© 1985 by Institute of Chartered Foresters
Autumn Frost Damage on Young Picea sitchensis 2. Shoot Frost Hardening, and the Probability of Frost Damage in Scotland
Institute of Terrestrial Ecology, Bush Estate, Penicuik, Midlothian Scotland
The natural increase in frost hardiness of detached shoots of Picea sltchensis during August to November was measured using a programmable freezing chamber. Oregon, Queen Charlotte Islands and Alaskan provenances were compared, and the effects on hardening of long days, warm temperatures and frosts were determined. A computer model was constructed to mimic the observed patterns of autumn frost hardening, as functions of air minimum temperatures, daylengths and the occurrence of frosts. The model was used (a) to describe the pattern of autumn frost hardening at different sites in northern Britain, using past meteorological records, and hence (b) to determine when frosts occurred that might have damaged young trees. The model accurately predicted known instances of autumn frost damage at Kirroughtree and Carnwath.
The predicted probability of autumn frost damage on young trees of P. sitchensis in upland areas of Scotland was much lower than that previously predicted for spring frost damage. The estimated return time for autumn frost damage to an Oregon provenance at Eskdalemuir was 8.3 years, and the return time for a Q.C.I. provenance was longer than 10 years. Most damaging frosts occurred in October, but frosts like those on 13–15 October 1971, which followed warm weather and caused wide spread damage in Scotland, have been quite rare. Alaskan provenances would rarely be damaged by autumn frosts, nor would trees of Q.C.I. provenance growing in lowland areas of Scotland, or at Masset on the Queen Charlotte Islands.