Many coniferous species have life history traits and
characteristics that greatly enhance their resistance to injury
from fire, thereby increasing post-fire survival rates. Douglas-fir
(Pseudotsuga menziesii (Mirbel) Franco), for example, is known for
its fire tolerance, in large part, due to thick insulating bark
that develops with age and protects the inner cambium from heat
injury. Mortality following fire, however, depends not only on tree
species, but also on type and degree of fire-caused injuries,
initial tree vigor, and post-fire environment. These same factors
may also influence timing of tree death, which can be delayed as
long as 4 years post-fire. Within a few months to a few years
following fire, bark and wood boring beetles may preferentially
attack, and wood deterioration caused by staining, decay pathogens,
and/or checking can occur. Parker and others provide an extensive
review of interactions between insects and fire (prescribed and
wildfire) in coniferous forests of interior western North America.
Development of management plans immediately following fire,
therefore, can be difficult due to the timing and uncertainty of
many interacting factors. Reliable estimates of post-fire
Douglas-fir mortality, predicted from field-based characterizations
of fire injury, would greatly facilitate informed post-fire
management, including salvage, following both mixed-severity
wildfires and applications of prescribed fire. Prediction of fire-
and beetle-caused delayed tree mortality is also an important
component in the development of prescribed burn plan objectives.
Managers must know what fire intensity levels are needed to
accomplish mortality related objectives. Also, in adaptive
management, a key part to determining if burn objectives were met
is installation of monitoring plots. By revisiting prescribed burns
and monitoring fire effects, future burn prescriptions can be
adjusted to better achieve desired results. To do this, field crews
must be able to accurately assess post-fire tree injury and the
potential for delayed mortality. Fire behavior and effects models,
such as the First Order Fire Effects Model (FOFEM) and BehavePlus,
are available for use in predicting post-fire tree mortality. The
tree mortality model in these software packages is based on models
developed by Ryan and Reinhardt (1988) and Ryan and Amman (1994).
However, this tree mortality model was developed from data for
several different tree species. More importantly, this model does
not fully account for bark beetle effects on post-fire tree
mortality. Douglas-fir bark beetles (Dendroctonus pseudotsugae
Hopkins Coleoptera: Curculionidae, Scolytine) are highly attracted
to fire-injured Douglas-fir and can cause significant tree
mortality, apart from fire injuries alone. If Douglas-fir beetle
populations are a concern following fire, it is important to
characterize the fire-related tree injuries most conducive to
beetle attack and successful brood production and survival. Hood
and Bentz (2007) developed a model to predict the probability of
Douglas-fir mortality and one to predict the probability of
Douglas-fir beetle attacks within 4 years post-fire based on data
collected from three mixed-severity wildfires in western Montana
and Wyoming. The intent of this guide is to facilitate use of these
models in post-fire management and prescribed burn planning. We
note that ecological and economic constraints make forest
management following wildfire a complex task. Our models are meant
to be used as part of a multidisciplinary strategy aimed at
maximizing benefits to post-fire ecological communities and forest
management. Following a brief description of the two models,
variables significant in predicting post-fire Douglas-fir mortality
and Douglas-fir beetle attack are described.
General
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