The response of plant and insect assemblages to the restoration of heather moorland
Heather moorland is highly valued for its economic, cultural and biodiversity interest. Recent declines in moorland extent are largely attributable to intense livestock grazing pressure and atmospheric nitrogen deposition. Their combined influence leads to a replacement of Calluna vulgaris as the dominant plant by graminoids, especially Molinia caerulea or Nardus stricta. Recent management has sought to reverse this process and restoration projects utilising either grazing control or more intensive mechanical methods have been initiated at a number of sites. However the effect of such management on wider aspects of moorland biodiversity is little studied. After characterising differences between plant and invertebrate assemblages of established and degraded heather moor the ability of such populations to reassemble on restored moors was tested. Moorland restoration was largely successful in re-establishing C. vulgaris but the remainder of the vegetation assemblage was in many cases impoverished. Moors restored solely by grazing control more closely resembled the original state than those restored by more intensive mechanical means. Restoration aided the reassembly of moorland Lepidoptera and Hemiptera assemblages to a variable extent. Lepidoptera species reassemble more completely on grazing exclusion sites on which the vegetation assemblage is most complete. Hemiptera reassemble more successfully on mechanically restored sites, possibly because they are more dependent on a continuous cover of C. vulgaris to disperse freely. The role of habitat isolation in impeding the colonisation of moorland fauna on restored land was studied in a field experiment. The success of colonisation of habitat patches by moorland Hemiptera declined with increased isolation. The rate of decline was greatest at up to 20 m though even short distances impeded colonisation.