ISHS Acta Horticulturae 168: II Symposium on Winter Hardiness in Woody Perennials
THE TIMING OF HARDENING AND DEHARDENING OF FOREST TREES |
| Author: | V. Koski |
| Abstract:
Frost damages are uncommon at autochtonous tree populations, because only properly adapted genotypes have survived. Man's impact on forests in form of geographic transfers, selection for improved growth rate, production of seedlings in favourable nursery conditions, fertilisation etc. has sometimes resulted in frost damages. Even origins from very severe climate have in some cases suffered from repeated frost damages when growing in a milder climate. The capability of tolerating low temperatures as such does not mean winterhardiness. Low temperatures both prior to hardening and after dehardening are harmful to trees. Thus the timing of hardening and dehardening is a crucial component of the climatic adaptation. If the temperature factor would follow as regular pattern from year to year as the photoperiod, the annual fluctuation of frost resistance could be simply derived from the alternation of the photoperiod. Temperature data from meteorological statistics display a conspicous variation between years in the occurence of late frosts, in the beginning and termination of the thermal growing season or any characteristics of the temperature factor. The avoidance of cold damages must be a fundamental goal of forest tree breeding and forest management. Thus the natural fluctuation of frost resistance and particularly the mechanism of the timing of hardening and dehardening are important research objects. The purpose of the experiments introduced in this report was: 1. To monitore the general pattern of the frost hardiness throughout the year for Pinus sylvestris, Picea abies and Betula pubescens and 2. To follow whether the timing of hardening and dehardening is consistent from year to year relative to time. These tests are a part of a comprehensive investigation on the annual rhythm and climatic adaptation of forest trees. | |
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