Thinning intensity and frequency enhance Quercus robur L. growth responses to drought in Southern Sweden

Drought can impact forests directly causing a decrease of growth, but also increase the vulnerability of trees to secondary pests and pathogens, causing additional loss of volume production. To develop new silvicultural strategies, it is crucial to understand if thinning can promote resilience of the remaining trees to drought by enhancing an efficient use of resources. Given projected drier vegetation periods in Southern Sweden, the aim of the study was to determine how tree growth is affected by severe summer droughts under different thinning regimes. We used an experiment established in 1991 in a 40-year-old pure oak (Quercus robur L.) stand with two thinning intensities and an unthinned control. We collected tree cores before and after specific drought events occurring after treatment. We observed that heavy thinning intensity increased drought resistance, and decreased recovery time and growth reduction when the time since the last intervention was 4–5 years. Our results suggest that heavy and frequent thinning interventions would be an appropriate management alternative to alleviate drought stress in pure oak stands close to the northern edge of their distribution.