In :
Silvicultural systems for the
maJor forest types of the United
Red Alder
States,
DC:
Dean S. DeBell
Pac((ic Northwest Forest a11d Ra11Re Experime11t Statioll
Thomas C. Turpin
Pac((ic Northwest Re[iioll
445. Washington '
Department of Agriculture·'
1983: 26-28.
w_as cr
Red alder (Alnus rubra Bong.) is the most widely
distributed hardwood type in the coastal Pacific Northwest,
occupying more than 3 million acres (1.2 million ha) of
commercial forest land in Oregon and Washington. This type
is identical to Society of American Foresters cover type 221
of the same name (4). The type is found from southern
California to southeastern Alaska, but stands seldom occur
east of the Cascade Range or the Sierra Nevadas. Red alder
stands grow on a wide range of soil and site conditions,
varying from well-drained gravels and sands to poorly
drained clays and organic soils (17). Because red alder can
tolerate poorly drained conditions and some flooding in the
growing season, it prevails on soils of restricted internal
drainage, along streams, and on swampy or marshy areas.
The most productive stands are usually found on deep,
well-drained Ioams or sandy Ioams derived from marine
sediments or alluvium; some very good stands also grow on
residual or colluvial soils of volcanic origin. Rapidly growing
red alder stands occur on hillsides as well as along streams at
elevations below I ,500 feet (460 m) in coastal areas of
northern Oregon , Washington, and British Columbia. At
mid-elevations in the Cascade Range, stands of commercial
dimensions are limited mainly to stream bottom sites.
Climate in the type's range is humid or superhumid,
with most precipitation occurring as rain during winter.
Summers are cool and dry, sometimes with considerable
morning fog. Annual precipitation and temperature extremes
are 16 to 220 inches (405 to 5590 mm) and -22° to 115° F
(-30.0° to 46. I o C) , respectively. Most stands , however,
are found where annual precipitation exceeds 40 inches (1015
mm) and winter temperatures are relatively mild.
Red alder occurs in both pure and mixed stands.
Common tree associates include coast Douglas-fir (Pseudotsuga
menziesii (Mirb. ) Franco var. menziesii), western hemlock
(Tsuga heterophylla (Raf.) Sarg.) , western redcedar (Thuja
plicata Donn ex D. Don), Sitka spruce (Picea sitchensis
(Bong.) Carr. ), black cottonwood (Populus trichocarpa Torr.
& Gray) , bigleaf maple (Acer macrophyllum Pursh), and
willow (Salix spp).
Red alder regenerates most commonly by natural seeding.
It has also been established by direct seeding and planting in
several research and pilot-scale trials (17). Survival of both
bare-root and container seedlings has been excellent (3). Red
alder will sprout vigorously from the stump wl)en young and
has been repeatedly coppiced on short cycles (6). Stumps of
pole- and sawlog-size trees may sprout, but prouts rarely
1
persist.
Individual trees reach sexual maturity at 3 to 4 years,
and most dominant trees in a stand will begin to produce seed
at 6 to 8 years (II). Red alder is a prolific seeder, with
moderate seed crops produced almost annually. Bumper
crops occur at 3- to 5-year intervals, and seed crop failure is
unusual. Seed dispersal begins soon after ripening in late
summer , but most seeds are shed during fall and winter.
Dissemination is primarily by wind, and sufficient seed for
26
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natural regeneration is usually present throughout the species'
range (17).
Germination and early growth is best on moist mineral
soil and in full sunlight. The species is a common pioneer on
landings , skidtrails, road cuts , and other areas where mineral
soil has been freshly exposed. Seeds will also germinate on
soil organic horizons and on rock-surfaced logging roads, but
the newly developing roots must quickly penetrate a moist,
nutritious substrate if the seedlings are to survive. Some early
mortality has been observed after girdling by meadow mice
or cutting by mountain beaver, but its extent is unknown.
Red alder is moderately intolerant of shade. Seedlings
will survive in partial shade for several years, but full
sunlight is required for normal development. Compared with
most of its associates, red alder is relatively tolerant of
flooding and salinity. Windthrow is not common except
along exposed cutting boundaries or where root systems have
been undermined by flooding or erosion. Mortality , stem
breakage, and other top damage have been observed in
natural stands after ice storms and unseasonable frosts (3,
17).
Red alder is the only commercial tree species native to
western North America that fixes atmospheric nitrogen symbioti­
cally in its root nodules; both content and availability of
nitrogen are increased in soils beneath red alder stands.
Accretion rates varying from about 40 to more than 300
pounds of nitrogen per acre (45 to 335 kg/ha) per year have
been reported for alder stands of 50 years and less (12, 13).
Soil organic matter is higher and bulk density is lower in red
alder stands than in conifer stands of comparable history
(12). Red alder has therefore been proposed for site improve­
ment purposes, either by itself or in crop rotations and
mixtures with other species.
Young stands of red alder may be very dense , having
more than 100,000 stems per acre (247 100 stems/ha) at 1
and 2 years (2). Self-thinning or suppression-related mortal­
ity begins at an early age in such stands, but they remain too
dense for optimum growth without management. Spacing
control or thinning in previously unmanaged stands is effec­
tive in stimulating growth if done before age 15 to 20.
Thinning in overly dense, older stands can salvage mortality
but is of questionable value for increasing growth on selected
crop trees (10, 15).
Young alder trees grow rapidly. On favorable sites,
seedlings grow 3 feet (0.9 m) or more in the first year; they
may attain 30 feet (9.1 m) by age 5 and more than 80 feet
(24.4 m) by age 30 (16). Good growth rates are maintained
from establishment to at least age 25; during this period,
growth of red alder surpasses that of any conifer or other
hardwood species in the Pacific Northwest, with the excep­
tion of black cottonwood on its best sites. Growth thereafter
slows, and the decrease begins earlier and is greater on poor
than on good sites.
Growth and yield information is available for natural,
unmanaged stands of red alder ( l , 2, 10, 13, 14, 16). On
. i
well-stocked sites of the highest quality, mean annual incre­
ment (total stem) may approach 150 cubic feet per acre (10.5
m3/ha) for 20- to 40-year rotations; a comparable value for
sites of average quality is 120 cubic feet per acre (8.4 m3/ha).
Projections based on early performance of experimental
plantings, results of thinning trials, and gains obtained with
spacing control of other species suggest that yields of
managed red alder stands will be much higher than natural
stands (2). For example, coppice stands can be grown on
cutting cycles of 2 or more years, and pulpwood-size (6-inch
(15 em) diameter at breast height (d.b.h.)) trees can be
produced in lO to 15 years on good sites. Sawlog- and veneer
Jog-size trees (12-inch (30 em) d.b.h.) can probably be
grown in 25 to 35 years on such sites. Annual total stem
yields are estimated at 170 to 210 cubic feet per acre (11.9 to
14.7 m3 /ha). Rotations longer than 40 years are not recom­
mended for timber production because of increased disease
problems and reduced growth of red alder at older ages (3,
13, 17).
Young, vigorous stands of red alder appear relatively
free from serious insect and disease problems, but such pests
could become more evident or serious as the species becomes
more widely managed (17). Insect damage observed in alder
stands include twig girdling by flatheaded borers, defoliation
by tent caterpillars and sawflies, and infestation by bark
beetles. Red alder is susceptible to several canker-causing
fungi and foliage and catkin diseases, but none have signifi­
cant economic importance. A white heart rot is the major
cause of defect in older trees, and many other fungi species
have been identified on alder as secondary invaders of dead
or dying tissues. Red alder is resistant to laminated root rot
(Phellinus weirii (Murr.) Gilb.), and therefore is a suitable,
non-susceptible species for growing on sites severely infested
with the fungus (5).
Fire rarely damages red alder stands-in fact, the
species has been planted as a fire break (17). The low fire
hazard is due to scarcity of flammable understory and organic
debris in closed alder stands and because natural alder stands
commonly occur on wet sites. Fire may be an important site
preparation tool in red alder management. Dense understories
of shrub species develop in older, unmanaged red alder
stands with less than full stocking, particularly on the more
productive sites. Such shrub species may take over the site
following harvest and thereby prevent successful regenera­
tion of alder or other commercial tree species, unless special
site preparation measures are taken. Tractor scarification is
rather expensive and is inappropriate on many red alder sites
because of steep terrain or excessive soil moisture. Broadcast
burning is usually difficult because of moist conditions,
green underbrush, and the non-resinous, light slash of such
s ands (17). Coupled with preparatory applications of herbi­
Cides and/or desiccants, however, broadcast burning can be a
suitable method for ameliorating the brush encroachment
problem following harvest cuts on such sites (9).
Although natural stands of red alder occupy about 15
percent of commercial forest lands in western Oregon and
Western Washington, foresters have had little experience in
managing the species. Historically, red alder has been
regarded primarily as a weed species limiting production of
more highly valued conifers. Stumpage values for red alder
are very low; available supplies far exceed present demand
(7). There is growing interest, however, in regeneration and
management of red alder because of its rapid juvenile growth
and bility to fix atmospheric nitrogen and improve other
hem1cal and physical properties of soils. Recent expansions
lfl use of the species in solid wood, paper, and other
reconstituted fiber products as well as recognition of its
.
Potential contributions in multiple-use situations have also
aided the developing interest in red alder management.
Because of the dearth of operational experience with the
species, present management recommendations are based
primarily on extrapolation of results from limited research
trials as well as management experience with other species
having similar biological traits.
Silvical characteristics and regeneration requirements of
red alder mandate a silvicultural system adapted to even-aged
management, specifically, clearcutting, seedtree, or shelterwood.
Of the three, clearcutting provides the greatest flexibility in
use of site lpreparation techniques to control brush and to
expose mineral soil. Natural seeding from adjacent uncut
stands, direct seeding, and planting of container or bare-root
seedlings have all resulted in satisfactory establishment of
new alder stands in clearcut areas (3, 17). Stocking in
naturally established stands, however, is commonly either
clumpy with much unoccupied growing space or extremely
·dense. Thus, planting may be preferable in situations where
red alder is managed primarily for wood production. In most
cases, clearcutting is probably the most effective silvicultural
system, followed, if necessary, by scarification or some other
form of site preparation. Clearcutting is also the appropriate
method to use in short-rotation management systems for fiber
and energy production (2, 6).
No attempts to reproduce red alder by the seedtree
method have been documented. Only in rare cases does seed
supply limit natural regeneration of red alder after clearcutting;
seedbed condition is more likely to be the limiting factor.
Leaving a few seed trees per acre, however, might provide a
more uniform distribution of seedlings where cutting units
are exceptionally large or where there are few adjacent uncut
red alders.
The shelterwood system might also be used to regener­
ate red alder, but there is little documented information to
recommend it. Seed is usually produced every year, and
established seedlings grow best in full sunlight. Moreover,
juvenile growth rate of red alder is so rapid that, even in areas
of high esthetic value, the overstory would probably have to
be removed in less than 2 years; excessive damage to the
young reproduction would otherwise be expected.
Because red alder can become established naturally in
abundance, precommercial thinning will probably be an
essential feature of management programs--especially those
that entail natural regeneration. There are several reports of
enhanced growth of the species following early spacing
control (10, 15); such cutting also provides opportunities to
favor stems of superior form. Uniform spacing may also
reduce the sweep or lean characteristic of red alder in
unmanaged, irregularly spaced stands (2).
Maintenance of the red alder type is no problem; the
estimated acreage occupied by red alder in western Oregon
and western Washington has more than tripled in the past
quarter century. Recent emphasis on conversion of red alder
stands to conifers, however, has resulted in an unbalanced
distribution of age classes in some areas. Individual alder
stands begin to break up by age 60 to 70; intact stands more
than 80 years old are rare. Much evidence points to maxi­
mum rotation ages of 40 years or less if wood production is
the primary objective of management.
Mixed stands of red alder and other species are more
common than pure red alder stands in many parts of the
species range. These mixtures are both even- and uneven­
aged, and may include most of the previously listed associ­
ated tree species. There is no specific management experi­
ence and little research data for most of these mixtures; the
intention of' most forest owners and managers is to convert
such stands to pure conifers after harvest of the existing
stands. There are some exceptions, however, and interest in
27
mixed-species management has increased substantially in the
last decade. For example, mixed stands of Douglas-fir and
red alder have been established on an experimental basis and
such mixtures are now being considered for limited opera­
tional use on some nitrogen-deficient soils. Interplanting
alder seedlings in a 4-year-old Douglas-fir plantation at a
ratio of nearly two alders to one Douglas-fir, increased soil
nitrogen and soil organic matter and lowered bulk density
(12); it also enhanced growth of Douglas-fir (8). Similar
benefits might be obtained with a lower ratio of red alder to
Douglas-fir. Mixed red alder -Douglas-fir stands are pre­
scribed on the Siuslaw National Forest for soils that are low
in nitrogen but are otherwise productive (site index class II).
Current management plans for these sites call for leaving
some naturally established red alder when Douglas-fir planta­
tions are precommercially thinned at about age 10 (14). The
red alder will be removed in a commercial thinning at about
age 40. It is assumed that nitrogen accumulated in the soil
during the period of alder's occupancy will enhance Douglas­
fir growth in the remaining years of the conifer rotation.
Red alder stands can be established and managed for
purposes other than, or in addition to, wood production.
Because of the species' tolerance of poor drainage and
flooding, alder is sometimes recommended for management
in riparian zones. It can be especially useful in the ameliora­
tion of coal mine spoils, landslides, and other eroded or low
fertility areas. Although red alder is not a preferred browse
species, its presence in pure stands, small clumps or stringers,
and mixed stands within extensive conifer forests provides
edges and adds structural diversity; it may therefore be used
to enhance the forest habitat for many wildlife species.
Esthetically, red alder stands provide variety in a landscape
covered mainly by stands of conifers, and its rapid juvenile
growth rate permits its use where rapidly established tree
cover is desired for protection or enhancement of visual
resources.
3. DeBell. D. S.; Harrington, C. A. Mini-monograph on Alnus ruhra. In:
Documents, Technical consultation on fast-growing plantation broadleaved
trees for Mediterranean and temperate zones: 1979 October 16 -20·
Lisbon, Portugal. Volume I. Invited Papers. Food and Agricultu
Organization of the United Nations: 1979: 169-186.
4. Eyre, F. H., ed. Forest cover types of the United States and Canada.
Washington, DC: Society of American Foresters: 1980. 148 p.
5. Hansen, E. M. Survival of Phellinus weirii in Douglas-fir stumps after
logging. Can. J. For. Res. 9(4):484-488; 1979.
6. Harrington, C. A.; DeBell, D. S.: Strand. R. F. An experiment in
biomass production: Results from three consecutive harvests of cotton­
wood and alder. In: Proceedings of Solar '79 Northwest. U.S. Seattle,
WA: U.S. Department of Energy and others: 1979:363-366.
7. McGillivray, R. Alder survey. Pullman, WA: State of Washington
Department of Natural Resources; 1981. 24 p.
8. Miller, R. E.; Murray, M. D. The effects of red alder on growth of
Douglas-fir. In: Briggs, D. G.; DeBell, D. S.; Atkinson, W. A.. comps.
Utilization and management of alder. Gen. Tech. Rep. PNW-70.
Portland, OR:U.S. Department of Agriculture, Forest Service, Pacific
Northwest Forest and Range Experiment Station: 1978: 283-306.
9. Newton, M. Herbicides in alder management and control. In: Briggs,
D. G.; DeBell, D. S.; Atkinson, W. A., comps. Utilization and
management of alder. Gen. Tech. Rep. PNW-70. Portland, OR:U.S.
Department of Agriculture, Forest Service, Pacific Northwest Forest
and Range Experiment Station; 1978: 223-230.
10. Smith, J. H. G. Growth and yield of red alder: Effects of spacing and
thinning. In: Briggs, D. G.; DeBell, D. S.; Atkinson, W. A.. comps.
Utilization and management of alder. Gen. Tech. Rep. PNW-70.
Portland, OR: U.S. Department of Agriculture, Forest Service. Pacific
Northwest Forest and Range Experiment Station; 1978: 245-263.
II. Stettler, R. F. Biological aspects of red alder pertinent to potential
breeding programs. In: Briggs, D. G.; DeBell, D. S.; Atkinson, W. A.,
comps. Utilization and management of alder. Gen. Tech. Rep. PNW-70.
Portland, OR:U.S. Department of Agriculture, Forest Service, Pacific
Northwest Forest and Range Experiment Station; 1978: 209-222.
12. Tarrant, R. F.; Miller, R. E. Accumulation of organic matter and soil
nitrogen beneath a plantation of red alder and Douglas-fir. Soil Sci. Soc.
Amer. Proc. 27(2): 231-234; 1963.
I3. Trappe, J. M.; Franklin, J. F.; Tarrant, R. F.; Hansen, G. M., eds.
Biology of alder. Portland, OR:U.S. Department of Agriculture, Forest
Service, Pacific Northwest Forest and Range Experiment Station; 1968.
292 p.
I4. Turpin, T. C. Managing red alder on the Siuslaw National Forest. In:
Proceedings, National Silviculture Workshop--Hardwood Management;
I981 June 1-5; Roanoke, VA. Washington, DC:U.S. Department of
Literature Cited
Agriculture; Forest Service, Timber Management; 1981: 268-272.
I. Chambers, C. J. Empirical yield tables for predominantly alder stands in
western Washington. Report No. 31. Olympia, WA: State of Washing­
ton Department of Natural Resources; 1974. 70 p.
Columbia Forest Service, Research Division; 1964. 7 p.
16. Worthington, N. P.; Johnson, F. A.; Staebler, G. R.; Lloyd, W. J.
2. DeBell, D. S.; Strand, R. F.; Reukema, D. L. Short-rotation production
Normal yield tables for red alder. Res. Pap. 36. Portland, OR: U.S.
of red alder: Some options for future forest management. In:Briggs, D.
Department of Agriculture, Forest Service, Pacific Northwest Forest
G.; DeBell, D. S.; Atkinson, W. A., comps. Utilization and manage­
and Range Experiment Station; 1960. 29 p.
ment of alder. Gen. Tech. Rep. PNW-70. Portland,
OR: U.S.
17. Worthington, N. P.; Ruth, R. H.; Matson, E. E. Red alder: its
Department of Agriculture, Forest Service, Pacific Northwest Forest
management and utilization. Misc. Pub. 881. Washington, DC:U.S.
and Range Experiment Station; 1978:231-245.
Department of Agriculture; 1962. 44 p.
..
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28
15. Warrack, G. C. Thinning effects in red alder. Victoria, BC: British