Final answer:
In an African drumming ensemble, it is usually the drummers who are allowed to improvise, adding their unique expression to the performance.
Step-by-step explanation:
In an African drumming ensemble, typically, the drummers are allowed to improvise. The drummers play a variety of rhythms and patterns that can be altered or improvised upon while maintaining the core rhythm of the piece. It's worth noting that improvisation does depend on the style of the ensemble and the piece being performed, but generally, drummers, especially the lead drummer, have the freedom to improvise as a form of expression and interaction with the other musicians.