Relation of Crown and Foliage Traits to Height Growth of Sitka Spruce D.L. Copes, USDA Forest Service, Pacific Northwest
Research Station, Forestry Sciences Laboratory, 3200 SW
Jefferson Way, Corvallis, OR 97331; W.H. Pawuk, USDA
Forest Service, Tongass-Stikine Area, Box 309, Petersburg,
AK 99833; W.A. Farr (deceased), USDA Forest Service,
Pacific Northwest Research Station, Forestry Sciences
Laboratory, 2770 Sherwood Lane Suite 2A, Juneau, AK
99801-8545; and R.R. Sileo (retired) USDA Forest Service,
Pacific Northwest Research Station, Forestry Sciences
Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331.
ABSTRACT. Four crown and foliage traits of a young Sitka spruce (Picea sitchensis) stand were tested with
rooted cuttings in greenhouse and field plots for possible thinning selection guidelines. Repeatability estimates
of the amount of genetic control over the four traits and the relation of those traits to height growth were
evaluated 5 years after rooting. Only the blue-green trait was significantly associated (P < 0.05) with height
growth. Average height of cuttings selected for green foliage was 17% greater than cuttings selected for blue
foliage. Under greenhouse conditions, repeatability estimates of green or blue foliage were 98%versus 66%,
respectively; 72% versus 89%for trees with dense or open crowns, respectively; 65%for the comparison of
upright and horizontal branches; and 75%for the comparison of long or short branches. West. J. Appl. For.
11(3):77--80.
C oastal Sitka spruce (Picea sitchensis) forests in southeast
Alaska develop natural regeneration soon after harvest (Har­
ns and Farr 1974). Stocking typically averages 4000 stems
per acre, often with patches of 20,000 stems per acre. Nearly
all clearcut areas need precommercial thinning to reduce
stocking when the trees become 4 to 6 m tall. Because of this
abundance of natural regeneration, it may be possible to use
thmning to achieve a small amount of genetic improvement
m Sitka spruce populations if growth rates are linked to easily
observable traits used in thinning guidelines.
Thinning programs in southeast Alaska currently use a
combination of spacing control, species selection, and phe­
notypic selection. Because of their higher value, Sitka spruce,
and Alaska-cedar (Chamaecyparis nootkatensis), and west­
em red cedar (Thuja plicata) are strongly favored over
western hemlock (Tsuga heterophyla). Traits with strong
genetic control are more useful as selection traits. We know
that heritability estimates of height growth range from 0.52 to
0 82 (family) and from 0.11 to 0.34 (individual) (Faulkner
1987). These results indicate moderate to good genetic con­
trol and, based on heights of 6 yr old trees, project l 0 to 22%
gams. Thus, all thinning favors taller specimens.
To maximize genetic change or gain by selection, all
easily differentiated and highly variable traits with high
heritabilities must be identified. Crown shape and size in
Sitka spruce result from variation in traits such as branch
length, branch angle, number of branches per whorl, and
number of internodal branches (Cannell 1974 and 1982), but
little is known of the degree of genetic control of branch,
foliage, or crown traits and any relatedness of crown traits to
growth traits. This paper reports the results of using rooted
cuttings to test the genetic control and relation to height
growth of the only four highly contrasting crown and foliage
traits that appeared practically observable in thinning-aged
stands.
Study Areas and Methods
Trait Selection
In 1985, several hundred 22 to 25 yr old Sitka spruce trees
growing in a well-stocked, naturally regenerated stand of spruce
and hemlock in southeast Alaska were scrutinized for potential
thinning traits. The area surveyed was about 17 k south of
Petersburg on Mitkof Island. We sought to identify easily
WJAF
11(3) 1996
77
discerned, contrastmg crown and foliage trmts that could be used
as criteria in precommercial thinning guidelines. Observations
of crown traits revealed only four that were both easily identified
visually and highly variable in the population. The traits were:
dark bluish-green (called blue in this paper) or normal green
foliage, wide or narrow crown (long or short branches), upright
or horizontal branch orientation (branch angle), and dense or
open crown density. Trees with wide crowns had branches that
were 30 to 50% longer than similar branches on trees selected for
narrow crowns. Trees selected for dense crowns were trees that
an observer could not see through the canopy, while an observer
could easily see through the canopy of trees selected for open
crowns.
Tree selection was based solely upon visual observa­
tion. Seven pairs of trees with contrasting phenotypes
(visible characteristics) were selected for each of the four
traits. To facilitate visual comparison, trees of each pair
were neighbors.
Propagation and Assignment of Test Trees
Branch tips were collected in January 1986 from the 56
selected trees and rooted at Corvallis, Oregon, and at Peters­
burg, Alaska. Rooting followed the procedures outline by
Copes (1987). In November 1986, the rooted cuttings at
Corvallis were lifted bareroot and transferred to the green­
house at the Petersburg nursery, where the rooted cuttings
from both locations were transplanted into 2 gal containers
filled with potting mix. The cuttings were grown in the
greenhouse during the 1987 growing season under standard
nursery procedures for conifers.
In September 1987, the cuttings were sorted into two
groups for the field test and the greenhouse test. Enough
cuttings were available to evaluate three traits with six pairs
of trees per trait in both environments. Cuttings observed for
the branch length trait were evaluated with only five pairs of
trees. Twenty cuttings per tree were allocated to the field, and
17 to 20 cuttings per tree were used in the greenhouse.
Greenhouse Test
The greenhouse was divided into two blocks, and each
block was divided into four trait subplots. For each paired
comparison, 8 to 10 rooted cuttings of each tree were placed
in the appropriate trait-subplot of each block. Several fertil­
izer applications were made during the 1989 and 1990 grow­
ing seasons, but none were made in 1991.
The 5 yr old cuttings were evaluated in September 1990.
Tree height was measured to the closest 0.5 em. Foliage color
and crown density were visually scored as blue or green and
dense or open, respectively. Early assessment of repeatability
of branch length (crown width) and branch angle required
measurements because relative differences in crown struc­
ture were difficult to see in small trees. The mean length of the
longest three branches in the 1990 whorl of each pair of
cuttings was determined, and a qualitative assessment of trait
repeatability was calculated from the branch measurements.
Repeatability in this case was the percentage of paired
cuttings of the trees that exhibited the same relative rank­
order difference (larger or smaller) as their parent trees. In
the same manner, repeatability of upright or horizontal
78
WJAF
11(3) 1996
branch angle was calculated from measurements of the
average angle of the three longest branches in the 1990
whorl (measured to± 5 ').
Field Test
Rooted cuttings for the long-term test were planted m
the field in early June 1988 on a clearcut unit at the same
elevation located 3 km south of the parent trees. The areq
was divided into 2 block,s and each block was divided into
4, randomly assigned trait-subplots. In each block, 20
cuttings of each pair of parent trees (10 per tree) were
randomly planted in adjacent rows at 3 by 3m spacing. The
7 yr old cuttings were measured in September 1992 after
5 yr of growth in the field. Measurement was limited to
cuttings of trees selected for blue or green foliage because
the greenhouse test revealed that only trees with that trait
exhibited a significant relation with height growth. The
same visual assessment of blue or green made in the
greenhouse test was done in the field. In addition, tree
height and annual leader increments from 1990 through
1992 were recorded for each cutting. All cuttings that were
severely suppressed by competing vegetation or exhibited
atypically slow growth due to extremely poor microsites
were excluded from measurement.
Statistical Analysis
Data from the greenhouse and field tests were subjected
to analysis of variance (ANOVA) using the SAS proce­
dures for general linear models (SAS Institute Inc. 1989)
The experimental design was a split plot (mixed model)
Contrasting pairs and the traits were random and fixed
effects, respectively. Separate analyses were performed
for each trait. The independent variables investigated m
the greenhouse test were the four crown or foliage traits,
but based upon greenhouse results, only the green or blue
trait was measured and analyzed in 1992 for the field test
Transformation of data before analysis was not necessary
Differences were judged significant when the probability
of obtaining a larger F-value by chance was ::; 0.05
Sources of variation and expected mean squares of the
ANOV As were:
Source
D F
Blocks (B)
B-1
Pairs (P)
P-1
B
(B-1)(P- 1)
x
P e( rror 1)
Phenotypic trait (H)
P xH e( rror 2)
Residual (error 3)
H -I
Expected mean squares
(j
+
h p + ph
(j
+
h p + bh;
(j
+
hp
2
(JE
2
h
2
l:8
+b-<JPH +bp
b-1
b-1
h
--
2
(P-l)(H - I)
cre +bHcrPH
P(B-l )(H - I)
cr2
E
Error 2 was used to determine the F-value for phenotype (H)
because the individual pairs of contrasting cuttings were the
experimental units of treatment. The total degrees of freedom
were 23 and 19 when the tests had 6 and 5 pairs of trees per trmt,
respectively.
Results
Discussion
Trait Repeatability
The relation between foliage color and leader growth was
significant in both the greenhouse and field environments. If
an increase in average height growth is desired and species,
spacing, and other selection criteria reveal no advantage of
one tree over another, field workers should select Sitka
spruce trees with green foliage. The actual gain in height
growth obtained from such selection will be less than the 17%
obtained in this study because only a fraction of the opera­
tional thinning choices will permit blue or green selection.
We selected only the trees with the darkest blue foliage for
comparison with trees with green foliage so the growth
potential of trees with intermediate foliage color is not
known.
A known physiological explanation exists that partially
explains why conifers with green foliage color may grow
taller than those with blue foliage. Clark and Lester (1975)
report that relative photosynthetic capacity of Colorado blue
spruce (Picea pungens Engelm.) decreases when blue foliage
increases. Salisbury and Ross (1978) show that blue-green
foliage reflects the higher energy blue light wavelengths (400
to 500 nm), whereas trees with green foliage absorb more
than 90% of those wavelengths. When other factors control­
ling growth are equal, trees with blue foliage will absorb less
light energy and may not support as much photosynthesis and
growth as trees with green foliage. This simple explanation
knowingly ignores many other variables that contribute to
growth and other important traits.
The other crown traits were not significantly associated
with height growth at 5 and 7 yr, but we feel that it is too early
to eliminate them from future study. The annual accumula­
tion of small differences over several decades may result in
large differences in photosynthetic area. The 21% difference
per year in average growth of branches (5.2 em) was not
significant at age 5, but that same difference accumulated
annually for 20 or 30 yr may result in significant differences
and trees with large crowns may produce more diameter
growth. A similar change over time may occur with the other
crown traits.
The amount of genetic control (repeatability) over
the four traits differed greatly. Repeatability of green
fohage was high in both environments, while repeat­
abtlity of blue foliage was high in the field but low in
the greenhouse due to irregular trait development in
cuttings of two blue trees grown under low nitrogen
conditions. The percentage of cuttings that exhibited
blue or green foliage identical of their parent was 90%
and 94% in the field, respectively, and 66% and 98% in
the greenhouse, respectively (Table 1).
Repeatability estimates for cuttings from dense or
narrow crown trees were 89 and 72% respectively (Table
1) Cuttings from trees selected for upright or horizontal
branches had branch angles that averaged 18% and 14%,
respectively, from horizontal. Repeatability of branch
angle was 65%. Cuttings of trees selected for wide or
narrow crowns (long or short branches) averaged 29.6 em
and 24. 4 em annual branch growth, respectively, and had
a repeatability value of 75% (Table 1).
Relation to Height Growth
The only significant trait to height-growth relation
detected was for blue or green foliage. Greenhouse-grown
cuttings from green trees averaged 17.4% taller (73. 7 em)
than cuttings from blue trees (6 2. 5 em), and field-grown
cuttings of trees selected for green foliage (113. 8 em)
averaged 16.5% taller than cuttings of trees for blue
fohage (97. 7 em) (Table l ). Both differences were signifi­
cant (P < 0. 05) (Table 2).
Greenhouse and field data for annual leader growth,
cumulative leader growth, tree height, and repeatability
for cuttings of each pair of blue or green trees are presented
m Table 3. Annual leader growth in 1990 and 1992 and the
1990 to 1992 cumulative growth were all significant in the
field test (Table 2). In both environments, only one blue
tree produced cuttings that averaged taller than cuttings of
the contrasting green tree.
Table 1. Number of trees tested, trait repeatability, and tree heights in the greenhouse for four foliage and crown traits.
Greenhouse
Trait
Needles
Blue
Green
Crown
Dense
Open
Branches
Upright
Horizontal
Branches
Long
Short
No. oftrees
Repeatability
(%)
6
6
66 .3
9 8.3
6
6
89. 2
71.7
6
6
6 5.0
5
5
7 5.0
Field
Average
phenotype
Tree height
e( m)
6 2.8
73 .7
I
No. oftrees
5
5
Repeatability
(%)
90 .1
93.6
Tree height
(em)
9 7 .7
I I3 .8
70.9
69 .9
I8 .I o2
14. 2
64 .I
63.7
29.6cm3
24.4cm
73.5
6 5.6
°
1 Repeatability was the percentage of cuttings of a tree or pair of trees that exhibited the same phenotype as their parent tree(s).
Branch angle denoted the average departure in degrees from the horizontal of the longest three branches in the top whorl.
Branch length was the average length of the longest three branches in the top whorl.
WJAF11(3)1996
79
Table 2
Probability of a
>
f:.value for leader length and tree height in the field and greenhouse for cuttings of blue and green trees
Field
Source of variation
Blocks ( B )
Pairs
Phenotype
BxH
1 990
1991
199 2
1990-9 2 Total
Tree height
Greenhouse
tree height
0.0 8 3
0. 73 2
0.034
0. 299
0.05 3
0.3 9 9
0. 13 7
0.5 9 9
0. 208
0.1 29
0.0 26
0.934
0.050
0. 288
0.0 2 2
0.5 4 1
0.04 1
0.0 79
0.040
0.65 3
0.069
0.04 1
0.030
0.606
Table 3. Field1 and greenhouse (G) data for leader growth, tree height, and trait repeatability2 for cuttings of trees selected for blue (b)
or green (g) needles.
Field
Number of
cuttings measured
Pair
Greenhouse
Leader growth
F
G
1990
16
18
1 2
10
14
20
20
20
13
13
4
14
18
19
20
20
20
20
20
20
18
18
20
20
25.0
24.8
20.6
2 7 .I
18.0
2 2 .I
2 1.5
25 .7
16. 2
19.8
Tree
199 2
199 1
Total
Tree height/trait
repeatability
Tree height/trait
repeatability
Pair mean
(em )
(em/%)
2 1.9
71.8
1 16.8/ 100
63.3/ 100
25. 2
84.3/8 9
1 1 6. 2/ 100
7 2.4
19.4
65. 11 100
6 2.6
I01 .9/9 2
26.9
8 2.9
78. 7/100
1 29.4/ 90
16.5
5 1. 2
84.9/100
63.0/100
I 7. 2
1 01.8/100
5 7.9
75.41100
21.4
63 .Oil00
64.4
106.1/ 100
28.I
67. 21100
136.1/100
78. 7
15 .6
70.3/0
46.9
8 2. 1/ 100
18 . 1
5 7.9
93.1/9 2
67.3/100
5 2.1/0
n
I sufficient samplel
Insufficient comparison sample
68.81 1 00
6 2.8/66
I8.8
97.7/90
58. 7
19.9
23.0
1 13.8/94
73.7/ 98
68.4
2 2.3
(em)
lb
2g
3b
2
4g
7b
4
8g
5
9b
l Og
13b
7
14g
l ib
6
1 2g
Average,blue tree
Average,green tree
19.9
2 3. 1
24.9
2 2.4
2 2.6
28.9
16.7
18.6
2 1.5
24.9
I5. 1
1 9.9
74
72
69
65
69
60
68
68
Cuttings suppressed by brush or planted in extremely poor microsites were not measured.
Repeatability of needle color was the percentage of cuttings that exhibited the same needle color as the parent tree. 3
Field data from trees
11 B and 12G
were not analyzed because only four cuttings of tree
The genetic control of foliage color was quite strong
except in cuttings of two blue trees when grown in the
greenhouse. Cuttings of those two trees developed blue
foliage in 1990 and 1991, but grew green foliage in 1992. We
believe that this irregularity resulted from nitrogen defi­
ciency in 1992 due to our failure to apply fertilize that year.
Cuttings of the same clones developed blue foliage in field
plots.
Selection of phenotypically taller trees in precommercial
thinning will continue to be the trait of choice. Precommercial
thinning of Sitka spruce in southeast Alaska might enhance
height growth of residual and future stands if trees with green
foliage also receive preference over trees with blue foliage.
Other potential uses of the foliage color and height relation
may be in nurseries when seedlings are sorted or in the field
when trees are selected for cone collection. One note of
caution to blanket endorsement of the above recommenda­
tion is that Faulkner (1987) suggests that in Scotland, seed­
lings from "blue-foliage" populations may be a better choice
on frosty or dry sites.
80
WJAF 11(3) 1996
11 B were alive and
measurable in
1992. Literature Cited
CANNELL, M.G.R.1974.
Pinus contorta
P
and
rod
u ction of branches and foliage by young trees of
Picea sitchensis:
simulation. J. Appl. Ec o.l
CANNELL, M.G.R.
1982.
provenance differences andtheir
11:1091-1115.
"Crop" and "isolation" id
e oty pe s: Evidence for
progeny differences in nursery-grown
Picea sitchensis.
Silvae Genet
31:60--66.
CLARK, J.B., AND G.R. LESTER.1975. The relationship of cuticle structureto
the visible ultraviolet sp
ectr al pr opertie s of needles from four coniferous
species. Plant
Physio.l 55:407-413.
Rooting Sitka spruce from southeast Alaska. USDA For
Serv. Res. N ot
e P N W-R N-465. 8 p.
FAULKNER, R. 1987. Genetics and breeding of Sitka spruce. Proc. R. Soc
Edinburgh93B : 4 1-50.
HARRIS, A.S. AND W.A. FARR.197 4. Forest Ecology and Timber Management
in The forest ecosystem of southeast Alaska. USDA For. Serv. Gen. Tech
Rep. P N W-25. 7 p.
SALISBURY, F
.B., AND C.W. Ross. 1978. Plantph ys iol og y Wadsworth Pub­
lishing Co., B
e lmont, CA.
SAS INSTITUTE. 1989. SAS/STAT User's Guide, Version 6. Ed.4. SAS
Institute Inc., Ca
r y, N C.
COPES, D.L.1987.
.