The mushroom is the part of a fungus that shows; the rest is already in the wood or the soil.

NC State Extension's gardener handbook defines a mushroom as a soft, stalked fruiting body and a conk as a tough, often shelf-like one from standing, fallen or buried wood, a "Sign of wood decay in progress." The fungus's threads, the handbook says, grow through soil or plant tissue and group together at some stage to make the conk or mushroom, so the threads come first. The useful question about a mushroom near a tree is what its fungus grows in.

On the tree itself, the sources read a fruiting body as decay. The USDA Forest Service guide to hazardous tree defects says "mushrooms, conks, and brackets growing on root flares, stems, or branches are indicators of advanced decay." The root flare is where the trunk widens into its main roots, the buttress roots, and the handbook calls decay "especially critical when buttress roots are involved."

Out in the lawn, the sources mostly read mushrooms as decomposers. Lee County's Extension center says the fungi behind turf mushrooms break down "buried wood, old tree roots, or thatch," Pender County's center finds mushrooms in mulch and where trees were removed, and the handbook says most mushrooms "are mycorrhizal or are secondary decomposers," mycorrhizal meaning partnered with tree roots.

Right at the trunk, the two readings meet: Richmond County's Extension center says Armillaria root rot is commonly recognized by honey colored mushrooms, which can be found in clusters at the base of infected trees.

Armillaria is the one mushroom genus the handbook calls a plant pathogen, and Richmond's center says it feeds on tree roots and trunks, "increasing their likelihood to fall." Extension's guide to ash diseases adds Ganoderma root rot, "red to brown shelf-like fungi" often at the base, whose decay spreads into the base and roots, and Laetiporus, yellow to orange shelves on the main trunk from a rot that starts in the heartwood.

Roots tie these rots to a tree's hold on the ground. The NC Forest Service says some root pathogens attack "the larger structural roots that stabilize trees," and Henderson County's Extension center says a blown-over tree often "seems to flop out of the ground without a structural root intact." The ground's own warnings are read on lifted or cracked soil at the base of a tree.

Mushrooms follow the weather: Richmond's Extension center says they tend to pop up after rain on warm days, Lee's says they typically disappear as the weather dries out, and Richmond's adds that Armillaria's mushrooms do not always appear. Pender County's center says removing the visible growth "does not get rid of the fungus because the majority of its body is left behind."

No page read for this guide measures how far decay reaches from the mushroom. Decay behind sound outer wood is traced in dead and rotten trunks and the crane, and a hollow with insects in it has its own page, sawdust and carpenter ants below a tree.

The home page's fence-line check labels mushrooms at the base "Worth a call," its general reading of the sign: a fruiting body shows a fungus at work, not a tree in motion. Henderson County's Extension center is firmer: it says to call an arborist when fungal growths appear on a tree, and that a professional arborist can determine whether the tree needs to be removed. The USDA guide lists advanced decay in the root flares among its reasons to take action.

A look at the tree takes in the root flare, the soil, any lean, and what stands within its reach, the pairing of a defect and a target at the center of the hazard tree field guide. If the tree comes out, that is tree removal, and in the home page's steps the crew looks at it with you before any work starts.