Pine trees 3 inches or more in ground diameter have bark thick enough to protect the stems from damage by most prescribed fires. However, the crowns are quite vulnerable to temperatures above 135F. Pine needles will survive exposure to 130F for about 5 minutes, while similar needles exposed to 145F for only a few seconds will die. Very high temperatures are produced in the flames of burning forest fuels. Fortunately, the hot gases cool rapidly above the flame zone and are back to a few degrees above normal air temperature a short distance from a prescribed fire unless the wind is calm. Adequate wind should be present to help dissipate the heat and slow its rise into the overstory canopy.
Wind is also important in cooling crowns heated by radiation from fire.
Southern pines generally survive complete crown scorch as long as there is little needle consumption. Severe needle scorch will, however, retard growth for a year or more after damage and, in this weakened state, the trees are more susceptible to drought and beetle attack. Temperatures of the air and vegetation at the time of burning are critical factors. The effect of high air temperature is recognized in using fire to control understory hardwoods. Although winter burns will topkill hardwoods, summer burns are generally required to kill hardwood rootstocks.