It’s a boardwalk winding through a dense forest of mangroves along the coast. The tangled root systems of the trees poke out of the water, like tent poles holding up the tree trunks. Teenagers in this town of roughly 3,000 people take selfies with the dense leafy canopy as a backdrop, while families stroll along the boardwalk. None of this may have been here if it weren’t for Hidayat Palaloi. “Before, this area was not like this, it was just empty land, coastline and a beach,” says Palaloi, the head of a mid-sized conservation nonprofit based in Makassar, Indonesia, called...