I realized that the foam structure would not work as a suitable template for the wood exterior. I originally planned to join thicker pieces together as a shell, but instead decided to create a wood interior of bulkheads, with a thinner surface to create a more naturalistic surface.
Since my wood was not wide enough to get single template pieces from, I had to divide them into small pieces. 
The edges then need the saw marks removed and the edge squared up, in order to create a strong doweled butt joint. 
After drilling and setting the dowels in place, I needed a way to clamp them together, which was difficult due to the curvilinear nature of the shape.
I devised a way to bind the seam using two wood dowel passing through holes straddling the joint. Using jute twine, I was able to generate anough clamping force to create a stong bond. 
After only a couple of tries, I realized that I needed to spread the joining force over a wider area and to not drill such large holes in my structural supports. I switched to using four smaller holes and nails as anchors. Using a long peice of woven paracord to bind both sides, I generated an exceptionally strong clamping force. 
After joining about 60 individual pieces together, to create 15 solid tree sections, I was ready to assemble them using 6 foot long threaded rod (all thread), fender washers and nuts. 
I quickly realized that spinning the nuts down 6 feet of all thread will take a lot of time, so I experimented with belt-drive system on my drill to limited success. 
As it turned out, the "belt-drive" system proved to be unreliable. I opted for a direct-drive system using some self-adhesive rubber sheet, normally used as a sandblasting mask, applied directly to the drill's chuck.
Turns out that it's so fun to do that the kids joined in.
Layer by layer, the tree trunk begins to take form.
Now for the "simple" matter of covering it in five different species of steam-bent, custom cut wood strips.