The Unique Flora of a “Mountain Summit at Sea Level”—Serpentine Debris on the Shetland Isles

Billions of years of geologic upheaval, eons of gradual weathering by rain, sun and frost, and millennia of evolutionary divergence have resulted in a global network of unique plant communities that are collectively referred to as “serpentine.” Serpentine soils derived from ultramafic igneous rocks have been of high interest to botanists for centuries due to their distinctive flora that are noticeably different to surrounding vegetation. They are typified by low calcium-to-magnesium ratios, high heavy metal concentrations and poor availability of essential plant nutrients including nitrogen, potassium and phosphorus. Serpentine systems can be found all over the world but the plant communities that are adapted to these harsh environments have a number of common traits that belies the geographic and ecological diversity of their locations. In this account, the Keen of Hamar, a serpentine site of national importance on the Shetland Isles, Scotland, exhibits many of the typical serpentine characteristics resulting in a distinctive, albeit species-poor flora. The multiple threats of eutrophication, agricultural conversion, invasive species and climate change each show their mark on reductions in the extent of serpentine habitat on the Keen. Habitat restoration may have a place in the ongoing management of the debris substrate but recent research also demonstrates that climate change may actually reduce the encroachment of invasive species and alleviate interspecific competition, at least in the short-term. The long-term prospects for this unique site are discussed as a case study of the problems faced in conservation today.