Pine trees are cone-bearing evergreens that comprise the genus Pinus of the family Pinaceae. The conifers are naturally widely distributed north of the equator, but are also grown in many areas in the Southern Hemisphere. A number of pine species grow rapidly and are tolerant of poor conditions, such as acid or arid soils or high elevations, making them a popular planting choice in many locales uninhabitable by other trees. The characteristics of pines also make them well suited for use in reforestation projects. Some varieties of the trees, however, require fire to complete their reproduction process, which can hinder their proliferation in stands where fires are habitually suppressed by human interference.