Spatial pattern of invading Dendroctonus micans (Coleoptera: Scolytidae) populations in the United Kingdom

Abstract

The spatial pattern of Dendroctonus micans (Kug.) attacks on individual spruce stands was analysed at the regional scale in Britain using data collected between 1982 and 1984 by the British Forestry Commission. These survey data reflect at least 10 years of D. micans spread, in the absence of natural enemies and of pest management control measures. A large-scale spatial gradient in the attack density at the stand level was identified and modelled. The large-scale spatial trend model explained 31.3% of the variability, and divided the study area in three separate areas: a zone where the insect was well established and where attack density presented low variations, a transition zone where attack density sharply decreased, and a zone not yet colonized. Attack density was related to site and stand factors, and to landscape neighbourhood in a linear spatial regression model. The factors correlated to attack density and the spatial autocorrelation structure of remaining variability were found to vary according to the zones, reflecting the predominance of different ecological processes occurring in colonized and uncolonized areas. The shape and orientation of the large-scale spatial model was shown to be mostly influenced by the spatial distribution of early attacks.