The fungi in this genus have been found throughout extremely large land areas. My point is that they seem to be everywhere, just waiting for the right conditions to attack. Just as the sun and the cold are triggers for other problems, so it is with Armillaria species. The gun must be loaded or in a state where the trigger, once pulled, will set it off. Again, low defense is the condition for infection.
Roots have many branch roots, just as trunks have many branches.
As described briefly above, there is a protection zone at the base of branch roots just as in trunk branches. When energy reserves are low, the protection zones are weak. Roots in forests where no human activities have gone on for many years still have many wounds. As roots squeeze against each other, dead spots and cracks may form. As roots squeeze against rocks, the same type of wounds may occur.