DES MOINES — Gov. Terry Branstad opened what he called a “challenging” budget cycle Friday with hearings on a fiscal 2016 spending plan and a swelling list of demands fueled by multiyear commitments, higher costs and surprise developments. “We want to be very careful and very frugal and yet be able to provide the resources needed to meet the priorities,” Branstad said at the start of hearings on state agency general fund budget requests approaching $7.05 billion, a 3.8 percent increase over current appropriations. Projections assembled by the Legislative Services Agency expect the state treasury to have a $520.4 million surplus on June 30, 2015.