J. L. GANEY ET AL.
in surface fuel loads in ponderosa pine forests following dis-
turbance by bark beetles and wildfire, respectively. Loadings of
1000-hr fuels exceeded recommended ranges for dry coniferous
forests in 20% of plots sampled by Hoffman et al. (2011) five
years after a bark beetle outbreak, and they expected other plots
to exceed those ranges as remaining snags fall. Similarly, areas
suffering high mortality from wildfire exceeded recommended
levels for CWD by up to 28% by 10 yrs postfire (Stevens-Ru-
mann et al., 2012). In contrast, Passovoy and Fulé (2006) did
not observe levels of CWD exceeding recommended levels in a
27-yr chronosequence of postfire ponderosa pine forests.
Fuel loads in our sample plots also will continue to increase
in the short term as dead trees fall (Ganey & Vojta, 2010;
Hoffman et al., 2011; Stevens-Rumann et al., 2012). Increasing
loads of surface fuels may pose challenges for fuels managers
in this region, particularly because tree densities in many pon-
derosa pine and mixed-conifer stands fall significantly outside
of the natural range of variability for these forest types (Cov-
ington & Moore, 1994; Fulé et al., 2009). These high tree den-
sities can interact with surface fuel loads to create high fire
hazard even when fuel loads are within normal ranges (Brewer,
2008).
Drought-mediated tree mortality is simultaneously reducing
the tree densities and canopy fuels that interact with surface
fuel loads, however (Passovoy & Fulé, 2006; Hoffman et al.,
2011; Stevens-Rumann et al., 2012). Ultimately, fire risk in
these stands will represent the interplay between these factors
(surface fuel loads and canopy fuels), as well as other aspects of
forest structure such as fuel ladders that permit fire to reach the
forest canopy. The high spatial variability observed in both
surface fuels (this study) and tree mortality (Ganey & Vojta,
2011) suggests that the outcome of this interplay also will ex-
hibit high spatial variability across the landscape.
Conclusion
Climate change has been implicated in recent large-scale tree
mortality events throughout the world (Allen et al., 2010), and
studies in the southwestern US have documented increases in
CWD levels due to climate-related disturbances such as bark
beetle outbreaks and wildfire (Hoffman et al., 2011; Stevens-
Rumann et al., 2012). This study extends those findings by
documenting rapid climate-driven increases in log populations
across the general landscape, including areas not subject to bark
beetle outbreaks and wildfire. These findings suggest that
managers should plan for increased fuel loads where climate
models predict increasing warmth and aridity.
Acknowledgements
We thank J. Jenness, G. Martinez, M. Stoddard, B. Stroh-
meyer, R. White, and especially A. and J. Iníguez for their as-
sistance in establishing plots, and D. and N. Ganey for assis-
tance with sampling plots. For assistance with initial plot selec-
tion, we thank J. Ellenwood, B. Higgins, K. Menasco, C. Nel-
son, G. Sheppard (Kaibab National Forest), and C. Beyerhelm,
A. Brown, H. Green, T. Randall-Parker, C. Taylor, and M.
Whitney (Coconino National Forest). L. S. Baggett provided
general advice on statistical analyses, and L. S. Baggett and A.
Casas conducted the ANU tests described in the text. Com-
ments by J. Iníguez, C. H. Sieg, and an anonymous reviewer
improved earlier versions of this paper.
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