There are a number of waste byproducts from the steel making process. Mine tailings from the ore beneficiation process are returned to the mining site. Growing vetches (a species of plant valuable for fodder), grasses, and trees on some of these barren landscapes has been a project of biologists and foresters. Gases that are given off from the coke ovens, blast furnaces, and steel furnaces are largely recovered for reuse. After use in iron and steelmaking, most slags are used for other purposes such as railroad ballast and road fill, an ingredient in cement or blocks, insulating material, or fertilizer.