Dennis S. Ojima, William J. Parton, Rebecca McKeown, and William M. Pulliam
NREL, Colorado State University, Fort Collins, CO 80532, USA
http://www.nrel.colostate.edu/projects/century5/
http://www.cgd.ucar.edu/vemap/abstracts/CENTURY.html
The CENTURY model simulates carbon, nutrient, and water dynamics for different types of ecosystems. CENTURY includes a soil organic matter/decomposition sub-model, a water budget sub-model, two plant production sub-models (grassland and forest), and functions for scheduling events. The model computes flows of carbon, nitrogen, and (optionally), phosphorus, and sulfur through model compartments. The four elements have identical organic matter structure, but they differ in inorganic compounds.
Carbon uptake in CENTURY is controlled primarily by nitrogen availability (VEMAP 1995). Elevated CO2 influences NPP predictions by altering the C:N ratio of decomposing organic matter, as well as soil moisture. The soil organic matter sub-model includes three soil organic matter pools (active, slow, and passive) with different potential decomposition rates, above and below ground litter pools, and a surface microbial pool (decomposition of surface litter). The water budget model calculates monthly evaporation, transpiration, water content of the soil layers, snow water content, and saturated flow of water between soil layers. Both plant production sub-models (a grassland/crop sub-model and a forest production sub-model) assume that the monthly maximum plant production is controlled by moisture and temperature, and that maximum plant production rates depend on the availability of nutrients. The grassland/crop production model simulates plant production for different herbaceous crops and plant communities (e.g., warm or cool season grasslands, wheat, and corn). The forest model simulates the growth of deciduous or evergreen forests in juvenile and mature phases. To simulate savanna or shrubland ecosystems, CENTURY combines the grassland and forest sub-models with simulation of nutrient competition and shading effects.
CENTURY conceives disturbances as central components of an "equilibrium" ecosystem, and applies a natural disturbance regime during equilibrium simulation. Disturbances such as fire, harvest, grazing and cultivation are simulated via the management and events scheduling functions.
The CENTURY model uses a monthly time step. This model has the finest partitioning of soil/litter (15) and vegetation (8) pools. Soil organic matter is represented by an active fraction, with a high turnover rate, a protected fraction, and a fraction that is highly resistant to decomposition.
None
Initial soil carbon, nitrogen (phosphorus and sulfur optional) are provided to the model as input variables.
Parton et al. (1993) found that CENTURY simulated soil C and N levels and peak live biomass and production within 25% of the observed values. However, shorter-term changes in biomass were not predicted well by the model. Gilmanov et al. (1997) found that CENTURY reproduced the seasonal, mid-term, and in some cases, long-term dynamics in aboveground biomass in a wide range of grassland ecosystems across the former USSR. Model discrepancies were attributed to changes in species composition and short-term responses to intermittent rainfall that are missed by the monthly timestep of the model.
Gilmanov, T. G., W.J. Parton, and D. S. Ojima, 1997. Testing the CENTURY ecosystem level model on data sets from eight grassland sites in the former USSR representing a wide climatic/soil gradient. Ecological Modelling 96, 191-210.
Parton, W.J., J.M..O. Scurlock, D.S. Ojima, T.G. Gilmanov, R.J. Scholes, et al. 1993. Observations and modeling of biomass and soil organic matter dynamics for the grassland biome worldwide. Global Biogeochemical Cycles 7(4): 785-809.
Parton, W. J. 1996. The CENTURY model. In: D. S. Powlson, P. Smith, and J. U. Smith, (Eds.), Evaluation of soil organic matter models using existing long-term datasets, Springer-Verlag, Berlin, Germany, pp. 283-293.