General growth resilience patterns of Scots pine and Norway spruce mixed forest caused by drought events

Climate change is projected to lead to more frequent and intense climate extremes such as heat waves and severe droughts. Boreal tree species are not an exception, and extreme drought events have already been evidenced as one of the main causes of dieback for Norway spruce and Scots pine along Europe. Consequently, the increment of tree species diversity by mixed stands has been widely proposed as an effective measure to counteract the adverse impacts of droughts on tree growth. Here, we aim to identify generalizable growth response patterns from drought events for former species in mixed versus monospecific stands. We used tree ring data from triplets (mixed and monospecific stands) included into REFORM project to show differences in drought resilience indices (resistance, recovery and resilience) involving drought events between 1985 and 2015. Significant differences were found between the species and between stand composition, i.e., mixed compared with monospecific stands. Commonly, Scots pine showed a higher resistance but lower recovery than Norway spruce in pure stands. Scots pine in mixed stands exhibited a higher growth resistance but lower recovery compared with monocultures. Species mixing decreased drought recovery and resilience for Norway spruce. Resilience components were also modified by site characteristic for both species studied. Results obtained here may evidence that mixing effect mainly results from one-sided competition release, where Scots pine improves resources availability with detrimental effects on Norway spruce growthMiškų ir ekologijos fakultetasVytauto Didžiojo universiteta