James J. Worrall, Suzanne Bethers, Leanne Egeland, Roy A. Mask and Thomas Eager
Sudden aspen decline
in southwest Colorado
US Forest Service, Rocky Mountain Region, Forest Health Management, Gunnison, Colorado, USA
(INT-EM-07-01, year 2)
Note the elevation
gradient: healthy aspen
above, increasing crown
loss at lower elevations.
Note that regenerated
clearcuts are healthy,
surrounded by dead and
dying residual overstory
Preliminary results
25
§Worrall JJ, Egeland L, Eager T, Mask RA, Johnson EW, Kemp PA,
300,000
R2 = 0.0008
P = 0.71
15
10
15
10
5
Average regen.
in uncut, intact
stands in SW
Colorado:
2,500 ha-1
5
Dead roots
0
Damaged plots
0
0
200,000
40
60
Recent crown loss (%)
80
100
2006
2007
Year
2008
a
80
R2 = 0.002
P = 0.418
60
40
20
40
30
20
25
50
75
100
125
150
Mean age of stems in plot (years)
0
Galleries and adult of
an aspen bark beetle,
Trypophloeus populi.
Backslope
Shoulder
Summit
10
There is a clear trend of increasing crown
loss from toeslopes to summits, but the
differences are not significant.
Bronze poplar borer
galleries and larva
in live bark.
Cytospora canker
Footslope
Slope Position
Biotic agents significantly associated with SAD
Armillaria root
disease on aspen.
Photo by Jim Blodgett.
40
0
175
Despite the widespread belief that SAD is
related to age structure, neither age nor DBH
of over-story stems are related to SAD.
60
20
Toeslope
R2 = 0.100
P < 0.001
80
10
0
1. Location, elevation, topographic position, slope,
and aspect
2. Understory vegetation
3. Soil pit (soil class, mollic depth, texture, waterholding capacity, stoniness, etc.)
4. Root trench (quantifying live and dead aspen
roots)
5. Tree data (prism plot, stand structure, crown
loss, damage agents, increment cores)
6. Regeneration plot
Damaged plots have significantly
fewer live roots and significantly more
dead roots than healthy plots.
100
100
2005
In 2007 and 2008, we completed 162 intensive field
plots (81 pairs) in southwestern Colorado to identify
additional causes and stand impacts of SAD. We
randomly selected damaged plots (>25% crown loss)
in aerial survey polygons and nearby, paired healthy
plots (≤25% crown loss). Measurements included:
20
No significant regeneration response to crown loss (including mortality)
associated with SAD. This confirms earlier results from two sites.§
100,000
Methods
30
50 70 90
Site index
Site index is significantly related to
crown loss, but this explains a small
part of the variation in crown loss.
Preliminary Conclusions
1. Two sources of data indicate that regeneration is
not responding to recent crown loss and mortality.
2. Poor regeneration in damaged stands is
associated with dying root systems.
3. Within the overstory (stems ≥12 cm DBH), neither
age nor DBH are related to crown loss and
mortality, on either a plot basis or a tree basis.
4. Regeneration (stems <12 cm DBH) is generally
healthier than the overstory.
5. Each biotic agent associated with SAD (left) has
distinct patterns of occurrence in healthy vs.
damaged plots, host DBH, contagion, etc.
Early summer field work
Soil pit
analysis
20
Healthy plots
0
and Shepperd WD. 2008. Rapid mortality of Populus tremuloides in
southwestern Colorado, USA. Forest Ecology and Management 255:
686-696.
Mean # of roots
Live aspen regen. (103 stems ha -1)
400,000
20
Recent crown loss
Work has been in two phases. The results of the first
phase, including landscape and stand factors
associated with damage and a hypothesis on the
causes, are published§ and are not presented here.
500,000
Live roots
Average regeneration
one year after
clearcutting aspen in SW
Colorado: 76,600 ha-1
Recent crown loss (%)
We initiated a project in 2007 to determine the
severity, site/stand factors and causes of SAD.
As of 2008, over 17% of
Colorado’s aspen acreage
was affected
Recent crown loss (%)
In 2004, foresters in south-west Colorado began to
report unusual, rapid dieback and mortality of aspen.
Mortality has increased rapidly in Colorado and
has attracted intense media interest and concern from
wildlife officials, forest managers, forest products
industry, environmentalists, and others. We have
named the syndrome sudden aspen decline (SAD).
Aspen damage in CO (aerial survey acres)
Background and earlier work
25
Poplar
borer
6. Many site variables contribute small parts of the
variation in crown loss (a measure of SAD).