Rätt björk på rätt mark : Visuell identifiering av naturligt föryngrad björk

Sammanfattning: The silver birch (Betula pendula Roth) and the downy birch (Betula pubescens Ehrh) are the most common broadleaved species in Swedish forests. Both species have a lot in common in appearance and are often misleadingly referred to simply as ”birch”. They have however different requirements and possibilities to grow on different sites. Downy birch grows well on moist and wet sites thanks to the fact that its roots are adapted to these type of environments. Silver birch has on the other hand the ability to grow on dry sites. Both species prefer soil moisture class somewhere in between wet and dry.   To be able to promote the correct birch species on each site, it is important to identify the two species during the clearing process. Both buds and shoots are characteristic for each species why those parts can be used to separate them. Buds from silver birch are pointy shaped and those from downy birch are round shaped. When it comes to shoots the silver birch has nubby shoots and the downy birch has hairy shoots.  The aim of this study was to a) investigate the occurrence of each of the two birch species on sites with different soil moisture class, b) investigate if it was possible to visually identify each species during clearing with a clearing saw and c) to find out if and how the height of the stand influenced the possibility of species identification. This study shows that it is possible to identify the two species. It is however important to start the clearing process at an early age, since the parts of the tree used for identification otherwise will grow beyond sight.  This is particularly important on moist sites, where both birch species regenerate willingly. In the long run, downy birch will have higher ability to develop high quality timber on these sites. In order to do that, the right stems must be chosen at each clearing occasion. It is important to start the clearing process at an early age, since the characteristic parts of the tree otherwise will grow beyond sight.  Keywords