Dr David Boshier, a member of the BIHIP Ash Group, has just completed some EU-funded research together with Janet Stewart and Sarah Rendell, all at the Oxford Forestry Institute, on the genetics of ash. European and national guidelines currently encourage planting local tree seed, rather than seed from more distant sources on the grounds that it is likely to be best adapted to the locality. But what does ‘local’ mean ? One objective of the FRAXIGEN project was to provide scientific evidence to answer the question: “How local is local ?”
They attempted to establish whether ash stands show local adaptation, and, if so, over what geographic scale ? How much similarity exists between woods ? Are neighbouring ash stands more similar than distant ones ? FRAXIGEN addressed these questions through a combination of field and laboratory studies.
Some of the key outcomes of the research are:
- While material should not be transferred over very large latitudinal, or longitudinal ranges, provenance delimitation for ash can operate at the scale of at least 200-300 km without compromising local adaptation, i.e. good seed sources can be moved to other sites within this range without adversely affecting their performance. This is in marked contrast to recommendations in current Forestry Commission guidelines (Practice Note on Using local stock for planting native trees and shrubs of August 1999).
- High levels of gene flow between stands provide evidence against subdividing large provenance regions into small zones for seed collection.
- Native populations of ash in Britain have high levels of genetic variation. They are not threatened, or in need of specific conservation programmes.
- Nevertheless, seed collectors should observe the following recommendations, to maintain local genetic diversity without affecting future productivity and adaptability:
- Collect seed from at least 10 trees
- Collect at least 500 seeds per tree
- Seed trees should be at least 150 m apart
- Collections can be from female, or hermaphrodite trees, and in either mast, or non-mast years, without reducing genetic diversity.
THE NURSERYMAN'S POINT OF VIEW
There is a current movement to encourage the planting of trees and shrubs from “native” seed sources. Why is this encouraged and what effect is this having on the nursery industry?
Luckily we are only asked very occasionally for “native” origin plants – most of our customers are pleased to receive high quality plants – so we do not suffer personally, but I sympathise with many other nurseries.
We should concentrate on producing the high quality plants that the industry is known for, that will grow in the conditions in which they are put, rather than worrying about the exact location that the seeds may have come from.
Niel Nicholson, Nicholson Nurseries Ltd