Impacts of Mountain Pine Beetle Outbreaks on Forest Fuels and Other Stand Attributes in the
Intermountain West
Christopher J. Fettig1, A. Steven Munson2, Kenneth E. Gibson2, Carl L. Jorgensen2, Jose F. Negrón3, Justin B. Runyon3, and Brytten E. Steed2
1Pacific Southwest Research Station, 2Forest Health Protection, and 3Rocky Mountain Research Station, USDA Forest Service
Bark beetles influence forest ecosystem structure and
function by regulating certain aspects of primary
production, nutrient cycling, ecological succession and
the size, distribution and abundance of trees (Fettig et
al. 2007, For. Ecol. Manage. 238: 24-53). In recent
years, the mountain pine beetle, Dendroctonus
ponderosae Hopkins (MPB), has impacted >8.9 million
hectares of forests in the western U.S. (USDA Forest
Service 2012), requiring evaluation of ecological
impacts and development of resource strategies that
will address current and future forest conditions.
In 2012, we expanded the methods to include survey of
invasive plants; monitoring of bark retention and number of
checks (cracks) visible on each tree as this influences wood
quality and salvage potential; and reconstruction of stand
histories through use of dendrochronology (CO only). We
hope to expand the latter throughout the network in 2013.
All plots are monitored annually for levels of tree mortality
and fall rates of individual trees.
Updates
With reduction in live pine volume, substantial
changes in the amount and distribution of fuels
measured in 2010 will occur as needles, branches,
limbs and boles fall to the forest floor. Fall rates of
trees were negligible (Table 1), but increased
dramatically in 2012, specifically in CO (data not
shown).
Table 1. Fall rates of lodgepole pines in Idaho and Utah, 2011.
State
In August 2012, five plots in
Idaho were burned in the
Halstead Fire at mixed to high
severity. These plots were not
surveyed in 2012. The five plots
will be removed from the
network in 2013.
Idaho
Utah
1
Location
of
evaluation
monitoring plots (filled circles,
n = 25/state, but overlapped).
Green = National Forest.
Since 2004 there has been a significant loss of pines in the
larger diameter classes across all sites, due primarily to MPB.
350
300
Methods
a
100
MPB
Other causes
2004
2011
a
80
250
Trees/ha
Twenty-five 0.08-ha circular plots were established in
each of five states (CO, ID, MT, UT, WY; above) in
predominately lodgepole pine stands with recent
MPB-caused tree mortality (N = 125). Within each
plot, all trees ≥7.6 cm dbh were tagged with species,
dbh, height, height to base crown, status (live or
dead), and year since death (Klutsch et al. 2008, For.
Ecol. Manage. 258: 641-649) recorded. Three 16.1-m
Brown’s transects (Brown 1974, INT-GTR-16) were
established at 0°, 120° and 240° from plot center to
estimate surface fuels (Fig. 3). A 1-m² plot was
established at the end of each Brown’s transect (n =
3/plot) to determine forest floor composition, and a
0.004-ha plot was established at plot center to
estimate tree regeneration. Increment cores were
collected from the three tallest trees on each plot (N =
375) to determine stand age and site productivity.
a
a
a
200
b
Percent mortality
Mountain pine beetle-caused
tree mortality, Montana, U.S.,
2010.
a
150
b
100
a
50
b
a
60
40
20
b
0
0
10
15
20
25
30
>32.5
Diameter class (cm)
Mean (+ SEM) number of live pines
per hectare per diameter class (midpoint of 5-cm diameter classes shown
except for largest). Bars followed by
the same letter within diameter class
are not significantly different (P >
0.05). Data collected in 2012 are not
included in these analyses.
10
15
20
25
30
>32.5
% fall of
% fall of
trees
No. killed
trees
No. killed
1
killed by
YSD
by all
killed by
by MPB
all
sources
MPB
sources
0-6 years
588
871
1.2%
0.7%
>6 years
12
140
0.0%
7.9%
0-6 years
>6 years
823
0
1128
87
0.0%
N/A
0.5%
6.9%
YSD= years since death; based on crown characteristics according to Klutsch et al. (2009).
Future Work (2013-2015)
Our goal is to continue to monitor tree mortality,
tree degradation, and the fall rates of individual
trees on an annual basis. With sufficient funding,
we plan to (1) remeasure regeneration, ground flora
(including invasives), fuel loads, and all surviving
trees (i.e., some have grown into the minimum size
class since initiation of this study) in 2014; (2) to
calculate changes in carbon in 2015, and (3) to
reconstruct stand histories through use of
dendrochronology (2013-2015).
Diameter class (cm)
Mean (+ SEM) percentage of pines
killed by diameter class (mid-point
except for largest) caused by MPB
and other sources. Data collected
in 2012 are not included in these
analyses.
Due to the significant mortality of pines in larger diameter
classes, reductions in live pine volumes ranged from 49%
(Idaho) to 67% (Montana) between 2004 and 2011.
Acknowledgments
We thank D. Balthrop, R. Cruz, C. Dabney, V. DeBlander, L.
Dunning, R. Gerrard, C. Hayes, L. Lazarus, S. McKelvey, J. McMillin,
R. Mendoza, P. Mocettini, A. Morris, J. Neumann, J. Popp, A. Sills,
and C. Toone for technical assistance. Furthermore, we thank the
Arapaho-Roosevelt, Beaverhead-Deerlodge, Boise, Bridger-Teton,
Salmon-Challis, and Uinta-Wasatch-Cache National Forests and
Grand Teton National Park for their continued support of this
work. This project is funded, in part, by a Forest Health
Monitoring-Evaluation Monitoring grant (INT-EM-F-10-03). Three
papers describing effects on (1) fuels and carbon, (2) stand
structure and composition, and (3) snag demographics and
degrade are planned.