12.4.4 Forests, shrublands and grasslands
Forest ecosystems in Europe are very likely to be strongly influenced by climate change and other global changes (Shaver et al., 2000; Blennow and Sallnäs, 2002; Askeev et al., 2005; Kellomäki and Leinonen, 2005; Maracchi et al., 2005). Forest area is expected to expand in the north (Kljuev, 2001; MNRRF, 2003; Shiyatov et al., 2005), decreasing the current tundra area by 2100 (White et al., 2000), but contract in the south (Metzger et al., 2004). Native conifers are likely to be replaced by deciduous trees in western and central Europe (Maracchi et al., 2005; Koca et al., 2006). The distribution of a number of typical tree species is likely to decrease in the Mediterranean (Schröter et al., 2005). Tree vulnerability will increase as populations/plantations are managed to grow outside their natural range (Ray et al., 2002; Redfern and Hendry, 2002; Fernando and Cortina, 2004).
In northern Europe, climate change will alter phenology (Badeck et al., 2004) and substantially increase net primary productivity (NPP) and biomass of forests (Jarvis and Linder, 2000; Rustad et al., 2001; Strömgren and Linder, 2002; Zheng et al., 2002; Freeman et al., 2005; Kelomäki et al., 2005; Boisvenue and Running, 2006). In the boreal forest, soil CO2 fluxes to the atmosphere increase with increased temperature and atmospheric CO2 concentration (Niinisto et al., 2004), although many uncertainties remain (Fang and Moncrieff, 2001; Ågren and Bosatta, 2002; Hyvönen et al., 2005). Climate change may induce a reallocation of carbon to foliage (Magnani et al., 2004; Lapenis et al., 2005) and lead to carbon losses (White et al., 2000; Kostiainen et al., 2006; Schaphoff et al., 2006). Climate change may alter the chemical composition and density of wood while impacts on wood anatomy remain uncertain (Roderick and Berry, 2001; Wilhelmsson et al., 2002; Kostiainen et al., 2006).
In the northern and maritime temperate zones of Europe, and at higher elevations in the Alps, NPP is likely to increase throughout the century. However, by the end of the century (2071 to 2100) in continental central and southern Europe, NPP of conifers is likely to decrease due to water limitations (Lasch et al., 2002; Lexer et al., 2002; Martínez-Vilalta and Piñol, 2002; Freeman et al., 2005; Körner et al., 2005) and higher temperatures (Pretzch and Dursky, 2002). Negative impacts of drought on deciduous forests are also likely (Broadmeadow et al., 2005). Water stress in the south may be partially compensated by increased water-use efficiency (Magnani et al., 2004), elevated CO2 (Wittig et al., 2005) and increased leaf area index (Kull et al., 2005), although this is currently under debate (Medlyn et al., 2001; Ciais et al., 2004).
Abiotic hazards for forest are likely to increase, although expected impacts are regionally specific and will be substantially dependent on the forest management system used (Kellomäki and Leinonen, 2005). A substantial increase in wind damage is not predicted (Barthod, 2003; Nilsson et al., 2004; Schumacher and Bugmann, 2006). In northern Europe, snow cover will decrease, and soil frost-free periods and winter rainfall increase, leading to increased soil waterlogging and winter floods (Nisbet, 2002; KSLA, 2004). Warming will prevent chilling requirements from being met, reduce cold-hardiness during autumn and spring, and increase needle loss (Redfern and Hendry, 2002). Frost damage is expected to be reduced in winter, unchanged in spring and more severe in autumn due to later hardening (Linkosalo et al., 2000; Barklund, 2002; Redfern and Hendry, 2002), although this may vary among regions and species (Jönsson et al., 2004). The risk of frost damage to trees may even increase after possible dehardening and growth onset during mild spells in winter and early spring (Hänninen, 2006). Fire danger, length of the fire season, and fire frequency and severity are very likely to increase in the Mediterranean (Santos et al., 2002; Pausas, 2004; Moreno, 2005; Pereira et al., 2005; Moriondo et al., 2006), and lead to increased dominance of shrubs over trees (Mouillot et al., 2002). Albeit less, fire danger is likely to also increase in central, eastern and northern Europe (Goldammer et al., 2005; Kellomäki et al., 2005; Moriondo et al., 2006). This, however, does not translate directly into increased fire occurrence or changes in vegetation (Thonicke and Cramer, 2006). In the forest-tundra ecotone, increased frequency of fire and other anthropogenic impacts is likely to lead to a long-term (over several hundred years) replacement of forest by low productivity grassy glades or wetlands over large areas (Sapozhnikov, 2003). The range of important forest insect pests may expand northward (Battisti, 2004), but the net impact of climate and atmospheric change is complex (Bale et al., 2002; Zvereva and Kozlov, 2006).