Plant herbivore interactions within a complex mosaic of grassland, mire and montane communities

Holland, John Peter (2001) Plant herbivore interactions within a complex mosaic of grassland, mire and montane communities. PhD thesis, University of Glasgow.

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Abstract

Commercial sheep farming in the Highlands of Scotland has had a considerable influence on the landscape, ecology and economy of the region. The hill sheep industry developed in the Highlands in the mid 18th Century and remains the dominant form of agriculture in the hills and uplands. The hill grazings used by these sheep are dominated by unimproved semi-natural grassland, heather moorland and blanket bog. There is considerable concern from conservationists over the impact that sheep grazing is having on these semi-natural habitats, in particular the loss of heather moorland and the expansion of Nardus stricta-dominated grasslands. The government response to this has revolved around encouraging hill farmers to reduce sheep numbers (i.e. extensify). The semi-natural hill grasslands are of considerable economic importance to the sheep industry. Nardus stricta and Juncus squarrosus dominate a large proportion of these grasslands. The production and grazing utilisation of these semi-natural hill grasslands, and their response to extensification are therefore of considerable interest. This study investigated the effect that changes in grazing management had on species composition, vegetation structure, above-ground biomass, production and utilisation of a range of hill grassland and mire communities. The data collected from the study was then used to test and evaluate the vegetation component of the Hill Grazing Management Model (HGMM). The HGMM is a computer model designed to assist grazing management decision-making on British hill farms. The HGMM has a number of weaknesses, the main one being the limited range of vegetation types. The model does not include communities dominated by Juncus squarrosus, and although it does include Nardus stricta grassland it is only considered in terms of the Festuca - Agrostis growing between the Nardus stricta tussocks. One of the main aims of this study was to modify the HGMM to improve its predictive ability for sites with high proportions of Nardus stricta and Juncus squarrosus dominated grassland, using data collected from the study site. The study was carried out at a system scale level, using three large enclosures of approximately 40 hectares each. Two enclosures were grazed by sheep at mean annual stocking rates of 0.074 LU ha-1 and 0.051 LU ha-1, and the third enclosure was grazed by sheep and summer grazing cattle at a mean annual stocking rate of 0.096 LU ha-1. A quadrat survey and a vegetation mapping exercise were carried out to provide detailed information on the floristic composition of the vegetation community types, their areas, and spatial and altitudinal distributions. A detailed vegetation map was produced using a total survey station and a geographic information system. The study site consisted of a complex mosaic of twenty-two NVC vegetation types. Communities dominated by Nardus stricta covered over half the study area. Permanent nested quadrats and monthly sward surface height measurements were used to monitor changes in the composition and structure of the vegetation under the different grazing treatments. Few changes in species composition or the abundance of dominant species were observed, and none of the monitored vegetation types changed their NVC type. A number of ruderal and grazing tolerant species increased in frequency within the sheep and cattle grazed enclosure, as did the area of bare ground. The sward was also significantly shorter in the sheep and cattle grazed enclosure. Monthly above-ground biomass values of four vegetation types were estimated by harvesting strips of vegetation, sub-sampling, sorting, drying and weighing. Biomass varied significantly through the year. Mean summer biomass values varied from year to year. The biomass of both the Nardus stricta grassland and Juncus acutiflorus mire were significantly lower in the enclosure with the sheep and summer grazing cattle. The work presented in this thesis indicates that in the short term, extensification has very little impact on the species composition of hill grasslands and only minor effects on the structure and biomass of these grasslands. Entering into short-term management agreements to reduce sheep numbers is unlikely to result in any major environmental benefits if Nardus stricta and Juncus squarrosus dominate the hill vegetation. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Tony Waterhouse
Keywords: Range management
Date of Award: 2001
Depositing User: Enlighten Team
Unique ID: glathesis:2001-73135
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: http://theses.gla.ac.uk/id/eprint/73135

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