The Role of Hedgerows in the Ecology of Invertebrates in Arable Landscapes.

Abstract

A series of field experiments were designed to examine the role of hedgerows in maintaining a rich and diverse invertebrate community and to determine the function of hedgerows as corridors along which invertebrates can move through farmland.
Intrinsic and extrinsic hedgerow characteristics were assessed for their potential to provide a suitable habitat for a diverse and abundant invertebrate population, in order to develop a classification system based on their attractiveness to invertebrates. Although this was not possible due to the great number of interacting variables and small sample size, some interesting associations were nevertheless revealed between floral and fauna species. The taxonomic composition and spatial distribution of invertebrates in the hedge was explored by means of a new sampling technique, developed to allow a reliable method for assessing arthropod populations within hedges. From only 4% of the total hedge area, 15 orders and 70 families of invertebrates were identified, with 90% of the 13,390 individuals belonging to six dominant orders. The spatial distribution of arthropods was found to be aggregated at both ends and in the middle of the hedge.
Invertebrate movement along hedges was examined in two consecutive years by monitoring reinvasion back into a repeatedly sprayed section of hedge, in order to explore the role of the hedgerows as a movement corridor. A wide variation in the ability of invertebrates to recolonise was displayed. In the first year polyphagous predators were fastest to reinvade, possibly regulating the rest of the population by predation to a new lower level, while scavengers were the first to recolonise in the second year. The influence of spatial continuity (gaps) and connectivity (nodes) of the hedge on movement was explored for ground-dwelling arthropods. Gaps in the hedges of between 7-9m did not inhibit movement of carabid beetles, while hedge nodes, seemed to attract a high number of carabids, possibly due to local microclimatic conditions.
It was concluded that hedges provide one of the most important non-crop habitat in agroecosystems, in terms of the diverse and abundant invertebrate fauna they support, and through their connectivity with other landscape features provide an important continuum of habitat for invertebrates on farmland.