Betula pubescens is the most common treelike birch in Finland. Its typical growing sites are peatlands and other wetlands. At the moment there is a great demand for birch for raw material in paper industry. It is also popular as fuelwood. The vegetative regeneration, ecology and growing methods of Betula pubescens have recently been under seveal studies (Ferm 1989, Kauppi 1989). However, our knowledge of the development, biomass production and decay of Betula pubescens coppice stands is still poor. The sprouts of Betula pubescens are usually regarded as decayed, although there exist no investigations on the topic. Altogether the decaying process of young birch stands has been very little investigated. The development of the height and diameter of the sprouts in five young (9-23-years-old) Betula pubescens coppice stands (Table 1, Fig. 1) was investigated by means of stem analyses (64 sample trees). Decay was determined by means of 274 felled sample trees (Table 2). Roots were also included in the investigation. The branch and stem dry mass and the average annual dry mass production were measured in four stands. The field work was carried out in North Karelia in 1981. The height and diameter development of Betula pubescens coppice stands were in the most advanced stands better than the development of natural normal Betula pubescens stands (Figs. 3 and 4, Table 3), but owing to the small number of stands the result cannot be generalized. There were also considerable differences between the stands. The average branch and stem dry mass of coppice stands was 54 t/ha, the branch proportion of which was 19% (Fig. 5). The mean annual production was 3.1 t/ha. The best production was in stands on nutritionally good sites. There are signs that the biomass production of birch coppice stands would, at the age of 15-20 years and after, fall behind seedling thickets. Butt rot was encountered in 54% of the measured sprouts (Table 4). The results remain within the range that has been earlier observed in peatland birch stands. The decaying process was most severe in the oldest stand (Fig. 6). The average diameter of the decayed area of the affected trees was 1.0 cm (Table 4, Fig. 6) and height 112 cm (Fig. 7). The origin of decay was in most cases unknown (Table 5). In one fourth of the cases the origin of decay was in roots or the parent stump i.e. decay may have been caused by coppicing itself. An average of 4.9% of the cross-sectional area of roots had decayed. Especially in the oldest stands root decay was, however, noticeably abundant (Fig. 8). This may result from several sprouting cycles and be a symptom of an overall poor shape. The averae proportion of old roots i.e. the roots of the parent tree was 19.9% out of all the roots at the tree base, although variation was considerable.
