Pine Weevil Population Density and Damage to Coniferous Seedlings in a Regeneration Area With and Without Shelterwood GO ¨ RAN NORDLANDER 1 , HELENA BYLUND 1 , GO ¨ RAN O ¨ RLANDER 2,3 and KRISTINA WALLERTZ 3 1 Department of Entomology, Swedish University of Agricultural Sciences, P.O. Box 7044, SE-750 07 Uppsala, Sweden, 2 School of Industrial Engineering, Va ¨ xjo ¨ University, SE-351 95 Va ¨ xjo ¨, Sweden, and 3 Asa Forest Research Station, Swedish University of Agricultural Sciences, SE-360 30 Lammhult, Sweden Nordlander, G. 1 , Bylund, H. 1 ,O ¨ rlander, G. 2,3 and Wallertz, K. 3 ( 1 Department of Entomology, Swedish University of Agricultural Sciences, P.O. Box 7044, SE-750 07 Uppsala, Sweden, 2 School of Industrial Engineering, Va ¨xjo ¨ University, SE-351 95 Va ¨xjo ¨, Sweden, and 3 Asa Forest Research Station, Swedish University of Agricultural Sciences, SE-360 30 Lammhult, Sweden). Pine weevil population density and damage to coniferous seedlings in a regeneration area with and without shelterwood. Received Nov. 29, 2002. Accepted Apr. 29, 2003. Scand. J. For. Res. 18: 438  /448, 2003. Damage to planted conifer seedlings by the pine weevil, Hylobius abietis (L.), is considered to be less severe in shelterwoods than in clear-cuttings. To evaluate possible reasons for this reduction, this study investigated the relationship between seedling damage and pine weevil population density in the presence and absence of shelter trees. Assessments of seedling damage throughout a full growth season and absolute population density estimates were made at a fresh clear- cutting and an adjacent shelterwood (1 ha each). A grid of 100 pitfall traps was placed over each area, and population estimates were made using the mark  /recapture technique. Pine weevil damage to seedlings was about twice as high in the clear-cutting, whereas pine weevil density was estimated to be higher in the shelterwood or about the same in the two treatments ( /14 000 weevils ha 1 ). Existing differences in microclimate between the shelterwood and clear-cutting did not seem to be the cause of the differences in damage levels. Thus, the hypothesis that seedling damage is reduced in shelterwoods because of increased availabilityof alternative food remains a candidate for further testing. Key words: Curculionidae, Hylobius abietis, mark  / recapture, microclimate, population density, reforestation, seedling damage. Correspondence to: G. Nordlander, e-mail: Goran.Nordlander@entom.slu.se INTRODUCTION Damage to conifer seedlings by the pine weevil Hylobius abietis (L.) seems to be generally less severe in forest regenerations with shelterwood than on clear- cuttings (von Sydow & O ¨ rlander 1994, Lo ¨f 2000, Petersson & O ¨ rlander 2003). The damage-suppressing effect of shelterwoods is not necessarily related to a lower abundance of pine weevils (von Sydow & O ¨ rlander 1994). Instead, it has been suggested that seedlings suffer less damage in shelterwoods because of the greater availability of food sources other than seedlings (O ¨ rlander et al. 2000, 2001, Nordlander et al., 2003). It has indeed been demonstrated that a rich supply of food can decrease damage to seedlings caused by adult pine weevils. In a field experiment it was shown that the amount of pine weevil feeding on the stem bark of seedlings was reduced by two-thirds by placing fresh pine branches on the ground between the seedlings (O ¨ rlander et al. 2001). It has not yet been demonstrated that food availability is responsible for the low levels of seedling damage seen in shelterwoods, but feeding patterns observed at the edge of a clear- cutting in a previous study support the hypothesis (Nordlander et al. 2003). At the sun-exposed edge, pine weevil feeding was only about half of that nearer the centre of the clear-cutting, although light inter- ception and soil temperature were not significantly different at the edge. This suggests that the decline in seedling damage towards the edge was related to richer food resources, e.g. roots and branches of the edge trees. Similarly, the low levels of damage under shelterwoods may be related to food resources directly or indirectly provided by the presence of living trees. There is some correlation between pine weevil population density and the amount of weevil feeding on seedlings (Nordlander 1987, von Sydow 1997). However, the intensity of pine weevil feeding on seedlings also depends on other factors, so weevil numbers alone can give only a limited indication of likely damage (Wilson & Day 1994, O ¨ rlander et al. Scand. J. For. Res. 18: 438  /448, 2003 # 2003 Taylor & Francis ISSN 0282-7581 DOI: 10.1080/02827580310001634