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CROP ROTATION OF DOUGLAS-FIR AND RED ALDER: A PRELIMINARY
BIOLOGICAL AND ECONOMIC ASSESSMENT
W.
A. ATKINSON, B. T. BORMANN, AND D. S. DE BELL
College of Forest Resources, University of Washington, Seattle, Washington 98195; Department of Botany University of Washington, Seattle, Washington 98195; and Forestry Sciences Laboratory, Pacific Northwest F rest and Range Experiment Station, USDA Forest Service, Olympia, Washington 98502 Estimates of wood yield and nitrogen accretion for pulpwood and sawlog rotations of red alder on good
sites were coupled with information on managed yields of Douglas-fir to compare six management systems:
unfertilized Douglas-fir, fertilized Douglas-fir, alder-pulpwood rotation followed by Douglas-fir densely
seeded ll;lder killed by herbicides and followed by Douglas-fir, alder-sawlog rotation followed by one D ouglas­
fir rotatIOn, and alder-sawlog rotation followed by two Douglas-fir rotations. A net-worth analysis indicated
that all systems are profitable and that systems involving red alder, though not as profitable as systems
involving only Douglas-fir, show considerable promise. The criteria and assumptions involved in these
results and pertinent ecological and management considerations are discussed. It is concluded that crop
rotation merits pilot-scale testing in the Douglas-fir region.
Introduction
Forests of coastal Douglas-fir (Pseudotsuga men­
ziesii [Mirb.] Franco var. menziesii) occupy about
12 million acres! on the west side of the Cascade
Range in Washington and Oregon. Wood products
from Douglas-fir, the most intensively managed
tree in the Pacific Northwest, are of major impor­
tance. Although northwestern forest soils are among
the most productive in the United States, growth of
Douglas-fir is frequently limited by inadequate
supplies of a'lailable nitrogen. Nitrogen deficiencies
may become more pronounced in the third and fourth
rotation due to increased nitrogen losses from timber
harvesting and site-preparation practices. Wide­
spread tests demonstrated that Douglas-fir growth
can be stimulated on most sites by applying nitrogen
fertilizer ( GESSEL, STOATE, and TURNBULL 1969),
currently an integral part of intensive management.
Nearly 1 million acres have been fertilized during
the past decade. Probably more land would have
been fertilized, except for the shortage and higher
cost of urea fertilizer since 1973. Uncertainties re­
garding fertilizer costs are now a cause for much
concern in Douglas-fir management and have stim­
ulated interest in other means of enhancing nitrogen
status, particularly in biological fixation of nitrogen
by red alder (Alnus rubra Bong.).
Red alder is the major commercial hardwood
species in the region. Because of rapid initial growth,
volunteer alder often overtop planted Douglas-fir
in young plantations and are, therefore, often re­
garded as a weed species. Red alder not only has
commercial value but also the capacity to improve
the site through atmospheric nitrogen fixation. For
land managers to take advantage of these desirable
features of red alder and yet profit from the high
value of Douglas-fir, silvicultural systems using red
1 English units are used throughout this paper. Factors for
conversion to the metric system are: 1 acre = 0.405 ha, 1 ft =
0.3048 m, 1 inch = 2.54 em, 1 ft3 = 0.0283 ma, lib/acre =
1.12 kg/ha, 1 cunit = 3.625 ma.
alder must be compatible with intensive Douglas-fir
management.
Two basic systems use alder to supply nitrogen
for Douglas-fir growth: admixtures and crop rota­
tions. The beneficial effects of an admixture of red
alder in a Douglas-fir plantation on the Wind River
Experimental Forest in the southern Washington
Cascades have been well documented (TARRANT
1961; TARRANT and MILLER 1963; MILLER and
MURRAY 1978). At this highly nitrogen-deficient
site, mixed stands of red alder and Douglas-fir were
more profitable than unfertilized pure Douglas-fir
stands but substantially less profitable than pure
Douglas-fir with added nitrogen fertilizer (ATKINSON
and HAMILTON 1978). The possibility of using red
alder in crop rotation with Douglas-fir to improve
or maintain soil productivity was suggested by
TARRANT and TRAPPE (1971). Assessment of crop­
rotation schemes has been hampered by lack of
information on yields of managed alder stands as
well as on rates of nitrogen accretion for red alder
stands growing on productive forest land.
Recently developed yield estimates for managed
alder plantations (DEBELL, STRAND, and REUKEMA
1978) and new estimates of nitrogen accretion in
alder stands on productive sites2 make it possible to
evaluate crop-rotation systems.
This paper examines the feasibility of using red
alder as a rotation crop, even though current infor­
mation is limited. Four options for alternate cropping
of Douglas-fir and red alder are considered and
compared to continuous cropping of pure Douglas-fir
with and without application of nitrogen fertilizer.
Wood yield and profitability are compared. These
comparisons are used for evaluation of prospective
research involving the establishment of field trials
with various alder/Douglas-fir systems.
2 UnpUblished data of B. T. BORMANN and D. S. DEBELL
on file at Forestry Sciences Laboratory, Olympia, Washington
98502.
S102
S103
ATKINSON ET AL.-DOUGLAS-FIR/ALDER
Management options
The options (table 1) include management re­
gimes in common use on highly productive forest
land (options 1 and 2) and those that may offer
practical management possibilities in the near future
(options 3-6). Option 1 is used as a base and is a
standard management prescription for Douglas-fir
on industrial forest land: planting, two commercial
thinnings, and clear-cut harvest at age 45. Option 2
is similar to option 1 but nitrogen fertilizer is applied
immediately after each thinning. Option 3 involves
short-rotation (13-yr) production of alder pulpwood
followed by a 45-yr rotation of Douglas-fir. In
option 4, alder is artificially seeded to provide a very
dense stand and rapid nitrogen accretion for 8 yr,
at which time it is killed by herbicides. Douglas-fir
is then planted among the standing dead alder
stems. Some beneficial shade is provided by this
option, and all components of the alder stand remain
on the site to decompose and ultimately to nourish
the subsequent Douglas-fir crop. Options 5 and 6
involve production of high-quality alder savvlogs
followed by one and two 45-yr Douglas-fir rotations,
respectively. In each, the alder phase includes one
thinning for pulpwood at age 11 and clear-cut
harvest at age 32.
Procedures
ECONOMIC ASSESSMENT.-Profitabilities of the six
management options were determined and compared
on the basis of present net worth (discounted returns
minus discounted costs). Because the options include
TABLE 1
DEFINITION OF FOREST-MANAGEMENT OPTIONS
Option
no.
1. ......
2 .......
3 .......
4 .......
5 .......
6 ...... .
Description
Plan 400 Douglas-fir trees per acre; commercially
thm for sawlogs when mean stand diameter
equals 9.0 inches; commercially thin again 10 yr
following first thinning; clear-cut harvest at age
45. Repeat the regime.
Identical to option 1, except that 200 lb of nitrogen
fertilizer per acre are applied immediately after
each commercial thinning.
Plant 540 red alder trees per acre; clear-cut harvest
for pulpwood at age 13; plant Douglas-fir and
follow thinning and harvesting regime for option
1. When Douglas-fir is clear-cut, repeat the se­
quen e: 13 yr of red alder, 45 yr of Douglas-fir.
Seed With red alder; kill alder with herbicide at age
8; plant Douglas-fir and follow option 1. Repeat
the sequence: 8 yr of red alder, 45 yr of Douglas­
fir.
Plant 340 red alder trees per acre; thin for pulp­
wood at age 1 1; clear-cut harvest alder for saw­
logs at age 32; plant Douglas-fir and follow
option 1. Repeat the sequence: 32 yr of red alder, 45 yr of Douglas-fir. Identical to option 5, except grow two rotations of
Douglas-fir before repeating the red-alder rota­
tion. Hence the sequence is: 32 yr of red alder
45 yr of Douglas-fir, and another 45 yr of
Douglas-fir. Then repeat.
rotations of varying lengths, a perpetual time horizon
(repeated regimes) was used for more realistic com­
parisons. Assumptions regarding physical yields in
the analysis are in the next section. Cost assumptions
for essential forest-management activities are based
on a survey of current costs in the northwestern
United States (table 2).
Future costs and returns were discounted at a
7% annual interest rate. Costs were entered into the
analysis in constant (1978) dollars to eliminate
effects of general inflation. Thus, the 7% rate can be
considered as the "real" rate of return, a rate of
earning over and above the inflation rate. Because
timber prices have been increasing more rapidly
than the general inflation rate, we assume that, over
the first rotation, stumpage prices of Douglas-fir and
red alder will increase at a real rate of 3% per year,
based on historical trends (U.S. DEPARTMENT OF
AGRICULTURE, FOREST SERVICE 1973, p. 148). Start­
ing (1978) stumpage prices for the two species, as
related to average tree size, assume gentle terrain,
straight boles, and wide spacing (fig. 1). All analyses
are done on a pretax basis.
YTELD ESTIMATEs.-Anticipated Douglas-fir and
red alder yields for the six management options are
summarized in table 3. Yield estimates for Douglas­
fir rotations are based on the Douglas-fir managed
stand simulator (DFIT) developed by BRUCE,
DEMARS, and REUKEMA (1977). We have assumed
that forest land of site 165 (100-yr index)3 is planted
with 400 Douglas-fir trees per acre. The stand is
thinned for small sawlogs when average breast­
height diameter of the merchantable portion of the
stand attains 9.0 inches. This first thinning occurs
at age 27 for options 1 and 2; however, if red alder
has previously grown on the site, it occurs at age
25 or 26. A second thinning is made 10 yr after the
first, and final harvest by clear-cutting at age 45.
TABLE 2
COST ASSUMPTIONS FOR ECONOMIC ANALYSIS
(1978 dollars)
Item
Initial site preparation for all options. . . . .. ..... ..
Site preparation for Douglas-fir following alder (op­
tion 3) . .. .. .... ... .... .... . .. .. .. ........ .. .
Herbicide treatment of alder (option 4)..... .. .. .. .
Site preparation for Douglas-fir following alder
(options 5 and 6).... .. .... ... ... ...... ... ... ..
Douglas-fir planting cost (400 trees per acre)... ....
Red alder planting cost (540 trees per acre)........
Red alder planting cost (340 trees per acre). .... .. .
Red alder seed and seeding cost (option 4).. ... .. ..
Fertilization cost (200 lb nitrogen per acre) . .. .. . . .
Annual costs of management... ... ..... .. ....... .
Cost
(S/acre)
120
60
30
80
65
80
60
20
55
3
SOuRcE.-Data on file at College of Forest Resources ' University of
Washington, Seattle, Washington 98195.
3 Site index is a measure of forest productivity. Index 165
means that average height of dominant and codominant trees
will be 165 ft at age 100.
S104
[MARCH
BOTANICAL GAZETTE
(SUPPL. )
60
50
E
z
:::>
40
<IJ
u
L
0.-
30
<IJ
OJ
o
D-
E 20
::J
+-'
Vl
10
o
10
20
30
40
Average Volume
50
Per
Tree
60
70
80
90
(ft 3)
FIG. 1.-Average stumpage prices by tree size (dollars per cunit), Douglas-fir and red alder, 1978
TABLE 3
SUMMARY OF EXPECTED YIELDS
Stand
age
(yr)
Yield
(cunits/acre)·
Average volume
for harvested
trees (ft3)
Douglas-fir .......
I)ouglas-fir . . . ....
Douglas-fir . . . ....
27
37
45
11 . 75
16.03
63.51
10.2
19.3
45 . 7
Douglas-fir ..... . .
Douglas-fir . . ..... Douglas-fi r. . . .... 27
37
45
11.75
17 . 70
67.58
10.2
20 . 2
50.3
Red alder . . ....... Douglas-fir ....... Douglas-fir . .. . . ..
Douglas-fir . . . . . .. 13
26
36
45
31 . 20
11 . 66
16.91
68.92
5.6
10.2
19.8
50.6
Douglas-fir .......
Douglas-fir . . .....
Douglas-fir . . .. . . . 26
36
45
11 . 66
16.91
68.92
10.2
19.8
50.6
Red alder. . ..... . .
Red alder... . . . .. .
Douglas-fir....... Douglas-fir . ..... .
Douglas-fir. . .....
11
32
25
35
45
8.60
45.80
10.84
16.65
72.07
5.2
27.0 9.6
19.3
52.4
Red alder . .. .....
Red alder.........
Douglas-fir . ...... Douglas-fir . . ... . . Douglas-fir ... . ...
Douglas-fir . . ..... Douglas-fir ....... Douglas-fir . . . . ... 11
32
26
36
45
26
36
45
8.60
45.80
11 . 66
16.91
68.92
11.66
16.91
68 . 92
5.2
27 . 0
10.2
19.8
50 . 6
10.2
19.8
50.6
Option no. and species
1:
2:
3:
4:
5:
6:
Cunit = 100 ft.' Volumes are to a 4-inch top and exclude stump volume.
PUlpwood yields of red alder (yields at age 11 and 13) are based on total
stem volumes.
Estimates of additional yield due to nitrogen
fertilizer in option 2 are based on an adjustment for
fertilizer included in the stand-simulation program
(BRUCE et al. 1977). The two applications of 200 Ib
of nitrogen fertilizer are expected to increase total
yield by 5.74 cunits,4 an increase of 6.3% above
total yield of unfertilized Douglas-fir.
The amount of nitrogen added by red alder was
considerably more than that added in the fertilizer
applications (table 4). We assumed that the Douglas­
fir crops following the alder crops in options 3, 4,
and 6 would grow about 6% more rapidly than
unfertilized Douglas-fir in option 1. For option 5,
we assumed that growth of Douglas-fir would lllTABLE 4
ESTIMATES OF NITROGEN INPUTS RESULTING FROM THE
PRESENCE OF A RED ALDER STAND AS DESCRIBE D FOR EACH CROP-ROTATION SCHEME
OPTIONS (lb N/acre) 4
Accretion:
Vegetation... . ............
Forest floor . . . . . .... ......
Soil (0-8 inches) . . ........ .
Total . ..... . . . ... . .......
Losses (from harvesting and
site preparation). . . . . . .....
Net addition.... . .... . . .... .
5 and 6
200
250
350
800
150
200
250
600
500 550 950 2,000
,...,200
600
,...,0
600
",,500 1,500
SouRcE.-Unpublished data on file at Forestry Sciences Laboratory,
Olympia, Washington 98502 .
•
4
One cunit
=
leo ft3.
1979]
ATKINSON ET AL.-DOUGLAS-FIR/ALDER
crease by 8% over that in option 1. The considera­
tions involved in these estimates are examined later.
Estimated yields for red alder crops in options 3,
5, and 6 are taken from DEBELL et al. (1978).
Option 3 requires alder planting at a density of 540
trees per acre, and then clear-cutting for pulpwood
at age 13. Options 5 and 6 involve an initial planta­
tion spacing of 8 X 16 ft (340 trees per acre), and
thinning for pulpwood at age 11 to 16 X 16 ft. The
remaining 170 trees are harvested for sawlogs at
age 32.
NITROGEN-ACCRETION ESTIMATES.-Estimates of
nitrogen added to the site during the alder phase of
the alternate cropping options (table 4) are taken
from current work by BORMANN and DEBELL on
nitrogen accretion in red alder stands near Olympia,
Washington.5 These stands were located on produc­
tive forest soils, most likely to be managed intensive­
ly for timber production and, therefore, potential
candidates for alternate cropping schemes.
Some nitrogen is lost during alder harvesting and
site preparation before planting Douglas-fir (table
4). Therefore, in option 3, the net nitrogen addition
is 600 lb N per acre. Option 4 also provides 600 lb
N per acre in 8 yr because the vegetation and forest
floor are left undisturbed following herbicide appli­
cation. Alder stands in options 5 and 6 are estimated
to leave 1,500 lb N per acre potentially available for
subsequent Douglas-fir growth.
Our estimate of an average annual nitrogen ac­
cretion in the forest floor and mineral soil of 45-60 lb
N/acre per year are somewhat higher than those of
TARRANT and MILLER (1963) for a 30-yr-old mixed
stand of Douglas-fir and red alder. Since our mea­
surements were taken in fully stocked, pure red
alder stands, nitrogen accretion would be expected
to be higher. Conversely, our estimates are substan­
tially lower than values suggested by ZAVITKOVSKI
and NEWTON (1968) based on data collected in young
alder thickets on coastal Oregon sites which were
thought to be nitrogen deficient due to past use as
landings or scarification for brush removal. Our
values are also lower than average accretion (124 lb
N/acre per year) determined by TARRANT et al.
(1969) in a 40-yr-old alder stand on a highly produc­
tive coastal site. Thus, as a general estimate for
nitrogen accumulation by red alder stands, our esti­
mates of nitrogen input are probably conservative.
EQUIVALENCY OF ALDER NITROGEN TO FERTILIZER
NITROGEN.-Estimating the worth of nitrogen added
by alder in terms of accelerated growth to Douglas­
fir is much more difficult and must be speculative.
There are many factors to consider, and some are
discussed to provide a perspective regarding the
assumptions in our analyses and to point out infor­
mation gaps which require detailed studies.
6 Unpublished data of B. T. BORMANN and D. S. DEBELL
on file at Forestry Sciences Laboratory, Olympia, Washington
98502.
S105
We know of no data or studies that establish a
yield-value relationship for nitrogen accreted by
alder over long periods of time. There are consider­
able data from agriculture, however, on the value of
added legume residues compared with nitrogen fer­
tilizer for gro'wth of succeeding crops. Nitrogen in
legume residue was 65%-85% as effective as fertil­
izer nitrogen (FRIBOURG 1954), and STICKLER and
JOHNSON (1959) listed values ranging from 16% to
92%. In general, the addition of legume residue N
appears to have variable effects on growth of subse­
quent crops and is less efficient than the addition of
nitrogen fertilizer.
The alder crop may also affect mineralization of
bound nitrogen, thus making more nitrogen available
for plant growth. Pools of ammonium- and nitrate­
nitrogen sampled in June were about 15 times larger
under a 38-yr-old alder stand than under an adjacent
48-yr-old Douglas-fir stand (COLE, GESSEL, and
TURNER 1978). Expressed as a proportion of total
soil nitrogen in the stands, ammonium- and nitrate­
nitrogen pools were eight times larger in the alder
stands. The additional nitrogen available for plant
uptake may, therefore, be rather substantial as long
as the high mineralization rate persists. Such differ­
ences were not apparent, however, when lO-yr-old
stands were compared. In addition to N fixation and
effects of mineralization, red alder may affect subse­
quent plant growth through effects on other soil
properties. For example, soil organic matter content
increases under the influence of alder, bulk density
is lower, and pH decreases (TARRANT and MILLER
1963; BOLLEN and Lu 1968). The availability of
other nutrients may be enhanced by their redistribu­
tion of the soil surface by red alder by litterfall.
Thus, while the nitrogen fertilizer effect alone is
considered here, alder may have additional effects
on subsequent Douglas-fir growth.
In summary, the alder rotations in options 3, 4, 5,
and 6 are estimated to leave 600, 600, 1,500, and
1,500 lb of additional nitrogen, respectively. In­
creases in subsequent Douglas-fir growth from nitro­
gen inputs in options 3, 4, and 5 are estimated to be
6%, 6%, and 8% over option 1. In option 6, both
crops of Douglas-fir are expected to have 6% higher
yields. These projected growth increases represent
an equivalency of alder nitrogen to fertilizer nitrogen
of only 25%-65%. Because Douglas-fir crops follow­
ing alder have the potential to benefit from alder
nitrogen over the entire rotation, our estimated
yields of Douglas-fir following red alder may be
conservative.
Results and discussion
Our analyses in terms of mean annual increment
and present net worth for the six management
options (table 5) show that all options earned the
required 7% return on investment and, therefore,
had positive net worths ranging from $276 to $573
S106
BOTANICAL GAZETTE
TABLE 5
ECONOMIC AND YIELD COMPARISONS
AMONG MANAGEMENT OPTIONS
PRESENT
M EAN ANNUAL INCREMENTb
(W/acre)
NET WORTHB
OPTION
($/acre)
Douglas-fir
1. . . . . . . . .
2 .. . . . . . . .
3. . .. . . . . .
4. .. . . . .. .
5.........
6 . . . . ... . .
514
573
276
358
435
456
203
216
168
184
129
160
Red alder
54
71
45
Total
203
216
222
184
200
205
'.Present net worth at 7% interest rate of a perpetual series of identical
regImes.
b Mean annual increment is the average wood volume growth per acre per
year over the period needed to complete all phases of an entire option.
per acre. Mean annual increment ranged from 184 to
222 ftS per acre. Although all options have some
promise, there are differences in estimated profitabil­
ity and productivity.
Options 1 and 2, involving continuous cropping of
pure Douglas-fir, had the highest present net worth
and also were highest in Douglas-fir wood produc­
tion. They were medium to high in total annual
wood production. Several potential limitations may
exist vvith respect to these options which appear to
be most profitable. Our analyses assumed that option
1 yields would remain the same throughout a per­
petual series of rotations. In view of the borderline
nitrogen deficiency in many Douglas-fir soils through­
out the Pacific Northwest, it seems more likely that
yields would progressively deteriorate unless addi­
tional nitrogen was supplied. Option 2 assumed that
nitrogen fertilizer would be available in needed
amounts at present costs for several rotations. Be­
cause the production of nitrogen fertilizer is heavily
dependent on natural gas supply, its future avail­
ability and cost will be closely tied to national
decisions regarding production and Use of energy.
Consequently there are many uncertainties.
All options involving alternate cropping of red
alder and Douglas-fir had lower present net worths
than the continuous-cropping options. Total annual
wood productions, however, varied from the lowest
(184 ft3/acre per year) to the highest (222 ft3/acre
per year). As with the continuous options, uncer­
tainties may affect present net worth and mean
annual increment. A concern common to all options
involving alder is the lack of management experience
for the alder phase and also the lack of suitable data
to estimate benefits to Douglas-fir growth.
Option 3 had the lowest present net worth and the
highest total mean annual increment. A primary
factor in the low profitability of this option was the
[MARCH (SUPPL. )
low stumpage value ($4.25 per cunit) assigned to
young alder. Currently, small pulpwood-size alder
trees do not command high prices and markets are
lacking in many areas. If future markets for alder
as constituted wood products or as fuelwood should
expand, then option 3 could provide much higher
returns.
Because the dense thickets of alder in option 4 are
killed with herbicide and remain in place, this option
is not dependent on markets for the alder crop.
Present net worth of option 4 is, in fact, higher than
option 3, but wood production is the lowest of all
options. Option 4 is dependent on the availability
and authorized use of herbicides. Broadcast applica­
tion of herbicides on forest land is a controversial
issue, posing many uncertainties for the future. It is
interesting that in this option we have a "biological"
approach to enhancing nitrogen status, and thereby
productivity, which requires application of herbicides.
Options 5 and 6 are the most profitable of the
alternate cropping schemes and are intermediate in
wood production. Present net worth for option 6,
with two crops of Douglas-fir after the alder, is not
much higher than for option 5, which assumes only
one Douglas-fir crop, because returns from the sec­
ond Douglas-fir rotation are pushed far into the
future and hence are greatly reduced by the dis­
counting process. Feasibility of both options depends
on existence of markets for alder pulplogs and
sawlogs. Recently, the acceptance and value of alder
sawlogs have increased, especially in the furniture
industry. As supplies of other furniture-quality hard­
wood species decline, the value of red alder may in­
crease more rapidly than that of Douglas-fir.
Conclusions
Our analyses suggest that alternate cropping sys­
tems involving red alder can be profitable at current
costs and values. These systems do not, however,
appear to be as profitable as continuous Douglas-fir
cropping schemes. Thus, red alder crops appear to
be costlier than fertilizer applications for improving
nitrogen levels in Douglas-fir forests. Minor changes
in assumed trends of costs and values could cause
dramatic shifts in the relative profitability of these
long-term investments. For example, expanded mar­
kets for red alder, increased efficiency of small tree
harvest, or decreased availability and higher costs of
fertilizer nitrogen could tip the balance in favor of
alternate cropping systems. In view of the economic
performance indicated in our analyses, the uncer­
tainties involved in our estimates, and potential
increases in fertilizer costs in the future, we believe
that crop-rotation systems merit further study and
pilot-scale testing in the Douglas-fir region.
LITERATURE CITED
ATKINSON, W. A. , and W. 1. HAMILTON. 1978. The value of
red alder as a source of nitrogen in Douglas-fir-alder mixed
stands. Pages 337-352 itt D. G. BRIGGS, D. S. DEBELL, and
W. A. ATKINSON, comps. Utilization and management of
alder. U.S. Dep. Agr. Forest Service Gen. Tech. Rep.
PNW-70. 379 pp.
1979] ATKINSON ET AL.-DOUGLAS-FIR/ALDER
BOLLEN, W. B., and K. C. Lu. 1968. Nitrogen transformations
in soils beneath red alder in conifers. Pages 141-148 in
J. M. TRAPPE, J. F. FRANKLIN, R. F. TARRANT, and G. M.
HANSEN, eds. Biology of alder. Pacific Northwest Forest
and Range Experiment Station, Portland, Oreg. 282 pp.
BRUCE, D., D. J. DEMARS, and D. L. REUKEMA. 1977.
Douglas-fir managed yield simulator-DFIT user's guide.
U.S. Dep. Agr. Forest Service Gen. Tech. Rep. PNW-57.
26 pp.
COLE, D. W., S. P. GESSEL, and J. TURNER. 1978. Comparative
mineral cycling in red alder and Douglas-fir. Pages 327-336
in D. G. BRIGGs, D. S. DEBELL, and W. A. ATKINSON,
comps. Utilization and management of alder. U.S. Dep.
Agr. Forest Service Gen. Tech. Rep. PNW-70. 379 pp.
DEBELL, D. S., R. F. STRAND, and D. L. REUKEMA. 1978.
Short-rotation production of red alder: some options for
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