Vegetation dynamics

Overview

Vegetation dynamics describes the temporal evolution of the fractional coverage of plant functional types (PFTs) within a grid cell. In dynamic vegetation models, PFTs within a grid cell compete for space and resources, and their expansion is driven by establishment and constrained by mortality and disturbance processes such as fire.

abstract type AbstractVegetationDynamics{NF} <: Terrarium.AbstractProcess{NF}

subtypes(Terrarium.AbstractVegetationDynamics)

1-element Vector{Any}:
 PALADYNVegetationDynamics

PALADYN vegetation dynamics

struct PALADYNVegetationDynamics{NF} <: Terrarium.AbstractVegetationDynamics{NF}

variables(PALADYNVegetationDynamics(Float32))

Variables
├─ Prognostic: 
├── vegetation_area_fraction [-] on XY{Center, Center}
├─ Auxiliary: 
├─ Inputs: 
├── balanced_leaf_area_index [-] on XY{Center, Center}
├── carbon_vegetation [kg m^-2] on XY{Center, Center}
├── net_primary_production [kg m^-2 s^-1] on XY{Center, Center}
├─ Namespaces:

This implementation follows the Lotka–Volterra approach of PALADYN [4], in which the vegetation area fraction $\nu_i$ for each PFT $i$ evolves according to:

\[\begin{equation} \frac{d\nu_i}{dt} = \lambda_{\text{NPP}} \frac{\text{NPP}}{C_{\text{veg,i}}} \cdot \nu_i^* (1 - \sum_j c_{ij}\nu_j) - \gamma_v \nu_i^* \end{equation}\]

where $\lambda_{\text{NPP}}$ is the NPP partitioning factor computed by the vegetation carbon dynamics process (see Vegetation carbon dynamics), $\text{NPP}$ is the net primary production, $C_{\text{veg}}$ is the total vegetation carbon pool, $\nu^* = \max(\nu, \nu_{\text{seed}})$ where $\nu_{\text{seed}}$ is a small seeding fraction to ensure that a PFT is always seeded and $\gamma_v$ is the disturbance rate.

The first term on the right-hand side represents the expansion of PFT $i$ driven by the fraction of NPP allocated to spreading.

The second term is a Lotka–Volterra competition term that limits expansion through competition with other PFTs for space, with $c_{ij}$ describing the competitive effect of PFT $j$ on PFT $i$. Since only one PFT is considered per grid cell in the current implementation, this competition term is ignored for now.

The last term represents the loss of vegetation cover due to disturbance, for example from fire or other mortality related processes. In PALADYN, the disturbance coefficient $\gamma_v$ mainly represents fire-induced disturbance through a simple parameterization based on topsoil moisture and aboveground biomass, together with a minimum constant disturbance rate used to represent disturbances other than fire. In the current implementation, fire is ignored, and $\gamma_v = \gamma_{\min}$.

Process interface

compute_auxiliary!(
    state,
    grid,
    veg_dynamics::PALADYNVegetationDynamics,
    args...
)

compute_tendencies!(
    state,
    grid,
    veg_dynamics::PALADYNVegetationDynamics,
    vegcarbon_dynamics::PALADYNCarbonDynamics,
    args...
)

Methods

compute_γv(veg_dynamics)

compute_ν_star(veg_dynamics, ν)

Kernel functions

compute_ν_tendency(
    i, j, grid, fields,
    veg_dynamics::AbstractVegetationDynamics,
    vegcarbon::AbstractVegetationCarbonDynamics
)

compute_ν_tendencies!(
    tend,
    i,
    j,
    grid,
    fields,
    veg_dynamics::PALADYNVegetationDynamics,
    vegcarbon_dynamics::PALADYNCarbonDynamics
) -> Any

References