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.