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

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146 Chapter 5 100 Tundra & northern boreal sites Biomass (t/ha) 80 60 40 20 Thuja, Juniperus, Larix Populus spp. Picea mariana/rubens Picea glauca Betula spp. Abies spp. 0 Churchill Shefferville Armstrong Site Fig. 5.10: Steady-state species composition at tundra and northern boreal sites in eastern North America as estimated by the FORCLIM-E/P model. ing to the tundra-forest transition zone typical of this area (Rowe 1972). While the occurrence of Picea glauca is plausible, the large fraction of Larix laricina appears to be unrealistic (Rowe 1972). In eastern North America, L. laricina is characteristic of cold-air drainage situations and low peatlands, which are not simulated here. Although it may also grow in closed upland forests in the northern half of its range, the large abundance simulated by FORCLIM represents an anomaly. However, the physiognomic characteristics of the open woodland are reflected correctly in the simulation results. Typical species for real forests at boreal sites like Armstrong (Fig. 5.10) are Picea glauca, P. mariana, and Betula papyrifera (Rowe 1972). These species are correctly simulated as dominants, but other species attain anomalous abundance: Again, L. laricina should be of marginal importance or should even be absent from the simulation. Maybe the description of its natural history is inappropriate in FORCLIM: In reality, its establishment from seeds is strongly limited by light availability; this was accounted for in FORENA by preventing its establishment when LAI is above 0.05 m 2·m-2 , a factor that was not included in FORCLIM because the important European tree species appear to be more shade tolerant. Moreover, L. laricina grows more slowly than evergreen conifers because of the cost of developing new needles each year; thus, in reality it is outcompeted on uplands unless winter is cold enough to kill evergreen needles. However, competition is low in the simulated low-biomass forests (Fig. 5.10), which means that L. laricina establishes and grows well.
Parameter sensitivity & model validation 147 The large abundance of Populus spp. at Armstrong would be realistic only under a strong disturbance regime; however, the simulation experiment is for undisturbed forests. Pinus banksiana is not important at this site because its degree-day requirements are not met in the model, which may be due to erroneous parameter estimation (Rowe 1972, Hare & Thomas 1979). In reality, both Populus spp. and P. banksiana need abiotic disturbances (especially fire, but also windthrow) to provide them with full sunlight. Thus the occurrence of Populus spp. represents a model anomaly, and P. banksiana appears to be absent for the wrong reasons. In FORENA, Populus spp. is absent as well because its establishment is prevented by the LAI requirement mentioned above. Generally speaking, the characteristics of the transition zone from tundra to boreal forests, such as low tree species diversity, small tree stature and low total biomass, are simulated plausibly by the FORCLIM model (Fig. 5.10). SOUTHERN BOREAL FOREST The simulation results for Western Upper Michigan, the transition zone between boreal and deciduous forests, appear to be quite realistic (Rowe 1972, Frelich & Lorimer 1991; Fig. 5.11) and exhibit several features not present in the FORENA simulation results (Solomon 1986): The sugar maple (Acer saccharum) – eastern hemlock (Tsuga canadensis) forest simulated by FORCLIM is typical of rich, undisturbed sites (Rowe 1972, Küchler 1975). In this area, T. canadensis is a dominant species although it approaches its western boundary. The forest simulated by FORENA (Solomon 1986) was dominated by Thuja occidentalis, which is of low importance in the FORCLIM simulation chiefly because leaf area is calculated more accurately. In FORCLIM, the T. occidentalis trees generally are suppressed and do not come to dominance. Moreover, in reality T. occidentalis is competitive on calcareous soils only, a differentiation modelled neither in FORENA nor in FORCLIM. As soils become coarser, lower in organic matter and poorer in moisture capacity, pines take over, first Pinus strobus, then P. resinosa, and finally in pure stands, P. banksiana. With disturbance such as fire or windthrow, Populus tremuloides, which occurred in the FORCLIM simulation peaking at about 10 t/ha in the year 100, and Betula papyrifera dominate for periods of 50-100 years; the occurrence of these species during the first 400 years of the simulation thus appear to be realistic. Three species may be simulated with too high biomass: Picea rubens, which is not present in the Michigan area, Fagus
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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
Page 89 and 90: Behaviour of FORCLIM along a transe
Page 115 and 116: Parameter sensitivity & model valid
Page 139: 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
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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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