Climate and size of previous cone crops contribute to large-scale synchronous cone production in balsam fir

Abstract

Mast year occurrence in trees is often synchronized across large regions. In this study, we used dendrochronological methods based on cone scar characteristics on tree branches in order to reconstruct male and female cone production in balsam fir (Abies balsamea (L.) Mill.) during the period 1988–2018. Results indicate that mast years generally occur every second year and can be synchronized across distances >1000 km. The main predictors of current-year cone abundance were cone abundance during the two previous years, which can be considered a proxy for resource availability for cone bud development during the current year, together with relatively warm temperature during cone bud development. Presence of aborted male cones was positively correlated with the occurrence of relatively cold episodes during cone bud development. This finding suggests that the influence of weather on cone crop abundance is at least partly mediated by growth cessation in the developing cone buds. We also suggest that a change in weather patterns before and after the 2005–2010 period is responsible for a switch in mast years from even to uneven calendar years around that time.