Scotland. This thesis describes the ecology of moorland O. brumata populations, and tests the hypothesis that outbreaks are caused by increased host-plant quality. The principal moorland host, Calluna vulgaris (L.) Hull, common heather, is of low nutritional quality for O. brumata. Experimental nitrogen-enrichment of C. vulgaris enhances O. brumata development, although there is no evidence that outbreaks occur on nitrogen-enriched C. vulgaris in the field. Calluna vulgaris nutritional quality is not significantly affected by growth in carbon dioxide-enriched atmospheres. There is no evidence that moorland O. brumata populations are specialised to feeding on C. vulgaris, and no evidence that synchrony between larval emergence and C. vulgaris budburst affects larval survival and development. Compensatory feeding may enhance the ability of O. brumata to utilise C. vulgaris. Life history and metabolic differences are shown between moorland and non-moorland O. brumata populations. These differences are best explained as physiological adaptations to local climate, and are unlikely to be caused by nutritional specialisation of O. brumata populations to different hosts. Evidence is presented that winter weather conditions strongly affect O. brumata abundance in high-altitude moorland outbreak sites, and that O. brumata escapes from parasitism at such sites. The relative importance of "top-down" factors, such as natural enemies, and "bottom-up" effects, such as host quality, in determining O. brumata abundance is discussed. It is argued that, in high-altitude moorland sites, the interaction between winter weather conditions and the "top-down" effect of natural enemies is a more important determinant of outbreak potential than the "bottom-up" effect of host quality. The effects of future environmental changes on this system are considered.