Variation among seed sources of silver birch in 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 stoc k of Scandinavian origin is not advisable in Scotland, or probably elsewher e in the UK, as it has poor survival and grows slowly (i.e. volume growth a t years 16-22 is only 7-26 per cent of the Scottish controls). It is partic ularly prone to climatic damage due to late spring frosts. Recently establi shed trials of seed sources from Scotland and Northern England showed signi ficant: variation among Scottish populations in growth and dates of flushin g and senescence. Variation in 1-year height growth between the fastest and slowest growing provenances was about 30 per cent. Some geographic pattern s of variation in early height growth and flushing were apparent among diff erent seed sources at year 1, but equally there was considerable variation among sources which could not be simply attributed to location. A prelimina ry study of isozyme variation suggests that: populations are unlikely to ha ve passed through severe population bottlenecks; that there is no consisten t evidence for inbreeding within the populations; extensive gene exchange o ccurs between populations by pollen and/or seed flow; and there is no evide nce for more than one postglacial origin for the nine populations tested. T here is a need for more information on provenance performance among indigen ous populations of birch in order to give useful guidance to nurseries, for esters and policy makers.