From what I've read... Softwoods tend to start with a left spiral which changes to more vertical or right spiral as the tree matures. Hardwoods tend to start with a right and move towards a straight or left spiral.
From what I've worked with... I tend to, seem to, think, I have more trouble with lefties in softwoods. They are rarer, catch my eye and so I probably look at them harder.
What I speculate... in softwood the lefty is often a juvenile with all the troubles that accompany immaturity. Shrinking from duty in any direction possible, not able to hold up their end of a job, rigidly stubborn as all get out.
Restrictions on lefties is being written into log codes that are moving through the ICC in the last draft as I recall. Several authors have claimed a scientific basis for this. Mackie claims lefties are proven to be weaker and inferior. The grading instructor looked at me like I just fell off the truck when I asked there. I have asked if anyone knows of this research to back up what is being written into law. Thus far I haven't seen any. As I said, I'm not sure I disagree, just would like to see some backup.
Whenever lefties and righties come up I think of gums and elms and other interlocked grains. The tree grows righty for awhile, then lefty, then back again. I guess it depends on when you fell it
