Parameterization Workbook (pdf version)
Contents
1. If If If schedule file But if you want to include precise initial conditions then enter measured or estimated values for rwcf 1 n These parameters set the initial relative water content RWC for each soil layer RWC W WP FC WP where W is the measured soil water content WP is the soil water content at wilting point and FC is the soil water content at field Capacity sniq is the liquid water in the snowpack cm H O snow is the snowpack water content cm H O 6 OTHER PARAMETERS Check the parameters listed below and be sure they are set to the indicated values wllig 0 0 w2lig 0 0 w3lig 0 0 crop 100 file The crop 100 file is used to represent cropped and grassland systems The CENTURY installation package contains a crop 100 file for many common crops corn wheat etc and grasses C3 C4 etc that have been used in the past Most of the grasses were parameterized with data from LTER sites while many of the crop parameterizations use data from VEMAP sites We suggest that you use one of these existing parameterizations as a starting point and use the following suggestions to modify the parameters as needed to represent the vegetation in your particular system Do not hesitate to change the recommended values of parameters to better represent your vegetation especially if you have data See Appendix 2 1 in the Century User s Manual for definitions of the parameters in this file 1 MAXI2. NPP fcfrac 2 1i fine root production total NPP fcfrac 3 i fine branch production total NPP fcfrac 4 1 large wood production total NPP fcfrac 5 1i coarse root production total NPP 6 BIOMASS TURNOVER RATES 6 a SET LEAF DEATH RATES Monthly leaf turnover is set in leafdr In a deciduous or drought deciduous system the values of leafdr indicate mortality during the growing season from causes such as herbivory physical damage or early senescence The leaf mortality at the end of the growing season for deciduous or drought deciduous trees is determined by the value entered for wooddr 1 In an evergreen or semievergreen system leafdr indicates all leaf turnover including seasonal senescence and litterfall In any case these values are the fraction of leaves that are transferred to litter each month These values should be estimated from observed rates of litterfall in comparison to observed or estimated leaf biomass In deciduous and drought deciduous systems wooddr 1 is the fraction of leaves that are lost during the month of leaf drop For temperature deciduous systems the months of leaf out and leaf drop are controlled by temperature and day length while for drought deciduous systems leaf drop occurs when monthly soil water content is below the wilting point Typical values for wooddr 1 for are 0 95 for temperature deciduous and 0 3 for drought deciduous but use estimates that best represent your
3. biomass use them BIOMASS FRACTION EXPRESSION VARIABLE VALUE standing dead biomass 0 50 stdcis 1 PS t t SY Set all the corresponding cis 2 pools to 0 0 if you are not simulating isotope labeling Nutrient pools P and S calculations are necessary only if nelem 2 or 3 Calculate each as biomass concentration FRACTION VARIABLE isl i 2 i 3 belowground bgliv i fe 3 b FOREST ORGANIC MATTER INITIAL PARAMETERS Carbon pools if you have actual carbon data rather than just biomass use them BIOMASS FRACTION EXPRESSION VARIABLE VALUE COARSE ROOT biomass 0 50 ertcis 1 fe Set all the corresponding cis 2 pools to 0 0 if you are not simulating isotope labeling Nutrient pools P and S calculations are necessary only if nelem 2 or 3 Calculate each as biomass concentration N P S FRACTION VARIABLE i 1 i 2 i 3 3 c INITIAL WOODY DEBRIS AND ROOT LITTER POOLS This parameterization is only necessary for forest systems Enter the woody debris and belowground litter pools below Small woody debris is the wood litter typically measured in forest floor sampling Large woody debris is highly clumped spatially hence measures of its mass usually only come from deliberate efforts to quantify it specifically Data for belowground woody debris are rarely available a rough estimate can be made by assuming the ratio of belowground aboveground large woody debris is equal to the ratio
4. of coarse root large wood live biomass In the absence of any woody debris estimates these values can be crudely estimated as anywhere from 10 30 of their corresponding live pools Belowground litter is approximately the mass of dead fine roots in the absence of data it can be estimated as of the same order of magnitude as live fine roots If there is no data from which to initialize these pools they may be set to zero and will gradually equilibrate during the model run Calculate the initial pools Initial woody debris and root litter pools Pool Mass g m Variable Expression VALUE g m ES peso pin aerie e raen n Coarse root wd3cis 1 dead coarse debris root 0 50 Fine root 3 dead fine Set all the corresponding cis 2 pools to 0 0 if you are not simulating isotope labeling Source for woody debris data 4 MINERAL INITIAL PARAMETERS minerl 1 n 1 These set the initial N g m in each soil layer you have no data or estimates for this use 1 for the layers that include the top 20 cm of soil minerl 1 n 2 These set the initial P g m in each soil layer you have no data or estimates for this use 1 for the layers that include the top 20 cm of soil minerl 1 n 3 These set the initial S g m in each soil layer you have no data or estimates for this use 1 for the layers that include the top 20 cm of soil 5 WATER INITIAL PARAMETERS This is not necessary if you include an equilibrium block in your
5. per month in terms of carbon NOT total mass Common values are 300 400 g C m mo prdx 3 3 CONTROLS ON PRODUCTION 3 a TEMPERATURE RESPONSES The effect of temperature on production is controlled by the parameter ppdf Typical values for generalized forest types are listed below the example genera listed are heavily northamericano biased and are general guidelines only For temperate forests ppdf 1 is approximately equal to the mean temperature of the warmest month ppdf 2 is at least 15 degrees higher ppdf 3 and ppdf 4 affect production mostly at the extremes 1 0 and 3 0 will serve adequately in most cases Select values for ppdf MEANING Optimum Maximum Left Right temp temp shape shape Arctic alpine shrub Ledum Betula Salix Boreal subalpine conifer Ce E Northern hardwoods 27 45 1 0 3 0 Temperate conifer Pinus Juniperus Temperate hardwood 25 45 1 0 3 0 Quercus Carya etc Tropical and subtropical hardwood and conifer 20 9 Tap one 3 b BIOMASS CHEMISTRY You have three options for calculating the biomass C E If you have actual carbon data instead of just biomass then use C data instead of the generalized carbon percentages listed below Select which option you prefer mark it with a check calculate the C E ratios and retranslocation controls and fill in the table with the values for cerfor __1 Simulate tissue chemistry as fixed with no retranslocation or response to nutr
6. CENTURY Parameterization Workbook lt site gt 100 file Most of the parameters in the lt site gt 100 file will have to be adjusted to account for the unique properties of your particular system However some sets of parameters are more important than others For example climate and soil physical are very important but the initial organic matter and water parameters are not important if you include an equilibrium block in your schedule file See Appendix 2 12 in the Century User s Manual for definitions of the parameters in this file SITE INFORMATION CENTURY PARAMERERIZATION Site Name Latitude Longitude Elevation System simulated Modeler Date 1 PHYSICAL ENVIRONMENT 1 a CLMATE PARAMETERS Enter below the mean climate for the site These are averages for each calendar month of daily maximum and minimum air temperatures and monthly total precipitation Standard deviation and skewness of monthly precipitation totals are needed only if the stochastic precipitation option is to be used and can be generated by using the FILE100 utility TEMPERATURES C PRECIPITATION cm MONTH MINIMUM MAXIMUM MEAN S D SKEWNESS Ec e a a E S S a A e e o oOo o e Source for climate data 1 b SITE AND CONTROL PARAMTERS ivauto controls how SOM pools are initialized ivauto 0 the initial SOM values in your lt site gt 100 file are used ivauto 1 an equation for native grass soil initializes SOM pools ivauto 2 an equatio
7. MUM PRODUCTION Maximum production is rarely directly observed in either the model or reality and must be inferred Maximum net production is expressed as the theoretical maximum net biomass production per month in terms of total mass not C Values of 200 300 for grasses and slow growing crops e g winter wheat and up to 600 g biomass m mo for fast growing crops corn have been used prdx 1 2 TEMPERATURE RESPONSES The effect of temperature on production is controlled by the parameter ppdf Typical values for vegetation types are listed below For temperate crops ppdf 1 is approximately equal to the mean temperature of the warmest month ppdf 2 is 15 degrees higher ppdf 3 and ppdf 4 affect production mostly at the extremes values near 1 0 and 3 0 will serve adequately in most cases ee MEM ME Alfalfa VALUE CHOSEN 3 REDUCTION FACTORS CENTURY allows for growth to be restricted due to physical obstruction of above ground live and standing dead material Growth may also be reduced during the planting month Values for these parameters that we have used include bioflg 0 for crop 1 for grass biok5 1800 for crops 60 200 for grass pltmrf 0 4 0 5 for annual crops 1 for annual grass and 0 for perennial grass or crops see Fig 3 10 in the Century User s Manual fulcan 100 150 see Fig 3 10 in the Century User s Manual 4 C ALLOCATION CENTURY accounts for variable allocation of C as plants m
8. OMASS AND NPP DATA Enter below your best estimates for biomass pool sizes chemistry annual production and turnover comments on estimating values follow BIOMASS NPP LITTER FRACTION g w g m yr g m yr ZN SP S ear e LEAF XXXXXXX LITTER XXXXXXX XXXXXXX BRANCH woos o ooo oo y y oO rooms doo o y o FINE goora fF TT Large wood is branch and stem wood gt 10 cm diameter Fine roots are lt 2 mm diameter Measured wood litterfall collected in traps usually indicates fine branch litterfall and can be used as an estimate of fine branch production in older forests Large wood litterfall is rarely measured and must be estimated from guesses about turnover time and tree longevity Coarse root production is likewise rarely measured often even biomass data are lacking Educated guesses as to biomass and turnover rates must be used in these cases Sources for biomass and production data 5 b PRODUCTION ALLOCATION PATTERN CENTURY allows for different C allocation patterns for juvenile and mature forests Age indicator i is 1 for early forest 2 for late forest If you are simulating only 1 types of forest set swold 0 0 and fcfrac the same for i 1 and 2 Otherwise perform the following calculations for each forest type and set swold number of years after beginning of simulation when the forest changes from juvenile to mature fcfrac 1 i leaf production total
9. ature The user specifies the initial allocation final allocation and the number of months after the planting month when the final value is reached These parameters only apply to crops and annual grasses see Fig 3 11 in the Century User s Manual frtc 1 0 4 0 6 for crops 0 for grass frtc 2 0 1 for most crops 0 for grass frtc 3 3 for most crops 0 for grass 5 C E RATIOS CENURY allows for flexibility in the ranges of C E ratios as above ground biomass increases The following parameters pramn i j and pramx i j control the maximum and minimum C E ratios E N P or S for shoots when plant biomass is above and below biomax The following table shows values that we have used for pramn and pramx biomax 400 for most grasses and crops See Fig 3 13 in the Century User s Manual eee ee eee a prama so ao so fes oo ao prem 2 2 290 faeo oso fioo fiso Maso prawasa feo x00 fos fas fo feo prbmn i j and prbmx i j control the minimum and maximum C E E N P or S of roots We believe these parameters are mainly a function of plant type and commonly use a slope of 0 0 However users have the option of making C N of roots vary with precipitation see parameter definitions Tall Winter Short Alfalfa Soy Corn E rae ae nm en prbmn 1 1 ramea o ojo fo o fpromeaa feo feo ss fa fe fo emman o o fo Joo C fo ojo fo o_o 6 LIGNIN CONTENTS The lignin content of above and below ground mate
10. deling N see nelem in your lt site gt 100 file then these parameters are irrelevant If you do want to model P and S then there are 2 ways to supply P inputs and 3 ways to supply S inputs P and S can be supplied by weathering of parent material in which case you should appropriately adjust parent 2 and parent 3 in your lt sSite gt 100 file and pparm 2 and pparm 3 in the fix 100 file parent i controls the amount of P or S in parent material and pparm i controls the weathering rate in units of the fraction of parent material weathered to mineral form per year P and S can be supplied as fertilizer inputs in which case you should make an appropriate option in the fert 100 file Atmospheric S inputs are accounted for in your lt Site gt 100 file If you have estimates of parent material P and S and atmospheric deposition of S you can use the following table to parameterize parent i and pparm i this scheme is not necessarily appropriate for detailed examination of long term P dynamics and pedogenesis First run the model for 3 years using mean weather and monthly output Calculate the average value of defac then complete Phosphorus Sulfur Atmospheric deposition wet dry g m yr Literature source b Weathering inputs that occur a the e zone g m yr TOTAL INPUTS a b rae e u lt site gt 100 pparm i c d e fix 100 Set the flag for texture effect on parent P mineralization for
11. e Record the values for cerfor below C N C P c s VARIABLE i 1 i 2 i 3 cerfor 1 1 1i cerfor 2 1 1i cerfor 3 1 i cerfor 1 2 i cerfor 2 2 1i cerfor 3 2 i cerfor 1 3 i cerfor 2 3 1i cerfor 3 3 i cerfor 1 4 i cerfor 2 4 1i cerfor 3 4 i cerfor 1 5 i cerfor 2 5 i cerfor 3 5 i Set values for forrtf as in option 2 above 4 WOOD DECOMPOSITION RATES No good general scheme exists for estimating wood decomposition rates from chemical or physical properties of the wood therefore CENTURY sets wood decomposition as a system specific parameter To set this first estimate the mean turnover times of each wood pool then calculate the values for decw Mean turnover times can be estimated as the half life in terms of mass loss of an average piece of woody debris or assuming steady state questionable for large wood as standing stock input rate Again for belowground woody debris there is often very little data a value similar to that for large wood can be used in the absence of other information Calculate values for decw Perform a 3 year simulation using default parameters and mean weather for your system Output and calculate average values of defac and anerb for the third year and complete the table DEBRIS COMPONENT TURNOVER TIME yr EXPRESSION decw FINE BRANCH 2 5 turnover geowi defac 2 5 turnover 7 EA O l defac Ee 2 5 turnover F 5 BIOMASS AND WOODY DEBRIS D a BI
12. educed if nitrogen availability is high enough Enter the value used below snfxmx 2 g N fixed g C NPP 10 DOUBLED CO PARAMETERS CENTURY allows simulations to be conducted assuming a doubling of atmospheric CO concentration from 350 ppm to 700 ppm The following parameters control the effects of doubled CO on NPP transpiration C E ratios and root shoot ratios co2ipr 1 is the multiplier that represents the effect of doubled CO on NPP co2ipr 1 1 for C4 and 1 3 for C3 co2itr 1 is the multiplier that represents the effect of doubled CO on transpiration rate co2itr 1 0 6 co2ice 1 i j is the multiplier that represents the effect of doubled CO on minimum and maximum C E ratios co2ice 1 i j 1 0 co2irs 1 is the multiplier that represents the effect of doubled CO on root shoot ratio co2irs 1 lt 1 3 tree 100 The CENTURY installation package contains tree 100 parameterizations for deciduous coniferous and tropical systems that have been used in the past We suggest that you use one of those files as a starting point and use the following procedure to modify parameters as needed to represent the trees in your particular system See Appendix 2 10 in the Century User s Manual for definitions of the parameters in this file 1 FOREST TYPE Decide whether to simulate your forest as evergreen deciduous or drought deciduous In evergreen systems allocation is fixed through the year and leaf fal
13. ers available for plant growth and nlayer total layers in solum Rooting zone Total DEPTH nlaypg nlayer 0 22 cm 1 1 23 37 cm 2 2 38 52 cm 3 3 53 74 cm 4 4 75 104 cm 5 5 105 134 cm 6 6 135 164 cm 7 7 165 194 cm 8 8 195 cm or more 9 9 Sources for soils data 1 d STREAM FLOW CALBRATION If you want you can calibrate stream flow stream 1 by adjusting the parameters stormf and basef These parameters control monthly distribution of streamflow but they have no effect on water balance decomposition or production stormf is the fraction of excess water that runs off immediately in the current month the remainder goes to the baseflow storage pool in asmos nlayer 1 basef gives the fraction of this storage pool that runs off each month These parameters can be calibrated iteratively by comparing an observed time sequence of streamflow to the model predictions Note that to do this you must drive the model with the actual climate for the period not simply with the mean climate l e FIELD CAPACITY AND WILTING POINT Soil water contents at field capacity FC and wilting point WP for each soil layer can be set by the user or can be calculated based on different equations If you want to use you own FC and WP values set swflag 1 and enter appropriate WP and FC values for awilt 1 10 and afiel 1 10 If you want to use an equation consult the Century User s Manual for the interpretation of different values of swflag we usual
14. ic very young or highly disturbed soils Examine the estimates for the initial pools on the previous page and enter values chosen below somici 1 1 g C m somlci 2 1 g C m som2ci 1 g C m som3ci 1 g C m clittr 1 1 g C m Unless you want to simulate isotope labeling all som ci 2 and clittr 2 parameters should be set to zero Sources for soil carbon data 2 b INITIAL SOM C N C P C S RATIOS Enter bulk C N C P C S ratios for SOM below make these calculations only for those elements you intend to simulate enter zeros for other elements a Litter or Forest floor C N C P C S b Mineral soil C N C P C S c TOTAL C N C P C S Calculate ratios for CENTURY pool VARIABLE EXPRESSION C N i 1 C P i 2 C S i 3 rces1 1 i a 2 0 rces3 i c 0 7 a ee i a 3 0 reelit 2 i Sources for soil nutrient data 3 BIOMASS INITIAL PARAMETERS This parameterization is not necessary for annual grasses or crops and is only necessary for perennial grasses and crops if ivauto 0 If you are simulating a forest or perennial grass or crop proper initialization of these pools is not essential if you include an equilibrium block in your schedule file If you have biomass and nutrient concentration estimates and want to set initial conditions calculate as indicated below 3 a GRASS CROP ORGANIC MATTER INITIAL PARAMETERS Carbon pools if you have actual carbon data rather than just
15. ient availability Record the values for cerfor below VARIABLE EXPRESSION i l i 2 i 3 1 1 litter conc cerfor 50 fine 3 1 branch conc LA cerfor 50 large 4 i wood conc cerfor 50 coarse 5 i root conc Set all values for forrtf equal to 0 _ 2 Use fixed tissue chemistry no response to nutrient availability but simulate retranslocation of nutrients from senescent leaves before litterfall Record the values for cerfor below C N C P c s VARIABLE EXPRESSION i 1 i 2 i 3 1 1 leaf conc 2 1 root conc LA cerfor 50 fine 4 i wood conc 5 i root conc Set values for forrtf as forrtf 1 1 leaf litter N f N forrtf 2 1 leaf litter P green leaf P f S green lea forrtf 3 1 leaf litter S green lea __3 Use both variable tissue chemistry and retranslocation Based on data from fertilization trials site comparisons literature and or educated guesses widen the allowable range for one or more of the biomass fractions Foliar N content has the most extensive data but this option can be implemented for any or all biomass pool s and nutrient s Assign the minimum C E ratio maximum nutrient content to cerfor 1 the maximum C E ratio minimum nutrient content to cerfor 2 and the initial C E ratio to cerfor 3 Note that the maximum C E ratio will never actually be achieved in practice so it must be set higher than the observed highest valu
16. l is calculated each month In deciduous forests 80 of first month production goes to leaves and a given percentage of leaves senesce and fall at the end of the growing season which occurs when the days are shortening and temperatures are dropping into the fall seasonal range In a drought deciduous forest allocation is fixed throughout the year and a given percentage of leaves senesce and fall at the end of the growing season which is marked when the soil moisture reaches wilting point In general if the large majority of the canopy is deciduous say 80 or greater one of the deciduous system options will be adequate otherwise use the evergreen option For evergreen or semi evergreen systems decid 0 For deciduous systems decid 1 For drought deciduous systems decid 2 2 MAXIMUM PRODUCTION There are two maximum production values one for gross production and the other for net production Either of these can be disabled by setting it to a very high value e g 10000 and allowing the other to control production Maximum production is rarely directly observed in either the model or reality and must be inferred Maximum gross production This is expressed as the theoretical maximum gross production per month in terms of total organic matter produced NOT in terms of carbon Common values are 1200 1500 g m mo prdx 2 Maximum net production This is expressed as the theoretical maximum net biomass production
17. ly recommend swflag 2 1 CONTROLS ON PHOSPHORUS SORPTION Set the value for sorpmx to the maximum P sorption capacity for the soil 0 20 cm expressed as g P sorbed m extreme values are 1 3 for sands and 10 20 for high sorption capacity clays sorpmx Set the value for pslsrb to the ratio between sorbed P and total sorbed labile P extreme values are 5 for sands to 95 for highly sorbing clays pslsrb Source for P sorption data 1 g EXTERNAL NUTRIENT INPUT PARAMETERS The lt site gt 100 file includes parameters for atmosphereic N and S deposition described below Parameters controlling P and S inputs from weathering are in the fix 100 file 1 h NITROGEN Enter your best estimates for rates of nitrogen input below Atmospheric deposition wet dry g N m yr Non symbiotic biological N fixation g N m yr Symbiotic biological N fixation g Nm yr For deposition and non symbiotic fixation you have two choices for each input 1 Have input be fixed constant amount each year epnfa 1 deposition epnfa 2 0 0 epnfs 1 fixation epnfs 2 0 0 2 Have input vary linearly with annual precipitation epnfa 2 dependence on average average precipitation annual annual fraction 0 1 deposition precipitation 4 g N m cm H O epnfa 1 average EPNFA 2 average annual annual deposition precipitation g Nm yr epnfs 2 pa ne fh dependence on average a
18. n for cropped disturbed soils initializes SOM pools nelem controls the number of elements you want to model For example nelem 1 means that P and S will not limit C flows C N nelem 1 C N P nelem 2 Ci N P S nelem 3 sitlat lat deg N sitlng long deg E for reference only Enter the soil texture pH and bulk density for the top 20 cm of mineral soil for organic soils use top 20 cm enter actual mass fractions of sand silt and clay these need not total to 1 PROPERTY VALUE VARIABLE SAND fraction 0 1 SILT fraction 0 1 CLAY fraction 0 1 Check the appropriate soil drainage class below and circle the corresponding value for the variable DRAIN Excessively to moderately well drained drain 1 0 Somewhat poorly drained drain 0 75 Poorly drained drain 0 5 Very poorly drained drain 0 25 No drainage from solum drain 0 0 dC SOIL LAYERS Enter the rooting zone depth depth above which the large majority of fine roots are found cm Enter the soil thickness to be used for the soil water model For soils on deep saprolite or unconsolidated material enter the greater of rooting zone depth or depth to base of Bt For shallow soils enter depth to lithic contact For permafrost soils enter depth of summer thaw Soil thickness cm Convert rooting zone depth and soil thickness to numbers of soil layers using the tables below Circle the corresponding values for nlaypg lay
19. no effect TEXEPP 1 0 0 Sources for P and S input data
20. p 20 cm Subdivisions by pedogenic horizons are not required but may help set apportioning to CENTURY SOM pools Observed soil carbon storages a Litter g C m b Mineral soil g C m c TOTAL a b g cm Calculate apportioning of SOM into CENTURY pools I Based on simple horizons ma pte 1 somlci 2 1 som2ci 1 som3ci 1 clittr 1 1 bro fra fers oo a Forest soils Enter the initial forest floor and soil carbon storages For mineral soil enter total in top 20 cm for organic soils enter 0 20 cm totals as forest floor divided by horizons Forest floor excludes woody debris This parameterization can be done using simple horizons or subhorizons Observed soil carbon storages Simple Horizons Sub Horizons a Forest floor g C m al L F layer 01 a2 H layer 02 b Mineral soil g C m bl A Ap b2 B Bt E b3 Bh c TOTAL a b g Cm Calculate apportioning of SOM into CENTURY pools I Based on simple horizons E 1 somlci 2 1 som2ci 1 som3ci 1 clittr 1 1 a0 es ees a O o II Based on subhorizons a2 08 eee 03 Lae 55 meee ee b2 02 b2 55 b2 43 The values calculated from simple horizons generally indicate the Steady state proportions of the soil pools around which the model will tend to settle over 1000 s of years Those based on horizons suggest non steady state values for younger or disturbed soils Usually they differ little except in organ
21. rial can be constant or made a function of annual rainfall See parameter definitions This table shows values we have used Tall Winter Short Alfalfa Soy Corn T ceed ee eee Wael fligni 1 1 0 oso fo 1s 15 0 02 e 02 fo 04 0 12 12 7 HARVEST SENESCENCE PARAMETERS The user controls the amount of C and nutrients allocated to grain effects of water stress on harvest and N volatilized at harvest or senescence through the following parameters See parameter definitions and Fig 3 15 the Century User s Manual Tall Winter Short Alfalfa Soy Corn E el e A himax T A e mamo o o e a sm0 fos evs o oo paro sm fos fos o o as os aose oos ooa os oa oo oo 8 SHOOT AND ROOT DEATH RATES AND NUTRIENT RETRANSLOCATION PARAMETERS The user controls the maximum monthly shoot death rate senescence month shoot death rate the influence of shading on death rate shoot fall rate maximum root death rate and the fraction of nutrients retranslocated from leaves at death See Fig 3 16 the Century Users s Manual __ tase mear cess AMR bean ee e ed eee fsdeth 1 a a E a oe sma oz fo oe oa e e ferret fos fo fo fo e ov meo fo fo fo fe e gt 9 SYMBIOTIC BIOLOGICAL N FIXATION N fixation is parameterized as snfxmx 2 maximum g N fixed per g C NPP This can be approximated as symbiotic N fixation annual NPP g C Remember to set this to the maximum value it will be r
22. s the multiplier that represent the effect of doubled CO on root shoot ratio co2irs 2 lt 1 3 9 SAVANNA MODEL PARAMETERS CENTURY allows the user to simulate competition between trees and grasses If you are not simulating a savanna i e are only growing trees set the following 3 parameters to 1 basfc2 relates tree basal area to grass N fraction basfc2 0 5 basfct ratio between basal area and wood biomass basfct 400 sitpot relates grass N fraction to N availability This represents the above ground peak standing grass biomass without tree competition Units are pounds acre and values range from 1000 4000 sitpot 2400 10 OTHER PARAMETERS Check the parameters listed below and be sure they are set to the indicated values 035 15 to 28 laitop del13c fix 100 If you want to simulate the effects of changes in atmospheric CO concentration you must specify the initial parts per million co2ppm 1 and final parts per million co2ppm 2 of CO concentration and set co2rmp to specify a step 0 or ramp 1 function Most of the other parameters in the fix 100 should not be changed However some parameters may need to be adjusted to represent differences in C N ratios of SOM inputs for grasslands and forests and differences in P and S availability among various systems No other parameters in the fix 100 should be changed unless the user has strong experimental evidence to justify the change See Appendi
23. system All forest systems leafdr 1 leafdr 7 leafdr 2 leafdr 8 leafdr 3 leafdr 9 leafdr 4 leafdr 10 leafdr 5 leafdr 11 leafdr 6 leafdr 12 Sources for litterfall seasonality information 6 6 ROOT AND WOOD DEATH RATES Turnover of other pools is constant through the year and is in the parameter wooddr Monthly fine root death rate wooddr 2 is equal to annual fine root production fine root biomass 12 Monthly fine branch death rate wooddr 3 is equal to annual f branch litterfall f branch biomass 12 Monthly large wood death rate wooddr 4 is equal to annual 1 wood litterfall 1 wood biomass 12 It may also be estimated as approximately the rate of whole tree mortality per month Monthly coarse root death rate wooddr 5 is very difficult to estimate directly It is typically similar in magnitude to large wood death wooddr 3 Enter the value used here Sources Eras LEAF AREA CONTROLS Set the leaf area to biomass ratio based on biomass not carbon btolai leaf area m projected leaf dry mass g m g Set the allometric controls on LAI as follows maxlai maximum allowable LAI m m klai large wood mass g C m at which half of the maximum LAI is achieved g C m Source for LAI data 6 d SAPWOOD ALLOMETRIES Set the relationship between sapwood and total wood as sapk Maximum sapwood mass in mat
24. ure stand can be approximately estimated as 10 years worth of wood production g C m Symbiotic biological N fixation is parameterized as snfxmx 2 maximum g N fixed per g C NPP This can be approximated as symbiotic N fixation annual NPP g C Remember to set this to the maximum value it will be reduced if nitrogen availability is high enough Enter the value used below snfxmx 2 g N fixed g C NPP Sources for N input data 7 LIGNIN FRACTION OF FOREST COMPONENTS The lignin content of tree components is system specific The following table shows ranges of values we have used tree component parameter lignin fraction fine roots wdlig 2 0 09 0 28 fine branches wdlig 3 0 20 0 35 large wood wdlig 4 0 20 0 35 coarse roots wdlig 5 0 20 0 35 8 DOUBLED CO PARAMETERS CENTURY allows simulations to be conducted assuming a doubling of atmospheric CO concentration from 350 ppm to 700 ppm The following parameters control the effects of doubled CO on NPP transpiration C E ratios and root shoot ratios co2ipr 2 is the multiplier that represent the effect of doubled CO on NPP co2ipr 2 1 3 co2itr 2 is the multiplier that represent the effect of doubled CO on transpiration rate co2itr 2 0 75 for deciduous and 0 9 0 95 for coniferous co2ice 2 i j is the multiplier that represent the effect of doubled CO on minimum and maximum C E ratios co2ice 2 i j 1 2 co2irs 2 i
25. verage precipitation annual annual fraction 0 1 fixation precipitation g N m cm H O epnfs 1 meee ae a average annual EPNFS 2 average annual fixation precipitation g N m yr Fiz SULFUR Atmospheric deposition of S is simulated in the same manner as for N deposition above with a slope and intercept based on annual precipitation You can choose fixed or variable S inputs Average atmospheric deposition wet dry g S m yr Input as a fixed constant amount each year satmos 1 Average deposition satmos 2 0 0 Have input vary linearly with annual precipitation satmos 2 dependence on average average precipitation annual annual fraction 0 1 deposition precipitation g S m cm H O satmos 1 average satmos 2 average annual annual deposition precipitation Sa oni a ge S can also be added in irrigation water If you are irrigating set sirri equal to the S concentration mg S l of the water oherwise set sirri 0 2 SOIL BIOGEOCHEMISTRY 2 a INITIAL SOIL CARBON POOLS This parameterization is necessary only if ivauto 0 Two procedures are described one for grassland cropped soils and one for forest soils Choose the appropriate procedure but note that precise initialization of these pools is not necessary if your schedule file includes an equilibrium block Grassland cropped soils Enter the initial litter and soil carbon storages Enter total in to
26. x 2 5 in the Century User s Manual for definitions of parameters in the fix 100 file 1 FLOATING C N RATIOS IN SOM POOLS The parameters controlling the C N ratios may need to be adjusted from the default values particularly for temperate forest soils The default values listed in the table below are for grass crop soils and forest soils with a bulk C N lt 15 In most cases you will use the default values from the table If however your soil has a bulk C N gt 15 use the alternate values from the table Parameter Default Bulk soil C N gt 15 pcemic 1 1 16 16 pcemic 2 1 10 10 varatl1 1 1 14 16 varatl1 2 1 3 8 varat2 1 1 20 40 varat2 2 1 T2 12 varat3 1 1 8 20 varat3 2 1 6 8 2 C E OF NEWLY FORMED SOM The parameter radlp is used to adjust the C E ratio of newly formed slow SOM produced from surface active SOM This value is calculated from the parameter radlp as a function of C E ratios of the surface active SOM pool You can either set it up as fixed values or let it float When using fixed values for radlp it is a prescribed value that is generally higher when leaf litter is of lower initial quality Typical fixed values for different systems are Sos _ erest marwad _ nartiooa E a ARPE E E E E A E fe ite ie freaoz 2y oie ide sie Typical floating values for different systems are ae Ee ee a crops ce o Ee aoe O E Ee a C 3 PHOSPHORUS AND SULFUR If you are only mo
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