Seen very close, hands and soggy knees close, a bog is a fascinating place of multi-coloured mosses, small, berry-bearing plants and sundews.
Endocronartium gall on young tree stem.
The fungus sporulates, the galls split open, looking like, well, a tree with poison oak, and the spores drift away in hopes of landing upon a new, thin-skinned stem. Western gall rust is an unusual fungus in that it spreads directly from pine to pine, lacking an unrelated intermediate host.
The galls on branches can eventually cause the distal portion of the branch to die and fall off, or, if the fungus has infected a trunk, a hip-canker can result.
Sporulating surface of hip canker. ("Sporulate" is flagged by the spell-checker. Imagine that.)
The hip canker will not kill the tree, although associated disruption of the bark may lead to secondary infections by other pathogens or insects, but the biggest threat is a local weakening of the trunk caused by irregular growth around the fungus. After strong winds, a walk through the bog will reveal toppled pines, and almost invariably the point of trunk failure with be at an old hip canker.
Wind damage: failure at hip canker.
In most cases the worst damage western gall rust causes is aesthetic, but this is not a problem unless you have unreasonable expectations of environmental neatness. The bumps, galls and hip bulges the western gall rust sprinkles through the pine forest enhance the floral strangeness of a bog, which is good. The bog would be a more tidy but less interesting place without them.