CCMLP1:  Grand Slam Task

 

Experiment Protocol, Outline for Manuscript, and Action Items

 

October 12, 1999

Modified by A. D. McGuire based on Jena meeting (5 - 7 October 1999)

 

 


IMPORTANT NOTE

 

The following is the Grand Slam protocol for accounting for land use (croplands only) in historical simulations.

For the C4MIP exercise, we now have crops and pasture historical distribution from Ramankutty and Goldewijk. Therefore, the following protocol should be used as a guide line only.

 

 

3.0 Model modifications/LU protocol

            The land use data set assigns each 0.5 degree grid cell as either natural vegetation (0) or agriculture (1) for the historical period 1860 through to 1995. Note that agricultural land is a subset of the total land appropriated for human use, and only includes croplands.  Other land uses, which include pastures and important activities such as forestry/logging, are not considered in this simulation. Here we wish to understand and model the following:

 

3.1 Conversion from natural vegetation to cultivation

         In general, the methodology of simulation 3 builds on the approach of Houghton et al., 1983 (Houghton et al. 1983. Ecological Monographs 53:235-262).

 

3.1.1 Temperate/Boreal forest conversion

Fate of carbon in vegetation at time of clearing:                        

Left dead in soils (from ROOTS) 33  %  

1st year conversion loss (CONVERSION FLUX)         40 %

10 year product pool (PROD10) 20 %

100 year product pool (PROD100)   7 %

 total          100 %

             

3.1.2 Tropical Forest conversion

Fate of carbon in vegetation at time of clearing:                        

Left dead in soils (from ROOTS)        33  %  

1st year conversion loss (CONVERSION FLUX)         40 %

10 year product pool (PROD10) 27 %

100 year product pool (PROD100)                              0 %

 total          100 %


3.1.3 Grasslands/Tundra

Fate of carbon in vegetation at time of clearing:                                                                         

Left dead in soils (from ROOTS) 50 %  

1st year conversion loss (CONVERSION FLUX)         50 %

10 year product pool (PROD10)                             0 %

100 year product pool (PROD100)                             0 %                                                            total           100 %

 

3.1.4 Shrublands, Woodlands & Savannas

            If a group uses a mixed pixel approach and disaggregates these biomes into forest and grassland fractions, then the appropriate conversion estimates given above should be used for each fraction. Otherwise use the estimates below for the fate of carbon in vegetation at time of clearing:                        

Left dead in soils (from ROOTS)       50 %  

1st year conversion loss (CONVERSION FLUX)         40 %

10 year product pool (PROD10)                            10 %

100 year product pool (PROD100)                                        0 %

total           100 %

 

3.1.5  Additional Considerations

            Each model should use the fractions and decay rates given by Houghton if they are not already explicitly modelled.  For example, if a model explicitly estimates below ground vegetation carbon (roots), Houghton’s fraction of vegetation carbon left dead in soils may be ignored. In this case, the estimate of above ground vegetation carbon is assigned to the product decay pools using the given ratios (e.g., 40:27 for the case of tropical forest conversion).  Therefore, potential inconsistencies are avoided and reliance on the book keeping approach is minimized.  Each group should decide how to assign the vegetation carbon left dead in soils to particular soil pools.  Decisions on the seasonal timing of inputs into the soil and product pools are left to each modeling group.

 

 

3.1.6 Agricultural NPP

The annual agricultural NPP is divided into above ground and below ground biomass, i.e., harvest vs. residue, using the ratio 40:60 based on information in Table 2 of Malmstrom et al. (1997. Global Biogeochemical Cycles 11:367-392). The above ground biomass is placed in the agricultural productivity pool (AGPROD1).  This pool decays to the atmosphere in one year.  The below ground biomass enters the soil.  Each group should decide on the seasonal timing of these inputs into the soil and AGPROD1.


3.3 Abandonment of cultivated sites

Each model should grow back vegetation biomass from the extant state of the grid cell at the time of abandonment.  Because, the time required for the ecosystem to fully recover is not prescribed, time to recovery will be site specific.

 

3.4 Land Use Fluxes and Pools to be tracked during the simulation 

At the end of each year each group should define four fluxes for each grid cell: the CONVERSION FLUX and three PRODUCT FLUXES. The product fluxes represent the sum of the CO2 releases from the AGPROD1, PROD10 and PROD100 pools, which are also tracked for each grid cell.  Releases from the AGPROD1, PROD10, and PROD100 pools are calculated as a linear decay of the initial carbon inputs into these pools over 1, 10 and 100 years, respectively.  For example, the annual release from the PROD10 pool represents 10% of the initial carbon entering the PROD10 pool during the previous 10 years.  Therefore, 10 years after conversion to agriculture the initial carbon entering the PROD10 pool will have been released to the atmosphere.  Please note that the releases from AGPROD1 (AGPROD1FLUX), PROD10 (PROD10FLUX), and PROD100 (PROD100FLUX) are to be calculated for each grid cell.  Each group should decide on the seasonal timing of the CONVERSION FLUX and CO2 releases from the AGPROD1, PROD10 and PROD100 pools.