Characteristics and effects of management fire on blanket-bog vegetation in north-west Scotland

Abstract

The wet and mild climate in north-west Scotland has resulted in a landscape dominated by wet heath and blanket-bog vegetation.Blanket bog is of high conservation value, but of poor agricultural quality. Along with wet heath, it is used as extensive grazing for sheep and deer and, over these large unfenced areas, fire is one of the few viable management options available to estate managers and crofters. Fire in these areas is used to promote the rapid spring regrowth of grass and sedge species (the `early bite'), in contrast to the better-known grouse moor (dry heathland) fires where regeneration of Calluna vulgaris is the aim. The characteristics and effects of management fires in blanket-bog vegetation are virtually unknown, and this lack of knowledge is reflected in the almost universal recommendation of conservationists that blanket-bog vegetation should not be burnt at all, or that burning should be minimised. Information about the management fires themselves and their effect on the blanket-bog habitat, is therefore required in order to refine burning guidelines in accordance with the management objectives.

This thesis firstly describes the background to the use of fire in north-west Scotland, putting fire in the context of a changing landscape and culture. Using fires from the spring of 1996,1997 and 1998, the fuel complex is described, and equations to predict fuel load from pre-fire survey variables are presented. The results emphasise the very high spatial variability in fuel load, and this is in turn reflected in the variability in fire temperature regimes and in estimates of fire intensity. The usefulness of different fire characteristics is discussed with respect to possible objectives for fire studies, and the importance of appreciating the different spatial and temporal scales at which various processes and fire effects operate, and at which fire characteristics should be measured,is stressed.

The effects of fire on the Sphagnum layer are described with respect to fuel availability, grazing, and position, and the recovery of the Sphagnum followed for up to three years after burning. The regrowth rates of the two most important vascular species, Calluna vulgaris and Molinia caerulea, are compared under grazing and no-grazing treatments.The considerations for and against burning blanket bog are reviewed, and recommendations for management of prescribed burning given. The urgent need for further research into fire characteristics and effects in the UK is stressed with recommendations made for the areas most in need of further study.