The Forestry Forum

I have heard that a tree that is leaning too much is under so much stress that it is no good for timber.  Is there any rule of thumb (like 30% for example) after which it is not practical to try to make boards out of a leaning tree ?

Makes a fine keel. 

Honestly the answer is "it depends".  Species, why it's leaning, how big it is and what you are trying to get for lumber.  Adjusting what you saw from it might fix the issue - ie shorter, narrower, or quarter sawn, to help overcome the stress issues.  1x12 - 18' lumber, not so much.  

 
 This is the butt end of a slash pine that had a little, not much lean to it.  The pith was much more centered on the top end of the log.  This was a 16' log with some sweep so I cut it into two 8' ers.  I cut full 2"x10's out of it and got 10 1/2 plus some 1"x side lumber. The boards looked good coming off the mill and have been cut into 4' pieces for axe targets (the reason for the 2x10x4).  The cant was sawn to the bed with the log rotated 90° from the way it is pictured. 

(https://forestryforum.com/gallery/albums/userpics/22883/8CB35D6B-0E0A-41A5-8EF3-812F393A142E.jpeg?easyrotate_cache=1624798675)
 

Absolutely.  The side lumber could have a mind of it's own, but that was not the targeted yield.