Anatomy, basic density and shrinkage of birch bark

Abstract

Some structural features, basic density and transverse shrinkages of bark were studied in Betula pendula Roth and B. pubescens Ehrh. Average values for the thickness of double inner bark (secondary phloem) and double outer bark (rhytidome), basic density and radial and tangential shrinkages are presented. Withinspecies variation was found to be least in basic density and highest in bark thickness of both species. Bark of B, pendula is thicker and heavier than that of B. pubescens. Bark thickness mainly depends on height level and diameter of the stem. It decreases steeply from the butt end up to 2 m height and then more slowly towards the top of the trees. The logarithm of height level explains about 72.5 per cent of the variation in total bark thickness in B, pendula and 55.8 per cent in B. pubescens. Correlation coefficients are given to elucidate the relationships of inner, outer and total bark thickness to basic density and radial and tangential shrinkages. No consistent relationships were found, although some of the correlation coefficients are statistically significant.