Widespread increase of tree
mortality rates in the western
United States
VAN MANTGEM, PHILLIP J. (1), STEPHENSON, NATHAN L. (1), BYRNE, JOHN C. (2), DANIELS, LORI D. (3),
FRANKLIN, JERRY F. (4), FULÉ, PETER Z. (5), HARMON, MARK E. (6), SMITH, JEREMY M. (7), TAYLOR, ALAN H. (8),
VEBLEN, THOMAS T. (7)
(1) USGS, Sequoia and Kings Canyon Field Station, 47050 Generals Highway, Three Rivers, CA 93271, (2) Rocky
Mountain Research Station, 1221 South Main Street, Moscow, ID 83843, (3) Department of Geography, University of
British Columbia, 217-1984 West Mall, Vancouver, British Columbia V6T IZ2, (4) College of Forest Resources, Box
352100, University of Washington, Seattle, WA 98195, (5) School of Forestry and Ecological Restoration Institute,
Northern Arizona University, Box 15018, Flagstaff AZ 86011, (6) Department of Forest Science, 210 Richardson Hall,
Oregon State University, Corvallis, OR 97331, (7) Department of Geography, Campus Box 260, University of
Colorado, Boulder, CO 80309, (8) Department of Geography, The Pennsylvania State University, University Park, PA
16802
U.S. Department of the Interior
U.S. Geological Survey
The Western Mountain Initiative
Climatic change is here, NOW.
IPCC / Mann, Bradley, & Hughes
Basagic and Fountain 2005
What does this mean for forests in the
western United States?
Background mortality rates are increasing
in old growth forests across the western
United States.
Increasing mortality rates appear to be
related to external causes.
A growing body of evidence suggests that environment
(particularly climate) affects forest demographic rates
Large-scale die-off
Credit: USFS
Background mortality
A growing body of evidence suggests that environment
(particularly climate) affects forest demographic rates
Large-scale die-off
Background mortality
(1) subtle, slow, neglected
(2) ... but important!
Credit: USFS
Tropical forests are changing
RAINFOR plot network
• Increasing
recruitment and mortality rates (Phillips et al. 2004)
• Increasing
stand biomass (Körner et al. 2004)
• Changes
in species composition (increasing liana densities)
(Phillips et al. 2002, Laurence et al. 2004)
Credit: O. Phillips
Credit: Y. Malhi
Could similar changes be
occurring in temperate forests?
Forest mortality
across western
North America
Criteria (76 plots)
• undisturbed old-growth forests
• fates of individual trees
• at least three complete censuses
over ≥ 10 years
• ≥100 sampled trees per plot
• plot area ≥0.25 ha
P<0.0001, n=76
-1
Mortality rate (% yr )
2.0
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
A widespread trend?
• regional differences
• elevational differences
• size differences
• taxonomic differences
1
Forest mortality
across western
North America
5
2
3
6
4
7
1
PNW Coastal Forests
w. red cedar, w. hemlock, sitka spruce
n = 10 plots, 6 ha, > 1,800 trees
Trend: Increasing
P = 0.03
Mortality rate (% yr-1)
2.0
PNW Coastal
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
Cascades
douglas fir, w. red cedar, w. hemlock
n = 37 plots, 44 ha, > 17,000 trees
Trend: Increasing
P < 0.0001
2
Mortality rate (% yr-1)
2.0
Cascades
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
Credit: USFS
Swain Mt, CA
red fir, white fir
n = 2 plots, 1.5 ha, > 1000 trees
Trend: Increasing
P < 0.12
3
Mortality rate (% yr-1)
2.0
Swain Mountain, CA
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
Sierra Nevada
white fir, incense cedar, sugar pine, etc.
n = 18 plots, 20 ha, > 17000 trees
Trend: Increasing
P = 0.0001
4
Mortality rate (% yr-1)
2.0
Sierra Nevada
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
5
Priest River, ID
grand fir, w. hemlock, w. red cedar
n = 1 plot, 1 ha, > 500 trees
Trend: Increasing
P = 0.06
Mortality rate (% yr-1)
2.0
Priest River
1.5
1.0
0.5
Credit: D. Powell
0.0
1960
1970
1980
Year
1990
2000
Colorado Rocky Mountains
lodgepole pine, subalpine fir, engel. spruce
n = 7 plots, 10 ha, > 10,000 trees
Trend: Increasing
P < 0.001
Mortality rate (% yr-1)
2.0
Colorado
6
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
Mortality rate (% yr-1)
2.0
Fort Valley, AZ
Fort Valley, AZ
ponderosa pine
n = 1 plot, 16 ha, > 3000 trees
Trend: Increasing
P < 0.0001
1.5
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
7
1
-1
Mortality rate (% yr )
2.0
2 1.5
5
1, P<0.03, n=10
2, P<0.0001, n=37
3, P<0.12, n=2
4, P<0.0001, n=18
5, P<0.06, n=1
6, P<0.001, n=7
7, P<0.02, n=1
1.0
30.5
6
0.0
4
1960
1970
1980
Year
7
1990
2000
A widespread trend?
1
• regional differences
5
• elevational differences
• taxonomic differences
2
• size differences
3
6
4
7
Recruitment rates
-1
1.5
1, P<0.03, n=10
2, P<0.0001, n=37
3, P<0.12, n=2
4, P<0.0001, n=18
5, P<0.06, n=1
6, P<0.001, n=7
7, P<0.02, n=1
1.0
0.5
0.0
1960
1970
1980
Year
2.0
-1
Mortality rate (% yr )
2.0
Recruitment rate (% yr )
Recruitment rates
1990
2000
1.5
2, P=0.14, n=37
3, P=0.63, n=2
4, P=0.44, n=18
5, P=0.40, n=1
1.0
0.5
0.0
1960
1970
1980
Year
1990
2000
Elevational differences?
Credit: A. Caprio
3
y = 2 .7 6 - 0 .0 0 0 6 6 x
-1
Forest turnover (% yr )
Elevational differences?
r 2 = 0 .4 9 , P < 0 .0 0 1
2
1
0
1500
2000
2500
3000
E le v a tio n (m )
3500
Stephenson and
van Mantgem (2005)
Credit: A. Caprio
Elevational differences?
Mortality rate (% yr-1)
2.0
1.5
<1000 m, P<0.0001, n=32
1000-2000 m, P<0.0001, n=20
>2000 m, P<0.0001, n=24
1.0
0.5
0.0
1960
1970
1980
1990
2000
Year
Credit: A. Caprio
Tree size differences?
Credit: NPS
Tree size differences?
<15 cm, P<0.0001, n=61
15-40 cm, P<0.0001, n=76
>40 cm, P<0.0001, n=76
-1
Mortality rate (% yr )
2.0
1.5
1.0
0.5
0.0
1960
1970
1980
1990
2000
Year
Credit: NPS
Taxonomic groups
Credit: NPS
Taxonomic groups
Abies, P<0.0001, n=62
Pinus, P<0.0001, n=37
Tsuga, P<0.0001, n=47
Other species, P=0.0002, n=64
Mortality rate (% yr-1)
2.0
1.5
1.0
0.5
0.0
1960
1970
1980
1990
2000
Year
Credit: NPS
What does this mean for forests in the
western United States?
Background mortality rates are increasing
in old growth forests across the western
United States.
Increasing mortality rates appear to be
related to external causes.
Trends in stand density & basal area
Increased mortality from self-thinning?
750
-1
Density, P<0.001
Basal Area, P<0.002
100
Basal Area (m ha )
90
2
Density (stems ha-1)
800
700
80
650
600
70
550
500
60
1960
1970
1980
Year
1990
2000
Density dependence?
Density dependence?
Density dependence?
Probability of mortality
0.3
0.2
0.1
0.0
0
2
4
6
8
10
Average radial growth (mm yr-1)
Fire regime
Credit: E. Knapp
Fire regime
Mortality rate (% yr-1)
2.0
1.5
<25 yrs, P<0.0001, n=15
25-250 yrs, P<0.0001, n=31
>250 yrs, P<0.0001, n=30
1.0
0.5
0.0
1960
1970
1980
1990
2000
Year
Credit: E. Knapp
Climatic trends
Relationship to mortality trend
Average
o
Temp.( C)
8
7
Ave. temperature: P = 0.001
6
Deficit
(mm)
150
100
Climatic water deficit: P = 0.005
50
0
1960
1970
1980
1990
Water Year
2000
What does this mean for forests in the
western United States?
Background mortality rates are increasing
in old growth forests across the western
United States.
Increasing mortality rates appear to be
related to external causes.
Hemingway on long-term research
There are some things which cannot be
learned quickly, and time...must be paid
heavily for their acquiring.
-- Ernest Hemingway
Hemingway was a jerk.
-- Harold Robbins
Die-back event of piñon pine in the Southwest
October 2002
May 2004
Photo credit: C. Allen
Die-back event of piñon pine in the Southwest
Annual temperature (oC)
Annual precipitation (mm)
Die-back occurred in the context of increasing temperatures coupled with a
reduction in precipitation -leading to stronger drought response than in the past!
Breshears et al. 2005
Stressed trees are more susceptible to fire
van Mantgem et al. 2003
What does this mean for forests in the
western United States?
Current NPS natural resources policy:
-- When possible, restore and maintain naturallyfunctioning ecosystems.
-- When this is not possible, “maintain the closest
approximation of the natural condition.”
What does this mean for forests in the
western United States?
Current NPS natural resources policy:
-- When possible, restore and maintain naturallyfunctioning ecosystems.
-- When this is not possible, “maintain the closest
approximation of the natural condition.”
Early vs. late mortality trends
Fraser Exp. Forest
Fort Valley Exp. Forest
-1
Mortality rate (% yr )
1.0
0.8
P=0.025
0.6
0.4
P=0.29
0.2
P=0.18
P=0.015
0.0
1920
1940
1960
1980
2000
Year
Credit: E. Knapp
Changes in western North America
Hydrologic changes
Barnett et al., 2008
Changes in the Sierra Nevada
Glacier retreat
Repeat photography at ~100 years reveal that all ten of the
glaciers surveyed have experienced a reduction in ice volume and
surface extent
Basagic and Fountain 2005
Changes in the Sierra Nevada
Range shifts
The Yosemite Grinnell Resurvey
Up 2000’ elevation
• Piñon mouse
• Ground Squirrels
• Alpine Chipmunk
• Pika
(Patton and Chow 2005)
17 historically new bird
species now at 10,000’
many from lower elev.
some breeding
(Rush 2005)
Tree-ring isotope analysis
Mortality rates are increasing in the Sierra Nevada
Annual mortality rate
Thick black line, predicted trend
0.020
0.015
0.010
0.005
0.000
1984
1988
1992
1996
2000
2004
Year
Annual increase = 3% yr-1, P = 0.0004
van Mantgem & Stephenson 2007
Causation:
The Importance of Annual Resolution Data
Stress
mortality
Stress
mortality
(standing dead:
insects, fungi,
or no symptoms)
Average mortality rate
Water deficit, 3 yr. running average
0.015
250
0.010
200
0.005
150
0.000
100
1984
Related to water deficit
300
-1
Annual mortality rate
0.020
Water deficit (mm yr )
βD = 0.005, s.e. = 0.001, P = 0.0002
1988
1992
1996
2000
2004
Year
van Mantgem & Stephenson 2007