The European aspen is a medium-sized fast-growing hardy broadleaf tree with a long slender trunk with smooth to slightly wrinkled grey bark, often pitted with diamond-shaped pores. The leaves (5-7 cm) are round-ovate with large wave-shaped teeth at the margins. Branches are perpendicular giving the crown a conic-pyramidal shape.

Behaviour

Aspen is found on a wide range of sites from sea-level up to the tree-line and occurs in most types of woodland, but most commonly associates with birch. One of the most characteristic features of the aspen is the sound of the leaves as they flutter, or tremble (hence its specific name – tremula) in the slightest breeze. This rustling, whispering sound may be heard even though the trees may be out of sight. It is a result of light leaves and very flexible flattened leaf stalks close to the leaf blade. The aspen leaf, which first opens in the spring (May), has a distinctive coppery colour, turning green in the summer and changing to bright yellow or even red in the autumn.

Aspen is dioecious, meaning that individual trees are either male or female. Flowers appear in March and April, with both male and female trees producing catkins. Male catkins (5-10 cm long) are grey-brown and yellowish in mid-March when shedding pollen. Female catkins are green and extend to 10-12 cm when mature in early summer. They bear capsules each containing numerous seeds embedded in downy fluff dispersed by wind. However, despite being native to the UK, populus tremula trees rarely flower in this country. Flowering occurred in Scotland in 2019, for the first time since 1996. The aspen’s usual method of reproduction is therefore, vegetative (asexual). New suckers, or ramets, grow off the roots of mature trees and remain joined to the parent tree via their roots. They are, therefore, clones, being of the same sex and exhibiting synchronous behaviour.

Size

• Height: 10-15 m (up to 40m; rare in Scotland)
• Lifespan: 30-40 years (when growth culminates); can reach an age of 200 years

Status

Aspen has probably suffered more from deforestation than any other native tree in Scotland. Despite the lack of any specific species action plan, a Scottish Wildlife Trust project entitled “Aspen 2020” aims to restore aspen to the Scottish landscape.

Distribution

The European aspen is one of the most widely distributed trees in the world and native to cool temperate and boreal regions of Europe and Asia. Although common across the northern hemisphere, in Scotland, aspen is increasingly scarce, usually occurring in small and isolated unmanaged populations in the Highlands, (up to 550m), which are inaccessible to grazing animals.

 

When to see

January to December

Facts

• Aspen wood is lightweight and very buoyant when dried, making it a popular choice for oars, paddles, surgical splints and paper-production.
• The place name Crianlarich is derived from the Gaelic name for Aspen, ‘critheann’.
• Like birch, alder, and mountain ash, aspen is a pioneer species – i.e., it is one of the first to colonise an area of open ground in a wood or forest.
• Aspen is important in woodland biodiversity. It is considered to be a keystone species in Europe, being ecologically important for other species, such as herbivores, beetles, flies, moths, fungi, lichens, mosses and birds. In the UK, five priority species (of the UK Biodiversity Action Plan) depend on aspen and it is a preferred species for beavers.