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EFFECTS OF FERT IL IZAT ION ON MORTAL ITY IN WESTERN HEMLOCK AND DOUGLAS-F IR STANDS Richard E. Miller Overstocking in hemlock and/or Douglas-fir
stands is often associated with low site
productivity. Although stocking control or
precommercial thinning Is desirable In such
stands to concentrate growth on fewer trees,
costs are high and benefits may be low.
Fertilizing can be a tool for thinning pure
stands and/or weeding mixed stands if fer­
tilization enhances site productivity and
induces faster suppression or loss of noncrop
trees.
Overstocking In hemlock and/or Douglas-fir
stands is often associated with low site
productivity. Although stocking control or
precommerclal thinning is desirable in such
stands to concentrate growth on fewer trees,
costs are high and benefits may be low.
Fertilizing could be a tool for thinning pure
stands and/or weeding mixed stands if ferti­
lizing would enhance site productivity and
induce faster suppression or loss of noncrop
trees.
To explore this alternative or supplemental
tool for thinning overstocked stands, I
reviewed published and unpublished data
seeking answers to two questions:
Several studies in pure hemlock and Douglas­
fir stands indicate that fertilizing with
nitrogen at dosages up to about 400 pounds
per acre generally stimulates diameter growth
of upper crown class trees more than lower.
Although there Is a general trend for tree
losses in fertilized plots initially to
exceed those of unfertilized, differences are
usually small and not statistically signifi­
cant.
Besides changing the relative competitive
status of upper and lower crown classes,
fertilizing Douglas-fir with 200 to 400
pounds of N per acre at several locations
increased crown breakage and tree mortality
from winter damage. Mortality was generally
in smaller-than-average trees.
In an overstocked mixed stand of Douglas-fir
and hemlock, fertilization stimulated basal
area growth of dominant Douglas-fir and
significantly (p < 0.09) increased rate of
mortality during a 6-year period after
treatment. Net reductions In live stems
averaged 2 percent on control plots compared
to 12 and 24 percent for the two fertilizer
treatments, 600N and 300N + 150P + lOOK +
50S. Fertilized plots averaged signifi­
cantly (p < 0.08) greater mortality In
smaller diameter classes, which were primari­
ly hemlock. Despite these initial and prob­
ably continued reductions In stand density
following fertilizing, these mixed stands
will probably remain overstocked for effici­
ent production of sawtimber. If increased
pulpwood or fiber production through fertili­
zation is not an acceptable option for gros­
sly overstocked, pure, or mixed stands, then
increased investments In mechanical thinning,
preferably early and In combination with
fertilizing, or even stand replacement should
be considered.
I.
Can fertilizer serve as a thinning tool
in pure stands of hemlock or Douglas­
fir?
2. Can fertilizer serve as a selective
weeding tool in mixed stands of these
two species?
Results and Discussion
IntuitiVe bases
A review of knowledge about stand growth and
mortality is desirable before considering
empirical evidence from fertilizer trials In
western hemlock and Douglas-fir.
Stand density and site index
In pure, even-aged, normally stocked stands
of Douglas-fir and western hemlock, there are
generally fewer trees present at a given
stand age on high-quality sites than on low­
quality sites (McArdle et al. 1961; Barnes
1949). These general relations between stand
density and site quality integrate differ­
ences in (1) seedfall, (2) germination and
seedling survival, and (3) subsequent rates
of growth and mortality. Unquestionably,
faster rates of stand growth on high-quality
sites lead to faster reductions in stem
numbers.
RICRA U h
LLER
USFS Forestry Science Laborator.
ruy ia !
253
'
Based on these trends in natural stands. we
can expect increased rates of mortality In
overstocked stands wherever fertilizer In­
creases rate of growth ( I.e., temporarily
increases site productivity). Although
extremely large fertilizer dosages, espec­
ially on soils of low buffering capacity,
could cause direct and rapid increases in
mortality due to toxicity, moderate ferti­
lizer dosages that enhance growth will prob­
ably cause slow changes in mortality rates by
increasing competition among trees.
Landing, basal area growth of Intermediate
and suppressed trees during the 3-year period
after treatment was apparently increased by
the 400- but not· the 200-pound N dosage
(Table I). Basal area growth of dominant and
codominant trees was Increased at both dosage
levels. As indicated by ratios of growth,
the competitive position of the upper canopy
classes was improved by fertilization.
In a less excessively stocked stand at Port
Renfrew, however, 3-year basal area growth of
intermediate and suppressed trees was in­
creased by both N dosages and the relative
competitive position of dominants and co­
dominants was not improved (Table I).
Although initial differences in stocking and
diameter distribution among plots at both
areas may be masking true treatment effects,
it is more likely that fertilizer will
induce mortality in lower crown classes at
Jeune Landing than at Port Renfrew in the
future.
Relative response by tree size
When fertilizer is applied to unthinned
stands, not all trees respond equally. Thus,
the relative competitive position of some
trees will be improved to the disadvantage of
others. For example, nitrogen fertilizer
applied in dense Douglas-fir stands usually
stimulates diameter growth of large more than
of small trees (Gessel et al. 1965; Gessel et
a1. 1969; Miller and Pienaar 1973).
These results in western hemlock and Douglas­
fir suggest that upper crown classes in
overstocked stands generally respond more to
fertilization than do lower crown classes.
Such differential response should accelerate
losses in lower crown classes by making them
less competitive for light, moisture, and
nutrients.
In two 32-year-old hemlock stands, DeBell et
al. (1975) also found that upper crown clas­
ses responded much more to nitrogen ferti­
1 izer than did lower crown classes. Initial
results, however, in one of two sapling
hemlock stands on Vancouver Island (Lee 1972)
were not consistent with this generalization.
In an excessively stocked stand at Jeune
Average basal area growth of hemlock by crown class and N
Table 1.
1
dosage, 3-year perio
Crown classll
N dosage
S + 1
(pounds per acre)
CD
Quotient11
Initial stand
+ D
---Number----
--Square feetJeune Landing (11 lears old)
0
0.008
0.018
2.25
13,700
200
.008
.026
3.25
17,630
400
.013
.032
2.46
12,770
Port Renfrew (13 lears old)
0
.006
.028
4.67
6,370
200
.010
.028
2.80
9.870
400
.009
.041
4.56
7,280
11 Source:
11 S
m
Lee (1972).
suppressed, I
11 Quotient
-
m
Three plota per treatment. intermediate, CD
growth of CD + D
t
S + I.
254
q
codominant, and D
m
dominant.
Relative response by tree species
In the 35-year-old site V plantation In
southwestern Washington, nitrogen dosages of
280 and 420 pounds per acre increased tree
losses by twofold and fourfold, respectively,
during the 7 years after treatment (Table 2).
Lighter dosages of 140 pounds per acre did
not increase tree losses. Mortality was
mostly related to winter damage and largely
confined to smaller trees; 60 percent were in
the lower third of the diameter range whereas
only 5 percent Were in the upper third.
However, a higher proportion of larger trees
was affected at the largest dosage.
Tree species vary in their tolerance and
response to fertilization; thus, fertilizing
mixed stands may Increase growth of some
species to the detriment of others. Stand
composition will probably shift to spec Ies
benefiting most from treatment.
Changes in susceptibility to climate or
biotic agents
So far we have considered effects of ferti­
Ilzation in changing the relative competit Ive
position among trees which Initially d Iffer
In size or species. Fert IlIzation may also
affect tree mortality by changIng tree re­
sistance to climatlc damage or biotic attack.
Direct Evidence:
Tool
Mortality data from field trials provide
direct evidence about fertilizer as a thin­
ning tool. In assessing the effects of
fertilization on mortality, we shOUld con­
sider losses in number of trees by diameter
class. Stem volume is a less reliable para­
meter because larger volume of mortality on
fertilized plots could indicate that more
trees died and/or that the same number of
trees died, but the volume of the Indlvidu '
trees was greater.
One might assume that If fertilizer Improves
nutrition and general vigor of trees, then
tree resistance to climatic damage or biotic
attack should be increased.
We have much to learn about the effects of
improved, or overly improved, nutrition on
susceptibility of Douglas-fir and western
hemlock to climatic extremes and attacks from
disease and insects. There Is, however, one
recurring observation about Douglas-fir that
is pertinent; fertilization with moderate to
heavy dosages of nitrogen can increase winter
damage and mortality. This was ·flrst noted
in a fertilizer trial in southwestern Wash­
ington by Reukema (1968) and later confirmed
by Miller and Pienaar (1973). Increased
winter damage and mortality has also been
observed in two locations of the cooperat Ive
Regional Forest Nutrition Research Project
administered by the University of Washington
(Atkinson, personal communication).
Table
2.
Fertilizer as a Thinning
Effect of fertilization on mortality rates
in Douglas-fir
Although pub I ished information suggests that
addition of nitrogen to dense juvenile
stands of Douglas-fir accelerated competition
and mortality (Crossin et al. 1966; Gessel
and Shareeff 1957), these conclusions were
based on unreplicated plots. This lack of
replication coupled with initial differences
in diameter distribution between fert Ilized
and control plots constrain conclusions about
fertilizer effects.
Average lOBS of trees after seven growing seasons by treatment and cause, per acre basi
N dosage
(pounds per acre)
Live
Total dead
1963
1963-70
-�
--
---
Winter breakage
Breakage mortality
Total mortali ty
Total
-Percent-
Died
---�---
-Percent-11
---Percent--
0
600
93
16
113
73
65
78
140
573
67
12
107
53
50
79
280
627
193
31
220
167
76
87
420
620
227
37
260
200
77
88
1/
Source:
11
Percent of damaged trees.
Miller and Pienaar
(1973).
II
Three plots per treatment.
255
lng, In Itial stems averaged 14, 700 per acre.
Dur Ing the 3-year period after fertil Iz Ing,
the basal area growth of upper crown class
trees was stimulated more than lower (Table
I). Concurrent tree losses on plots treated
with 200 and 400 pounds N per acre averaged 4
and 17 percent greater than losses on the
control plots.3 These differences, however,
were not statistically significant (p < 0. 95)
after plots were adjusted for Initial diff­
erences In tree numbers by covariance analy­
sis.
A reanalysIs of a repl Icated ser Ies of plots
near Darrington, Washington, showed that
fertilizing this 15-year-old stand (I) In­
creased basal area growth during the next 22
years and (2) accelerated Ingrowth Into
merchantable diameter classes, but probably
failed to Increase rates of mortalIty
(Table 3).2 Fertilizing with heavy dosages
of NPS clearly Increased growth. The CaMg
treatment may have slightly Increased growth.
The Initial variability of this stand In
diameter distributions precludes further
conclusions.
Additional data for reanalysis provided by
Dr. Stanley P. Gessel, Professor, Universi
of Washinqton. on June 1. 1976.
Effect of fertilization on mortality rates
in hemlock
11
As previously mentioned, Lee (1972) examIned
effects of various nitrogen dosages up to 400
pounds per acre In young, overstocked hemlock
stands on Vancouver Island. At Jeune Land­
Table 3.
Additional data for reanalysis provided by
Dr. Y. Lee, Research Hensuratlonist,
Canadian Forestry Service, Victoria, British
ColUmbia, on April 22, 1976.
A 10 percent probability of making a Type I
error (p < 0.10) was accepted in this paper
as being statistically significant.
Average stand conditions and changes during a 22-year period
after treatment of a 15-year-01d stand near Darrington,
Washington, per acre basis
11
Repeated applications of various fertilizers provided specified
approximate elemental dosages (pounds per acre) of 700N, 385P. 700S, 950Ca.,
and 100Mg.
See Gessel et a1.
256
(1965) for more details.
Initial stand density at the second locaton
near Port Renfrew was also excessive (7,840
stems per acre). Although th Is density was
about half that at Jeune Landing, mortality
was about twice as much. . An average of 34
percent of the original trees on the control
plots died during the 3-year period. After
adjustment for initial differences In stand
density, losses on plots treated with 200 and
400 pounds N per acre averaged 13 percent
less and 33 percent greater than the control
plots. Again, these differences were not
statistically significant (p < 0. 30). In
summary, short term evidence from both areas
suggests that the 400-pound-N dosage per acre
could have increased the rate of natural
thinning. The large with-treatment variation
in initial stand density and tree losses
precludes more definite conclusions at this
time.
In conclusion, these data from replicated
plots of pure Douglas-fir or hemlock stands
fail to support firm conclusions about the
ultimate effect of moderate dosages of N on
rates of mortality. After adjusting mor­
tality losses for initial differences in
number of trees, differences in mortality
between fertilized and control plots were
small and not statistically significant. In
most cases, however, mortality on fertilized
plots exceeded that on untreated plots,
suggesting a contributory benefit from fer­
tilizing these overstocked stands. It seems
unlikely that measurable effects on mortality
can be expected without a strong positive or
negative effect on tree growth.
Direct Evidence:
Weeding Tool
Most conifer stands in the Pacific Northwest
are composed of more than one species.
Mixtures with hemlock are prevalent, presum­
ably because hemlock Is a prolific seeder and
shade-tolerant. Depending on relative stum­
page values and projected rates of growth,
program to reduce stocking will attempt to
weed the least desirable species.
Data from replicated plots In two pole-sized
stands in northwestern Oregon also showed
that a conventional 200-pound-N per-acre
dosage had only a slight effect on tree
growth and rate of tree mortality. During a
12-year period following fertilization of a
30-year-old heavily stocked hemlock stand,
about 12 percent more stems died on plots
fertil ized with 200 pounds of N as urea than
on untreated plots (Table 4). 5 This increase
in mortality was small and did not differ
significantly from that lost on control plots
(p < 0. 20). A closer examination of the
mortality trends within the 12-year period
showed that 92 percent of this mortality
occurred during the first 7 years on the
fertilized plots compared to 69 percent on
the control plots (Table 4). This suggests
that fertilization accelerated rate of mor­
tality and normal trends toward fewer trees.
. These slight effects on mortality trends are
understandable since fertilizing had l Ittle
affect on net or gross basal area growth
(Table 4).
In 1969 we began comparing various treatments
for increasing merchantable yields In two
grossly overstocked, mixed conifer stands on
the Quilcene Ranger District of the Olympic
National Forest (Table 6). Our study at Gold
Creek and Deadfall Creek followed an earlier
one by the Ranger District in which 3-year
diameter growth of dominant trees at Gold
Creek was increased sevenfold by fert Ilizing,
slightly by heavy thinning, and increased 3. 5
times by combining thinning and fertilizing
(Beamer 1967).
In each area we compared eight treatments
with a control. Three treatments Included
thinning and N dosages of 0, 300, and 600
pounds per acre. The remaining five treat­
ments were In unthlnned plots. We again
compared nitrogen dosages of 300 and 600
pounds; moreover, we combined N at the 300­
pound dosage with P, P + S, or P, K, S in
three additional treatments. We appl ied
both thinning and fertilizing treatments to
1/20-acre plots centering on codominant
Douglas-fir nominally spaced on a I-chain
grid.
In a second well-stocked stand of hemlock in northwestern Oregon, diameter growth of dominant trees was reduced by about 20 per­
cent duri g the first 2 years after ferti­
1ization with 200 pounds of nitrogen per acre as urea (DeBell et al. 1975). During the 4-year period after treatment, tree losses in the fertllized plots averaged 15 percent of the initial stand compared to 12 percent for the control. In a 9-year period prior to fertilization the reverse was true; mortality in the same plots was greater on the control plots (Table 5). 6 This reversal illustrates the general irregular pattern of mortality and the uncertainty in ascribing small changes In tree growth or mortality to fertilizing or other treatments. 2!
Y
Unpubl ished data supplied by Bruce Rottlnk,
Research Plant Physiologist, Crown
Zellerbach Corporation, Camas, Washington,
on April 24, 1976.
Ibid.
Fertilizer as a Selective
257
We periodically measured diameter and height
of subject trees and tallied 1ive trees
larger than 0. 5 Inches d. b. h. initially and
after 6 years on at least two quadrants. The
differences between tallies represents the
net change In number of stems. We cannot
determine actual losses from the initial
stand because our direct tally of dead trees
after 6 years was unreliable. Notches cut
Into the dead trees In the initial tally were
no longer visible after 6 years. Thus, we
Table 4.
Average loss of trees during a l2-year period after fertilizing
1
a 30-year-old hemlock stand, per acre basi&-1
N dosage in pounds
Item
o
200
1,413
1,260
92
92
6
5
253
236
Hemlock - percent
81
86
Douglas-fir - percent
17
15
Initial stand
Stems
Hemlock - percent
Douglas-fir - percent
Basal area
5.7
D.b.h. - inches
5.9
Growth in basal area
63
58
101
110
Years 1-7
413
620
Years 8-12
183
50
Years 1-12
596
671
96
96
Net - square feet
Gross - square feet
Losses
Stems - numbeJ-1
Hemlock - percent of total
11 Source:
per treatment.
Bruce Rottink, Crown Zellerbach Corporation.
Three plots
Trees 1.5 inches d.b.h. and larger.
I Adjusted for initial differences in total stems.
cannot distinguish between dead trees ini­
tially present in the stand and those which
died after treatment.
Results at Gold Creek
During the 6 years after treatment, net
losses of stems averaged about 20 percent.
At less excessive stand densities there were
few trees under the I-Inch diameter class,
so the net reduction was essentially In trees
lost from the originally tallied stand. At
more excessive Initial densities, Ingrowth
Into the I-Inch class partially offset losses.
In the six control plots, tree losses were
positively and nearly perfectly correlated
with initial number ( r
0. 99). The greater the number of initial stems, the greater net loss during the intervening 6 years. =
258
In contrast, tree losses In fertilized plots
were variable and poorly correlated with
Initial number of trees. Bartlett's test of
homogeneity of variance substantiated that
variation in tree losses among fertilizer and
control treatments was unequal. The fertl­
Ilzer treatments were obviously causing the
difference. This Implies that the fertilizer
treatments In the unthinned stand Increased
variation In mortality, among plots, poss­
ibly because the effect of fertilizer de­
pended on initial site and stand conditions
at each plot. An alternative interpretation
15 based on the fact that a greater propor­
tion of the fertilized plots was Initially
more heavily stocked ( Figure I) . Therefore,
net losses of trees on fertilized plots were
not likely affected by variation In amount of
Ingrowth Into the I-Inch diameter class.
Table 5.
Average trends of mortality before and after fertilizing a
42-year-old hemlock stand, per acre basis
!!
Year (and age).
N dosage in pounds
1971 (42)
1974 (46)
650
430
380
640
470
400
1962 (33)
Live stems
o
200 Loss - numbers
o
200 50
170
70
Loss - percent
o
200
1/
220
Source:
34
12
27
15
Bruce Rottink, Crown Zellerbach Corporation.
Two p lots
per treatment.
Table 6.
Initial stand statistics
Gold Creek
Item
Deadfall Creek
Dominant age - years
70 - 80
30 - 40
Site
IV -
IV - V
V-
Stems per acre
5,200
7,800
Douglas-fir - percent
28
9
Western hemlock - percent
67
72
5
19
All - number
Western redcedar - percent
'
Itio , and d. b. h. distribution ( Figure 2).
Tests of homogeneity of variance showed that
only two of the five fertilizer treatments
sampled conditions comparable to those on the
control plots. Subsequent statistical
analyses of mortality were restricted to
treatments 4 (600 pounds of nitrogen as urea)
and 7 (300N + 150P + lOOK + 50S).
In conclusion, fertilization probably In­
creased among-plot variation In tree losses.
This finding hinders a generalization about
the effect of fertilization on rate of tree
loss and necessitates further effort to
explain this Interaction between fertiliza­
tion and the site and stand conditions at
Gold Creek.
Results at Deadfall Creek
Despite random allocation of the six repli­
cations of each treatment at Deadfall Creek,
treatments did not equally sample the Initial
variation in tree numbers, species compos-
259
In the 6 years after fertilizing, net losses
of trees on the control plots averaged 2
percent compared to 12 and 24 percent on
plots treated with 600N and 300N + PKS,
respectively ( Table 7). Losses on fertilized
Figure I. Net change in stem numbers durIng a 6-year perIod after
fertilizing, per acre basis, Gold Creek. Treatment means
are circled.
a
-2
-Lt
-Ei
-8
.,
."
<l
...
."
<l
.a
.,
...
III
<l
<l
00
<l
'"
.a
u
...
'"
<l
>.
'"
-Ia
-12
- I Lt
-lEi
-
18
-2
-22
20
Gold Creek
-2Lt
Pounds/acre
-2Ei
-28
1 3
-3kl
5
-32
N
S:z:mbo1
P
0
0
3
0
6
0
3 1.5
3 1.5
3 1.5
4
7
6
fa
X
K
s
0
0
0
0
0
1
0
0
0
.5
.5
.5
:=
Table 7. 100
:3
30
Initial stems - thousands
Lt
Ei
7
8
9
Ikl
Average net change in live tree number and basal area 6 years
after fertilizing
( Deadfall
Treatment Creek )
Net change by d.b.h. clas
ell
(pounds of
Basal area
Live stems element
per acre)
All
1-3 inches
4+ inches
All
1-3 inches
4+ inches
----------------------Percent-----------------------
o
600N
300N +
11
PKS
4
25
6
-22
36
9
-26
43
- 2
- 2
14
12 -12
-18
24
-24
-35
34
Treatment means adj usted for initial differences in stems and·
bssal area.
260
3
II
12
Net change in stem numbers during a 6-year period after
fertilizing, per acre basis, Deadfall Creek.
Treatment
means are clr€led.
Figure 2. -2
-Y
-6
-8
-I
ru
§
3
-12
-IY
s
ru
- 16
ru -18
ro ru
-20
ro
u
-22
Gold Creek
-2Y
S mbol
-26
-28
1 3
-3
5
4
6
7
-32
20
Pounds/acre X
P
N
0
3
6
3
3
3
0
0
0
1.5
1.5
1.5
I
2
100
K
s
0
0
0
0
0
.5 .5 0
0
0
1
I
3
.
5
3
30
I
Y
E
7
B
9
I
II
12
Initial stems - thoussnds
plots averaged significantly greater than
those on control plots (p < 0.09), but the
effects of the two fertll izer treatments did
not differ significantly from each other
(p < 0.24). Net Increases In live stand
basal area averaged slightly greater on the
control plots but did not differ signifi­
cantly from increases on fertilized plots.
Net losses of trees and basal area in the
'1- to 3-inch d.b.h. classes were signifi­
cantly increased after fertilization
(p < 0.08). Losses of smaller stems--nearly
all hemlock in the initial stand--averaged
2 percent on the control plots compared
to 18 and 35 percent on those treated with
600N and NPKS (Table 7). Total basal area
in smaller trees increased by 4 percent In
the control plots, and decreased by 22 and
26 percent in the fertilized plots (Table 7).
It is Important to note that these net
losses In the 1- to 3-inch diameter classes
resulted from (I) mortality among the
original trees, (2) growth into the 4-inch
class, and (3) ingrowth into the I-inch
class which offset losses.
Net changes among larger trees (4-lnch
class and above) resulted from (I) Ingrowth
from the 1- to 3-lnch class, (2) growth of
the original trees, and (3) any mortality
that offset gains. During the 6 years
after treatment, control and fertillzed
plots Increased In number of trees and
basal area In the 4-inch and larger classes.
These Increases were consistently greater
for the two fertilizer treatments, but
differences were not statistically sIgnifi­
cant (p < 0. 35).
261
Basal area growth of dominant subject trees
(one per 1/20-acre plot) increased after
fertilization, but these gains were not
statistically significant (p < 0.25). Re­
lative to the average growth of untreated
dominants, 6-year growth after 600N and 300N
+ PKS averaged 20 and 12 percent greater.
The NPKS fertilization stimulated growth of
the 20 largest trees per acre less than the
N fertil ization, and reduced numbers of
smaller trees more than the N fertilization.
One explanation is that the complete treat­
ment probably increased salt concentration in
the soi 1 more than did the 600-pound N treat­
ment with urea.
This increased salt concen­
tration could have reduced growth improvement
of dominant trees and increased mortality in
smaller trees through a direct toxic effect
as well as by decreasing availability of soil
moisture.
I conclude that fertilizing at Deadfall Creek
reduced overall stand density and especially
that in smaller trees.
Species composition
was also shifted because most of the smaller
trees were hemlock.
Net losses in hemlock
trees averaged 0 percent on the control plots
compared to 20 and 40 percent on the 600N and
300N + PKS. Fertilizer probably caused a
greater net shift of trees and basal area
into the 4-inch and larger diameter classes
and increased growth of the 20 largest stems
per acre.
Figure 3.
This 75-year-old hemlock/Douglas-fir stand averaged 5,200
stems per acre.
efficient sawtimber or even pulpwood or fiber
production is the land manager's objective,
then some investment in mechanical stocking­
control and/or fertilizing appears necessary.
The lack of increased diameter growth by the
20 largest trees per acre during the 6-year
period after thinning is disappointing but
not unusual for low-quality sites.
Increased
growth of these largest trees after fertili­
zing is encouraging, but the response was
less than that measured in a nearby prelimi­
nary trial by the ranger district.
Costs and Benefits of Treatments
Despite increased rates of mortality at
Deadfall Creek during the 6 years following
treatment, current stocking remains excessive
for efficient production of sawtimber.
Although greater and quicker reductions in
stand density could be obtained using another
tool, the power saw, costs of mechanically
thinning this stand are high.
For example,
in thinning our thirty-six 1/20-acre plots
(nearly 2 acres), experienced operators
needed between 80 and 90 hours per acre
(Figure 3).
On an operational basis at least
50 hours per acre is a 1ikely expenditure of
manpower.
This equals $300 per acre thinning
costs, assuming a $6-per-hour cost for labor
These estimates are probablY
and equipment.
conservative because 2 years earlier district
foresters estimated costs of $400 to $450 per
acre to thin the Gold Creek stand to about
the same spacing.
By far the best treatment was the combination
of thinning and fertilizing, but it was also
the most expensive. Response to all treat­
ments was probably slowed by poor crowns
after initial overstocking. For example)
crown expansion after fertilizing was notice­
able only in the fourth year after treatment.
Undoubtedly, additional benefits will accrue
to all treatments in the future.
A fifth treatment option is also available
for grossly overstocked stands, particularly
those with some merchantable volume or little
1 ikelihood for adequate response to thinning
or fertilizing.
Such stands could be harves­
ted or destroyed, then replaced with neW
stands scheduled for early control of growing
stock.
The Quilcene Ranger District is
selectively using this option.
Although stocking control or precommercial
thinning is particularly necessary in exces­
sively overstocked stands to concentrate
growth on fewer trees, costs are high and
benefits may be low because of the inherently
Thus, managers of
low site productivity.
such overstocked, low qual ity sites have
difficult decisions.
For example, in the 40-year-old stand at
Deadfall Creek we examined costs and shori
term benefits of four options (Figure 4).
If
Th inning with a powe r sm. to about 400
stems per acre required 50 manhours per acre.
262
The land manager should have sufficient funds
and manpower to reduce stocking to desired
levels on all stands within a short period of
time.
If this is not the case, a priority
system is necessary.
Early stocking control
to concentrate growth on potential crop trees
is most desirable for increasing usable
yields and reducing initial thinning costs.
For example, power saw thinning the 40-year­
old stand at Deadfall Creek from about
Figure 4. Costs and effects of four silvicultural options in a
35-year-old, overstocked stand, per acre basis.
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Deadfall Creek
6-year change - percent
6P.l
Treatment
Cost
Stems
B.A.
growth (dams)
-Do11ars-
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F
T
T + F
0
150
300
450
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20
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-18
-95
-95
100
121
78
198
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Live stems . - thou s an ds
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7
a
8,000 stems per acre to 500, cost a conserva­
tive $300 per acre ( approximately 50 man­
In contrast, It cost $90 per acre to
hours ) .
reduce stocking from 30,000 to 500 stems per
acre in a nearby, 12-year-old plantation
( Figure 5) having much natural fill-in ( Vag­
Ie, personal communication ) . Although we
have no measure of tree response following
thinning in this younger stand, a quicker and
greater response to thinning is Iikely be­
cause the trees had better crowns and a
shorter period of competition.
Conclusions for Land Managers
Analysis of a portion of data available from
existing field trials in pure hemlock and
Douglas-fir shows a general trend for tree
losses in fertilized plots initially to
exceed those of unfertilized. Although these
differences were statistically nonsignifi­
cant, I conclude that where fertilizing
improves tree growth in overstocked stands,
it probably will also increase rates of
263
This 10-year-old, site V Douglas-fir plantation with
natural fill-in averaged 30,000 stems per acre.
With conventional dosages of N (100-400
pounds per acre), reductions In overstocking
will probably be slow--certalnly much slower
and In most cases less beneficial than those
from a chain saw. If Increased pulpwood or
fiber production through fertilization is not
an acceptable option for overstocked stands
of hemlock and/or Douglas-fir, then Increased
investments in mechanical thinning, prefera­
bIy early and combined with fertil izing, or
even stand replacement should be considered.
natural thinning. With llght-to-moderate
dosages of nitrogen (100-400 pounds per
acre), release will be slower and much less
than that from a chain saw. With Increasing
dosage, faster and greater release Is likely
because the fertilizer could have a toxic
effect or temporarily reduce available soil
moisture.
Moreover, moderate-to-heavy dosages of nit­
rogen to Douglas-fir will I ikely Increase
winter damage and mortality (Miller and
Plenaar 1973). The main potential benefit
from conventional fertilizer dosages is
Increased stand growth. The acceleration of
competition or rate of suppression mortality
which Is likely to accompany growth Increases
is a contributory benefit.
Conclusions for Researchers
Analysis of these field experiments demon­
strates the uncertainty in ascribing changes
in tree mortality or growth to fertllization
or other treatments. Effects of treatment
are frequently influenced and masked by
Interacting stand and site factors. To
improve sensitivity and discriminating power
of field experiements, we need to identify
factors which interact with treatment causing
erratic responses. Knowing these factors, we
can reduce their influence by stratifying
experimental designs. These refinements are
necessary for improving our ability to pre­
dict where fertilizers will be most and least
effective.
In a 40-year-old overstocked hemlock/Douglas­
fir stand of low site quality, fertilizer
increased basal area growth of the dominant
Douglas-fir and markedly increased losses of
1- to 3-inch 6iameter trees. Most of the
small trees in this stand were hemlock, so
these increased losses cannot be considered
as selective weeding.
REFERENCES
Atkinson, William A. 1975. Personal commu­
nication. College of Forest Resources,
University of Washington, Seattle.
August 19.
Gessel, S. P. and Abdulla Shareeff. 1957.
Response of 30-ye r-old Douglas-fir
to fertllization. Soil Science Soci­
ety of America Proceedings 21(2):236­
239.
Barnes, George H. 1949. Yield of even-aged
stands of western hemlock. U.S.D.A.
Forest Service Technical Bulletin No.
1273, 52 pp., Washington, D.C.
Gessel, S. P., T. N. Stoate, and K. H. Turn­
bull. 1965. The growth behavior of
Douglas-fir with nitrogenous fertilizer
in western Washington. A first report.
College of Forestry, Institute of For­
est Products, University of Washington Research Bulletin No. 1, 204 pp. Seattle, Washington. Beamer, Haroid. 1967. The Gold Creek-Dead­
fall Creek fertilizatIon project. Un­
published report. U.S. Forest Service,
Quilcene Ranger District. Copy on file
at Olympic National Forest, Olympia, Washington. Gessel, S. P., T. N. Stoate, and K. J. Turn­
bull. 1969. The growth behavior of
Douglas-fir with nitrogenous fertilizer
In western Washington. The second
report. 119 pp. InstItute of Forest
Products, University of Washington,
Seattle.
Crossin, E. C., J. A. Marlow, and C. L.
Alnscough. 1966. A progress report
on forest nutrition studies on Vancou­
ver Island. Forestry Chronicle 42(3):
265-284.
DeBell, D. S., E. H. Mallonee, J. Y. Lin,
and R. F. Strand. 1975. Fertilization
of western hemlock: A summary of exist­
Ing knowledge. Crown Zellerbach Corp­
oration, Central Research Forest Re­
search Note No. 5, 15 pp. Camas, Wash­
Ington.
Lee, Y. 1972. Report on fertilization of
dense Juvenile western hemlock. Unpub­
lished Internal Report BC-31, 11 pp.
Canadian Forestry Service, Victoria,
British Columbia.
264
McArdle, Richard E., Walter H. Meyer, and
Donald Bruce. 1961. The yield of Doug­
las-fir In the Pacific Northwest.
U.S.D.A. Forest Service Technical
Bulletin No. 201, 74 pp. Washington,
D.C.
Reukema, Donald L. 1968. Growth response
of 35-year-old, Site V Douglas-fir
to nitrogen fertilizer. U.S.D.A.
Forest Service Research Note PNW-86,
9 pp. Pacific Northwest Forest and
Range Experiment Station, Portland,
Oregon.
Miller, R. E. and L. V. Plenaar. 1973.
Seven-year response of 35-year-Old Doug­
las-fir to nitrogen fertilizer.
U.S.D.A. Forest Service Research Paper
PNW-165, 24 pp. Pacific Northwest
Forest and Range Experiment Station, . Portland, Oregon.
Vagle, Nick. 1976. Personal communication.
Quilcene Ranger District, Olympic
National Forest. Quilcene, Washing­
ton. Reproduced from Proceedings of Western Hem10ck Management Conference,
of Forest Resources,
University of Washington,
U.S. Department of Agriculture,
May 1976,
for official use.
265
College
by the Forest Service,