Carbon, Nitrogen and Water Cycle

Terrestrial Carbon Model, description

Model description

Each cell is characterized by its monthly climate (temperature and soil moisture), soil, and natural or agricultural land cover. Biomass within the cells is divided into different compartments as follows:

• Living biomass (leaves, branches, stems, roots)
• Non-living biomass (litter, soil humus and charcoal)
• C storage in pulpwood and particles (with a turnover of 10 years)
• C storage in sawlogs, veneer and industrial roundwood (with a turnover of 100 years).                

Net Primary Productivity

The terrestrial carbon model is driven by Net Primary Productivity (NPP, plant photosynthesis minus plant respiration), a function of climate, soil, atmospheric CO₂ concentration, altitude, land-cover type and land-cover history. NPP is allocated over the living biomass compartments, and then slowly shifts to the non-living biomass compartments, where it is decomposed and returns as CO₂  to the atmosphere. The allocation fractions and turnover times are defined for each land-cover type and C compartment.

Soil respiration 

Soil respiration is the C flux to the atmosphere resulting from the transformation of soil organic matter (litter, humus and charcoal). During decay of litter and dead roots, part is transformed into soil humus, while another (major) part is oxidized to CO₂  and lost to the atmosphere. An important part of the soil humus pool is also oxidized to CO2 and lost to the atmosphere, while a small fraction is transformed into charcoal. Charcoal is a major carbon pool in many land-cover types. Its respiration flux is therefore significant, despite its long lifetime.

Net Ecosystem Productivity

The net C flux between the atmosphere and biosphere is called 'Net Ecosystem Productivity' (NEP) and is equal to the NPP minus soil respiration. Negative values indicate a net release of CO₂, while positive values indicate a net uptake of CO₂  by the biosphere. NEP is influenced by land cover (changes) and soil and climatic factors.
Climate feedbacks (effect of temperature and CO₂  fertilization on plant growth, and effect of climate on soil respiration) are calculated at monthly intervals by using different response functions dependent of temperature, soil water and species characteristics for each grid cell (Klein Goldewijk et al.,1995). These monthly values are aggregated to annual totals for use in C-balance calculations (using the approach of Melillo et al., 1993). However, the monthly resolution allows different plant responses in different seasons to be taken into account. This temporal resolution is also consistent with the downscaling of monthly climate-change patterns in the atmosphere-ocean system.

• to  Terrestrial Carbon Model, land cover conversions
• to  external references
• to  MNP references