This thesis reports a study of the flowering response of heather, <i>Calluna vulgaris</i> (L.) Hull and of experimental procedures designed to modify the time of onset of that process, with particular reference to year-round production of the flowering plant, in line with recent expansion in the European and British pot plant industries. Microscopic apical examinations were employed throughout to identify and monitor development of floral primordia. Research concentrated on flowering responses to photoperiodic stimuli, provided by various lighting regimes, including fluorescent and tungsten sources, differing in spectral composition and irradiance intensities. <i>Calluna</i> clearly required long day lighting for both floral initiation and development. This response was shown to be influenced by temperature conditions, with higher temperatures promoting flowering. Various changing-temperature regimes were also investigated. Reduced-temperature storage of plants with floral buds was successfully employed as a method of delaying flowering time. Influences of cultivar and seasonal flowering type were also investigated. Results indicated that seasonal flowering sequences were maintained under artificial lighting conditions; so that later flowering types required longer periods of lighting. Evidence suggested a cultivar-dependent sensitivity to irradiance intensity. This information was incorporated in an evaluation of costs incurred during photoperiodic induction, and from this an economic protocol for production of flowering <i>Calluna</i> was compiled; commercial viability being an integral part of the overall study. The minimum plant size capable of floral induction was investigated and related to different modes of propagation; in both macro- and micro-propagated plants flowering occurred soon after root development. Seedlings, however, had to pass through a juvenile phase. The limited micropropagation study revealed that adventitious shoot production involved transitory tissue rejuvenation.

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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.

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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.

Thesis (M.F.A.)--Washington State University, May 2009. / Title from title screen (viewed on Nov. 23, 2009). "Department of Fine Arts."

The plant communities of the Long Mynd plateau are the culmination of over 3000 years of human intervention that largely deforested the uplands, and subsequently maintained the generally treeless heath and grassland communities now extant. The capacity of these communities to respond to directional change is well known, indeed the traditional mode of heathland management, burning, depends on the regenerative capacity of the target species, generally heather (Calluna vulgaris), for its success. However, changes in post WW2 stocking practice; the loss of ponies followed by an increase in the numbers of sheep and a change to them being overwintered on the hill, led to excessive grazing and damage to the heath. This coincided with the spread over the hill by bracken (Pteridium aquilinum) and other changes in the distribution and nature of the vegetation. A sequence of vegetation surveys made by various individuals and organisations over the past 75 years or so has been analysed in an attempt to delineate spatial and temporal changes in the vegetation. This demonstrated the need for a standardised survey methodology to allow consistent monitoring. The analysis showed that bracken had been infiltrating most of the communities from its origins outside the lower limits of the Common as well as from some of the valley sides. Within the last decade, this expansion has apparently been contained in line with the current management plan for control. A survey of 730 quadrats in some 30 stands was made to characterise the variation of the vegetation on the plateau, and to relate it to some of the associated environmental factors. Classification, unconstrained ordination and ordination constrained by the abiotic environmental variables, showed that, a) the strongest trend in the vegetation distinguished water-flushed communities, b) non-wetland communities differentiate between heathland and grassland, c) this trend can be only partly be attributed to the measured abiotic environmental variables, d) the amount of pure Pteridietum [U20] is limited, although much of the heathland and grassland has bracken within it. There are indications that invasion by bracken often correlates with a loss of dominance of Calluna in favour of Deschampsia flexuosa and Vaccinium myrtillus. Difficulties in associating these trends with measured abiotic variables suggests, other factors probably management processes, are critical in driving this trend. Distribution of ‘heathland’ bryophytes was found to be associated more with the structure of their ‘host’ vascular communities rather than with abiotic factors. Finally, this investigation considers the practical implications with regard to the future encouragement of heather and the control of bracken. Cutting rather than burning appears to be the ecologically most suitable method for heather regeneration and bracken control.