Stump grinding management enhances pine weevil (Hylobius abietis) abundance on clear-cuts

The pine weevil ( Hylobius abietis ) is a major pest that affects conifer reforestation, breeding in stumps left in clear-cuts after harvesting. Fresh stumps attract pine weevils by emitting volatile compounds during their decomposition. With recent bark beetle outbreaks leading to more clear-cuts, the economic losses from pine weevil feeding on young seedlings have risen. Stump grinding has become a popular post-harvest management strategy. This technique helps to remove stumps, prepare sites for reforestation, and reduce pine weevil populations. However, we observed a higher abundance of pine weevils in mulched clear-cuts, leading us to hypothesize that fresh stump grinding may increase volatile compound production, making these areas more attractive to the beetles. To test this, we studied 60 clear-cuts that varied by post-harvest management (mulched vs. retained stumps), clear-cut age (newly created vs. one-year-old), and stand type (coniferous vs. deciduous). We trapped pine weevils using five pitfall traps at each site throughout the summer season (June-August). Our results showed that pine weevils were significantly more abundant in newly mulched clear-cuts compared to those with retained stumps. In contrast, one-year-old mulched clear-cuts showed a lower abundance of pine weevils. Additionally, freshly mulched clear-cuts were highly attractive to pine weevils even in deciduous stands. These findings highlight that stump grinding strongly increases the short-term attractiveness of clear-cuts to pine weevils. Moreover, the timing of mulching is critical: applying it just before or during the swarming period greatly increases the risk of high pine weevil abundance on regeneration sites. • Stump grinding enhances the colonization of clear-cut areas by pine weevils. • Even clear-cuts in mixed stands showed high pine weevil abundance after mulching. • The timing of stump grinding is crucial relative to pine weevil flight activity.