Mountain Ash


The brilliant red berries and changing leaves to match mark the onset of autumn

Common Name: Mountain Ash, Rowan tree, American Mountain Ash – The pinnate leaves are similar in appearance to those of the ash tree, which is otherwise unrelated; it is most frequently found in mountainous terrain.

Scientific Name: Sorbus americana – The generic name is Latin for ‘service tree’ which alludes through Indo-European roots to the color red; the crimson berries are a notable characteristic. The species assignation indicates that it is indigenous to North America; the most common European service tree is Sorbus aucuparia, which was introduced and has become naturalized. The two species are very similar in appearance.

Potpourri: The American Mountain Ash is contrarian in being a service tree and not an ash tree; its pinnately compounded ash-like leaflets are deemed the cause for the misnomer. The confusion is exacerbated by the American serviceberry tree, whose red berries reminded early colonists of the service trees of their homeland; the fusion of Old and New World cultures resulted in many botanical malapropisms. The resultant ‘ash tree’ is really a service tree and the serviceberry tree is neither. It was the multitude of new American species that inspired Linnaeus to formulate the genus-species taxonomy in the 18th century to bring some order to the chaos in botany; the resultant morphological Linnaean system is being validated for DNA consistency according to the strictures of the 21st century. The tree will be the mountain ash regardless.

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European Mountain Ash in the Pyrenees of Andorra

The Europeans solved the nomenclature problem by naming the indigenous Sorbus aucuparia “mountain ash” the rowan tree, eschewing the service tree assignation altogether. Rowan is also etymologically related to the red color of the berries, derive from the Old Norse reynir which meant to redden. While there are several other Eurasian service trees which notably hybridize frequently leading to variable descriptions, S. aucuparia is the most prevalent, notably in northern and mountainous regions; a similar geographical dispersion of S. americana in North America. Due to the import and naturalization of the European rowan tree and its similarity to the indigenous mountain ash, the names are typically used interchangeably; the latter is sometimes referred to as the American rowan tree in the United States and the former is sometimes called the European mountain ash in the United Kingdom. To confuse matters further, there is a third mountain ash; indigenous to Tasmania and Southern Australia, the giant Eucalyptus regnans is second in size globally only to the California coastal redwood. In this case, it is its ash-like wood, and not the leaves that inspired the comparative name. Common names are not required to make sense.

The diminutive apple-like fruits of the mountain ash (and rowan) ripen in late autumn and persist into early winter; they are accordingly a major food source for many birds and mammals, particularly those that neither migrate nor hibernate and must periodically struggle to survive when a paucity of nutrition persists. The crimson color is an obvious flag for concomitant sugary reward. Moose browse has been measured to be as high as 80 percent in controlled plots in northern Michigan; it has been estimated that these massive herbivores get more than fifty percent of their calories from mountain ash leaves, twigs, and berries. It is also one of the most palatable plants for deer and squirrels; the berries are 4.66 percent fat and 5.44 percent protein by dry weight. Among the birds, ruffed grouse, American robins, blue jays, and ptarmigans heavily browse mountain ash berries, providing the ecological impetus for the geographical dispersion of the tree across vast swaths of the sun-exposed hillsides that comprise its primary habitat. Avian field studies have shown that the average time between ingestion of the berry and defecation of the seeds is thirty minutes, allowing for dispersal for up to a mile from the host plant; why and how trees evolved to produce fruits in the first place. Since mountain ash is shade intolerant, seedling success depends on sun exposure. The tenuous nature of survival is reflected in the statistics of mountain ash dispersal, growth and maturation. In a study conducted in Michigan, seedlings averaged 1,660 per acre of which about 500 survived as saplings; only 80 reached full maturity. The effect of herbivore browsing of saplings is profound, as anyone subject to the white-tailed deer population bomb can attest. Where browsing occurred in the Michigan study area, there were only two or three fully grown mountain ash trees per acre; beyond decimation to near annihilation. Deer have essentially wiped out mountain ash in parts of Pennsylvania and New York.

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Mountain ash berries are a major food source for birds in early winter

The historical relevance of S. americana to Native Americans and S. aucuparia  to Eurasians is significant, the trees having served as food, medicine, and, somewhat ironically, bird bait. The species name aucuparia is taken directly from the Latin aucupor meaning ‘to catch birds.’ Rowan berries were used as bait to attract birds for fowling, an erstwhile euphemism for killing birds, ostensibly for food but also for sport. It is not clear whether this meant that the hunter would skulk rowan tree habitats to await an avian visit or whether the berries were removed and positioned strategically to effect entrapment, likely both. According to one account, the berries were used to make birdlime, a sticky adhesive smeared on branches to immobilize and capture roosting birds, a practice used historically in Europe using boiled holly tree bark pounded into a viscous paste. It is unlikely that mountain ash/rowan trees were used in this manner, but were rather directly used as bird bait taking advantage of their inherent allure.

The renowned German chemist August von Hofmann discovered a number of chemicals derived from the distillation of rowanberry oil; using the genus name Sorbus as the root word, he synthesized sorbic acid in 1859. The importance of this discovery was not manifest until the middle of the next century, when its antimicrobial properties were first noted; when converted to a salt such as potassium or sodium sorbate to facilitate handling, sorbic acid became a mainstay additive in food processing to minimize the risk of bacterial or fungal contamination, notably Clostridium botulinum which causes botulism. It is still widely used by vintners as a stabilizer to curtail yeast multiplication. Hofmann’s work ultimately established the scientific foundation for the development of the transformational German aniline chemical dye industry. The inherent anti-microbial properties of sorbic acid from mountain ash and rowan were exploited in Europe for the treatment of sore throats and hemorrhoids (both involve orifices) and in North America for a wide assortment of conditions that varied according to individual tribal custom.

With a modicum of cultural stereotyping, the chemistry of nutritive hydrocarbon sweetness that characterizes the berries of the rowan tree was discovered by a French chemist at about the same time that the German von Hofmann discovered sorbic acid. Jean-Baptiste Boussingault also used the genus Sorbus for the neologism sorbitol, a white, water- soluble compound that is of crystalline form that imparts sweetness to the palate; it is now widely used as one of myriad low calorie sugar substitutes. Boussingault operated one of the first agricultural research stations in the world where he established the importance of soil nitrogen to plant growth and laid the foundations for crop rotation. The berries were historically rendered into jams and jellies and even eaten raw as a somewhat bitter food of last resort on both sides of the Atlantic.