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Issue No. 149 - January 30, 2005
by Sue Sweeney
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| Our native black walnuts are forest trees; they like to
stretch their roots in deep, rich, moist, acidy forest soil. However,
even the babies can’t tolerate shade, so new black walnut trees have
trouble getting started except in clearings and at the forest edge.
Further, the nuts are so large and heavy that the squirrels can’t
transport them very far. Thus, the only way for the seeds to be
disbursed over long distances is by water (hence, the prevalence of
black walnuts along forest streams) and by human. |
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picture: mature black walnut with the back
of the new courthouse in the background (Juglans nigraa),
Bedford
Street Stamford, CT January 2004 |
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While young black walnuts (Juglans nigra) can be easily
confused with the alien ailanthus, and with other trees with
palm-like pinnately compound leaves, such as the native staghorn
sumac, ash, and locust, there’s no mistaking the lime green
“golf ball” nuts on teenage and mature black walnut trees. |
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picture: mature black walnut (Juglans
nigraa), Bedford Street Stamford, CT September 2004 |
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Black walnuts have developed two strategies to help over
come these reproductive limits. First, the young trees
grow fast (for a hardwood tree, that is). This
trait helps a sapling take advantage of a short-term gap
in the forest canopy or other shade source. Second, like
the ailanthus, the black walnut is an allelopath. It
produces chemicals that literally kill off competing
plants. Interestingly, the chemicals that black walnuts
produce are particularly poisonous to the solanaceae
family (tomatoes and kin- see Issue 117),
several other garden vegetables, conifers, and the malus
family (apple, hawthorn, serviceberry, etc). The
conifers make sense because juniper, for example, would
be an edge-of-forest competitor. However, as for the
others, who knows what happened a million years ago when
these survival traits were evolving?
In pre-Columbian times, there were absolutely HUGE
black walnuts, 100 to 150 feet, gracing the eastern
American forest from Zone 4 to Zone 8, west through the
Great Plains. These mature black walnuts were massive,
long-lived beings, standing tall and straight with a
high, small crown in the forest; and spreading wide as a
white oak when alone in a meadow. However, the dark,
hard, satin grained lumber was so prized by the European
settlers that, sadly, almost all of the old growth trees
were chopped down long ago. The wood continues to be so
valued today that medium-size trees are cut down to use
for veneer – crafting objects out of solid black walnut
is a thing of our colony past. |
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picture: massive, spreading form of a
mature open-grown black walnut. Stamford CT January 2005. |
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Despite the wonders of the wood, the nuts may be the
tree’s best and worst feature. The nut meats are
delicious—we like them in deserts; squirrels and mice
take theirs plain. However, getting to the meat is a
challenge. The thick, soft outer shell covering which
starts out lime green and ages to dark brown, contains a
dye which will stain you hands and clothes. It’s not
generally harmful to people but it does contain the
black walnut’s allelopathic chemicals so don’t throw the
husks in the compost heap. Then, inside the husk is a
very, very hard shell. Try a hammer. |
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picture: fallen black walnuts, striped of
the outer husk; one has been gnawed open by a squirrel or a mouse.
Stamford CT Winter 2004-05 |
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The other problem with the nuts is that there are so
many of them on an adult tree. Generally, many more than
a family (and the neighborhood squirrels) can use, and
what do you do with the rest? Remember, also that the
nuts are big – do not plant this tree close to your
house unless you’d like your decedents to stay awake
nights listening to the thud of walnuts hitting the
roof. |
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pictures: detail of nuts which persist
on the branches after the leaves have fallen. |
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IDENTIFICATION: It’s easy to distinguish black
walnuts from other trees when the signature nuts are
present (which is most of the time, if you count the
shells on the ground). With a little more information,
you can tell the difference the rest of time, too.
FORM AND BARK: The young black walnut trees have the
same up-reaching, blunt, twigless branches like
ailanthus and staghorn sumac. However, there are clear
differences. First, the black walnut develops rough,
craggy back at a very young age, while ailanthus and
staghorn sumac are still smooth-ish with prominent
lenticels (bark pores). The mature black walnuts have a
craggy, spreading nut tree shape—staghorn sumac don’t
get this big and ailanthus are always up-swept, and
comparatively lithe and curvy. The mature black walnuts
have very deeply furrowed bark. Also, the bark is much
darker than that of mature ailanthus and staghorn sumac. |
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picture: believe it or not;
the young tree on the left is a black walnut and the one of the right is
a slightly older ailanthus. |
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pictures: bark of 3”, 12” and 24”
diameter black walnut trunks. Note that even the young 3” tree to the
left has very rough bark. The base of tree to the right is encircled
with an invasive euonymus. Unfortunately, even the black walnut
allelopathic properties don’t deter this unwanted alien. |
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TWIG AND BUD: the winter twig and bud are very
different from ailanthus and staghorn sumac. As you
recall from last week, the ailanthus and staghorn sumac
winter twigs are smooth and blunt with knobby buds,
prominent lenticels, and large, flattish leaf scars, the
black walnut has whitefish –grayish furry buds and
3-lobed leaf scars often called “monkey faces”. |
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pictures: close up of bud and of prior
years’ leaf scars Stamford CT January 2005 |
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Picture: buds and leaf scars. January
2005. |
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LEAVES: while the leaves of staghorn sumac,
ailanthus, black walnut, ash, etc, look much alike for a
distance, close up, the leaf detailing is different.
Like ailanthus and staghorn sumac, the black walnut’s
numerous stemless leaflets are opposite on the long leaf
stalk and the leaf stalks are alternate.
However, there’s one leaf detail that only the black
walnut has: a tiny notch on one side of the midrib just
where the leaflet attaches to the stalk. In addition,
the leaflets are toothed, with paler, hairy undersides;
this rules out ailanthus which has a smooth leaf margin
with a single lobe at the leaf’s bottom. The teeth are
much finer than the sumac’s. In addition, the black
walnut often lacks the single, terminal leaflet that
ailanthus and staghorn sumac always have. |
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pictures: leaf detail; note the notch
at the base of the leaflet, the fish tail like curve of the leaflets and
the missing terminal leaf. (Some black walnuts have a small terminal
leaf). |
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picture: in midsummer, the black walnut
provides dappled shade. Stamford CT 2004 |
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Wildlife: For reasons unknown, the eastern
screech owl prefers to roost in black walnuts (perhaps
they’re attracted by the mice nibbling on fallen nuts).
Several birds are said to eat the nuts as do squirrels
and mice. (Query: how do the birds get the nuts open?).
Deer, rabbit, and mice will browse the young trees. |
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