Impact of Climate Change on Agriculture and Forestry

Many recent studies have assessed effects of climate change on agricultural productivity (e.g. Harrison et al., 1995a, 2000). These studies have been mainly made on cropping systems (annual and perennial crops, grassland, etc.), however, livestock systems have also been examined.

The climate warming is expected to expand the area of cereal cultivation (e.g. wheat and maize) northwards (Kenny et al., 1993; Harrison et al., 1995b; Carter et al., 1996) (Figure 3). For wheat, a temperature rise will lead to a small yield reduction, whereas an increase in CO2 will cause a large yield increase and the net effect of both for a moderate climate change is a large yield increase (Harrison and Butterfield, 2000; Nonhebel, 1996). Drier conditions and increasing temperatures in the Mediterranean region and parts of eastern Europe may lead to lower yields and the need for new varieties and cultivation methods. Yield reductions have been estimated for eastern Europe, while yield variability may increase, especially in the steppe regions (Alexandrov, 1997; Sirotenko et al., 1997). In Figure 4 the response of wheat yields to change of climate and CO2 concentration for a GCM scenario for 2050 (Harrison and Butterfield, 2000) is reported. The largest increases in yield occur in southern Europe, particularly in northern Spain, southern France, Italy and Greece. Relatively large yield increases (3-4 t ha-1) are also seen in Fenno-Scandinavia. In the rest of Europe, yields are between 1 and 3 t ha-1 greater than

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Figure 3. Change in the duration from sowing to maturity for winter wheat (cv. Avalon) under UK Transient scenario 2066-75 (from Harrison et al., 1995b).

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Figure 3. Change in the duration from sowing to maturity for winter wheat (cv. Avalon) under UK Transient scenario 2066-75 (from Harrison et al., 1995b).

Figure 4. Change in water limited yield for wheat using HadCM2 scenarios for 2050 (from Harrison and Butterfield, 2000).

at present. There are small areas where yields are predicted to decrease by up to 3 t ha-1, such as in southern Portugal, southern Spain and the Ukraine. For maize, future climate scenario analyses carried out for selected sites in Europe suggest mainly increases in yield for northern areas and decreases in southern areas (Wolf and van Diepen, 1995). This is due to a small effect of increased CO2 concentration on growth (maize is a C4 plant which responds less positively to CO2 increases than C3 plants such as wheat and barley) and a negative effect of temperature on the duration of growing season. This latter effect, however, can largely be prevented by growing other maize varieties (Wolf and van Diepen, 1995).

Seed crops are generally determinate species, and the duration to maturity depends on temperature and day length. A temperature increase will therefore shorten the length of the growing period and possibly reduce yields (Peiris et al., 1996). At the same time, the cropping area of the cooler season seed crops (e.g. pea, faba bean and oil seed rape) will probably expand northwards into Fenno-Scandinavia, leading to increased productivity of seed crops there. There will also be a northward expansion of warmer season seed crops (e.g. soybean and sunflower). Harrison et al. (1995b) estimated this northward expansion for sunflower, but also found a general decrease in water-limited yield of sunflower in many regions, particularly in western Europe (Figure 5). Analysis of effect of climatic change on soybean yield for selected sites in western Europe suggests mainly increases in yield (Wolf, 2000a). This is due to a positive effect of CO2 concentration on growth and only a small effect of temperature on crop duration.

Vegetable responses to changes in temperature and CO2 varies among species, mainly depending on the type of yield component and the response of phenological development to temperature change. For determinate crops such as onions, warming

Figure 5. Change in water limited yield for sunflower (cv. Cerflor) under UK Transient scenario 2066-75 (from Harrison et al., 1995b).

will reduce the duration of crop growth and hence yield (Harrison et al., 1995b), whereas warming stimulates growth and yield in indeterminate crops such as carrots (Wheeler et al., 1996). Onion yields are sensitive to the degree of warming (Harrison et al., 1995b), with a yield decrease for warmer future climate scenarios and a yield increase for cooler future climate scenarios. There is also a spatial gradient with yield increases in northwest Europe to decreases in southeast Europe (Figure 6). For lettuce, temperature has been found to have little influence on yield, whereas yield is

Figure 6. Change in potential yield for onion under UK Transient scenario 2066-75 (from Harrison etal., 1995b).

stimulated by increasing CO2 (Pearson et al., 1997). For cool-season vegetable crops such as cauliflower, large temperature increases may decrease production during the summer period in southern Europe due to decreased yield quality (Olesen and Grevsen, 1993).

Root and tuber crops are expected to show a large response to rising atmospheric CO2 due to their large underground sinks for carbon and apoplastic mechanisms of phloem loading (Farrar, 1996; Komor et al., 1996). On the other hand, warming may reduce the growing season and enhance water requirements with consequences on yield. Climate change scenario studies performed using crop models show increases in potato yields in northern Europe and decreases or no change in the rest of Europe (Wolf, 2000b). The simulation results showed an increase in yield variability for the whole Europe, which enhance the risk for this crop. Indeterminate root crops such as sugar beet may be expected to benefit from both the warming and the increase in CO2 concentrations (Davies et al., 1997).

Perennial crops (e.g. grapevine, olive and energy crops) have been relatively less studied than annual crops. For grapevine, a study on the potential cultivation of grapevine in Europe under future climate scenarios has shown that there is a potential for an expansion of the wine growing area in Europe and also for an increase in yield (Figure 7). Moreover, detailed predictions made for the main EU viticultural areas have shown an increase in yield variability (fruit production and quality) (Bindi et al., 1996,2000). For olive, it was shown that in 2 x CO2 case, the suitable area for olive cultivation could be enlarged in France, Italy, Croatia, and Greece due to changes in temperature and precipitation patterns (Bindi et al., 1992). For indeterminate energy crops that are favoured by the longer growing season and by increased water use efficiency due to higher CO2 levels, higher temperatures and CO2 concentrations would generally be favourable. A study of willow production in

Figure 7. Change in potential yield for grapevine using HadCM2 scenarios for 2050 (from Harrison and Butterfield, 2000).

Figure 7. Change in potential yield for grapevine using HadCM2 scenarios for 2050 (from Harrison and Butterfield, 2000).

the UK thus found that a warming would generally be beneficial for production with increases in yield up to 40% for a temperature increase of 3 K (Evans et al., 1995).

Livestock systems may be influenced by climate change directly by means of effects on animal health, growth, and reproduction, and indirectly through impacts on productivity of pastures and forage crops. Heat stress has several negative effects on animal production, including reduced reproduction and milk production in dairy cows and reduced fertility in pigs (Furquay, 1989). This may negatively affect livestock production in summer in currently warm regions of Europe. Warming during the cold period for cooler regions is likely to be beneficial due to reduced feed requirements, increased survival, and lower energy costs. The impact of climate change on grasslands will affect the indirectly livestock living of these pastures. In Scotland studies of the effect on grass-based milk production indicate that these vary depending on the locality. For herds grazed on grass-clover swards milk output may increase regardless of site, due to the CO2 effect on nitrogen fixation (Topp and Doyle, 1996).

The response of forest ecosystems to climate change can be expressed in terms of boundaries shift, changes in productivity and in risk of damages (e.g. fire damage).

In northern Europe, Boreal forests are dominated by Picea abies and Pinus sylvestris; these species under warmer conditions would invade tundra regions (Sykes and Prentice, 1996). In the southern Boreal forests, these species will be expected to decline due to a concurrent increase of deciduous tree species (Kel-lomaki and Kolstrom, 1993). Most climate change scenarios suggest a possible overall enlargement of the climatic zone suitable for Boreal forests by 150-550 km over the next century (Kirschbaum et al., 1996). In particular, in the Russian region tundra and taiga areas would be sharply reduced and replaced by leaf-bearing and steppe (Sirotenko et al., 1997).

In large areas of western and central Europe, the temperature increase would determine a replacement of natural conifers with the more competitive deciduous trees. Site-specific assessments performed for Germany suggests that conifers (e.g. Picea abies) may be replaced by deciduous species (e.g. Fagus sylvatica) (e.g. Krauchi, 1995; Bugmann, 1997). Furthermore, the increase in winter temperature seems to allow the survival of exotic species (e.g. Nothofagus procera in Britain) (Cannell, 1985).

In southern Europe, most forests consist of sclerophyllous and some deciduous species that are adapted to summer soil water deficit. Climate scenarios indicate reduced water availability in the summer months and associated increases in temperature. These conditions may determine the relative importance of sclerophyllous and deciduous species changes, with, for example, expansion of some thermophilous tree species (e.g. Quercus pyrenaica) when water availability is sufficient (e.g. Gavilan and Fernandez-Gonzalez, 1997).

Global warming, increasing CO2, increased nitrogen deposition and changes in management practices are all factors assumed to favour increase of forests productivity. In northern Europe, effects of precipitation changes are likely to be much less important than the effects of temperature changes (Kellomaki and Vaisanen, 1996; Talkkari and Hypen, 1996); thus it could be concluded that climate change and CO2 increase would be favourable for northern forests, e.g. due to increased regeneration capacity. In central and southern Europe, limited moisture due to increasing temperature and (possibly) reduced summer rainfall may regionally generate productivity decline. However, CO2 enrichment will likely increase water use efficiency, which makes growth less drought-sensitive (Kellomaki, 2000). Furthermore, in the Mediterranean region, the elevation of summer temperature and reduction of precipitation may further increase fire risk. In temperate eastern Europe, forest fire increase is less likely, but very dry and warm years could occur more frequently, and promote pest and pathogen development. Estimates of the possible influence of climate change on insect infestation are uncertain due to complex interactions between forests, insects and climate. However, some preliminary studies indicates that increases in climate aridity would promote occurrence of some diseases (e.g. root and stem fungi decays) (Kellomaki, 2000).

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