Effects of Altitude on Growth in Ecotypes of Mountain Birch (Betula pubescens Ehrh.) and Iowland Birch (Betula pendula Roth.)

1993

30 S.

48 Lit. Ang.

Unselbständiges Werk

200037956

Seedlings of mountain birch (Betula pubescens Ehrh.) and lowland birch (B. pendula Roth.) were grown during two seasons in fertilized peat at two different elevations in western Norway (50 and 450 meter). Large differences occurred between various populations regarding growth rates and climatic adaptation. Seedlings from a local mountain birch population from West Norway were most successful at the high-elevation site in terms of annual production and had the highest carbohydrate/nitrogen (C/N) ratio, while the lowland birch population and lowland populations of mountain birch showed the highest growth rates at the low-elevation site. The C/N ratio in these plants, however, was very low. It is concluded that the survival strategy is different at the two sites. At low-elevation sites the competition factor seemed to be the main selective force and the most fast-growing plants were the most successful, while at high elevation abiotic factors came into account, and a high source strength rather than high growth rates seemed to be most important for plant survival. Chemical analysis of annual stem tissue showed that all birch populations increased their concentration of soluble sugars, soluble proteins and organic phosphorus in winter as a response to frost hardening, the highest concentration was found in subarctic and -alpine populations.