Alder

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Alder catkins - 1 (2222383479)

Alnus serrulata

LUT SEM Alder pollen 3kx

Alnus incana rugosa leaves

Alnus serrulata leaves

Alder is a common name for trees belonging to the genus Alnus, which is part of the birch family, Betulaceae. This genus comprises about 35 species of monoecious trees and shrubs, which means that they bear both male and female flowers on the same plant. Alders are native to the temperate zones of the northern hemisphere, including parts of North America, Europe, and Asia. They are particularly noted for their ability to thrive in wet conditions, often found near streams, rivers, and wetlands. Alders play a significant ecological role in forest ecosystems, especially in riparian zones.

Description

Alders are characterized by their glossy green leaves, which are typically serrated or scalloped. The trees produce catkins, with the male catkins being long and pendulous and the female catkins more compact and oval-shaped. After pollination, female catkins mature into woody cones that contain the seeds. Alder wood is light and soft but is durable under water, making it historically valuable for various uses, including the construction of water pipes, clogs, and foundations for buildings in waterlogged areas.

Ecology

One of the most remarkable features of alders is their symbiotic relationship with the nitrogen-fixing bacterium Frankia alni. This bacterium forms nodules on the roots of alder trees, converting atmospheric nitrogen into a form that the tree can use. This ability allows alders to grow in poor soil conditions and also enriches the soil with nitrogen, making it more fertile for other plant species. This nitrogen-fixing capability makes alders an important pioneer species in disturbed environments, where they can help to stabilize the soil and pave the way for the succession of other plant species.

Uses

Historically, alder wood has been used for a variety of purposes due to its resistance to decay when submerged in water. It has been utilized in the construction of bridges, boats, and even the foundations of buildings in Venice. In addition to its use in construction, alder wood is valued for furniture making and as a source of charcoal for gunpowder and cooking. The bark of the alder tree has been used in traditional medicine and for dyeing.

Species

Some well-known species of alder include the Black Alder (Alnus glutinosa), native to Europe, and the Red Alder (Alnus rubra), which is the largest species of alder native to North America. Each species of alder has adapted to its specific environment, with variations in size, leaf shape, and habitat preferences.

Conservation

While alders are not currently listed as endangered, their habitats, especially wetlands and riparian zones, are under threat from human activity, including development and pollution. Conservation efforts are important to preserve these ecosystems, which are vital for the biodiversity they support, including the alder trees.