Role of substrate on the dendroclimatic response of Scots pine from varying elevations in northern Scotland

The influence of substrate was evaluated by comparing annual ring widths of Scots pine (Pinus sylvestris L.) with climate data at 13 new sites (five bog, three peat, and five soil), together with 17 previously studied soil sites in northern Scotland. Radial growth rates <1.0 and >1.5 mm·year–1 differentiate well between pine growing on bog and peat, respectively, highlighting the role of pine as a indicator of water levels in these environments. Scots pine chronologies from bog are shown to have a weak temperature–growth response and so limit potential in dendroclimatic reconstructions. However, correlation analysis shows temperature in January–February and July–August to be important determinants of the radial growth of Scots pine on soil. Moving correlation analysis indicates that the relationship between the radial growth of pine on soil near the altitudinal tree line and summer temperature (July–August) is time stable, despite an increase of temperature in northern Scotland. However, winter (January–February) temperature has become less limiting since the 1920s. Scots pine at some soil, bog, and peat sites have increased or developed correlation with October temperature since the 1940s, suggesting an extension of the growth season, particularly on the western coast of Scotland.