Securing Biodiversity in Breckland - European Commission

Nested HeterogeneityA further important principle is that of Nested Heterogeneity. Fine-scale heterogeneity, in terms ofsward mosaics, is important at scales of tens of centimetres or a few metres within habitat patches.Some assemblages, particularly Hymenoptera, require the local juxtaposition of grazed swards ortrampled and compacted bare ground very close to ungrazed (but often intermittently disturbedground) that can provide nectar resources. Other examples of species needing fine-scaleheterogeneity include those that require the juxtaposition of scrub margins and open grazed habitatse.g. Osmia (Neosmia) bicolour (see box) and those that require the juxtaposition of contrastinghabitat across ecotones, for example forest and heath, heath and fen, or dry heath and wetwoodland e.g. Crabro scutellatusWet open woodland (structural and moisture ecotone)Crabro scutellatus – Notable:AHymenoptera – Sphecidae (thread-waisted wasps)A psammophilus black and yellow sphecid wasp which nests in dry, bare sandy fully exposedto the sun. However, it preys on Dolichopodidae (long-legged flies) which are associatedwith wet areas such as pools, bogs, streamsides and wet heath, and adults require flowerparticularly umbellifers. Therefore a combination of fairly dry areas for nesting with wetareas for hunting are required. Management at sites would need to encourage baregroundby disturbance on dry areas, while former peat diggings and new pond creation maypromote good prey populationsA guiding principle would be to ensure that at least one or two margins of each heathland sitesupported: An internal rotovated fire break comprising an annually rotovated or cultivated strip adjacentto another strip disturbed in alternate years. This would provide for both annual andpaucennial species and species requiring re-vegetating tussocky broken ground both locatedclose to unbroken turf Wherever possible adjacent arable fields should incorporate an ungrazed cultivated marginalongside the grazed heath site, providing complex juxtaposition Homogenously grazed sites will be improved by a range of different physical disturbancetreatments, more episodic variation in grazing intensity, and allowing some ungrazed scrubmargin to develop alongside areas with intermittent disturbance.160