FIRE TEMPERATURES IN PLANT-COMMUNITIES OF THE NORTHERN MIXED PRAIRIE

Temperatures during prescribed spring burns were monitored for selecte d mixed prairie plant communities near Saskatoon, Saskatchewan. In fes cue, spear grass, and brome communities the fires peaked quickly at an average maximum temperature of approximately 500 degrees C, then reve rted to ambient conditions within about 1 minute. The highest temperat ures were recorded 10 cm aboveground. A temperature of 60 degrees C wa s considered the upper tolerance limit for plant tissue; such conditio ns persisted for approximately 1 minute within the grass stands. Simil ar temperatures were observed in a stand of Silverberry. Temperatures above 800 degrees C were recorded in snowberry and aspen and a more pr otracted cooling phase was noted because of the coarser woody fuel. In all grass and shrub stands there was little change in temperature in the mineral soil at a depth of 5 cm. However, in the aspen grove avera ge temperatures at this depth increased to about 450 degrees C because the thermocouple was embedded in the thick litter layer.