Risk of damage by the pine weevil Hylobius abietis in southern Europe: Effects of silvicultural and landscape factors

The pine weevil (Hylobius abietis) is one of the most devastating pests of regenerated coniferous forests in northern and central Europe. Although it is also present and potentially harmful in southern Europe, little attention has been paid to this pest in that region. With the aim of quantifying the potential risk of the pine weevil as a forest pest in southern Europe, we performed an intensive assessment of weevil abundance and damage in 21 Pinus pinaster and P. radiata plantations established in recent coniferous clear-cuts in Galicia (NW Spain), i.e. in the south-western part of the natural distribution of H. abietis. The effect of several silvicultural and landscape factors as modulators of weevil risk was analyzed. Abundance of adult pine weevils was highly variable across the sampling plots, with the number of trapped insects significantly correlated with mean air temperature during each trapping period. Damage rate was, however, fairly constant across the whole study period. No significant relationship between pine weevil abundance and damage was observed. Up to 85% of the planted seedlings were attacked and the mortality rates reached 45% in some plots. No weevil preferences were found between the two pine species. Pine weevil damage was positively related to the amount of slash (logging waste) on the ground and negatively related to the time since clear-felling occurred. Once these factors were accounted for, the abundance of mature coniferous forest in the vicinity (500-2000 m) of the clear-cut significantly and positively affected pine weevil damage. We conclude that a high risk of pine weevil damage does exist in NW Spain. Low-intensity forest management together with the scarcity and discontinuity of mature conifer forest in the region seem to be the reason why this forest pest is largely ignored by forest owners and forest-health services. If the forest sector intensifies in this area, care should be taken to protect pine plantations against this devastating pest.