When most people think about Saguaro National Park, they think of the desert, and the concept of fire seems totally foreign. Actually, Saguaro National Park is in two separate worlds in terms of fire. In the desert, below about 4,500 feet elevation, historically fire played almost no role. The sparse grasses and forbs in the desert rarely allowed fire to spread.
However, as elevation increases, temperatures moderate and rainfall increases. Above about 4,500 feet grasses and forbs increase in abundance, eventually creating continuous ground cover that can support fire spread.