Improving the availability of native Aspen for use in northern Scotland
The Biodiversity and Management of Aspen woodlands: Proceedings of a one-day conference held in Kingussie, Scotland, on 25th May 2001
Mark Banham
Broom Field Nurseries, Birchen, Dornoch, Sutherland. IV25 3NE. Email: markbanham@quista.net
Paul Young
Woodland Officer, Woodland Trust Scotland, Henrietta Park, Balblair, Dingwall, Ross-shire. Email: paulyoung@woodland-trust.org.uk
The opportunity to expand the area of Aspen in Northern Scotland has largely been missed in the extensive native plantings of recent years due to a lack of suitable planting material. The species rarely, if ever, produces viable seed in the north and nurseries have been unwilling to invest in the facilities necessary to produce stock vegetatively. The current nursery catalogues list mainly Dutch and English origin stock, which is not acceptable provenance for Highland use.
Some stock has been produced from restricted seed sources in Perthshire and using micro-propagation techniques from a Strathspey clone. Many of the latter propogules suffer from poor apical dominance, and there appears to be reluctance to buy these in for growing on at £250 per 1000. There is also the problem of no breadth of genetic variability in such stock. As this method only becomes economic with large runs, it is not suitable for smaller scale multiple clone use where 10-20 separate clones are used for plantings up to 5ha.
The best method of improving the availability of northern zone origins would seem to be to produce stock from root cuttings along the lines of Forestry Commission Research Information Note 200 'Vegetative Propagation of Aspen'.
There are, however, exceptional costs associated with this method of propagation to enable suitable stocks to be made available at affordable cost to potential users (now frequently plant-for-grant crofters). The particular costs are those associated with root collection and provision of heated mist and wean polytunnel facilities.
Propagation Technique
Aspen roots are located in the field from suckers and lengths are dug up; this is a very laborious process. The root lengths are wrapped to prevent damage, and at the nursery are cut into lengths to fit compost filled boxes. They are laid horizontally and covered with further compost at about 16m root lengths per m2.
In the spring the roots send up suckers. Surface roots with existing sucker points are the most productive producers of cutting material. When the sucker shoots have reached several centimeters in height, they are cut and transferred to mist and wean beds. Here automated misting keeps the foliage moist and soil warming cables provide a rooting zone temperature of 24oC.
After three-four weeks, the cuttings are sufficiently rooted to allow potting on into cells. They are then kept under mist for a further few days. The collected roots send up a second set of suckers, which are left to grow on to keep the rootstock alive. These are cut the following winter and the process is then repeated in following years. Sucker production varies greatly between clones, but on average a 1m length of root will produce 15 suckers.
Rooting success also shows clonal variation but is typically about 70%. About 40% of potted-on cuttings will produce a plantable 20-40cm one year plant given a reasonable growing season. Forty percent will take two years and 20% will be culled. From these figures, it can be seen that to produce 1,000 plants per annum, about 95m of root stock needs to be collected.
Root Collection
As there is such great clonal variation in suckering and rooting success, it is thought advisable to undertake root collection over a two year period. Limited root collection from a number of clones per zone is undertaken in the first season, and the performance of the clones monitored to determine which stands should have further root collections in the following year.
A collection of 25m root length from each of 10 clones should be sufficient to provide planting stock for an annual planting of about 3ha. Collection costs will vary greatly with site and access etc, but would be in the order of £3/m assuming material could be gathered from two clonal populations in a locality in one day.
Propagation Facilities
It is estimated that each 25m collection would require 4.4m2 of polytunnel space @ £14/m3. Each collection would require 1.5m2 of root bed @ £14. Each collection would require 1.0m2 of heated mist bed @ £30. There would be a fixed cost of £330 for the control units for the mist and wean and heating components. These units would cope with the production from 10 collections.
The total cost per 10 collections is therefore estimated as:
| Root collection |
£ 750 |
| Propagation facilities |
£1390 |
| |
------- |
| |
£2140 |
It is estimated that this investment would produce 2,600 Aspen per annum.
For a nursery to recover this cost over a five year period, pay 10% finance charges and seek to make a modest 10% return on capital/available finance employed, it would be necessary to charge £330 per 1,000 more for Aspen than for species raised from seed. At this price it would be unlikely that Aspen could ever be planted in significant quantities where Woodland Grant Scheme (WGS) funding is required to meet costs.
Chicken and egg
It would seem that such 'technical difficulties' allied to high unit costs, in producing sufficient volumes of stock at reasonable commercial rates, is prohibitive to the reproduction of this valuable species at present (notwithstanding the work of Trees for Life and others in propagating Aspen stock on a small scale for local use). Consequently, it is under-represented in most, if not all, appropriate WGS schemes in the northern Highlands and elsewhere.
In the short term, it is expected that under such proposals sufficient Aspen planting stock could be generated from sources locally to fulfil modest planting requirements over the next three years (7,600 plants from 10 separate clonal populations).
If such clonal collection and propagation could be produced by nurseries over a wider area, sufficient northern Scotland provenance stock could be produced within an Aspen Bank for future planting schemes. Once set up, nurseries would be keen to expand the bank to accommodate other clones from wider provenances. If successful, this would do much to expand this valuable habitat in the long term.
Such local initiatives are to be welcomed. However, the start up capital costs are prohibitive to many small regional nurseries, and such a project on a larger scale will require targeted incentives to assure success. Whilst Enterprise companies or European Funding could be accessed by individual nurseries in the Highlands, other sources would need to be found. This raises a number of interesting questions, such as:
Would an Aspen challenge fund be the way forward or an Inter agency funding partnership?
Is there scope to offer sufficient incentives through the WGS at present?
Could the Forestry Commission be persuaded to accept lower stocking densities for Aspen planting, thereby reducing the 'per hectare' costs to compare favourably with other planting stock? The ability of Aspen to sucker would ensure fully stocked stands, under favourable conditions, in the future.
Of course, even if such incentives were to be put in place, nurseries still have to produce sufficient stock. Did someone say chicken and egg?
Reference
Hollingsworth, M.K. and Mason, W.L. 1991. Vegetative propagation of Aspen. FC Research Information Note 2000.
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Trees for Life: Propagating Aspen from root cuttings
