Made in the United States of America
Reprinted from FOREST SCIENCE
Vol. 26, No.2, June 1980
Forest Sci., Vol. 26, No.2, 1980, pp. 283-290
Copyright 1980, by the Society of American Foresters
pp.283-290
Site Index, Growth, and Foliar Chemical
Composition Relationships in
Western Hemlock
M. A. RADWAN
D, S.
ABSTRACT.
AI,
DEBELL
Site index, growth, and foliar contents of the essential macro- and microelements,
and the chlorophylls of 20- to 30 -year-old western hemlock (Tsliga heterophylla) trees were
examined during the winter in eight natural stands in both the coastal and Cascade zones of
western Washington and northwest Oregon. Site index at 50 years ranged from 22 to 39 m .
Terminal growth and needle concentrations o f most nutrients and the chlorophylls varied among
the eight sites and the two zones. Site index was correlated positively ,with terminal growth, total
N, chlorophyll 'a', total chlorophyll, and Fe, and negatively with Mn and sulfate-S. Also, total
N was correlated with both chlorophyll 'a' and total chlorophyll . Results suggest that lower foliar
concentrations of some important nutrients on some coastal sites may be factors in the reported
general lack of success with N fertilizers in the coastal hemlock forests. Site productivity for
western hemlock may be improved by cultural treatments that would enhance N, chlorophyll,
and Fe contents of the needles. Levels of one or more of these components may be useful as
indicators to assess site quality for hemlock production . In addition, chlorophyll may be used as
a simple means to estimate N status of hemlock trees . F O REST
ADDITIONAL
KEY WORDS.
SCI.
26:283-290.
TSlIga heterophylla, nutrients, essential elements, chlorophyll .
WESTERN HEMLOCK, (Tsuga heterophylla (Raf,) Sarg.), is one of the most pro­
ductive forest tree species in the Pacific Northwest. As with other species, how­
ever, growth of hemlock varies by site. In addition, growth responses of natural
stands of hemlock to nitrogen fertilization have been extremely variable. Thus,
trees in the coastal hemlock zone have generally failed to respond or have even
showed negative response to fertilizer; stands located on the lowlands west of
Puget Sound and on the west slopes of the Cascade Mountains, on the other
hand, have often responded favorably to nitrogen application (DeBell and others
1975, Webster and others 1976).
Understanding the causes of response variation to fertilizer application and
. developing guides for successful fertilization of hemlock stands require studies
of the fundamental aspects of hemlock"s growth and nutrition. In the present
investigation, therefore, we assessed growth traits and foliar chemical composi­
tion of hemlock trees from sites of different productivity both in the ooastal and
Cascade hemlock zones. Comparative determinations included site index, various
growth parameters, as well as foliar contents of total nitrogen and nitrogen frac­
tions, the chlorophylls, and important mineral elements.
The authors are, respectively, Principal Plant Physiologist and Principal Silviculturist, Pacific
Northwest Forest and Range Experiment Station, USDA Forest Service, Olympia,
WA
9 850 2. Manu­
script received 9 May 1979.
VOLUME 26, NUMBER 2, 1980/283
BELLINGHAM
88
-3
FORKS
SEATTLE
82
.5
TACOMA
OLYMPIA
87
.6
SEASIDE
84
FIGURE I.
Approximate geographic location of study sites in western Washington and northwest
Oregon. Sites 1- 4 occur in the coastal hemlock zone and sites 5-8 are located on the west slopes
of the Cascade Range.
MATERIALS AND METHODS
Site a nd Tree Selection.-Eight natural stands of western hemlock on sites of
different productivity were chosen for investigation. The sites are located in west­
ern Washington and northwest Oregon. Four sites occur in the coastal hemlock
zone w ithin 50 km of the Pacific coast, and the other four are located inland on
the west slopes of the Cascade Range (Fig. O.
At each site, three replications of five trees each were randomly selected for
study. Test trees were 20 to 30 years old; and only healthy, dominant and co­
dominant trees with no evidence of previous top damage were used.
Estimation of Site Index.-At each site, test trees were felled during the 1976-77
dormant season. Tree heights and ages were determined and site index at 50-year
breast-height age was estimated from Wiley's (1978) site index tables using data
from all trees.
Height Growth Measurements.-Terminal growth of the test trees for each of the
3 years immediately before felling was measured, and average height growth per
year was computed.
Sa mpling Foliage.-One composite sample of about 500 g (fresh weight) was
collected in midmorning immediately after felling from the five trees of each
replication at each site.
Sampling was limited to vigorous branches in the upper third of the crown.
Each sample consisted of 5-cm tips of the current year's growth of secondary
laterals cut from all sides of the trees. Samples were individually sealed in pre­
cooled glass containers and transported to the laboratory in a portable cooler.
284/FOREST SCIENCE
/
Determination of Needle Weights and Numbers.-Five lateral tips were taken at
random from each composite sample. Needles were separated from stems and
buds. Stem length was measured, and needles were counted and then dried to
constant weight at 65°C. Weights of individual needles as well as numbers and
weights of needles per centimeter of twig length were calculated.
Chemical Analysis.-For each composite sample, needles were separated from
the stems and buds as outlined above and subsamples taken for determination of
moisture and the various nitrogen fractions. Remaining tissue was dried to con­
stant weight at 65°C, ground to 40 mesh in a Wiley mill, and stored in closed
containers at -15°C until analyzed. All chemical analyses were carried out at
least in duplicate on each of the three replicate samples of each site.
Moisture was dete'rmined by drying to constant weight at 65°C. Needles for determination of the nitrogen fractions were extracted in a homogenizer with ethanol at a final concentration of 70 percent, and homogenate was centrifuged. The clear solution containing the alcohol-soluble components was extracted with chloroform, and the organic layer containing the lipids and chlorophylls was separated and discarded. Remaining aqueous solution was filtered and completed to volume with distilled water. The aqueous solution was used to determine total soluble N by the standard micro-Kjeldahl procedure, ammonium nitrogen and nitrate nitrogen according to Bremner (1965), and amide N by the method of Pucher and others (1935). Ovendry needles were used to determine total N (including nitrate) by the
standard micro-Kjeldahl procedure. The insoluble nitrogen fraction was calcu­
lated by subtracting the soluble N from total N content.
The chlorophylls Ca' and 'b') were extracted from the dry needles with 80-per­
cent acetone. Optical densities of the extracts were measured at 663 and 645 nm in
a spectrophotometer, and contents were computed using Arnon's equations (Ar­
non 1949) derived from MacKinney absorbancy index values (Mac Kinney 1941).
Analyses for the minerals were performed on the dry needles or on solutions
of the tissue's ash as follows: P by the molybdenum blue technique (Chapman
and Pratt 1961); CI, as chloride, by a modification of the Volhard method (Cald­
well and Moyer 1935); total S and sulfate-S (extracted with 0.6 N HC\) by a
turbidimetric technique (Butters and Chenery 1959); Mo by the thiocyanate col­
orimetric method (Chapman and Pratt 1961); B by the quinalizarin procedure
( Horwitz 1975); and Ca, Mg, K, Fe, Mn, AI, Cu, and Zn by standard atomic
absorption spectrophotometric technique (Perkin-Elmer Corporation 1976).
,
Statistical Analysis.-Data were subjected to analysis of variance, after arc-sine
transformation when necessary, and means were compared according to Tukey's
test. Correlation coefficients (r) between each of the variables measured and site
index and between selected chemical characteristics of foliage were also calcu­
lated (Snedecor 1961) using mean values for each location (i.e., n = 8).
RESULTS
Site Index.-The site index at 50-year breast-height age varied significantly (P <
0.01) among the eight sites (Table I). It ranged from 22.0 m for site 8 in the
Cascades to 39.0 m for site 1 on the coast and averaged 32.1 m over the eight
sites. Also, :the average site index for the coastal sites, 36.0 m, was significantly
(P < 0.01) higher than that for the sites in the Cascade Zone, 27.8 m.
Growth Characteristics.-Terminal growth per year over the last 3 years imme­
diately before harvest varied significantly (P < 0.01) among the eight sites and
between the two geographical zones (Table 1). As with site index, terminal growth
VOLUME
26, NUMBER 2, 1980/285
TABLE 1.
Site number
and general
location2
Coastal zolle
I
Site index and growth chara cteristics of western hemlock.1
Site index
at 50 years
Terminal
growth
per year"
Needle dry
weight
Needle
weight per
em of twig
tissue
m
cm
mg
mg
Needle
number per
em of twig
tissue
3 8. 2 a
97. 2 a
2 . 0 ab
21. 4 a
2
36. 2 ab
74 . 5 b 2. 1 ab
20 . 8a
9.9 a
3
35. 6ab
72. 8be
2. 0 ab
20. 7 a
10. 4 a
4
34. 2 b 7 2. 2 be 1. 7 b
19 . 3 a
11.3 a
Average
3 6. 0 x
1 .9 x 79. 2 x
20. 6 x
10 . 9 a
10. 6 x
Cascade ZOlle
5
30. 1 c
63. 0 c
2 . 1 ab
23.3 a
6
29. 8 c
61. 0 c
2. 5 a
25. 0 a
9.9 a
7
29 . 4 c
60. 0 be
2 . 1 ab
20.3 a
9.9 a
8
21. 8d
2. 1 ab
21. 7 a
10.3 a
Average
1
3 8. 6 d
27. 8 y
2. 2 Y 55. 6 Y
22. 6 x
11 . 2 a
10.3 x
Values in the same vertical column which are followed by the same letter designation are not'
statistically different (P
<
0.05) .
2 Within zones,sites are arranged in order of descending site index .
3
Average term:nal growth per year for the 3 years 1974-7 6.
was significantly higher in the coastal zone at 79.2 cm/yr than in the Cascades at
55.6 cm/yr. Terminal growth was also strongly correlated with site index (r
0.95, P < 0.05).
The average dry weight per needle was about 2.0 mg. Weights of needles from
TABLE 2. Concentrations of tota l nitrogen a nd nitrogen fra ctions in foliage of
western hemlock.1
Site number and general
location2
Coastal ZOlle
I
2
Total
N
Soluble
N
Ammonium
N
Nitrate
N
Amide
N
Percent
ppm
ppm
ppm
ppm
Insoluble N
Percellt
1.3 6 a
629 be
47 ab
27 be
68ab
1.30 a
1.30 ab
60 6 c
25 c
23 cd
57 cde
1. 24 abc
3
1 . 24 ab 737 a 53 a
52 a
53 e
1. 17 abc
4
1. 17 be
45 6d
26 c
24 be
75 a
1. 12 c
Average
1. 27 x
60 7 x
38 x
32 x
63 x
1. 21 x
Cascade ZOlle
5
1.30 ab
5 86c
4 6b
23 cd
75 bed
6
1. 21 b
60 2 c
45 b
22 cd
67 abc
1. 15 be
7
1.31 ab
649 be
49 ab
19 d
69 ab
1 . 25 ab
8
1.04 c 699 ab
49 ab
29 b
·55 de
Average
1
1 . 22 y 634 x 47 y
23 y
64 x
1 . 24 abc
0 .9 7 d
1. 15 y
Values in the same vertical column which are followed by the same letter designation are not
statistically different (P
<
0 . 05).
2 Within zones, sites are arranged in order of descending site index .
286/ FOREST SCIENCE
TABLE 3.
Site number
and general
location2
Coastal zone
Chlorophyll levels in western hemlock foliage.1
Chlorophyll
'a'
__________________________________
Chlorophyll
'b'
mg/g dry tisslle
Total
chlorophyll
____________________________________
1.676 a
0.426 abc
2. 102 a
2
- 1.645 a
0.368 abc
2.0 13 ab
3
1.625 a
0.369 abc
1.995 ab
4
1. 556 a
0.350 bc
1.906 ab
Average
1.626 x
0.378 x
2.004 x
Cascade zone
5
1.595 a
0.477 a
6
1.4 18 a
0.4 19 ab
1.837 b
7
1.654 a
0. 4 15 abc
2.069 ab
8
1. 12 1 b
0.284 c
1.404 c
Average
1
1.447 y
2.072 ab
0.399 x
1.845 y
Values in the same vertical column which are followed by the same letter designation are not
< 0. 0 1).
2 Within zones, sites are arranged in order of descending site. index.
statistically different (P
coastal trees were significantly (P < 0.05) lower than those from the Cascade
Zone, but differences are primarily due to the highly significant difference be­
tween sites 4 and 6. Average needle weight was not correlated with site index or
terminal growth. Needle weights per centimeter and numbers per centimeter of
twig tissue varied little among the eight sites and did not correlate with site index
or terminal growth.
Total N a nd the N Fra ctions.-Total N of the needles averaged 1.24 percent over
the eight sites (Table 2). As with site index and terminal growth, average total N
levels were significantly (P < 0.01) higher on the coast (1.27 percent) than in the
Cascades (1.22 percent). In addition, sites 1 and 8 had the highest (1.36 percent)
and lowest (1.04 percent) N values, respectively. Total N, therefore, was cor­
related with both site index (r = 0.71, P < 0.05) and terminal growth (r = 0.75,
P <,6.05).
Ammonium N and nitrate N varied significantly (P < 0.01) among the eight
s ites and between the two zones. Similarly, the sites differed significantly in
amide N and total soluble N; but there were no significant differences between
zones. Levels of the individual soluble N fractions determined were very low,
ranging from 19 to 75 ppm, and the total soluble N concentrations were less than
0.10 percent. Also, these soluble fractions and total soluble N were not correlated
with site index.
Most of the N in the needles occurred in the alcohol-insoluble form. Insoluble
N ranged from 0.97 to 1.30 percent and varied significantly between sites (P <
0.01) and among zones (P < 0.05). In addition, as with total N, insoluble N was
correlated with site index (r = 0.72, P < 0.05) and with terminal growth (r
0.76, P < 0.05).
=
The Chlorophylls.-There were significant differences (P < 0.01) in chlorophyll
'a' ( C'a'), chlorophyll 'b' (C'b'), and total cholorophyll among the sites (Table 3).
The zones also varied significantly (P < 0.01) in C'a' and total chlorophyll, but
not in C'b' content. As expected, levels of C'a' were consistently higher than
.those of C'b'; C'a':C'b' ratio averaged about 4:1 for the eight sites. In addition,
VOLUME
26, NUMBER 2, 1980/287
TABLE 4.
Macronutrient concentrations in western hemlock foliaf?e. 1
Site number and general location"
K
P
- ---------------------------------
Coastal zone
Mg
Ca
Percent
Total S
Sulfate-S
- - - --- -------- - --- --- - -- --- -- ---- - --
ppm
I
0. 2 1 cde
0.75 cd
0.23 b
0.15 b
0. 12 cd
2
0. 12 f
0.69 d
0.29 ab
0. 1 7 ab
0. 1 1 d
160 c
3
0.22 bcd
0. 79 bcd
0.28 ab
0. 19 a
0 . 12 cd
2 70 abc
4
0. 1 7 e
0.69 d
0.23 b
0. 16 ab
0.11 d
205 bc
Average
0. 73 x
0.18 x
0. 1 7 x
0.26 x
200 bc
209 x
0. 12 x
Cascade zone
5
0.28 a
0.98 a
0. 3 1 ab
0 . 18 ab
0. 1 5 a
43 0 a
6
0.2 7 ab
0. 8 1 bc
0.33 a
0. 18 ab
0. 13 bc
3 50 ab
7
0.2 5 abc
0.89 ab
0.3 1 ab
0.19 a
0. 1 4 ab
42 0 a
8
0 . 19 de
0.74 cd
0.30 ab
0. 18 ab
0.13 be
450 a
Average
I
0. 3 1 Y
0.18 x
412 Y
0. 1 4 Y
Values in the same vertical column which are followed by the same letter designation,. are not
statistically different
2
0.86 Y
0.25 y
(P
<
0.05).
Within zones, sites are arranged in order of descending site index.
as with site index, terminal growth, and total N, site 1 was highest and site 8 was
lowest in both Ca' and total chlorophyll. In summary, C'a' and total chlorophyll
were related to site index (r = 0.84, P < 0.01; r = 0.78, P < 0.05), terminal
growth (r = 0.79, P < 0.05; r = 0.75, P < 0.05), and total N (r = 0.91, P < 0.01;
r = 0.94, P < 0.01). The correlation between N and chlorophyll contents is in
agreement with earlier findings with other forest tree species (Viro 1965, Heinze
and Fiedler 1976).
TABLE 5.
Site
numbei· and
general
location"
Concentrations of microelements in foliaf?e of western hemlock. 1
Fe
Mn
Percent
B
Cu
CI
PPill
_____ _______ ___________ ___________
Coastal zone
I
0. 1 1 bc
2 5. 7 a
4.2 a
2
0. 10 c
72. 7 ab
13.2 b
4.4 a
3
0.10 c
52. 7 b
20,6 ab
3.7 a
4
0.10 c
53 .6 b
19.6 ab
4. 0 a
Average
100.2 a
69.8 x
0.10 x
19.8 x
4. 1 x
Zn
Mo
---_----- ----------__------_--------
1 1 7. 0 be
30.2
c
71.0 bc
Percent
18.3 a
0.01 a
0.09 a
20.3 a
0.01 a
0.06 b
1 7. 5 a
0.01 a
0.09 a
18.4 a
0. 0 1 a
0.06 b
540.0 a
189.6
AI
18.6 x
x
0.0 1 x
0.08 x
Cascade zone
5
0 . 16 ab
59. 4 b
29.2 a
4.0 a
30. t c
20.2 a
0.01 a
0.10 a
6
0. 1 5 ab
56. 3 b
22.0 ab
3.9 a
50.8 bc
19.9 a
0.02 a
0.08 ab
7
0. 12 bc
55.6 b
23.0 ab
4.5 a
8 1 .8 be
19. 1 a
0.01 a
0.08 a
8
0 . 19 a
45.0 b
2 5.9 a
3.9 a
44. 7 bc
1 5.9 a
0.02 a
0.06 b
Average
I
25.0 Y
4. 1 x
5 1.8 y
18.8 x
0.01 5 x
0.08 x
Values in the same vertical column which are followed by the same letter designation are not
statistically different
2
54. 1 Y
0.16 y
(P
<
0. 05).
Within zones,sites are arranged in order of descending site index.
288/ FOREST SCIENCE
Macronutrients Other Than N.-Concentrations of P, K, Ca, Mg, total S, and
sulfate-S varied significantly (P < 0.05) between the eight sites (Table 4). Also,
except for Mg, levels of the macronutrients were significantly (P < 0.01) higher
in the Cascades than on the coast. There were no significant correlations between
site index or terminal growth and levels of P, K, Ca, Mg, or total S. Sulfate-S,
however, was negatively related to site index (r = -0.87, P < 0.01) and terminal
growth (r = -0.79, P < 0.05).
Microelements.-There were no significant differences among sites in Cu, Zn, or
Mo contents (Table 5). Levels of AI varied significantly (P < 0.01) among sites
but not between zones. Concentrations of Mn, Fe, B, and CI differed significantly
both among sites (P <: 0.01) and between zones (P < 0.05); Mn and B were
significantly higher while Fe and CI were significantly lower in the Cascades than
in the coastal zone. Among all the microelements determined, only Mn and Fe
concentrations were correlated with site index (r = -0.89, P < 0.01; r = 0.69,
P < 0.10) and terminal growth (r = -0.77, P < 0.05; r = 0.85, P < 0.01).
DISCUSSION AND IMPLICATIONS
Site index was significantly higher in the coastal sites sampled in our study than
in the Cascade sites. This finding parallels a general concensus among foresters
that the most productive hemlock stands occur in the moist coastal belt. More­
over, hemlock site indices listed by Steinbrenner (1976) for soils of the Coast
Range averaged higher than those for soils of the glaciated plains and foothills
surrounding Puget Sound and soils occurring at elevations above 800 m in the
Cascades. Growth in coastal forests is already high, and cultural practices (e.g.,
fertilization) aimed at stimulating growth on such areas must be more selective
and prescribed with greater care than on poorer sites.
Foliar concentrations of chemical components determined were within the
range of values found in the literature (Beaton and others 1965a and b, van den
Driessche 1976). Levels of the major macronutrients N, P, and K, however, were
substantially lower than those reported as adequate foliar concentrations in hem­
lock seedlings (van den Driessche 1976). Although seedling values may not be
directly applicable to older trees, the markedly lower concentrations suggest that
foliar nutrient content and perhaps growth of western hemlock, in both coastal
and Cascade zones, may be increased by fertilization.
Nitrbgen concentration of hemlock foliage from coastal sites averaged higher
than that from Cascade sites, but only. one site (No. 8) in the Cascades was
significantly lower than most coastal sites. Therefore, it does not appear that
differences in foliar N status can account for differences in response to N fertilizer
by coastal and Cascade sites. Rather, differential response may be associated
with the different levels of essential minerals in needles of the two hemlock zones
which reflect the capacity of the sites to supply mineral nutrients. Foliar concen­
trations of P, K, Ca, total S, sulfate-S, B, and Mn were significantly lower on the
coast than in the Cascades. Concentrations of one or more of these nutrients may
be limiting in coastal hemlock stands so that added N cannot stimulate growth.
Turner and others (1977) found that Douglas-fir trees with low foliar sulfate-S
reserves had lower response to N fertilizer than those with high levels of this
important nutrient.
Productivity of hemlock, as indicated by site index, was positively correlated
with total N, insoluble N, total chlorophyll, chlorophyll 'a', and Fe concentra­
tions; it was negatively correlated with Mn and sulfate-S contents of the foliage.
Chlorophyll and total N were also strongly correlated. These results suggest that
productivity of western hemlock may be improved by cultural treatments, in-
VOLUME
26, NUMBER 2, 1980/289
eluding fertilization, which would enhance N, chlorophyll, and Fe contents of the
need s. Amendments of other elements may also be beneficial and prerequisite
to obtaining a response to N fertilizer 'on some coastal sites. Levels of N, chlo­
rophyll, sulfate-S, and Fe/Mn ratios may be usefl)l as indicators to assess site
quality for hemlock production. In addition, chlorophyll may be used as a simple
means to estimate N status of hemlock trees. A similar suggestion has been made
recently for other conifers (Heinze and Fiedler 1976).
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BEATON, J. D., G. BROWN, R. C. SPEER, I. MACRAE, W. P. T. MCGHEE, A. Moss, and R. Ko­
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BEATON, J. D., A. Moss, r. MACRAE, J. W. KONKIN, W. P . T . MCGHEE, and R. KOSICK.
196 5b.
Observations on foliage nutrient content of several coniferous tree species in British Columbia.
For Chron 41: 222- 236.
BREMNER, J. M. 196 5. Inorganic forms of nitrogen. III Methods of soil analysis,part 2 (C. A. Black,
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1959. A rapid method for the determination of total sulfur in
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CALDWELL, J. R.,and H . V . MOYER.
1935. Determination of chloride . A modification of the Vol hard
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CHAPMAN, H. D., and P . F . PRATT.
196 1. Methods of analysis for soils, plants, and waters. Div
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DEBELL, D. S., E. H. MALLONEE, J. Y. LIN, and R. F. STRAND.
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hemlock: A summary of existing knowledge. Crown Zellerbach Forest Res Note 5, 15 p. Crown
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HEINZE, M., and H . J. FIEDLER.
1976 . Correlations between chlorophyll content and site factors,
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1975. Official methods of analysis of the association of official analytical chem­
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MACKINNEY, G.
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1976. Analytical methods for atomic absorption spectrophotometry.
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1935. Determination of ammonia and
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State Univ Press. 534 p .
STEINBRENNER, E . C.
1976 . Soil-site relationships i n comparative yields o f western hemlock and
Douglas-fir. III Western Hemlock Manage Conf Proc (W. A. Atkinson and R. J. Zasoski, eds),
p 236- 238 . Univ Wash, Seattle.
TURNER, J., M . J. LAMBERT, and S. P. GESSEL. 1977. Use of foliage sulfate concentrations to predict
response to urea application to Douglas-fir. Can J For Res 7: 476- 48 0.
VAN DEN DRIESSCHE, R . 1976. Mineral nutrition of western hemlock. III Western Hemlock Manage
Conf Proc (W. A. Atkinson and R . J. Zasoski, eds), p 56- 70. Univ Wash, Se.attle.
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59(3): 1- 42.
WEBSTER, S . R ., D. S. DEBELL, K. N . WILEY, and W. A . ATKINSON. 1976. Fertilization of western hemlock. III Western Hemlock Manage Conf Proc (W. A. Atkinson and R. J. Zasoski, eds), p 247- 252. Univ Wash, Seattle. WILEY, K. N. 1978. Site index tables for western hemlock in the Pacific Northwest. Weyerhaeuser
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PURCHASED BY THE FOREST SERVICE, U .S . DEPARTMENT OF AGRICULTURE, for official use.
290 /
FOREST
S CIENCE
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