As near as I can tell, there are two types of ripple/curl. One is reaction wood where it reacts to stresses in the tree like the compression wood under where a branch comes in to the main trunk. Think of it as doing an accordion thing so the fiber can stretch and compress as the wind causes swaying. There is almost always similar compression in the buttress part of the tree where the trunk angles out away from the main part for support. Crotch figure can do the same thing. Trees growing on the side of a hill do have stress, but from talking to an old logger, they need wind as well to develop that type of ripple. Now, the other type, which I think of it being more the quilted type and bigger wave type of ripple seems to have a lot of genetics behind it. If nothing else, some will tend to have it more than others, and it can be pretty consistent along a very long trunk rather than just in spots. Birds eye (not the spots in burl, but the dimples that look like percussion cones) that is found mostly in maple, seems to be genetic, but when they take cuttings/clones from the parent tree, some develop the birds eye, some don't. I read a fascinating article about it in an old Fine Woodworking magazine. The only common thing was that all that had it were 'stressed' trees. So, some times it is genetic, some times nature, and some times, just because.... Like a couple of big crotches I got. One was a walnut. The branches were 20 inch diameter. No feather at all, and I mean none. It was deep in a valley, and surrounded by big fir trees.

robo hippy