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Title: Hypericum linariifolium (Toadflax-Leaved St. John's Wort) Factors Influencing the Presence of the Species at Four Sites on Dartmoor
Author: Moden, Georgina Pauline Rhoda
ISNI:       0000 0001 3412 9361
Awarding Body: University of the West of England
Current Institution: University of the West of England, Bristol
Date of Award: 2008
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Hypericum linariifolium is a rare, heathland species. Ninety percent of its U~ population is found within Dartmoor National Park in Devon. Whilst the (' conservation status of H. Iinariifolium is krrown to be rare, little quantifiable work has been undertaken into the abiotic and biotic factors with which it is associated. Similarly, there has been no formal classification of the plant communities within which the species exists. This thesis aims to increase the knowledge of the habitat and abiotic requirements of H. Iinariifolium, which will facilitate the future development of management plans suitable for the conservation of the species. In particular, the research examines the species and edaphic factors with which H. Iinariifolium is correlated. A National Vegetation Classification of the vegetation present is also undertaken, and the communities within which H. linariifolium is found most frequently are identified. The most likely species strategy employed by ,..f: linariifoliuln is considered. Research was carried out at four sites on Dartmoor. H. linariifolium was present at three of the sites (Bigport Farm, Broadmoor Common and Hunters Path), and . absent from the other site (Steps Bridge). This enabled comparison between sites of any factors that may restrict the presence of the species. Vegetation was quantified using stratified sampling and the 'percentage cover by eye' method, and NVC community types were identified from the data collected using the software programme Tablefit (Hill, 1993). Soil samples were collected and analysed for levels of soil moisture, organic matter, pH, nitrate, nitrite, phosphate, calcium, fluoride, chloride, sodium, magnesium, potassium and sulphate. At Bigport Farm, vegetation management was carried out to identify the effect it would have on H. Iinariifolium, as previous research had surmised that population levels of the species were declining as a result of scrub (U1ex spp.) encroachment. The site was split into two areas. One area was cleared completely of any U. europaeus present, whilst the U. europaeus'in the other half of the site was left untouched. Comparisons were made between the managed and unmanaged areas in terms of biotic and abiotic factors in relation to the mean population levels of H. Iinariifolium found. (' Analysis showed that levels of H. Iinariifolium were highest at Bigport Farm, and these levels increased following clearance. The species was found most frequently within H3c (U1ex minor-Agrostis curtisii heath, subcommunity A. curtisil), U3 (Agrostis curtisii grassland) and W23c (U1ex europaeus-Rubus fruticosus scrub, sub-community Teucrium scorodonia) community types, but was absent from the H6 (Erica vagans-U1ex europaeus heath), H8 (Gal/una vulgaris-Ulex gallii heath) and W10 (Quercus robur-P. aquilinum-R. fruticosus woodland) communities. It is hypothesised that shading created by canopyforming communities and species may result in the decline of H. Iinariifolium. However, H. Iinariifolium was not negatively correlated with U. europaeus (a canopy-forming species· removed dUring management) despite an increase in the mean levels of H. Iinariifolium following clearance. It was found that management had an influence on the communities present at Bigport Farm, and there were differences in community composition between the managed and unmanaged areas. H. Iinariifolium was not found within taller community stands. It is therefore argued that H. Iinariifolium levels can be positively affected by the implementation of management. Vegetation clearance would reverse succession to a sere composed of lower growing vegetation than is found within climax communities. These climax communities encroach when succession is allowed to continue unabated, resulting in a decline in H. Iinariifolium levels. H. Iinariifolium was found to be positively associated with two species, Primula vulgaris and Agrostis curtisii. P. vulgaris and H. Iinariifolium were found to share seed dispersal mechanisms, and both responded to management in a similar manner at Bigport Farm. However, H. linariifolium responded more slowly than P. vulgaris. A. curtisii was found within similar community types to H. Iinariifolium. The two species were also associated with similar abiotic factors. H. linariifolium was found to be correlated with organic matter, soil moisture, bare earth, calcium and pH of >4.0. It is likely that H. Iinariifolium is positively correlated with calcium to protect against root stress caused by 10yf'pH levels. The ability of H. Iinariifolium to withstand low pH and soil moisture levels suggests that the species is a stress-tolerator. Its frequent presence in quadrats of stress-tolerators and stress-tolerant competitors would further confirm this finding. However, the increase in percentage cover levels of the species following clearance (distUrbance) is indicative of a ruderal. These findings have increased the knOWledge of H. Iinariifolium, which in tum will help to inform management at sites where the species is present. Future research will need to encompass identification of the most appropriate management strategy for the species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available