How is the growing seasonal of crops?

Rate of change of crop growing season length 1975-2007

Note: The map shows the rate of change of crop growing season leght

Data source:

MARS/STAT database (Genovese, 2004a, 2004b).

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Length of frost-free period in selected European areas 1975-2007

Note: Length of frost-free period in selected European areas 1975-2007

Data source:

MARS/STAT database (Genovese, 2004a, 2004b).

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Past trends

Many studies report a lengthening of the period between the occurrence of the last spring frost and the first autumn frost. This has occurred in recent decades in several areas in Europe and more generally in the northern hemisphere (Keeling et al., 1996; Myneni et al., 1997; Magnuson et al., 2000; McCarthy et al., 2001; Menzel and Estrella, 2001; Tucker et al., 2001; Zhou et al., 2001; Walther et al., 2002; Root et al., 2003; Tait and Zheng, 2003; Yan et al., 2002; Robeson, 2002; Way et al., 1997). An analysis of the growing period in Europe between 1975 and 2007 (Figure 1) shows a general and clear increasing trend. The trend is not uniformly spread over Europe. The highest rates of change (about 0.5-0.7 days per year) were recorded in central and southern Spain, central Italy, along the Atlantic shores, and in the British Isles, Denmark and the central part of Europe. The extension of the growing season is either due to a reduction in spring frost events or to a progressive delay in the start of autumn frosts (Figure 2). However, a decline has been observed in the Mediterranean countries, in the Black Sea area and in parts of Russia. In areas where a decrease in the length of frost-free period occurred, in particular in southern Europe, the plants are more at risk from frost damage due to a delay in the last winter-spring frost.

Projections

Following the observed trends (which have accelerated even more in the past decade) and in line with projections for temperature increase, a further lengthening of the growing season (both an earlier onset of spring and a delay of autumn) as well as a northward shift of species is projected. The latter is already widely reported (Aerts et al., 2006). The length of the growing season will be influenced mainly by the increase in temperatures in autumn and spring (Ainsworth and Long, 2005; Norby et al., 2003; Kimball et al., 2002; Jablonski et al., 2002). According to the IPCC analysis, Europe will warm in all seasons for all scenarios, but warming will be greater in western and southern Europe in summer and northern and eastern Europe in winter. More lengthening of the growing season is therefore expected in these northern and eastern areas, while in western and southern Europe the limited water availability and high temperatures stress during summer will hinder plant growth.