Adaptation of Boreal Field Crop Production to Climate Change

The average annual global temperature increased by 0.76°C during the past century (Intergovernmental Panel on Climate Change (IPCC), 2007) and climate modelling results show an increase in annual temperature in boreal regions of 0.1 – 0.4°C/decade over the 21st century, depending on the scenario and model. Warming will be unevenly distributed, being greater in summer in lower and middle latitudes but greater in winter at higher latitudes, and this differential will increase. Mean annual precipitation is projected to increase in the North and decrease in the South, and winter precipitation will increase in northern and central Europe, continuing the trends established in the 20th century of a 10 – 40% increase in northern Europe and a decrease of up to 20% in southern Europe (IPCC, 2007). The increase in winter precipitation is due to the increased water carrying capacity of the atmosphere resulting from the higher temperature. Global warming will increase the frequency of soil freeze-thaw cycles (FTCs) in cooltemperate and high-latitude regions previously subject to prolonged winter soil frost (Kreyling et al., 2007; Henry, 2008). Warmer winters will result in fewer soil freezing days and in boreal Europe, lowland permafrost is expected to eventually disappear (Harris et al., 2009). The length of the frost-free season has already increased in most midand highlatitude regions of both hemispheres over the values established in the middle of the 20th century. In the Northern Hemisphere, this is mostly manifested as an earlier start to spring, which will arrive progressively earlier in Europe by 2.5 d per decade (Menzel et al., 2006). Increased precipitation in winter, when there is little plant growth, increases the probability of leaching, runoff and erosion from unprotected boreal soils. Climatic warming can paradoxically lead to colder soil temperatures in winter when it reduces the thickness of the insulating snow cover (Henry, 2008 and references therein) leading to root injury (Kreyling, 2010). Increased soil freezing when snow was removed led to root injury, increased leaching of C, N and P, and decreased soil microarthropod abundance (Groffman et al., 2001; Weih & Karlsson, 2002; Henry, 2008), but it is unclear what impacts FTCs and lower soil temperature will have on soil biological and physical processes. Observed nitrate losses to the groundwater after deep soil frost events are attributable more to reduced root uptake due to root injury than to increased N net mineralization (Matzner & Borken, 2008) (Figure 1). The intensity and frequency of summer heat waves is likely to increase (IPCC, 2007). Between 1977 and 2000, these trends were more extreme in central and north-eastern Europe and in mountainous regions than in the Mediterranean region. Temperatures are increasing