b.Environmental pressures (e.g. pollution, climate change)

Natural Heritage

The main potential threat is the accidental reintroduction of alien species, both plants and animals. Fortunately the number of human visitors per year is small so the opportunities for other invading plants and animals to arrive is minimal.Excavation at The Gap Landing by visitors on the islands and stacks other than Hirta is strictly controlled (for reasons of both accidental introduction of new plant seeds or small animals and for Health and Safety reasons). The warden on Hirta monitors arrivals during the visitor season in summer. No vessel is allowed to tie up alongside the small pier (which is barely suitable anyway) and all visitors by boat decant into small tenders to come ashore at the steps on the pier. Landings are rarely possible anywhere else. Supplies for the base arrive either by helicopter, or by landing craft. The vessels are screened for rats and other undesirable species and the warden is equipped with cage traps, etc. in the event of any mammals getting ashore. There is a very low risk of non-native marine species being introduced, either through ship ballast or as fouling organisms falling off the hull of visiting vessels. No dogs are allowed on the island to minimise disturbance to nesting birds and sheep, and to prevent the accidental introduction of sheep parasites.

 

Cultural Heritage

Most of the standing structures and archaeological sites are under no particular threat from environmental conditions, other than their everyday exposure to the sometimes ferocious elements on St Kilda. A very small number of sites are under threat from coastal erosion, which is likely to become worse if there is an increase in storminess linked to global climate change. Of particular note, and under regular monitoring, is the landfall at Village Bay, where archaeological deposits from as early as the Neolithic period (perhaps 5,000+ years ago) are eroding from the cliff face, while the Store is just over a metre from the start of the beach. The site of a ‘boat-shaped setting’ at The Gap was recently excavated in advance of further cliff-falls in the area, and the remaining structural elements are expected to succumb to cliff-fall at some time in the next few decades.

Because there are no rabbits, moles or other burrowing mammals on St Kilda, and of the burrowing birds the Atlantic puffins do not colonise known archaeological sites, although the petrels do, animal-related threats are minimal, although some conservation work does get hampered by the presence of nesting birds –especially northern fulmars. The lack of trees on the islands also eliminates a common threat to archaeology, but bracken rhizomes in the Village are thought to be damaging – causing ‘bioturbation’ of stratified archaeological deposits. Recent research has suggested the expansion of bracken in this area, and action is programmed to assess the damage being done.