Date of budburst of fifteen tree species in Britain following climatic warming.
Accumulated day-degrees >5°C since Jan. 1 to vegetative budburst (T) after various durations of chilling (days ≤5°C) since 1 Nov. were measured for 15 woody perennials. The species were classified into 5 groups with decreasing values of T: (1) Fagus sylvatica; (2) Robinia pseudoacacia, Tsuga heterophylla, Picea sitchensis; (3) Rubus idaea, Sorbus aucuparia, Betula pendula, Corylus avellana; (4) Sambucus nigra, Rosa rugosa, Salix viminalis, Larix decidua, Prunus avium; and (5) Populus trichocarpa, Crataegus monogyna. Late-flushing species (1) had large values of T even after 145 chill days, and T increased greatly with decreased chilling. Early-flushing species (5) had small values of T which did not increase much until there were fewer than 80-100 chill days. It is concluded that climatic warming in the UK would not markedly shift date of budburst of most woody species at lowland sites, but at upland sites, species with small chilling requirements (3-5) would flush earlier and benefit from a longer growing season.