black walnut (Juglans nigra)
eastern black walnut
SCIENTIFIC SYNONYMS: There are no scientific synonyms for
CONFIRMATION STATUS: Confirmed.
TAXONOMY: The currently accepted scientific name for black walnut
is Juglans nigra L. There are no recognized subspecies, varieties, or forms.
Black walnut and butternut (Juglans cinerea) often grow together but
apparently never cross naturally.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS: Black walnut is a
native, deciduous tree that can grow to a height of 125 feet (38 m) but
ordinarily grows to around 80 feet (25 m). Black walnut develops a long,
smooth trunk and a small rounded crown when growing in the forest. In
the open, the trunk forks low with a few ascending and spreading coarse
branches. The root system usually consists of a deep taproot and several
wide-spreading lateral roots. The bark on young trees is dark and scaly
but becomes darker with rounded intersecting ridges on mature trees.
REGENERATION PROCESSES: Black walnut produces abundant seed
crops irregularly, perhaps twice in 5 years. Although open-grown trees
produce seed as early as 8 years after planting, the minimum seed-bearing
age for commercial quantities of seed is about 12 years. Best seed
production begins when the tree is about 30 years old and continues for
another 100 years.
Black walnut seed is heavy. The seeds are dispersed by squirrels carrying
seed from beneath the tree and burying them at a distance.
Many black walnut seedlings germinate from the nuts cached by squirrels
in the fall. Normal freezing and thawing usually causes the seeds to break
dormancy the following spring, but germination is often delayed, sometimes
until the second year.
Small black walnut trees usually sprout from the stump when they are cut
or killed back by fire. Shoots originating high on the older stumps often
decay, but shoots from the root crown generally are free from defect.
SITE CHARACTERISTICS: Black walnut is found on a variety of sites
but grows best on deep, well-drained neutral soils that are moist and fertile.
It grows slowly on wet bottomlands, dry ridges, and slopes. Black walnut is
common on limestone soils and grows extremely well on deep loams and
fertile alluvial deposits. Good agricultural soils are generally favorable sites
for black walnut. In the Appalachians, the best wlanut trees are found on
bottomlands and coves below 4,000 feet (1,200 m). Common tree
associates include American elm (Ulmus americana), hackberry (Celtis
laevigata), green ash (Fraxinus pennsylvanica), box elder (Acer negundo),
and butternut (Juglans cinerea).
SUCCESSIONAL STATUS: Black walnut is classified as shade
intolerant. In mixed forest stands, it must be dominant to survive,
although it can survive in the relatively light shade of black locust. Black
walnut is found in many of the climax associations but because of its
intolerance is not classified as a climax tree in the strict sense. In general,
black walnut maintains itself in most stands as scattered single trees
occupying openings in the canopy.
SEASONAL DEVELOPMENT: Black walnut normally begins flowering
about mid-April in the southern part of its geographic range and mid-June
in the northern part of its range. The fruit ripens in September or October
of the same year, dropping shortly after the leaves fall.
GENERAL DISTRIBUTION: Black walnut is found throughout the
eastern United States. It grows as far north as southern Minnesota,
southern Wisconsin, southern Michigan, and southern Ontario. Isolated
populations occur in the southern half of New York, Vermont, western
Massachusetts, and northwestern Connecticut. Its range extends south to
northwestern Florida, and to Mississippi, Arkansas, and Louisiana except
for the Mississippi Valley and Delta regions. In the Midwest, isolated
populations occur in eastern Texas, western Oklahoma, central Kansas,
and southeastern South Dakota. Black walnut is cultivated in Hawaii.
SKY MEADOWS DISTRIBUTION:
Tree specimens can be found on trails marked in red.
Appalachian Trail/Old Trail
South Ridge/North Ridge
Rolling Meadows/ Lost Mountain
HABITAT TYPES AND PLANT COMMUNITIES: Black walnut grows
in many of the mixed mesophytic forests but is seldom abundant. Usually it
is found scattered among other trees; pure stands are rare, small, and usual-
ly located on the forest edge. Black walnut is a common associate in five
forest cover types in the central hardwood zone and the Appalachian high-
lands, Yellow-Poplar at lower elevations of the Appalachians, Yellow-Poplar
-White Oak-Northern Red Oak at lower elevations, Beech-Sugar Maple in
the Midwest, and Silver Maple-American Elm in southern Ontario wash-
board swamps where high and low ground intermingle. It is also found as
an occasional associated species in four cover types: Chestnut Oak, White
Oak-Black Oak-Northern Red Oak, Northern Red Oak on moist sites, and
Sassafras-Persimmon in older stands.
Chief associated species include yellow-poplar (Liriodendron tulipifera),
white ash (Fraxinus americana), black cherry (Prunus serotina), basswood
(Tilia americana), beech (Fagus grandifolia), sugar maple (Acer
saccharum), oaks (Quercus spp.), and hickories (Carya spp.). Near the
western edge of its range, black walnut may be confined to floodplains,
where it grows either with American elm (Ulmus americana), hackberry
(Celtis occidentalis), green ash (Fraxinus pennsylvanica), and boxelder
(Acer negundo), or with basswood and red oak (Quercus rubra) on lower
slopes and other favorable sites. No universal vegetative indicator of a
good walnut site is known, but the presence of Kentucky coffeetree (Gym-
nocladus dioicus) seems to indicate such a site. In general, where yellow-
poplar, white ash, red oak, basswood, sugar maple, or slippery elm (Ulmus
rubra) grow well, black walnut thrives also.
An antagonism between black walnut and many other plants growing within
its root zone has been recognized and is attributed to juglone, a toxic sub-
stance found in the leaves, bark, nut husks, and roots of walnut trees. Some
tree species apparently are immune, but others, such as paper birch (Betula
papyrifera), red pine (Pinus resinosa), white pine (Pinus strobus), Scotch
pine (Pinus sylvestris), and apple (Malus spp.), reportedly are sensitive.
Tomatoes are especially susceptible. In a laboratory study, juglone at high
concentrations was lethal to four coniferous species, but seedling growth
was actually promoted when exposed to minute concentrations. Although
tomatoes are especially susceptible to juglone, black walnut trees may be
compatible with some agricultural crops and might even improve the growth
of bluegrass (Poa spp.).
IMPORTANCE AND USES: The nuts of black walnut furnish food
for many rodents and make up about 10 percent of the diet of eastern
fox squirrels. The nuts are also eaten by a variety of birds. Although not
considered a choice browse, black walnut leaves are palatable to white-
tailed deer. The eastern screech-owl roosts on the limbs of black walnut.
Black walnut has been successfully planted on surface mined areas in the
eastern United States. In southwestern Indiana, black walnut had a 30 to
50 percent increase in survival rate on old mine field sites where weed
competition had been chemically controlled or removed.
Black walnut wood is heavy, strong, and highly resistant to shock. It ranks
with the most durable U.S. hardwoods, including cedars (Thuja spp.),
chestnuts (Castanea spp.), and black locust (Robinia pseudoacacia). It can
be satisfactorily kiln dried and holds it shape well after seasoning. Black
walnut is normally straight grained, is worked easily with hand tools, and
has excellent machining properties. When finished, the wood takes on a
smooth velvety surface and a handsome grain pattern.
Black walnut is used principally for dining room and bedroom furniture;
bookcases; desks; tables; radio, television, phonograph, and piano cabinets;
and as an interior finish in cafes and public buildings. The veneer is used for
the highest grade cabinets and plywood panels. Figured black walnut stocks
are prized for expensive shotguns and sporting rifles.
The nuts of black walnut are used as food by humans and are harvested
commercially. The nuts are eaten plain or with honey and used to flavor
cakes, candy, and ice cream. Native Americans used the nuts for food and
extracted black dye from the roots. The black walnut is mentioned in
Native American creation myths. Black walnut is cultivated as an
The ground shells of black walnut are used as a nonslip agent in automobile
tires, as an air pressure propellant in strip paints, and as a filtering agent
for scrubbers in smoke stacks. The automobile industry uses the ground
shell products to deburr precision gears, and the airline industry uses the
ground shells to clean jet engines.
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