Climate change has affected the rates of chilling and heat accumulation, which are vital for flowering and production, in temperate fruit trees, but few studies have been conducted in the cold-winter climates of East Asia. To evaluate tree responses to variation in chill and heat accumulation rates, partial least squares regression was used to correlate first flowering dates of chestnut (Castanea mollissima Blume) and jujube (Zizyphus jujube Mill.) in Beijing, China, with daily chill and heat accumulation between 1963 and 2008. The Dynamic Model and the Growing Degree Hour Model were used to convert daily records of minimum and maximum temperature into horticulturally meaningful metrics. Regression analyses identified the chilling and forcing periods for chestnut and jujube. The forcing periods started when half the chilling requirements were fulfilled. Over the past 50 years, heat accumulation during tree dormancy increased significantly, while chill accumulation remained relatively stable for both species. Heat accumulation was the main driver of bloom timing, with effects of variation in chill accumulation negligible in Beijing's cold-winter climate. It does not seem likely that reductions in chill will have a major effect on the studied species in Beijing in the near future. Such problems are much more likely for trees grown in locations that are substantially warmer than their native habitats, such as temperate species in the subtropics and tropics.
1.Chinese Acad Sci, Kunming Inst Bot, Ctr Mt Ecosyst Studies, Kunming 650201, Yunnan, Peoples R China 2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China 3.Chinese Acad Sci, Inst Geog Sci & Nat Resources Res, Beijing 100101, Peoples R China 4.World Agroforestry Ctr, East Asia Node 650201, Kunming, Peoples R China 5.World Agroforestry Ctr, Nairobi 00100, Kenya
Guo,Liang;Dai,Junhu;Ranjitkar,Sailesh;Yu,Haiying;Xu,Jianchu;Luedeling,Eike.Chilling and heat requirements for flowering in temperate fruit trees,INTERNATIONAL JOURNAL OF BIOMETEOROLOGY,2014,58(6):1195-1206