Black alder

Profile

Family

Betulaceae

Habit

Tree

Height

25 m

Spread

10 m

Growth

very fast

Lifespan

120 years

First yield

after 6 years

Hardiness

zone 4–8

Shade tolerance

partial shade

Soil

Silt, Loam, Clay

Soil moisture

semi-dry – near water

pH

4.4 – 7.2

Synonyms

rle

Flowering & harvest

Times apply to the northern hemisphere in a temperate climate and shift with altitude and cultivar.

Uses

Medicinal: Although no specific medicinal uses have been identified for this species, members of this genus are generally very healthy additions to the diet. They contain sulfur compounds that give them their characteristic onion flavor. Consumed regularly, they can help lower blood cholesterol levels, strengthen the digestive system, and support the circulatory system.

Other uses: Alder trees are resilient to pruning and exposure to saltwater, suitable for windbreaks or hedgerows. They have a rapid growth rate of over one meter per year, making them ideal pioneer species for restoring forests on abandoned farmland and challenging terrains. Alders facilitate the fixation of atmospheric nitrogen by binding bacteria to their roots, benefiting neighboring plants. Additionally, they are valuable for land reclamation and biomass production. The annual productivity of alders ranges from 6 to 9 tons per hectare, with an estimated yield of 11.8 tons of pulverized fuel ash and 8.66 tons per hectare annually. Alders are recommended for firewood plantations in tropical highlands. The bark of alder trees has been historically used in toothpaste and as a natural dye. Alder wood, known for its water resistance, flexibility, softness, and ease of handling, is commonly utilized in furniture making, pencil production, bowl crafting, and other wooden items.

Growing

The black alder thrives in heavy soils and moist areas, tolerating flooding and standing water up to 30 cm deep. It can grow rapidly in drier regions but has a shorter lifespan there. Black alders do well in clay soils, limestone, and nutrient-poor locations, preferring a pH above 6. They are highly tolerant of maritime conditions. Leaves typically stay green on the trees until late autumn, especially in young plants. The seeds have air-filled tissue layers that enable them to float in water for about 30 days before getting waterlogged, aiding in their dispersal. Black alders grow rapidly in their initial years, with specimens reaching 4 meters in height by age 5, even in windy areas like Cornwall. This species forms a symbiotic relationship with soil microorganisms that fix atmospheric nitrogen in nodules on the roots. The tree utilizes some of this nitrogen, with the rest benefiting nearby plants. Nitrogen fixation rates range from 125 kg/ha/year for trees up to 8 years old to 56–130 kg/ha/year for 20-year-old trees. The trees develop adventitious roots near the trunk base, enhancing stability in loose soils. Black alders are a vital food source for caterpillars of various butterfly and moth species, as well as for small birds in winter. Around 90 insect species are linked to this tree. Numerous ornamental cultivars have been named for their aesthetic appeal. Black alders can withstand heavy pruning and were historically pruned extensively for their versatile wood.

Propagation

Seeds are most successful when sown right after reaching maturity in a cool environment, lightly covered. Spring-sown seeds can also sprout well if left uncovered. Germination usually occurs in spring with the warming weather. Once the seedlings are sufficiently grown, they should be moved to individual pots. If they grow well, they can be transferred to their final spot in the summer; otherwise, they should stay in outdoor pots and be planted in the spring. There are approximately 700,000–750,000 seeds per kilogram, but typically only 20,000–25,000 viable seedlings are produced. Seeds can stay viable for up to a year after floating in water. They germinate equally well in continuous darkness as in regular daylight. Seeds that are air-dried and stored at 1–2°C can remain viable for two years. Nonetheless, seeds can also be sown immediately after reaching maturity. If you have an ample supply of seeds, they can be thinly sown in an outdoor bed in the spring. The seedlings can be transplanted to their permanent spot in the fall/winter or left to grow in the bed for another season before transplanting. Cuttings from mature wood should be taken outdoors and placed in sandy soil right after the leaves fall in autumn.

Notable

Special features: Calorific value per annual growth: 32,800 kWh/ha; 70 kg nitrogen/ha; At 20-25 years, the wood is already ready for harvest; low calorific value, but low smoke; black ink from alder cones; young twigs as sticky mosquito traps; stilt houses like those in Venice on water-resistant alder wood; ~2.1% of German forests; 1,500 kWh/m²; 4.1 kWh/kg waterlogged wood is as hard and strong as oak

Origin & habitat

In water bodies, along rivers, wet areas, and as part of bogs.

Forests and dense vegetation, particularly in deep, well-drained soils rich in calcium.

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