Alders

Doctors of the Earth

Metchosin council recently passed an amendment to our tree management bylaw that designated some species of trees as protected, meaning you need a darn good reason before you are allowed to cut them down! They rate preferential status because they are uncommon or threatened and we need to husband the ones we have left. But I was thinking, as I took a hike through Blinkhorn Nature Park with a rather boisterous, ball-mad dog, about the value of our more common trees, in particular about our alders.

One of the things I appreciate about red alders (Alnus rubra) is their ability to create an almost instant forest. When I first moved to Metchosin, almost twenty years ago, the drive through the gravel pit took a different path. When it was rerouted to the location we drive through now, it was a forbidden, barren landscape. Almost immediately, at the bottom of the hill, some alders sprang up on both sides of the road and I watched with interest as they quickly grew tall and robust. From nothing but bulldozed devastation there sprang a forest. I haven’t been into that forest, to see what other plants might have been able to transplant themselves, but the trees themselves have been fascinating to watch. At first they were growing tooth by jowl, thick as promises in an election year. Then, as they grew and began crowding each other, some have succumbed to competition and started to die off. Fungi and bacteria are quick to find an alder in distress and they further weaken a struggling tree. The softened wood allows woodpeckers to drill holes and use them for a short while, followed by other cavity nesting birds and small mammals. The trees provide food for the green comma caterpillar, the juvenile form of a relatively long-lived, spotted, orange butterfly.

Alders are considered a pioneering species, able to quickly colonise disturbed sites such as burnt areas, roadsides and avalanche tracks. They act as healing doctors to the earth, repairing wounds left by the disturbance. Alders are nitrogen fixing plants; they have an association with a bacteria that allows them to capture nitrogen from the air and eventually increase soil fertility through their roots but also from decomposing leaf litter and branches, rotting roots and trunks and through leaching from the leaves. In pure stands that can amount to 320/kg per hectare (290 lb/acre). They cover the exposed mineral soils, shading them from the harsh effects of the sun and weather conditions. Their leaf litter adds valuable organic matter to impoverished soils and provides habitat for insects, mice and amphibians.

As they rapidly age, they relinquish their hold on the landscape, allowing other tree species to dominate, in a process known as succession. Douglas-firs or western red cedars, depending on site conditions, will now find the landscape more to their preference.

Alders are sometimes found in pure stands in floodplains that experience fluctuating water tables and have nitrogen rich soils. Here their dense fibrous root systems hold fast the soil deposits and streambanks, reducing the effects of erosion and sedimentation. Walking along an alder lined creek you can often observe the firm overhanging bank, tied in place by alder roots and providing crucial hiding places for cutthroat trout, among other fish. The nitrogen rich leaves fall into the water, decompose, and increase the productivity of the water, enabling more insects and fish to survive. The shading provided by the trees reduces the harmful effects of too much sun and cools the water, making it more salubrious for water dwelling creatures.

Alders are fast growing trees, one metre in their first year and by two to five years they can produce three metres of growth per year. Some trees can reach 30-40 m in height and generally average out at about 55-75 cm in diameter, although some record trees have topped out at almost two meters in diameter! They have short life spans, not dissimilar to our own, usually dying off by seventy-five years with occasional ones making it to a venerable one hundred years.

All these wonderful qualities have finally been recognized and alders are planted in restoration efforts at coal mine sites and along destroyed rivers, promoting soil fertility and reducing erosion at the sites. Formerly, forest companies had been quick to denigrate alders and considered them a weedy plant that should be removed, now they are sometimes used as a nurse species for shade tolerant conifers, especially on nitrogen deficient sites. They also offset some of the more detrimental effects of logging, particularly near streams and waterways. Because the trees are self pruning and the branches rot easily, they are quite fire retardant and are planted as fire breaks. In alder stands, the interlocking of branches and roots, the deep rooting habit and the absence of leaves in winter, makes them resistant to windthrow.

In his co-authored book, Wildlife and Trees, local writer and forest ecologist Todd Manning explains the value of various trees to native wildlife populations. Huge old trees that are starting to rot and die, such as veteran Douglas-firs rate high on the list and the book suggests that we should cut down alders preferentially over these slower growing conifers, when cutting for firewood. It takes many hundreds of years to replace a huge, wildlife friendly conifer and a relatively short time to replace an alder. The cut alder pieces are also an excellent stratum if you wish to try growing oyster mushrooms at home.

First Nations people harvested alder cambium tissue as a food and used the bark in preparation of steamed camas bulbs, which would impart a red tint to the food, the bark was also used as a dye. Alder catkins are said to be high in protein and edible, but not very tasty and used only as a survival food. The bark is reportedly the best material for imparting that indefinable West Coast flavour when smoking salmon. Alders are said to possess strong antibiotic properties and have been used in the treatment of tuberculosis and other lung ailments. The wood is light, soft and porous and is utilized in furniture making, as pulp, as well as firewood.

By mid-March, the alder catkins have appeared and turned a rusty-red, about to discharge their pollen upon the upright, female, pine cone-like “flowers”. When ripe, they will release seeds that are dispersed widely by the wind. If they land in some bare mineral soil, in full sun, they stand a good chance of germinating. As I write this, I can look from my window to a small stand of alders, the myriad straight, grey trunks covered in a tapestry of whitish lichens, the small crowns glowing a soft pink from the thousands of pendulous catkins and I wonder how we have come to be so dismissive of such a valuable tree, as if to imply they are worthless…

References:
http://www.na.fs.fed.us/pubs/silvics_manual/volume_2/alnus/rubra.htm
Wildlife and Trees by Fenger, Manning et al. 2006
Plants of Coastal BC by Pojar and MacKinnon. Revised edition 2004
Edible and Medicinal Plants of the West by Tilford. 2003 reprint.
Food Plants of Coastal First Peoples by Nancy Turner. 2003 reprint.
Indicator Plants of BC by Klinka et al. 1995 reprint.