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468 | werner | 2 | #include "snag.h" |
3 | #include "tree.h" |
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4 | #include "species.h" |
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5 | #include "globalsettings.h" |
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6 | #include "expression.h" |
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490 | werner | 7 | // for calculation of climate decomposition |
8 | #include "resourceunit.h" |
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9 | #include "watercycle.h" |
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10 | #include "climate.h" |
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468 | werner | 11 | |
12 | /** @class Snag |
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13 | Snag deals with carbon / nitrogen fluxes from the forest until the reach soil pools. |
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490 | werner | 14 | Snag lives on the level of the ResourceUnit; carbon fluxes from trees enter Snag, and parts of the biomass of snags |
468 | werner | 15 | is subsequently forwarded to the soil sub model. |
522 | werner | 16 | Carbon is stored in three classes (depending on the size) |
468 | werner | 17 | |
18 | */ |
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19 | // static variables |
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522 | werner | 20 | double Snag::mDBHLower = 0.; |
21 | double Snag::mDBHHigher = 0.; |
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22 | double Snag::mCarbonThreshold[] = {0., 0., 0.}; |
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23 | |||
468 | werner | 24 | double CNPool::biomassCFraction = biomassCFraction; // get global from globalsettings.h |
25 | |||
522 | werner | 26 | void Snag::setupThresholds(const double lower, const double upper) |
27 | { |
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28 | if (mDBHLower == lower) |
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29 | return; |
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30 | mDBHLower = lower; |
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31 | mDBHHigher = upper; |
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32 | mCarbonThreshold[0] = lower / 2.; |
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33 | mCarbonThreshold[1] = lower + (upper - lower)/2.; |
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34 | mCarbonThreshold[2] = upper + (upper - lower)/2.; |
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35 | //# threshold levels for emptying out the dbh-snag-classes |
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36 | //# derived from Psme woody allometry, converted to C, with a threshold level set to 10% |
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37 | //# values in kg! |
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38 | for (int i=0;i<3;i++) |
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39 | mCarbonThreshold[i] = 0.10568*pow(mCarbonThreshold[i],2.4247)*0.5*0.1; |
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40 | } |
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41 | |||
42 | |||
468 | werner | 43 | // species specific soil paramters |
44 | struct SoilParameters |
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45 | { |
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522 | werner | 46 | SoilParameters(): kyl(0.15), kyr(0.0807), ksw(0.015), cnFoliage(75.), cnFineroot(40.), cnWood(300.), halfLife(15.) {} |
468 | werner | 47 | double kyl; // litter decomposition rate |
48 | double kyr; // downed woody debris (dwd) decomposition rate |
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49 | double ksw; // standing woody debris (swd) decomposition rate |
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50 | double cnFoliage; // C/N foliage litter |
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51 | double cnFineroot; // C/N ratio fine root |
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52 | double cnWood; // C/N Wood: used for brances, stem and coarse root |
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522 | werner | 53 | double halfLife; // half-life period of the given species (for calculation of SWD->DWD transition) |
468 | werner | 54 | } soilparams; |
55 | |||
56 | |||
57 | Snag::Snag() |
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58 | { |
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490 | werner | 59 | mRU = 0; |
476 | werner | 60 | CNPool::setCFraction(biomassCFraction); |
523 | werner | 61 | Snag::setupThresholds(20., 60.); |
468 | werner | 62 | } |
63 | |||
490 | werner | 64 | void Snag::setup( const ResourceUnit *ru) |
468 | werner | 65 | { |
490 | werner | 66 | mRU = ru; |
67 | mClimateFactor = 0.; |
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468 | werner | 68 | // branches |
69 | mBranchCounter=0; |
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70 | for (int i=0;i<3;i++) { |
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71 | mTimeSinceDeath[i] = 0.; |
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72 | mNumberOfSnags[i] = 0.; |
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522 | werner | 73 | mAvgDbh[i] = 0.; |
74 | mAvgHeight[i] = 0.; |
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75 | mAvgVolume[i] = 0.; |
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76 | mKSW[i] = 0.; |
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77 | mCurrentKSW[i] = 0.; |
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468 | werner | 78 | } |
475 | werner | 79 | mTotalSnagCarbon = 0.; |
468 | werner | 80 | } |
81 | |||
475 | werner | 82 | // debug outputs |
83 | QList<QVariant> Snag::debugList() |
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84 | { |
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85 | // list columns |
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86 | // for three pools |
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87 | QList<QVariant> list; |
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88 | |||
523 | werner | 89 | // totals |
90 | list << mTotalSnagCarbon << mTotalIn.C << mTotalToAtm.C << mSWDtoSoil.C << mSWDtoSoil.N; |
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477 | werner | 91 | // fluxes to labile soil pool and to refractory soil pool |
524 | werner | 92 | list << mLabileFlux.C << mLabileFlux.N << mRefractoryFlux.C << mRefractoryFlux.N; |
475 | werner | 93 | |
94 | for (int i=0;i<3;i++) { |
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95 | // pools "swdx_c", "swdx_n", "swdx_count", "swdx_tsd", "toswdx_c", "toswdx_n" |
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96 | list << mSWD[i].C << mSWD[i].N << mNumberOfSnags[i] << mTimeSinceDeath[i] << mToSWD[i].C << mToSWD[i].N; |
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524 | werner | 97 | list << mAvgDbh[i] << mAvgHeight[i] << mAvgVolume[i]; |
475 | werner | 98 | } |
99 | |||
100 | // branch pools (5 yrs) |
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101 | list << mBranches[mBranchCounter].C << mBranches[mBranchCounter].N |
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102 | << mBranches[(mBranchCounter+1)%5].C << mBranches[(mBranchCounter+1)%5].N |
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103 | << mBranches[(mBranchCounter+2)%5].C << mBranches[(mBranchCounter+2)%5].N |
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104 | << mBranches[(mBranchCounter+3)%5].C << mBranches[(mBranchCounter+3)%5].N |
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105 | << mBranches[(mBranchCounter+4)%5].C << mBranches[(mBranchCounter+4)%5].N; |
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106 | return list; |
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107 | } |
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108 | |||
468 | werner | 109 | void Snag::newYear() |
110 | { |
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111 | for (int i=0;i<3;i++) { |
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112 | mToSWD[i].clear(); // clear transfer pools to standing-woody-debris |
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522 | werner | 113 | mCurrentKSW[i] = 0.; |
468 | werner | 114 | } |
115 | mLabileFlux.clear(); |
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116 | mRefractoryFlux.clear(); |
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476 | werner | 117 | mTotalToAtm.clear(); |
118 | mTotalToExtern.clear(); |
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119 | mTotalIn.clear(); |
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477 | werner | 120 | mSWDtoSoil.clear(); |
468 | werner | 121 | } |
122 | |||
490 | werner | 123 | /// calculate the dynamic climate modifier for decomposition 're' |
522 | werner | 124 | /// calculation is done on the level of ResourceUnit because the water content per day is needed. |
490 | werner | 125 | double Snag::calculateClimateFactors() |
126 | { |
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127 | double rel_wc; |
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128 | double ft, fw; |
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129 | double f_sum = 0.; |
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130 | for (const ClimateDay *day=mRU->climate()->begin(); day!=mRU->climate()->end(); ++day) |
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131 | { |
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523 | werner | 132 | rel_wc = mRU->waterCycle()->relContent(day->day)*100.; // relative water content in per cent of the day |
490 | werner | 133 | ft = exp(308.56*(1./56.02-1./((273.+day->temperature)-227.13))); // empirical variable Q10 model of Lloyd and Taylor (1994), see also Adair et al. (2008) |
134 | fw = pow(1.-exp(-0.2*rel_wc),5.); // # see Standcarb for the 'stable soil' pool |
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135 | f_sum += ft*fw; |
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136 | } |
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137 | // the climate factor is defined as the arithmentic annual mean value |
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138 | mClimateFactor = f_sum / double(mRU->climate()->daysOfYear()); |
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139 | return mClimateFactor; |
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140 | } |
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141 | |||
522 | werner | 142 | /// do the yearly calculation |
143 | /// see http://iland.boku.ac.at/snag+dynamics |
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468 | werner | 144 | void Snag::processYear() |
145 | { |
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522 | werner | 146 | mSWDtoSoil.clear(); |
477 | werner | 147 | if (isEmpty()) // nothing to do |
475 | werner | 148 | return; |
149 | |||
468 | werner | 150 | // process branches: every year one of the five baskets is emptied and transfered to the refractory soil pool |
151 | mRefractoryFlux+=mBranches[mBranchCounter]; |
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523 | werner | 152 | mSWDtoSoil += mBranches[mBranchCounter]; |
468 | werner | 153 | mBranches[mBranchCounter].clear(); |
154 | mBranchCounter= (mBranchCounter+1) % 5; // increase index, roll over to 0. |
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155 | |||
156 | // process standing snags. |
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157 | // the input of the current year is in the mToSWD-Pools |
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522 | werner | 158 | |
490 | werner | 159 | const double climate_factor_re = calculateClimateFactors(); |
468 | werner | 160 | for (int i=0;i<3;i++) { |
161 | |||
522 | werner | 162 | // update the swd-pool with this years' input |
163 | if (!mToSWD[i].isEmpty()) { |
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164 | // update decay rate (apply average yearly input to the state parameters) |
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165 | mKSW[i] = mKSW[i]*(mSWD[i].C/(mSWD[i].C+mToSWD[i].C)) + mCurrentKSW[i]*(mToSWD[i].C/(mSWD[i].C+mToSWD[i].C)); |
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166 | //move content to the SWD pool |
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167 | mSWD[i] += mToSWD[i]; |
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168 | } |
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475 | werner | 169 | |
522 | werner | 170 | if (mSWD[i].C > 0) { |
171 | // reduce the Carbon (note: the N stays, thus the CN ratio changes) |
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172 | // use the decay rate that is derived as a weighted average of all standing woody debris |
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523 | werner | 173 | double survive_rate = exp(-mKSW[i] *climate_factor_re * 1. ); // 1: timestep |
174 | mTotalToAtm.C += mSWD[i].C * (1. - survive_rate); |
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175 | mSWD[i].C *= survive_rate; |
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468 | werner | 176 | |
522 | werner | 177 | // transition to downed woody debris |
178 | // update: use negative exponential decay, species parameter: half-life |
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179 | // modified for the climatic effect on decomposition, i.e. if decomp is slower, snags stand longer and vice versa |
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180 | // this is loosely oriented on Standcarb2 (http://andrewsforest.oregonstate.edu/pubs/webdocs/models/standcarb2.htm), |
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181 | // where lag times for cohort transitions are linearly modified with re although here individual good or bad years have |
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182 | // an immediate effect, the average climatic influence should come through (and it is inherently transient) |
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183 | // note that swd.hl is species-specific, and thus a weighted average over the species in the input (=mortality) |
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184 | // needs to be calculated, followed by a weighted update of the previous swd.hl. |
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185 | // As weights here we use stem number, as the processes here pertain individual snags |
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186 | // calculate the transition probability of SWD to downed dead wood |
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468 | werner | 187 | |
522 | werner | 188 | double half_life = mHalfLife[i] / climate_factor_re; |
189 | double rate = -M_LN2 / half_life; // M_LN2: math. constant |
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190 | |||
191 | // higher decay rate for the class with smallest diameters |
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192 | if (i==0) |
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193 | rate*=2.; |
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194 | |||
523 | werner | 195 | double transfer = 1. - exp(rate); |
522 | werner | 196 | |
468 | werner | 197 | // calculate flow to soil pool... |
522 | werner | 198 | mSWDtoSoil += mSWD[i] * transfer; |
199 | mRefractoryFlux += mSWD[i] * transfer; |
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200 | mSWD[i] *= (1.-transfer); // reduce pool |
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468 | werner | 201 | // calculate the stem number of remaining snags |
522 | werner | 202 | mNumberOfSnags[i] = mNumberOfSnags[i] * (1. - transfer); |
523 | werner | 203 | |
204 | mTimeSinceDeath[i] += 1.; |
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522 | werner | 205 | // if stems<0.5, empty the whole cohort into DWD, i.e. release the last bit of C and N and clear the stats |
206 | // also, if the Carbon of an average snag is less than 10% of the original average tree |
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207 | // (derived from allometries for the three diameter classes), the whole cohort is emptied out to DWD |
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208 | if (mNumberOfSnags[i] < 0.5 || mSWD[i].C / mNumberOfSnags[i] < mCarbonThreshold[i]) { |
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209 | // clear the pool: add the rest to the soil, clear statistics of the pool |
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468 | werner | 210 | mRefractoryFlux += mSWD[i]; |
522 | werner | 211 | mSWDtoSoil += mSWD[i]; |
468 | werner | 212 | mSWD[i].clear(); |
522 | werner | 213 | mAvgDbh[i] = 0.; |
214 | mAvgHeight[i] = 0.; |
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215 | mAvgVolume[i] = 0.; |
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216 | mKSW[i] = 0.; |
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217 | mCurrentKSW[i] = 0.; |
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218 | mHalfLife[i] = 0.; |
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219 | mTimeSinceDeath[i] = 0.; |
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468 | werner | 220 | } |
522 | werner | 221 | |
468 | werner | 222 | } |
522 | werner | 223 | |
468 | werner | 224 | } |
522 | werner | 225 | // total carbon in the snag-container on the RU *after* processing is the content of the |
475 | werner | 226 | // standing woody debris pools + the branches |
227 | mTotalSnagCarbon = mSWD[0].C + mSWD[1].C + mSWD[2].C + |
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228 | mBranches[0].C + mBranches[1].C + mBranches[2].C + mBranches[3].C + mBranches[4].C; |
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468 | werner | 229 | } |
230 | |||
231 | /// foliage and fineroot litter is transferred during tree growth. |
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232 | void Snag::addTurnoverLitter(const Tree *tree, const double litter_foliage, const double litter_fineroot) |
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233 | { |
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234 | const SoilParameters &soil_params = soilparams; // to be updated |
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235 | mLabileFlux.addBiomass(litter_foliage, soil_params.cnFoliage); |
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236 | mLabileFlux.addBiomass(litter_fineroot, soil_params.cnFineroot); |
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237 | } |
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238 | |||
239 | /// after the death of the tree the five biomass compartments are processed. |
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240 | void Snag::addMortality(const Tree *tree) |
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241 | { |
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242 | const SoilParameters &soil_params = soilparams; // to be updated |
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243 | |||
244 | // immediate flows: 100% of foliage, 100% of fine roots: they go to the labile pool |
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245 | // 100% of coarse root biomass: that goes to the refractory pool |
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246 | mLabileFlux.addBiomass(tree->biomassFoliage(), soil_params.cnFoliage); |
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247 | mLabileFlux.addBiomass(tree->biomassFineRoot(), soil_params.cnFineroot); |
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248 | mRefractoryFlux.addBiomass(tree->biomassCoarseRoot(), soil_params.cnWood); |
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249 | |||
250 | // branches are equally distributed over five years: |
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477 | werner | 251 | double biomass_branch = tree->biomassBranch() * 0.2; |
468 | werner | 252 | for (int i=0;i<5; i++) |
477 | werner | 253 | mBranches[i].addBiomass(biomass_branch, soil_params.cnWood); |
468 | werner | 254 | |
523 | werner | 255 | // just for book-keeping: keep track of all inputs into branches / swd |
256 | mTotalIn.addBiomass(tree->biomassBranch() + tree->biomassStem(), soil_params.cnWood); |
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468 | werner | 257 | // stem biomass is transferred to the standing woody debris pool (SWD), increase stem number of pool |
522 | werner | 258 | int pi = poolIndex(tree->dbh()); // get right transfer pool |
259 | |||
260 | // update statistics - stemnumber-weighted averages |
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261 | // note: here the calculations are repeated for every died trees (i.e. consecutive weighting ... but delivers the same results) |
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262 | double p_old = mNumberOfSnags[pi] / (mNumberOfSnags[pi] + 1); // weighting factor for state vars (based on stem numbers) |
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263 | double p_new = 1. / (mNumberOfSnags[pi] + 1); // weighting factor for added tree (p_old + p_new = 1). |
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264 | mAvgDbh[pi] = mAvgDbh[pi]*p_old + tree->dbh()*p_new; |
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265 | mAvgHeight[pi] = mAvgHeight[pi]*p_old + tree->height()*p_new; |
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266 | mAvgVolume[pi] = mAvgVolume[pi]*p_old + tree->volume()*p_new; |
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267 | mTimeSinceDeath[pi] = mTimeSinceDeath[pi]*p_old + 1.*p_new; |
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268 | mHalfLife[pi] = mHalfLife[pi]*p_old + soil_params.halfLife * p_new; |
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269 | |||
270 | // average the decay rate (ksw); this is done based on the carbon content |
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271 | // aggregate all trees that die in the current year (and save weighted decay rates to CurrentKSW) |
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272 | if (tree->biomassStem()==0) |
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273 | throw IException("Snag::addMortality: tree without stem biomass!!"); |
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274 | p_old = mToSWD[pi].C / (mToSWD[pi].C + tree->biomassStem()* biomassCFraction); |
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275 | p_new =tree->biomassStem()* biomassCFraction / (mToSWD[pi].C + tree->biomassStem()* biomassCFraction); |
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276 | mCurrentKSW[pi] = mCurrentKSW[pi]*p_old + soil_params.ksw * p_new; |
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277 | mNumberOfSnags[pi]++; |
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523 | werner | 278 | |
279 | // finally add the biomass |
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280 | CNPool &swd = mToSWD[pi]; |
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281 | swd.addBiomass(tree->biomassStem(), soil_params.cnWood); |
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468 | werner | 282 | } |
283 | |||
284 | /// add residual biomass of 'tree' after harvesting. |
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522 | werner | 285 | /// remove_{stem, branch, foliage}_fraction: percentage of biomass compartment that is *removed* by the harvest operation (i.e.: not to stay in the system) |
468 | werner | 286 | /// the harvested biomass is collected. |
287 | void Snag::addHarvest(const Tree* tree, const double remove_stem_fraction, const double remove_branch_fraction, const double remove_foliage_fraction ) |
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288 | { |
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289 | const SoilParameters &soil_params = soilparams; // to be updated |
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290 | |||
291 | // immediate flows: 100% of residual foliage, 100% of fine roots: they go to the labile pool |
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292 | // 100% of coarse root biomass: that goes to the refractory pool |
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293 | mLabileFlux.addBiomass(tree->biomassFoliage() * (1. - remove_foliage_fraction), soil_params.cnFoliage); |
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294 | mLabileFlux.addBiomass(tree->biomassFineRoot(), soil_params.cnFineroot); |
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295 | mRefractoryFlux.addBiomass(tree->biomassCoarseRoot(), soil_params.cnWood); |
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296 | |||
297 | // residual branches are equally distributed over five years: |
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298 | for (int i=0;i<5; i++) |
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523 | werner | 299 | mBranches[i].addBiomass(tree->biomassBranch() * (1. - remove_branch_fraction) * 0.2, soil_params.cnWood); |
468 | werner | 300 | |
523 | werner | 301 | mTotalToExtern.addBiomass(tree->biomassBranch()*remove_branch_fraction + tree->biomassStem()*remove_stem_fraction, soil_params.cnWood); |
468 | werner | 302 | // stem biomass is transferred to the standing woody debris pool (SWD), increase stem number of pool |
522 | werner | 303 | // TODO: what to do with harvest and stems??? I think harvested stems (that are not removed) should |
304 | // go directly to the DWD?? |
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468 | werner | 305 | CNPool &swd = mToSWD[poolIndex(tree->dbh())]; // get right transfer pool |
306 | swd.addBiomass(tree->biomassStem() * remove_stem_fraction, soil_params.cnWood); |
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307 | if (remove_stem_fraction < 1.) |
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308 | mNumberOfSnags[poolIndex(tree->dbh())]++; |
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309 | } |
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310 |