[Carry_Okie]

While some fire experts expressed skepticism about a six-day reignition,

There are a lot of factors involved: species, size, soil, depth of root, etc. but I've seen roots from a substantial Douglas Fir stump smolder for several days almost 20ft away.

[HartleyMBaldwin]

When I worked for the Forest Service, I saw more than one time that a buried log from winter slash burning would smoke up during the summer, sometimes over 6 months after the original burn.