The effects of burn entry and burn severity on ponderosa pine and mixed conifer forests in Grand Canyon National Park

Over a century of fire exclusion in frequent-fire ponderosa pine and dry mixed conifer forests has resulted in increased tree densities, heavy surface fuel accumulations and an increase in late successional, fire-intolerant trees. Grand Canyon National Park uses prescribed fires and wildfires to reduce fire hazard and restore ecosystem processes. Research is needed to determine post-fire vegetation response thus enabling future forest succession predictions. Our study focussed on the effects of burn entry and burn severity on species composition and regeneration in two forest types: ponderosa pine with white fir encroachment and dry mixed conifer. We found no difference in tree composition and structure in a single, low-severity burn compared with unburned areas in the white fir encroachment forest type. We found no white fir seedlings or saplings in a second-entry, low-severity burn in the white fir encroachment forest type. Second-entry burns were effective in reducing white fir densities in the white fir encroachment forest type. There was significant aspen regeneration following high-severity fire in the dry mixed conifer forest type. This research suggests that repeated entries and an increase in burn severity may be necessary for prescribed fire or wildfire to be effective in meeting management objectives.