Climatic determinants of introduced Sitka spruce in Hiiumaa Island, Estonia.
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 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. Both the native and non-native species responded positively to precipitation in June and negatively to precipitation in April. The growth of Sitka spruce in Hiiumaa may actually be less tolerant to winter temperatures. 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 individuals of this species in Hiiumaa.