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

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150 Chapter 5 species of the former two genera, agrees well with descriptions of the near-natural forests of the area. The overall performance of FORCLIM thus is fairly good. Major differences between the two models become evident with the Arkansas climate (Fig. 5.12): While the FORENA simulation is dominated by southern oaks, FORCLIM produces stands dominated by Carya spp. and northern oaks. However, the most important oak species simulated by FORCLIM are also prominent on the landscape: Q. alba and Q. velutina (Küchler 1975). Carya spp. is a warmth and drought-adapted genus, as are many of the oak species, which makes the FORCLIM simulation results quite realistic. The decrease of the total aboveground biomass as compared to Missouri (Fig. 5.12) is due to drought stress; yet the real forests of the area are less dense, and biomass should be lower (DeAngelis et al. 1981). If the field capacity in the FORCLIM model is reduced to 10-15 cm, total aboveground biomass decreases below 200 t/ha, which may be more plausible. SOUTHEASTERN DECIDUOUS FORESTS The simulation results from Georgia, the southernmost site along the transect, are given in Fig. 5.13. Southern oaks and Carya spp. dominate this forest. However, there is a large discrepancy between real and simulated forests both in FORCLIM and in FORENA: On the landscape, southern pines (Pinus spp. in Fig. 5.13) dominate the forests, which is due to the occurrence of extrinsic disturbances such as fire and the droughtiness of the sandy soils prevailing in that area. However, on the clay soils of the piedmont, for which the simulation results are more representative, oaks and hickories dominate. Thus, as a statement about the potential natural forest vegetation in the absence of disturbance, the FORCLIM model is rather successful. Similar simulation results are obtained for Cumberland Plateau, Tennessee (not shown). Although the annual precipitation sum is high, the area is subject to considerable drought because of the sandy soils, leading to low-biomass forests. However, at Cumberland Plateau FORCLIM produces the largest amount of aboveground biomass along the transect. The FORENA model also misrepresents the effects of drought at this site. It is clear that the assumption of 30 cm water at field capacity does not represent sandy soils; unfortunately, the large amount of aboveground biomass simulated by FORCLIM is by and large independent of the value of the field capacity parameter that is used in the simulations. These anomalies may constitute a serious problem for both models.
Parameter sensitivity & model validation 151 300 SW Georgia (E/P) Ulmus spp. Quercus spp. (S) 250 Quercus spp. (N) Prunus serotina Biomass (t/ha) 200 150 100 Pinus spp. Nyssa sylvatica Liriodendron tulipifera Liquidambar styraciflua Ilex opaca Fraxinus spp. Fagus grandifolia 50 Celtis laevigata Carya spp. 0 0 400 Year 800 1200 Acer spp. Fig. 5.13: Simulation results from FORCLIM for Southwest Division, Georgia. The results presented above were based on the FORCLIM-E/P model; the simulations conducted with FORCLIM-E/P/S revealed only small differences concerning the steady-state species composition of the simulated forests, although the simulated transient behaviour differed to some extent, especially for the southern locations. There the abundance of species such as Liquidambar styraciflua, Liriodendron tulipifera, and Nyssa sylvatica is reduced if nitrogen availability is modelled explicitly, which is due to their intolerance of the low nitrogen availability during early succession (cf. section 4.3). On the other hand, the biomass of Pinus spp. increased considerably under these conditions. 5.4.4 Conclusion The application of the FORCLIM model along a latitudinal gradient in eastern North America and the comparison of the results with those obtained by Solomon (1986) and with descriptions of near-natural forests of the area (Rowe 1972, Küchler 1975) reveals several interesting features: First, FORCLIM successfully simulates the general pattern observed in the landscape, i.e. the transition from tundra to the boreal forest down to northern deciduous forests. However, the model misrepresents the increased influence of drought on forest structure when
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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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The forest model FORCLIM 45 carbon
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The forest model FORCLIM 47 TREE GR
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The forest model FORCLIM 49 gBFlag
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The forest model FORCLIM 51 Disturb
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The forest model FORCLIM 53 decay o
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The forest model FORCLIM 55 the est
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The forest model FORCLIM 57 3.3 Mod
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The forest model FORCLIM 59 Light a
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The forest model FORCLIM 61 Overall
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The forest model FORCLIM 63 D (cm)
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The forest model FORCLIM 65 a) b) c
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The forest model FORCLIM 67 Growth
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The forest model FORCLIM 69 Stress-
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The forest model FORCLIM 71 Tab. 3.
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The forest model FORCLIM 73 3.3.2 F
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The forest model FORCLIM 75 where k
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The forest model FORCLIM 77 NITROGE
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The forest model FORCLIM 79 peratur
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The forest model FORCLIM 81 of degr
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The forest model FORCLIM 83 microcl
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The forest model FORCLIM 85 Tab. 3.
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The forest model FORCLIM 87 3.4.3 F
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The forest model FORCLIM 89 All the
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The forest model FORCLIM 91 The mas
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The forest model FORCLIM 93 FORCLIM
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Behaviour of FORCLIM along a transe
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Behaviour of FORCLIM along a transe
Page 93 and 94: Behaviour of FORCLIM along a transe
Page 115 and 116: Parameter sensitivity & model valid
Page 143: Parameter sensitivity & model valid
Page 147 and 148: 153 6 . Model applications Climatic
Page 149 and 150: Model applications 155 The simulate
Page 151 and 152: Model applications 157 6.2 Possible
Page 153 and 154: Model applications 159 simulation s
Page 155 and 156: Model applications 161 Simulation e
Page 157 and 158: Model applications 163 At the site
Page 159 and 160: Model applications 165 Bever Biomas
Page 161 and 162: Model applications 167 tainty inher
Page 163 and 164: Model applications 169 scenario cho
Page 165 and 166: Discussion 171 Finally, the analysi
Page 167 and 168: Discussion 173 bitrarily chosen par
Page 169 and 170: Discussion 175 comparably small imp
Page 171 and 172: Discussion 177 end of the 21st cent
Page 173 and 174: Conclusions 179 Ecological factors
Page 175 and 176: Conclusions 181 species composition
Page 177 and 178: References 183 Begon, M., Harper, J
Page 179 and 180: References 185 Burger, H., 1951. Ho
Page 181 and 182: References 187 Faber, P.J., 1991. A
Page 183 and 184: References 189 Huntley, B. & Birks,
Page 185 and 186: References 191 Leemans, R. & Prenti
Page 187 and 188: References 193 Olson, J.S., 1963. E
Page 189 and 190: References 195 Rudloff, W., 1981. W
Page 191 and 192: References 197 Smith, T.M., Leemans
Page 193 and 194: 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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