Are you kidding?
Sedimentation. Localized floods like the annual flooding of the Nile. Basically, anything that produces strata can produce polystrate trees if the trunks stand there long enough.
By the way, why do you ask and what is the relevance of the question?
Are you going to claim that conventional geology denies the rapid formation of any strata whatsoever?
This ought to be good.
**********************************
Edit:
Upon re-reading post 1, I realized I (like you, apparently) had missed where he EXPLICITLY DESCRIBED the non-catastrophic event that produced polystrate trees. I'm embarassed, as you should be.
[This message has been edited by zephyr, 11-18-2003]