Development of suckers by two‐year‐old birch (Betula pendulaRoth) at different temperatures and light intensities

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Abstract
Two‐year‐old seedlings of Betula pendula Roth of three provenances were cut to stump heights of 0 and 10 cm. The birch stumps were exposed to different light levels (25–400 μEm−2s−1) and temperatures (6–24°C) for 100 days in climate chambers. Birches were also cut down to seven stump heights (0, 2, 5, 10, 15, 20 and 25 cm) and exposed to light intensity 25 and 200 μEm−2s−1 at 12/6°C for 100 days in climate chambers. In the third experiment 10 cm stumps of birch were exposed to different light intensities (10–400 μEm−2s−1) for 30 days in a greenhouse at 20°C. Starch content in root systems was analyzed before and after treatment. Ten stumps per treatment were used in the experiments except the third experiment where 15 stumps were used. The number of sprouting stumps was correlated with light intensity and temperature. None of the stumps exposed to 6 or 9°C produced suckers. At stump height 0 cm fewer sprouting stumps were produced than at 10 cm. The mean height of suckers was higher the higher the temperature both on 0 and 10 cm stumps. There were differences between provenances in height growth. The number of suckers per sprouting stump was not related to temperature or light intensity. Starch content in root systems of 10 cm high stumps was 4.0% compared with 14.7% in root systems of non‐stumped birch plants after 30 days in the greenhouse. Starch content decreased from 4.0 to 3.0% with decreasing light intensity (400–10 μEm−2S−1). The number of suckers and their mean height were correlated with starch content depending on light intensity.