Date of Budburst of Fifteen Tree Species in Britain Following Climatic Warming

(1) The thermal times (T) (day 'C > 5 'C since 1 January) to vegetative budburst were measured on fifteen woody perennials in Britain after different durations of chilling (C) (number of days < 5 'C since 1 November). (2) Late-flushing species, like Fagus sylvatica, had high values of T, even after 145 chill days, and T increased greatly with decreased chilling. Early-flushing species, like Crataegus monogyna, had small values of T, which did not increase much until there were fewer than 80-100 chill days. (3) Relationships of the form T= a + b exp (r C) were fitted for each species, which were then classified into five groups. Past meteorological records were then used to estimate the mean dates of budburst of each group of species at Edinburgh (26 m altitude) and Braemar (339 m) with 0-3 'C uniform climatic warming. (4) Climatic warming did not markedly shift the date of budburst of any group of species at Edinburgh, so they flushed in warmer conditions and failed to exploit the earlier springs. However, at Braemar, the species with small thermal time and chilling requirements, like C. monogyna, flushed much earlier following climatic warming.