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Sitka alder, a candidate for mixed stands
CONSTANCE A. HARRINGTON AND ROBERT L. DEAL
Volume 12
•
Number 1
•
1982
Pages 108 -111
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National Research
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Conseil national
de recherches Canada
108
Sitka alder, a candidate for mixed standsl
CONSTANCE A. HARRINGTON AND ROBERT
L.
DEAL
Pacific Northwest Forest and Range Experiment Station, Forestry Sciences LaboratOlY, 3625-93rd Avemte SW, Olympia, WA, U.S.A. 98502 Received May 7, 19812 Accepted August 27, 1981 HARRINGTON,
C. A., and R. L. DEAL. 1982. Sitka alder, a candidate for mixed stands. Can. J. For. Res. 12: 108-111.
Juvenile height growth of Sitka alder (Alnus sillllata (Regel) Rydb.), a nitrogen-fixing shrub, was examined on eight sites.
The potential compatibility of mixed stands of Sitka alder and Douglas-fir (Pseudotsuga l11enziesii (Mirb.) Frahco) was then
assessed by comparing height-growth curVes of the two species at early ages. Based on Sitka alder's low height and early
slowdown in height growth, it appears to be a reasonable candidate for mixed stands on sites where additions of nitrogen or
organic matter are desirable. On poor quality Douglas-fir sites, however, Douglas-fir should be given a head start to insure
that it is not suppressed.
HARRINGTON,
C. A., et R. L. DEAL. 1982. Sitka alder, a ca didate for mixed stands. Can. J. For. Res. 12: 108-111.
La croissance juvenile en hauteur de I'aulne de Sitka (Alnus sinllata (Regel) Rydb.), un arbuste fixateur d'azote, fut examinee
sur huit sites. Le potentiel de compatibilite de peuplements mixtes de I'aulne de S'itka et de la fausse pruche taxifoliee
(Pseudotsuga mellziesii (Mirb.) Franco) fut evalue par comparaison aux courbes de croissance juvenile en hauteur des deux
especes. Base sur une faib1e hauteur de I'aulne de Sitka et d'une diminution de sa croissance juvenile en hauteur, celui-ci parait
etre un candidat raisonnable de populations mixtes sur des sites OU l'addition d'azote ou de matiere organique sont desirables.
Par contre, sur des sites OU la fausse pruche taxifoliee est defavorisee, celle-ci devrait etre implantee en premier pour empecher
sa suppression.
[Traduit par Ie journal]
Introduction
Several species of the nitrogen-fixing genus Alnus
have been used in various forestry systems to amelto­
rate or improve soil conditions (e.g., Haines and
DeBell 1970; Mikola 1975; Plass 1977; Tarrant and
Trappe 1971). In the Pacific Northwest, the native red
alder (Alnus rubra Bong.) has received increasing at­
tention for its proposed use in young conifer stands to
serve as natural nitrogen source for the crop trees. Red
alder is an efficient nitrogen-fixing species (Tarrant and
Miller 1963; Tarrant and Trappe 1971); it does, how­
ever, grow rapidly in early life, thus offering severe
competition to associated, intolerant conifers (Miller
and Murray 1978; Newton et al. 1968).
Another native alder, however, Sitka alder (Alnus
sinuata (Regel) Rydb.), has also been shown to be an
efficient nitrogen fixer (Binkley 1981; Carpenter et al.
1979; Crocker and Major 1955) and should be consid­
ered as a candidate for species mixtures (Carpenter et
al. 1979; Heilman 1979; Tarrant and Miller 1963). Sit­
ka alder is a large shrub or small tree with a maximum
height on favorable sites of 7 to 9 m. Although not
having the advantage of producing sawlog-sized mateIThis article was written and prepared by U. S. Government
employees on official time, and it is therefore in the public
domain. '
2Revised manuscript received August 10, 1981.
rial, Sitka alder's shrubby form and slower growth may
make the species more compatible than red alder for
interplanting with conifers. Sitka alder also has a wider
geographical and elevational range than red alder; this
may mean the species is suitable for planting over a
wider range of site conditions. Successful species mixtures require compatible juve­
nile height-growth patterns, especially when using in­
tolerant conifers, such as Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) or noble fir (Abies procera Rehd.). The purpose of this study was to compare juve­
nile height growth and to assess the compatibility of
Sitka alder and Douglas-fir for growing in mixed
stands. Douglas-fir was used for the comparison be­
cause it is the most widely managed species in the
Pacific Northwest; the Sitka alder height-growth curves
developed in this paper could also be compared with
those of other tree species.
Materials and methods
We selected eight sites in western Washington to provide a
range in elevation and geographical location (Fig. 1,
Table 1). In Washington, Sitka alder is most commonly found
. in the middle to high elevations of the Cascade and Olympic
Mountain Ranges. We were unable to locate any natural Sitka
alder growing below 500 m.
At each site, four or five stems were selected that were part
of the main shrub canopy, had no obvious signs of past dam­
age, and were far enough apart to minimize the possibility of
109
NOTES
LEGEND
A 5 ----681
HEIGHT
.,,"""'''''''
3 •••••••••
C 2 ............
4 v_,_,_,___
8 _._ ••
D7--
(METRES)
7
Site
No.
1
2
3
4
5
6
7
8
Name
Layout Creek
St. Helen's Vista
McClellan
Meadows
Falls Creek
Planting Creek
Slab Camp
Snoqualmie Pass
Wagon Trail
Elevation,
m
Tree age, years
(minimum-maximum)
1290
925
9-11
13-29
925
11-12
1075
500
625
1160
655
10-15
10-15
12-14
37-55
11-25
FIo. 1. Sitka alder study sites in western Washington.
their coming from the same root system. The selected stems
were cut at ground level.
Each stem was cut into 10-cm sections which were num­
bered and marked to indicate the bottom side. The bottom
surface of each section was sanded to obtain a clear, smooth
surface and then aged. Sections within each stem were ran­
domly ordered for aging; the use of random selection, rather
than aging the sections in numerical order, provided a check
on the accuracy of the ring counts. The cross sections were
lightly coated with petroleum jelly or very lightly coated with
a wood preservative to enhance the ring boundaries. Where
the rings were narrow, diagonal cuts were made into the
section to increase the apparent ring widths.
The original pattern of height growth was determined for
each stem, and an average height-over-age curve was drawn
for each site. Most stems were completely analyzed; however,
for the older, high-elevation stands only the first 15 years of
height growth were reconstructed. Analysis of one stem re­
vealed past .damage, and its height growth was reconst,ructed
only up to the time of damage.
3
4
5
6
7
8 9
TOTAL AGE (YEARS)
10
11
12
13
14
FlO. 2. Height growth of Sitka alder by study site.
Results and discussion
Height-growth curves of Sitka alder (Fig. 2) start
approximately linear; height growth slows quickly on
the poorer sites, more slowly on the better sites. Our
height-growth curves seemed to fall into four site
classes: class A included the two low-elevation sites
with the best growth (sites 5 and 6); class B had the two
mid-elevation sites (1 and 3); class C had the high­
elevation sites (2 and 4), plus the lower of the sites near
Snoqualmie Summit (8); and class D included only the
poorest site (7).
Height growth generally decreased with increasing
elevation. Slab Camp (site 6) had somewhat better
height growth than would be expected for its elevation.
Slab Camp receives less snow than the other sites
(Anonymous 1 969), however, and thus may have a
longer growing season than areas at the same elevation
on the west slope of the Cascades. The two sites near
Snoqualmie Summit (7 and 8) had poorer height growth
than might be predicted from their elevations. This gen­
eral area receives more snowfall than corresponding
elevations further south (Anonymous 1969). In addi­
tion, the strong east winds that funnel through the pass
may also affect growth at these sites. In these study
areas, the number of days in the growing season is
apparently a major factor influencing height growth of
Sitka alder. Further work is needed, however, to define
110
CAN. J. FOR. RES. VOL. 12. 1982
5
b
a
--- Sitka alder
------ Douglas·fir
-- Sitka alder
----- Douglas-fir
TOTAL
HEIGHT
(METRES)
HEIGHT
(METRES)
1
I
I
/,//
I
I
/,'
I
I
I
I
I
I
I
I
I
I
I
/ "
"
"
,','
/
I ,
I
I
I
,
" /"
, , ,
, ,'I ,
I ' ,, ,
;.:;
....
SHka alder 0
4
Douglas-fir 2
6
6
8
10
TOTAL AGE (YEARS)
10
12
12
14
14 Sitka alder 1
16 Douglas-fir 3
3
5
9
9
11
TOTAL AGE (YEARS)
11
13
13
15
15
17
FIG. 3. Height-growth curves for Sitka alder (classes A-C) and Douglas-fir (sites III-V) with Douglas-fir given a 2-year
advantage in total age. (a) The Sitka alder is seeded in a natural Douglas-fir stand. (b) 1-0 Sitka alder and 2-1 Douglas-fir
seedlings are planted at the same time.
more accurately the alder site classes and the site factors
associated with those classes.
Because of its low total height and early slowdown in
height growth, Sitka alder appears to be a reasonable
candidate for mixed stands. On many sites, however,
giving Douglas-fir a head start may be desirable. The
optimum head start (i.e., the Douglas-fir advantage in
total age) would depend, in part, on the expected
growth of Douglas-fir and Sitka alder on a particular
site. Douglas-fir and Sitka alder do differ somewhat in
their site requirements. For example, Sitka alder at
Planting Creek (site 5) was in class A, but the area is a
fairly poor site for Douglas-fir (site IV or V).3 Some of
this difference in site quality for the two species is
probably related to the fact that growth of Douglas-fir
is partially dependent on nitrogen availability, but
growth of Sitka alder is relatively independent of the
soil's ability to supply nitrogen.
In addition to the expected height growth of the two
species, the stocking and spacing in the mixture would
3Height at age 50 (breast-height age) for the Douglas-fir site
classes: site I, 44 m; site II, 38 m; site III, 32 m; site IV,
26 m; and site
V,
19 m.
also influence the optimum head start. If initial survival
of Douglas-fir in an area was poor and replanting was
necessary, an additional delay in the introduction of
Sitka alder would probably be desirable. Use of large
Douglas-fir planting stock could reduce the head-start
period.
If Douglas-fir were initially outgrown by Sitka alder,
its height growth could be depressed because of shading
or leader damage. Height-growth losses would depend
on spacing in the mixture and the height and age at
which the two species' height-growth curves cross. In
this analysis, we assumed that if the height-growth
curves crossed by age 10 (age of the Sitka alder), with
average height equal to or less than 4 m, the long-term
benefits of the mixture would outweigh any short-term
detrimental effects. We also assumed that early age
height growth of Douglas-fir in a mixed stand would be
about equal to that in a pure stand (i.e., during this
period the positive and negative effects on height
growth would cancel out); this assumption may be
somewhat conservative on very nitrogen-deficient sites.
We compared Bruce's (1 982) regional curves of
height growth for Douglas-fir (sites III-V) with our
smoothed height-growth curves for Sitka alder (classes
NOTES
A C) and assumed different starting times and planting
stock types. We concentrated on the poorer quality
Douglas-fir site classes for two reasons: (1) the lower
site classes are most likely to benefit from mixture with
a nitrogen-fixing plant, and (2) on the better conifer
sites, Douglas-fir can rapidly overtake even the fastest
growing Sitka alder we sampled. Similarly, we do not
further discuss Sitka alder in class D because Douglas­
fir of all site classes can outgrow the alder in this site
class before it reaches about I m.
We graphed two hypothetical situations comparing
the growth of the two species. In the first, we assumed
that Sitka alder was seeded in a 2-year-old natural
Douglas-fir stand (Fig. 3a). In the second, we assumed
that 1 -0 Sitka alder containerized seedlings (20 cm tall)
and 2-1 Douglas-fir seedlings (55 cm tall) were planted
at the same time (Fig. 3b). In both situations, Douglas­
fir was given a 2-year advantage in total age. Other
possible situations can be examined by shifting the ap­
propriate curves horizontally for different age advan­
tages, and vertically for different seedling types or
sizes.
In the first comparison (Sitka alder seeded in a natu­
ral Douglas-fir stand), Douglas-fir growing on site III
can surpass Sitka alder in classes B and C, but not in
class A before age 10 (height above 4 m). Douglas-fir
on site IV can outgrow only the Sitka alder in class C,
and Douglas-fir on site V would be outgrown by all
three classes of Sitka alder.
For any combination of the Douglas-fir and Sitka
alder height curves, Douglas-fir will surpass Sitka alder
in total height at an earlier age in the second situation
(planted 1 -0 Sitka alder and 2-1 Douglas-fir), than in
the first. Large planting stock gives Douglas-fir an
additional advantage, because its initial height growth
under natural conditions is slow. Douglas-fir on sites III
and IV should probably be given a 2- to 4-year total-age
advantage; if large Douglas-fir planting stock is used,
the age advantage could be reduced by 1 to 2 years.
Managers should be somewhat more cautious in design­
ing mixtures with Douglas-fir on site V. On such sites,
we would recommend that Douglas-fir be given a 3- to
6-year advantage in total age; however, this lead time
could be reduced if large Douglas-fir planting stock
were used or if height growth of Sitka alder was not as
great as that in the A site class.
We have not addressed the related problems of initial
spacing in mixed stands and how long the Sitka alder
component of a mixed stand should be maintained. The
benefits provided by the Sitka alder (e.g., additions of
nitrogen and organic matter) are directly related to its
net photosynthetic rate; the more closely spaced the
Douglas-fir, the sooner it would shade out the Sitka
alder. On the other hand, while wide spacing of the
Douglas-fir would help maintain Sitka alder in the mix­
-
111
ture for a longer period, it would also reduce the stock­
ing of the commercially valuable component of the
mixture. We do not yet have enough information to
prescribe optimum, site-specific species mixtures. We
believe, however, that Sitka alder - Douglas-fir mix­
tures are promising for sites low in total nitrogen and
organic matter and that this species mixture should now
be tried under various field conditions.
ANONYMOUS. 1969. Climatological handbook, Columbia Ba­
sin States, precipitation. Vol. 2. Pacific Northwest River
Basins Commission Meteorology Committee. Vancouver,
WA.
BINKLEY, D. 1981. Nodule biomass and acetylene reduction
rates of red alder and Sitka alder on Vancouver Island, B.C.
Can. J. For. Res. 11: 281-286.
BRUCE, D. 1982. Consistent height-growth and growth-rate
estimates for remeasured plots. For. Sci. In press.
CARPENTER, C. V., L. E. BARIBO, L. R. ROBERTSON, F. VAN
DEBOGART, and G. M. ONUFER. 1979. Acetylene reduction
by excised root nodules from Alnus rubra and Alnus sinu­
ata. In Symbiotic nitrogen fixation in the management of
temperate forests. Edited by J. C. Gordon, C. T. Wheeler,
and D. A. Perry. Oregon State University, Corvallis, OR.
p. 475.
CROCKER, R. L., and 1. MAJOR. 1955. Soil development in
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ka. J. Ecol. 43: 427-448.
HAINES, S. G., and D. S. DEBELL. 1979. Use of nitrogen­
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soils. In Impact of intensive harvesting on forest nutrient
cycling. College of Environmental Science and Forestry,
Syracuse, NY. pp. 279-303.
HEILMAN, P. E. 1979. Use of alders in coal spoil reclamation
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MIKOLA, P. 1975. Afforestation of bogs after industrial ex­
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MILLER, R. E., and M. D. MURRAY. 1978. The effects of red
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PNW-70. pp. 283-306.
NEWTON, M., B. A. EL HASSAN, and J. ZAVITKOVSKI. 1968.
Role of red alder in western Oregon forest succession. In
Biology of alder. Edited by J. M. Trappe, J. F. Franklin,
R. F. Tarrant, and G. M. Hansen. Pacific Northwest Forest
and Range Experiment Station, Portland, OR. pp. 73-84.
PLASS, W. T. 1977. Growth and survival of hardwoods and
pine interplanted with European alder. USDA For. Servo
Res. Pap. NE-376.
TARRANT, R. F., and R. E. MILLER. 1963. Accumulation of
organic matter and soil nitrogen beneath a plantation of red
alder and Douglas-fir. Soil Sci. Soc. Am. Proc. 27:
231-234.
TARRANT, R. F., and J. M. TRAPPE. 1971. The role of Alnus
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