I too have a birch bark tree cake to do too and have been wondering the same thing. I would love to read what others have to say.
I bought some black dusting powder and a light brown one but that is as far as I have gotten.
I'm thinking a dark brown or black base icing, then fondant over it and slashed gently with a knife to expose the dark underneath. Or do the slashes after rolling it out but before covering the cake -- though the heart would probably stretch out of shape doing that.
this is just thinking out loud, never actually tried anything like that....
to me it looks like it is simply dark fondant that has been cut and shaped and then a large dry brush has been used to cover it in lustre dust or something like that so that it only sticks to the sticky-out bits and doesn't colour the indents.
I have never done this; it's just my opinion from the pic!
There is another forum with this cake. If you search you may find it.
If you look for a forum on here titled "How to Make Birch Bark on a Cake" you'll find some good references for doing bark on a cake.
Did you manage to get the effect you desired for this cake? I've recently had someone send me this exact picture asking me to make this for their wedding, I'm slightly nervous as I have no idea what so ever how I'm going to achieve this effect without looking terrible - there are some really bad copies out there :(
AKind of. It didn't turn out anything like it in the end, but the Bride & Groom were very happy. They didn't want it in the same colours, so it's gonna look different, but trying to get the effect was definately a challenge![ATTACHMENT=1526]TreeBarkCloseUp.JPG (1,212k. JPG file)[/ATTACHMENT]