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

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52 Chapter 3 ForClim-E: Environment uAET LITTER gLign LOM gImmob gNMR HUMUS ForClim-S: Soil submodel HOM N mineralization ForClim-P: Plants Plant litter uAvN LN HN Fig. 3.3: Structure of the soil organic matter submodel FORCLIM-S. The identifiers are explained in the text. The litter produced by the trees in a given year loses carbon continuously during decomposition, but the rate of nitrogen uptake by the microbes attacking the tissue is initially greater than the release of nitrogen from the tissue; this results in a net immobilization of nitrogen (e.g. Berg & Staaf 1981, Waring & Schlesinger 1985). Thus, in FORCLIM-S two state variables are used to characterize litter: its organic matter content (LOM), and its nitrogen content (LN; Fig. 3.3). The litter becomes progressively richer in recalcitrant compounds, and the rate of nitrogen release begins to exceed the uptake, leading to nitrogen mineralization. Pastor & Post (1985) call the material in this stage “humus”. The change from immobilization to mineralization – and thus the transition from “litter” to “humus” – generally happens at nitrogen concentrations of about 2% of weight (Alexander 1977). Similar to the litter, the humus is divided into organic matter (HOM) and nitrogen content (HN, Fig. 3.3). The basic idea behind the decomposition module in LINKAGES is to formulate decay rates based directly on the wealth of data obtained from litterbag studies (e.g. Meentemeyer 1978, Melillo et al. 1982, Pastor et al. 1984, Coûteaux et al. 1991). To this end, the
The forest model FORCLIM 53 decay of each year's litter is tracked through time, thus mimicking many litterbag studies. When the critical nitrogen concentration (Alexander 1977) is reached, the litter is transferred to a common “humus” compartment, and nitrogen mineralization starts. The amount of nitrogen available for plant growth (uAvN) is calculated as the difference between the nitrogen mineralized from the humus pool and the immobilization demand of the litter cohorts (gImmob, Fig. 3.3). Pastor et al. (1984) and Pastor & Post (1985) found good correlations between litter decay rates, actual evapotranspiration (uAET), litter lignin content (gLign), and the nitrogen to mass ratio of the litter (gNMR); these indices are used to formulate litter decay rates in LINKAGES and FORCLIM (Fig. 3.3). The leaching of nitrate from nitrogen-rich litter is taken into account (Cole & Rapp 1981) as well as a constant atmospheric deposition rate of soluble nitrogen compounds. The more recalcitrant litter types (twigs and wood) are assumed to decay at a constant rate. The hypothesized effects of canopy openings on litter and humus decay rates as incorporated in LINKAGES were not included in the FORCLIM model (Fig. 3.3). Most of the litterbag studies to date were conducted under boreal conditions and/or in America; only few data are available for central European conditions and species (e.g. Berg & Staaf 1981, Ellenberg 1986, Lüscher 1991). Thus it was necessary to collapse the 17 litter types distinguished in LINKAGES to three types of leaf litter (fast, medium, and slow decay), twig litter, root litter, and stemwood litter. At least two weaknesses remain in the LINKAGES as well as the FORCLIM-S model: First, there is no compartment with a very slow turnover rate of soil organic matter. It is well known that part of the organic matter is “protected” or “stabilized” and very recalcitrant to decay (e.g. Parton et al. 1987, Verberne et al. 1990); neither the LINKAGES nor the FORCLIM model simulate these processes. Second, Pastor & Post (1985) had to use the N:C ratio of the litter to formulate the mineralization rate of the humus compartment; while this approach was phenomenologically correct (Pastor et al. 1984), it represents an empirical, not a causal relationship. Lüscher (1991) investigated the dynamics of the forest floor and the humus of many soils in Switzerland; however, this data base does not allow to reformulate the rate of nitrogen mineralization from the humus as a function of abiotic variables on a more mechanistic basis. Thus, the data from Pastor et al. (1984) had to be used again in FORCLIM (Fig. 3.3).
Page 1: Diss. ETH No. 10638 On the Ecology
Page 4 and 5: ii Table of contents A BSTRACT.....
Page 6 and 7: iv APPENDIX .......................
Page 8 and 9: vi Harald BUGMANN, 1994: On the eco
Page 10 and 11: viii Harald BUGMANN, 1994: Aspekte
Page 13 and 14: 1 1 . Introduction 1.1 Climatic cha
Page 15 and 16: Introduction 3 1.2 Methods for the
Page 17 and 18: Introduction 5 in a changing climat
Page 19 and 20: Introduction 7 Their integrative ca
Page 21 and 22: Introduction 9 (1984) provides a mo
Page 23 and 24: Introduction 11 The main advantage
Page 25 and 26: 13 2 . Analysis of existing forest
Page 27 and 28: 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: The forest model FORCLIM 51 Disturb
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 and 88: The forest model FORCLIM 93 FORCLIM
Page 89 and 90: Behaviour of FORCLIM along a transe
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Behaviour of FORCLIM along a transe
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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
Page 179 and 180:
References 185 Burger, H., 1951. Ho
Page 181 and 182:
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
Page 189 and 190:
References 195 Rudloff, W., 1981. W
Page 191 and 192:
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 :=
Page 229 and 230:
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
Page 251 and 252:
Appendix 257 Tab. A-22 (continued)
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