Alder

Introduction

The Alder is a common name for a genus of flowering plants, Alnus, belonging to the birch family Betulaceae. The genus comprises about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the North Temperate zone, and extending southwards in the Andes, the mountains of northern Africa, and from southwest Asia eastwards to Japan.

Description

Alders are generally small to medium-sized trees and shrubs. They are characterized by simple, serrated leaves that are often alternately arranged on the branches. The flowers are catkins with elongate male catkins on the same plant as shorter female catkins, often before leaves appear; they are mainly wind-pollinated, but also visited by bees to a small extent. These trees differ from other members of the birch family in that they have surface roots, and the leaves are usually more or less rounded.

Alder tree with its distinctive serrated leaves and catkins.

Distribution and Habitat

Alders are commonly found near streams, rivers, and wetlands where they help to control erosion and provide shade. Climate-wise, they are often found in cool temperate regions. In the Americas, alders are distributed from Alaska and Newfoundland south to Central America, but are mostly absent from the southeastern United States. In Europe, it is the second most common tree species.

Ecology

Alders play a crucial role in maintaining a healthy ecosystem. They improve the fertility of the soil where they grow by fixing nitrogen from the air into a form that other plants can use. This is done through a symbiotic relationship with a nitrogen-fixing bacterium called Frankia alni. This bacterium is found in the root nodules of alders, and together they enrich the soil, allowing other plants to thrive in areas where they would otherwise struggle.

Uses

Alders have been used for a variety of purposes throughout history. The wood of certain alder species is often used for smoking fish and meat, as it imparts a distinct flavor. The bark of alders has been used in the traditional medicine of several indigenous North American tribes to treat various ailments. Alders are also used in reforestation efforts and for erosion control due to their ability to thrive in poor soils and their rapid growth.

Conservation

While alders are not typically considered endangered, some species are under threat due to habitat loss. Conservation efforts for these species are focused on habitat preservation and the prevention of further loss. In areas where alder populations have declined, reforestation efforts are often undertaken to help restore the balance of the ecosystem.