GENETIC-VARIATION IN THE DATE OF BUDBURST IN SCOTTISH BIRCH POPULATIONS - IMPLICATIONS FOR CLIMATE CHANGE

To estimate the heritability of budburst, seedlings from up to 10 birch trees at each of 10 sites in Scotland (seven of Betula pubescens Ehrh. and three of B. pendula Roth) were grown together in a randomized field experiment near Penicuik, Scotland (55-degrees 51 'N, 198m). Using a nine-stage scale, budburst and leaf elongation were assessed in late April 1984 and 1986. Heritability of budburst varied from 0.00 to 0.65. The potential for dates of budburst to evolve within birch populations in response to climatic warming depends on the amount of additive genetic variation and on the rate at which the environment is changing. The selection differentials needed for populations to change in response to climatic warming of 2-degrees-C over a period of 60 years show that, even in the most genetically variable populations, the rate of change in temperature (assuming an increase in mean annual temperature of 0.7-degrees-C every 20 years) is too rapid for native populations to evolve in the absence of gene flow from birch populations with earlier dates of budburst.