Sprouting of 2- to 5-year-old birches ( Betula pubescens Ehrh. and Betula pendula Roth) in relation to stump height and felling time

Abstract

Naturally regenerated 2- to 5-year-old pubescent birches ( Betula pubescens Ehrh.) were cut monthly during 1983. Three 2–3 m high birches per month were cut with 0-cm and three with 10-cm high stumps in each of five blocks giving a total of 15 birches per stump height per month. The birches were located at Latitude 60° 15'N and Longitude 16° 00'E. Four-year-oldsilver birches ( Betula pendula Roth) planted on a nursery field located at Latitude 60° 25'N and Longitute 14° 35'E were cut on 10 dates, between 19 June and 21 August 1986, with 10-cm high stumps. Four blocks with seven replications, totalling 28 stumps, per cutting period were used. The stumps were measured annually and after 5 years. The number of living stumps and sprouts, and also the dry weight of sprouts and leaves were measured. The number of leaves and the leaf area were also registered. Carbohydrate concentration in roots of stumps and undisturbed plants was analyzed. After s further 5 years 90%, 10-cm high pubescent birch stumps were living, compared with 78% on 0-cm high stumps. Most living 0-cm high stumps were found after cutting in February, March, and May and in April, May, September and December on 10-cm stumps. The lowest number of living stumps was found in October at both stump heights. On silver birch the highest number of living stumps (64%) was found on 19 June and the lowest number on 21 August. The mean number of sprouts per living pubescent birch stumps varied little; 1.4–2.6 on 0-cm and 1.3–2.2 on 10-cm high stumps. Most sprouts occured in stumps cut in October (2.6) for 0-cm and in August and October (2.2 and 2.1) for 10-cm high stumps. Silver birch stumps produced most sprouts per living stump (1.9) at 19 June and 14 August and fewest number (1.2) at 21 August. There were no significant differences in sprout height in different cutting periods betweet 0- and 10-cm stump heights. Significant differences were observed in diameter at 10 cm height of pubescent and silver birch sprouts between cutting periods. There were significant differences in dry weights of pubescent birch sprouts growing on both 0- and 10-cm high stumps. The same pattern was observed on silver birch. No real trend in starch level between cutting periods was found pubescent birch roots. Some practical implications are given for biomass production after cutting at various periods during the year. Many vigorous sprouts, used as a shelter, are an excellent way to avoid damage by frost on young Norway spruces. The best period for cutting is in May–June when the sprout growth is highest and there is no risk for frost damage on the young birch sprouts. When a high biomass production is desired cutting during June–October must be avoided as the fewest number of sprouts is produced at that period.