Ryzyko masowego występowania pędraków chrabąszczy (Melolontha spp.) w strefie ekotonowej drzewostanów dojrzałych na terenie Nadleśnictwa Lubaczów

This study evaluated the environmental risk drivers affecting the occurrence of cockchafer grubs in mature stands bordering with open spaces. The following factors were taken into the consideration: the distance from the edge towards the forest interior, the forest site type, species composition, canopy openness and the cover of forest floor with vegetation as well as cutting treatment in some of the investigated stands. In one of the biggest cockchafer outbreak centers in Poland (Lubaczów Forest District; SE Poland) 6 mature stands were chosen and estalished 5 transects in each of them. Each transect was 250 m long and consisted of 6 pits (1×0.5×0.5 m) in a regular distance of 50 m with the first pit on an open space bordering with forest. Pits were used to determine the grub infestation of the soil. In the area of 100 m² around the pit, the general vegetation cover and tree species composition of a stand were characterized. The forest light environment was defined by hemispherical photography. The distance in transect and the fact that stand was harvested were also taken into consideration. The applied logistic regression model demonstrated that the site fertility is the most important factor that significantly increases the risk of cockchafer grubs occurrence. The other characteristics that also cause that stand is more attractive for the cockchafer grubs are: participation of the broadleaved species in stand composition and the dense vegetation cover. Furthermore, the cockchafer grubs occurrence was more frequent in the forest interior than in an open space or at the forest−meadow ecotone.