Climatic determinants of introduced Sitka spruce in Hiiumaa Island, Estonia

Abstract

Tree-ring records of Sitka spruce growing in Hiiumaa (Estonia) were investigated to illustrate their growth variability and its climatic determinants. A chronology comprising ring-width series of eight big individuals from the Suuremõisa forest park was correlated with local climatic records. The growth variability of this species introduced to Hiiumaa was statistically explained profoundly by winter temperature and early-spring precipitation. Comparisons were also made with local tree-ring data of Norway spruce. Interestingly, both the native and non-native species responded positively to precipitation in June and negatively to precipitation in April. Previous studies have shown that the winter temperature response, demonstrated here for Sitka spruce, is found as Norway spruce growth responses in eastern Estonia, whereas in western Estonia the growth of the latter species is more clearly connected, similar to our findings, to early-summer precipitation. These findings indicate that while the both spruce species remain sensitive to spring/summer moisture regime, the growth of Sitka spruce may actually be less tolerate to winter temperatures, as evident here in western Estonia where the winters may likely be milder than in eastern Estonia. Common to Sitka spruce results from Hiiumaa, tree-ring data representing conspecific native populations from north-west North American sites indicated positive responses to mid-winter temperatures. Based on these results, low winter temperatures and early-summer droughts may both threaten the survival of the remnant individuals of this species in Hiiumaa.