The ponderosa pine is the source of the most timber used by forest-product firms in the Black Hills of South Dakota. Deserts are areas where more water is lost through evaporation than is gained through precipitation. There are about 350 species of sharks, and although they are all carnivorous, only a few species will attack people. The quince is an attractive shrub or small tree that is closely related to the apple and pear trees. Many gases, including nitrogen and oxygen in air, have no color or odor.