Purchased by the U.S. Ji'orest Service for official use.
Earlier Forecasting of
Douglas-Fir Cone Crop
Using Male Buds
ABSTRACT.-Ear/ier forecasting of Douglas-fir cone
crops depends upon some indirl'Ct method of estimating
female cone buds before they differentiate in late August.
This study discusses correlation of female with male buds,
recognizable early by position on the twigs while female
buds are still indistinguishable fro1n vegetative buds. In
1964, at Corvallis, Ore[Jon, samples of 12 trees each at
200-, 1,500-, 2,900-, and 3,600-foot elevations ievea/ed
about_ the san1e total number of buds per sample in spring;
but by September, abortion of male buds diminished these
numbers almost linearly with increasing elevations. Ninety
percent had developed at 200 feet, whereas 93 percent had
aborted at 3,600 feet. Female bud counts at three of four
elevations correlated fairly well with nonaborted rnale
counts, but were uncorrelated with total bud counts sa1n­
pled on lateral twigs. Twig samples collected at 1nonthly
intervals sho}ved that abortion was mostly over by late
July. This finding pennits reasonably accurate estimates in
late July of the September female bud numbers. In this
study, rnost of the male cone crop variation, and presu111a­
bly female cone crop, could be explained by differential
abortion of buds.
The so-called aborted buds in male
positions were found to contain live meriste1ns and could
he forced into vegetative growth. The 111ajority of male
bud abortion occurred in July irrespective of elevation.
---- -----
-·------
FORECASTING Douglas-fir cone crops depends initial­
ly upon some means of sampling relative numbers of
female buds. As pointed out by Allen, 1 such sampling
can accurately forecast a crop failure but not necessar­
ily a successful crop. Insects, frosts, poor pollination. or
abortions often seriously reduce a potential crop be­
tween late August, when female buds are first readily
recognized, and a year later, when the seed is ripe.
This paper discusses means of forecasting relative
numbers of female buds two to four months earlier
than heretofore from observation of male buds, thus
updating the earliest possible forecast of a crop by this
interval of time. It is an extremely important updating,
since this period-late May to early August-is usual­
ly early enough to be considered in planning seed
procurements from the current year's crop. The meth­
od involves recognition of male buds during early
development, their pattern of occurrence, amount and
THE AUTIIOR is principal plant geneticist, Forestry Sciences
Laboratory, Pacific Northwest Forest and Range Expt. Sta.,
Forest Service, U. S. Dept. Agric., Corvallis, Ore.
1A1Jen, G. S. A basis of forecasting seed crops of some
coniferous trees. Jour. Forestry 39:1014-1016. 1941.
Roy R. Silen
stages of abortion, and relationship of male bud num­
bers to female bud numbers.
Male buds do not differentiate earlier than female
buds,• but the males are usually recognizable earlier in
the season from their position on the twig. Except on
the terminal and subterminal shoots of any branch,
male buds are almost the only buds that develop on
the proximal half of each twig. By mid-May at low
elevations, and later at progressively higher elevations,
they appear as tiny but unmistakable buds near 1he
leaf axils of the expanding twig. By July, a twig
destined for male bud production has clusters of buds,
I to 2 millimeters in diameter, along its lower side.
Materials and Methods
In 1963, 28 Douglas-fir trees, 50 to 100 feet tall,
near Corvallis, Ore., were climbed each month from
February to September as part of a separate study on
cone crop manipulation. As soon as male buds occame
recognizable on upper-crown branches, their presence
or absence was noted. Then in the fall, counts of
female and male buds were made on each of these
branches. This preliminary study indicated that use of
early male bud counts might be a promising approach
to earlier cone crop predictions.
Therefore, in 1964, 48 trees were sampled, 12 at
200-foot elevation near Corvallis and 12 each at
1,500-, 2,900-, and 3,600-foot elevation on Marys
Peak, 12 miles west of Corvallis in the Coast Ranges.
All were 50 to I 00 feet tall and had evidence of
previous cone production. After the vegetative buds
began to swell in late April, two branches were
collected monthly from the top, the middle, and the
lower crown of each tree. For male-bud counts, five
nonterminal twigs were used from each branch at each
level. Thus, 30 twigs per tree were sampled at each
collection. Subsamples of these twigs were preserved in
killing solution (FAA) for a monthly record of bud
development.
In late September, female buds on two opposite
limbs in the third to seventh whorl from the tree top
were counted for use as an index of female bud
production for the tree. Except for prolific cone pro­
ducers, these whorls usually contained most of the
female cone production of the tree. It was felt that this
2Qwens, J. N., and F. H. Smith. The initiation and ear]y
development of the seed c9ne of Douglas-fir. Can. Jour. Bot.
42: 1031-1047. 1964.
·
third-to-seventh-whorl stratification would give a less
variable estimate of the tree's relative female bud
product!uu than total count.
Counts of male buds on sample twigs were made
under a binocular microscope if they were not plainly
visible to the naked eye. Bud data for 1964 were
analyzed by simple correlation methods. The preserved
twig samples from each monthly collection provided
and subsequently a good female cone crop in 1964,
had few or no abortions of the developing male buds
between May and August 1963. But abortion of part
material for estimating when bud abortions occurred.
Final counts of aborted and nonaborted male buds
were 1t1ade on fall-collected twigs.
male bud abortion. The 1964 cone crop was poor at
1,500, 2,900, and 3,600 feet, corresponding to the
heavy abortion of male buds at higher elevations. The
crop was medium to good at low elevation, where the
sampled trees also showed least abortion of male buds.
Results
1963 observations.-At first glance, results of the
or all the potential male buds was commonly observed
on the trees producing medium, poor, or no crops. This
proved to be the key to the problem.
In retrospect, the prediction would have been quite
useful had we considered the elevational differences in
1963 exploratory study, presented in Table 1, would
seem entirely negative. Of 24 trees displaying signs of
1964 study.-Following the major lead from the
1963 study, attention in the 1964 study was concen­
male buds in spring, 12 produced cone buds in that
fall and 12 did not. Two further observations, howev­
trated on
( 1) ascertaining if counts of nonaborted
er, were more encouraging. First, the four trees that
showed no buds in male position in the spring were
male buds were closely related to female bud counts
and ( 2) learning the developmental pattern of normal
and aborted buds by observing time that buds are first
without cone buds that fall. Secondly, it was noted that
the trees having a good male bud potential in 1963,
visible, when abortions occur, and fate of aborted
buds.
Fig. 4.-Male, female, and total bud
numbers related to elevation. Total buds
refer to all lateral buds seen on the twig.
By adjusting female bud count scale to
same length as male count scale, all four
relationships of the paper are illus­
trated: (1) the strong reationship be­
tween female bud counts and counts. of
nonaborted male buds, (2) lack of rela­
tionship between female and total bud
counts, (3) similarity of total-bud counts
at all elevations, and (4) almost linear
decrease in cone buds with increasing
elevation. Each point is the composite
count of the sample from 12 trees.
TOTAL ANO
MALE bud count
1.600
FEMALE
bud count
1.000
900
1.400
BOO
1.200
1.000
'l
'\\ Nonaborted llALE
\
BOO
"'
600
\
500
Fig. 1.
Fig. 2.
Fig. 3.
600
400
Fig. 1.-Buds within a bud. Douglas-fir buds1 presumably male1 were seen on the tiny
shoot still inside the bud scales in April. Bud scales and needles are removed. (9XJ
400
Fig. 2.-Budsi presumably male, on a partially elongated Douglas-fir shoot in late
May. Needles have been removed. (2XJ
200
Fig. 3.-Dougas-fir twig in September showing male buds. Large buds in clusters are
normally developing buds. Others have aborted at earlier stages, the maiority by mid­
July, 12Xl
Dl!CEMBER, 1967
300
200
',L--.,-",i,",..--.,,,.,ioo"'o--,•"o'=ooc- """,:-!.o·oo
ELEVATION
I-)
889
Table 1.-Results of 1963 Male Bud and 1964 Cone-Crop
Sampling on Marys Peak and Near Corvallis, Ore. (Basis is
seven trees at four elevations}
Spring 1963
1nale bud
indication
Elevation
(feet)
Tree s
with
200
1,500
6
7
3,600
5
2.900
1 AU four
cone crop.
trees
whereas predictions depending on numbers of nona­
borted male buds could not be made before late July.
An observation u( possible significance w_.. s that
much of the halting of bud development of the 1964
season occurred sometime between the July I and
August I collection at all elevations. Buds were fairly
well developed at the 20Moot elevation but hardly
pinhead size at 3,600 feet when bu<!s aborted.
Dissection of many aborted 1>uds in the fall of 1964
revealed that each had a living meristem. To deter­
mine if these could be forced into growth, all twigs on
three branches of three trees were pruned at about
half length and all developing male or vegetative buds
on the basal portion of the branch were removed,
leaving only "aborted" buds. On all treated branches.
these aborted buds began to grow, some breaking in
the spring of 1965 as vegetative buds. Most had
developed or burst by fall of 1965, and all were
vegetative. (Although the so-called aborted buds were
found to be simply latent, the terms "aborted" and
"nonaborted" will still be used for consistency.)
1964 number of trees with-
Trees1
without
Over
500
cones
100Less
500 than 100 No
cones
cones
cones
1
0
1
2
3
1
5
5
5
2
1
I
I
I
1
with no early male crop indication had no 1964
Bud de ve/opment.-Observations made in 1964
from twigs fixed in FAA at times of collection showed
that the whole complement of 1965 buds was visible
on the slightly elongated shoot still inside the unburst
bud in the spring of 1964 (Fig. 1). This observation
can be made as early as April at low elevations. Bud
counts on these tiny shoots were made by stripping
away the small needles. Total bud counts per shoot in
this stage (mean 10, range 4-19, based on 36 observa­
tions) correspond closely to total bnd counts made on
shoots of similar origin at season's end.
Relationship between male and female bud num­
bers.-Luckily, the developmental history of each bud
is clearly visible on the fall-collected twigs. Hence,
these can be used to compare directly the total number
of buds that started with the number that were still
developing in the fall (i.e., the nonaborted buds), thus
avoiding the problem of sampling error between sepa­
rate spring and fall collections.
Table 2 and Figure 4 summarize numbers of fe­
male, nonaborted male, and total (lateral buds of all
types) buds observed in the fall twig collection from
the 48 trees. Female bud numbers on the four plots
decreased with increased elevation in almost a linear
manner, especially when fall totals for each sampled
elevation were compared. So did fall numbers of
nonaborted male buds. The relationship of total female
and total nonaborted male bud numbers, pooled for 12
trees at each of the four elevations, is strikingly straight­
forward (r = 0.99, 2 d.f.). Thus, to the extent that
abortion is complete at time of sampling, an adequate
Records were made of the stages when bud abortion
occurred. Some buds developed no further following
bud burst but were still visible under a binocular
microscope in the fall, appearing as tiny mounds near
the axils of the leaves. Others developed for a few
weeks to the stage shown in Figure 2, then stopped
growing. Still others continued to develop only to abort
after considerable increase in size-some were nearly
full size before aborting. An example of a twig having
all stages of aborted buds is seen in Figure 3. Twig
samples collected at monthly intervals indicated that
most abortions had occurred by mid-July. Hence,
useful predictions of failures could be made very early
Table 2.-Female,1 Nonaborted Male, and Total Lateral Bud2 Numbers in the Upper Crowns of 12 Trees at Each of 4 Elevations
near Corvallis, Ore., Fall 1964
Sampled
tree
number
I
2
3
4
5
6
7
8
9
200
feet
183
27
21
5
5
29
12
18
6
76
167
159
202
Total
898
IO
II
1,500
feet
130
1 00
4
0
0
51
2,900
feet
55
0
0
0
103
62
36
42
17
8
15
134
0
48
13
0
0
581
333
0
Percent male buds nonaborted
200
1,500
feet
2,900
feet
0
214
168
172
113
112
27
0
131
114
84
94
133
205
162
96
0
0
87
0
92
97
76
90
3
24
113
0
13
0
29
38
0
18
18
0
0
125
1,362
908
253
90
62
20
3,600
feet
0
0
25
42
5
0
33
7
0
3
IO
Total lateral bud sample (aborted, nonaborted, and vegetative) at elevations of-·
Nonaborted male buds at
elevations of-
Female buds at . levations offeet
3,600
foet
200
1 , 5 00
feet
2,900
feet
3,600
feet
0
216
169
178
118
126
205
115
127
145
93
0
0
0
0
0
0
43
143
130
84
99
147
90
138
112
83
104
93
120
134
58
86
64
134
90
129
127
137
81
95
117
111
116
187
180
123
133
90
115
138
116
108
II
1,519
1,476
1,255
1,534
0
0
I
IO
0
feet
66
Ill
1
Female bud sample is total number of female buds from two opposite limbs in whorls 3 to 7 from the top of the tree.
s Male and total bud sample is from five twigs each from two main branches in the upper crown. Total bud number includes all lateral
buds in this sample.
890
JOURNAL OF FORESTRY
Table 3.-Correlation Coefficients of Bud-Number Comparisons
Elevation
(feet)
200
1,500
2,900
3,600
Pooled
Female vs.
nonaborted
male buds
Female vs.
total buds
Number of
comparisons
77'
81'
18
71'
58'
19
66'
17
49
30'
12
12
12
12
48
t Significant at I percent level.
2 Significant at 5 pcrct'nt level.
development. A crop failure apparently can be reliably
forecast if few buds are found in the male position or
alternatively as soon as bud abortion is evident. This
could be as early as June. Apparently, male catkins
never develop from buds that halt development for an
appreciable part of the growing season.
On the other hand, the risks associated with forecast­
ing a cone crop from early male bud development
are, of Course, even higher than from sampling femalt!
buds in September. However, if the only information
desired in July and August is whether there is a
potential for a crop next year, then this information
sample of nonaborted male buds pooled for at least 12
trees in a stand is useful in predicting nnmber of
female buds in a similarly pooled sample.
No relationship was found between total buds and
female buds. Both male and total bud numbers are
from the male-bud sample made in the fall. At every
elevation, total bud numbers were surprisingly similar,
whereas female bud numbers differed almost 7: 1
between high and low elevation. Jn a year when there
is little abortion, total bud count might correlate better
with female bud numbers. These results, like those in
1963, indicate that the aborted buds arc the key to the
problem.
Despite the clear pattern (Fig. 4) that emerged
from a pooled sample of trees, comparisons of 1nale
and female bud numbers on individual trees revealed
surprising variation. Some trees produced female buds
but few or no nonaborted male buds, and vice versa.
The 2,900-foot plot had several such trees that over­
rode the general trend. However, at three elevations
the relationship of nonaborted male to female buds is
highly significant, and the pooled correlation coeffi­
cient is 0.58 which is highly significant (Table 3). Part
of the aberrant relationship between nonaborted male
and female bud numbers on some trees arises from
characterizing a whole tree from a sample of two
upper-crown branches. Most of the trees that produced
over I 00 female buds in the sample showed little
abortion of male buds, and most of the trees where
male abortion was complete produced few or no
female buds.
The best sampling of male buds was from the upper
crown. This might be expected since most female buds
are produced in the upper crown. Increasing variation
was found in samples from middle and lower crown.
Part of the variation in lower-crown samples was be­
cause many of the trees were in stands with shaded
lower crowns.
Discussion
Both the 1963 and 1964 studies suggest .that, with
seems clearly obtainable.
These results suggest a first prediction of the coming
crop can be made as soon as shoots begin elongation,
or 16 months prior to seedfall. Failure to find general
clustering of buds on nonterminal twigs in upper-crown
branches would be a first indication of crop failure.
After mid-July, male buds that continue developing
have reasonably good predictive value for female bud
production. By this time, developing and aborted buds
are easily distinguished by size. A more accurate
prediction is possible if male bud counts are made in
August. For any one location, a composite sample
from trees of potential cone-bearing size is necessary,
since prediction for a single or sn1all number of trees is
risky due to natural variation. For instance, a 12-tree
sample was adequate at three of four locations, but a
single aberrant value in the 2,900-foot sample caused
the relationship there to be nonsignificant. Sampling is
most accurate on branches of the upper crown. The
climbing necessary for obtaining such samples poses a
question of a practical sampling method for commer­
cial seed collectors. A promising area for further study
would be to sample the lower crown of open-grown
trees in comparing areas, since such trees are capable
of setting good female crops on lower limbs.
The study raised several interesting questions. One
was the finding that the majority of buds that halted
development did so between the July I and August I
collections, irrespective of elevation. In 1964, we also
collected samples of twigs at the Dennie A hi Seed
Orchard near Shelton, Wash., and our best estimates
were that the majority of abortions occurred at stages
corresponding to the July period. Does hailing of bud
development occur at the same time over much of the
region? No speculations are presently appropriate as to
whether these observations were mere coincidences or
what factors may be involved.
Another observation that aborted buds have living.
though dormant, meristems raises more questions. Are
these clusters of dormant buds the source of epicormic­
like shoots on limbs and branches? Apparently so.
Even without forcing treatments, 1nany break dorman­
cy several years later and finally appear as clusters of
short shoots on branch or stem. The finding that these
skillful interpretation, numbers of normally developing
buds in the male position are useful in forecasting the
relative numbers of female buds in the fall. By time of
differentiation, numbers of nonaborted males are fairly
well correlated with female bud numbers on a stand
basis and ronghly correlated on a tree-by-tree basis.
The stand basis is of far more importance commer­
cially.
buds, when forced, become vegetative and not male
raises the question of whether they were ever male.
The most compelling evidence that there was a floral
potential in these buds sometime before development
halted is that on 12 trees at each elevation about the
same number of buds started development, but, after
Reliability of any prediction using male buds varies
with type of information desired and course of bud
varying degrees of bud abortion, each elevation ended
up with greatly differing male and female bud nmn-
DECEMBER, 1967
891
bers. Apparently all the buds, latent or active, were
conserved. Does each tree have the capacity to cause
floral buds to become dormant and vegetative at any
time in the growing season?
Perhaps the most basic question raised by the study
is seen in Figure 4. Differences in the cone crop at four
elevations seem based on the differing amounts of
abortion rather than on failure of floral bud initiation.
Is there a switching from potentially floral to potential­
ly vegetative stage Jong before the buds differentiate?
This question has led us to a number of studies to be
subsequently reported, aimed at learning if floral initi­
ation could have taken place before bud bursting-five
months before cone buds have differentiated and 17
months ahead of seedfall-and if change from floral to
vegetative stage is a major process in control of cone
crops. If so, techniques that might prevent bud abor­
tions would be of more immediate use in enhancing
cone production than those aimed at floral initiation.
Our observations of two seasons, plus bud counts on
twigs of earlier years, indicate buds will usnally be
found in adeqnate numbers on enough trees in most
stands to produce cone crops almost every year if al l
the buds continue normal development.