,.
New Forests 21:
71-87,2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Growth and early stand development of intensively
cultured red alder plantings
PETER D. HURD and DEAN S. DEBELL
Pacific Northwest Research Station, 3625 93rd Ave. Sw, Olympia, WA 98512-9193 USA
Accepted 8 November 2000
Abstract. This study evaluates the performance of Alnus rubra in three square spacings
(0.5-, 1.0- and 2.0 -m), two irrigation regimes (low and high), and two pre-planting fertilizer
treatments (0 and 300 kg P ha-1 ). Initial survival and growth were excellent, and differences
among various cultural treatments were apparent by the end of the second growing season. At
age ten, mean tree sizes in specific regimes ranged from 4.8 cm to 11.5 cm in diameter and
7.7 m to 13.1 m in height, with largest trees produced in regimes with wide spacing and high
irrigation. Beneficial effects of fertilizer were minimal and were limited primarily to enhanced
early survival during the first two years in the closest spacing. Growth of the plantings was
greater than that estimated for fully stocked, natural stands of the same age and site index (or
height). Data from our study provided general confirmation of the level and slope of the tree
size-stand density lines currently used in density management guidelines for alder, except that
mortality in the densest spacing occurred at diameters smaller than those assumed to indicate
the threshold for inter-tree competition. This difference, however, was lessened by irrigation.
Key words: Alnlls rubra, fertilization, irrigation, self-thinning, spacing, stand density
Introduction
Red alder (Alnus rubra Bong.) grows naturally from central California to
southeastem Alaska and is the most abundant hardwood tree species in
westem Oregon, Washington, and British Columbia. It grows in pure stands
and in mixed stands with Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco
varmenziesii), westem hemlock (Tsuga heterophylla (Raf.) Sarg.), westem
redcedar (Thuja plicata Donn.), Sitka spruce (Picea sitchensis (Bong.)
Carr.), grand fir (Abies grandis (Dougl.) Lindl.), black cottonwood (Populus
trichocarpa Torr. & Gray), and bigleaf maple (AceI' macrophyUum Pursh)
(Harrington 1990). Once regarded as a weed species by forest managers, alder
is now appreciated for its unique ecological attributes (e.g., N2-fixation and
immunity to Phellinus root rot) and its contribution to the forest products
The U.S. Government's right to retain a non-exclusive, royalty free licence in and to any
copyright is acknowledged.
About This File: This file was created by scanning the printed
publication. Misscans identified by the software have been
corrected; however, some mistakes may remain.
72
economy of the region (Tarrant et al. 1994). Several operational alder planta­
tions have been established, the biology and management of the species
have been summarized (Hibbs et al. 1994), and a university-industry-agency
cooperative (The Hardwood Silviculture Cooperative) exists to foster silvi­
cultural research (Hibbs 1999). Nevertheless, research data and experience
concerning various silvicultural options remain limited. This paper describes
a trial undertaken to evaluate several short-rotation, intensive culture prac­
tices for producing wood, fiber, or biomass in red alder plantations. We
report the influence of spacing, irrigation, and phosphorus fertilizer treat­
ments and their interactions on patterns of survival, growth in height and
diameter, mortality, and accumulation of basal area over a lO-year period. We
compare performance of the planted stands with characteristics of unman­
aged but fully stocked, naturally regenerated stands of the same age and
site index (Worthington et al. 1960). In addition, we examine stand trajec­
tories (depicted as mean diameter plotted over stand density) in relation to
a stand density diagram and currently used density management guidelines
(Puettmann et al. 1993).
Methods
Study area
The study was established in 1986 in cooperation with the Washington State
Department of Natural Resources (WDNR) at the WDNR Meridian Seed
Orchard, 12 km east of Olympia (47°00' N, 122°45' W). Climate is mild with
an average growing season of 190 frost-free days (US Dept. of Commerce
1961). Based on data collected from a weather station at the site from 1986 to
1992, precipitation averaged 112 em yet with only 15 em falling from May
1 through September 30. The average July temperature was 17 °C.
The site, previously farmed for strawberry and hay crops, was prepared
for planting by plowing and disking in the winter of 1985-1986. The soil is
Nisqually loamy fine sand (a sandy, mixed, mesic Pachic Xerumbrept); it is
a deep, somewhat excessively drained, medium acid (pH 5.6) soil formed in
glacial outwashes (Pringle 1990) and would not be considered suitable for
alder growth without irrigation. Slope is 0-1 %; elevation is 50 ill. Adjacent
unmanaged land is occupied either by prairie vegetation or Douglas-fir mixed
with several species of hardwood trees and shrubs.
Experimental design
The experimental design was a split-split-plot replicated on three adjacent
blocks. Two irrigation rates (high and low) formed the main plots that were
73
split to provide a test of pre-planting fertilizer application (none and a one­
time application of triple superphosphate at 300 kg P/ha). The second split
involved three square spacing (0.5-, 1.0- and 2.0-m) treatments. Each plot was
planted in spring 1986 with container-grown seedlings from each of 19 open­
pollinated alder families. The size of the treatment plots varied with spacing;
all plots were large enough to provide 100 interior measurement trees and a
buffer of eight, four, and three rows of similarly spaced trees for the 0.5-, 1.0-,
and 2.0-m spacing treatments, respectively. The intent was to provide a buffer
at least one-half as wide as the estimated height of measurement trees at the
end of the study. All plots were irrigated by a drip system. The irrigation lines
were laid down 2.0 m apart with emitters spaced at 1.0-m intervals in each
line. During the first year, 25 cm of water was applied in addition to rainfall.
Thereafter, the high-inigation treatment received 40 to 50 cm of supplemental
water during each growing season. The low-irrigation treatment received no
supplemental water during the second year and minimal applications «8 cm
per growing season) in subsequent years. The high-irrigation treatment was
intended to increase tree growth and accelerate the rate of stand development
on the dry site, while the intent of the minimal application was to prevent
mortality caused by water stress alone. Phosphorus fertilization was chosen
because response to P fertilizer had been observed in other studies (Hughes
et al. 1968; Radwan 1987; Radwan and DeBell 1994). Prior to planting, the
fertilizer was applied with a spreader and disked into the surface soil. All
plots were kept weed-free by tilling, hoeing, and selective application of
herbicides.
Data collection and analyses
Total height of all trees was measured annually from plantation age 1 to
plantation age 6 and a sub-sample of trees in each plot was measured at ages
7, 8, and 10. Breast-high diameter (dbh) was measured on all trees annually
from age 2 to age 8 and at age 10. A regression equation to predict height
from dbh was developed for each treatment combination; predicted heights
then supplemented the measured height samples for the 7-, 8-, and l O-year
measurements.
Treatment means for survival, tree size, and basal area were plotted to
illustrate trends in tree and stand development over time as well as the nature
of significant interactions. Effects of irrigation, fertilization, and spacing
treatments on survival, tree size, and basal area per hectare at plantation age
10 were tested with ANOVA for a split-split-plot experiment by using SAS's
GLM procedure (SAS Institute, Inc. 1988). Sizes of the 2000 largest and
800 largest trees per hectare as well as overall means were tested. Treatment
effects were judged significant at P ::::: 0.05.
74
Stand characteristics at age 10 were compared with estimates for fully
stocked natural stands given in published yield tables (Worthington et al.
1960).
Stand trajectories were examined by plotting quadratic mean diameter for
each treatment combination at each age over stand density (number of trees
per hectare), and results were compared with a density management diagram
and guidelines published by Puettmann et al. (1993).
Results and discussion
Establishment and subsequent trends in survival and growth
Establishment
Initial survival averaged 97% at the end of the first growing season. Survival
in the two wider spacings was very high (97 to 99%), but the O.S-m spacing
had somewhat lower initial survival (91 to 96%). High levels of irrigation
and fertilization improved survival in the O.S-m spacing treatment during the
first two growing seasons (Table 1). At the end of the second growing season,
survival in the O.S-m spaced plots averaged 3% higher in the high-irrigation
plots than in the low-irrigation plots, and fertilized plots averaged 4% higher
survival than the unfertilized plots. Fertilizer provided negligible gain (1 %)
in high-irrigation plots but increased survival by 7% in the low-irrigation
plots. High-irrigation provided no benefits to survival in fertilized plots yet
increased survival of unfertilized plots by 6% over the low-irrigated unfertil­
ized plots. We suspect water as the primary factor limiting survival in these
densely planted plots. High-irrigation directly affected water availability and
we suspect that application of phosphorus fertilizer enhanced root growth
(Pritchett 1979; Radwan 1987) and thereby indirectly increased amounts of
water accessed and absorbed by the seedlings. Differences in survival in
the two wider spacings (1.0-m and 2.0-m) during the first two years were
negligible and unrelated to irrigation and fertilization.
Subsequent trends in survival
In general the high-irrigation treatment over time decreased the number of
trees (i.e., percent survival) which is a natural outcome of enhanced growth
and increased competition-related mortality (Figure 1). The effect of fertiliza­
tion on survival was also generally negative, though markedly less than that of
irrigation and with less of an effect in wider spacings (Tables 1 and 2). Such
reductions in survival associated with fertilization were probably associated
with improved growth and increased competition (cf. Diameter, height, and
survival in Table 2).
75
Table 1. Initial average percent survival and standard deviations of O.5-m
spacing plots as related to in'igation and fertilization.
Age
Low-irrigation
Unfertilized
(years)
High-irrigation
Fertilized
Unfertilized
Fertilized
91±3
96±6
94±6
96±2
2
86±6
93±8
92±4
93±5
3
67±6
67±12
51±2
51 ±5
4
53±7
55±7
45±2
40±5
40000 �------�
-- O.5-m flow-irrigation
0--··0
30000
Q)
..c:
Oi 20000
O.5-m / high-irrigation
flow-irrigation
f high-irrigation
2.0-m flow-irrigation
2.0-m f high-irrigation
---- 1.0-m
0-··0
",- • • />.
1.0-m
a.
o +--'--�--'---'--'�-'--4
o
2
3
4
5
6
7
8
9
10
age (years)
Figure 1.
Number of trees surviving as related to spacing, irrigation and age.
Closer spacings also increased competition-related mortality and resulted
in decreased survival throughout the study. Survival at the end of the second
growing season in the O.5-m spacing treatment was 7% and 8% lower
than in the l.O-m and 2.0-m spacing treatments respectively. This trend of
decreased survival with closer spacing, high-irrigation, and fertilizer applic­
ation continued, and generally intensified, through age 10 (Figure 1 and
Table 2).
Patterns of height, diamete7; and basal area growth
The annual increments for diameter and height increased during the first three
years and tended to decline gradually in subsequent years as age, size and
inter-tree competition increased (Figures 2a and 2b). After the second year,
annual increments for diameter growth increased with wider spacing in both
-..l
0\
Table 2. Tenth-year averages and standard deviations of survival and tree and stand characteristics as related to spacing, irrigation and fertilizer
treatments.
Mean tree size
Quadratic mean breast% Survival
Spacing
high diameter (cm)
Unfertilized
Fertilized
(m)
Irrigation
Unfertilized
Fertilized
0.5
Low
26±7
23±8
4.8±1.4
5.4±1.0
High
11±2
8±4
8.6±0.2
9.1±0.3
Low
67±9
60±3
6.1±1.1
7.0±0.7
High
34±2
35±3
10.2±0.4
10.1±0.4
Low
95±1
90±3
8.8±1.5
9.3±0.4
High
81±2
78±7
11.4±0.4
11.5±0.2
1.0
2.0
Height (m)
Basal area
2
(m ha-1)
Fertilized
Unfertilized
Fertilized
7.7±2.1
8.2±1.2
18.2±7.6
20.0±4.1
12.4±1.0
12.8±0.3
26.4±4.7
20.8±9.9
8.2±0.8
9.0±0.6
19.0±3.7
23.1±4.6
13.1±0.2
13.1± 0.2
27.6±2.4
27.2±0.9
9.0±1.2
9.4±0.2
14.4±4.8
14.7±1.3
12.5±0.1
13.1±0.1
20.4±2.5
19.6±1.6
Unfertilized
1
77
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age (years)
;-2 =
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14
12 10
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'iii 4
2
0 0.5-m 1.0-m 2.0-m
.J::
low-irrigation
O.5-m 1.0-m 2.0-m
high-Irrigation
Figure 2.
lO-year growth as related to spacing, irrigation and age: (a) quadratic mean
diameter; (b) height.
irrigation treatments. This trend is presumed to be associated with increased
room for crown expansion and associated leaf area as spacing widened.
Height growth was initially greater in the l .O-m spacing in both high­
and low-irrigation environments. By age 5, however, best growth in low­
irrigated plots occurred in the widest spacing whereas in the high-irrigation
plots, subsequent growth was similar in the l.0- and 2.0-m spacings. As a
result, the l.O-m spacing in high irrigation plots remained best in cumulative
height growth through age 10. Growth-enhancing effects of close spacings
78
on trees - particularly on height growth - are common early in the life of a
stand but they have yet to be explained physiologically and they are usually
reversed at older ages (DeBell and Giordano 1994). Similar results have been
observed in poplars (DeBell et al. 1997), loblolly pine (Adams et al. 1973),
and Douglas-fir (Scott et al. 1998).
Our data suggest that the initial beneficial effects of high or intermediate
densities may be more pronounced and of longer duration in more favorable
(i.e., high irrigation) than less favorable (i.e, low irrigation) growing environ­
ments. Such a relationship is also consistent with a comparison of results from
two Douglas-fir spacing trials: (1) on a low quality site, trees were taller at age
5 in higher density than in lower density plantings but differences disappeared
by age 10 (Isaac 1937), and (2) on a high quality site, trees were taller in
intermediate densities through age 20 (Reukema and Smith 1987).
Our results indicate that subsequent beneficial effects of wider spacing
on height growth of red alder in later years is greater under more adverse
growing conditions (low irrigation vs. high irrigation). This observation also
is consistent with a comparison of long term results in the Douglas-fir trials
on low quality (Reukema 1979) and high quality sites (Reukema and Smith
1987).
Basal area per hectare was greater with high irrigation than with low
irrigation throughout the study (Figure 3). Within a given irrigation treat­
ment, basal area increased with higher density through age six, after which
basal area was greatest in the 1.0-m spacing and least in the 2.0-m spacing.
Basal area growth tended to accelerate through year seven in most treatments.
Exceptions were in the high-irrigated, 0.5-m and 1.0-m spacing treatments
which had the greatest growth during the first three years, had a temporary
depression in growth rate at age 5 and 6, respectively, and then resumed
the former growth rate in year 7. Beyond these periods, basal area growth
decreased due to increased competition and associated mortality. Cumulative
basal area in the high-irrigated, 0.5-m spacing treatment decreased between
the eighth and tenth growing seasons, and basal area growth was substantially
reduced in the low-irrigated, 0.5-m spacing treatment during the same period,
as compared with other treatments. Such losses in cumulative basal area and
the reduced basal area growth from age 8 to age 10 probably are associated
with high levels of competition-related mortality; numbers of trees dying in
the 0.5-m spacing averaged 2.7 times the number of trees dying in the1.0-m
spacing under the same irrigation treatment.
79
30 25
20
Co
---
O.5-m !Iow-irrigatlon 0-.-0
0.5-m ! high-irrigation
--- 1.0-m !Iow-irrigation
D-·IJ
1.0-m ! high-irrigation
A---4
2.0-m !Iow-irrigation
A-- .b,
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IJ
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;::/'
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//
IJ
10
:
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O �------.---,--�
6
4
8
2
10
age (years)
Figure 3.
Basal area as related to spacing, irrigation and age.
Tree and stand characteristics at age 10
Survival
Irrigation, fertilization, spacing, and the interaction of irrigation and spacing
significantly affected survival at age 10 (Tables 2 and 3). Spacing impacted
survival the most with the greatest survival (86%) occurring in the 2.0­
m spacing treatment and the lowest survival (17%) occurring in the 0.5-m
spacing treatment. Survival was, on average, 19% lower in the high-irrigated
than in the low-inigated treatments, and 3% lower in the fertilized than in
the unfertilized treatments. Irrigation differentially affected survival in each
of the spacings. The greatest differences between the high- and low-irrigated
treatments were in the 1.0-m spacing (29%), whereas differences were only
14% and 13% in the 0.5-m and 2.0-m spacing treatments, respectively. This
apparent curvilinear relationship is largely attributable to the use of percent of
original number of planted trees as the parameter of survival. If the reduction
in survival associated with high irrigation was assessed in terms of absolute
numbers of trees or as a percent of the number surviving with low irrigation,
the reduction would decline more or less linearly with increased spacing.
80
Table 3. Significance of ANOVA model components on lO-year survival, breast-high
diameter, height, and basal area.
Probability of>F-value
Quadratic mean breasthigh diameter(cm)
Source of
variation
Survival
Df
(0/0)
trees
1
2
2
2
2
0,02
0.02
0.13
0.00
0.00
0.96
0.60
0.03
0.06
0.17
0.00
0.01
0.80
0.56
lITigation
Fertilization
Irrigation x fertilization
Spacing
Irrigation x spacing
Fertilization x spacing
lITigation x fertilization
All
Largest
Largest
2000 trees 800 trees
0.03
0.28
0.08
0.00
0.02
0.71
0.62
0.03
0.64
0.16
0.00
0.26
0.58
0.61
Height(m)
All
trees
0.02
0.10
0.62
0.03
0.16
0.97
0.66
Largest
Largest
Basal area
2
i
(m ha- )
0.02
0.24
0.84
0.02
0.30
0.80
0.82
0.02
0.70
0.88
0.32
0.66
0.34
0.76
0.05
0.91
0.11
0.00
0.84
0.53
0.65
2000 trees 800 trees
x spacing
Note: Irrigation tested using irrigation x block as the elmr term (df 2); fertilization and
il1'igation x fertilization tested using block x fertilization(irrigation) as the error telID (df
4); the split-split-plot error term had 16 df.
=
=
Diameter
Quadratic mean breast-high diameter at the end of the tenth year varied
significantly with irrigation, spacing, and the interaction of irrigation and
spacing (Tables 2 and 3). Diameters increased with higher irrigation and
wider spacing. Mean breast-high diameter increased 47% (+3.3 cm) with
higher irrigation and 46% (+3.3 cm) as spacing increased from 0.5-m to 2.0­
m. The irrigation and spacing interaction was also significant; the greatest
increase in mean breast-high diameter due to high-irrigation was 75% (+3.8
cm) in the 0.5-m spacing treatment with increases of 55% (+3.6 cm) and 27%
(+2.4 cm) occurring in the l.O-m and 2.0-m spacing treatments, respectively.
Even though fertilization was non-significant (p = 0.06,) there tended to be
larger diameters in fertilized plots in the low irrigation treatment and in the
closest spacing; i.e., the low- and high-irrigation, 0.5-m spacing treatments
and the low-irrigation, 1.0-m and 2.0-m spacing treatments. With fertilization,
diameters were 6% (+0.5 cm) greater in the low-irrigated, 2.0-m spacing
treatment and 15% (+0.9 cm) greater in the low-irrigated, l.O-m spacing
treatment.
Diameter, largest 2000 and 800 trees per hectare
Quadratic mean diameters of the largest (in diameter) 2000 trees per hectare
responded to the cultural treatments similarly to all trees or mean trees as
discussed above (Tables 2 and 3). This comparison considers equal numbers
of trees per hectare in all treatments (i.e., approximately 2000 trees per
hectare survived in the high irrigation treatment of the widest spacing; all
other treatments had more than 2000 trees). The mean diameters of the largest
81
800 trees per hectare also responded to treatments in the same fashion as did
all trees. This stand component was selected because it represented the fewest
trees that could be examined with what we considered a minimum acceptable
sample from each plot (i.e., 2 trees in each plot planted at 0.5-m spacing).
Height
Heights were significantly greater in the high-irrigation treatment and, on
average, at wider spacing (Tables 2 and 3). Mean height increased 49% (+4.2
m) due to higher irrigation and 7% (+0.7 m) as spacing increased from 0.5-m
to 2.0-m. Mean height increased more or less linearly with increasing spacing
in the low-irrigation treatments. It was curvilinearly related to spacing in
the high irrigated treatment, however. Mean height increased 4% (+0.5 m)
as spacing increased from 0.5-m to 1.0-m, but decreased 2% (-0.3 m) as
spacing increased from l.O-m to 2.0-m. Mean height was slightly greater with
fertilization though differences were not significant (p = 0.10); the greatest
difference was 10% (+0.8 m) in the low-irrigated, l .O-m spacing treatment;
as with diameter, the greatest benefits from fertilizer application occur in the
low-irrigation treatments and in the closest spacing.
Height, largest 2000 and 800 trees per hectare
Heights of the largest (in diameter) 2000 trees per hectare were significantly
related to spacing and irrigation in much the same manner discussed above for
all trees (Table 4). Heights of the 800 largest trees were significantly related
to irrigation (p = 0.02) but not spacing (p = 0.32). Mean height of these trees
is probably the best approximation we have of site productivity: 10m at age
10 for low-irrigation and 14 m at age 10 for high-irrigation. These values
suggest a SI20 (Harrington and Curtis 1986) of 17 m (or average site) for the
low-irrigation plots and a SI20 of 24 m (or high site) for the high-irrigation
plots.
Basal area
Basal area at the end of the tenth year varied significantly with irrigation
and spacing (Tables 2 and 3). High-irrigation increased basal area by 30%
(+5.4 m2 ha-1 ) on average. Basal area was curvilinearly related to spacing
and increased 13% (+2.8 m2 ha-1) as spacing widened from 0.5-m to 1.0­
m and decreased 29% (-6.9 m2 ha-1)as spacing increased from 1.0-m to
2.0-m. Overall, fertilization had no effect on basal area (p = 0.91); however,
basal area tended to increase with fertilizer application in the low-irrigated
treatments and to decrease with fertilization in the high-irrigated treatments
(fertilizer x irrigationp = 0.11).
82
Table 4. Diameter and height averages and standard deviations at age 10 as related to
spacing and irrigation treatments of all, 2000 largest, and 800 largest trees ha-1 .
Spacing
(m)
0.5
1.0
2.0
All
Irrigation
Low
High
Quadratic mean breast-
high diameter (cm)
Largest
Largest
All
2000 trees 800 trees
trees
5.1 ± 1.2
7.2 ± 1.1
7.9 ± 1.2
Largest
trees
7.9 ± 1.6
Height (m) Largest
2000 trees 800 trees
9.2 ± 1.4
9.7 ± 1.3
8.8 ± 0.4 10.2 ± 0.6 11.4 ± 0.8 12.5 ± 0.7 13.0 ± 0.5 13.3 ± 0.4
6.5 ± 0.9
9.1 ± 1.2
9.3 ± 1.2
8.6 ± 0.7
9.8 ± 0.9
9.9 ± 0.8
Low
High
10.1 ± 0.4 12.9 ± 0.7 13.3 ± 0.8 13.1 ± 0.2 14.0 ± 0.4 14.0 ± 0.4
Low
High
11.5 ± 0.3 11.5 ± 0.4 13.9 ± 0.5 12.8 ± 0.3 12.8 ± 0.5 13.6 ± 0.5
9.1 ± 1.0
9.4 ± 1.0 11.0 ± 1.2
9.2 ± 0.8
9.5 ± l.3
9.9 ± 1.2
Comparison with natural stands at age 10
The most relevant unmanaged natural stand data available for comparison
with our results are those published in the normal yield tables for red alder
(Worthington et al. 1960). The latter data were derived from plots centered in
the most uniform part of pure fully stocked red alder stands (> 80% red alder
by basal area with a closed canopy) and result from a combined multiple
regression analyses of characteristics of more than 400 plots.
Compared to trees in 1O-year-old natural stands growing in height at the
same rate (i.e., same site index), the planted trees in the l .O-m spacing of the
high irrigation treatment (i.e., the "high site"), had identical mean diameters
and basal areas that were 46% (+8.6 m2 ha-1) greater. Diameter and basal area
of trees in the low irrigation treatment ("the average site"), were 8% (+0.5
em) and 24% (+4.1 m2 ha-1) greater, respectively, than trees in a 1O-year-old
natural stand. In addition, basal area of the 2.0-m, high-irrigation treatment
at age 10 was slightly greater (20.0 m2 ha-1 vs. 18.8 m2 ha-1 ) than that of
1O-year-old natural stands even though there were more trees in the natural
stand. The reason for this is that the average diameter of the study trees was
about 13% greater. The 2.0-m, low-irrigation treatment (the "average site")
had lower basal area than a 1O-year-old natural stand (14.6 m2 ha-1 vs. 17.0
m 2 ha-1), but average diameters were nearly 50% (+3.0 em) larger.
Thus, it is evident that planted stands will produce wood more rapidly
than uniform natural stands, even when we assume that the natural stand and
the plantation have similar height growth (i.e., same site index). Most likely,
however, initial height growth and the apparent site index will be higher in
plantations and will provide even greater gains in stand productivity.
83
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0"
1000
10000
100000
trees per hectare
-- O.5-m I low-irrigation
0-..0
-- 1.0-m I low-irrigation
_ .. Q
1.0-m I high-irrigation
2.0-m I low-irrigation
A,- .. A
2.0-m I high-irrigation
/1>.-----10.
O.5-m I high-irrigation
Figure 4.
Stand trajectories in relation to density management diagram for red alder
(Puettmann et al. 1993).
Density management
The l O-year data from this study provide further support for the density
management guide developed for red alder (Puettmann et al. 1993). This
guide was based on data from several alder spacing and thinning studies
including the first five years of this study (Figure 4). The biological maximum
line for alder (2540 trees per hectare at 15 cm breast-high diameter) defines
the potential maximum diameter attainable for any given density and is the
basis for the relative density measures. The average maximum line is the
average relative density that stands approach as trees grow and mortality
reduces their numbers, and is sometimes referred to as the self-thinning
asymptote. Alder stands can be expected to have appreciable density­
dependent mortality (i.e., 20% of initial tree numbers) at a relative density
of 45% which is considered to be the operating maximum. The suggested
management zone is 25%-45% relative density; this assures full-site occu­
pancy while maximizing growth and minimizing mortality.
86
tions more closely than did the low-irrigation, O.5-m spacing treatments. Such
anomalies associated with the O.5-m spacing provide some information on
early growth patterns in very dense stands and may stimulate research and
yield insight into the limits of productivity. For the present, the existing
guidelines for red alder (Puettmann et al. 1993) can be used to manage stand
density within the range of spacings typical of operational plantations.
Acknowledgments
This research was supported in part by the Short Rotation Woody
Crops Program (now Biofuels Feedstock Development Program) of the
U. S. Department of Energy under interagency agreement No. DE-A105­
31OR20914. We thank Karl Buermeyer, Constance Harrington, David Hibbs,
and David Marshall for constructive reviews of this manuscript.
References
Adams, W.T., Roberds, lH. and Zobel, B.J. 1973. Intergenotypic interactions among families
of loblolly pine. Theoretical and Applied Genetics 43(7): 319-322.
DeBell, D.S. and Giordano, P.A. 1994. Growth patterns of red alder, pp. 116-130. In: Hibbs,
D.E., DeBell, D.S. and TalTant, RF. (Eds.) The Biology and Management of Red Alder.
Oregon State Univ. Press, Corvallis.
DeBell, D.S., Harms, W.R and Whitesell, C.D. 1989. Stockability: A major factor in
productivity differences between Pinus teada plantations in Hawaii and the southeastern
United States. Forest Science 35(3): 708-719.
DeBell, D.S., Clendenen, G.w., Harrington, C.A. and Zasada, lC. 1997. Tree growth and
stand development in short-rotation Populus plantings: 7-year results for two clones at
three spacings. Biomass and Bioenergy 11(4): 253-269.
DeBell, D.S. and Harrington, C.A. (Report on file at Olympia FSL - ApialY Study).
Harrington, C.A. 1990. Alnus rubra Bong. - red alder, pp. 116-123. In: Burns, RM. and
Honka1a, B.H. (Technical coordinators) Silvics of North America, vol. 2, Hardwoods.
USDA Forest. Serv., Agric. Handbook 654. Washington, D.C.
Harrington, C.A. and Curtis, RO. 1986. Height Growth and Site Index Curves for Red Alder.
USDA Forest. Serv., Pacific NW Research Station, Res. Pap. PNW-358.
Hibbs, D.E. 1999. Hardwood Silviculture Cooperative. A descriptive pamphlet published by
College of Forestry, Oregon State University, Corvallis. 8 p. See also the Cooperative's
website - http://www.cof.orst.edu/coops.hsc.
Hibbs, D.E., DeBell, D.S. and Tarrant, RF. 1994. Biology and Management of Alder. Oregon
State Univ. Press, Corvallis. 256 p.
Hughes, D.R., Gessel, S.P. and Walker, R.B. 1967. Red alder deficiency symptoms and feltil­
izer trials, pp. 225-237. In: Trappe, lM., Franklin, IF., TalTant, RF. and Hansen, G.M
(Eds.) Biology of Alder. USDA Forest Serv., Pacific NW Forest and Range Exp. Sta.,
Portland, OR
87
Issac, L.A. 1937. 10 Years' Growth of Douglas-Fir Spacing-Test Plantations. USDA Forest
Serv., Pacific NW Research Station, Res. Note 23.
Peterson, E.B., Ahrens, G.R. and Peterson, N.M. 1996. Red Alder Manager's Handbook for
British Columbia. For. Can. and B.C. Min. For., Victoria, B.C. FRDA report 240, 124 p.
Pringle, RF. 1990. Soil Survey of Thurston County, Washington. US Dept. of Agriculture,
Soil Conservation Service. p 62.
Pritchett, W.L. 1979. Properties and Management of Forest Soils. John Wiley and Sons, Inc.,
New York, NY. 500 p.
Puettmann, K.J. 1994. Growth and yield of red alder, pp. 229-242. In: Hibbs, D.E., DeBell,
D.S. and Tarrant, R.F. (Eds.) The Biology and Management of Red Alder. Oregon State
Univ. Press, Corvallis.
Puettmann, K.J., DeBell, D.S. and Hibbs, D.E. 1993. Density Management Guide for
Red Alder. Forestry Research Laboratory. Oregon State University, Corvallis. Research
Contribution 2. 6 p.
Puettmann, K.J., Hann, D.W. and Hibbs, D.E. 1993b. Evaluation of the size-density relation­
ships for pure red alder and Douglas-fir stands. Forest Science 39(1): 7-27.
Radwan, M.A. 1987. Effects of Fertilization on Growth and Foliar Nutrients of Red Alder
Seedlings. USDA Forest Serv., Pacific NW Research Station, Res. Pap. PNW-375.
Radwan, M.S. and DeBell, D.S. 1994. Fertilization and nutrition of red alder, pp. 216--228. In:
Hibbs, D.E, DeBell, D.S. and Tarrant, R.F. (Eds.) The Biology and Management of Red
Alder: CD):e-g@IT State Univ. Press, Corvallis.
Reukema, D.L. 1979. Fifty-Year Development of Douglas-Fir Stands Planted at Various
Spacings. USDA Forest Serv., Pacific NW Research Station, Res. Pap. PNW-253.
Reukema, D.L. and Smith, J.H.G. 1987. Development over 25 Years of Douglas-Fir, Western
hemlock, and Western Redcedar Planted at Various Spacings on a Very Good Site in
British Columbia. USDA Forest Serv., Res. Pap. PNW-381.
SAS Institute. 1988. Inc. SAS/STAT - User's Guide, Release 6.03 Edition. SAS Institute Inc.
Cary, NC, pp. 549-640.
Scott, W., Meade, R., Leon, R, Hyink, D. and Miller, R 1998. Planting density and tree-size
relations in coast Douglas-fir. Can. J. For. Res. 28: 74--78.
Tanant, R.F., Hibbs, D.E. and DeBell, D.S. 1994. Red alder and the Pacific Northwest, pp. ix­
xi. In: Hibbs, D:E., DeBell, D.S. and Tan'ant, RF. (Eds.) The Biology and Management of
Red Alder. Otegon State Univ. Press, Corvallis.
US Department of Commerce Weather Bureau. 1961. Local Climatological Data with
Comparative Data, 1960, Olympia, Washington. US Dept. of Com., Weather Bureau,
Asheville, NC, 4 p.
Worthington, N.P., Johnson, F.A., Staebler, G.R and Lloyd, W.J. 1960. Normal yield tables
for red alder. USDA Forest. Serv., Res. Pap. PNW-36. 3 p. plus 13 figures and 13 tables.