VSEM: Very simple ecosystem model

Description

A very simple ecosystem model, based on three carbon pools and a basic LUE model

Usage

VSEM(pars = c(KEXT = 0.5, LAR = 1.5, LUE = 0.002, GAMMA = 0.4, tauV = 1440,
  tauS = 27370, tauR = 1440, Av = 0.5, Cv = 3, Cs = 15, Cr = 3), PAR,
  C = TRUE)

Arguments

pars

a parameter vector

PAR

Photosynthetically active radiation (PAR) MJ /m2 /day

switch to choose whether to use the C or R version of the model. C is much faster.

KEXT

Light extinction coefficient m2 ground area / m2 leaf area

LAR

Leaf area ratio m2 leaf area / kg aboveground vegetation

LUE

Light-Use Efficiency (kg C MJ-1 PAR)

GAMMA

Autotrophic respiration as a fraction of GPP

tauV

Longevity of aboveground vegetation days

tauR

Longevity of belowground vegetation days

tauS

Residence time of soil organic matter d

Value

a matrix with colums NEE, CV, CR and CS units and explanations see details

Details

This Very Simple Ecosystem Model (VSEM) is a 'toy' model designed to be very simple but yet bear some resemblance to deterministic processed based ecosystem models (PBMs) that are commonly used in forest modelling. The model determines the accumulation of carbon in the plant and soil from the growth of the plant via photosynthesis and senescence to the soil which respires carbon back to the atmosphere. The model calculates Gross Primary Productivity (GPP) using a very simple light-use efficiency (LUE) formulation multiplied by light interception. Light interception is calculated via Beer's law with a constant light extinction coefficient operating on Leaf Area Index (LAI). A parameter (GAMMA) determines the fraction of GPP that is autotrophic respiration. The Net Primary Productivity (NPP) is then allocated to above and below-ground vegetation via a fixed allocation fraction. Carbon is lost from the plant pools to a single soil pool via fixed turnover rates. Heterotropic respiration in the soil is determined via a soil turnover rate. The model equations are -- Photosynthesis $$LAI = LAR*Cv$$ $$GPP = PAR * LUE * (1 - \exp^{(-KEXT * LAI)})$$ $$NPP = (1-GAMMA) * GPP$$ -- State equations $$dCv/dt = Av * NPP - Cv/tauV$$ $$dCr/dt = (1.0-Av) * NPP - Cr/tauR$$ $$dCs/dt = Cr/tauR + Cv/tauV - Cs/tauS$$ The model time-step is daily. -- VSEM inputs: PAR Photosynthetically active radiation (PAR) MJ /m2 /day -- VSEM parameters: KEXT Light extinction coefficient m2 ground area / m2 leaf area LAR Leaf area ratio m2 leaf area / kg aboveground vegetation LUE Light-Use Efficiency (kg C MJ-1 PAR) GAMMA Autotrophic respiration as a fraction of GPP tauV Longevity of aboveground vegetation days tauR Longevity of belowground vegetation days tauS Residence time of soil organic matter d -- VSEM states: Cv Above-ground vegetation pool kg C / m2 Cr Below-ground vegetation pool kg C / m2 Cs Carbon in organic matter kg C / m2 -- VSEM fluxes: G Gross Primary Productivity kg C /m2 /day NPP Net Primary Productivity kg C /m2 /day NEE Net Ecosystem Exchange kg C /m2 /day

Description

Usage

Arguments

Value

Details

See Also