I have just started making wedding cakes for friends when they ask me. I offered to make on for a couple at our church and she wanted a rustic tree stump wedding cake, but did not want it done in fondant. I actually found it a lot easier to do in buttercream.
This cake is done with a 14 inch, 10 inch, and 6 inch cake. All three tiers were a double layer of cake put together with buttercream frosting in between.
The 14 inch cake was put on a 16 inch thick cake board. I hot glued dark brown ribbon around the edge. The second two tiers had a thin cake board the size of the cake. To start with I made butter cream colored with ivory food coloring. I used this to fill in the cracks in between the cake layers and frosted the tops with it. To paint the tree rings on top I used a 1 inch wide clean paint brush dipped in ivory gel food coloring. I just dipped it once for each ring which gave it the blended effect.
For the bark on the sides of the cake I colored the buttercream with black and chocolate brown gel food coloring. It gave it a nice earthy gray color that was perfect for the bark of the tree stumps. To apply the frosting I just used a small frosting spatula and applied it from the bottom going up in rows. What is nice about doing a tree stump is you want lots of texture. Just let the frosting do it's thing!!