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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6 . Model applications<br />
Climatic change is a common phenomenon that may occur not only <strong>in</strong> <strong>the</strong> future: <strong>Climate</strong><br />
has been chang<strong>in</strong>g cont<strong>in</strong>uously <strong>in</strong> <strong>the</strong> past both on long and short timescales (Barnola et<br />
al. 1987, Briffa et al. 1990, 1992). Thus, a look at past climatic variations on a similar<br />
timescale as <strong>the</strong> anticipated future climatic change, i.e. for <strong>the</strong> last few centuries, will<br />
allow to analyse <strong>the</strong> ecological effects <strong>of</strong> such variations, e.g. to determ<strong>in</strong>e how well<br />
buffered forest ecosystems are (section 6.1). Subsequently, <strong>the</strong> possible ecological implications<br />
<strong>of</strong> future climatic changes will be explored (section 6.2).<br />
6.1 Effects <strong>of</strong> historical climate anomalies on forest dynamics<br />
6.1.1 Input data and simulation experiments<br />
In a unique effort, Pfister (1988) developed a system <strong>of</strong> monthly <strong>the</strong>rmic and hydric <strong>in</strong>dices<br />
to characterize <strong>the</strong> temperature and precipitation regime <strong>of</strong> every month between<br />
1525 and 1979 AD <strong>in</strong> Switzerland. The <strong>in</strong>dices were based on a wealth <strong>of</strong> historical data<br />
sources, rang<strong>in</strong>g from temperature measurements at a few sites and written records <strong>of</strong> extreme<br />
events (e.g. lake glaciations) to agricultural yield data and tree-r<strong>in</strong>gs. The temperature<br />
<strong>in</strong>dices refer to <strong>the</strong> site Basel, while <strong>the</strong> precipitation <strong>in</strong>dices are an average <strong>of</strong> <strong>the</strong><br />
sites Bern, Cottens/Begn<strong>in</strong>s, Rickenbach, Basel, Geneva, and Zurich (Pfister 1988).<br />
Based on <strong>the</strong>se <strong>in</strong>dices and <strong>the</strong> regression equations developed by Pfister (1988), <strong>the</strong><br />
monthly temperature and precipitation data <strong>of</strong> a virtual site “CLIMINDEX” were reconstructed<br />
for <strong>the</strong> present study (Tab. 6.1). This site is representative <strong>of</strong> a large fraction <strong>of</strong><br />
<strong>the</strong> Swiss Plateau, <strong>the</strong> area <strong>of</strong> Switzerland most densely populated throughout history.<br />
The FORCLIM-E/P model was selected for this study because it is more efficient than <strong>the</strong><br />
full E/P/S model but produces very similar results at low-elevation sites (chapter 4). The<br />
follow<strong>in</strong>g simulation experiment was designed based on <strong>the</strong> climatic data by Pfister<br />
(1988): First, <strong>the</strong> model was allowed to reach its steady-state under current climatic conditions<br />
by runn<strong>in</strong>g it for 1000 years (525-1525 AD) and 200 patches start<strong>in</strong>g from bare<br />
ground and assum<strong>in</strong>g a constant climate, i.e. by sampl<strong>in</strong>g wea<strong>the</strong>r data stochastically