date reagent for the determination of total
phosphorus in soil. Soil Sci Soc Amer Proc 32:
48-51.
WATANABE, F. S., S. R. OLSEN, and R. E. DANIEL­
SON.
1960. Phosphorus availability as re­
lated to soil moisture. Trans 7th Intern Congr
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456. Elsevier Pub! Co, Amsterdam.
WILDE, S. A., and G. K. VOIGT. 1955. Analysis
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igan. 117 p.
July-Stimulated Flowering in Douglas-fir
Note by Roy R. Silen
Abstract. Grafted seed-orchard trees lifted and
replanted June 30-July 1 produced an average of
23 cones compared with near zero production for
corresponding unmoved ramets. Evidence is thus
provided for a reversal of partially differentiated
vegetative buds to floral differentiation. forest
Sci. 19:288-290.
Additional key words. Seed orchards, clones, lift­
mg
BY MOVING seed orchard trees in early July,
new information was inadvertently gained on
the question of how late in bud development
Douglas-fir can be strongly stimulated to
flower. Of the 6,000 grafted trees of the
Beaver Creek Seed Orchard, Siuslaw Na­
tiOnal Forest, near Corvallis, Oregon, the 91
trees moved to new positions within the
orchard in 1971 were practically the only trees
that produced a crop. Forty-five trees were
moved May 10-12 but rains delayed moving
the remaining 46 until June 30--July 1. Al­
though both groups subsequently flowered
about equally, it is the latter movement date
-13 to 14 weeks after onset of spring
growth-that is of high theoretical interest.
288 I Forest Science
The 1.2- to 3.1-m tall grafted trees were
moved with a large mechanical tree spade.
This machine lifts the tree with jaws that
leave an inverted pyramid of about half a
cubic meter of earth around the roots. Con­
siderable root pruning occurred, and subse­
quent drought symptoms resulted from the
operation, but all trees survived.
Studies by Owens ( 1969) leave little ques­
tion that by 10 weeks after onset of spring
growth, lateral buds of Douglas-fir are already
distinguishable as floral or vegetative by
histochemical techniques. After 15 weeks
they can be distinguished visually by dissec­
tion. Perplexingly, a few studies have re­
ported enhanced or reduced cone production
from treatments 12 to 22 weeks after onset
of spring growth when some floral structure
must already be formed. These include fertil­
izer applied September 7-8, by Steinbrenner
et al. (1960), foliar fertilizer applied June
17, by V. Allen (USDA 1963), and shading
The author is Principal Plant Geneticist, Pacific
Northwest Forest and Range Exp. Stn., USDA
Forest Service, Corvallis, Oregon 97331. Manu­
script received Jan. 26, 1973.
and removal of seed-cone buds in July­
August, by Silen (1968). Since 1968 I have
also conducted several field studies employ­
mg shade, foliar fertilizer, girdling, cold, heat,
moisture stress, and floral bud or leaf re­
moval aimed at clarifying floral responses in
this period. Results have been inconclusive,
often conflicting and are unpublished. In
contrast, this chance field observation adds
a particularly convincing case of such a late
floral response.
Observations. The odd flowering pattern first
was noticed by Don Oliver, Seed Orchardist,
Siuslaw National Forest. On May 25, 1972,
when vegetative shoots were elongating, we
made observations of the moved trees together
with a like number of unmoved trees of the
same clones. Records were made of total
bud count, seed cone count, presence of pollen
cones, elongation of longest terminal shoot
of the top whorl, tree height, graft height, and
1971 terminal growth. Data were tabulated
according to movement date, clone, and seed
orchard block. Statistical analyses were per­
formed where appropriate. The nearly total
absence of cones in the control group elim­
Inated the need for a statistical analysis of
cone number data.
A detailed examination was made of dis­
sected buds from six clones collected on July
1, 1972, to determine developmental stage.
Samples were also sent to Dr. J. N. Owens,
University of Victoria (B.C.). Both of us
found that some differentiation of primordial
leaves or bracts was taking place at the
base of the apical dome. Each of us found
at least one bud showing megasporangiate
development. Apical domes were still un­
differentiated.
Data. Following the heavy 1971 cone crop,
Douglas-fir trees in the Corvallis country­
side were generally barren of a crop in 1972;
and among the 6,000 grafted trees of the
Beaver Creek Seed Orchard, less than a dozen
bore cones. Of the 91 seed orchard trees
carefully inspected as controls, only one bore
a few seed cones for a 1972 crop. In con­
trast, 54 of 91 moved trees bore an average
of 23 seed cones in addition to numerous
pollen cones for a 1972 crop. An addi­
tional five trees bore only pollen cones. Thus,
about 65 percent of the moved trees displayed
an obviously significant floral response to
the treatment.
The July-moved trees produced a somewhat
stronger floral response than the May-moved
trees. Of the 46 moved on June 30-July 1,
the 31 that bore cones (67 percent) had an
average of 22.6 seed cones. Of the 45 trees
moved May 10-12, the 23 that bore seed
cones (51 percent) averaged 23.7 seed cones
The larger percentage of trees bearing cones
in July, although not statistically significant,
could possibly be due to the slightly larger
grafts characteristic of the seed orchard
blocks involved. Frequency distributions were
very similar between the two dates.
As expected, moved trees grew less m
height (32.3 em) in 1971 than unmoved trees
(50.4 em). There was no difference in
growth between May- and July-moved groups
Counts of active or latent buds showed no
consistent difference between moved and
unmoved trees.
Discussion. Profuse flowering of moved
garden trees and shrubs is commonly ob­
served. Also, the essentially all-or-nothmg
response reported here is strikingly similar
to results following drought treatment of
potted Douglas-fir grafted plants by Ebell
( 1967). Floral responses from some en­
vironmental treatments of Douglas-fir applied
in the period from bud burst through shoot
elongation have been reported ( Stoate et al
1961, Silen 1968, Ebell 1971). What IS
rare, and has important theoretical aspects, IS
so strong a floral response to a treatment
when bud development is so far advanced.
Previous studies of floral responses resultmg
from various treatments during the period of
bud differentiation (July-September) have
been cautiously viewed as possible artifacts
by the authors (Steinbrenner et al. 1960, Silen
1968) . The theoretical meaning of these re­
ports must now be reconsidered.
Douglas-fir cone crops appear to vary pn­
marily because of yearly differences in num­
ber of buds that stop developing, rather than
from number initiated (Silen 1968, Owens
1969, Ebell 1971). As a consequence, a
normal assumption was that a tree starts m
spring with maximum floral bud potential
which can be successively reduced by change­
over during development to active or dor­
mant vegetative bud types. This unidirec­
tional assumption was supported by observa­
tions that potentially good cone crops begm
with a profusion of buds on the expandmg
shoot (Silen 1968). Owens' (1969) evi­
dence, that metabolic pathways probably
begin to diverge in early spring into floral and
vegetative bud development, added further
support. Likewise, response to stimulatory
volume 19, number 4, 1973 I 289
treatments to the tree (Ebell 1971, Silen
1968) suggested that pre-existing floral buds
were preserved, rather than new floral de­
velopment stimulated. Conversely, inhibitory
treatments such as shading caused increased
abortion or latency of buds. Later ( unpub­
hshed) field studies in which I attempted to
stimulate new floral bud development were
mconclusive. Hence, there has been no pre­
vious firm evidence for suggesting that any
new floral initiation normally occurs after
early spring. Indeed, a unidirectional hy­
pothesis (Silen 1968) based upon abortion
or latency mechanisms seemed adequate to
explain the tree's habits in balancing floral
With vegetative needs over the 17 months of
cone crop development.
The equally strong stimulus to floral bud
development, provided by moving the trees
at the seed orchard in either May or early
July, now suggests that responses sometimes
go strongly in the other direction as well. That
IS, a developmental changeover, possibly from
newly-activated genes, may occur from vege­
tative to floral at any month of the bud de­
velopment period. It seems more tenable, con­
sidering how often a barren year has followed
a bumper crop, that most of the 6,000 trees
were physiologically and anatomically well
along toward commitment by differentiation
to vegetative buds by July 1, and that a
strong changeover to floral bud develop­
ment occurred in the moved trees. The alter­
native, an assumption that buds on about
two-thirds of the 6,000 trees were proceed­
mg on floral pathways that changed to vege­
tative pathways in the last few weeks before
290 I Forest Science
differentiation in all but the moved trees,
does not seem as tenable. This and the papers
previously cited suggest the possibility that
such late changeover of bud type occurs if
the stimulus is sufficiently strong.
The practical aspect is to suggest tree
lifting as a new tool for floral studies on
whole trees.
Literature Cited
EBELL, L. F. 1967. Cone production induced
by drought in potted Douglas-fir. Can Dep
For, Bi-Mon Res Notes 23(4) :26-27.
1971. Girdling: its effect on carbohy­
drate status and on reproductive bud and cone
development of Douglas-fir. Can J Bot 49
453-466.
OWENS, JOHN N. 1969. The relative importance
of initiation and early development on cone
production in Douglas-fir. Can J Bot 47
1039-1049.
SILEN, RoY R. 1968. How early can Douglas­
fir cone crops be predicted? In Western Re­
forestation. West Forest Conserv Assoc Conf
Proc 1967:12-18.
STEINBRENNER, E. C., J. W. DUFFIELD, and R. K
CAMPBELL. 1960. Increased cone production
of young Douglas-fir following nitrogen and
phosphorus fertilization. J Forest 58:105-110
STOATE, T. N., I. MAHOOD, and E. C. CROSSIN.
1961.
Cone production in Douglas-fir
(Pseudotsuga menziesii). Empire Forest Rev
40(2): 104-110.
USDA FoREST SERVICE. 1963. Dennie Ahl Seed
Orchard. Olympic Nat! Forest, Reg 6. 19 p.