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Environmental Effects of Postfire
Logging: Literature Review and
Annotated Bibliography
James D. McIver and Lynn Starr
Technical Editors
In 2000, the Forest Service's Pacific Northwest
Research Station conducted a literature review of 21 studies
of postfire logging. The conclusions are reported below. To access the
full study, click here.
We are confident that most major studies published in the primary literature are presented
here, and from this it is clear that information on the environmental effects of
postfire logging is scanty at best. Only 21 major studies have examined the wide range
of potential effects of postfire logging, and yet this practice is likely to increase in relative
importance, at least in federally managed forests. From these 21 major studies,
and the available information on the effects of wildfire itself, we can list the following
environmental effects likely to occur when intensely burned sites are logged:
1. Intense wildfire causes significant and fairly predictable changes in soil and vegetation
structure, which often lead to catastrophic erosion (Campbell and others 1977,
DeBano 1991, Durgin 1985, Megahan and Molitor 1975). Accelerated erosion usually
is associated with increases in overland flow that result from decreases in infiltration
(Helvey 1980). In turn, limited infiltration is generally caused by fire-induced water repellence
of the soil and by decreased evapotranspiration in the tree-killed stand (Helvey
1980, Mackay and Cornish 1982, Marston and Haire 1990). These studies support
work in unburned watersheds suggesting that postfire logging associated with road
building, conducted with ground-based log retrieval systems, or undertaken in stands
having steep slopes and sensitive soils likely will have the greatest potential for exacerbating
the erosional problems typically observed in burned watersheds.
2. The scope and scale of immediate environmental effects of management in the postfire
environment depend on several specific features of burned stands, including the
intensity of the burn, slope, soil texture and composition, the presence or building of
roads, and postfire weather conditions. Activity effects of logging systems occur within
the context of these site-specific factors (Chou and others 1994a, 1994b; Potts and
others 1985).
3. Log retrieval systems differ substantially in their immediate effect on soils in the postfire
environment, in ways similar to those observed in green tree stands. In general,
ground-based skidding causes the greatest immediate soil effect, followed by skidding
over snow, skyline, and helicopter retrieval (Klock 1975).
4. Proper recovery and rehabilitation techniques by managers may be capable of mitigating
soil loss and erosion problems associated with postfire logging (Simon and
others 1994). For example, ground disturbance caused by postfire logging could disrupt
water-repellent layers, increase infiltration, and thus decrease overland flow and
sediment transport to streams (see footnote 3), which could be a benefit during severe
hydrological events. This hypothesis, however, has not been tested experimentally.
5. Logging residue can decrease erosion in postfire logged sites by impeding overland
flow (Shakesby and others 1996).
6. If postfire logging is undertaken after establishment of new seedlings, significant
mortality of these seedlings can occur (Roy 1956).
7. If postfire logging is followed by broadcast or slash burning, significant changes in
future plant succession can result (Grifantini and others 1991).
8. By creating patches of disturbed soil, postfire logging can encourage establishment
of a unique array of plant species (including nonnatives), relative to postfire unlogged
sites (Greenberg and others 1994b, Sexton 1994).
9. Skid trails formed in postfire stands can influence productivity of trees growing directly
on them (Smith and Wass 1980).
10. Postfire logging can reduce vegetation biomass, increase exotic plant species, increase
graminoid cover, reduce overall plant species richness and increase conifer
growth in the first years after logging (Sexton 1994).
11. Postfire logging normally removes a great percentage of large dead woody structure
and thus has the potential for significantly changing postfire habitat for wildlife
(Lindenmayer and Possingham 1995, 1996). These changes include “structural” effects,
such as removal of existing and future snags and large woody material, and
“functional” effects, such as reduction in insect populations that serve as food for
various wildlife species (Blake 1982, Saab and Dudley 1998, Sallabanks and McIver
1998).
12. Many of the insects attracted by fire-killed trees are considered pests. Through
removal of vulnerable trees, postfire logging can reduce the probability that insect pest
populations will build up and infest adjacent green tree stands (Amman and Ryan 1991,
Salman 1934, Scott and others 1996).
13. In four recent independent studies conducted in the intermountain West, postfire
logging caused significant changes in abundance and nest density of cavity-nesting
birds, although the effect differed somewhat by location (Caton 1996, Hejl and
McFadzen 1998, Hitchcox 1996, Saab and Dudley 1998). Most cavity-nesters showed
consistent patterns of decrease after logging, including the mountain bluebird and the
black-backed, hairy, and three-toed woodpeckers; abundance of the Lewis’ woodpecker
increased after logging.
14. Several authors point out that on a landscape scale, wildfire creates patches of
highly attractive habitat for a distinct array of species (Hutto 1995). To maintain healthy
metapopulations of these species over the landscape, postfire patches should be managed
with great care (Caton 1996, Hejl and McFadzen 1998, Hitchcox 1996, Saab and
Dudley 1998).
15. In general, postfire logging enhances habitat for some wildlife species, and diminishes
it for others; the end result is changes in species composition but not necessarily
in species richness (Blake 1982, Haim and Izhaki 1994).
16. No studies have specifically looked at how postfire logging alters the size distribution
of fuel and the concomitant changes in future fire risk. Work examining fuels on
harvested green tree stands suggests that postfire logging may increase short-term
fuel loads and fire risk, owing to increased fine activity fuels, but reduce intermediate
and long-term fire risk through removal of larger dead structure (Brown 1980).
We know enough about both logging activity and structural change to recommend
caution. Although ground-based logging activity could mitigate for erosion problems
under certain conditions, it is more likely that it will either have no effect or produce
more sediment than that produced by the fire. More importantly, we do not know how
site-specific effects accumulate over watersheds, and this knowledge is essential if forest
management is to be linked to aquatic integrity. Operational research at the watershed
level that integrates terrestrial and aquatic components is needed to inform management
about the risks and opportunities available in the postfire landscape.
Similarly, four recent studies on cavity-nesting birds suggest that structural changes
made by logging in postfire forests have the tendency to decrease the use of these
sites by many species, probably owing to lower habitat quality. Yet we know very little
about how habitat preferences translate into bird productivity at the metapopulation
scale. Without productivity estimates, and a landscape perspective, it generally will not
be possible to understand how postfire logging influences source and sink dynamics of
these cavity-nesting bird populations.
Finally, we believe that like most practices, postfire logging is certain to have a wide
variety of effects, from subtle to significant, depending on where the site lies in relation
to other postfire sites of various ages, site characteristics, logging methods, and intensity
of fire. Even though additional research will be necessary to more completely
understand the mechanisms behind the various effects of postfire logging, there is no
substitute for the practice of adaptive management, particularly if it is undertaken with
unlogged controls, replicated units, and response (monitoring) variables that can be
measured with good precision. Because adaptive management is by definition undertaken
in an operational context, it has the unique advantage of providing the kind of
information on environmental (or economic) effects that allows assessment of tradeoffs.
To the manager faced with making decisions in an uncertain world, information of
this kind is extremely valuable. Adaptive management may be particularly useful after
fire, because economic incentives encourage a postfire management response almost
before the fire is out. A manager equipped with an understanding of the basic tools of
experimental design can quickly develop alternative postfire treatments that can be
compared through variables critical to that time and place. It is likely that postfire logging
will continue, with a high degree of uncertainty about its long-term effects. Adaptive
management is one way for the manager to learn by doing and to gradually reduce
the uncertainty behind selected site-specific practices and prescriptions.
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