That looks like a pine slab. Maybe loblolly? It does indeed show rapid growth in the earliest years and then shuts down pretty quickly. Then it opens up (wide rings) for a number of years and then slows again. What I see is modern forest management. Trees were free to grow until the canopy closed and the rings got quite compacted. Then somebody selectively harvested the forest and left that tree standing. That's the second set of wide rings. Then the canopy closed again and the rings narrowed.

But you know what? IT could be any number of things. It could be that the tree grew up next to an impervious surface (driveway, road, etc) and struggled for water and nutrients as it got older.

Or maybe it was climate cycles.

Etc.

This is why the dendrochronologist should take numerous cores off several trees of the same apparent enviro circumstances and of the same species. Depending on a single sample to drive interpretation is a waste of effort.