The Whitty Pear - Sorbus domestica L. A Natural Pioneer Millennium Award Project, Work in Progress

Introduction

The importance of S.domestica is clear from European to local level. Europe-wide S.domestica is recognised as needing action in the EU GENRES programme2. It is the most endangered tree species in Switzerland with 300 individuals, which contrasts with 23 wild individuals plus 22 suckers that have been found in the UK3. In the UK, the species is classed as 'critically endangered'4. English Nature has chosen S.domestica as the only tree species to have a current 'Species Recovery Plan'. The Royal Botanic Gardens, Kew who chose S.domestica to be one of its 'Threatened Plant Appeals' species has found that it has stimulated a greater response than any other current TPA species, including tropical species. Locally, there is an individual Species Action Plan for the True Service Tree within the Worcestershire Biodiversity Action Plan.

Eleven tree species in Britain are in danger of extinction - all of which are members of the Sorbus genus5. It was the opinion of Sorbus experts who participated in a workshop held at Wakehurst Place in April of 1996, that Sorbus domestica shared joint top priority in terms of conservation in the UK, with S.bristoliensis, S.leyana and S.wilmottiana6. Others would go further and point out that, since S.domestica is in a subgenus of its own, subgenus Cormus, and it is the only sexual species of the four, that S.domestica could be considered priority number one in terms of conservation of tree species in the UK.

A brief history

In 1983 a population was found by Marc Hampton on a South facing Lias limestone seacliff in Glamorgan. An individual in this population has been estimated to be c.400 years old!7 Since then a second site has been found in Glamorgan and three sites had been discovered in Gloucestershire8. In August 1999 while Mark and Clare Kitchen were showing me the Gloucestershire sites Mark Kitchen discovered another individual. The new tree is sufficient distance away from another site on the River Severn to be considered a separate population.

Project objectives and progress (See Table 1)

Day 1:

Moving down stream to Winnall coppice naturally wooded slope with marsh at base of slope and then woodland at the Hollies we saw the same tree species composition occurred at both sites. All three woodlands are on sandstone with unstable soil surfaces.

Day 2:

Two miles north of Homme Castle, just north of Furnace Farm, surveying South to the Shelsley Walsh.
We surveyed Rock Coppice round to the top of Devil's Den and Hell Hole. Along this stretch there are some veteran Yews of an impressive girth on the slope. Finally we descended returning to Shelsley Walsh.

Comments

Figure 1 The original Whitty Pear (Nash 1799)

Since visiting all six suspected wild sites known of in the UK, I am now certain that there are more unrecorded S.domestica individuals, perhaps even in Worcestershire! In brief, the reasoning behind my optimism is based on the characteristics of the Gloucestershire sites. The Glamorgan sites have individuals suckering for up to 200m stretches of South facing exposed Lias limestone seacliffs, undercut by salt marsh. The individuals seemed to be repelled by encroaching woodland on less sheer gradients and on both sites there was Maiden Hair Fern Adiantum capillus veneris, Purple Gromwell Lithospernum purpureocaeruleum and a Fleabane Inula. Combined, these site characteristics are very specific. Many sites that share these characteristics in the UK, have already been identified, and have been relatively easy to survey with binoculars.9 In contrast, sites in Gloucestershire have many characteristics that are found frequently in Worcestershire and elsewhere. For example, the geology has Lias limestone as a small component of the slope profile, the rest of the slope is comprised primarily of sandstone. The slopes are densely wooded, sheer, unstable and in most cases can not be viewed from the top of the slope. These qualities make them very difficult to actively survey either close up or with binoculars. I feel the only safe way that botanists could be certain about an 10area of slope would be to carry out transacts at regular intervals on ropes from the top of the slope. However, it is more likely that sites will continue to be discovered by seeing new windows into the wooded slopes due to land slippage, which is how new site was discovered in August of this year. The species that are consistently associated with S.domestica in Gloucestershire are S. torminalis and wild madder Rubia peregrina.[latter does not occur in Worcestershire] .I would be interested to see the results of a coincidence search of sites in Worcestershire, or elsewhere, which share the Gloucestershire geological and botanical characteristics. This would be very useful information on which to base further surveying.

Molecular research

With the help of local enthusiasts I collected leaf samples from 28 S. domestica individuals. (A note for future samplers: using polepruners would have been a really good idea!) All these samples were from Worcestershire with the exception of two from Gloucestershire. Up to five grams of fully formed leaf material was collected from each tree, torn into small pieces and added immediately to a 50g bag of fine grain silica gel. The silica gel removes moisture from the leaves, indicated by a colour change in a gel. . It is important that leaf material is dried within 24 hours of collection to avoid DNA degradation. Therefore the silica must not be overloaded. It was also important to avoid leaves with rust where possible. A herbarium sheet of the material serves as the voucher for the DNA of each sample and these are best pressed between paper in the field. In addition, Pam Thaw arranged for the collection of the Taunton sample, Harry Green collected the Italian (Umbria) sample and Jon Stokes of the Tree Warden Scheme/Tree Council collected the Suffolk sample.

These 28 samples were added to others from England, Wales and from throughout Europe, totalling 74 samples from eight countries, (see Table 2). Currently, DNA of 71 samples has been totally extracted. All totally extracted DNA from this research is stored in Kew's DNA bank available for use in this and future research involving Sorbus domestica. The three remaining samples are late comers and are half way through extraction. Every sample goes through the AFLP and electrophoresis process in triplicate. This is because a different genetic 'primer' or label is attached to each one of these, to obtain different information about the sample. Forty-five samples have already gone through the AFLP process and electrophoresis, and the data is being edited on the Genotype™ computer program. The remaining 29 samples plus a number of repeats will also go through this process. Once all the data is collated and edited, the three sets of information will be combined for each sample, then phylogenetic analysis of the data will begin. I am very lucky that Kew have given me the opportunity to write the report with them for English Nature. I am unable to realistically predict the timing of the final report as this is the first time I have carried out this process. However one snippet of information based on the information from one primer suggests that the Croome Perry Wood tree and the Oxford Botanic Garden maliform specimen are genetically indistinguishable using this technique. This suggests that they could have been vegetatively reproduced from the same origin.

List 1: Sites of samples included in the current molecular research at Kew, part of the work for English Nature's Species recovery plan for Sorbus domestica.

As for the wild populations, I hope the molecular work, which is one of the starting points of the English Nature Species Recovery Plan, will be the first step towards the active conservation of this amazing survivor in the UK.

Acknowledgements

References

Notes

1. The local Biodiversity Action Plan is available form at the Worcester Wildlife Trust.
2. EU GENRES programme is the European programme on characterisation, collection and utilisation of genetic resources in agriculture. S. domestica is in project 29.
3. Taken from 'The Conservation Status of Sorbus in the UK with the addition of the August 1999 site. See footnote no. 8.
4. From the Red Data Book of rare plant species, under the Joint Nature Conservation Committee.
5. A fact reported by the World Conservation Monitoring Centre and the World Conservation Union, 1998. 'Tree News', Autumn 1998.
6. Taken from 'The Conservation Status of Sorbus in the UK proceedings of the Workshop held at Wakehurst Place 28th April 1996', edited by Andy Jackson and Mark Flanagan from Royal Botanic Gardens Kew, Wakehurst Place. Published by Kew February 1998.
7. 'Sorbus domestica L., new to Wales and the British Isles', by M. Hampton and Dr Q. O. N. Kay of University of Wales, Swansea. Watsonia 20 (1995).
8. All the Gloucestershire sites have been discovered by Mark and Clare Kitchen, the vice-county botanical recorders for Gloucestershire.
9. Mark Hampton has conducted much surveying throughout the UK.
10. The picture on this page is from K Tomkinson, D&E Everett (1984) Collections from the History of Worcestershire by T Nash 2nd edition 1799 - a natural history plate showing the Wyre Firest Sorbus domestica.
11. AFLP Plant Mapping Protocol, Part number 402083, Revision B, May 1996. PE Applied Biosystems. (A Division of Perkin-Elmer)
12. By Kausch-Blecken von Schmeling. Out of print.