Species of the month – rowan

The rowan tree (Sorbus aucuparia) has deep roots in Celtic folklore, thanks mostly to its bright red berries, which have long been associated with spirits and all things magic. But never mind the myths; the rowan is a ubiquitous feature of the Scottish landscape, and has a very important ecological role to play.

Rowan berries

Rowan berries ©Lorne Gill

The rowan is found in most parts of Britain, reaching altitudes close to 1,000 m in the Scottish Highlands.  Seedlings can be found far from any parent tree, as the berries are carried by birds. The rowan is not finicky about its habitat, as long as the soil is well-drained; it grows on abandoned mines and wasteland, as well as rocky slopes and cliffs, crevices in rock outcrops and on top of boulders.  In the uplands, seedlings and young trees may be abundant in these inaccessible habitats, which offer protection from large herbivores, such as cattle and red deer

However, the rowan tree is very tolerant to damage, and it quickly grows protective tissue over feeding wounds; this is an important adaptation, because it reduces water loss and prevents infections. Moreover, rowans are attacked by relatively few herbivore insects, which are possibly repelled by the trees’ chemical defences.

Rowan flowers on the other hand are quite attractive to pollinating insects, but this tree may be bit of an oddity; it appears to be a cantharophilous plant, that is, one that is pollinated primarily by beetles. There aren’t many of them around, but the flowers’ sweet, heavy smells are especially attractive to beetles. Flies are also frequent visitors. Pollination results in quite a few berries, which are very important food items for a variety of birds. In fact, rowan is well known to be one of the most important food sources to fruit-eating birds in northern Europe

Song thrush in a rowan tree laden with red berries

Song thrush in a rowan tree laden with red berries

The rowan has a characteristic of profound consequence to berry-eating birds; it produces large crops of seeds in some years, and very little to almost none in others (plant ecologists call this physiological feature ‘masting’). As a result of berry masting, the annual distribution and migratory behaviour of birds are affected on large spatial scales. For example, the location and abundance of bullfinches in parts of the Fennoscandian region (Norway, Sweden, Finland, and Denmark) are synchronised with rowan masting episodes, and the arrival of fieldfares and redwings flocks to Britain is regulated by the onset of winter and the dwindling supply of rowan berries in Scandinavia and continental Europe.

Not bad, for such as unpretentious, small tree.


Further reading :

There are several good web pages – Trees for Life have two.  One on the botanical/ ecological aspects at http://www.woodlandtrust.org.uk/visiting-woods/trees-woods-and-wildlife/british-trees/native-trees/rowan/ and one on the mythology at http://treesforlife.org.uk/forest/rowan/.

This entry was posted in Species of the month and tagged , , , . Bookmark the permalink.