Aspen Dieback and Decline in Northern Arizona
Mary Lou Fairweather1, Kelly Barton2, Brian Geils3, and Mike Manthei4
1Arizona
Zone, Forestry and Forest Health; 2 University of Arizona; 3Rocky Mountain Research Station; 4Coconino National Forest.
2003 Aspen Tree Densities (>5" DBH) in Sites
Affected by Aspen Dieback, Coconino NF.
9,500
8,500
Dead
8,000
elevation
400
7,500
7,000
300
300
6,500
200
6,000
100
5,500
5,000
2851
3288
3277
2567
3305
2247
2288
2456
9,500
Live
Trees per acre
Trees per acre
500
Live
0
One of the most severe drought events on record occurred in 2002 and dieback and mortality of aspen
was observed during the growing season.
Aspen tree densities (>9" DBH) in affected sites on the
Apache-Sitgreaves NF.
9,000
600
Dead
8,500
200
elevatio
8,000
7,500
150
7,000
100
6,500
2337
6,000
50
5,500
Site
0
Live aspen tree densities (>5" DBH) 2003-2005.
We began evaluation and monitoring of affected aspen at the stand level on the Coconino National
Forest (NF) in 2003, followed by the Apache-Sitgreaves NF in 2004. This monitoring project describes
mortality levels, regeneration condition, and stand and site variables that are influencing decline.
Plots were established on the Apache-Sitgreaves National Forest in 2004 and remeasured on the
Coconino National Forest. Areas with aspen decline were randomly selected from off-plot aerial
detection survey data, and a series of 1/20th acre permanent plots established. Plot data includes
slope, aspect, and elevation. Large tree data information includes species, status, dbh, height, crown
fullness, and severity of any damaging agent. Regeneration on 1/100th acre subplots were sampled for
species and number.
5,000
1
4554
5218
6282
6046
6509
5219
5757
5755
Site
450
2003
400
Trees per acre
Methods
9,000
250
Feet
700
Feet
Introduction
An accelerated dieback of aspen communities has occurred across northern Arizona, following two
defoliation events and several years of drought. The Southwestern Region’s 1998 aerial detection survey
showed a doubling of defoliated aspen acres (>85,000), compared to previous years, followed by another
doubling in 1999 (>170,000). Although 1998 defoliation was caused by foliar insects and pathogens, the
1999 defoliation was due to frost damage following a severe June snowstorm, which occurred across
most of Northern Arizona. Since 2000, aerial surveyors have switched from reporting acres defoliated,
from which trees recovered, to acres of dieback, marked by thinning crowns and mortality.
2004
350
2005
300
Results and Discussion
250
200
150
One hundred and forty-four plots were established in 18 randomly
located sites on the Coconino (2003) and Apache-Sitgreaves National Forests
100
50
0
2851
3288
3277
2567
3305
2247
2288
2456
Site
2337
(2004). All sites were revisited in 2005. A diversity of aspen communities is
represented. Plots are laid out on a grid dispersed throughout an affected area.
A preliminary analysis of data from the Coconino plots follows. Elevation varied from
6,800 to 9,300 feet and was a key factor in both tree species composition and severity
of decline. Lower elevation sites (<7,500 feet) were on northerly aspects, dominated
by aspen, and had a ponderosa pine and oak component. In general, these sites have
a higher ratio of dead aspen to live aspen, and more than one-half of the overstory
aspen died in the past 3 years. Death is gradual and mortality is expected to continue
as many live trees currently have only 10 to 30 percent of their original crown. Higher
elevation sites were on various aspects, had mixed conifer component and a higher
ratio of live to dead aspen.
Estimated year of death was determined by presence of leaves, buds, fine branches. Categories
included current year, 1 year, and more than 2 years.
All live aspen trees greater than 5 inches dbh were tagged and tree height measured on the first two
live aspen in each plot. The species, number and type of regeneration were collected on a 1/100th acre
sub-plot.
Secondary pathogens and insects included canker fungi, wood borers, and clear wing
moths.
Aspen Defoliation/Decline in Region3
180,000
acres
160,000
Regeneration by suckering followed overstory dieback on many sites. Timing of
regeneration appears to be correlated with elevation, with lower elevation sites the
most sprouting occurred in 2003 and for higher elevation sites the spike was in 2004.
Currently, there is little aspen regeneration. Ungulate browse is heavy at all sites,
especially to aspen regeneration. All sites had some level of browse damage; the
percent ranged from 50 to 100 percent.
Aspen Decline in Coconino NF
San Francisco Peaks Area
2002/2003
Heavy mortality in an aspen clone at Dry Lake Park near Flagstaff, Arizona
140,000
Acres
120,000
100,000
80,000
Drought stressed overstory trees are expected to sprout suckers only within a year or
two of tree death. The large die-off of mature aspen trees in many lower elevation sites
coupled with browsing by ungulates is expected to result in type conversion of many
ecologically unique and important sites across the state.
60,000
40,000
20,000
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
0
Year
Aspen Regeneration in Sites Affected by
Dieback and Decline, Coconino NF.
Aspen Decline 2002/2003
Aspen Forest Type
2003
Stems per acre
5000
Acres of Aspen Defoliation/Decline in Arizona
1995-2003
160000
High
140000
Mod
120000
Low
Defoliators of Aspen in Arizona.
2005
3000
2000
1000
0
100000
acres
2004
4000
80000
2851 3288 3277 2567 3305 2247 2288 2456 2337
60000
Site
40000
Fresh bark stripping by elk.
20000
Marsonina Leaf Spot
0
1995
1996
1997
1998
1999
2000
2001
2002
2003
Year
Acknowledgements: We wish to thank Brian Howell, Steve McKelvey, Allison Honahni,
Joleen Atencio, and Kevin Johnson. Funding was provided by Forest Health Monitoring,
Evaluation and Monitoring Funds.
Large Aspen Tortrix
Melampsora rust