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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122 Chapter 5<br />
fore was assumed to be twice as high as for <strong>the</strong> kDDM<strong>in</strong> parameter, i.e. ±40%. The uncerta<strong>in</strong>ty<br />
associated with <strong>the</strong> w<strong>in</strong>ter temperature parameter (kWiT) is also large and was<br />
assumed to be ±2 °C. S<strong>in</strong>ce drought gradients <strong>in</strong> <strong>the</strong> landscape are steep, <strong>the</strong> drought tolerance<br />
parameter (kDrT) is difficult to determ<strong>in</strong>e. Its uncerta<strong>in</strong>ty was assumed to be ±0.1.<br />
Please note that an absolute uncerta<strong>in</strong>ty was used s<strong>in</strong>ce small kDrT values are not more<br />
precise than large ones, ra<strong>the</strong>r <strong>the</strong> reverse is true. Tab. 5.1 gives an overview <strong>of</strong> <strong>the</strong><br />
plausibility range <strong>of</strong> each species parameter. Two tables with <strong>the</strong> m<strong>in</strong>ima and maxima for<br />
all parameters may be found <strong>in</strong> Appendix V.<br />
5.1.2 Simulation experiments<br />
The site Airolo (Appendix III) was chosen for <strong>the</strong> sensitivity analysis because it is located<br />
<strong>in</strong> <strong>the</strong> transition zone between subalp<strong>in</strong>e coniferous and mixed deciduous forests, where<br />
<strong>the</strong> simulated community may be especially sensitive to parameter changes. Each species<br />
parameter was set to <strong>the</strong> lower and <strong>the</strong> upper end <strong>of</strong> its plausibility <strong>in</strong>terval, and <strong>the</strong><br />
steady state species composition <strong>of</strong> <strong>the</strong> FORCLIM-E/P/S model was estimated for each parameter<br />
change, thus result<strong>in</strong>g <strong>in</strong> 2·420 = 840 samples. The steady states were estimated<br />
us<strong>in</strong>g n = 200 po<strong>in</strong>ts and ∆t = 150 years (cf. section 4.4). Two types <strong>of</strong> analyses<br />
were performed:<br />
1) To quantify <strong>the</strong> robustness <strong>of</strong> <strong>the</strong> simulated species composition to changes <strong>of</strong><br />
species parameters, <strong>the</strong> simulated steady states were compared to a conjectured<br />
standard steady state calculated with <strong>the</strong> default parameter set given <strong>in</strong><br />
Tab. 3.11 (n = 20'000 po<strong>in</strong>ts, ∆t = 150 years). For <strong>the</strong>se comparisons, <strong>the</strong><br />
percentage similarity coefficient (PS, Eq. 2.3) was used. A sample steady state<br />
is significantly different from <strong>the</strong> standard steady state if PS < 0.871<br />
(α = 5%, determ<strong>in</strong>ed from an <strong>in</strong>vestigation for FORCLIM-E/P/S at <strong>the</strong> site<br />
Airolo similar to <strong>the</strong> ones performed <strong>in</strong> section 4.4).<br />
2) To quantify <strong>the</strong> response <strong>of</strong> particular species to changes <strong>of</strong> <strong>the</strong>ir parameters, it<br />
was tested whe<strong>the</strong>r <strong>the</strong> average biomass (µ) <strong>of</strong> <strong>the</strong> correspond<strong>in</strong>g species is<br />
significantly different from <strong>the</strong> standard biomass (µ * ) <strong>of</strong> that species. S<strong>in</strong>ce <strong>the</strong><br />
sampl<strong>in</strong>g distribution <strong>of</strong> <strong>the</strong> mean tends to normality with <strong>in</strong>creas<strong>in</strong>g sample<br />
size (and here, n = 200; Zar 1984), <strong>the</strong> range µ * ±1.96·SE <strong>in</strong>cludes µ at a confidence<br />
level (α) <strong>of</strong> 5%, where SE is <strong>the</strong> standard error <strong>of</strong> <strong>the</strong> mean. For <strong>the</strong><br />
species with significant differences, <strong>the</strong> percentage change was calculated.