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

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94 4 . Behaviour of FORCLIM along a transect in the European Alps The modular structure of FORCLIM makes it possible to examine the behaviour of each submodel in isolation before considering combinations of the three submodels. This allows to quantify e.g. the effects of FORCLIM-E on FORCLIM-P, and to evaluate the feedback mechanisms between FORCLIM-P and FORCLIM-S. Thus, in a first step each submodel will be run on its own, either for all or a selection of the sites given in Appendix III (sections 4.1 – 4.3.1). Second, two interesting combinations of submodels will be examined: (1) FORCLIM-E/P, a setup corresponding to many other forest gap models (section 4.3.2), and (2) the full FORCLIM-E/P/S model, a setup coming closer to a true ecosystem model (section 4.3.3). Finally, a method for estimating efficiently the steady state species composition of FORCLIM will be developed (section 4.4). 4.1 FORCLIM-E The FORCLIM-E model was run for the time window 0…5000 years at all 12 sites (Tab. 4.1). These sites correspond to an ecological gradient from cool to warm and from ecologically wet to dry (cf. the variables uDD and uDrStr, Cleuson – Sion in Tab. 4.1). There is an emphasis on sites around uDD = 1900 °C·d (Huttwil – Basel) because these conditions are typical for a large part of the Swiss Plateau. It is evident from Tab. 4.1 that these sites do not correspond to a smooth gradient of the drought stress index. For example, there are no sites with 0.06 < uDrStr < 0.2. In fact, drought gradients are very steep in the European Alps. In central alpine valleys precipitation decreases from around 800 mm to 600 mm over distances as small as 30 km (e.g. from Martigny to Sion; Martigny has similar climatic parameters as Basel, Tab. 4.1); yet this corresponds to a strong increase of drought stress. These gradients will be explored in more detail in chapter 5. The cross-correlation coefficients between monthly temperature means and monthly precipitation sums affect both the actual evapotranspiration (uAET) and the drought stress
Behaviour of FORCLIM along a transect in the European Alps 95 index (uDrStr). The effect on uAET itself is negligible (Tab. 4.1): at average this variable is only 0.25% higher if cross-correlations are neglected, and the distributions are not significantly different. The distributions are slightly left-skewed at all sites (Fig. 4.1). The drought stress index responds strongly to small increases of uAET when the actual is close to the potential evapotranspiration, and this explains the pattern evident from Tab. 4.1: The strongest increase of drought stress occurs at sites where drought stress is low, which leads to significant differences in the distributions of uDrStr (Fig. 4.2); at the other extreme, simulated drought stress remains essentially the same at the site with the highest stress (Sion, Fig. 4.3). At average, drought stress decreaes by 9.6% if the crosscorrelation between monthly mean temperature and monthly precipitation sum is disregarded (Tab. 4.1). Thus it can be concluded that it has a considerable effect on simulated drought stress at many sites in the European Alps. While the analysis of simulated actual evapotranspiration and drought stress may reveal interesting patterns, the realism and precision of the Thornthwaite & Mather model of soil moisture remains to be determined. The variable uDrStr itself can not be measured in the field, and actual evapotranspiration rates are difficult to determine. However, soil moisture content, the state variable of the soil moisture balance model, can be measured more Tab. 4.1: Averages of the output variables of FORCLIM-E at the 12 test sites estimated from simulation experiments covering 5001 years. uDD – degree-days; uWiT – winter temperature; uAET – actual evapotranspiration; uDrStr – drought stress. Asterisks (*) denote values that have been calculated without taking into account the cross-correlation between monthly temperature means and precipitation sums. Site uDD [°C·d] uWiT [°C] uAET [mm/yr] uAET * [mm/yr] uDrStr [%] uDrStr * [%] uAET * / uAET uDrStr * / uDrStr Cleuson 566.9 -7.313 390.1 391.6 1.955 1.593 1.0038 0.815 Bever (north) 1 773.0 -10.189 373.4 373.8 1.351 1.243 1.0011 0.920 Bever (south) 2 773.0 -10.189 518.6 519.9 4.182 3.962 1.0025 0.947 Davos 900.6 -7.497 453.4 454.1 0.877 0.723 1.0015 0.824 Montana 1309.8 -3.711 493.6 496.0 5.236 4.812 1.0049 0.919 Adelboden 1203.0 -3.146 504.9 505.6 0.629 0.512 1.0014 0.814 Huttwil 1862.9 -2.178 587.0 587.8 1.466 1.362 1.0014 0.929 Bern 1933.4 -2.17 591.9 593.6 2.347 2.105 1.0029 0.897 Schaffhausen 1993.5 -2.3 588.6 590.9 4.321 3.998 1.0039 0.925 Basel 2096.1 -1.148 595.5 597.6 5.431 5.152 1.0035 0.949 Sion 2285.1 -1.441 514.1 514.3 20.612 20.643 1.0004 1.002 Airolo 1399.3 -3.372 519.7 521.0 2.322 2.108 1.0025 0.908 Locarno 2777.0 2.0 688.3 690.3 2.606 2.355 1.0029 0.904 average 1.0025 0.904 1 north-facing slope, kSlAsp = –2 2 south-facing slope, kSlAsp = +2
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Diss. ETH No. 10638 On the Ecology
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ii Table of contents A BSTRACT.....
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iv APPENDIX .......................
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vi Harald BUGMANN, 1994: On the eco
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viii Harald BUGMANN, 1994: Aspekte
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1 1 . Introduction 1.1 Climatic cha
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Introduction 3 1.2 Methods for the
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Introduction 5 in a changing climat
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Introduction 7 Their integrative ca
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Introduction 9 (1984) provides a mo
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Introduction 11 The main advantage
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13 2 . Analysis of existing forest
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Analysis of existing forest gap mod
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Page 37 and 38: Analysis of existing forest gap mod
Page 39 and 40: The forest model FORCLIM 45 carbon
Page 41 and 42: The forest model FORCLIM 47 TREE GR
Page 43 and 44: The forest model FORCLIM 49 gBFlag
Page 45 and 46: The forest model FORCLIM 51 Disturb
Page 47 and 48: The forest model FORCLIM 53 decay o
Page 49 and 50: The forest model FORCLIM 55 the est
Page 51 and 52: The forest model FORCLIM 57 3.3 Mod
Page 53 and 54: The forest model FORCLIM 59 Light a
Page 55 and 56: The forest model FORCLIM 61 Overall
Page 57 and 58: The forest model FORCLIM 63 D (cm)
Page 59 and 60: The forest model FORCLIM 65 a) b) c
Page 61 and 62: The forest model FORCLIM 67 Growth
Page 63 and 64: The forest model FORCLIM 69 Stress-
Page 65 and 66: The forest model FORCLIM 71 Tab. 3.
Page 67 and 68: The forest model FORCLIM 73 3.3.2 F
Page 69 and 70: The forest model FORCLIM 75 where k
Page 71 and 72: The forest model FORCLIM 77 NITROGE
Page 73 and 74: The forest model FORCLIM 79 peratur
Page 75 and 76: The forest model FORCLIM 81 of degr
Page 77 and 78: The forest model FORCLIM 83 microcl
Page 79 and 80: The forest model FORCLIM 85 Tab. 3.
Page 81 and 82: The forest model FORCLIM 87 3.4.3 F
Page 83 and 84: The forest model FORCLIM 89 All the
Page 85 and 86: The forest model FORCLIM 91 The mas
Page 87: The forest model FORCLIM 93 FORCLIM
Page 91 and 92: Behaviour of FORCLIM along a transe
Page 115 and 116: Parameter sensitivity & model valid
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Parameter sensitivity & model valid
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153 6 . Model applications Climatic
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Model applications 155 The simulate
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Model applications 157 6.2 Possible
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Model applications 159 simulation s
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Model applications 161 Simulation e
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Model applications 163 At the site
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Model applications 165 Bever Biomas
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Model applications 167 tainty inher
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Model applications 169 scenario cho
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Discussion 171 Finally, the analysi
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Discussion 173 bitrarily chosen par
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Discussion 175 comparably small imp
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Discussion 177 end of the 21st cent
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Conclusions 179 Ecological factors
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Conclusions 181 species composition
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References 183 Begon, M., Harper, J
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References 185 Burger, H., 1951. Ho
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References 187 Faber, P.J., 1991. A
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References 189 Huntley, B. & Birks,
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References 191 Leemans, R. & Prenti
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References 193 Olson, J.S., 1963. E
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References 195 Rudloff, W., 1981. W
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References 197 Smith, T.M., Leemans
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References 199 Whittaker, R.H., 195
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Appendix 201 II. Derivation of para
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Appendix 203 Tab. A-4: Tree species
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Appendix 205 Tab. A-7: Values for m
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Appendix 207 The minimum winter tem
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Appendix 209 Tab. A-11: Shade toler
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Appendix 211 Tab. A-14: Climatic pa
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Appendix 213 IV. Source code of the
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Appendix 215 FROM SimBase IMPORT De
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Appendix 217 END; (* IF *) prevDay
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Appendix 219 PROCEDURE InitializeFW
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Appendix 221 InstallSeparator( fMen
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Appendix 223 FROM FCPFileIO IMPORT
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Appendix 225 modelSp^.p.kHm := sens
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Appendix 227 DeclMV( meanLitt[leafS
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Appendix 229 Swiss Federal Institut
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Appendix 231 (*********************
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Appendix 233 BEGIN WITH sp^ DO d :=
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Appendix 235 Definition module FCPB
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Appendix 237 Purpose Simulation mod
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Appendix 239 END Immobilization; PR
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Appendix 241 CONST lem = 3; VAR ef:
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Appendix 243 Purpose Provides the b
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Appendix 245 Example of a text file
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Appendix 247 Tab. A-15: Lower end o
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Appendix 249 Tab. A-17: Percentage
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Appendix 251 Tab. A-19: Significant
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Appendix 253 VI. Derivation of para
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Appendix 255 Tab. A-21: Species-spe
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Appendix 257 Tab. A-22 (continued)
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