East of Cascade Range Crest, Oregon and Washington

Fire-Scarred Trees

Fire significantly shapes the old-growth ponderosa pine forests. In fact, in some locations these forests depend upon it. Before the 20th century, fire swept through these forests every 8 – 20 years reducing competition from more shade tolerant species such as Douglas-fir and the true firs. These fires were generally not very intense as they burned along the forest floor consuming grasses, shrubs, young saplings as well as dead limbs, pine needles, and other plant debris. This helps give the forest its characteristic park-like feel and gives most of the ponderosa pines numerous fire scars along their trunks.

Ponderosa pine is especially well adapted for fires. Its bark is thick and corky. It has an open canopy. It self-prunes its branches to reduce aerial fires, has high moisture content within its needles, and insulates its scale buds. In fact, ponderosa pine seedlings preferentially germinate on soils modified by recent fires.

Fire also modifies the understory vegetation. In general, fires favor grasses over shrubs. Antelope bitterbrush is highly susceptible to fire and doesn’t re-sprout very well. Big sagebrush is also killed by most fires but reseeds rapidly from unharmed individuals and seeds within the soil. Bluebunch wheatgrass loses most of its above ground foliage but its buds are protected and can re-sprout after fires move on. Idaho fescue, another grass species, also survives fire but with some damage depending on fire severity.

Fires happen naturally as when lightning strikes, but they were also due to common Native American burning practices. These practices may have been used to modify the environment to favor certain species over others, to promote seed germination, seed formation, and the clearing of land for larger animals, such as deer and elk. There is still some uncertainty as to the extent of Native American burning practices within these ponderosa pine forests. One reason may be that this zone consists of serveral non-overlapping regions within Oregon and Washington that fall within different Native American tribal ranges.

During the 20th century the fire policy has generally been one of suppression - if one starts, stop it. As a consequence, there has been a build up of the shrub layer and dead, woody material – called ‘fuel load’ by fire managers. With more fuel, fires burn longer and hotter and therefore affect the forest more severely than it would otherwise. Recent fire management research has begun to examine the use of controlled fires to better maintain the traditional fire pattern while still protecting settlements, roads, and other human resources.