Dibs!

Often in nature the line between saprophytic (decomposing) fungus and parasitic fungus is blurred, with some mushrooms being classified as "facultative parasites," which means that they will move in on a sickly tree and finish it off. They will kill the tree and then decompose it.

However, the line between saprophytic fungus and mycorrhizal fungus is also often blurred. Many species of mushroom are endophytic, which means that they actually live within the tissues of the tree, helping it survive. Some of those are also decomposing mushrooms. Elm oyster mushrooms (Hypsizygus ulmarius) have been shown to increase the growth of garden vegetables that they are growing with, even though they are primarily a decomposing mushroom.

Maybe that's just nature's way of calling dibs.