Kevin,
I used a pattern to get that effect. My pattern was actually a flat diamond sharpener that my kids broke. The metal section with the cutout ovals. I'm sure that you could find or make a pattern that would work.
I lighlty sanded the limbs, then primed them. I sprayed the whole limb a light tan. Then, I used the template and worked down the limb with a light green. After that dried I repeated the process with the template in tan. I moved the pattern over to get an overlapping effect. When I pick up more paint I'm going to finish it out to get a slightly darker look. I might even mask off the template into a "V" pattern and make it look like a rattler skin.
If that doesn't make sense I'll see if I can post some pics of how I did it.
Chris