Effects of Three Prescribed Fires on Dwarf Mistletoe Infection in Southwestern Ponderosa Pine

摘要

Results are presented from three prescribed fires (underburns) conducted in 1995, 1996, and 1997 on the Santa Fe National Forest, Espanola Ranger District, in northern New Mexico. Average crown scorch on six monitoring plots (n=877 ponderosa pine sample trees) ranged from 28 to 77 percent$ tree mortality three years after the fires ranged from 9 to 36 percent. About 25 percent of the ponderosa pines that received 100% crown (needle) scorch survived. Infection levels (DMRs) were reduced on all plots, with reductions ranging from 0.3 to 1.6, compared to projected values, three to four years after the fires. In two of the fires (timber litter models), heavily infected trees had higher mortality rates than other trees, and reductions in plot DMR increased with increasing average scorch. In the third fire (a timber slash model), reductions in plot DMR were less (relative to scorch) than in the other fires$ here a recent thinning had already reduced stand DMR considerably, limiting potential for further reduction. Dwarf mistletoe infection reduced survival of fire-scorched trees, although not to the extent reported by Harrington and Hawksworth (1990)$ the effect was pronounced only for DMR 6 trees with 90 to 100 percent crown scorch. Scorch pruning contributed toward the reduction in average DMR on each of these six plots$ DMRs were reduced on about 30 percent of the surviving infected trees. Monitoring will continue on these plots and others established in more recent burns to better quantify the effects of fire on dwarf mistletoe.