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BIHIP Tree improvement and regional diversity

The theme for the scientific part of the 2002 meeting was Tree improvement and regional diversity. This highly topical issue could have impacts on the work of BIHIP because the Forestry Commission is about to set up a genetic management policy review group. The decisions reached as a result of its deliberations could have implications for the use of improved seed.

Sam Samuel of Forest Research

Told us of two sorts of variation which exist in trees:

  • Adaptive or selective variation, which is the basis of most field trials to determine suitability of genotypes for planting. Trials with many species generally show that native material performs better than foreign stock since it has often adapted well to the locality in such aspects as time of bud burst, though trials are often lacking with a British emphasis.
  • Neutral, non-selective or random variation, which is most commonly determined by molecular methods, can help elucidate such questions as the origin of particular populations and gene flow.

He also explained three terms about which there is often confusion. Adaptation is the variation in a population that exists as a result of selection in the local environment. Adaptability is the potential of a population to adapt to heterogeneous or changing environmental conditions. Conservation aims to maintain or increase adaptability. The important questions for BIHIP are whether a combination of adaptation and selection for quality and performance are acceptable, or are they mutually exclusive, and at what level breeding programmes should address the region of provenance or seed zone structure? There are four regions of provenance in Great Britain, which are subdivided into a total of 24 local seed zones, and Ireland as a whole is regarded as only one provenance region and seed zone at present.

Gordon Patterson of the Forestry Commission’s Policy and Practice Division

Gave us a valuable overview of 12 issues concerning policy on the genetic conservation of native trees, stressing that he had no clear answers yet, though developments to date are outlined in FC Technical Paper 31 (2000). Among those that will be important to BIHIP are:

  • The use of genetically improved material rather than local seed sources
  • The choice of seed origin and rules about transfer
  • The use of foreign material (e.g. eastern European oak) in existing woods
  • Responses to environmental change
  • The influences of tree genotype on woodland fungi and fauna

Particular research needs will be into adaptive variation and choice of seed origin, and the potential for seed supply in Britain. At present about two thirds to three quarters of all broadleaved planting stock comes from continental Europe, and large scale movement of seed across Britain is common. The Forestry Commission’s current policy is to encourage the use of local seed sources, especially in ancient semi-natural woodlands (ASNW). Though the use of improved material in ASNW is not likely to be ruled out if genetic conservation is not compromised, a particular problem is likely to arise if a large amount of specially selected stock is planted in native woodlands, especially if it is introduced from distant sources. Research is needed to determine how local it should be. Major reasons for this are that the UK is a signatory to the European Convention on Biodiversity, and also the "precautionary principle".

A wide spectrum of policy responses is likely to be developed between conservation on the one hand and production on the other. Where timber production is a major objective the use of improved stock would be allowed, and even encouraged. The main aim is not to allow the British gene pool to be changed too rapidly, and the challenge is to determine the desirable balance between genetic conservation and production. The genetic management policy review group mentioned earlier will almost certainly have a representative of BIHIP on it.

David Boshier (Oxford Forestry Institute)

Quoted the EC Biodiversity Strategy guideline which states that "native species and local provenances should be preferred where appropriate", and forest certification requires this approach too. The problem is to decide what "local" means. For example, should seed be collected from the same wood, the same watershed or anywhere in the same country? Two sources of information are available to help determine this:

  • Molecular studies which enable neutral variation, gene flow and population structure to be investigated, and
  • Field trials which allow adaptive variation to be studied. The extent of this will depend upon the number of generations over which selection has occurred, and also the extent of environmental variability.

He said that it is necessary to maintain genetic variation in trees (which are twice as diverse as herbaceous plants):

  • To provide adaptation to changing environments
  • Because it can be of direct use (as in BIHIP’s work)
  • To maintain viability of populations in the short term and avoid inbreeding and outbreeding depression. While there is no evidence yet for outbreeding depression in temperate trees, there is plenty for inbreeding.
  • Dr Boshier went on to explain that the "reciprocal transplant" experiments being planned at Oxford with ash will, at least for this species, elucidate the scale at which adaptation occurs, relating geographic distances between seed sources to ecological differences. This will provide a scientific basis for any adjustments that may be needed to the existing provenance regions and seed zones. However, policies for one species may not necessarily apply to another, for example due to different dispersal mechanisms or responses to site differences. He suggested that it would be important for BIHIP to identify where there is genotype-environment interaction in its trials and what this was caused by.

Other speakers were John Fennessy (COFORD), Ireland, and Hugh Williams (National Forest) who outlined their organisations’ perspectives on these points.

Dr Peter Savill, Woodland Heritage Trustee

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