The effects of site and provenance on survival, growth, stem form and fruiting of Sorbus aucuparia

Abstract: Sorbus aucuparia (rowan) is a widespread and common tree in Europe, the species has a large amount of genetic diversity and provenance variation. There is little silvicultural knowledge of the species and it is rarely used in forestry. One provenance trial was visited in northern Sweden and four in Great Britain, the aim was to understand provenance and site variation. Seven main traits were studied dbh, number of corymbs or fruit clusters, stem form, number of stems per tree, fork height, percentage of forked trees and survival, in addition height was measured in Sweden. There was a lot of variation from both site and provenance; both factors had an effect on all variables except provenance on survival. One British site, North York Moor, was unsuitable for the species, which was explained by an extreme site gradient and unfavourable site vegetation such as Vaccinium. At other sites competition from other vegetation was found to have a large effect on rowan, resulting in higher survival at the most northerly of the British sites and many stems in the southernmost site. Trees with larger diameters and more fruits showed that productivity was higher at southern sites, however the best site overall had the highest altitude and is located in South Wales. Northern provenances generally had better attributes in northern Sweden, such as large trees and more corymbs. Northern British provenances also generally had higher rankings in northern Britain. Some provenances from Southern Britain were better in all UK locations although some had very poor performance in the north and some costal provenances were even low ranking in the south. Southern provenances had more fruits in all locations. Provenance selection is important in rowan and if poorly done can lead to reduced performance. A general silvicultural recommendation would be not to use provenances from a more northern origin than their site. Provenances from high altitudes should be considered in northern locations due to higher seed quality.