Effect of prescribed burning on mortality of presettlement ponderosa pines in Grand Canyon National Park

Ponderosa pine (Pinus ponderosa) trees established before Euro-American settlement are becoming rare on the landscape. Prescribed fire is the prime tool used to restore ponderosa pine ecosystems, but can cause high mortality in presettlement ponderosa pines. This study uses retrospective techniques to estimate mortality from prescribed burns within Grand Canyon National Park (GCNP). Live and recently dead presettlement ponderosa pines were sampled in four prescribed burns and three adjacent unburned areas. Presettlement ponderosa pine mortality (not including areas of crownfire) was higher than that of control sites in all four burns, although control areas showed elevated mortality rates compared to presettlement times. The highest mortality (23 percent) was found on a prescribed natural fire converted to a wildfire, the second highest (17 percent) on a site with extremely heavy mistletoe, the lowest (10 percent) on a spring burn. Bole scorch height and bole char severity were higher on dead trees than live trees, and may be useful in predicting postfire mortality. GCNP management objectives for overstory mortality are probably being met, but these guidelines do not account for the possibility of mortality delayed more than 5 years.