I've done a couple birch cakes with swiss meringue BC in the past.. here's how I did the cake posted below.

1. I did a crumb coat of SMBC and let it set in the fridge.
2. I made very rough vertical blobby lines of grey and white SMBC alternating around the cake.

3. Using a pallet knife I had to smooth that out with swirly/ stucco texture producing sweep like motion (hard to explain) which created the tie-dye-ish look of the bark.. then back to the fridge.

4. then with a dark grey/brown/ black SMBC I made the horizontal lines as thin as possible using a parchment paper cone piping bag.
5. With a semi-solid chocolate ganache mixed with grey/brown/green SMBC I created the lumpy "eye" bits of the log by using a small pointed offset spatula/ pallet knife to create shape and texture I wanted.
6. The top rings (which aren't necessary but I like the extra detail) I made by scrunching up brown paper towel and gentle pressing it onto the top of the chilled cake and spinning the cake stand at the same time (you could use a cake comb too but wouldn't get the different depths that make it look more authentic).

So basically its just a lot of layering of icing and playing with different techniques and textures. =)