Associated Forest Cover
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Natural alder communities include ash, birch, willow, and oak, "forming
ash-alder wood on low-lying ground of high soil fertility and
moisture, alder-willow thickets in areas liable to seasonal
flooding, and alder-birch wood on higher lying, less fertile,
generally acid soils.... Pure stands are ... common, but not as
extensive in Britain as, for example, in northwest Germany"
(60). European alder and gray willow, Salix cinerea
atrocinerea, form a tidal woodland near the upper limits of a
salt marsh on the Cornish coast. In the absence of disturbance,
the alder-willow community succeeds the marsh (78).
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Climate
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The duration of low winter temperature limits the range of
European alder in Scandinavia because the species does not extend
into regions where the mean daily temperature is above freezing
for less than 6 months of the year. The southeastern boundary of
European alder distribution in Eurasia corresponds closely with
the 500 mm (20 in) annual rainfall line (60). European alder is
hardy to winter temperatures of -54° C (-65° F) (36),
but apparent winter damage to young European alder plantings in
North Carolina resulted in partial to complete dieback of 80
percent of the trees. Relatively early low temperatures in
November and December were probably responsible for the damage,
rather than extreme cold, as the overwinter minimum was only -18°
C (0° F) (9).
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Damaging Agents
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In a Scottish plantation survey,
European alder suffered less damage by deer browsing and rubbing
than did birch, willow, or other hardwood species (2). In
contrast, deer browsed more than half the European alder
seedlings in a 2-yearold plantation in Pennsylvania; damage was
much less on Japanese larch (Larix leptolepis), white
spruce (Picea glauca), eastern white pine, and red pine
(Pinus resinosa) (26).
Dozens of insects and diseases have been observed on European
alder but few cause serious damage. Among pests recognized as
potentially troublesome is the striped alder sawfly, Hernichroa
crocea, a native of Europe that is now found across northern
United States and Canada. It produces two generations per year.
From July through September larvae occasionally eat all of the
alder leaves except the midrib and larger veins (93).
The European alder leafminer, Fenusa dohrnii, is another
introduced species. It makes blotch mines on alder leaves in the
northern United States and southeastern Canada (5). The alder
flea beetle, Altica ambiens alni, feeds on both surfaces
of alder leaves from Maine to New Mexico. It is sometimes a pest
of alders in recreational areas and along roadsides (93). The
woolly alder aphid, Prociphilus tesselatus, is
distributed throughout the eastern United States and is often
abundant on alder. Although it causes little direct damage, it is
suspected of weakening the trees and providing infection courts
for subsequent fungal attack.
Several fungus species have been isolated from Alnus glutinosa
trees that died back following woolly aphid infestations.
They include Botryodiplodia theobromae (76) which has not
been confirmed as pathogenic. In an A. glutinosa seed
production plantation in Kentucky, Phornopsis alnea caused
basal stem cankers and eventual mortality as great as 17 percent
(71). In northern Mississippi, occasional alder trees infested
with woolly aphids are heavily damaged by sapsuckers (103). Alder
seems to be very resistant to chronic ozone fumigation (45); in
contrast, it is more susceptible to S02 damage than most species
(94).
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Flowering and Fruiting
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European alder is
monoecious; flowers of both sexes emerge from buds that begin to
develop about 9 to 10 months before pollination. These preformed
buds allow an early estimate of the following year's seed crop.
Male buds are distinctly longer than female buds-about 1 cm (0.4
in) compared to about 3 mm (0.1 in)-and grow nearer the tips of
branchlets. They remain green until December and grow
intermittently throughout the winter (74). Female flowers are 1
to 1.5 cm (0.4 to 0.6 in) long when mature; male catkins are from
5 to 13 cm (2 to 5 in) long. They vary in color from tree to
tree, over a range from light peach to deep purple. Occasional
bisexual catkins are found.
A general calendar of seed formation is as follows (61,74): Styles
begin to form in July, year 1; rest period follows from August,
year 1 to February, year 2; pollination occurs in February to
March, year 2; placenta forms in May, year 2; ovules form in
June, year 2; ovary begins to grow from June to July, year 2;
embryo sacs are formed in July, year 2; fertilization takes place
from late July to early August, year 2; embryo grows throughout
August, year 2; embryo ripens throughout September and
germination first becomes possible during this month. Seeds are
mature when their pericarps turn brown, although the cones remain
green until the seeds are released.
As an exception to this calendar, pollination is sometimes delayed
until early April in the northeastern United States. The
flowering schedule is typically dichogamous.
Most European alder trees are virtually self-sterile (61), but
certain selfed trees have produced seed with germination
percentages as high as 8 percent (81). Viability of
cross-pollinated seed ranged from 8 to 90 percent (61,81).
Viability of pollen was greater than 99 percent at the time of
collection (61) but fell to about 1 percent after 50 days storage
(73). Individual trees in Iowa set a good crop of seed every
year, but the percentage of filled, viable seed ranged from 0 to
90 percent. Because fertilization occurs in July and August, the
developing embryo may be especially vulnerable to heat and
moisture stress. Seed with little or no viability was produced in
years of severe summer drought (37).
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Genetics
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Population Differences
In an extensive progeny test of select European alder parent
trees, heritability of height growth was good at age 7. Most good
clones performed consistently when used as either male or female
parents. The general superiority of alders from the moraine
region of upper Bavaria was confirmed (102).
Races and Hybrids
Over the broad range of European alder, racial development is to
be expected, but within regions, variation is sometimes slight.
Fifteen European alder provenance collections, grown on
calcareous spoil banks in southern Ohio for 16 years, differed
sharply in both growth and survival. Most of the trees originated
in central and north-central Europe; survival was best for three
seedlots of central German provenance. Trees from Diessen,
Bavaria, grew to be 21 percent taller and 20 percent larger in
diameter than the plantation mean and averaged 0.57 rn (1.87 ft)
per year in height growth over the past 10 years. Alders of
Uppland, Sweden, provenance were almost complete failures, being
only 3.5 m (11.5 ft) tall with 11 percent survival after 16 years
(29).
The 16-year results reported above are reasonably consistent with
those at age 6, with one striking exception. Trees from Peiting,
Bavaria, formerly second tallest in the plantation (28), have
virtually collapsed, with survival declining to 37 percent, and
height growth over the past 10 years least of all except for the
trees from Uppland, Sweden (29). Similar results are reported
from European alder trials in the Netherlands, where trees from
three German seed sources grew rapidly for 7 years and then
slowly for the following 3 years (96). The need for caution in
making early selections is obvious.
In a larger but younger provenance trial in Pennsylvania, most
trees burst buds with a 4-day period well before the beginning of
the frost-free season. Most of the fastest growing trees
originated from the central part of the species'natural
distribution. About half the variation in total height was due to
rate of growth; the other half was due to length of the growing
season (23).
European alders that grow fastest are more likely to be
single-stemmed. At age 6 in the Ohio test, the correlation
between height and number of stems per tree was -0.31 (28).
European alder hybridizes readily with many other alders.
Particularly vigorous hybrids have been reported for A. cordata
x A. glutinosa (48), A. glutinosa x A. incana
(47), A. glutinosa x A. rubra (53), and A.
glutinosa x A. orientalis (95).
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Growth and Yield
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Height growth begins in midApril
and continues through July or August. Saplings may continue
growing into September or October (59,101). In the mountains of
Czechoslovakia, 90 percent of diameter growth takes place between
midMay and mid-August, a growing season almost identical to that
of European beech (Fagus syluatica) (12). In Switzerland,
alder root growth commenced about 4 days after the beginning of
vegetative bud swelling and about 5 weeks before the beginning of
branch extension growth (51). Root growth resumes in October and
continues throughout the winter except when the ground is frozen
(79).
Height growth of alder seedlings planted on rather acid (pH 4.3 to
4.5) strip-mined lAnd in Ohio falls between normal yield values
(table 1) for site classes I and 11 at age 16 (29). On a
moderately permeable bottom-land site in southern Illinois,
9-year-old European alder outgrew predicted height values and
averaged 11.2 m (36.8 ft) tall, and 13.7 cm (5.4 in) in d.b.h.
(72). Height growth slowed markedly (80) over the next 5 years in
this widely spaced plantation, and at age 14 the trees averaged
12.3 m (40.4 ft) tall and 20.1 cm (7.9 in) in d.b.h. (table 2).
European alder usually reaches two-thirds of its maximum height
by age 25 (33) but may survive for 120 years on the best sites,
growing to be at least I in (3 ft) in diameter (60). The root
wood of European alder has lower specific gravity than the stem
wood but longer fibers with thinner walls (100). In an Ohio
stripmine plantation, stem wood specific gravity averaged 0.39
and did not vary with age or geographic origin of the trees.
Fiber length increased from 0.71 min (0.28 in) at age 5 to 0.93
min (0.36 in) at age 17 (83).
Representative percent chemical composition of European alder from
two points of view has been reported. The first was based on
total aboveground biomass, 4-year-old trees (104); the second was
based on leaf litter from four stands (69):
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Reaction to Competition
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The alder is primarily a pioneer
and opportunist species, and is capable of direct colonization of
even the rawest of soil material.... The species acts as a
pioneer on hydroseres, being capable of colonizing at very early
stages in the primary succession if good seed is available. Alder
carr (deciduous woodland or scrub on a permanently wet, organic
soil) does not succeed an earlier Salix and Rharnnus
carr, though these species may colonize simultaneously, and
pure alder carr eventually results from the greater vigour and
longevity of the alders" (65).
In central Switzerland, alder is considered to be more shade
tolerant than willow (Salix spp.), larch (Larix spp.),
poplar (Populus spp.), birch (Betula spp.), or Scotch
pine (Pinus syluestris); equal in tolerance to ash Traxinus
spp.); apd less tolerant than eastern white pine (Pinus
strobus) or Douglasfir (Pseudotsuga menziesii) (50). Overall,
it is classed as intolerant of shade (18).
In Yugoslavia and Germany, European alder is grown on 40- to
80-year rotations, depending on intensity of thinning and
products desired. The stand is clearcut at the end of the
rotation and replanted with 1-year seedlings or 1-1 transplants.
Nursery practice for European alder is fairly routine, and 1-year
seedlings are usually large enough for outplanting. Liberal
irrigation following sowing is essential for good seed
germination.
Alder has generally beneficial effects on associated plants. Part
of the nitrogen fixed by alders soon becomes available to other
species in mixed stands, especially through mineralization of
nitrogen leached from litter. Norway spruce (Picea abies)
grown in pots with European alder "obtained nitrogen
fixed in the root nodules of alder although leaves falling in
autumn were always carefully removed" (98).
In a 3-year-old Wisconsin plantation, hybrid poplars in a
plantation spaced at 1.2 by 1.2 in (3.9 by 3.9 ft) grew 21
percent taller in a 1:2 mixture with European alder than when
grown without alder (4.9 m versus 4.0 m; 16.0 ft versus 13.1 ft).
This growth increase corresponded closely with that achieved
through optimal ammonium nitrate fertilizer treatment, which
stimulated a 24 percent increase (39). Similar results were
obtained in Quebec where mixed plantings of two alders per poplar
yielded slightly more total biomass at age 3 than pure alder
plantings and 50 percent more than pure hybrid poplar (16).
European alder often is recommended for use in mixed plantings
with other species on nitrogen-poor sites. On strip-mined sites
in eastern Kentucky, 10 coniferous and broadleaved species were
grown in alternate rows with European alder at 2.1 by 2.1 m (6 :
9 by 6.9 ft) spacing; after 10 years, trees grown in mixture with
alder were 11 to 84 percent taller and 20 to 200 percent larger
in diameter than the same species grown without alder (75).
In northern Bohemia, Populus x berolinensis used for
strip-mine reclamation averaged 12.5 m (41 ft) tall at age 14 in
pure plantings but grew to 14 m (46 ft) in mixture with Alnus
glutinosa; poplars in the mixed planting were also much
straighter (24).
In southern Indiana, European alder seedlings were interplanted
into a 2-year-old plantation of black walnut (Juglans nigra)
on well-drained silt loam soil. Ten years after
interplanting, walnuts grown in mixture with alder averaged 5.3
in (17.5 ft) tall against 4.2 in (13.8 ft) in pure stands; alder
stimulated an increase in walnut diameter from 5.6 cm (2.2 in) to
6.9 cm (2.7 in) (14). In contrast, at four locations in Illinois
and Missouri, alder interplanted with walnut suddenly declined
and died after 8-13 years. Allelopathy caused by juglone was the
only cause of death that could be substantiated (80).
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Rooting Habit
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Alder has been characterized as
possessing an extensive root system of both surface and deep
branches, which enables it to survive on either waterlogged soils
or those with a deep water table (60). In Germany, European alder
is considered to be the deepest rooting indigenous tree species
(86). Alder's deeply penetrating taproots often extend well below
normal water table; if the water level falls, these roots are
well situated to use deep-lying soil moisture not available to
the upper portion of the root system. This may explain alder's
outstanding success on spoil banks (37,64).
Generally, there are two kinds of alder root nodules. One is a
large, perennial, usually single nodule sometimes 5 cm (2 in) or
more in diameter (21) and most often situated near the root
crown. These nodules may persist as long as 10 years, with those
in the 4- to 5-year age class making up the greatest proportion
of the weight of nodules per tree (1). The other type is
ephemeral, much smallertypically 1.5 to 3 mm (0.06 to 0.12 in) in
diameterand generally distributed throughout the surface root
system. Becking found that molybdenum-deficient alder plants
formed many small nodules of much reduced total dry weight and
exhibited associated nitrogen deficiency. Plants with an adequate
molybdenum supply had mainly single large nodules (6).
The most striking effect of alders on soil is nitrogen enrichment.
Not only is alder leaf litter rich in nitrogen (68), but many
nitrogenous compounds are heavily concentrated in alder roots and
root nodules (99). In European alder seedlings, rate of nitrogen
fixation is closely related to nodule fresh
weight and total plant dry weight, suggesting that selection for
growth should also achieve gains in nitrogen fixation (4). In
Quebec, 3- and 4-year-old alders planted at 33 cin by 33 cm (13
in by 13 in) spacing fixed nitrogen at an annual rate of 53 kg/ha
(47 lb/acre) (15).
Fixation of atmospheric nitrogen by alders takes place in root
vesicles (67) and nodules (8). In a greenhouse experiment,
maximum nitrogen fixation in young European alder plants occurred
in late August; throughout the growing season about 90 percent of
the nitrogen fixed was steadily transferred from the nodules to
the rest of the plant (91). In an alder grove growing on peat in
the Netherlands, nitrogen fixation was also found to peak in
August (1).
European alder (as well as other Alnus species) differs
from most deciduous tree species in retaining much foliar
nitrogen in the leaves until they fall (17). In a southern
Illinois plantation, nitrogen content of leaves decreased by only
one-sixth from midsummer until leaf fall. At the time of the last
collection, in mid-November, leaf nitrogen content was about 2.6
percent; thus there was a substantial quantity of nitrogen to be
dropped in the leaf litter (21).
In Finland, a 13-year-old European alder plantation and a
55-year-old natural stand were sampled for 4 years. Alder litter
averaged 2690 and 3705 kg/ha (2,400 and 3,305 lb/acre) per year
(ovendried), respectively, and contributed about 82 percent of
the total annual litter production. Total nitrogen content of the
leaf litter averaged 77 kg/ha (69 lb/acre) per year, reaching a
high of 101 kg/ha (90 lb/acre) in 1 year in the plantation.
NH4-nitrogen in the upper 3-cm layer of soil rose from 180 mg/kg
(180 p/m) before leaf fall to 270 mg/kg (270 p/m) after leaf
fall, indicating that at least part of the nitrogen of alder leaf
litter was rapidly mineralized (69).
Prodigious amounts of litter can accumulate under alder stands.
For instance, 10 species of pines and deciduous trees were
planted on a Kentucky strip mine with and without alternate rows
of European alder. After 10 years, 28.7 t/ha (12.8 tons/acre) of
litter accumulated in the plantings without alder, while 61.7
t/ha (27.5 tons/acre) built up under the stands with a 50 percent
alder component. The relative contribution of alder leaf fall and
increased litter production of the other species, stimulated by
the alder, could not be determined. In the spring of the 10th
growing season, the pH of the spoil beneath the stand containing
alder was significantly lower than the plantings without alder.
Similarly, the concentration of total soluble salts was
consistently higher, both spring and fall, in the stands with
alder than in those without (75).
European alder leaf litter readily gives up watersoluble organic
substances, losing 12 percent of its dry weight after only 1
day's leaching in cold water. Alder litter was also found to
decompose faster than that of beech or oak (70). The C:N ratio of
alder foliage suspended in a stream declined rapidly from 19 to
about 13 within a month after leaf fall, then more slowly to 11
(near the effective mineralization optimum) after 6 months (13).
Other components of alders also accumulate considerable nitrogen.
In a plantation on a good alluvial site in western Kentucky the
following nitrogen contents (percent dry weight) were measured at
the end of the fourth growing season (adapted from 104):
Even young alders can fix and add significant amounts of nitrogen
to soil. A Padus silt loam in Wisconsin averaged 966 mg/kg (966
p/m) of nitrogen in the upper 4 cm (1.5 in) of dry soil before
1-year-old European alder seedlings were planted. After two
growing seasons, soil nitrogen (at the same depth) had increased
222 mg/kg (222 p/m) in soil immediately adjacent to the alders
and by 158 mg/kg (158 p/m) at a distance of 15 cin (6 in) (39).
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Seed Production and Dissemination
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In Europe,
alder may not produce a uniform seed crop every year (61) but
abundant crops are frequent (56). Plantations in the eastern
United States seem to bear out both points: seed crops do vary
from year to year and they are generally rather heavy. European
alder (fig. 1) is precocious; some trees begin to flower at the
beginning of their second growing season and by their sixth or
seventh year are producing large quantities of seeds. Several
hundred strobiles may develop on a 6- to 9-m (20- to 30-ft) tree,
and in summer and early autumn the mass of maturing fruit
approximates the mass of foliage (74). Seeds average 60 per
catkin (60). The seeds are very small brown nuts, ranging from
about 240,000/kg (110,000/lb) (56) to as many as 1,400,000/kg
(639,000/lb) (87).
Seeds begin to fall in late September or early October and the
best seeds usually fall first (11,92). Seed dispersal continues
throughout the winter. Very few alder seeds remain viable beyond
the first germination season (62). Seed production as high as 18
kg/ha (16 lb/acre) has been achieved in a 14-year-old grafted
orchard in southwestern Germany; yields of 5 to 13 kg/ha (4.5 to
12 lb/acre) were more typical (54).
Although European alder seeds can germinate immediately after they
are shed, stratification and cold treatment enhance their
germination capacity (85). Seeds collected before strobiles turn
brown require several months of afterripening to germinate (60).
Epigeal germination in the nursery is prompt; it begins 10 to 20
days after spring sowing and is essentially complete within 2
weeks. Germination is notably better at pH 4 than at higher or
lower pH (85).
Production of containerized alder seedlings allows them to be
inoculated with Frankia and assures their nodulation
prior to planting. A I to 1 ratio of peat and vermiculite in the
potting mix is recommended (7).
European alder seeds have no wings; therefore, despite their small
size they are usually not spread more than 30 to 60 in (100 to
200 ft) by the wind, although they may occasionally be blown much
farther over the top of crusted snow. Where wind is the only
likely means of dissemination, alder saplings are rarely found
more than 20 to 30 in (65 to 100 ft) from the parent tree. The
seeds contain an air bladder and float in water, and McVean holds
that rather than wind, running water and wind drift over standing
water are the principal agents of dispersal (62). Naturalized
European alder stands in the United States are most commonly
found adjacent to streams.
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Seedling Development
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Seeds buried more than 0.5
cin (0.2 in) deep germin4e satisfactorily but many of the new
seedlings fail to emerge (62). The soil need not be saturated to
gain good seed germination, but high air humidity is essential.
In regions with only 50 to 65 cm (20 to 25 in) of annual
rainfall, "alder seedlings will only establish where the
surface soil falls within the capillary fringe of the water table
so that it remains constantly moist for 20 to 30 days in the
spring (March to May)" (63).
Alder seedlings can survive, although not thrive, under conditions
of flooding that would kill off the seedlings of most other
forest trees. In a British experiment, seedlings did not live
indefinitely with their entire root systems completely submerged
and were quickly killed by such treatment during the growing
season. Nevertheless, when the water level was maintained flush
with the top of the soil, the more robust seedlings were able to
produce adventitious roots at the soil surface and their growth
was hindered very little (63). The original roots of European
alder can grow actively during periods of flooding lasting for as
long as 1 week and resume growth after longer periods of flooding
(31). In another greenhouse study, alder seedlings were
successfully grown in oxygen-free soil, outperforming white
willow (Salix alba) under such conditions (10).
Growth of young potted European alder seedlings was not inhibited
by addition of foliage litter of six herbaceous species that did
inhibit growth of black locust (Robinia pseudoacacia). Alder
seedling growth and root nodulation were more than doubled by
addition of crownvetch (Coronilla varia) litter (49).
A light intensity equivalent to about 5 percent of full daylight
is essential for first-year alder establishment; for survival in
subsequent years about 20 percent of full daylight is required
(63). "First-year seedlings and 2- to 3-year-old plants up
to 5 cin (2 in) in height are frequent in some woods, but
complete internal regeneration is seldom seen. Regeneration tends
to be peripheral, or to occur with the formation of an even-aged
stand" (60).
Natural alder seedlings in Croatia grow to be about 0.5 in (1.7
ft) tall in their first year (32), but seedlings in American
nurseries are not always as large.
Alder seedlings are associated with actinomycetes and mycorrhizae.
Development of nitrogen-fixing root nodules in European alder is
induced through root-hair infection by actinomycetes of the genus
Frankia. Actinomycetous endophytes isolated from European
alder are cross-infective with other Alnus species and
even other genera such as sweetfern (Comptonia) and
bayberry (Myrica) (38). Thus, even though European alder is not
native to the United States, suitably infective actinomycetes may
be available wherever it is planted (20). On the other hand, in a
greenhouse study, European alders inoculated with native European
endophytes grew six times faster than those inoculated with a
Comptonia isolate (59). Strongly infective Frankia
strains are not necessarily effective in stimulating rapid
alder growth, and those that produce spores may be weak ly
parasitic, rather than symbiotic (58).
European alder has been found associated with at least six
mycorrhizal fungi. Suitable symbionts appear to be widely
available, as both ectomycorrhizae and endomycorrhizae were found
on root samples taken from European alder plantations in Iowa, on
coal strip mines in Ohio, and on kaolin spoils is Georgia (38).
Ecto-, endo- and ectendomycorrhizae were described as associated
with European alder of Bohemian lignite spoil banks. The
endomycorrhizae were found only below 10 cm (4 in) depth (66).
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Soils and Topography
provided by Silvics of North America
European alder grows well on acid soils, and its growth is reduced
under the alkaline or near-neutral conditions that are desirable
for many other species.
The author is Assistant Director, Northeastern Forest Experiment
Station, Radnor, PA.
During their first growing season in most types of soils alder
seedlings form root nodules that are the site of nitrogen
fixation. Seedlings already nodulated grow satisfactorily when
outplanted on sites with pH as low as 3.3; plants not already
nodulated usually die under these very acid conditions (27,77).
Nodules develop satisfactorily at pH as low as 4.2 (8), but
seedlings were stunted and had poor root systems and chlorotic
leaves when grown in clay soil with pH between 8.0 and 8.5 (63).
Optimum soil pH for nodulation appears to be between 5.5 and 7.0
(35). Spoil-bank plantations in Ohio and Kentucky verify the
minimum pH for satisfactory European alder growth as about 3.4
(30,55). On very acid (pH 2.9) coal spoils in Indiana, alder
survival, growth, and root nodule weight were all increased by
liming sufficient to raise pH to at least 6.1 (eventually
declining to 4.8) (41). In a greenhouse experiment using acidic
Pennsylvania mine spoil, alders did not respond to lime
amendments until phosphorus was also added (89).
Both nodulated and nonnodulated alders require molybdenum for
nitrogen metabolism (6,42); adequate amounts of Mo are present in
most soils, although it may not be available on strongly acid
sites. On sites with poor internal drainage, European alder can
tolerate iron concentrations normally toxic to many plants (44).
On tidal flats adjacent to the English Channel, the chlorine
concentration of the soil solution in the root zone of mature
alders occasionally rises to 5 percent of that of sea water
immediately following equinoctial high tides (78).
European alder is responsive to differences in soil moisture
(5,40), and growth often is notably better on lower slopes than
on upper slopes. Alder utilizes intermittently moist sites very
well (56). It is "a species of stream and lake sides and ...
soils of impeded drainage throughout the British Isles,"
although not topographically limited to such sites if rainfall is
high (60). Even though alder tolerates heavy soils better than
most trees, reduced soil oxygen (especially below 5 percent)
inhibits root nodulation and the growth of nodulated plants (57).
In a species with such a broad natural range, altitudinal
distribution is bound to be related to latitude. European alder
is found at sea level at the northern limits of its range, up to
300 in (985 ft) in Norway, 600 in (1,970 ft) in the Harz
Mountains of Saxony, 850 in (2,790 ft) in the Bavarian Mountains,
1300 in (4,270 ft) in the Tyrol and in Greece, and 1800 in (5,900
ft) in the Caucasus (60,88). The most common soils on which it
grows in North America occur in the orders Histosols,
Inceptisols, and Entisols.
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Special Uses
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European alder is valuable f-or wildlife. Because the cones open
gradually and release seed throughout the winter, they are a
dependable source of food for seed-eating birds such as pine
siskins and goldfinches. European alder is recommended for use in
shelterbelts to provide cover for pheasants. When combined with
Prunus laurocerasus and Sorbus aria it makes a
compact planting suitable for establishment adjacent to cropland
(34).
Alders have been recommended for afforestation of disturbed areas
throughout much of the temperate world (46,52). Their tolerance
of low pH and their rapid growth, abundant leaf litter
production, and ability to fix atmospheric nitrogen combine to
make European alder especially desirable for planting on spoil
banks, which typically contain little organic matter and
available nitrogen.
Establishing European alder on mined sites apparently improves
their suitability for earthworm habitat. Ten adult Lumbricus
terrestris worms were released in a 4-year-old A.
glutinosa plantation growing on calcareous coal spoil in
southern Ohio. After 5 years the population had increased to
60/m' (6/ft') as far as 15 m (50 ft) from the point of
introduction and was apparently still increasing, with obvious
desirable implications for hastening soil development (97).
Alder is useful in urban forestry. A system for producing
containerized alder seedlings suitable for park and roadside
planting has been described. Trees grown in Iowa according to
these methods averaged 94 cm (37 in) tall after only 8 months
(19).
Biomass use of European alder has potential. On a river terrace
site in northern Alabama, 6-year-old European alder produced more
than six times as much volume per tree as sycamore (Platanus
occidentalis) of the same age (22). Alders in southern
Illinois, planted at only 998 trees per hectare (404/acre) on a
bottom-land site, produced 54.7 t/ha (24.4 ton/acre) at age 9
(dry weight of entire tree, above ground) (72). Alder may be a
more promising species to grow in short-rotation,
intensive-culture plantations for cattle feed. Protein yield was
nearly that of alfalfa (3).
Aboveground parts of European alder have energy values of about 5
Kcal/g (9,000 Btu/Ib) dry weight. Calorific value of branchwood
is 10 percent greater than that of bolewood (43).
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Vegetative Reproduction
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- European alder commonly
sprouts from the stump after cutting, and live branches can be
layered successfully. Root suckers are rare (60). In coastal
southern Sweden, alders live to maximum age of 100 years
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Distribution
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European alder has a broad natural range that includes most of
Europe and extends into North Africa, Asia Minor, and western
Siberia (82). Densest distribution is in the lowlands of northern
Germany, northern Poland, White Russia, and the northwestern
Ukraine (33). The species is locally naturalized throughout the
northeastern United States and maritime Canada.
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Brief Summary
provided by Silvics of North America
Betulaceae -- Birch family
David T. Funk
European alder (Alnus glutinosa), also called black alder
or European black alder, was introduced to eastern North America
in colonial times. This tree ranges in size from a large shrub to
a large tree. It has escaped cultivation and grows naturally on
lowlying lands. Its rapid growth, tolerance for acid soils, and
nitrogen-fixing role make European alder desirable for
shelterbelts, reclamation areas, landscapes, and biomass
production. It is valuable to wildlife for providing good cover
and a source of seeds.
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