Studies on variations in chilling and heat accumulation in apple trees and their effects on
first flowering date under climate change are important for guiding apple planting and productions．
In this study，we carried out experiments in representative stations of apple planting areas in the
northern China，including Fushan of Shandong，Wanrong of Shanxi，Xifeng of Gansu and Akesu of
Xinjiang． The first flowering data and hourly temperature data during 1996－2018 were used to cal-
culate the daily chilling and heat accumulation units by applying the dynamic model and growing
degree hour model． Partial least squares regression (PLS) correlated daily chilling and heat units
with the first flowering dates was used to identify the chilling and heat accumulation periods for
apple flowering． We evaluated the impacts of temperatures during these periods on apples’flowering．
Our results showed that the chilling accumulation period of apple trees in the examined sites startedat October 1，ended in late February or mid-March，with chilling accumulations of 74．1－89．3 CP
(chill portion)． The heat accumulation periods were from late January to the first flowering dates
with the heat accumulation of 4010－5770 GDH (growing degree hour)． The chilling accumulation
at Xifeng and Akesu was correlated positively with mean temperature during the respective accumu-
lation period，with 3．8 and 5．0 CP enhancement following 1 ℃ increase during the accumulation
period． Heat accumulation at all stations correlated positively with mean temperature during the
respective accumulation period，with 725－967 GDH enhancement following a 1 ℃ increase during
the accumulation period． Compared to the effects of chilling accumulation on tree flowering，the first
flowering data of apples in the main planting areas were mainly affected by mean temperature during
the heat accumulation period． Climate warming is beneficial for apple blossom and production in the
areas with low mean temperature during the chilling accumulation period．
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