The Isles of Scilly Biodiversity Audit 2008 - Cornwall Wildlife Trust

2.2.2.5 Hedgerows and BoundaryFeaturesOverviewThere are virtually no true native hedgerows in theIsles of Scilly. The few hawthorn Crataegus monogynahedges that exist on St Mary’s are of little conservationinterest. Although not a BAP habitat there are anumber of different boundary features in the Isles ofScilly.Stone ‘hedges’ come in three main types, dry-stonewalling (single leaved), ‘Cornish hedges’ (doubleleaved) and granite masonry (such as the Garrisonwalls). Then there are green ‘fences’ of various speciesof trees and shrubs, alien evergreen species such asAustralasian natives that were planted to protect thebulb fields. Elm Ulmus spp. hedges are more frequentthan hawthorn although they too suffer in exposedplaces and stay gnarled and low. In more shelteredsites the elms are able to grow into trees and on StMary’s for example form shelterbelts. On St Mary’sand Tresco there are also planted conifer windbreaksof Monterey pine Pinus radiata and lodgepole pineP.contorta. Boundaries with both stone hedges anda green fence alongside are very common on all theinhabited islands.Distribution and ExtentThere are many kilometres of hedges and fences onall the inhabited islands. On the larger uninhabitedislands there are also relict stone hedges from formercultivations.Conservation ImportanceHedges play a role in enabling species to movethrough the landscape by connecting semi-naturalhabitats.Double-leaved or ‘Cornish hedges’ which have a soilcore between two courses of stone are an importancerefuge for many plants, particularly species such aswestern fumitory and ferns. They are also refugesfor invertebrates - some are used as nesting sites bysolitary bees, and mammals including the Scilly shrew.Dry-stone or single-leaved hedges also supportpopulations of lichens, ferns and other plants andprovide shelter for mammals and invertebrates.The mortared walls also act as refuges to many plants.The tops of the Garrison walls for example have anunusual and rich flora. House sparrow and starlinguse crevices for nesting and it is suspected bats mayroost in walls sometimes.The evergreen fences are important sites for nestingbirds; song thrush, blackbird, linnet, dunnock andoccasionally by house sparrow.Trends and IssuesThe use of herbicides to clean stone hedges has led toloss of species.Neglect has led to bramble and bracken overwhelmingsome stone hedges.Neglect allows loose stones to fall, leading todisintegration and instability of stone hedges.Work is needed with the farming community to ensuresympathetic conservation of field boundaries.ResearchAn investigation could be made to determine thecomparative value of the green fences both as shelterand for nature conservation.Stone hedges on St Martin’s. Photo: Rosemary ParslowIsles of Scilly biodiversity audit Page 60