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Résumé :
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These Technical Guidelines provide recommendations for the conservation of the genetic resources of the white elm at the European scale. They are based on the available knowledge of the species and on widely accepted methods for the conservation of forest genetic resources. They should be regarded as a commonly agreed basis to be complemented and further developed in local, national or regional conditions. White elm is distributed from the Ural Mountains to France, and from southern Finland to the Caucasus and Bosnia. Its typical habitat is riparian deciduous forest, where it can tolerate prolonged flooding. White elm is allogamous, and does not hybridize with the other European elm species which belong to a different section of the genus. Flowers are hermaphroditic and wind pollinated. Habitat destruction for agriculture or poplar cultivation has caused enormous damage to white elm populations. Consequently, white elm is now often restricted to fragmented populations of a limited size, facing the risk of genetic drift. The impact of DED on white elm populations is more serious in central and eastern Europe than at the western fringe of its natural range. This is largely due to the bark beetles (Scolytus sp.) which are the vectors of the DED fungal agent (Ophiostoma novo?ulmi), which prefer to feed on field elms in western Europe and rarely visit white elms. Despite this pathological threat, the in situ conservation of white elm genetic resources is still possible through the establishment of a network of conservation stands. Complementary ex situ conservation measures must be undertaken when no legal habitat protection measure can be taken, when populations are small and fragmented, or when the impact of DED is too strong. In emergency cases, 'static' conservation measures, such as clonal archives and cryopreservation of seed lots can be applied. However, 'dynamic' ex situ conservation units, such as conservation seed orchards and reconstructed populations, are highly recommended.
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