Autumn Frost Damage on Young Picea sitchensis 1. Occurrence of Autumn Frosts in Scotland compared with Western North America

Abstract

Dates of first autumn air frosts (in Stevenson screens) of −2.5°C and 4.5°C were obtained for 42 meteorological stations in northern Britain with runs of 18 to 116 years. Frequency distributions of first frost dates were approximately normal. Altitude, distance from the sea, latitude and distance from the NWSE axis of Britain together accounted for 75% and 81% of the variation in dates of first −2.5°C and −4.5°C frosts, respectively, at the 42 stations. The variance in dates of first frosts decreased from lowland coastal to upland inland sites. Multiple regressions were used to produce maps of first frost dates in 20 × 20 km grid squares of Scotland. Dates of first 28°F (−2.2°C) and 24°F (−4.4°C) frosts were obtained for 20 sites in western North America, spanning the natural range of P. sitchensis . Mean dates were earlier, and variances decreased, from south to north. Upland sites like Eskdalemuir and Kielder Castle experience –2.5°C and −4.5°C frosts earlier in the autumn than all coastal stations in western North America south of about latitude 58°N (between Cordova and Sitka), and about 4 weeks earlier than at Masset on the Queen Charlotte Islands. Thus, P. sitchensis from Q.C.I. and further south may often experience autumn frosts in Scotland before the trees have experienced the cool/short days that they require to induce frost hardening.