On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
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1<br />
1 . Introduction<br />
1.1 Climatic change and mounta<strong>in</strong>ous forests<br />
Carbon dioxide and o<strong>the</strong>r trace gases <strong>in</strong> <strong>the</strong> earth's atmosphere are relatively transparent<br />
to <strong>the</strong> <strong>in</strong>com<strong>in</strong>g solar radiation, but <strong>the</strong>y absorb a large portion <strong>of</strong> <strong>the</strong> <strong>in</strong>frared energy radiated<br />
back <strong>in</strong>to space (Schneider 1989). This phenomenon is known as <strong>the</strong> “greenhouse<br />
effect”. It causes <strong>the</strong> average surface temperature <strong>of</strong> <strong>the</strong> earth to be 35 °C higher than its<br />
radiation temperature as seen from <strong>in</strong>terplanetary space (Siegenthaler & Oeschger 1978).<br />
Without <strong>the</strong> greenhouse effect, our planet simply would be too cold to support life.<br />
With <strong>the</strong> onset <strong>of</strong> fossil fuel burn<strong>in</strong>g, large amounts <strong>of</strong> carbon dioxide were emitted <strong>in</strong>to<br />
<strong>the</strong> atmosphere, caus<strong>in</strong>g a steady <strong>in</strong>crease <strong>of</strong> its concentration from <strong>the</strong> pre<strong>in</strong>dustrial level<br />
<strong>of</strong> 285 ppm to 355 ppm at present (Siegenthaler & Oeschger 1987, Houghton et al.<br />
1992). The palaeoclimatic record shows that <strong>the</strong> concentrations <strong>of</strong> carbon dioxide and<br />
methane were closely correlated with temperature and have been chang<strong>in</strong>g cont<strong>in</strong>uously<br />
dur<strong>in</strong>g <strong>the</strong> last 200'000 years (Barnola et al. 1987, Kuo et al. 1990, Jouzel et al. 1993).<br />
So why should we bo<strong>the</strong>r if climate changes today due to human activities?<br />
Dur<strong>in</strong>g <strong>the</strong> last 1'500 years <strong>the</strong> 20-year means <strong>of</strong> summer temperatures <strong>in</strong> Scand<strong>in</strong>avia<br />
oscillated less than ±1 °C around modern values (Briffa et al. 1990, 1992), with some<br />
longer warm (e.g. Medieval Warm Epoch) as well as cool periods (e.g. Little Ice Age).<br />
Brimblecombe & Pfister (1990) showed that such relatively small climatic changes had<br />
major impacts on agricultural yield and, consequently, on <strong>the</strong> welfare <strong>of</strong> <strong>the</strong> human population.<br />
Houghton et al. (1990, 1992) produced various scenarios <strong>of</strong> future greenhouse<br />
gas emissions, and Wigley & Raper (1992) exam<strong>in</strong>ed <strong>the</strong> implications for climate and sea<br />
level <strong>of</strong> <strong>the</strong> latest, moderate scenarios (Houghton et al. 1992). They found that both <strong>the</strong><br />
magnitude and <strong>the</strong> rate <strong>of</strong> <strong>the</strong> expected global temperature change are far beyond <strong>the</strong> limits<br />
<strong>of</strong> natural variability. Thus, future climatic change may have severe consequences for <strong>the</strong><br />
biosphere and its components (Bol<strong>in</strong> et al. 1986, Davis 1990).<br />
Many studies dealt with <strong>the</strong> possible impact <strong>of</strong> climatic change on soils (Bouwman 1990,<br />
Anderson 1992), agricultural land (Parry et al. 1988a,b), forests (Shugart et al. 1986,