Tuesday, 18 November 2003: 9:00 AM
Monitoring fuel consumption and mortality from prescribed burning in old-growth ponderosa pine stands in eastern Oregon
We monitored mortality of large ponderosa pines as part of a series of experiments designed to quantify fuel consumption during prescribed fires in eastern Oregon. Operational burn units with old-growth characteristics (i.e., presence of >50 cm diameter at breast height ponderosa pine trees with basal accumulations of needle and bark litter and duff) were inventoried to quantify consumption of woody and forest floor fuels. Fuel conditions and consumption around the bases of 10-20 large ponderosa pine trees were monitored specifically to explore potential links between reduction of basal accumulation by fire and tree mortality. Prescribed fires occurred in the spring of 1994 and 1995, and in the fall of 1997 and 1998. Post-fire monitoring occurred in the fall of 1998 and again in the summer of 2000. Fuel consumption was varied throughout many of the units, however, consumption was considerable and approached 100 percent at the bases of many of the monitored trees. Mortality of the monitored trees was as high as 25 percent (5 of 20 trees for a 1994 spring-burn unit) in 1998 and 30 percent (3 of 10 trees for a 1997 fall-burn unit) for a different unit in 2000; there was no mortality of monitored trees in the years following fire for 6 of 14 burn units. Three out of ten burn units showed increased mortality from 1998 to 2000. Preliminary qualitative analysis did not reveal a relationship between basal fuel consumption and tree mortality. Other measures of fire intensity/severity and more intensive sampling may be required to adequately evaluate old-growth ponderosa pine mortality during prescribed fires.