The aim of this study was to compare the sprouting ability of stumps of different diameters of downy (Betula pubescens Ehrh.) and silver (Betula pendula Roth) birch. The number of living stumps, and the number and height of sprouts were recorded annually and the biomass of the sprouts was calculated. Two hundred naturally regenerated downy and silver birches were examined. These were part of a commercial cleaning in late August 1983, which left 20-cm-high stumps. The experimental site was located on forest land in central Sweden (latitude 60 degrees 15'N, longitude 16 degrees 01'E). The stumps were categorised into four diameter classes: 10-19, 20-29, 30-39 and 40-50 mm. The site was examined in September of the year after cutting and on a number of occasions up to 9 years after cutting. The number of living stumps of each species was recorded. When the sprouts were 9 years old, their diameter at breast height was recorded. Then, the sprouts were cut and stems and branches were dried and weighted. After 1 and 9 years, the percentage of surviving downy birch stumps was 90% and 61%, respectively. The equivalent figures for silver birch were 82% and 55%. The number of sprouts per stump differed significantly between the species and the stump diameter classes. The greatest mean number of downy birch sprouts per stump (2.8 +/- 0.3) was for the diameter class 40-50 mm, and for silver birch sprouts (2.3 +/- 0.2), for the 30-39 mm stumps. The diameter at breast height, height and weight of individual sprouts 9 years after cutting were significantly different between downy and silver birches and the diameter classes. The mean downy birch sprout weight (1.00 +/- 0.01 kg d.w. stump(-1)) varied between diameter classes and the heaviest sprout weight (1.18 +/- 0.02 kg d.w. stump(-1)) was produced by 30-39 mm stumps. The heaviest silver birch sprout, 1.94 +/- 0.04 kg d.w., was also produced by 40-50 mm stumps. The mean weight was 1.55 +/- 0.05 kg d.w. The sprout biomass per living stump was significantly different between the species and the diameter classes. The mean sprout biomass per downy birch stump was 1.76 +/- 0.15 kg and for silver birch sprouts 2.19 +/-0.22 kg. Equations for estimating the aboveground biomass (stem+branches) from diameter at breast height were developed for downy and silver birch sprouts. (c) 2008 Elsevier Ltd. All rights reserved.