Chilling and forcing requirements to budburst for early and late – flushing tree species

Abstract

Most of the temperate tree species has to fulfill chilling requirement during fall and early winter in order to start budburst in spring. Many researchers warn that some species might not attain their chilling requirements in a changing climate conditions. Our aim in this study was to detect the dates when chilling requirements are attained for different tree species and to evaluate tradeoffs between chilling and forcing. We collected dormant twigs in the cold period of the year 2015 – 2016 from the wild in Schoodic Peninsula of Acadia National Park, Maine, USA. Our results showed that early–flushing species (Betula papyrifera, Alnus glutinosa) has very low chilling requirements whereas late–flushing species (Picea mariana, Abies balsamea) has much higher chilling requirements. The transition from endodormancy to ecodormancy for the early–flushing species appeared in the middle of November and for late–flushing species in the second part of December. For the all investigated tree species non–linear and in all cases strong relationship was detected between accumulated thermal time and chilling.