The effects of red deer (Cervus elaphus) on the regeneration of birch (Betula pubescens) woodland in the Scottish highlands
This thesis examines the relationships between red deer and the natural regeneration of birch woodland in the Scottish Highlands. Red deer may influence regeneration at the germination and establishment phases and these effects are considered separately. All studies were carried out at the Creag Meagaidh National Nature Reserve (NNR), where the red deer population has been reduced by culling since 1986. As a result, deer density is low in comparison to many Highland estates. The potential for regeneration was considered in terms of the germinability of seeds collected within the NNR. The results indicated that the availability of germinable seeds was unlikely to be limiting to regeneration in the near future. The potential germination success of birch at the NNR was investigated experimentally by sowing seeds into gaps created in Calluna- and Molinia-dominated vegetation. Germination was compared between bared-soil gaps (6x6cm, 10x10cm, 25x25cm), hoof-print gaps and undisturbed controls. Germination was improved in bared soil only, but there was no benefit for seedling establishment. In a concurrent experiment, there was little evidence to suggest that red deer at low density created bared-soil gaps and were therefore unlikely to improve the potential for regeneration. Red deer browsing patterns were examined at the NNR and an adjacent estate, with higher deer density. There were strong seasonal patterns in browsing, with peak browsing recorded at both sites in winter, when deer selectively browsed birch in both Calluna- and Molinia-dominated vegetation. There was no evidence of a consistent effect of sapling morphology on the selection of individual saplings by deer. Sapling selection varied with vegetation type and site location and it was suggested that the visibility of saplings to deer may be influenced by site-specific factors, including vegetation structure.