Young forests in this region are susceptible to recurring severe fires, Thompson said. Compared to an older forest with branches high above the forest floor, young trees are very vulnerable, whether they are planted or naturally regenerated.
However, in the aftermath of a wildfire, removal of large dead trees followed by planting conifer seedlings does not appear to lessen the risk of severe fires in the first 10-20 years, Thompson said. This may be because the logging process leaves more available fuel on the forest floor; the dense, homogenous replantation of young trees provides a good setting for fire; or some combination of these factors over time. Dead woody fuel . . . is only part of the fire risk story, and it may not be the most important after a few years, the study noted.
By contrast, natural regeneration of forests, he said, appears to result in at least slightly, and sometimes significantly less risk of severe future fires. This could be because the regenerating trees are more patchy, have open gaps, more species diversity, or other factors. But the study showed that total consumption of tree crowns in a recurring fire situation is more severe in the managed stands than the natural ones, at least when there are one to two decades between fires.
This research was done with satellite data, government agency records and aerial photography, in the mixed-conifer, mixed-evergreen hardwood zones of the Siskiyou Mountains. It analyzed burn severity patterns with a commonly used metric of fire damage on almost 45,000 acres of the Biscuit Fire that had also burned 15 years earlier.
Among its conclusions: