Ten years after: Release cutting around old oaks still affects oak vitality and saproxylic beetles in a Norway spruce stand

Abstract

Abstract It is often suggested to release oaks (Quercus robur) from competition, to ensure their survival and boost their conservational value. However, few studies have explored how long‐lasting this effect is and how it affects saproxylic beetles. Ten years after cutting, we investigated effects of different release cutting levels (high, medium, and no release) around 140‐year‐old retained oaks in a commercial forest with Norway spruce (Picea abies). We evaluated oak vitality using crown and dead wood measurements. Saproxylic beetles were caught in window traps, identified to species level, and grouped according to their association with oak and/or Norway spruce. Released oaks had more light, higher temperatures, greater crown growth, and less dead wood in the crown compared to the no‐release control. After 10 years we still found a higher abundance of oak‐associated beetles and higher overall species richness of saproxylic beetles in the released oaks. Beetle species composition significantly differed between released oaks and control. We suggest avoiding planting trees beneath retained oaks when regenerating conifer forests and to proceed with conservation management during subsequent thinning by removing regeneration under the oak crowns. We emphasize the benefits of monitoring the retained oaks to maintain tree vitality, habitat quality, and insolation.