Tree canopy accession strategy changes along the latitudinal gradient of temperate Northeast Asia

Aim: Understanding how natural forest disturbances control tree regeneration is key to predict the consequences of globally accelerating forest diebacks on carbon stocks and forest biodiversity. Tropical cyclones (TCs) are important drivers of forest dynamics in Eastern Asia and it is predicted that their importance will increase. However, little is known about TC impact on forest regeneration. Location: Latitudinal gradient from south Korea (33°N) to the Russian Far East (45°N). Time period: Last 300 years. Major taxa studied: Quercus mongolica, Abies nephrolepis and Pinus koraiensis. Methods: We explore the effects of TC activity on canopy accession strategies derived from long-term tree radial growth patterns along a 1500-km latitudinal gradient of decreasing TC activity. We analyzed canopy accession strategies for more than 800 trees of three widely distributed tree species by dividing them into gap trees (GTs) that established immediately after gap formation, and released trees (RTs) that accessed the upper canopy after a period of competitive suppression. Results: We found a substantial decrease in GTs and increase in RTs proportionally along the gradient of decreasing TC activity. P. koraiensis and A. nephrolepis exhibited high variability in the proportions of the individual canopy accession strategies along the latitudinal gradient, while it was more stable for Q. mongolica. We identified the gradient of TC activity as the main driver influencing canopy dynamics and thus changes in life history traits for P. koraiensis and Q. mongolica, while maximal growth rate was the main driver for A. nephrolepis. Main conclusions: Flexibility in growth strategies enabled the studied species to cover extensive areas and indicates that they will be able to cope with shifts in disturbance regimes induced by the poleward migration of TCs and increasing TC intensity. Our results highlight the canopy accession strategy as an ecological indicator of past disturbance activity.