4 Winter 2015 conservationnw.org
Fire is a prominent and inevitable natural disturbance in
many forests of western North America. It provides essential
ecological services such as nutrient recycling , regulating the
density and composition of trees, and creating and main-
taining wildlife habitat. At the landscape scale, large wildfire
events reshape vegetation patterns and alter sediment move-
ment, flood activity, and other watershed processes. Fires his-
torically created a mosaic of forest types and structural condi-
tions across landscapes that enhanced resistance and resilience
to future disturbance events.
But fires are not all the same. Wildfire behavior varies dra-
matically among forest types and regions. As we seek to manage
wildlands, these differences must be considered to ensure that
management actions will be effective and will sustain ecological
values such as healthy wildlife populations.
e ecological variability within our forests defies a simple,
one-size-fits-all management prescription for wildfires. How-
ever, certain forest types have predictable relationships to fire
regimes, and those relationships can be used to inform wildfire
and forest management strategies even in highly altered forests
or topographically complex wild landscapes.
Fire regimes can be classified according to severity as follows:
• Low-severity fire regime: Many pine and dry mixed-
conifer forests at lower elevations are characterized by
low-severity fires. Such fires historically burned fine fuels
(e.g., grasses and forest floor litter) at regular and frequent
intervals, killing many smaller trees but few large, fire-
resistant overstory trees. Reducing small tree density
while retaining and cultivating large and/or old trees and
snags and dispersed clumps of smaller trees is critical to
restoring and maintaining ecological functions.
• High-severity fire regime: Forests characterized by
high-severity fires include moist, marine-influenced for-
ests, subalpine and high elevation forests, and spruce,
true fir, and lodgepole pine forests. Forests subject to
high-severity fires typically support high densities of
trees and large fuel loads. In these forests, high-severity
fires are relatively infrequent—occurring at intervals of
one to many centuries—and are predominantly driven
by climate, so fire exclusion has had little to no effect on
fuels or forest structures. Hence, management actions
are generally ecologically inappropriate.
• Mixed-severity fire regime: Fire is variable in sever-
ity and frequency in many mid-elevation and some low
elevation dry and mixed-conifer forests. Topographi-
cally complex mountain landscapes may be especially
prone to mixed-severity fire because drier south-facing
slopes with lower fuel loads can burn at low severity
when adjacent, moister north-facing slopes that support
higher tree densities experience high-severity fire. Such
complex mosaics necessitate planning at larger spatial
scales to identify portions of the landscape that may
warrant management actions.
As we dive further into the topic of wildfire in this issue,
and its effects on wildlands and wildfire, we'll be discussing
the primary factors agencies, land managers, and organiza-
tions like Conservation Northwest must consider when it
comes to restoring fire to its rightful place on the landscape.
As we'll see, the key to managing fire for the future is learning
to see this natural process at the scale of the landscape that it
transforms and renews.
Reducing density of small trees while retaining older trees, snags,
and dispersed clumps of smaller trees (as shown here) is critical
for ensuring wildfire behavior that creates and maintains healthy
forest habitat. Photo: David Heflick
a wildfire primer
FIrE: ThE GrEAT rECyClEr
Dave Werntz Science and conservation director,
dave@conservationnw.org
Photo: © Brett Cole, brettcolephotography.com
Wildfire science
