During the recent snowstorm, I took a walk down behind the house. We have a trail that winds down to the floodplain along the river. There is one area that is becoming quite a thicket – I think the previous owners kept it cleared. However, in the past few years, speckled alders have been filling in. I’m glad because these are one of my favorite wildlife-attracting plants.
Speckled alders (Alnus incana) are fast-growing shrubs that form dense, impenetrable thickets, which provide food and shelter for moose, deer, rabbit, woodcock, grouse and others. Beavers browse on the twigs and foliage and use the wood in dam and lodge construction. They are a favorite winter food of goldfinch, redpolls, pine siskins and other songbirds. We have plenty of goldfinch already. I'm hoping that more alders will mean greater diversity.
Humans have a long history of speckled alder use. A variety of medicines have been derived from the bark and the roots. You can even eat the catkins, they are high in protein, though bitter, so best left for dire emergencies. They are best in the spring when loaded with nutritious pollen. In addition, the wood burns fast and hot, giving it the common name "biscuit wood" because it is perfect for baking biscuits. Speckled alders also provide erosion control, function as windbreaks, and improve nutrient levels in surrounding soil through a very special relationship with bacteria that they house in nodules in their roots.
In addition to being one of my favorite plants, speckled alders have one of my all time favorite symbiotic relationships - a mutually-beneficial relationship with nitrogen-fixing bacteria. Nitrogen is one of the most important nutrients for plant growth and is often in short supply – it’s called a limiting factor for plant growth. The wet area where my speckled alder is growing is typically low in nitrogen. There is a ton of nitrogen in the atmosphere - 78% of the atmosphere is composed of nitrogen. However it is useless to plants and most other life unless the bond that holds atmospheric nitrogen is broken –something specialized nitrogen-fixing bacteria (and lightning) can do.
Nitrogen-fixing bacteria convert atmospheric nitrogen into a usable form - ammonia. Plants can use ammonia to build the molecules of life-proteins, DNA and RNA, promoting plant growth, enriching the soil where they grow. Not only that, there is also evidence from the study of one of speckled alder's close relatives, red alder, that these nitrogen-fixing trees are also able to solubilize other vital nutrients found in rocks, further enriching the soil around them.
Speckled alder are fairly common around here. Winter is a good time to look because these shrubs have very distinctive catkins that remain on the branches after the leaves have dropped in the fall. The male pollen-bearing catkins hang in dangling clusters (this is how you can tell these are in the birch family), and the erect brown seed-bearing cones (female structures) bristle from branch tips. In addition to the telltale catkins, speckled alder have prominent light-colored lenticels — spongy openings used for gas exchange — speckling the bark; hence the name. Speckled alders most commonly form thickets by both root suckering (shoots emerging from the roots) and a process called layering where branches that grow low to the ground take root and subsequently detach to become independent plants. For this reason, these can be incredibly easy shrubs to transplant if you want to try introducing them to your backyard.
Speckled alders are, in my opinion, one of the unsung heroes of our wetlands, frequently derided as a weedy, thicket-forming, swamp-dweller, but now we know these are all good, dare I say great, attributes. Winter is finally settling in and thin layers of ice have formed in my neighborhood wetlands, signaling the start of the best time of year to traipse about your local swamps in search of the lovely speckled alder.
Susan Pike, a researcher and an environmental sciences and biology teacher at Dover High School, welcomes your ideas for future column topics. She may be reached at firstname.lastname@example.org. Read more of her Nature News columns online at Seacoastonline.com and pikes-hikes.com, and follow her on Instagram @pikeshikes.
This article originally appeared on Portsmouth Herald: Nature News: Speckled alders have hidden superpowers