Seasonal changes in phenological traits and cold hardiness of F1-populations from plus-trees of Pinus sylvestris and Pinus contorta of various geographical origins

A 3 yr phenological study of six F1-populations from plus-trees of Scots pi ne (Pinus sylvestris L.) from 61 to 68 degrees N and five F1-populations fr om plus-trees of lodgepole pine (Pinus contorta var. latifolia Engelm.) fro m 55 to 63 degrees N was performed in a Swedish field trial at latitude 64 degrees 15' N. Lodgepole pine generally dehardened slightly earlier in spri ng, and had earlier onset and later cessation of shoot elongation than Scot s pine. Early onset and early cessation of shoot elongation were more close ly related to a northern latitude of origin in Scots pine than in lodgepole pine. Frost hardiness, needle dry matter proportion, and needle attachment to current year shoots in late summer and autumn were positively related t o the latitude of origin in both species. Freeze tests showed that the cold acclimation rhythm of lodgepole pine in the autumn was comparable to that of Scots pine of 5-9 degrees of latitude more northern origin. With respect to timing of dehardening in spring, shoot elongation rhythm (excluding gro wth cessation), cold acclimation (cold tolerance) in the autumn and winter cold hardiness, lodgepole pine from above 60 degrees N appears phenological ly as adapted to the climate of the test site on latitude 64 degrees N as t he recommended Scots pine from latitude 66 degrees N. However, later growth cessation, lower dry matter content and needle attachment in the autumn, a nd possibly a greater tendency to deharden occasionally in late winter indi cated poorer adaptation of these northern lodgepole pine populations.