·
Reprinted from the JOURNAL OF FORESTRY, Vol. 62, No. 4,' April 1964
Purchased by the U.S. Forest Service for officiall.lse.
Simultaneous Variations in Seasonal Height
and Radial Growth-of Young Douglas-Fir
Edward J. Dimock II
RELATIONSHIPS between seasonal in­
crements in height and diameter of
forest trees have long stirred more
than casual interest among plant
scientists (7, gy. It has been found
that bud bursting generally shows a
.
close correlation with' cambial re­
activation following' winter dor­
mancy. However, the physiologi­
eal relationship between apical and
cambial growth J.:emains obscure.
and leaves much for further study.
To date; the bulk of published find­
ings stems from study of seedlings
,
and saplings. This paper reports
within-season changes in diameter
and height on Douglas-fir trees ex­
ceeding 30 feet tall. These changes,
recorded s i m ult a n e o u s l y, were
charted throughout two growing
seasons to elucidate grosser fea­
tures of the height-diameter rela­
.
tionshi:r>'
Tree Description
Ten. dominimt- Douglas-fir trees.
were selected for measurement. At
'
time of first observation during
the spring of 1957, these trees
averaged 16 years in total age, 6.03
THE AUTHOR is research forester on the
.staff of the Pacific Northwest Forest
and Range Expt. Sta., Forest Service,
tr. S. Dept. Agric., Portland, Ore.
Abstract. Progressive changes in bole circumference and total height were
simultaneously measured in 10 Douglas-fir trees during the 1957 and 1958 grow­
ing seasons.· At the start of each season, substantial increases in circumference
'began by mid-April and preceded comparable increases in height by approxi­
mately one month. Swelling or bursting of terminal buds did not seem to be 1m
essential precursor to radial growth. Height growth was mostly complete by
August, whereas' apparent radial increments were still evident during October
and November.
illches in breast-high diameter,
and 32.6 feet in total height. They
formed part of an open stand that
originated naturally on an old
field site of medium quality near
McCleary, Wash. All trees were
growing rapidly and possessed the
smooth bark and long' terminal
shoots characteristic of their age
and thrift. They were sufficiently
separated to minimize direct com­
petition for growing space. Meas­
urements during the growing sea­
sons of 1957 and 1958 showed re­
spective annual increases averag­
ing 1.006 and 1.336 i n c h e s in
breast-high circumference, and 2.69
and 2.73 feet in total height (Ta­
ble 1).
Tree nleasurement
Simultaneous determinations of
circumference and height were re­
corded weekly early in each seaso'n;
4.
TABLE I.-ANNUAL INOREASES IN HEIGHT AND CIROUMFERENOE OF DOUGLAS-FIR TREES DURING THE 1957 AND 1958 GROWING SEASONS Tree
no.
I
2
3
4a
4b1
5
6
F 7
8
r 9
10
\
Initial measurements,
spring of 1957
Age
D.h.h.
Height
Years
Inches
Feet
17
17
15
15
17
16
22
13
13
14
14
6.22
5.12
5.46
6.49
6.84
6.97
7.56
5.60
5.75
5.90
5.27
34.8
32.2
30.3 '
31.7
34.5
31.1
46.0
28.9
31.3
32.3
27.8
Annual circumferential increase
1957
1958 '
-Inches -- .
-
0.860
1.180
.465
1.000
.960
1.140
.960
.805
1.275
1.425
Annual terminal
increase
1957
--
1958
Feet--
1.230
1.550
1.015
3.24
2.91
1.24
2.51
3.04
2.50
.945
1.600
1.025
1.285
1.350
1.740
1.610
3.01
2.20
2.69
2.83
3.17
2.93
3.06
2.70
2..02
2.85
2.72
3.42
2.53
1Tree substituted in 1958 for tree' No. 4a whieh sustained a broken terminal shoot
during the· 1957 grow.ing season. Age, d.b.h., and height are for spring of 1958.
APRIL 1964
then, biweekly as seasonal incre­
ment rates began to drop. Meas­
urements were not made over the
late fall and winter months, al­
though small amounts of radial
stem change (7.2 percent in 1957
and 2.8 percent in 1958) occurred.
All measurable height growth, how­
ever, fell within each spring-to­
fall period.
Ohanges in c i r cmuf e r e n c e at
breast height were determined by
vernier tree-g'rowth bands of the
type described by Hall (6) and
recently modified by Liming (12)
and Mesavage and Smith (.13).
These dendrometers, custom fitted
to each tree, were constructed of
%-inch-wide aluminum tape such
as used for numbered tree tags.
Measurement and vernier scales
were scribed by hand and cali­
brated to indicate circumferential
changes to the nearest 0.005 inch.
Oadmium-plated s t e e I springs,
which held the bands in place,
proved satisfactory throughout two
years of use.
Since tree t o p s w eI' e beyond
reach, a surveyor's transit was
used to determine height changes.
Two permanent hubs, each marked
by a finishing nail driven into the
top of a firmly anchored stake,
served for all 10 trees; 4 trees were
measured from one hub, 6 from the
other. Thus, although instrument
height varied slightly, orientation
and horizontal distance from hub
to tree remained identical at each
measurement. Horizontal distances
between each hub and the bole axes
of trees common to it ranged from
44.5 to 82.0 feet.
The observer read two vertical
angles to the nea.rest minute for
each tree-'--all as deflections from
horizontal: (1) a base angle for
fixed reference to the top edge of
each tree's growth band and (2)
an angle to the tree top. Periodic
height changes were determined
by comparing total heights calcu­
lated separately for each observa
tion date in the following manner:
height = (h - til)d + 4.5
where h = tangent of angle to
tree top
where t2 = tangent of angle to
top edge of growth
band
where d = horizontal distance
to tree in feet.
253'
"
o
,
1958
1.25
w
u
:z:
w
'"
1.00
1957
§j
o
0.75
W
to
:z:
"'"
:I:
U
W
>
0,50
§
:0
§
0.25
U
..J
"'"
JUNE
----
oYr
----
--
AUG.
--
175
145
205
SEPT.
OCT.
L----,-L---.
235
NOV.
----,-
265
__
325
NUMBER of DAYS since b gj ning of each year
FIG. I.-Relationship of change in circumference (b.h.) to time for 10 Douglas-fir
trees during 1957 and 1958 growing seasons.
1'----'---,
3.00,,
1958
1957
o
=-
2.50
to iii
::z: 2.00
0; W
to
:z:
"'"
{51.50
W
>
;;;
:3
],00
'"'
:0
U
..J 0.50
:z:
:z:
"'"
APRIL 85
AUG.
,
115
145
175
NUMBER of DAYS since beginning of each year
205
1
I
SEPT.
235
OCT.
I
265
NOV.
295
I
325
.
FIG. 2.-Relationship of change in total height to time for 10 Douglas-fir trees during
1957 and 1958. growing seasons.
loo �f------t_-��::�����---�
80
..J 60
W
;"
:z:
o
i)l
40 o
20o
------iL---�--+--�
o
oL-,
APRIL
85
l1S
JUNE
MAY
I
145
----
HUMBER of DAYS since beginning of each yeor
175
ULY
I --+_
J
I
205
AUG.
I
-
SEPT.
-L-
265
235
'
OCT.
-
NOV.
r._
--
325
295
.
'
FIG. 8.--Oumulative change in .circumference (b.h.) and in total height for 10
Douglas-fir trees in relation to time (av rage for combilied 1957 and 1958 growing
'
seasons).
254
JOURNAL OF FORESTRY
Seasonal Growth MeasuraJ:>le circumferential in­
creases began at different times
during the 1957 and 1958 growing
seasons (Fig. 1). In 1957, detect­
able increases began in mid-April.
However, in 1958, all trees were
increasing during the first measure­
ment interval, and it appears likely
t11at radial growth began shortly
before the first 0 b s e r v a t i o n on
March 28. Growth rates during both
years, though lower in 1957 than
in 1958, remained fairly constant
through mid-July. Then, while
1957 growth generally leveled off
gradually" in 1958 there was an
abrupt and prolonged period of
circumferential shrinkage, and ex­
pansion did not resume until late
August. In both years, a' slow
increase continued through the
last observation period, which
ended on October 25, 1957 and on
November 21, 1958.
Seasonal p a t t el' n s of height
growth showed much greater simil.
arity between the two observed
years. Detectable increases, due
to swelling of a few terminal buds,
began in both years during the
latter half of April (Fig. 2). How­
ever, most terminal buds did not
burst until nearly mid-May, and
significant increments in height did
not begin until then. The terminals
of all trees lengthened rapidly
until early August, when growth
quickly leveled off in a manner
fairly' consistent for both seasons.
Height growth was 95 percent com­
plete by early August 1957 and
by late JUly 1958. Erratic meas­
urements were responsible for ap­
parent slight decreases in height,
which appeareq. once in 1957 (Sep­
tember) and twice in 1958 (April
and August).
Major growth trends in both
radius and height were rehitivel;Y
consistent for all trees within the
10-tree sample. For example, the
shrinkage in circumference during
the 6-week interval from July 18
to August 29, 1958 was based on
changes Over three 2-week inter­
vals. Among 30 individual circum­
ference measurements, 26 showed
decrease, 2 no change, and 2 a
slight increase. At both ends of
the major growth periods, how­
ever, deviations of individual trees
significantly affected averages of
height and circumference. To ilhis­
trate, one tree, by rapidly straight­
ening a'leaning terminal shoot be­
tween September 27 and October
11, 1957, increased 0.48 foot in
height-eight times as much change
as shown by any other tree during
the same period.
Cumulative changes in height
and circumference described a sig­
moid-curved relationship with time
(Figs. 1 and- 2). Height curves
tended to sho'w l' a t h e l' abrupt
changes in rate both preceding and
following the major growth period.
Changes in circumference showed
a similarly abrupt increase leading
into the period of rapid growt.h,
but seasonal reduction in rate was'
gradual and somewhat erratie
These general trends are more clearly illustrated by combining
data for the 1957 and 1958 sea­
sons and e x p r e s s i n g periodic
changes as proportional to total
change (Fig. 3). Though such a
procedure masks significant be­
tween-season differences, stemming
from varying climatic patterns, it
defines trends that are probably
closer to long-term averages. From
the combined data it is evident that
substantial increases in height did
not begin' until about May 10fully one month after the start of
comparable increases in circumfer­
ence. Height growth then pro­
ceeded at a faster rate than eircum­
ference growth until both reached
80-percent completion by JUly 10.
Height growth reached its maxi­
mum for the season shortly there­
after, while the curve of circum­
ferential growth was still ascend­
ing gradually and nearly 6 percent
short of its maximum.
Measurement of height changes
by transit proved to be a workable
means for determining gross trends.
However, the transit did not have
precision commensurate with the
dendrometer. During the ea:r;ly weeks of rap.
id shoot elongation, a number of
terminals leaned or bent sufficient­
ly to cause serious underestimation
of actual height growth. This effect
was reversed later as the shoots
regained their turgidity and grad­
ually straightened. Much of the
apparent height growth fter early
August stemmed from this mechan.;
ical straightening, and not from
actual. cell divisions or elongation.
Discussion
The apparent initiation of height
growth after radial growth is a
noteworthy departure from trends
suggested by other workers (8,10,
15,16,.17). In most instances, bud
bursting and termhial 'elongation
have been observed to precede the
start of radial growth 01" to occur
nearly simultaneously with it. Tho
downward translocation of hor­
monal substances produced by ac­
tivity of the apical iner'istems is
reputed to trigger the cambial' ae­
tivity necessary for radial growth
(1, 4, 5, 11, 14, 18). This theory
cau,uot be refuted on the' basis of
gross ob,servations reported in this
study. Hpweve,r, the possibi, lity is
raised that hormones necessary to
stimulate radial growth of Doug­
las-fir Juay be translocated through­
out the cambium conside ably be­
fore the initiation of any obvious
growth in vegetative terminals.
Moreover, as is typical with the spe­
cies, reproductive buds' oc urring
on several of the study trees burst
shortly before mid-April in both
1957 and 1958. The appearance of
strobiles fully one month before
bursting of vegetative buds was
more nearly coincident with the ap­
parent initiation of radial growth.
In any case, many physiological
processes undoubtedly operate in
initiating cambial activity, and in
Douglas-fir the bursting of vegeta.
, r to be
tive buds does not appea
an essential stimulus.
Though dendrometers ,accurate­
ly measure external fluctuations
(2), each radial change combines
the :llet effect of both swelling due
to cambial growth and of shrink­
'
age or sweliing due to moisture
changes within the t ee (3). Hy­
dration levels in both living and
dead tissues may vary sufficiently
to caUSe considerable over- or un­
derestimation of growth by en­
largement of cambial initials or by
cell division. Though this effect
is minimized during periods of
most rapid growth, it can mask
actual growth trends when cambial
activity is slight.
The radial growth initiation
dates observed in this study may
.APRIL 1964
precede the start of actual growth
because radial swellings induced
by accelerated moisture uptake
from the soil would appear similar
to those resulting from early sea­
son cambial activity. In view of
climatic conditions in the Pacific
Northwest, however, it is felt that
hydration levels remain sufficiently
high during the dormant months
.' to minimize swelling due to' re­
activating sap flow in late winter,
and that earliest recorded increases
reasonably approximate the start
of actual growth.
Circumferential shrinkages oc­
curring later· in the growing sea­
son, particularly at the time of
normally decelerated cambial ac­
tivity, suggest thE) more prollounced
effect of dehydration as it affects
apparent growth. The 6.week pe­
riod of "negative" circumferential
growth in 1958, occasioned by a
sustained period of rainless weath­
er, shows that dehydration can
lfiore than offset. any existing low­
level cambial activity. Further.
more, rehydration of living and
dead tissues with the onset of late
' ummer or fall rains undoubtedly
exaggerates whatever real tissue
255
building is taking place in the cam­
bium at that time. Hence, the
actual cessation of seasonal radial
growth can only be inferred from
data in this study, and probably
could no have been reliably de­
tected short of histological exam­
ination..
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