Imagine an autumnal Scottish riverbank, resplendent with the golden hues and quivering leaves of a thriving aspen woodland.
Scotland’s native aspen, Populus tremula, has disappeared from much of our landscape. Readily browsed by grazing animals and rarely setting seed in Scotland, the bright yellow groves of autumnal aspen that would once have been commonplace now survive only in scattered fragments, often clinging to rocky slopes and gorges beyond the reach of hungry herbivores.
Let’s paint Scotland yellow!
The Painting Scotland Yellow campaign shines a light on this spectacular tree, revealing its unique and multi-faceted role in our landscape.
Supported by a wide range of organisations and businesses, Painting Scotland Yellow seeks to inform and inspire more people, at all levels, to recognise aspen as a key component of healthy woodlands. As a result, we will see more aspen in the landscape – through natural regeneration, as well as increased planting.
Would you be able to identify aspen while out walking? We want to make aspen as well-known and widely appreciated as oak, hazel and rowan!
Aspen is a fast-growing native tree that would be abundant across Scotland without intense grazing pressure.
Considered a pioneer species, which typically grow fast and die young, their rapid growth efficiently locks away carbon, while their high rate of leaf fall and production of deadwood enriches the soil – creating the conditions for other plants and trees.
Aspen likely became established in the Scottish landscape, alongside trees like birch and hazel, after the ice retreated around 9,000 to 10,000 years ago, roughly 2,000 years before Scots pine. Today it can be found in a wide range of habitats, from riparian woodland to temperate rainforest, Caledonian pine forest to scrub and wood pasture.
However, the palatability of aspen to deer and livestock means the species is now scarce in Scotland and most often found in places inaccessible to browsing animals. Given the chance to flourish, aspen can quickly form large stands in almost any soil and setting.
When aspen produces seed, a single catkin can hold 1,000 to 2,000 seeds and a single tree can hold 40,000 catkins. That’s potentially 40 million to 80 million seeds per tree!
Getting aspen back into our woodlands isn’t easy. Natural regeneration and expansion from existing stands would be preferable, but this relies on reducing the impact of high deer numbers, which in many places is economically and culturally sensitive. In the meantime, fencing is an option but this too is challenging, with many aspen stands fragmented and consisting of only a small number of trees, in addition to the visually intrusive nature of high fences.
Aspen is now being planted as part of a drive to restore native woodlands, but the availability of saplings is a limiting factor. Unlike most trees, aspen rarely sets seed in Scotland and instead relies on the root system of one tree sending up ‘suckers’ to create clones of itself. As a result, most aspen growers take cuttings from these roots and grow them on – a labour intensive job – or they wait for one of the few years in which aspen flowers in order to collect seed.
It’s easy to see why restoring aspen to our diminished native woodlands is less than straightforward.
Aspen is important for biodiversity, supporting a wide range of flora and fauna, including rare priority species.
The tree supports an astonishing range of species, from the tiniest of lichens to large woodland birds and mammals.
266 fungi, about 300 lichens, at least 35 bryophytes, 25 moths and 39 species of deadwood-dependent flies have been recorded on aspen in Scotland.
In Scotland, four UK Biodiversity Action Plan (BAP) species rely on aspen: the dark-bordered beauty moth, aspen hoverfly, aspen bristle-moss and blunt-leaved bristle-moss. Critically, different species rely on the myriad niches provided by aspen at different stages of the tree’s life cycle – young regeneration, smooth bark, rough bark, deadwood, trees that grow close together and those that offer open glades. This means that multigeneration stands of aspen, with all their structural complexity, support more life.
Aspen is a key component of healthy woodland ecosystems, driving natural processes such as soil generation.
The world’s largest living organism is the Pando aspen grove in Utah, USA. What appears to be 47,000 individual trees is actually the same tree – clones of a single root system, which if laid out would stretch 12,500 miles!
It is in this underground network of roots, fungi and bacteria – sometimes known as the Wood Wide Web – that connects trees and plants to one another, where arguably, aspen does its best work.
Above the ground, aspen’s bark is significant. Unlike more common species like birch and Scots pine that have an acidic bark, aspen has the opposite – a basic bark. This vital substrate provides a niche for species that might otherwise struggle and therefore aspen adds both abundance and diversity to our woodlands.
Aspen is a preferred food source for beavers, now beginning to spread in range and number across Scotland. Despite concerns to the contrary, aspen responds well to beaver coppicing, which stimulates the tree to send up more growth.
Aspen and beavers work well together. The combined effort of two ecosystem engineers, each responding to the presence of the other, creates a mix of fresh tree growth and valuable deadwood alongside rivers and watercourses.
Beavers typically avoid getting too far from their ponds and canals but they have been recorded making a 238m foray to target a tasty stand of aspen!
Aspen thrives alongside watercourses, providing vital food, shade and sanctuary for young fish.
Aspen is particularly adapted to thrive alongside rivers and watercourses – the so-called riparian zone. Riparian woodland in Scotland is vastly diminished with many of our rivers now running through open, de-wooded landscapes.
Trees bind loose, gravelly riverbanks, their falling leaves enrich the water and their roots provide sanctuary for young fish. More significantly perhaps, the shading provided by riparian woodland helps to reduce water temperatures. This is critical for fish such as Atlantic salmon that rely on clean, cold water.
THE LOST TREE?
Aspen is common across Europe, yet could be considered Scotland’s lost tree, such is its relative scarcity here.
We’re living in the United Nations Decade on Ecosystem Restoration, the first time there’s been a global movement to restore and recover our degraded ecosystems. And, although Eurasian aspen is thought to be the most widely distributed tree in the world – occurring from Iceland to Japan, and from the boreal fringes of Norway to northern Africa – it has become something of a lost tree in Scotland.
Aspen is but one tree among many. But the global crisis of nature loss has happened in part because we’ve allowed nature to slip away, bit by bit, species by species. By protecting and restoring this spectacular tree, with all its life-giving characteristics, we can put a piece of the ecological jigsaw back, enrich our woodlands and, in doing so, enrich our own lives.
Let’s not just imagine an autumnal Scottish riverbank, resplendent with the golden hues and quivering leaves of a thriving aspen woodland. Let’s make it reality. Let’s paint Scotland yellow.