The litter model#

Model overview#

The litter model is simple enough that its integration over time has an exact analytic solution. The major assumption we have to make to get this to work is that all inputs to the model occur at a constant rate across the model time step. With this assumption made, finding the new values for the litter pools then involves the following steps:

  1. The amount of litter consumed by animals is subtracted from the relevant pools and diverted into animal digestion processes.

  2. Decay rates are calculated for the remaining litter in the pools. These rates vary based on environmental conditions and the lignin proportion of each pool.

  3. Plant inputs are considered from two sources, which have different stoichiometric properties.

    • The nutrient concentrations of turned over plant tissues generally have reduced nutrient concentrations because plants translocate nutrients out of them before dropping them.

    • Plant inputs generated during herbivory, where animals drop unconsumed biomass, are not depleted in nutrients and herbivores may be actively selecting plant matter rich in limiting nutrients.

    The litter model combines these input streams, retaining information on the total input mass and chemistry of these different input routes, along with flows into the different litter pools.

  4. Given the litter loss to consumption and decay and the new inputs, updated litter pool sizes are calculated.

  5. The chemistry of these new pools is then found.

  6. The mineralisation rates at which nutrients enter the soil are then found. We track carbon, nitrogen and phosphorus.

Future directions 🔭

However, there is an issue with this approach in that it gives animals preferential access to litter over microbes (which drive the decay processes). This is something we may have to address in future, potentially by only making a limited portion of the litter available for animal consumption.

If you want to understand the model flow in greater detail, please consult the litter model API documentation.

Model variables#

There are five different relationships that models can have with variables. The links in the list below provide summaries of all variables the litter model has each specific relationship with: