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
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
re-sprout after fires move on. Idaho fescue, another grass
species, also survives fire but with some damage depending on fire severity.
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
such as deer and elk. There is still some uncertainty as to the extent
of Native American burning practices within these ponderosa pine forests.
may be that this zone consists of serveral non-overlapping regions within
Oregon and Washington that fall within different Native American tribal ranges.
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
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.