Plants protected from burns around the bases of trees

I find it interesting that a number of plant species get an early start by growing in the bare zone around the bases of trees, especially our large oaks. There is always a bare area around these big trees. Because there is little or no fuel here, there is no fire. Away from the tree bases, plants that had already started to grow at the time we burned are knocked back. They aren't killed, but if their leaves are already up, they have to start over again. But since fire doesn't penetrate near the tree, plants can get a head start.

One of the woodland species where this phenomenon is obvious is zig-zag goldenrod (Solidago flexicaulis), as the two photos here show.

This plant is especially interesting because it is one of the "first" plants to appear in our savannas, but it is one the "last" plants to flower and set seed. Generally, it doesn't flower until October.

I assume that it is a classical "short-day" plant, and is inhibited from flowering by long days. Only after the day-length starts to decrease in the late fall, is it triggered to flower. (There is an interesting plant physiology among short-day plants that is worthy of study.)