What can you do when a tree dies? Dead trees, whether they are still standing as snags or have fallen down to become logs, provide crucial habitat for a wide range of terrestrial and aquatic species. Snags provide food and shelter for cavity-dwelling critters like woodpeckers, owls, and bats. Logs on the forest floor and in water bodies provide habitat for insects and fish, and reduce erosion by slowing down the velocity of water.