Spatial distribution of an arthropod community in a pear orchard (southern France) : identification of a hedge effect
Résumé
This study analysed specific features of the spatial distribution of a global population of arthropods in an experimental orchard of pear trees, Pyrus communis (L.), in southern France. Insect fauna was sampled by regular beating of the 210 trees in the experimental orchard from spring to autumn in three consecutive years (2004–2006). This orchard, where no chemical treatments had been applied since 2000, is bordered to the north by a mixed hedge, to the south by a cypress hedge of Cupressus sempervirens (L.), and to the east and west by other crops. Statistical analyses of climatic variables comparing the 3 years showed no differences with respect to rainfall, temperature or wind variables during psyllid proliferation periods. However, statistical spatial analyses demonstrated a hedge effect on local ecological variables, such as population abundance, species richness and the Shannon diversity index, in a zone close to the mixed hedge, by comparison with zones close to other margins of the orchard. This spatial distribution exhibited temporal stability and pointed to two distinct zones: one unprotected and one protected by the mixed hedge from the Mistral wind. The first zone contained a population of psyllids that was significantly larger than that in the protected zone, which harboured a great majority of beneficial insects. This spatial stability over 3 years suggested in particular that climatic factors were related to psyllids, while spatial factors, such as distance from the mixed hedge, were related to beneficial insects. In the light of these results, we concluded as to the strong potential role that hedges could play in reducing crop pest populations.