DEFENDERS magazine, Winter 1992/93
Seeking Meanings
Douglas H. Chadwick

[Excerpt]

My first clear glimpse came in Alaska's wild heart, on the edge of Denali National Park. It was a quiet encounter. No howling wolves. No grizzly bears. I was simply looking at trees. They were white spruce, and several had clumps of short, knotty branches. The cause was a rust fungus that invades the tree and produces a hormone that stimulates dense branching at the site of infection. More needles, more food for the fungus. The needles eventually die, leaving that part of the tree with a dry twig cluster known as a witch's broom.  

At it turns out, red squirrels like to nest and store food in witches' brooms. One of their favorite foods is a quite different fungus, a truffle-like species that grows underground. In the course of digging up the mushrooms, eating some and carrying others to their nests, the squirrels drop dung pellets full of spores, seeding the fungus across the forest floor.  

Mushrooms, remember, are only the fruiting bodies of certain fungi. The organism itself is mainly a web of long, thin threads spread through the soil. When those threads associate with the roots of a tree, they are called mycorrhizae. Nearly all trees support mycorrhizae, which in turn extract moisture and nutrients from pores in the soil too microscopic for even the trees' finest root hairs to penetrate. This is one of the most important symbiotic relationships in nature. The particular species of fungus spread by the squirrels forms the mycorrhizae that associate with white spruce. They are a key to its ability to survive on cold, nutrient-poor soils at the very northern edge of treeline.  

When you consider that the rust fungus requires a second host to complete its life cycle, and that this other host is the arctic huckleberry bush, a prime food source for grizzly bears, foxes, ptarmigans and an array of smaller birds and mammals, you can see that an odd-looking clump of needles on a white spruce is much more than an unfortunate case of blight. It is an intersection in an almost inconceivably wide and elaborate network of paths.  

Mowry: Red squirrels, flying squirrels, truffles and witches' brooms. (2008)

Phytoplasma-caused Witches' Broom on Peach

Mycorrhizae