Walking through many neighborhoods in Montana towns through the fall and winter, you’ll find yourself brushing past clusters of showy orange berries, hanging down from the limbs of mountain ash. By late winter many of the berries have spattered to the sidewalk, but through much of the drab months they provide a warm pop of color against the gray sky and white snow.
The mountain ash is a popular decorative tree, especially amongst wildlife watchers who use its fruits to attract wintering birds. Its moderate height (usually topping out around 40 feet) means that the mountain ash isn’t too much of a problem for power lines, and it is tolerant of conditions like strong winds, clay soils and variable pH.
As one of the few trees that maintains its berries through the winter, the mountain ash can be an important source of nutrition for non-migratory bird species. If a human were to pull down some mountain ash berries and take a mouthful, however, the unlucky forager would probably spit them out immediately. Regardless of their appetizing appearance, the berries are bitter and rich in sorbic acid, only tolerable to humans after being cooked at high temperatures for jellies or jams. Despite that challenge, they were once taken aboard long sea voyages in those processed forms as a means of preventing scurvy, since they are rich in both vitamins A and C. The birds don’t mind the bitter taste, of course, and are quite content to eat the berries just as they are, although there are reports that hard frosts can cause the berries to ferment, leading to sightings of tipsy birds as their food source suddenly becomes inebriating.
The scientific name for the European variety of the plant is Sorbus aucopara, the second word of which is a homage to its importance to bird species. It derives from the phrase avis capere, literally “catches birds,” which will come as no surprise to anyone who has watched magpies flitting in and out of the branches.
The species indigenous to this continent are Sorbus americana and Sorbus decora, known colloquially as American mountain ash, and showy mountain ash, much preferred by those who are concerned about the growth of non-native species populations. The European mountain ash, although usually starting out as an intentional decorative planting, has escaped to grow wild in some areas.
All three species have narrow compound leaves with slightly serrated edges, light grey bark that may take on a plated appearance in older trees, and clusters of white blossoms in the spring, making them appear quite similar to the casual observer. Subtle differences in the appearance and texture of the buds can be used to distinguish between the varieties, and the two North American mountain ash species may have brighter displays of fall foliage, but it’s often difficult to be certain of the distinction.
Adding to the confusion is the fact that all three species have been bred into multiple sub-varieties over the years by gardeners attempting to yield plants that are shorter, more colorful or more fruitful. Unfortunately for native species enthusiasts, the European variety is the one that is most common in ornamental gardens, so it’s quite possible that many of the lovely trees that can be spotted in yards throughout western Montana are imports.
Despite being called ashes, all of the mountain ash varieties actually belong to a branch of the rowan family, a bit of trivia that has become important with the outbreak of the emerald ash borer. While true ash trees, once the primary street tree in many cities, have dwindled as a result of the pest, the mountain ash looks to brightening yards and feeding birds for years to come.
"Field Notes" is produced by the Montana Natural History Center.