Deciduous tree species chilling requirements and its importance to spring phenology

Abstract

Timing of bud burst and leaf unfolding is widely used indicator of climate change and it is also a very important measure of trees chilling requirements detection by setting certain experiments in the laboratory. It is well known that different tree species has different chilling requirements during the period of dormancy, but the transition from true-dormancy to post-dormancy is not well understood. Therefore I investigated two various tree species: one climax – Sorbus americana, the other pioneer - Betula papyrifera, trying to detect the date when chilling requirements for these species are fulfilled. This investigation was done in Schoodic Penninsula at Acadia National Park (Maine USA) in 2015/2016 cold period of the year. First cutting date was shortly after end of leaf fall (middle of November) and last cutting date was before leaf unfolding in spring (end of March). Twigs of the trees were collected weekly and kept in a cups filled with a tap water in the laboratory with a certain air temperature and humidity (T-18oC, humidity - 60%). The photoperiod was regulated automatically by full spectrum lamps and plants were exposed to 14 h of daylight. The observations of bud burst in the laboratory were done once (until March) and twice (since March) per week. The results showed that successional strategy and temperature are linked and that pioneer species (Betula papyrifera) has lower chilling and forcing requirements as compared with climax species (Sorbus americana). After collection in November the twigs of paper birch reacted to forcing temperatures in the laboratory in the beginning of January and bud burst was detected after 48 - 71 days being in the lab. Twigs of mountain ash collected in November and December did not show any signs and first bud burst appeared in the middle of March after 57 - 69 days spent in laboratory (collection date – beginning of January).[...]