Monitoring the Condition of Aspen in the Northern and Intermountain Regions (INT-F-06-01)
John C. Guyon II, James T. Hoffman and Leah D. Aquino
Introduction
Forest, range, and wildlife managers in the Intermountain and Northern Rocky Mountain have documented a
decline in aspen forest acreage and declining health within aspen forests the since the 1970’s. The two
primary forces most commonly sited as contributing to this decline are changes in fire regimes since
European settlement and ungulate browsing, but forest insects and diseases play a largely undefined role in
aspen decline. Published data from long-term permanent monitoring plots established by the Forest Inventory
and Analysis unit in Ogden, Utah in 2002 documented suspected decline symptoms and conditions throughout
the range of aspen forests throughout the entire Rocky Mountain area, from Canada to Mexico. The
publication also recommended the establishment of additional off-plot sites to further define the damage, and
also to refine extent and severity of the decline in aspen clone health by damage agent.
In our evaluation monitoring project (INT-F-06-1) we proposed to establish monitoring plots in aspen stands in
Nevada, Utah, Southern Idaho, Western Wyoming, and Montana to provide additional data on forest damage
agents in aspen forests to supplement the established Forest Health Monitoring plot system.
Preliminary Results
Seventy-five permanent plots were established in aspen stands in Utah and Nevada in 2006. In 2007 the project will
move into southern Idaho and Wyoming, with northern Idaho and Montana slated for evaluation in 2008. A
preliminary summary of the information collected showed substantial amounts of damage in all the forests
surveyed. Large tree mortality from all agents on all plots averaged 29% and varied from a low of 20% on the
Manti-LaSal National Forest (NF), to over 45% on one District on the Humboldt-Toiyabe NF. Moderate- to heavydamage from all agents on the remaining living stems ranged from 23% to 62%. The most common damage agents
on the larger trees were stem borers (Saperda calcarata, and Agrilus liragus); canker diseases (Cytospora
chrysosperma and Encoelia pruinosa cankers), and various defoliating insects such as the large aspen tortrix
(Choristoneura conflictana), and aspen leaf tiers (Sciaphila duplex and Enargia decolor). Forest tent caterpillars
(Malacosoma disstria) have long been thought to be the principle defoliating insect in aspen forests in the
Intermountain Region, but they were not recorded on any plot in 2006.
The density of aspen sprouts less than 2” DBH varied greatly across National Forests, with the Manti-Lasal NF
averaging over 5500 TPA and less than 500 on the Uinta NF. Ungulate browsing was the most common damage
agent, occurring on 23% of all sprouts, but was conspicuously absent in some areas. Defoliating insects also
played a significant role in several sites, particularly on the Dixie NF, defoliating and killing many sprouts even in
the absence of ungulate damage. Data analysis of the data from 2006 is ongoing, and will examine the role of
elevation, slope position, and relative importance of the damage agents.
Declining aspen stands in the Intermountain Region
Methods
In 2006 seventy-five plots were established on National Forest System (NFS) lands in Utah and Nevada. The 1/20
acre plots were randomly located within polygons identified by 2004 and 2005 aerial pest detection surveys as
having symptoms of aspen dieback or defoliation. Plot level data included slope, elevation, GPS location, relative
clone stability, and successional status. Large tree data taken included: tree species, DBH, percent dieback, tree
condition (live, fresh dead, older dead), crown class, and presence and severity of damaging agents. Small trees
were sampled on three nested 1/100th acre sub-plots within each plot. Tree species, number per plot and damage
agent(s) and severity were recorded on the nested sub-plots.
Sprout Damaged by Ungulates
Sprout damaged by Ungulates
with a Canker
Metallic Poplar Borer Galleries
Percent Dead and Damaged
70
60
M
ke
Fis
h la
tn
D
ix
s
6000
5000
4000
3000
2000
1000
0
ie
Overall
H-T Austin
H-T Jarbidge
H-T Ruby Mtns
Wasatch-Cache
Manti-LaSal
Fishlake
Uinta
Dixie
Bridger-Teton
0
Sooty Bark (Encoelia) Canker
Au
st
in
The Culprit
W
-C
20
10
Count of Trees from Regeneration Subplots
in Trees/Acre (TPA)
Poplar Borer
Entrance
Wound with
Cytospora
Canker
M
Damage
R
ub
y
Mortality
30
U
in
ta
an
tiLa
Sa
l
Ja
rb
id
ge
40
TPA
P e rc e n t
50
Mortality
ke
Fi
sh
la
M
tn
s
Au
st
in
ub
y
R
ge
W
-C
bi
d
Ja
r
ta
Sa
l
M
an
t i-
Percent
100
80
in
D
120
U
ixi
e
Mortality and damage of large stems on one District on the Dixie NF. Damages are to living
stems and stems and light damages were omitted.
80
60
40
20
0
La
Partially defoliated aspen
Percent
Precent of Sprouts Damaged in Regeneration
Subplots
60
Moderate to
heavy damage
40
20
Moose Feeding Damage
from Wyoming
0
1
2
3
4
5
6
7
8
9
Plot Number
Large aspen
tortrix
Aspen twoleaf tier
Stand of Aspen Heavily Damaged by Animals
Wild Horses, One Source of Animal Damage in
Nevada
Procryphalus sp. Beetles, Playing
a new role?
Plot Layout on the Escalante District, Dixie NF, with Aerial
Detection Survey (ADS) of Aspen Dieback.
Acknowledgements: We wish to thanks Tom Zegler, Kaylyn Little and Rachael Leisso, Marcus Jackson, Wayne Shepperd,
Dale Bartos and Jim Worrall. Funding was provided by Forest Health Monitoring, Evaluation Monitoring funds.