Prostrate juniper heath in north-west Scotland : historical, ecological and taxonomic issues
Prostrate juniper heath (H15 Calluna vulgaris-Juniperus communis subspecies nana heath) is of considerable conservation importance. Its infrequent distribution in northwest Scotland is often attributed to historical burning. The intraspecific taxonomy of Juniperus communis L (Cupressaceae) is unclear. This thesis seeks to understand the history and current status of the community, and to clarify the taxonomy of juniper in Scotland. The impact of current levels of land use on extant HI5 was found to be low. A study of the environmental conditions associated with HI5 revealed that the community was absent from large areas of north-west Scotland with suitable conditions. Other communities with only infrequent juniper exist in many such areas. Sites with environmental conditions suitable for HI5 were investigated using palaeoecological methods. Fire had occurred in both HI5and non-H15 sites, but there was a prolonged recent absence in HI5. A study of annual growth rings showed juniper in HI5 to be twice as old as in other communities, emphasising the lack of recent disturbance. Evidence of greater past juniper cover was not found on non-H15 sites. It is argued that the history of prostrate juniper heath is more dynamic and complex than previously believed. Comparative morphological, genetic marker, and reciprocal transplant studies of juniper populations showed that Juniperus communis ssp. nana is characterised by genotypic prostrateness, imbricate leaf arrangement, and abrupt leaf tips. It is argued that the conservation importance of HI5 and juniper are increased by the findings of this study. Implications for conservation practice, and future research, are considered.