黑胡桃种

Black walnut is an important tree commercially, as the wood is a deep brown color and easily worked. Walnut seeds (nuts) are cultivated for their distinctive and desirable taste. Walnut trees are grown for lumber and food, and processors have found additional markets for even the tough outer hulls by finely grinding them for use in products such as abrasive cleansers. Many cultivars have been developed for improved quality wood or nuts. In 2017, the United States Department of Agriculture valued U.S. walnut timber at $530 billion. A significant amount is grown in Missouri.

Black walnut is allelopathic, releasing chemicals from its roots and other tissues that may harm other organisms and give the tree a competitive advantage, but there is no scientific consensus that this is a primary competitive factor.

Black walnut is susceptible to thousand cankers disease, which provoked a decline of walnut trees in some regions.

Description

The tree grows to 30–40 m (100–130 ft) tall. Under forest competition, it develops a tall and straight trunk. When grown in an open area it has a short trunk and broad crown. The bark is typically grey-black and deeply furrowed into thin ridges that gives the bark a diamond-shaped pattern.

The pith of the twigs is chambered and light brown. The buds are pale silky and covered in downy hairs. The terminal buds are ovate, and 8 mm (5⁄16 in) long, and slightly longer than broad, the lateral buds are smaller and superposed.

The leaves are pinnately compound and alternately arranged on the stem. They are 30–60 cm (1–2 ft) long, typically even-pinnate but there is heavy variation among leaves. The stems have 15–23 leaflets, when terminal leaf is included, with the largest leaflets located in the center, 7–10 cm (2+3⁄4–4 in) long and 2–3 cm (3⁄4–1+1⁄4 in) broad. The leaflets have a rounded base and a long pointed (acuminate) tip as well as having a serrated edge. The leaves are overall dark green in color and are typically hairy on the underside.

Distribution and habitat

The species is native to North America. It grows mostly in riparian zones, from southern Ontario, west to southeast South Dakota, south to Georgia, northern Florida and southwest to central Texas. Wild trees in the upper Ottawa Valley may be an isolated native population or may have derived from planted trees. The range of the black walnut is strongly correlated with low maximum vapour-pressure deficit.

Ecology

Black walnut is primarily a pioneer species similar to red and silver maple and black cherry. Because of this, black walnut is a common weed tree found along roadsides, fields, and forest edges in the eastern US. It will grow in closed forests, but is classified as shade intolerant; this means it requires full sun for optimal growth and nut production.

Black walnut's native range extends across much of the eastern US. It is absent from the coastal plain south of North Carolina as well as the Mississippi Valley, and does not occur in the northern tier of the eastern US, where the frost-free season is too short for the nuts to develop. Its western range extends all the way to the eastern Great Plains, beyond which climate conditions become too dry for it.

Cultivation

The fruit production tends to occur irregularly with some years producing larger crops than others (see mast year). Fruiting may begin when the tree is 4–6 years old, but large crops take 20 years. Total lifespan of J. nigra is about 130 years. Like other trees of the order Fagales, such as oaks, hickories, chestnuts, and birches, it is monoecious, with wind-pollinated catkins. Male and female flowers are in separate spikes, and the female flowers typically appear before the male on a single tree (dichogamy). As a consequence, self-pollination is unlikely. However, individual trees are commonly self-compatible; if they are not pollinated by neighboring trees, they may set self-fertilized seeds. For maximum seed germination, the seeds should be cold-moist stratified for 3–4 months, although the exact time depends on the seed source. The seedlings emerge in April or May.

Uses

As food

Black walnut kernels are edible. The nut provides a robust, distinctive, natural flavor and crunch as a food ingredient. Common uses include ice cream, bakery goods and confections. Consumers include black walnuts in traditional treats, such as cakes, cookies, fudge, and pies, during the fall holiday season. The nuts are versatile for uses in other foods, such as salads, fish, pork, chicken, vegetables and pasta dishes.

Tapped in spring, the tree yields a sweet sap that can be drunk or concentrated into syrup or sugar not unlike that of sugar maple.

Nutrition

Black walnut kernels are 5% water, 59% fat, 24% protein, and 10% carbohydrates. In a reference amount of 100 g (3.5 oz), walnuts supply 619 calories and several micronutrients in rich amounts at 20% or more of the Daily Value (DV), including the dietary minerals manganese (169% DV) and copper (156% DV), among others, and the B vitamins, B6 (34% DV) and pantothenic acid (33% DV). Black walnut kernels are a moderate source (10–19% DV) of vitamin E and riboflavin.

Largest trees

The U.S. national champion black walnut, also known locally as the Sauvie Island Tree, was situated on a residential property on Sauvie Island, Oregon. It was 8 ft 7 in (2.62 m) diameter at breast height and 112 ft (34 m) tall, with a crown spread of 144 feet (44 m).

In the mid-2010s, it was clear that the tree was in visible decline. In 2019, it was confirmed that the tree was succumbing to Thousand Cankers Disease, and plans were set in place to fell the tree to mitigate the risk of disease being spread.

In August 2020, workers brought down the tree with the use of specialised equipment.

Slabs cut from the tree have been salvaged for reuse, as the timber is highly regarded in the woodworking industry.

The tallest black walnut in Europe is located in the Woluwe Park in the city of Sint-Pieters-Woluwe, Brussels, Belgium. It has a circumference of 3.50 m (11 ft 6 in), height of exactly 33.60 m (110.2 ft) (measured by laser), and was planted around 1850 (± 10 years).