Dundreggan tree nursery
Many of the trees we plant are grown at our own tree nursery based at Dundreggan. We want all our planted trees to have the best possible start in life, so using seed from trees that grow locally to Dundreggan and Glen Affric is a key part of our strategy. To do this we have established a centre of excellence for growing native trees and shrubs in Scotland. We concentrate on the rare or hard to grow species that more commercial tree nurseries can’t supply. Trees like local provenance woolly willow and downy willow which help us create new mountain woodlands at Dundreggan and, in partnership with Forestry and Land Scotland, at Glen Affric and elsewhere. We also specialise in growing aspen and are currently researching how to create a consistent supply of seed for this rare forest tree. The nursery is a hive of activity during the spring, summer and autumn, where volunteer groups help us through the whole life cycle of our trees – from seed collection to final planting.
In Scotland, native aspen trees rarely flower or set seed. The reasons for this are not well understood. The same species of aspen flowers more readily in Scandinavia in conditions very similar to Scotland. Irregular flowering and the difficulties of long-term seed storage, plus the fact that aspen does not grow easily from cuttings, make it hard to source local origin aspen trees for planting.
In the past we have grown local aspen from root cuttings, a method that involves collecting pieces of root from local aspen stands early in the year. These are placed in a polytunnel to encourage ‘suckers’ to grow in spring, however this method only produces a limited quantity of trees, and they are all clones of the parent trees.
If we want to produce larger quantities of aspen, we need seed. And so our recent aspen work has involved doing just that. We have been enlarging our aspen ‘seed stand’ – a collection of aspen trees housed in a polytunnel that is managed for seed production. This method is still fairly experimental and we are learning all the time but we have successfully been producing seed in varying quantities each year since 2020.
Each tree in the seed stand is grafted from a different local tree that has been known to flower, as we need aspen clones with some propensity towards flowering. The grafting process itself encourages the tree to flower at a younger age and smaller size, which is required for access to flowers and seed in the tunnel. The trees are pruned in a similar way to fruit trees to encourage flowering, but on top of this, it is necessary to stress the trees by wounding the bark on the stem when the sap is rising. The trees’ stress response is to reproduce; this seems to be the only way to stimulate them into flowering.
Aspen trees have male and female flowers on separate trees and they don’t necessarily flower at the same time. So we also need to collect the pollen by hand and then brush this onto the female flowers. If successfully pollinated, the female catkins will swell up and we can collect them to extract the seed. This seed extraction needs to be timed just right, so the seed doesn’t blow away when the catkins burst open.
Our aspen project is now producing enough seed both for our own woodland creation projects and for others too, increasing the amount of local provenance aspen available for planting across the Highlands.
As you walk through Scottish woodlands onto the open moorlands above, you will likely pass an abrupt boundary between trees and open ground. In a natural setting, trees gradually phase-out through the treeline, becoming stunted and twisted due to the extreme conditions. In the mountain areas of Scotland this is where you may find specialist montane trees. These wee trees are not easy to come by and neither are their seeds or cuttings, as such very little montane habitat survives in good condition in Scotland.
Our tree nursery specialises in growing these trees and making them available for planting schemes. At Dundreggan we are very lucky to have a large amount of dwarf birch, and as some of these plants have been fenced to exclude browsing by deer, they have been able to grow and produce seed. This seed has germinated well in the nursery and we grow over 10,000 dwarf birch a year.
Willow species are trickier to come by, trips further afield are required to collect materials. Many of the remaining willow communities are very small and fragmented and the seed may not be viable. It has to be collected at exactly the right time and sown immediately as seed will only live for a few days.
We have a range of species such as dark-leaved willow, tea-leaved willow, downy willow, whortle-leaved willow, as well as the much more common eared willow and the rarest one of all – the woolly willow. We will continue to developing our expertise and grow more of these vitally important and rare trees.
