Seasonal Changes in Phenological Traits and Cold Hardiness of F1-populations from Plus-trees of Pinus sylvestris and Pinus contorta of Various Geographical Origins

Abstract

A 3 yr phenological study of six F1-populations from plus-trees of Scots pine (Pinus sylvestris L.) from 61 to 68° N and five F1-populations from plus-trees of lodgepole pine (Pinus contorta var. latifolia Engelm.) from 55 to 63° N was performed in a Swedish field trial at latitude 64°15' N. Lodgepole pine generally dehardened slightly earlier in spring, and had earlier onset and later cessation of shoot elongation than Scots pine. Early onset and early cessation of shoot elongation were more closely 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 to 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° of latitude more northern origin. With respect to timing of dehardening in spring, shoot elongation rhythm (excluding growth cessation), cold acclimation (cold tolerance) in the autumn and winter cold hardiness, lodgepole pine from above 60° N appears phenologically as adapted to the climate of the test site on latitude 64° N as the recommended Scots pine from latitude 66° N. However, later growth cessation, lower dry matter content and needle attachment in the autumn, and possibly a greater tendency to deharden occasionally in late winter indicated poorer adaptation of these northern lodgepole pine populations.