Matthew VanBesien, 47, who has been with the Philharmonic for nearly five years, has said “he will leave to become the president of the University Musical Society of the University of Michigan, a respected campus-affiliated arts presenter. His decision to step down before his contract is up in 2018 leaves the Philharmonic with vacancies in its top managerial and artistic ranks as it prepares to face its biggest challenge in decades. The turnover at the orchestra is staggering, which threatens to make the planning process more chaotic, and give potential donors pause.”