On the Ecology of Mountainous Forests in a Changing Climate: A ...

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