The Color Splash of Mountain-ash

In a landscape of winter white, bits of color really pop. Recently I was on the North Shore of Minnesota when they received several inches of fluffy, wonderful snow. Gray clouds hung low and continued to sprinkle fairy dust throughout the following day. Out on the cross-country ski trails above Grand Marais, my yellow jacket shone against the snow. When a strip of blue sky finally peeked through the clouds, that, too, glowed brightly. Full sun would have been blinding!

Spots of red also caught my eye. The forest seemed decked out for Christmas with clusters of mountain-ash berries adding color in the woods along the ski trails, around town, and on the rocky shore of Lake Superior. One section of scrubby forest between Highway 61 and the lake seemed to be almost entirely composed of berry-laden mountain-ash trees.

As the days grow ever shorter and darker this time of year, splashes of color like these berries do wonders for my mental health. Ruffed grouse appreciate them even more, I’m sure, as they perch in the dark purple twigs and nibble both berries and buds. The berries are acidic enough to last on the tree all winter, but if a flock of cedar waxwings descends, all the fruits may disappear in a single day. Thrushes, jays, catbirds, and grosbeaks, plus squirrels and small mammals, sometimes share in the feast.

Mountain-ash berries brighten up the winter woods, especially along the North Shore of Lake Superior. Photo by Kevin Friedman.

Grouse eating mountain-ash berries. Photo by Kevin Friedman.

The twigs of mountain-ash apparently are tasty, too, or at least nutritious. When I taught a wolf ecology course on the North Shore years ago, we observed the impacts of deer browse in different parts of wolf territories. Any mountain-ash short enough for deer to reach was deformed from their nibbling. On Isle Royale, scientists observed that over eighty percent of mountain-ash stems in study plots were browsed by moose. Moose have the advantage of height. Snowshoe hares must browse the lowest twigs with their sharp incisors, or wait for deep snow to give them a lift.

Photo by Emily Stone.

Back in the day, when I took a plant identification course at Northland College, we only learned two species—American mountain-ash (a native) and European mountain-ash (Sorbus aucuparia, introduced for landscaping). So, for years, when I’ve found these trees away from towns, I’ve called them all Sorbus americana. Recently, I’ve discovered that showy mountain-ash, Sorbus decora, is also native here, and is more common, at least in Wisconsin.

The three species are almost identical to the casual observer. While the leaves are slightly different sizes and shapes, this time of year the hairiness of the buds and berry stems seems to be the best distinguishing characteristic. The buds of the European species will be covered with long, white hairs. Showy mountain-ash twigs and buds are pubescent (with short hairs) and American mountain-ash twigs and buds are usually smooth and hairless.

I always thought this tree was a European Mountain-ash. Now I'm not so sure--but it's been cut down so I can't go back and look closer! Photo by Emily Stone.

All of these species are good wildlife and landscaping trees, although planting the native mountain-ashes is preferred, since the European ones have been known to escape into the wild. While their showy, rounded clusters of white flowers don’t look like roses from afar, they are all part of the Rose Family. A closer look at the flowers reveals five white petals very similar to the blossoms on their cousins: strawberries, raspberries, cherries, and apples. Even the fruits of mountain-ash look like mini apples.

I took this photo of mountain-ash flowers on Hunger Mountain in Vermont during graduate school. From the leave length-to-width ration I measured off the photo, this is Sorbus decorum. Photo by Emily Stone.

Mountain-ash drupes that look like mini apples. Photo by Kevin Friedman. 

The hyphen in their name indicates that they aren’t really related to ash trees. Mountain-ash are called that because they have compound leaves with long, narrow leaflets, similar to true ash trees. Unlike true ash trees, these wonderful wildlife trees won’t be impacted by the deadly emerald ash borer insects.

Ash-like leaves on a mountain-ash. Photo by Emily Stone.

Both of our native species reach their southwestern edge in northern Wisconsin and Minnesota, and extend north and east from there. American mountain-ash also extends down the spine of the Appalachians. The happiest specimens seem to be concentrated along the north shores of Lake Superior and Lake Huron. They are quite common among the balsam fir trees on Isle Royale as well. On the water-limited bedrock along Artist’s Point in Grand Marais, I’ve noticed they can remain quite shrubby, and a heat wave last summer left their leaves brown and crispy.

The color these wonderful berries bring to our winter woods is only one reason I enjoy them. Getting to watch and listen to the flocks of birds they attract is another. And now, the challenge of learning to distinguish the two native species will give me an excuse to look more closely at their leaves and twigs. In doing that, I bet I’ll learn something else new, too.

Cedar waxwing in a tree that I once thought was European mountain-ash, and now can't be sure. Photo by Emily Stone. 

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Winter Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.