The whole area is divided in grid-cells in which an independent demographic model regulates the PFG life cycle. PFG abundances are structured by age into cohorts and each cohort is attributed to a height stratum according to the growth parameters.
Different submodels affect this cycle at various levels :
Competition through light and/or soil resources regulates interactions between cohorts affecting germination, recruitment and survival.
Habitat suitability affects the recruitment and fecundity rates.
The seed dispersal model makes FATE
spatially explicit by connecting grid-cells.
It depends on the amount of seeds produced by mature plants and affects each PFG’s seed bank in each cell.
Disturbances affect PFG survival and fecundity.
Only three age classes are considered : germinant, juvenile and mature.
Influence of environment (habitat suitability) :
SuFateh
model is selected.Is the habitat suitable ? :
Each year (timestep), the values contained in each PFG habitat suitability maps will be compared to a reference value :
if superior, the environment is considered suitable for the PFG (hence $\text{getEnv}...()$ functions will return 1
)
0
)Depending on the parameterisation chosen, (see HABSUIT_OPTION
parameter in GlobalParameter file), the reference value can be set in two different ways.
Lifespan & maturity :
$$\text{LifeSpan} * \text{getEnvMort}()$$
\begin{align} \text{maturityTime} &= (\text{LifeSpan} - \text{Maturity}) * (1.0 - \text{getEnvGrowth}()) + \text{Maturity} \ \text{maturityTime} &= ceil(\text{maturityTime}) \end{align}
If SuFateh
model is NOT selected, or the habitat is suitable, then $\text{maturityTime} = \text{Maturity}$.
Otherwise, it the habitat is NOT suitable, $\text{maturityTime} = \text{LifeSpan}$, which means there will be no fecundity, and then no seeds produced.
$$\text{Lifespan} - \text{Maturity}$$
Carrying capacity (mature vs immature) :
IMM_SIZE
parameter in Succession files).MAX_ABUNDANCE
parameter in Succession files and MAX_ABUND_{...}
parameters in GlobalParameter file).$$\frac{\text{MaxAbund}}{\text{Lifespan} - \text{Maturity}}$$
Germination :
\begin{align} \text{totAbund} &= \text{AbundMature} &+ \text{AbundImmature} * \text{ImmSize} \ \text{globalCC} &= \text{MaxAbund} &+ \text{MaxAbund} * \text{ImmSize}\ &\text{if (totAbund} < \text{globalCC)} \ &{ \ & ... \ &} \end{align}
ACTIVE_GERM
parameter in Light and Soil files).SuFateh
model is selected, the habitat must be suitable, otherwise the recruitment will be null.\begin{align} \text{RecruitmentRate} &= \text{GerminationRate} & \text{ getEnvRecrRate}() \ &= \text{AvailSeeds} * \text{MaxRecruitment} & \text{ getEnvRecrRate}() \end{align}
Fecundity :
POTENTIAL_FECUNDITY
parameter in Succession files). Due to lack of empirical data, this amount is often set at the same value for all PFG.SuFateh
model is selected (no seeds produced if the habitat is not suitable) :$$\text{Fecundity} = min(1, \frac{\text{AbundMature}}{\frac{\text{MaxAbund}}{\text{Lifespan} - \text{Maturity}}}) * \text{PotentialFecund} * \text{getEnvFecund}()$$
If $\frac{\text{AbundMature}}{\frac{\text{MaxAbund}}{\text{Lifespan} - \text{Maturity}}} \geqslant 1$, the PFG has reached its annual carrying capacity : it is in optimal conditions and will produce its maximum amount of seeds ($\text{PotentialFecund}$). Otherwise, this amount will be reduced in proportion.
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