How Early Can Douglas Fir Cone Crops be Predicted?
'
by
ROY R. SILEN
Project Leader, Forestry Sciences Laboratory
Pacific Northwest Forest and Range Experiment Station U.S. Forest Service, Department of Agriculture Corvallis, Oregon A funny thing happened to me about 11 o'clock. I
learned that, because of some communication fail­
ure, Dr. Owens had prepared material with a simi­
. lar message to mine. After checking at noon, we de­
cided most of our material was mutually supporting, and will be presented as prepared.
Until quite recently, forecasts of cone crops have
been limited to about 12 months prior to seedfall.
This was because there is no way of distinguishing
between female, male, and vegetative buds until
differentiation of floral buds is completed in late
August. A forecast . this early is very valuable, but
the most desired one is in July, 14 months ahead.of
seed.fall. By then, the ripening cones are full size,
seeds have been pollinated and have visible embryos,
and frosts, insects, and abortions have all taken tl1eir
toll. Any earlier forecast than mid-July runs an nn­
certain risk because the crop can be reduced by any
and all such hard-to-predict factors.
If, in July, foresters or seedsmen could look ahead
14 months to next y_ear's crop on· the same trees,
an important' decision could be inade. %en region­
al seed supplies are dwindling, a forecast of another
failure would probably result in collecting as much
. of his needs as possible from the existing crop, re­
gardless of high costs. A forecast of a bmnper crop
would probably result in collection of minimal needs
from the existing crop.
This paper touches lightly on forecasting of crops
in the 12-to-0-month period before seedfall, then de­
Purchased by the
U.S.
The Proceedings of the
Forest
1967
Service, U.S.
scribes a way of forecasting up to 17 months ahead
of seedfall, using buds in the male position on the
twig.
All forecasting of cone crops in the 12-to-O-month
period depends on recognizing female buds, a sub­
ject on which Dr. George Allen published the basic
information 26 years ago.1
What Dr. Allen described is shown in figure_ l,
in which bud and twig development is illustrated at
various months before seedfall in the development of
the cone crop at Corvallis, Oreg., that will produce
seed in September 1968, 12 mont11s earlier (September
1967), the subterminal buds will have inside them dif­
ferentiated female conelets complete with scales and
visible trident. bracts. Male buds will also be devel­
oped in more basal positions on the twigs. The figure
shows that these buds break in late March or early
April, 5 months ahead of seedfall. The female bud
goes on to develqp into a seed-bearing cone, and male
conelets dry up soon after· shedding their pollen in
April. Embryo development in the seed does not
'
start until June, even thougl1 cones are fuli size.
Confusion sometimes arises because unpollinated
seeds still look plmnp and full when sampled ' in.
early July. After that, they collapse into "empty"
seed, sometimes to the consternation of the cone col­
lector. The final sketch shows the seed dropping out
of the fresh cone in September 1968.
I Allen, G. S. A basis of forecasting seed crops of some
coniferous trees. ]. Forest. 39: 1014-1016.
1941.
Department of Agriculture, for Official
REPRINTED FROM
Annual Meeting of Western Reforestation Coordinating cohimi.free
A
Permanent Committee of
WESTERN FORESTRY AND CONSERVATION A:sSOCIATION
American Bank Building, Portland, Or.egon 97205
12
Use
,
Sept.
1968
5
0
rd"'S-sss5ss<§b
Poor pollination Frost Insects True abortion
Sept.
1967
12
16
14
17
\
Arrested development
Figure
1.
Development sequence of female- buds
a potential cone crop are indicated.
17
to
0
months. prior to seedfoll. Periods during which cert'1in factors reduce
The forecasting method in the 12-to-O month period
involves sampling female buds. The most practical
way is to drive branch-strewn forest roads in fall af­
ter a windstorm and sample sunlit branchlets blown
down from high in the tree crowns. Such branch­
lets have stiff needles surrounding stout twigs, as
contrasted to shaded branchlets that have a flatter
arrangement of needles and more slender twigs. If
no female buds are found in 30 to 50 of such sam­
ples, a cone crop failure is likely for that stand. If
numerous cone buds are found, particularly with pro­
fuse male buds as well, there is potential for a good
crop.
Although sampling methods can be devised to
gain any desired degree of sampling accuracy, a high­
ly accurate sample is scarcely ever attempted. This
is because so many events, like abortions, frosts, .in­
sect attacks, and poor pollination, can influence the
outcome that a fOrester's time is better spent in sub­
sequent observations of the oncoming crop.
Figure 1 shows the time of these events. Inade­
quate pollinations in April and May, 5 or 4 months
_
13
ahead of seedfall, are a problem in poor seed years,
but pollination is generally good in bumper years.
Rain during pollination periods seems to have no
adverse effect on pollination. Frost occurring soon af­
ter the floral buds open in spring can wipe out a
potential crop as it did over portions of the region
in May 1966. Various insects, working on both seeds
and parts of the cone from April through June, can
reduce a crop drastically, particularly when the crop
is light. The figure shows five such waves of midge,
chalcid, and cone worm attacks.
Abortions can occur at any stage of development.
Some buds abort over winter. Floral abortion soon
after bud opening is so regularly expected that we
geneticists commonly overdesign our studies by about
50 percent in expectation of such losses. Develop­
ing cones can abort at all stages, even when full size.
Seemingly, the tree has the capacity at all times to
reduce its Cone crop in response to the needs of its
nutrient budget by aborting buds or cones. This in­
ternal control of the crop undoubtedly works even
earlier but in different "'ays.
Up to very recently, any forecasting of cone crop
was limited to 12 months prior to seedfall. The!! in
the late fifties, several genetics workers noted that
profusions of small buds were sometimes visible after
June in the male position on the twig. Could these
buds be used to forecast a cone crop 13 or more
months ahead of seedfall? Ahnost immediately I be­
gan assuming that trees displaying profuse budding
were going to produce good cone crops. This assump­
tion proved faulty. They did not almrst as often as
they did.
In the early l960's, we learned that buds could
be distinguished at bud bursting time in early April,
17 months ahead of seedfall. Anatomical sectioning
\vill show tl1em even earlier. In other words, there
are buds within a bud. This slide shows a tiny
shoot taken from an expanding, but still unburst, bud
in early April. Once the emb1yonic leaves are stripped
away, all the tiny buds for that year's growth are
quite visible with a hand lens. Seen a month later
in early May, they are visible to the naked eye.
With the pressure of other studies, it was not un­
til 1963 and 1964 that I had opportunity to check
into various relationships between early bud produc­
tion in the male position on the twigs and cone
crops. I learned tl1at something akin to the abortion
process just described was also controlling numbers
of developing buds. This proved to be a key to
earlier forecasting. Apparently, floral bud numbers
were controlled by two processes in the 12- to 17­
month period ahead of seedfall. First, a tree could
start out in April with minimal bud numbers, indicat­
ing lack of potential, or with profuse budding,
indicating a high potential for floral cone buds.
Second, between April and August, a tree could
"abort" or transform part or all of the potential
floral buds into rudimentary vegetative buds, reduc­
ing thereby the number of female cone buds.
Let us pause here to look at some data taken in
14
1964 which illustrates each of the above points. The
study involved 12 cone-bearing trees, 50 to 100 feet
tall, chosen at each of four elevations near Corval­
lis - 200, 1,500, 2,900, and 3,600 feet. Twig collec­
tions were made monthly from each tree beginning
in March. That fall, on each tree all the buds, both
developing and aborted, were counted on 10 twigs in
the upper one-third of the crown. The ·buds were
tabulated in two classes - normally developed and
smaller aborted buds. Sometimes a hand lens was
needed to see all the early aborted buds. The next
slide shows normal buds in the fall and examples of
aborted buds at late and very early stages. Figure 2
shows the results of the study with plot elevations
as the horizontal axis. The vertical axes depict seV­
eral things. The first gives total numbers of lateral
.buds, both fully developed and aborted, that were
sampled on all 12 trees at each location. The second
gives total numbers of female buds in five upper­
crown whorls of the tree. The third gives total num­
bers of normally developing male buds (total laterals
less aborted buds).
Now, to illustrate the two key features. At every_
elevation, a profusion of buds started on 10 or more
of the 12 trees in 1964, with about 1,500 lateral buds
counted on 120 twigs sampled at each elevation.
Thus, most trees at every elevation appear to have
begun with a good cone-crop potential in April;
that is, 12 or more cones per twig. Note, secondly,
that developing male bud production recorded in fall
was linearly reduced by abortions as elevation in­
creased: Expressed in numbers of trees, all 10 pro­
fusely budding trees retained their buds at low ele­
vation; only one did at high elevation. Note, thirdly,
that the female cone bud production likewise was
progressively poorer with increasing elevations in a
linear manner. Again, expressed in numbers of trees,
eight of 12 trees produced crops at low elevation
and three of 12 produced crops at high elevation.
Average number of female buds was closely related
to average number of nonaborted male buds. This is
interpreted to mean that some environmental factor
had caused trees to drastically abort potential fe­
male as well as male bud crop at high elevations;
not nearly so many aborted at" low elevations.
Because we had followed month-by-month devel­
opment on the trees, we could pinpoint the time
male bud and presumably female bud abortions
were occurring. Although some buds stopped devel­
opment very early in May and others in June, most
halted development cf male buds in early July at all
elevations, with
_ minin1al losses after mid-July.
There is a distinct difference between abortion of
differentiated cone buds 12 to 0 months before seed­
fall and the abortion of undifferentiated buds I am
describing from 17 to 13 months before seedfall.
After cone buds differentiate, any subsequent abor­
tion results in death of the bud or developing cone
- a terminal event. Prior to differentiation, hovvever,
the potential male or - female bud is not lost by
abortion, but rather a "conservation of meristems"_pre­
I
.
I
I
I
I
I
I TOTAL and
MALE
FEMALE
bud count
1,600
bud count
I
!
I
1,000
. t
I
I
I
I
900 1,400 .
I
I
I
800 1,200
i
I I
'I
700 I
I
1,000
I
I I
600 800 500 600 400 400 300 200 200 O L..--��__.:���_:_���-.:...�--l.i::.._�
4;000
3,000
2,000
1,000
0
ELEVATION
(FEET).
15 Figure 2. Male, female, an-d 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 illustrated: (1) the strong
relationship between femal'e bud counts and counts of nonaborted male buds, (2) lack of
relationship 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. (Roy Silen, 1967.
Earlier forecasting of Douglas-fir cone crop using male buds. J. Forest. 65: 888-892.)
vails. Buds appear simply to change sex that is, floral
buds do not die but turn to vegetative buds. We
believe this happens from three kinds of evidence.
Seen in the next slide are twigs in which profuse
buds in male position on the twig aborted in May.
\ii/e use this expression because they did not in­
crease in size after May. Under the microscope, all
hac;! living meristems. If the twig is pinched off just
above such latent buds, they easily force into vege­
twigs, girdling, foliar fertilizing, shading, heating,
and cooling. Most of these treatments have, to some
degree, been shown statistically to cause or prevent
the switch from floral to vegetative status in buds
during the 15th, 16th, and 17th months before seed­
fall. For example, simply placing a kraft pollination
bag over a branch during the 16th month before
seedfall this spring has switched more than half of
the subterrninal female buds to vegetative buds. Re­
moving this year's floral buds, or applying fertiliz­
ers, acts similarly sometimes, but not consistently, in
bringing more floral buds through to full develop­
ment. Higher temperatures, even for as short periods
as 2 weeks in late May, appear to decre·ase female
bud numbers and enhance male bud numbers that
complete development. Cold appears to work in the
opposite way, decreasing male but increasing female
bud numbers. It has been difficult to obtain consis­
tent results from year to year in such responses. But
evidence of sex changes with short environmental
treatment during this period is rapidly accumulating.
The alternative explanation, that buds are all the
same until differentiated, is not ruled out by such
studies. Our treatments could still be influencing
something other than the sex that might predispose
the ·-.buds toward different sexual expression later.
But the demonstration of anatomical and histochem­
ical differences between floral and vegetative buds in
the 16-month period or earlier by Owens, 2 the
lack of profuse budding seen some years, and abort­
ing effects of various treatments for short intervals
favor the "early potential, subsequent sex-switch" in­
terpretation. This would mean that floral initiation
involves events more th:in 16 months before seed-_
fall.
For those of you who may wish to appraise a po­
tential cone crop in April or May, 16 to 17 months
tative growth. In the slide, new 1965 shoots are seen
on 1964 growth, having sprouted from these small la­
tent buds below the cut end of the twig. If we are
correct in assuming that profuse budding in April
is in response to some floral stimulus, then this
stimulus is lost when bud development halts, as in
no cas.e have I observed male buds when such forc­
ing was done.
The second kind of evidence for sex changes is
that we occasionally catch buds that presumably
changed sex during the 4- to 5-week period that dif­
ferentiation of bracts is completed from base to top
of the meristem, mostly during August. Here we see
one that started laying down female bracts, then
switched to vegetative growth. Evidence for this
switching is proving to be quite common once we
look for it. The switching is not always from female
to vegetative. Here is one that switched from female
to male growth. The record is held by this bud,
a triple sex reversal that started out female, switched
to male, switched back to female, then back to
g a
- male - a genuine queer one. We are catc
change part way through the differentiation process.
Since we find examples of switching sex early or late
in tl1is period, the assumption is that such changes
must take place earlier, as well as a chemical change.
The third kind of evidence is from a number of
treatment studies I have tried since 1961. I have at­
tempted to switch sex artificially with environmental
treatments like removing cone buds, pinching off
2·
Outcome
Forecast
Cone year 16
Personal communication. See Owen's article.
April,
17 mo.
July,
14 mo.
September,
0 months
Started
Completed
Elevation
1963
1964 Low
High
Good
Good
Fair
Very poor
Medium
Very poor
1964
1965 Low
High
Good
Good
Fair
Failure
Mediu1n
Failure
1965
1966 L·ow
High
Exoellent
Excellent
Excellent
Excellent
Good
Abundant
1966
1967 Low
High
Failure
Failure
Failure
Failure
Failure
Failure
1967
1968 Low
High
Poor
Fair (Not sampled) ahead of seedfall, this is the suggested procedure.
Choose a dozen or 'more dominant, preferably open­
grown, trees well spaced through .the area. Obtain 10
or more nonterminal twigs from the middle or up­
per crown, preferably twigs somewhat back on the
branch. The new twigs soon after bud bursting will
be succulent so the leaves can easily be stripped
away. The tiny buds can be seen .with a hand lens.
Count the buds developing on these twigs. If a tree
sample averages 12 to 18 per twig, this is profuse
budding. Less tha.n eight buds would be a sign that
the tree lacked potential for a crop.. If more than
half the trees show evidence of profuse budding, a
good crop potential is indicated. If only one or two
out of 12 s.how profuse budding, the crop potential
is low.
·
Samplings . made in late May or ,early June will
show the,developing buds plainly visible to the naked
eye. Some will have ceased development earlier but
will be visible with a hand I.ens. It is important to
obserne these latenCbuds as a possible first sign of
a reduced, .crop.
,
By mid-July, most of the buds that are going to
cease development will have done so. If a third or
more of the trees i 'have a profusion of male buds
still developing; this is evidence of a fair or better
crop potential. By mid-August, the femafo ,buds will
begin to be recognizable. By mid-September, female
buds can be·counted directly rather than by resort­
ing to the indirect correlation with male bud de­
velopment that as necessary in July or earlier when
female buds are inaistinguishable from vegetative
buds.
From· observations Over a 5-year period, \_ fEiel a
good forecast ·of ,potential crop·failure is possible at
low elevation by late April, 01.- 17 months ahead of
seedfall. If, in sampling a dozen or more trees soon
after bud bursting, no profuse clustering of buds is
evident on interior twigs of the upper crown, no po­
tential·· for a co e crop is lrldicat d. On the other
hand, if profuse buading is generally observed, this
is interpreted as the potential for a good cone crop
and bears watching. If most of the buds develop
through July, a favorable ·crop of female buds is
forecast. If heavy abortion of developing buds has
occurred by July, the forecast would be for a poor
crop of female buds.
•
Have such early appraisals been useful? The cone
crops of the last 4 years hear Corvallis presented a
considerable range of possibilities, each of which was
predicted fairly well. Each crop is tabulated giving
the forecast at 17 and 14 months. before seedfall along
with the outcome in the above table.
Both the bumper crop of 1966 and the · crop fail­
ure in 1967 were easily forecast 17 months in ad­
vance. Buds were very profuse in most trees in April
1965. By July 1965, bud losses were minor except
for a small percentage of the trees. No further ma­
jor ·losses happened to the crop most places, but a
May frost over parts of the region wiped out what
would otherwise have been a general bumper crop
in 1966. For the crop that started in 1966, the po­
tential was obviously absent 17 months ahead of
seedfall. Bud prodµction was mir;1im?-l on most trees,
resulting in the crop failure in 1967.
The crops that began in 1963 and 1964 followed a
different pattern. Both years started with large num­
bers of trees at. all elevations having profuse bud­
ding. However, at high ,elevations, heavy abortion
of buds was clearly indicated by July of both years,
and crop fa ilures were recorded at high elevations
in 1964 and 1965.
In 1967, our springtime sampling of buds in the
Corvallis area was limited. to low elevations. A pe­
culiar pattern developed. Only six trees out of about
40 examined showed profuse budding, an indication
of a very light potential crop if normal amounts of
bud abortion occurred. However, this season was un:..
usual in that practically every bud that started de­
veloped normally. As expected, six of the trees pro­
duced good crops of female cone buds in Septem­
ber: In addition, about 15 other trees produced poor
to fair crops - trees that had averaged only eight to
12 buds per twig in April. By mid-July, however,
our a:f>praisal Was for a fair crop based· on fall: num­
bers of developing buds in the male portions of the
interior twigs on about 15 of the 40 trees.
This experience suggests that a fair appraisal of
each Of these crops was possible in the 13- to 17­
month period before seedfall.
In closing this pr'esentation, one might ask what
the chances are for forecasting crops more than 17
months ahead of seedfall. Dr. William Lowry, at
Oregon State UniVersity, has made, some meteorolo­
gical studies in which past cone crops correlated with
past weather patterns as much as 27 months ahead
of a crop. When one considers that whatever weather
factors he might be talking abm.it are acting a whole
season ahead of the presence of even a "bud within
a bud,'' this seems fantastic.
·
Yet recently developed analysis was obtained from
an experiment started in 1963 in which some limbs
on seven trees at two elevations were shaded in
June, 27 months ahead of seedfall. To my surprise,
shaded limbs produced significantly fewer female
buds in 1964 and fewer cones in 1965 than the sun­
lit branches. Here is a strong treatment effect show­
ing up 27 months ahead of the cone crop. Thus, 17
months is not necessarily the limit of possible fore­
cast. For now, however, this is the earliest practical.
forecast.
·
17