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Carbon_pools
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LPJmL includes 3 carbon pools (and corresponding sub-compartments) which are available as outputs: vegetation, litter and soil.
The vegetation carbon pool integrates all carbon stored in the standing biomass. It is the sum over all PFT-specific tissue pools: leaves, sapwood, heartwood and fine roots for woody plant functional types (PFTs); leaves and fine roots for herbacious PFTs; and leaves, fine roots, harvestable storage organ and a pool representing stems and mobile reserves for crop functional types (CFTs). Carbon enters the vegetation carbon pool by the process of allocation of NPP. Several processes remove carbon from the vegetation pool: fire, harvest, land-use change, mortality, turnover.
Litter carbon pools are kept on a stand basis.
Turnover and mortality transfer carbon from the
vegetation to the litter pool of the same stand. Litter pools are
PFT specific for the aboveground part and
are created with establishment of the corresponding plants.
src/soil/addlitter.c (Litter pools that have been created
once do continue to exist even if the respective PFTs are not present
anymore). There is one belowground (bg) litter pool. The aboveground
(ag) component consists of one litteritem per PFT. The litteritem has a
pointer to the corresponding
PFT-parameters and a
trait, which consists of a leaf litter pool and various wood
litter pools that are distinguished by fuel classes. See
source:trunk/include/soil.h
Decomposition of soil organic matter (SOM) in the litter pools is
computed in src/soil/littersom.c. A linear decay function
is also implemented technically (compile with pre-compiler
switch LINEAR_DECAY), but the default setting has an exponential
decay function.
There is a slow and a fast decaying pool of litter.
Litter pools are PFT-specific following the publication by Brovkin et al. (2012): Plant-driven variation in decomposition rates improves projections of global litter stock distribution
Soil carbon stocks are kept on a stand
basis. Litter decomposition feeds carbon into the atmosphere,
and slow and fast soil carbon pools. Soil carbon pools are distributed
over the [soil](soil layers) by layer-specific shift rates, see
src/soil/equilsoil.c#L155 ff.
Decomposition of soil organic matter (SOM) is computed in
src/soil/littersom.c. A linear decay function is also
implemented technically (compile with pre-compiler switch
LINEAR_DECAY), but the default setting has an exponential decay
function.
There is a slow and a fast decaying pool of soil.
In terms of LPJmL output files (.bin or .nc), the balance equations are:
Carbon storage = vegC + litC + soilC
Carbon sequestration = mnpp + flux_estab + pft_rharvest - rh - fireC -
flux_harvest - deforest_emissions
The difference in carbon storage over 1 year must equal the carbon sequestration in the same time period.