dynamic vegetation: yes:
Forest dynamics are described by forest growth, regeneration/planting, management.
nitrogen limitation: yes
Different approaches are used to estimate the nitrogen depending reduction of NPP. Nitrogen supply is calculated by a soil model (water, temperature, C/N module) from the soil conditions, the litter input and nitrogen uptake and leaching.
CO2 effects: The annual course of net photosynthesis is simulated with a mechanistic formulation of net photosynthesis as a function of environmental influences (temperature, water and nitrogen availability, radiation, and CO2) where the physiological capacity (maximal carboxylation rate) is calculated based on optimisation theory (modified after Haxeltine and Prentice, 1996) plus calculation of total tree respiration following the concept of constant annual respiration fraction as proposed by Landsberg and Waring (1997).
light interception: yes:
The share of any tree cohort in the total stand’s net photosynthetic assimilation of carbon is proportional to its share of the absorbed photosynthetically active radiation. The total fraction of photosynthetically active radiation absorbed by each tree cohort is calculated each time stand phenology changes, based on the Lambert-Beer law. Four models exist to calculate light transmission and absorption through the canopy.
phenology: yes:
The phenological approach in 4C is based on the interaction of inhibitory and promotory agents that are assumed to control the developmental status of a plant.
The agents are driven by temperature and photoperiod, which play the most prominent role in phenology. Using these simple but basic principles a model for the
abundance or concentration of an inhibitory and a promotory compound made of a system of two difference equations is used (Schaber and Badeck, 2003).
water stress: yes:
After calculating water demand by forest stand and water supply from the soil for each tree cohort photosynthesis is being reduced if demand is greater than supply. Allocation is also affected.
Evapo-transpiration approach: yes:
Different approaches are used:
Turc/Ivanov, Priestley/Taylor, Penman/ Monteith.
Root distribution over depth: yes
4C uses an approach according to Jackson (1996), which assumes an exponential decrease of fine root biomass with soil depth. Additionally, a site and species specific root distribution can be used as input.
closed energy balance: It is not considered.
Coupling/feedback between soil moisture and surface temperature: yes:
4C includes a coupled soil moisture and temperature model.
latent heat: Latent heat is not calculated.
sensible heat: Sensible heat is not calculated.
