Rowan is a fast-growing pioneer tree in the Caledonian Forest, characterised by its brilliant red berries at the end of summer.
Rowan can be found in most parts of Europe and North Africa. It also grows in central and northern Asia into northern China. It can survive from sea level up to about 2,000 metres the Alps.
Distribution in Scotland
Rowan grows in most parts of Britain, but is more common in the north and west, and is found throughout Scotland. It grows at a higher altitude than any other tree in the country and occurs at elevations of almost 1,000 metres in parts of the Highlands.
This attribute, together with the similarity of its leaves to those of the ash tree gives rise to its alternative common name of mountain ash. At higher elevations it survives as small saplings which are often stunted in form.
In Scotland today, rowans are often found growing in inaccessible locations. Cliffs, steep stream-sides and on top of large boulders are among the places you can often find this tree. However, these are not the preferred locations for the species. It’s just that these are the only places where it has been able to grow out of reach of herbivores such as red deer and sheep.
Rowan is a fast-growing, short-lived pioneer tree in the rose family. It is a fairly small tree, reaching a maximum height of 10-15 metres, or exceptionally, 20 metres. It is slender in form, although mature trees can be quite substantial. An old rowan at Carnach Mor on the West Affric Estate has a trunk which is over 40 cm. in diameter. Multi-stemmed forms are quite common. This is usually a result of browsing by mammals. The tree sends up new shoots from its base in response to being eaten.
The greyish-brown bark is smooth and shiny when wet, with dark raised dots or lenticels scattered across it. The branches are typically upward-pointing and end in ovoid, purplish buds, which are often covered in grey hairs.
Rowan leaves are compound and pinnate in form. This means that each leaf is made up of matched pairs of leaflets on either side of a stem or rachis, with a terminal leaflet at the end. Leaves are up to 20 cm. in length, and are comprised of 9-15 leaflets, which are serrated with small teeth. Rowan is a deciduous tree, with the new leaves appearing in April. They turn a bright orange-red colour in autumn before being shed.
The flowers blossom after the leaves have appeared, usually in May or early June, and are creamy-white in colour. Individual flowers are about 1 cm. in diameter and they grow in dense clusters or corymbs. Each corymb contains up to 250 flowers, and measures 8-15 cm. across. The strong, sweet scent attracts pollinating insects, including many species of flies, bees and beetles.
The fertilised flowers grow into berries which are 8 mm. in diameter and these ripen to a bright red colour in August or early September. The berries are rich in ascorbic acid (vitamin C), and contain up to 8 small seeds, although 2 seeds per fruit is most common. They are eaten primarily by birds, who disperse the seeds in their droppings.
Seed production begins when the tree is about 15 years old, and in mild climates, rowan will fruit each year. However, in harsher environments such as Glen Affric, fruiting is irregular. Mast seed production, when all the trees produce a heavy crop, occurs every few years, with very little fruiting taking place in between. The tough coat of the rowan seed requires cold weather to break down. Germination usually occurs in the first or second spring after the berries have been produced. Seedlings and saplings are shade-tolerant. They are often found under the branches of large Scots pines where they have grown in the droppings of birds which perched on the branches above.
For similar reasons, rowans also germinate in the forks of the trunks of pines and other trees. But in most cases there isn’t enough organic matter for these seedlings to grow to more than a metre or two in size. Exceptions to this do occur. Near Glac Daraich in Glen Affric there is a good example of a rowan which became established about two metres up an alder. It grew into a mature tree, partly embracing the alder, after its roots reached the soil below.
Rowan is a key part of the Caledonian Forest. It is often found growing alongside Scots pine, sessile oak and other trees.
Like many other tree species, rowan forms special partnerships with fungi. These ‘mycorrhizal’ relationships are a plant and fungal version of ‘you scratch my back, I’ll scratch yours’. The fungus attaches to the tree’s roots and gets sugars from the tree. In return the fungus can access nutrients that the tree wouldn’t be able to get otherwise. Rowan partners up with several species of fungus in this way.
Rowan also has a strange and interesting relationship with another kind of fungus. The rust fungus called Gymnosporangium cornutum infects juniper, but in the spore phase of its life cycle it lives on rowan. Here it causes yellow pustules to form on the leaves.
Rowan is a good host tree for lichens, and is the second best in the UK for Graphidion lichens after hazel. A large, leafy lichen called tree lungwort is common on rowan trunks in wet or humid areas.
Mountain hares eat the leaves of young rowan. Rowan leaves are a favourite food of red deer, which also eat the bark and stems. Several mammals eat the berries, and pine martens and foxes are known to be important dispersers of rowan.
The orange-red fruits also provide a feast for many different birds. They’re popular with birds in the thrush family, including fieldfares and redwings. When these birds arrive from the continent in September and October, the berries provide a very welcome source of energy. Blackbirds play a key role in spreading rowan.
A range of invertebrates feed on different parts of rowan. These include the larvae of several species of leaf-mining moths which make mines in rowan leaves. The caterpillars of the Welsh wave moth eat the leaves while the larvae of the apple fruit moth are frequently found in the berries. The flowers are an important nectar source for insects including bees and flies. The larvae of some of these flies play an essential role in rotting down dead wood.
The IUCN have classed rowan as being Least Concern globally.
- Guitian, J and Munilla, I. (2010). Responses of mammal dispersers to fruit availability: Rowan (Sorbus aucuparia) and carnivores in mountain habitats of northern Spain. Acta Oecologica 36(2), 242-247.
- Harris, E. & Harris, J. (1989) Field Guide to the Trees & Shrubs of Britain. Reader’s Digest: London.
- Johnson, O. & More. D. (2006) Collins Tree Guide. Collins: London.
- Mitchell, A. (1982) Trees of Britain and Northern Europe. Collins: London.
- Rose, F. (2006) The Wild Flower Key. Warne: London.
- Assessing habitats for deadwood invertebrates. www.nature.scot/sites/default/files/2019-05/Guidance%20-%20Assessing%20habitats%20for%20deadwood%20invertebrates.pdf (Accessed September 2020)
- British Ecological Society – Rowan https://besjournals.onlinelibrary.wiley.com/doi/full/10.1046/j.1365-2745.2000.00502.x (Accessed September 2020)
- IUCN Red List https://www.iucnredlist.org/species/61957558/112304840 (Accessed September 2020)