This method is derived from techniques still in use in Scandinavia.
Bark from other tree species can be used but the best properties are still obtained from birch.

Make one or several holes in the bottom of a cake tin, with a dent to facilitate dripping of birch oil. Fill the tin with birch bark set vertically. Close the tin and leave it on top of another open tin set in a hole dug in the ground. Cover the lid with a stone and bring the earth around both tins. Build a log fire over the tins and let burn at least one hour, replenishing it with more wood, depending on the amount of bark.

Remove the embers and dig out the tins. Beware of the toxic and flammable smoke! If the conditions are right, a black oily substance should have collected in the tin. Leave the tin over the embers to reduce it to tar. This operation should be monitored because the transition from tar to charcoal is fast.

The hot tar can be coated on surfaces to affix. Once cold, it will set forming a strong bond.

Birch tar properties (from primitiveways.com)

It is alleged that birch tar has biocidal, antiseptic and pesticide properties; the oil (or birch creosote) is classified as a skin and eye irritant and is allergenic. The oil is used in many traditional cosmetics and medicines. However, the tar should not be very toxic to the environment (M. Hagner, O-P. Penttinen, T. Pasanen, Acute toxicity of birch tar oil on aquatic organisms, Agricultural and Food Science, Vol 19, 1 (2010)). (view document)