Parameter Descriptions

Parameters

ModVege makes use of a sizable number of different variables. Some of them are used as inputs to the simulation, some tune model behaviour and others are the actual state variables of the simulated grassland system.

The following section attempt to provide an as comprehensive as possible list of all of these. For a thorough understanding, the reader is referred to the original publication by [@jouven2006ModelPredictingDynamics].

State Variables

These values evolve during a model run and are stored in the respective fields in the [ModvegeSite] instance that was run.

BM Standing biomass in kg DM per ha.
BMG Standing green biomass (kg DM / ha).
cBM Cumulativeley grown biomass (kg DM / ha).
dBM Daily grown biomass (kg DM / ha).
hvBM Cumulative harvested biomass (kg DM / ha).
OMD Organic matter digestibility (kg / kg).
OMDG OMD of green matter (kg / kg).
ST Temperature sum in degree Celsius days.
REP Reproductive function. Gives the fraction of growth that is assigned to reproductive growth. The remainder goes into vegetative growth. Dimensionless.
PGRO Potential growth in kg DM / ha.
GRO Effective growth in kg DM / ha.
LAI Leaf area index, accounting for the proportion of light intercepted by the sward. Dimensionless.
LAIGV LAI of green vegetative biomass. Dimensionless.
AET Actual evapotranspiration in mm.
WR Water reserves in mm.
ENV Function representing environmental effects on growth. Acts as a multiplicative factor. Dimensionless.
ENVfPAR Part of ENV due to strength of incident radiation. Dimensionless.
ENVfT Part of ENV due to temperature. Dimensionless.
ENVfW Part of ENV due to water limitation. Dimensionless.

Initial conditions

AgeGV Age of green vegetative matter in degree Celsius days.
AgeGR Age of green reproductive matter in degree Celsius days.
AgeDV Age of dead vegetative matter in degree Celsius days.
AgeDR Age of dead reproductive matter in degree Celsius days.
BMGV biomass of GV (kg DM per ha).
BMGR biomass of GR (kg DM per ha).
BMDV biomass of DV (kg DM per ha).
BMDR biomass of DR (kg DM per ha).
BMDR biomass of DR (kg DM per ha).
SENG senescence of GV (kg DM per ha).
SENG senescence of GR (kg DM per ha).
ABSG abscission of DV (kg DM per ha).
ABSG abscission of DR (kg DM per ha).
ST thermal time (degree days).
cBM cumulative total biomass (kg per ha).

Model parameters

LON geographic longitude of site in degree.
LAT geographic latitude of site in degree.
ELV geographic elevation of site in m.a.s.l.
WHC water-holding capacity of site in mm.
NI site nutritional index (dimensionless).
RUEmax maximum radiuation use efficiency in g DM per MJ.
w_FGA relative weight of functional group A.
w_FGB relative weight of functional group B.
w_FGC relative weight of functional group C.
w_FGD relative weight of functional group D.
sigmaGV rate of GV respirative biomass loss (dimensionless).
sigmaGR rate of GR respirative biomass loss (dimensionless).
T0 photosynthesis activation temperature (degree C).
T1 photosynthesis plateau temperature (degree C).
T2 photosynthesis max temperature (degree C).
KGV basic senescence rate GV (dimensionless).
KGR basic senescence rate GR (dimensionless).
KlGV basic abscission rate GV (dimensionless).
KlGR basic abscission rate GR (dimensionless).
maxOMDDV organic matter digestibility in gram per gram DV.
minOMDDR organic matter digestibility in gram per gram DR.
CO2_growth_factor strength of effect of CO2 concentration on growth. See parameter b in [fCO2_growth_mod()].
crop_coefficient multiplicative factor K_c by which reference evapotranspiration ET₀ has to be multiplied to get the crop evapotranspiration ET_c: ET_c = K_c ET₀
senescence_cap fraction c_s of GRO to which SEN is limited: SEN_i^max = c_s GRO_i for i in GV, GR. Makes it less likely for grass population to die out. Can be set to large values in order to effectively disable senescence capping.
stubble_height float. Minimum height the grass can assume. The biomass will not fall below that height. This effectively presents a simple model of plant reserves.
SGS_method string. Choice of method to determine the start of the growing season. Can be either "MTD" for the multicriterial thermal definition (see [start_of_growing_season_mtd()]) or "simple" for a commonly used approach as described in [start_of_growing_season()]).

Functional group parameters

SLA Specific Leaf Area in m² per g.
pcLAM Percentage of laminae (number between 0 and 1).
ST1 Temperature sum in degree Celsiues days after which the seasonality function SEA starts to decrease from its maximum plateau. See also [SEA()].
ST2 Temperature sum in degree Celsiues days after which the seasonality function SEA has decreased back to its minimum value. See also [SEA()].
maxSEA Maximum value of the seasonality function [SEA()]
minSEA Minimum value of the seasonality function [SEA()]. Usually, minSEA = 1 - (maxSEA - 1).
maxOMDGV Maximum organic matter digestability for green vegetative matter in arbitrary units.
minOMDGV Minimum organic matter digestability for green vegetative matter in arbitrary units.
maxOMDGR Maximum organic matter digestability for green reproductive matter in arbitrary units.
minOMDGR Minimum organic matter digestability for green reproductive matter in arbitrary units.
BDGV Bulk density of green vegetative dry matter in g per m³.
BDDV Bulk density of dead vegetative dry matter in g per m³.
BDGR Bulk density of green reproductive dry matter in g per m³.
BDDR Bulk density of dead reproductive dry matter in g per m³.
fg_parameter_names Vector of strings of the variable names of all vegetation parameters governed by functional group composition.

Weather variables

DOY day of year in given year
Ta average temperature of given day (Celsius).
precip precipitation in millimeter per day.
PAR photosynthetically active radiation in MJ/m². Can be calculated from average sunlight irradiance SRad in J/s/m² as: PAR = SRad * 0.47 * 24 * 60 * 60 / 1e6
ET0 evapotranspiration in mm.