Associated Forest Cover
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Butternut is found with many other tree species in several
hardwood types in the mixed mesophytic forest. It is an
associated species in the following four northern and central
forest cover types (5): Sugar Maple-Basswood (Society of American
Foresters Type 26); Yellow-Poplar-White Oak-Northern Red Oak
(Type 59); Beech-Sugar Maple (Type 60); and River Birch-Sycamore
(Type 56). Commonly associated trees include basswood (Tilia
spp.), black cherry (Prunus serotina), beech (Fagus
grandifolia), black walnut (Juglans nigra), elm (Ulmus
spp.), hemlock (Tsuga canadensis), hickory (Carya
spp.), Oak (Quercus spp.), red maple (Acer
rubrum), sugar maple (A. saccharum), yellow-poplar
(Liriodendron tulipifera), white ash (Fraxinus
americana), and yellow birch (Betula alleghaniensis).
In the northeast part of its range, it is often found with
sweet birch (Betula lenta) and in the northern part of
its range it is occasionally found with white pine (Pinus
strobus) (4,15). Forest stands seldom contain more than an
occasional butternut tree, although in local areas it may be
abundant. In the past, West Virginia, Wisconsin, Indiana, and
Tennessee have been the leading producers of butternut timber.
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Climate
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Climatic conditions within the botanical range of butternut vary
widely. Mean annual temperature ranges from 16° C (60°
F) in Alabama to 4° C (40° F) in New Brunswick, with an
average maximum of 41° C (105° F) and minimum of -34°
C (-30° F). Annual precipitation ranges from 630 mm (25 in)
in southeastern Minnesota to 2030 mm (80 in) in the southern
Appalachians. The frost-free period is 210 days in the southern
part of the range and 105 days in the northern part (6).
Butternut is generally considered to be more winter-hardy than
black walnut.
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Damaging Agents
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Insect enemies of butternut are often
pests of associated trees as well. Some insects commonly found on
butternut include wood borers, defoliators, nut weevils,
lacebugs, husk flies, and bark beetles. The most serious insect
pest at this time is the butternut curculio (Conotrachelus
juglandis), which injures young stems and fruit (8,21).
The most serious disease of Juglans cinerea is butternut
decline or butternut canker. In the past the causal organism of
this disease was thought to be a fungus, Melanconis
juglandis; but now this fungus has been associated with
secondary infections and the primary causal organism of the
disease has been identified as another species of fungus, Sirococcus
clavigignenti-juglandacearum. Symptoms of the disease include
dying branches and stems. Initially, cankers develop on branches
in the lower crown. Spores developing on these dying branches are
spread by rainwater to tree stems. Stem cankers develop 1-3 years
after branches die. Tree tops killed by stem-girdling cankers do
not resprout (19,20). Diseased trees usually die within several
years (11,16). The disease is reported to have eliminated
butternut from North and South Carolina (1). The disease is also
reported to be spreading rapidly in Wisconsin; between 1978 and
1983 the incidence of butternut canker in a young, isolated
plantation increased exponentially from 5 percent in 1976 to 76
percent in 1983 (20). By contrast, black walnut seems to be
resistant to the disease.
Bunch disease also attacks butternut. Currently, the causal agent
is thought to be a mycoplasmalike organism. Symptoms include a
yellow witches'broom resulting from sprouting and growth of
axillary buds that would normally remain dormant. Infected
branches fail to become dormant in the fall and are killed by
frost; highly susceptible trees may eventually be killed.
Butternut seems to be more susceptible to this disease than black
walnut (2,17).
The common grackle has been reported to destroy immature fruit and
may be considered a butternut pest when populations are high
(14).
Butternut is very susceptible to fire damage, and although the
species is generally windfirm, it is subject to frequent storm
damage (4).
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Flowering and Fruiting
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Butternut flowers from April to
June, depending upon location. The species is monoecious; male
flowers are slender catkins that develop from axillary buds and
female flowers are short terminal spikes home on current year's
shoots. Flowers of both sexes do not usually mature
simultaneously on any individual tree (3).
The fruit is an oblong-ovoid pointed nut, 3.8 to 5.5 cm (1.5 to
2.2 in) long, that matures in September and October of the year
of pollination. Nuts occur singly or in clusters of from 2 to 5.
The kernel or seed of the nut is sweet, oily, and edible. The nut
is enclosed by an indehiscent husk that contains a glandular
pubescence on the surface. The fruit usually remains on the tree
until after leaf fall (3).
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Genetics
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Butternut hybridizes with English walnut (Juglans regia L.)
to produce J. x quadrangulata (Carr.) Rehd. It
also crosses with Japanese walnut J. ailantifolia Carr.
to produce J. x bixbyi Rehd. Butternut is also
reported to successfully hybridize with little walnut (J.
microcarpa Berland.) and Manchurian walnut (J.
mandshurica Maxim.) (6,14). Reports of crosses between
butternut and black walnut have not been substantiated. Butternut
is thought to have a haploid chromosome number of 16.
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Growth and Yield
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Butternut grows fast, especially as a
seedling, although it usually does not live longer than 75 years
and is short lived in relation to its common tree associates.
Mature trees rarely reach a height of more than 30 m (100 ft) and
a d.b.h. of 91 cm (36 in). Average-sized trees are from 12 to 18
m (40 to 60 ft) in height and 30 to 61 cm (12 to 24 in) in d.b.h.
(4).
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Reaction to Competition
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Although young trees may
withstand competition from the side, butternut does not survive
under shade from above. It must be in the overstory to thrive
and, therefore, is classed as intolerant of shade and
competition.
Like other members of the Juglandaceae family, butternut produces
a substance called juglone, a naphthoquinone that is selectively
toxic to associated vegetation. Greatest concentrations of
juglone are in root tissue and fruit husks with lesser amounts in
leaves, catkins, buds, and inner bark (12,13).
Within its optimum range and on good sites, butternut is usually
considered a desirable component of forest stands; it has been
classed as a "less desirable" tree in southern
Appalachian coves (4).
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Rooting Habit
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On favorable sites the root system is deep,
but it also may be widespreading.
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Seed Production and Dissemination
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Commercial seed-bearing
age begins at about 20 years and is optimum from age 30 to 60
years. Good crops can be expected every 2 to 3 years, with light
crops during intervening years. Thrifty trees may yield 9 to 35
liters (0.25 to 1 bushel) of cleaned seeds. A high percentage of
mature seeds are sound, but high premature seed losses in
butternut have been reported. Possible causes include consumption
by insects, birds, and rodents as well as natural pollination
failures due to a lack of pollinating trees in the immediate
vicinity (4,10,14,21).
Upon ripening, seeds are dispersed by gravity and by squirrels and
other rodents. At this time, the seeds are dormant. Cold
stratification for 90 to 120 days at temperatures of 20° to
30° C (68° to 86° F) overcomes dormancy.
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Seedling Development
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Seeds of butternut usually
germinate in the spring following seedfall.
Germination is hypogeal. Seedlings develop a taproot on all sites
except the most shallow soils, but the taproot is much less
pronounced than on black walnut. In general, butternut seedlings
have more fibrous root systems than black walnut.
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Soils and Topography
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Butternut grows best on streambank sites and on well-drained
soils; it is seldom found on dry, compact, or infertile soils. It
grows better than black walnut, however, on dry, rocky soils,
especially those of limestone origin.
Butternut is found most frequently in coves, on stream benches and
terraces, on slopes, in the talus of rock ledges, and on other
sites with good drainage, primarily on soils of the orders
Alfisols and Entisols. It is found up to an elevation of 1500 in
(4,900 ft) in the Virginias, at much higher altitudes than black
walnut (4,18).
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Special Uses
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Cultivars of this species have been selected for nut size and for
ease of cracking and extracting kernels. Several cultivars have
been named (14). Nuts are especially popular in New England for
making maple-butternut candy. Small amounts of wood are used for
cabinets, toys, and novelties.
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Vegetative Propagation
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Stumps of young butternut trees
and saplings are capable of sprouting. Also, butternut can be
propagated by grafting, although the techniques have not yet been
perfected. Various degrees of success have been demonstrated with
intra-specific as well as inter-specific grafting in the genus
(9).
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Distribution
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Butternut is found from southeastern New Brunswick throughout the
New England States except for northwest Maine and Cape Cod. The
range extends south to include northern New Jersey, western
Maryland, Virginia, North Carolina, northwestern South Carolina,
northern Georgia, northern Alabama, northern Mississippi, and
Arkansas. Westward it is found to central Iowa and central
Minnesota. It grows in Wisconsin, Michigan, and northeast into
Ontario and Quebec. Through most of its range butternut is not a
common tree, and its frequency is declining (4). The ranges of
butternut and black walnut (Juglans nigra) overlap, but
butternut occurs farther north and not as far south as black
walnut.
-The native range of butternut.
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Brief Summary
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Juglandaceae -- Walnut family
George Rink
Butternut (Juglans cinerea), also called white walnut or
oilnut, grows rapidly on well-drained soils of hillsides and
streambanks in mixed hardwood forests. This small to medium-sized
tree is short lived, seldom reaching the age of 75. Butternut is
more valued for its nuts than for lumber. The soft coarse-grained
wood works, stains, and finishes well. Small amounts are used for
cabinetwork, furniture, and novelties. The sweet nuts are prized
as a food by man and animals. Butternut is easily grown but must
be transplanted early because of the quickly developing root
system.
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