© 2000 by Institute of Chartered Foresters
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Variation among seed sources of silver birch in Scotland
1 Edinburgh, Scotland 2 Midlothian, Scotland
The results of five provenance trials of silver birch (Betula pendula Roth.) in Scotland are described. These comprise: (1) two trials laid out in the 1970s and 1980s comparing improved Finnish stock with unimproved Scottish material, and (2) three recently established provenance trails of Scottish seed sources for which 1–2 year results are available. Use of planting stock of Scandinavian origin is not advisable in Scotland, or probably elsewhere in the UK, as it has poor survival and grows slowly (i.e. volume growth at years 16–22 is only 7–26 per cent of the Scottish controls). It is particularly prone to climatic damage due to late spring frosts. Recently established trials of seed sources from Scotland and Northern England showed significant variation among Scottish populations in growth and dates of flushing and senescence. Variation in 1-year height growth between the fastest and slowest growing provenances was about 30 per cent. Some geographic patterns of variation in early height growth and flushing were apparent among different seed sources at year 1, but equally there was considerable variation among sources which could not be simply attributed to location. A preliminary study of isozyme variation suggests that: populations are unlikely to have passed through severe population bottlenecks; that there is no consistent evidence for inbreeding within the populations; extensive gene exchange occurs between populations by pollen and/or seed flow; and there is no evidence for more than one postglacial origin for the nine populations tested. There is a need for more information on provenance performance among indigenous populations of birch in order to give useful guidance to nurseries, foresters and policy makers.