The influence of mountain pine beetle outbreaks on carbon
and nitrogen cycling in lodgepole pine ecosystems
E. Matthew Hansen, Rocky Mountain Research Station, Logan, UT
Michael C. Amacher, Rocky Mountain Research Station, Logan, UT
Michael A. White, Utah State University, Logan
Helga Van Miegroet, Utah State University, Logan
James N. Long, Utah State University, Logan
Michael G. Ryan, Rocky Mountain Research Station, Ft. Collins, CO
INTRODUCTION
Possible influences of MPB outbreaks on C and N dynamics can be
hypothesized by considering a LPP developmental chronosequence following a
stand replacing event. As the landscape is re-colonized, increment (C uptake,
i.e., photosynthesis) slowly increases, reaching a maximum from age 30-60
years then slowly declines over the life of the stand as live volume approaches
some asymptotic value. Meanwhile, N dynamics are tied to the C cycle. Contrast
this to a LPP chronosequence with a cycle of MPB outbreaks every 40-60 years
beginning at stand age 100. The resulting death of overstory trees initiates a
chain of events that modify C and N accumulation, storage, and retention.
The objectives of this study are to characterize C and N dynamics in
LPP systems – in aboveground vegetation, downed woody material, and
soil - with regards to MPB outbreaks. That is, do MPB outbreaks:
- increase or decrease LPP ecosystem productivity?
- “regulate” carbon storage?
- increase or decrease N pools, availability, and retention?
- at what scales of time and space?
D
A
PRELIMINARY RESULTS AND DISCUSSION
1600
Uninfested
MPB every 50 y
Ryan and Waring
1400
Stand age ~25 y
160
180
160
Aboveground - live
Standing dead
Down woody material
Ashley NF
120
120
Mg C/ha
1200
1000
100
100
80
80
60
60
800
40
40
20
20
600
0
Fire
Infested
400
Green
0
Old growth
Ashley NF
0
0
50
100
150
200
250
300
Stand age ~120 y
Productivity In an uninfested stand, FVS predicts peak
productivity at about age 50 followed by a slow decline; empirical
data from Ryan and Waring (Ecology 73 (1992): 2100–2108)
support the simulation. Following MPB infestation, NPP sharply
declines initially but then rebounds, exceeding NPP in uninfested
stands within a few decades.
Stand age ~350 y
1.4
1.4
1.2
1.2
1.0
LPP overstory NPP (kgC/ha/yr)
200
Green
Clearcut
1200
Infested plots
Uninfested plots
Old growth
Fire
1000
800
600
600
400
400
200
200
2020
2030
2040
Year
2050
2060
Infested
Uninfested
Clearcut
1000
800
0
2010
Infested
Targhee-Gallatin NFs
1200
Fig. 1. Plot locations and LPP cover type
in the northern and central U.S. Rockies.
Targhee-Gallatin NFs
140
140
Stand age (y)
Stand age ~2 y
Fig. 2. Field measurements : A) ground
vegetation; B) forest floor and soil
samples; C) overstory and down woody
material; D) soil N flux using ion
exchange membranes; and E)
sapwood radius.
C
E
NPP (kgC/ha/y)
Table 1. Approximate stand ages and MPB
histories at established plot locations.
Ashley National Forest, Utah
Uninfested, stand-replacing fire 1985 (2 plots)
Uninfested, stand age 110-125 years (4)
Uninfested, stand age 250-375 years (4)
Infested ~25 y ago, stand age 110-125 (5)
Sawtooth-Challis-Boise National Forests, Idaho
Uninfested, stand-replacing fire 2006 (2)
Uninfested, stand age 95-110 years (3)
Infested ~80 y ago* (3)
Infested ~80 y ago and ~12 y ago* (3)
Infested ~80 y ago and ~7 y ago* (4)
Infested ~80 y ago and ~2 y ago* (4)
Targhee-Gallatin National Forests, Idaho and
Montana
Uninfested, ~50 y old clear cut (1)
Uninfested, stand age 110-130 (3)
Infested ~40 y ago, stand age 110-130 (3)
*Stand age not yet determined but likely »150 y.
B
0
2010
2020
2030
2040
2050
2060
Year
Carbon storage and flux Uninfested stands have more total C storage despite
relatively low amounts of standing dead and downed material (top panels; from
empirical field data). Infested stands, however, have notably greater C flux (NPP)
than uninfested stands (bottom panels; from FVS simulations).
MgN/ha
0.8
MPB ~80 y ago
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.6
Repeated MPB infestations may increase long term productivity
(cumulative C uptake)
0.4
0.2
0.0
0.0
Uninfested Infested
Old growth
0.0
Uninfested Infested
Forest floor N (total)
Uninfested
Old growth
30
100
80
Infested
Old growth
N (10-20 cm; total)
N (0-10 cm; total)
25
20
20
15
15
10
10
5
While soil nutrition appears not to differ among infested and
uninfested stands, these preliminary data suggest that older
stands have relatively low macronutrient levels
60
40
20
0
5
Uninfested Infested
Old growth
0
Uninfested Infested
Forest floor carbon
Uninfested
Old growth
90
40
30
20
1.4
70
60
Infested
Old growth
C:N (0-10 cm)
1.0
0.6
Uninfested
Infested
Old growth
Base saturation (0-10 cm)
But, these prelimnary results are from a subset of field plots with
incomplete data (e.g., flux data not yet available) and do not reflect
temporal and spatial variation - a primary goal of this project
Other than an in situ decomposition study, all field work is now
complete. Lab analyses of soil and flux devices are ongoing and
should be completed in 2011.
FVS and FVS-BGC simulations are being conducted now with
3PGS modeling beginning late 2011.
0.8
30
Uninfested
1.2
50
40
10
Old growth
1.6
80
50
Infested
Soil carbon (10-20 cm)
Soil carbon (0-10 cm)
60
Total C may be “regulated” in stands with repeated MPB outbreaks
albeit at lower levels relative to uninfested stands
25
g/cm^3
METHODS
A variety of methods will be used to measure and simulate C and N
dynamics during LPP development, with and without MPB disturbance and at
multiple temporal and spatial scales.
Empirical data Forty-one field plots (Table 1, Fig. 1), based on Forest Inventory
and Analysis “Phase 3” plots but with additional flux measurements (Fig. 2) and C
and N concentrations, are intended to quantify stand-level C and N pools and
fluxes. C and N pools and fluxes will be directly compared among infested and
uninfested areas.
Simulation models Two simulation models, FVS (Forest Vegetation Simulator ;
an empirical growth and yield model) and FVS-BGC (links FVS with Stand BGC,
a process-based, C balance model), will be used to simulate chronosequences of
LPP stand development, with and without MPB disturbance. Simulations will aim
to track C and N pools and fluxes from stand establishment through multiple
centuries of development.
Remote sensing Light use efficiency (LUE) models based on remotely sensed
data are widely used to estimate landscape- and global-scale gross and net
primary production (GPP and NPP). We will use the 3PGS model (Physiological
Principles Predicting Growth from Satellites) which includes a stand agedependent growth modifier. Assessment of MPB disturbance effects on C
dynamics, as estimated by 3PGS, will consider MPB history based on ground
and Forest Health Protection aerial detection survey data.
1.0
% base saturation
MPB ~40 y ago
MgC/ha
MPB ~25 y ago
C:N (ratio)
MPB ~10 y ago
1.0
Uninfested
Infested
Old growth
Manuscripts are expected: 2011 for simulation models; 2012 for
empirical data; and 2012 or 2013 for remote sensing analyses.
Bulk density (0-10 cm)
Soil characteristics Soil characteristics do not appear to differ
among infested and uninfested stands, though old growth stands may
be relatively depleted of macronutrients (K and Ca not shown). Note
that: 1) these data are from only a subsample of Ashley National
Forest plots; 2) N not speciated – nitrate and ammonium results not
yet available.
Acknowledgements FHP sponsors: Carl Jorgensen, Brytten Steed. Field crew: Mark Wagner,
Rochelle Jansen, Crest Simeon, Galen Trostle, Greg Townsley, Joel Martin, Kendra Schotzko.
Cooperators: Colette Webb, Mark Novak. FVS-BGC: Andrew McMahan. Lab: Kay Laird, Alicia Price,
Jessica Hoffman, Dave Evans. Dataloggers: Jim Vandygriff.