Tilia cordata and Tilia platyphyllos - Technical guidelines for genetic conservation and use for lime
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A network of conservation stands is needed to conserve the genetic variation of limes, which have evolved through adaptation to different ecological and environmental conditions. Conservation and breeding programmes in all countries where lime is found is required to ensure the conservation of the genepool. Specific strategies should include:
Sampling strategies: Inventories are needed to provide an overview of the status of genetic conservation in each individual country and at the European scale. For practical purposes, provenance regions can be identified on the basis of ecogeographic variation and can be modified to take into account either expected gene flow or general knowledge about genetic variation within the species.
Central core regions: Large genetic reserves within the central core regions of distribution are needed for effective gene conservation purposes and should be given high priority, as large genetic variation is expected to be present in the core distribution area. In general, Tilia occurs in mixed species forest and is associated with a number of different plant species. Existing protected areas will only partly serve as genetic conservation areas, as they are not selected at random nor do they cover the core regions of distribution.
Marginal regions: In some regions, large gene reserves of Tilia are lacking, and these genetic resources may be extensively fragmented. They may also be subject to pollen contamination from new plantations originating from non-local seed sources. For these situations, in situ conservation may not be effective. In some of the marginal regions the regeneration of Tilia is lacking or inadequate. Ex situ conservation of Tilia genetic resources is therefore recommended in marginal regions. Preferably, these ex situ conservation stands should be established on the basis of reproductive material from within the local regions, in accordance with in situ silvicultural management principles. In situ conservation in marginal regions should include a larger number of populations.
Use and management of genetic resources: Breeding, improvement and management of genetic resources of Tilia should be combined with gene conservation to allow evolutionary forces to continue. Combining conservation and use is especially necessary for species of low economic interest (“use it or lose it”). At some locations the lime trees may be eradicated, if costly and extensive precautions are not taken. Alternatively, these resources could be used to promote the establishment of new populations from local seed collections.