Dollar Tree has promoted a key executive as the discounter continues its rapid expansion.

The retailer, which plans to open 650 stores in 2017, has promoted Michael A. Witynski to president and COO of its Dollar Tree division. Witynski will be responsible for merchandising, marketing and store operations for Dollar Tree stores in the United States.

A Dollar Tree veteran, Witynski has served as COO since July 2015, and he previously served as senior VP of stores…