Station P a p e r No. 45
September 1959
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
Oecay of Aspen in Colorado
R o s s W. Davidson, Thomas E. Hinds, and F r a n k G. Hawksworth
ROCKY MOUNTAIN FOREST AND RANGE EXPERIMENT STATION
Raymond P r i c e ,
FOREST SERVICE
Director
F o r t Collins, Colorado
U.
S. DEPARTMENT O F AGRICULTURE
DECAY
O F ASPEN
IN C O L O R A D O
R o s s W. Davidson, Thomas E. Hinds, and F r a n k G. Hawksworth
Plant Pathologists
1/
Rocky Mountain F o r e s t and Range Experiment Station-
C O N T E N T S
Page
. . . . .
Location and type of stands sampled .
Review of previous work
Methods
Results
1
. . . . . . . . . . .
. . . . . . . . . . .
Relationship between decay and age
Fungi associated with aspen decay
.
.
Wetwood and associated defects . .
Summary . . . . . . . . . .
L i t e r a t u r e cited . . . . . . . .
Sporophores of aspen decay fungi
1/ Central headquarters is maintained in cooperation with
C o l o r ~ d oState University a t F o r t Collins. The senior author i s
now stationed a t the F o r e s t Disease Laboratory, Beltsville, Md.
DECAY
O F ASPEN
IN
COLORADO
by
Ross W. Davidson, Thomas E. Hinds, and F r a n k G. Hawksworth
Quaking aspen (Populus tremuloides Michx. ) stands a r e extensive in the c e n t r a l Rocky Mountains. The species r e a c h e s its
maximum development in the mountains and high m e s a s west of
the Continental Divide in Colorado (Baker, 1925). On the b e t t e r
s i t e s aspen yields a g r e a t e r volume of wood in a s h o r t e r period
than m o s t of the conifers growing a t comparable elevations.
The p r e s e n t study was undertaken to determine the relationship of decay in stands in different a r e a s and of different ages.
REVIEW
O F
PREVIOUS
WORK
Baker (1925), who made a study of aspen in the c e n t r a l Rocky
Mountains, s t a t e s : "It is found that while growth i s m o r e rapid in
New England, deterioration and decay take place e a r l i e r , s o that
the maximum and a v e r a g e s i z e s a r e about the s a m e in the two
regions and stands a r e v e r y s i m i l a r . " Likewise, growth i s m o r e
rapid in the better aspen a r e a s of the Lake States, but d e t e r i o r a tion is a l s o m o r e rapid there. Baker, who s e t up a c r i t e r i o n of
site quality based on height growth, s t a t e s that aspen grows on
a wide variety of s o i l types.
The studies of Meinecke (1929) in one locality in Utah indicate that m o s t of the r o t in aspen was caused by Fomes igniarius
var. populinus (Neu. ) campb.
and I?. applanatus ( P e r s. ex
W a l l r ) Gill. Decay was minor i n t h e y o u n g e r age c l a s s e s and
i n c r e a s e d with age. Decay accounted f o r 18 percent of the g r o s s
volume in the 101 to 110-year age c l a s s , and 41 p e r c e n t in the
121 to 130-year c l a s s .
9
-
-
Schmitz and Jackson (1927), working in Lake States aspen,
r e g a r d e d trunk r o t caused by F. igniarius a s the p r i m a r y loss,
but they a l s o recognized ~ r m i T l a r i am e l l e a (Fr. ) Quel. and F.
applanatus a s important decay fungi.
-
21
-
-
This fungus is h e r e a f t e r abbreviated F. igniarius.
Schrenk and Spaulding (1909) point out that in New England,
as well a s in Colorado and New Mexico, it i s a l m o s t impossible to
find stands of any age that a r e f r e e f r o m F. igniarius.
-
Russian investigators have conducted many studies on the decay
of European aspen (Populus t r e m u l a L. ) which is closely r e l a t e d to
-P. tremuloides. Ankudinov (1939) who reviewed the e a r l i e r Russian
work on this subject s t a t e s that, a s in North America, F. igniarius
is the m o s t important decay fungus. He r e p o r t s that th&e was no
consistent relationship between the amount of decay and s i t e quality
o r between decay and individual t r e e dominance. To minimize decay
l o s s e s , Ankudinov r e c o m m e n d s : (1) controlling the stand density
by e a r l y thinning, and (2) eliminating s t e m s that a r e injured, i n s e c t
damaged, o r broken topped, thus removing those m o s t susceptible
to F. igniarius.
-
Riley (1952) r e p o r t e d on the decay of aspen in Ontario caused
by F. igniarius. In stands u p to 70 y e a r s old no relation between
decay and site could be demonstrated where cubic foot volumes were
used, but a slightly higher percentage of cull o c c u r r e d on the poorer
s i t e s when the t r e e s w e r e m e a s u r e d in board feet. Basham (1958),
a l s o working in Ontario, reported that t h r e e types of h e a r t r o t s w e r e
important: white spongy r o t caused by F. igniarius, yellow stringy
r o t caused by Radulum c a s e a r i u m organ) Lloyd, and stringy butt
r o t s f r o m which s e v e r a l fungi, notably Pholiota spectabilis Fr. and
A. mellea, w e r e isolated. A pronounced relationship between age
and decay was found. The r elationship between decay and soil conditions was l e s s pronounced although t r e e s on d r i e r s i t e s were
somewhat m o r e decadent than those on m o i s t ones.
LOCATION
AND
TYPE
O F STANDS SAMPLED
Samples for the p r e s e n t study w e r e a l l located in w e s t e r n Color a d o in stands considered to be among the b e s t in the region. The
work was c a r r i e d out in the s u m m e r s of 1954, 1955, and 1956.
Sample plots w e r e a t elevations between 8, 000 and 10, 000 feet,
where aspen frequently o c c u r s in a l m o s t pure stands. At the lower
l i m i t s s e r v i c e b e r r y , s c r u b oak, and in some places Douglas -fir and
ponderosa pine m a y be intermixed, while a t the higher elevations
t h e r e i s often an understory of spruce and subalpine f i r . The b e t t e r
aspen stands in Colorado have abundant undergrowth of herbaceous
plants, which i s considered excellent forage for sheep. The climatic,
soil, and m o i s t u r e r e q u i r e m e n t s for aspen in the c e n t r a l Rocky
Mountain region a r e discussed by Baker (1925).
METHODS
Study plots of typical c o m m e r c i a l a s p e n f o r e s t s w e r e located
in old and medium-aged stands. Isolated s m a l l patches of a s p e n
w e r e not s a m p l e d n o r w e r e s t a n d s a t the lower elevations w h e r e
growth i s poor and c o m m e r c i a l values a r e m a r g i n a l . The m e n s u r a t i o n a l data w e r e taken to c o r r e s p o n d with c u r r e n t p r a c t i c e s f o r
pulpwood s a l e s in t h i s a r e a . E i t h e r 11 10- o r 1120-acre plots w e r e
used, depending on the t i m e available. All t r e e s over 4 . 0 inches
d. b. h . , and a few below this l i m i t , w e r e felled and d i s s e c t e d . The
t r e e s w e r e cut into 4 - o r 8 -foot bolts to a m i n i m u m top d i a m e t e r
of 4 . 0 inches d. i. b. 41 Where decay was encountered, the bolts
w e r e f u r t h e r d i s s e c t e d to d e t e r m i n e the extent of decay. Samples
f o r isolation w e r e r e m o v e d f r o m d e c a y infections where the c a u s a l
fungus w a s in doubt. Age was d e t e r m i n e d f r o m s a m p l e d i s k s taken
a t s t u m p height and l a t e r examined in the l a b o r a t o r y with a binocul a r m i c r o s c o p e . Wood volume was calculated for each bolt by
S m a l i a n ' s formula. Rot volumes w e r e calculated in the s a m e way
except t h a t w h e r e r o t ended within a bolt i t w a s t r e a t e d a s a cone.
RESULTS
A total of 976 t r e e s was d i s s e c t e d on 35 plots in 5 national
f o r e s t s in w e s t e r n Colorado (fig. 1). Decay was found in 517 t r e e s
(53. 0 p e r c e n t ) and a v e r a g e d 8 . 4 p e r c e n t of t h e total g r o s s volume
on the plots studied. Trunk r o t s accounted for 5. 0 p e r c e n t of the
g r o s s volume, and butt r o t s 3 . 4 percent. The b a s i c plot data by
s i t e c l a s s e s a r e given in table I . The a s p e n s t a n d s studied w e r e
in s i t e c l a s s e s 1 to 3, according to B a k e r ' s (1925) s i t e c l a s s i f i c a tion. The a v e r a g e height of dominant t r e e s a t 100 y e a r s i s 8 1 f e e t
on s i t e 1, 74 f e e t on s i t e 2, and 63 f e e t on s i t e 3. Nine of the plots
w e r e two-aged r a t h e r than even-aged, and on t h e s e each age c l a s s
w a s analyzed s e p a r a t e l y .
3/ About 60 percent of the t r e e s were felled in 1954 and 1955 when 4-foot bolts were cut.
In 1956, t r e e s were cut into 8-foot bolts except the top bolt was 4 feet if i t was too s m a l l to yield
an 8-foot bolt. A trimming allowance of 0. 25 foot was used for a l l bolts. The trimming allowance was not included in the volume totals for the 1954 and 1955 work but i t was included for the
t r e e s c u t in 1956. These variations in technique should have little effect on the overall r e s u l t s ,
which a t best, can only be considered a s indicative of general trends. Because of the g r e a t v a r i ation in the amount of decay in plots in the s a m e age and site c l a s s , the slight deviations due to
different techniques should be of little significance in determining r o t percentages.
Table 1. - - B a s i c plot d a t a by s i t e c l a s s e s
-
P l o t No.
-
.:
Tree basis
Number
j
Average age
Year
-
j
A v e r a g e d. b. h.
Inches
-
S I T E
GM-U-4
R-18
G-12(a)
R-21
GM-U-l(a)
GM-U-2
Total o r average
Total
'
: g r o s s volume
.
Butt
-
Cubic f e e t
Trunk
-
Percent
:
Total
--
1
41
52
58
63
66
68
6.7
6. 9
7. 6
6. 1
7.8
9.7
123.8
256.1
240.7
89. 6
174.3
321.2
21
19
6
10
16
18
86
114
119
126
150
17 0
12. 1
12.3
14. 1
14. 9
17. 3
15. 8
540.7
448. 3
200.7
291.1
811.2
833.9
433
78
10.5
S I T E
55
57
65
69
72
73
Decay
:
0. 2
3.2
2. 0
2.5
0.8
1.9
4.7
2.0
3. 5
3. 3
0.8
1.9
4. 9
5. 2
5. 5
5.8
.7
.2
.7
1.9
16. 8
9. 0
1.0
1.7
5.8
10.4
.5
6. 0
1.7
1. 9
6.5
12.3
17.3
15. 0
3. 9
2. 4
6. 3
66.7
96. 0
59. 5
173. 5
488.1
254.2
1. 4
.2
1. 3
4
.1
1.8
1. 6
.5
6.7
3.2
2.2
1.7
3. 0
.7
8. 0
3.6
2.3
3. 5
277.9
238.4
442. 1
352.0
246.3
566.1
2. 1
5
6. 0
19. 0
2. 5
1.7
21. 0
3.9
2.9
3. 0
19. 9
9.4
23. 1
4.4
8. 9
22. 0
22. 4
11.1
3. 3
6. 1
9.4
6,709.8
0
o
2
6. 0
6. 3
7.2
7. 6
9. 9
9.3
GM-U-6
GM-U -7
R-20
WR-10
G-11
R-19(a)
WR-11
GM-U-9
GM-U-8(a)
SJ-9
SJ-6
Total o r average
13
10
21
8
11
32
115
115
11 6
135
152
153
354
93
12.
12.
12.
18.
11.
10.
8
5
0
2
8
5
10. 6
S I T E
5,202.5
3
53
59
63
66
66
5. 2
4. 8
5. 6
6.8
5.8
75. 6
9. 5
21.4
68.4
113. 6
1.0
0
0
.1
2
.8
3.1
5.3
1.9
2.0
1.8
3. 1
5.3
2.0
2.2
23
5
10
4
12
66
104
130
130
131
6. 6
12. 5
14. 0
17.4
13. 8
75.4
92.8
280. 1
149.1
328.8
1. 5
4.1
1. 2
5.5
2. 6
6.0
12.1
22. 6
10.5
22. 0
7. 5
16.2
23. 8
16.0
24.6
Total o r average
189
73
9.2
1, 214.7
2.2
14.2
16.4
G r a n d total
o r average
97 6
82
9. 3
13, 1 2 7 . 0
3.4
5.0
8.4
G-lO(b)
WR-15(a)
GM-U-ll(a)
GM-U-12(a)
G-lO(a)
11
-
SJ
WR
G
GM-U
= San J u a n N a t i o n a l F o r e s t (plots e s t a b l i s h e d in 1954 o r 1955)
= White R i v e r N a t i o n a l F o r e s t (plots e s t a b l i s h e d i n 1954 o r 1955)
= G u n n i s o n National F o r e s t (plots e s t a b l i s h e d i n 1956)
= G r a n d M e s a - U n c o m p a h g r e N a t i o n a l F o r e s t (plots 1 - 3 e s t a b l i s h e d i n 1954 o r 1955;
plots 4-12 e s t a b l i s h e d i n 1956)
R
= R o u t t N a t i o n a l F o r e s t ( p l o t s e s t a b l i s h e d i n 1954 o r 1955)
Two-aged s t a n d s a r e i n d i c a t e d b y l o w e r - c a s e l e t t e r s in p a r e n t h e s e s . F o r e x a m p l e , o n plot S J - 7 t h e r e w e r e
22 t r e e s in the 4 1 - y e a r c l a s s [ S J - 7 @ ) ] and 27 a v e r a g i n g 7 3 y e a r s old [ S J - 7 ( a ) 1.
LEGEND
ASPEN DECAY PLOT
NATIONAC FOREST HEADQUARTERS
F i g u r e 1. --Map of
w e s t e r n Colorado
showing the
location of the
35 aspen decay
plots.
A detailed f i r e h i s t o r y for the a s p e n a r e a s was not available.
However, the younger stands up to 80 y e a r s a r e approximately
even-aged and a r e a s s u m e d to have originated following f i r e .
T h e r e i s considerable evidence that stands a l s o originate f r o m
c a u s e s other than f i r e . F o r instance, many of the older stands
(80 to 1 2 0 y e a r s o r o l d e r ) tend to b r e a k up rapidly because of
d i s e a s e , i n s e c t s , o r drought. Sometimes the r e s u l t i s a new
even-aged stand, o r t h e r e may be only a thinning out of the
older s t e m s , permitting s p r o u t s to develop a s an even-aged
understory.
RELATIONSHIP BETWEEN DECAY AND AGE
The relationship be tween the amount of decay and stand age
i s shown in figure 2. Although t h e r e is little relationship between
decay and site c l a s s for the younger stands, the differences a r e
f
24
-
SlTE 3
SITE 2
o
slrr I
-
10 PLOTS
17
PLOTS
17 PLOTS
Figure 2.
20-
5
- -Relation -
16-
ship be tween
12-
percent decay
0
Y
n
c-
w
z
a
0
L a4
and age on t h r e e
-
0
site clas ses.
I
0
20
1
I
40
60
,
I
100
80
STAND AGE
-
I
120
140
I
160
YEARS
m a r k e d in stands over 100 y e a r s old. The decay c u r v e s in figure 2
should be considered tentative because of the g r e a t variation in d e c a y in s o m e plots of comparable ages and a i t e c l a s s e s . A s u m m a r y
f r o m figure 2 of the average amount of decay in stands of different
a g e s on the 3 s i t e s is a s follows:
Stand age
in y e a r s
P e r c e n t decay
Site 3
Site 1
Site 2
The amount of decay in stands under 40 y e a r s old was negligible
on a l l 3 sites. In 100-year -old stands, decay averaged 4 p e r c e n t
on site 1, 8 percent on site 2 , and 13 percent on site 3.
Some of the variations in decay in plots of comparable a g e s
and s i t e s can be explained, but o t h e r s cannot. F o r instance, the
high volume of butt r o t in some of the older plots i s due to decay
following f i r e wounding about 80 y e a r s ago. Some of these old
wounds w e r e still open and extended to a considerable height on
the trunks. In other older stands the wounds had not been s o
sc vere and although decayed, had become a l m o s t completely
healed over in the 80-year period. F i r e wounds w e r e not
common in any of the stands under 85 y e a r s old. One of the m a i n
r e a s o n s f o r variations in r o t volume was that F. igniarius was
r a r e o r absent in some stands.
The incidence of decay in Colorado a s p e n i s considerably
lower than that r e p o r t e d by Meinecke (1929) f o r this species in
one locality in n o r t h e r n Utah:
Age c l a s s
in y e a r s
P e r cent decay
Utah
Colorado
Sites 1 and 2
Sites 1 and 2
Basham (1958) noted that for aspen in Ontario the r a t i o of
butt r o t s to trunk r o t s was highest on the d r i e s t sites. In the
p r e s e n t study in Colorado, butt r o t s amounted to 62, 3 5 , and
1 3 p e r c e n t of all decay volume on s i t e s 1, 2, and 3, respectively.
FUNGI ASSOCIATED WITH ASPEN DECAY-41
Identifications of the decay fungi w e r e made f o r 60 p e r c e n t
of the infections; these accounted f o r 69 percent of the total decay
volume a s shown below. The figures a r e based on 672 decay i n fections and a decay volume of 1, 145.8 cubic feet.
Type of decay
Infections
(Percent)
Decay volume
(Percent)
60
69
11
29
40
17
14
31
Identified d e c a y s :
Trunk r o t e
Butt r o t e
Unidentified decays :
Trunk r o t s
Butt r o t s
41 The authorities for the scientific n a m e s of the fungi
found i n this study a r e given in table 2.
Identified decays accounted f o r 7 5 p e r c e n t of the t r u n k r o t volume
but only 5 5 p e r c e n t of the butt r o t volume. The 17 decay fungi
identified and t h e i r r e l a t i v e importance a r e shown in table 2.
Some of the fungi l i s t e d r e q u i r e f u r t h e r study for positive identification, and t h e r e a r e undoubtedly o t h e r s t h a t c a u s e d e c a y but
have not y e t been identified.
Table 2. --Fungi associated with identified aspen decays
Fungus
:
:
Infections
Decay volume
Number P e r c e n t
Cu. ft. P e r c e n t
---
Trunk r o t s :
Cryptochaete polygonia (Fr. ) Karst.
114
28. 3
F o m e s igniarius var. populinus (Neu. ) Campb.
104
25.9
75.7
9. 6
466.9
59.1
38
9. 5
36. 2
4. 6
Polyporus dryophilus Berk. var. vulpinus ( F r . ) Overh.
3
.7
12.1
1.5
Daldinia concentrica ( F r . ) Cs. & DeNot.
2
.5
.5
.1
T r e c h i s p o r a brinkrnannia (Bres. ) Rogers & Jacks.
1
.3
8. 3
1.0
Collybia velutipes Curt. ex Fr.
48
11.9
78.7
10.0
F o m e s applanatus ( P e r s . e x Wallr. ) Gill.
32
8. 0
49.8
6. 3
Pholiota s q u a r r o s a (Fr.) K u m m e r
18
4. 5
20.2
2.5
Coniophora sp.
Libertella sp.
Total trunk r o t s
Butt r o t s :
14
3. 5
.5
.1
Pleurotus o s t r e a t u s (Fr. ) K u m m e r
9
2. 2
13.7
1.7
Polyporus adustus Willd. ex Fr.
7
1.7
4.4
.6
T r e c h i s p o r a raduloides (Karst. ) R o g e r s
5
1. 2
19.5
2.5
A r m i l l a r i a m e l l e a (Fr. ) Quel.
3
.7
Trace
--
Polyporus pargamenus Fr.
2
.5
Trace
--
Tricholoma unifactum P e c k
1
.3
3.3
.4
Radulum c a s e a r i u m (Morgan) Lloyd
1
.3
Trace
--
140
34.8
190.1
24. 1
40 2
100.0
Total butt r o t s
Total trunk and butt r o t s
789.8
100.0
More s p e c i e s of fungi w e r e isolated f r o m butt decay than
t r u n k decay, although the number of d e c a y infections was about
the s a m e in e a c h category. Trunk r o t s accounted f o r about
two-thirds of the total decay volume; butt r o t s , one-third. In
this study F. i g n i a r i u s and Cryptochaete polygonia w e r e c l a s s i
fied a s truKk r o t s , although in t h e c a s e of F. igniarius especially,
the r o t was s o m e t i m e s concentrated i n t h e x u t t . Collybia
velutipes was usually i s o l a t e d f r o m butt r o t , but i s known to
invade t r u n k wounds of s o m e t r e e species.
-
Of the s i x species c l a s s e d a s trunk decays, C. polygonia
(fig. 3) was isolated and identified m o s t frequentlym(28 percent
of identified infections). A p r e l i m i n a r y account of this fungus
f r o m Colorado a s p e n w a s given by Davidson and Hinds (1958).
Since C. polygonia does not f r u i t r e a d i l y on infected living t r e e s ,
it could be identified only f r o m isolations. T h e r e w e r e many
additional decay infections that appeared to be this fungus, but
which w e r e not positively identified e i t h e r because of f a i l u r e to
obtain a culture o r the isolate was of a secondary non-decay
species.
C. polygonia was white, often with a
Decay caused by reddish-brown margin. The decay was usually suggestive of an
incipient stage and never appeared to be in an advanced stage of
disintegration. When i t was exposed on c r o s s cuts with a power
saw, the infected wood s e e m e d to be m o r e b r i t t l e than n o r m a l
wood and the f i b e r s w e r e pulled out r a t h e r than c u t cleanly.
Entrance was a l m o s t e n t i r e l y through b ~ a n c hstubs. Incipient
decay of F. igniarius (fig. 3) can be distinguished f r o m that of
C. polygonia only when the black m a r g i n a l line, usually c h a r a c t e r i s t i c of the f o r m e r , i s present. F. igniarius caused much
g r e a t e r volume l o s s than any of the o t h e r decay fungi (59 p e r cent of the volume a s s o c i a t e d with identified decays). In stands
younger than about 8 0 y e a r s , both the proportion of t r e e s infected
and the amount of decay per t r e e was low.
T r e e s infected by F. igniarius had an a v e r a g e of 2 5 p e r c e n t
decayed volume. This a v e r a g e includes incipient infections in
young t r e e s s o the volume of decayed wood in the older stands
where sporophores a r e p r e s e n t i s somewhat higher.
Polyporus dryophilus var. vulpinus, which c a u s e s a white
pocket trunk rot, w a s isolated only t h r e e times. These infections
w e r e f r o m older t r e e s . Daldinia concentrica was p r e s e n t in two
living t r e e s but it caused little decay.
F. applanatus s e e m s to be the m o s t important butt and r o o t
r o t , chiefly because i t r e s u l t s in windthrow. The r o t i s white
mottledand i t was consistently concentrated in the l a r g e r o o t s
and b a s a l p a r t of the s t e m (fig. 4). In a l m o s t a l l aspen stands
observed, t h e r e w e r e numerous t r e e s that had blown over while
s t i l l alive. Nearly a l l these had r o o t s r o t t e d off by F. applanatus.
The decay affects both sapwood and heartwood but uFually does
not extend f a r above s t u m p height. The principal c o u r t s of e n t r y
a r e not known in detail, but presumably a r e in the roots, since
above-ground wounds w e r e not a s s o c i a t e d with this decay.
F i g u r e 3. - - I m p o i t a n t t r u n k d e c a y s in aspen. A and B. F o m e s i g n i a r i u s v a r . populinus, the
fungus r e s p o n s i b l e f o r about 60 p e r c e n t of t h e t o t a l decay. A. Sporophore (X 9/10), a n d 2.
C r o s a s e c t l o n of st(2m showing t y p i c a l d e c a y (X 113). C and-2,
Cryptochaete polygonia,
the fungus that w a s i s o l a t e d m o s t frequently but c a u s e d - b n l y about 10 p e r c e n t of the t o t a l
decay. 5. S p o r o p h o r e s on dead b r a n c h (X 1-71 10) and p. Decay (X 1 / 10).
Figure 4. --Important butt r o t s i n aspen. A and B. Sporophores and decay of Pholiota s q u a r r o s a
6 m e s applanatus, a butt r o t that a l s o a c t s parasitically
(both approximately X 116). 5 and.!
and c a u s e s weakening of the roots and windthrow. C. Sporophore a t base of living t r e e (X 116).
D. Top view of sporophore, c r o s s section of de:cayed stc
a1 section showing
decay i n the: s t u m p a nd r o o t s
-
Decay attributed to Collybia velutipes had a l a r g e r total volume
than any other butt rot. It was a l s o the m o s t frequently identified
butt r o t fungus. Incipient s t a g e s of decays a s s o c i a t e d with Pholiota
s q u a r r o s a and F. applanatus a r e s i m i l a r (fig. 4). Entrance of both
s e e m s to be thFough the r o o t s , but P. s q u a r r o s a does not a c t a s a
p a r a s i t e to the s a m e extent a s F. applanatus and does not r e s u l t in
weakening and subsequent windrhrow.
Tricholoma unifactum was found fruiting on the ground a t the
b a s e of a n infected t r e e . Cultures f r o m the sporophores and f r o m
the r o t in the t r e e w e r e identical.
Brown butt r o t s were f a i r l y common, especially in young stands.
Some of the c u l t u r e s obtained f r o m brown butt r o t w e r e f a i r l y typical
of Coniophora puteana (Schum. ) Karst. but their identification i s not
yet certain. T h e r e m a y be m o r e than one s p e c i e s involved s o for the
p r e s e n t they a r e grouped under Coniophora sp.
A r m i l l a r i a mellea was definitely identified only t h r e e t i m e s .
Its actual frequency i s probably somewhat higher a s t h i s fungus i s
difficult to isolate. No fungi w e r e isolated f r o m a number of decay
infections that appeared to be caused by A. mellea. The identified
infections were f r o m s m a l l pockets of r o r a s s o c i a t e d with b a s a l wounds.
Polyporus adustus o c c u r s a s a s a p r o t associated with wounds
but was not isolated f r o m typical h e a r t rot. Pleurotus o s t r e a t u s was
isolated f r o m nine t r e e s . It was usually found a s a h e a r t r o t in the
lower p a r t of the trunk, and decay was f a i r l y extensive.
Libertella sp. was associated with a white mottled top r o t in
38 t r e e s . This decay has a n odor s i m i l a r to green
walnut hulls.
Cultures of this fungus have a dense, buff, cottony mat, with d a r k
sporulating a r e a s developing a f t e r 3 to 4 weeks. Etheridge and
Laut (1958) isolated ~ i b e r t e l l asp. f r o m sound a s well as-decayed
aspen wood in Alberta s o its s t a t u s a s a decay-producing organism
i s uncertain.
SPOROPHORES O F ASPEN DECAY FUNGI
F. igniarius decay had conspicuous
Most t r e e s with extensive fruiting bodies on the trunk (fig. 3 -A). The number of such fruiting
bodies, which usually f o r m a t old branch stub t r a c e s , i s an indication
of the longitudinal s p r e a d of decay inside the trunk.
F o m e s applanatus fruiting bodies a r e usually p r e s e n t on the
b a s e s of the infected living t r e e s (fig. 4 - C ) but a r e often s o n e a r
the b a s e a s to be p a r t l y hidden by g r a s s o r h e r b a c e o u s plant growth
or leaf l i t t e r . F r u i t i n g bodies continue to develop a f t e r the t r e e s
a r e windthrown.
Sporophores of Pholiota s q u a r r o s a (fig. 4-A) and Tricholoma
unifactum develop on the s o i l a t the b a s e of infected t r e e s . P l e u r o t u s
o s t r e a t u s and Collybia velutipes frequently f r u i t on dead standing
o r down t r e e s but w e r e not s e e n on living t r e e s . The l a t t e r w e r e
m o s t frequently f o r m e d a t the b a s e of the t r u n k s o r f r o m dead
roots. The fruiting bodies of Daldinia concentrica w e r e s e e n on
one living t r e e . Cryptochaete polygonia f r u i t s abundantly on the
b a r k of recently fallen t r e e s and only occasionally on dead branch
s t u b s of living t r e e s . Coniphora puteana sporophore s have been
collected on a s p e n logs but not on living t r e e s . Polyporus a d u s t u s
w a s a l s o found on logs, but in a few instances i t a p p e a r e d to be a
wound saprophyte of living t r e e s .
WETWOOD AND ASSOCIATED DEFECTS
Wetwood i s a common defect in many hardwood t r e e s p e c i e s .
In s o m e aspen stands wetwood infections w e r e common, while in
o t h e r s they w e r e r a r e . No information on the possible influence
of wetwood on decay w a s obtained in this study. Wetwood was
commonly a s s o c i a t e d with wood b o r e r s and in these instances
decay was r a r e l y present. However, when wetwood was a s s o c i ated with wounds, decay was usually p r e s e n t also. Wetwood
infections on one plot on the Routt National F o r e s t appeared to
be a s s o c i a t e d with prominent f r o s t c r a c k s . However, other
stands in the s a m e vicinity with a high proportion of wetwood
infections had no f r o s t c r a c k s . B a c t e r i a c a u s e wetwood in
s e v e r a l t r e e s p e c i e s ( C a r t e r 1945), but no study was made on
the c a u s e of wetwood in aspen, More information i s needed to
provide a b e t t e r understanding of the r o l e of wetwood in the
pathology of aspen.
SUMMARY
A total of 976 a s p e n t r e e s over 4. 0 inches in d i a m e t e r w e r e
felled and d i s s e c t e d on thirty-five 1 / 1 0 - o r 1120-acre plots on
5 national f o r e s t s in w e s t e r n Colorado. Decay was found in
53 p e r c e n t of the t r e e s and accounted for 8 . 4 p e r c e n t of the
g r o s s volume. T h e r e was a definite r e l a t i o n s h i p between stand
age and decay and between s i t e quality and decay. In 50-year -old
s t a n d s the a v e r a g e amount of decay (cubic foot b a s i s ) w a s l e s s
than 2 p e r c e n t on s i t e s 1, 2, and 3. In 100-year-old stands, the
d e c a y a v e r a g e d 4, 8, and 13 p e r c e n t for s i t e s 1, 2, and 3, r e s p e c tively. Identified d e c a y s accounted f o r about two-thirds of the
t o t a l d e c a y volume. Cryptochaete polygonia was the m o s t f r e quently isolated d e c a y fungus (28 p e r c e n t of identified infections)
b u t F o m e s i g n i a r i u s v a r . populinus c a u s e d the g r e a t e s t volume
l o s s (59 p e r c e n t of decay a s s o c i a t e d with identified infections).
Most of the butt r o t w a s c a u s e d by Collybia velutipes, F o m e s
applanatus, and Pholiota s q u a r r o s a . C. velutipes w a s a s s o c i a t e d
with the g r e a t e s t volume of butt decay, and i t was a l s o the m o s t
F. applanatus i s i m p o r t a n t
frequently i s o l a t e d butt r o t fungus. a s i t i s a r o o t p a r a s i t e and c a u s e s weakening and windthrow.
LITERATURE
Ankudinov, A. M.
1939. S e r d t s e v i n n a i a gnil' o s i n y i m e r y
b o r ' b y s neiu. [ H e a r t r o t of a s p e n
and c o n t r o l of t h i s d i s e a s e . ]
Bolezni D r e v e s i n y i M e r y B o r 'by
s Nimi, Pushkino, VNILKH 7 : 3-68.
[ U . S. Bur. P l a n t Indus. T r a n s lation 842, 8 9 pp. ]
B a k e r , F r e d e r i c k S.
1925. Aspen in t h e c e n t r a l Rocky Mountain
region. U. S. Dept. Agr. Bul.
1291. 47 pp. , i l l u s .
Basham. J. T.
1958. D e c a y of t r e m b l i n g aspen. Canad.
J o u r . Bot. 36: 491 -505, i l l u s .
C a r t e r , J. C e d r i c .
1945. Wetwood of e l m s . Ill. Nat. Hist.
S u r v e y Bul. 23 : 407 -448, i l l u s .
Davidson, R o s s W., a n d Hinds, T h o m a s E.
1958. Unusual fungi a s s o c i a t e d with d e c a y
in s o m e f o r e s t t r e e s i n Colorado.
Phytopathology 48 : 21 6-218, i l l u s .
Etheridge, D. E.. and Laut, J.
1958. F u n g i a s s o c i a t e d with living and d e a d
b r a n c h e s of p o l e - s i z e d a s p e n . Canada
Dept. Agr. Sci. S e r v . F o r . Biol. Div.,
Bimo. P r o g . Rpt. 13(4): 2-3.
Agriculture
--- CSU,Ft.Collins
CITED
Meinecke, E. P.
1929. Quaking a s p e n : a s t u d y in applied
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Tech. Bul. 155. 34 pp.. i l l u s .
Riley. C. G.
1952. Studies in f o r e s t pathology. IX.
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Canad. J o u r . Bot. 30: 7 10-7 34.
illus.
Schmitz. Henry, a n d J a c k s o n , L y l e W. R.
1927. H e a r t r o t of a s p e n , with s p e c i a l
reference to f o r e s t management
in Minnesota. Minn. Agr. Expt.
Sta. Tech. Bul. 50, 4 3 pp., illus.
Schrenk, H e r m a n n von, and Spaulding, P e r l e y .
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U. S. Dept. Agr. Bul. 149,
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