The period of rule of a monarch is known as a reign.
I have been trying to find the equivalent word for an earl (or other member of the nobility) to describe the period during which he held this title and was in charge of his landed estates. It would be used as follows:
During the [insert word] of the second earl, many improvements were made on the estate.
So far I have been unsuccessful in coming up with a word – is there an equivalent?