Wednesday, January 30, 2008

Bumps, galls and bulgy hips.

Seen very close, hands and soggy knees close, a bog is a fascinating place of multi-coloured mosses, small, berry-bearing plants and sundews.

Sphagnum, bog blueberry, bog laurel, Labrador tea.

From far away, it can appear a lush pine forest.

It’s the in-between distance, the familiar walking-around inside it distance, where the bog might seem somehow disappointing. Everything is a small, scrawny, bent, a reflection of the nutrient-poor, acidic soil. In bogs in this region the dominant tree is the shore pine, Pinus contorta, which is definitely not the conifer you think of when you imagine the majestic rainforests of the Pacific Northwest. These pines are not only small, they are usually to some degree and in some way asymmetrical, often with flattened bulges in their trunks and dead and dying branches decorated with egg-sized swellings. This is a challenged forest, and diseased, too.

The culprit for these arboral imperfections is a very common rust fungus, known here as western gall rust, Endocronartium harknessii, although it also occurs in the east, where it is called something else (hence the usefulness of Latin names).

The western gall rust is a fungus of the “hard pines,” those with needles in clumps of two, and will also infect ornamentals such as Austrian and mugo pine. In late spring or early summer, under the right temperature-moisture regime, its airborne spores penetrate the thin-skinned covering of new growth. Over a few years, the fungus will grow and cause the surrounding wood to hypertrophy, producing egg-like galls on young stems and branches.

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.

Galls on branches and hip canker on trunk.

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.


Camera Trap Codger said...

Interesting post. I've been wondering about those galls, and sometimes burn them as kindling. I've also been meaning to section and sand one to see what the diseased wood looks like (though it will mean sacrificing a sanding belt). From what you've said the galls don't sound promising as sources of 'esthetically twisty wood figure'.

A Local Naturalist said...

No, I doubt they would provide the desired result. I've never cut one open, but I expect they would be crumbly and cavity-ridden.