Collecting for the National Tree Seed Project
Prioritising ash seeds
The priority this year has been collecting ash seeds. This is mainly because of high profile threats to ash trees in the UK caused by the pathogenic fungi, Chalara fraxinea, including its sexual stage Hymenoscyphus pseudoalbidus - more commonly known as 'ash dieback'.
Ash is an important tree in the UK. It is the third most commonly recorded broadleaved species in the most recent Census of Woodlands and Trees, and the second most widely planted broadleaved tree. The area covered by ash in the UK, including hedgerows and small woodlands, is 180,000 ha. Furthermore, the value of ash trees for commercial use is £22 million per annum, though this is dwarfed by the social and environmental benefits estimated at £150 million per annum!
Ash trees also have high conservation value. They create a relatively open woodland canopy, allowing light to penetrate to the forest floor. This creates perfect conditions for a rich and varied ground flora to develop.
The leaf litter can also have a positive effect on the biodiversity of soil ecosystems by reducing soil acidity. Additionally, the long-lived nature of ash trees, especially when coppiced, provides niches for a rich diversity of animal, plant and fungal life. Many such species depend on ash trees for their survival.
Genetic diversity of ash trees
Survival of ash trees in the UK also relies on the existing genetic diversity of ash trees. Resistance to ash dieback is thought to be present in a number of genes within the existing population. Therefore, preserving the genetic diversity of ash trees is the best way of supporting their overall survival: seed conservation is an excellent way of doing this.
So far we have collected roughly 160,000 ash seeds. The hope is that these seeds will provide an important resource for researchers and conservationists working to overcome these ecological threats.
Working with the Forestry Commission and Woodland Trust
It was clear from the outset that building a national tree seed collection was an ambitious commitment and was going to take more than a few workers from Kew so we enlisted the help of the Forestry Commission and the Woodland Trust. The Millennium Seed Bank is a partnership, working collaboratively across 80 countries to conserve and improve the use of seeds, so we have a good framework for working in this way.
The Forestry Commission has so far carried out 10 ash seed collections, focused in the east of England, central Scotland and in North Wales. It has also collected juniper seed in 19 sites in England and Scotland.
The Woodland Trust has recruited a team of devoted volunteers and collected hornbean and rowan seed at two of their ancient woodland sites. We have also been working closely with the Wakehurst Woodland Conservation team and together, so far, we have carried out ash seed collections at seven locations across the south and west of England.
Collecting seed in the field
How did we go about collecting ash seed? Firstly, we chose autochthonous populations, woodlands where trees have had a substantial history at a site over several generations. The theory is that in competitive ecosystems the trees we find are selectively adapted to local environmental conditions.
After choosing woodlands which are ancient or semi-natural, it was important that we gained the consent both of the landowner and also of Natural England, Natural Resources Wales or Scottish Natural Heritage who oversee the protection of these ecologically important sites.
When we got to a site, we checked the quality of seed to see if they were full and ripe. Then we aimed to collect seed from around 20 randomly selected trees.
The best method was to shake the high-up branches using a rope thrown up into the canopy. This released the seed which spun down onto a well-placed tarpaulin. When it worked this was a beautifully hypnotic sight, being surrounded by the twisting seed glistening in the low autumn sun.
As you can imagine, things didn’t always work out like that. There were a number of challenges including steep slopes, dense woodland and, of course, the much anticipated October storm. So we used other techniques, such as using pole saws to prune-off reachable branches and remove the seeds.
We tagged the trees we collected from so that we can return to them if necessary. So if you see one of these tags on a tree – you’ll know that the tree is a parent of seed in the national collection.
As a matter of course sub-samples are X-rayed to find the proportion of seed that is infested or dead, even after considerable effort to remove these seed. As you can see from these X-rays, ash seed play an important role in someone’s lifecycle - you can clearly see seed infested with invertebrate larvae.
We’ve learned a lot over the course of these collections and it’s been great working with other organisations in order to make a real and lasting legacy for the UK treescape.
- Simon -