CR prepress abstract  -  doi: 10.3354/cr00737

ABSTRACT: The winter wheat Triticum aestivum L. areas in Sweden (55-61° N) are at or close to the northern border of winter wheat cultivation. Yield variations at the county level for 1866 –2006 are analysed and compared with variations of length of winter. Yield deviations greater than ±25% occur on average once every five years in a county but more often in the North. In a maritime climate such as the one in the North-western Europe, the length of winter fluctuates considerably. Deviations in length of winter by more than ±45 days appear on average once every five years in a county but more frequently in the southern coastal counties. However, freezing temperatures are also more intermittent there compared to the continuous cold in the North. By means of a cluster analysis of the variations in length of winter the counties were divided in four groups. The general effect is that long winters give decreasing yields. Regressions between deviations in yield and lenght of winter show determination coefficients (R²s) in the range 0.13–0.30, which is high for a single variable. Winters are on average 48 days longer when yields are 25% below trend compared with yields 25% above trend. This pattern seems to be typical for climates with winter temperatures below 5–6°C.