Early height growth of silver birch (Betula pendula Roth) provenances and implications for choice of planting stock in Britain

Abstract

Results of nine replicated provenance trials of silver birch (Betula pendula Roth) growing in Great Britain and Ireland are described. Five of the trials compare provenances fromScotland and the north of England measured after 10 or 11 years of growth; the remaining four trials compare provenances fromacross Great Britain, Ireland and the nearcontinent measured after 8 years of growth. In total, 64 provenances were tested. Survival was generally high across all sites with a mean of 79 per cent for the first five trials, and 89 per cent for the remaining four. The study found significant differences in mean height growth between trial sites and between provenances within each trial site. Although there was statistically significant site by provenance interaction, the better and poorer provenances were consistent across the range of sites tested. Mean height growth of the provenances under test was inversely correlated with latitude of origins, southern origins generally performing better. There was some evidence that further variation can be explained by incorporating details of longitude, accumulated temperature and potential moisture deficit for the origin. Elevation had little impact on explaining provenance performance. There was no evidence for the superior performance of provenances originating close to the trial site, other than for the southern-most trials. The relatively poor height growth of provenances from upland Scotland at even local trial sites suggests excessively conservative adaptation. The data suggest northernmovement of provenances byat least 2 degrees latitude or 200 kmwould bring the benefits of improved height growth and yet carry little risk of poorer survival under current climate conditions and could perhaps be extended further according to predictions of future climate warming.