The long-term effects of climatic factors on radial growth of downy birch (Betula pubescens) and rowan (Sorbus aucuparia) in East Iceland

The aim of this study was to investigate the tree-ring growth of rowan (Sorbus aucuparia L.) and downy birch (Betula pubescens Ehrh.) in Ranaskógur, a forest in East Iceland, and to determine its response to climate factors during the past century. Tree-core samples were collected in September 2018 and from those a tree-ring width (TRW) chronology and a standardized tree-ring index (TRI) chronology were produced. A statistical analysis between the chronologies and monthly mean temperatures and total monthly precipitation was carried out. The study found that both species had similar radial growth during the past century. The growth of birch responded significantly positively to June and July temperatures, while rowan responded significantly positively to July and August temperatures. The growth of neither species was significantly affected by precipitation across the whole period. However, in the 1940s to early 1960s, rowan growth correlated significantly with June precipitation, and birch with April and May precipitation.