Alder trees (Alnus glutinosa) are small trees that belong to the birch family. Mostly bees pollinate its male and female flowers. Alders are the most common tree in a riparian forest, which is a forested area next to a body of water such as a stream or river. These trees have been linked with superstition, as in Ireland where it's thought to be unlucky to pass an Alder tree when travelling on a journey.
The Alder tree's main characteristic is its catkins, which are thin cylindrical flowers without visible petals that are clustered together. These catkins, which are elongated, fall off at the same time the tree's fruit falls. Alders have round leaves with jagged margins and short stalks. When the leaves are young they're gooey and hairy; their Latin name, glutinosa, means "sticky." As leaves mature they develop a dark olive green colour.
Size and Longevity
According to Rosawood.com, some alders can grow considerably tall, reaching a height of about 82 feet (about 25 meters), although the typical Alder tree rarely is about over 65 feet tall (about 20 meters). They grow quickly, at a rate of almost 3 feet (about 90cm) a year, but are somewhat short-lived having a lifespan of around 150 years.
The Alder tree is found in Japan and throughout Asia north of the Himalayas, as well as North Africa, Europe and North America. In South America Alders grow along the Andes Mountains into Chili. Although Alders are mostly grown as shrubs in most of the United States and Canada, they're tree-sized in the higher elevations of Oregon and Alaska.
Alder trees have many benefits such as serving as natural windbreaks. They play an important role in stream woodlands. The tree's foliage provides shade for fish such as brown trout and salmon. Because they have deep roots, they help maintain soils in riverbanks which reduces damage from erosion. Wood from the tree is useful in cabinetry and furniture making. It's used to build bridges, pumps and troughs. Alder timber is water resistant, making it useful in underwater construction. The wood also produces excellent charcoal.
There are 30 species of alders, including both trees and shrubs. The Red Alder is the largest of all alder trees. This tree grows on the western coast of North American. The Black Alder grows throughout Europe and gives a wintergreen fragrance when crushed. The Green Alder, which is the rarest type, is so small, it's considered a shrub.
Alder trees do best in acidic soil and when their roots are somewhat above water, although they can tolerate stagnant water more than any other types of European tree, according to 2020Site.org. On the other hand, because burnt forests have shown alders growing there, it's also evident that they can tolerate dry soil. They're diverse trees and are good choices for areas where other trees and shrubs cannot grow.