Alder Trees In California: 4 Native Types To Know

In California landscapes, alders are not as common as many other species, such as oak and palm. However, their ability to stand in water without rotting is a huge plus point for flood-prone and coastal regions.

Only four of the thirty or so species of Alders found worldwide are native to the California region. And, in this article, I will walk you through 4 of the native alder trees in California, along with their appearance, habitat, and other details.

So, let’s get started.

1. Red Alder

• Scientific Name: Alnus rubra
• Common Name(s): Red Alder, Pacific Red Alder, Mountain Alder
• Mature Height: 40-100ft
• Flowers: Catkins
• Uses: Furniture, Novelty items, Cabinets, Firewood, and Medicinal uses.

One of the most commonly seen native alder trees in California, the Red Alder tree has a medium-sized tree with a single trunk and a relatively short lifespan. Its clear trunks and narrow to broad crown help it grow to a height of 24–30 meters. 

From southeast Alaska to San Luis Obispo County, California, the red alder tree can be found growing in a variety of coastal and montane woodlands and forests. Most of its natural habitat is on gentler slopes, where the soil is rich and the altitude is less than 900 meters. 

The leaves of this tree are elliptic, with sharp points at both ends and a tapered, rounded base; they fall off the tree in the fall. These leaves are dark green and hairless on top, with lighter green veins that are more prominent in color and a rusty orange color on the underside. 

The catkins have a cone shape and are 1–3 cm in length. They have many scales covered in tiny, round, broad-winged nutlets. The twigs range in color from bright red to reddish brown, while the bark is thin and grey with bluish-gray, tan, and grayish-white mottling.

It can’t live in the shade, so other evergreens that can do so easily beat it in the competition. Red alders can withstand surface fires despite having a thin bark because of their age. 

Many different things, including furniture, novelty items, cabinets, and firewood, are made from the wood of this tree. Both beavers and deer and elk enjoy munching on its leaves and bark. The natives smoked salmon with it and used it medicinally.

2. Mountain Alder

• Scientific Name: Alnus Incana ssp. tenuifolia
• Common Name(s): Mountain Alder
• Mature Height: 6-30ft
• Flowers: Conelike Catkins
• Uses: Protect stream banks, wildlife habitat

The mountain alder is a large, multistemmed shrub or small tree that often grows in thickets. It can reach a mature height of 2-9 meters and a diameter of 10-20 centimeters. 

It comes from the Rocky, Cascade, and Sierra Nevada mountains in the western United States. It grows best in the shade of trees and bushes, near running water, and near montane and upper montane meadows. 

The leaves of the mountain alder are between 5 and 10 centimeters in length and 2.5 and 6 centimeters in width. They are alternate in arrangement, simple in composition, and deciduous. The edges are double-serrated, the points range from rounded to sharp, and the bases are round to heart-shaped. 

Mountain alder produces fruit in cone-like catkins that are between 1 and 1.5 centimeters in length and are covered in many woody scales. Mature plants have thin, light green, hairy twigs and thin, grey to reddish grey, scaly bark. 

Though it is eventually topped by conifers and cannot tolerate shade, the mountain alder can reseed itself with the help of seasonal flooding. This species is important because it can prevent erosion of stream banks and watersheds.

3. White Alder

• Scientific Name: Alnus rhombifolia
• Common Name(s): White Alder, California Alder
• Mature Height: 15-50ft
• Flowers: Cone-like Catkins
• Uses: Firewood, Ornamental purposes

Native to the western coast of North America, from British Columbia to California, the white alder is small to medium-sized, single-stemmed tree. Its tallest known height is 24 meters, but most adult trees are between 15 and 50 feet (79 feet) tall. 

White alder is a pioneer species in riparian areas since it cannot survive in shade and must have a constant supply of moisture. 

Its leaves are alternate, thick, egg-shaped, oval to rhombic, and serrated along their unrolled margins. The cone-shaped catkins range in size from 6 to 12 mm, and each scale bears a tiny round nutlet without wings. 

The twigs are stalked and orange-red, and they bear thin buds at the branch’s outer edges. This tree is easy to recognize because its bark is thin and grey with white and grey spots. Furrows and plates of greyish brown in the bark as the tree ages.

White alder has many purposes, including as a decorative tree, a building material, and a fire starter. 

Native Americans used it for both its aesthetic and medicinal value, creating a red dye from the bark and brewing a tea that causes sweating.

4. Sitka Alder

• Scientific Name: Alnus viridis ssp. sinuata
• Common Name(s): Sitka Alder
• Mature Height: 6.5-15ft
• Flowers: Conelike catkins
• Uses: Used to protect watersheds, stabilize slopes, etc.

Sitka alder is a multi-stemmed, tall shrub or small tree that grows in thickets. It can grow to a height of 11 metres (37 feet) and a diameter of 22 centimetres (8.5 inches). 

Its natural habitats in California are the northern Coast Ranges and the Klamath Mountains, which are between 1,000 and 2,700 meters (3,200 and 8,800 feet) above sea level. And, it is most commonly found near streams, seeps, and meadow margins.

The crowns are broadly rounded and widely spread. The leaves are deciduous, alternate, simple, thin, oval to egg-shaped, and range in length from 6-15 centimetres (2.5-6 inches) and width from 4-9 centimetres (1.5-3.5 inches). The edges are serrated twice, the tips are sharply pointed, and the bases are round to tapered. 

The upper surfaces of the leaves are yellowish-green and shiny, while the lower surfaces are green, and most of the hairs are only in the spaces between the main veins. 

The flowers are conelike catkins about 13 millimetres (0.5 inch) long, with a small, round, broad-winged nutlet on each scale. The twigs are slender, smooth, and reddish to yellowish brown. The bark is thin, reddish to greyish brown in colour, and has prominent lenticels.

Because Sitka alder is shade intolerant, it can be overtaken by conifers on most sites with no recurring disturbances. It does, however, move quickly into places where flooding, avalanches, or landslides have changed the environment. 

Its most valuable feature is its ability to protect watersheds and stabilize slopes. It’s also a sign of high water tables.

Alder Trees In California – Frequently Asked Questions (FAQs)

Here are answers to some of the most common questions people have about native alder trees in California. These questions are taken from online gardening forums and discussions.

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Sources

The Regional Gardening team makes sure that the information in our articles is accurate by only using sources that are known to be trustworthy. Some of these sources are peer-reviewed journals from government agencies, well-known universities, and scientific research organizations.

1. California Forests, University Of California
2. California Native Plant Society
3. Native Plants, California Department Of Fish & Wildlife
4. California Natural Diversity Database