Fire Temperatures and Physical Characteristics of a Controlled Burn in the Upper Sonoran Desert

Abstract

Fire temperatures at 4 vertical locations within 3 desert microhabitats were measured during a controlled bum using both temperature pellets and thermocouples. Examples of maximum air temperatures (30 cm) during the fire were 1380 C in open interspaces, 352O C within a shrub, and 442” C under a palo Verde tree. Fire temperatures among other levels and microhabitats varied considerably. Environmental conditions during the fire were monitored. Soil water repellency at 4 vertical locations within 3 microhabitats showed minimal changes after burning. Soil surface rlbedo increased by 5% following the fire resulting from 70% perennfal plant cover removal and subsequent white ash release. Soil and air temperatures did not vary significantly after the fire when compared to an unburned control. North American deserts are commonly used as rangelands, especially those portions containing adequate shrub and herbaceous plant cover. Rangeland in the Upper Sonoran Desert is relatively lush because of a bimodal rainfall pattern and bums frequently when enough fuel is present. Traditionally, the Upper Sonoran Desert has been considered to be less affected by fire than other ecosystems (Humphrey 1974). However, in central Arizona following a moist year, the desert floor is covered with sufficient annual plant fuel and litter to carry a fire. This results in increases in both man-caused and natural brush fires during the following seasons. Research on Sonoran Desert fires has been limited primarily to southern Arizona desert grasslands (Humphrey 1949, Humphrey and Everson 195 1, Humphrey 1963, Cable 1967, and White 1969). These studies focused on fire recovery processes and use of fire as a tool for controlling certain undesirable species on grazing land. Physical parameters related to fires in deserts characterized by shrubs and cacti have not been previously reported in fire ecology literature.