It is very common in sycamore and in western larch, particularly in the butt portion.

Its occurrence is most frequent at the junction of two growth layers of very unequal thickness.

Consequently it is likely to occur in trees which have grown slowly for a time, then abruptly increased, due to improved conditions of light and food, as in thinning.

Old timber is more subject to it than young trees.

The damage is largely confined to the butt log.