Z304 Forest destruction and CO2 dynamics

The original model

The text in the following sections is taken verbatim (with the author's permission) from Bossel, H. (2007) System Zoo 3

1. Simulation task

Forests store more carbon in biomass and soil than fields under agricultural cultivation, and these in turn store more carbon than fallow land. If land use changes into another mode by clearing, afforestation, degradation, and housing development, corresponding amounts of CO₂ are released into the atmosphere or stored in biomass and humus. The CO₂ flows arising from changes of land use can be computed from the dynamics of change of land areas and the specific values of carbon storage in the different land use modes. Of particular interest are the CO₂ flows resulting from the clearing of tropical forests and their successive transformation to farmland, pastureland or degraded land.

2. Simulation model

The simulation model is documented completely in Figure Z304a and the following model equations. A constant total area is assumed which corresponds to the area covered originally by tropical forests. The state variables forest area and agricultural area – both changing with time – are deducted from the total area; the residual area is degraded land area (including settlements, streets, fallow land etc.).

CO₂ releases (or CO₂ sequestrations) result from (positive or negative) storage differences between original and subsequent land use modes and annual change of land use in the different categories by the processes deforestation, reforestation and regeneration as well as degradation (fallowing, housing developments, road construction etc.). For deforestation, reforestation and degradation after 1990 appropriate scenario parameters can be provided to allow investigation of different developments and their consequences for CO₂ release.

3. Model diagram

4. Model equations

Parameters

TOTAL AREA = 4e+007 [km²]

FOREST AREA 1990 = 1.8e+007 [km²]

AGRICULTURAL AREA 1990 = 2e+007 [km²]

DEFORESTATION 1990 = 250000 [km²/Year]

ANNUAL DEFORESTATION AFTER 1990 = 250000 [km²/Year]

REFORESTATION 1990 = 10000 [km²/Year]

ANNUAL REFORESTION AFTER 1990 = 10000 [km²/Year]

LAND DEGRADATION RATE 1990 = 0.005 [1/Year]

LAND DEGRADATION RATE AFTER 1990 = 0.005 [1/Year]

CO2 SEQUESTRATION IN FARMLAND = 25000 [tCO2/km²]

CO2 SEQUESTRATION IN FALLOW LAND = 5000 [tCO2/km²]

CO2 SEQUESTRATION IN FOREST LAND = 100000 [tCO2/km²]

Dynamics

degraded land area = TOTAL AREA –forest area -agricultural area [km²]

regeneration rate = 1/RECOVER TIME OF DEGRADED SOIL [1/Year]

regeneration = degraded land area *regeneration rate [km²/Year]

reforestation = IF THEN ELSE (Time <= 1990, REFORESTATION 1990, ANNUAL REFORESTION AFTER 1990) [km²/Year]

reforestation and regeneration = reforestation +regeneration [km²/Year]

increase of forest area = IF THEN ELSE (forest area > 100000, reforestation –deforestation +regeneration, 0) [km²/Year]

forest area = INTEG (increase of forest area, 3.5e+007) [km²] deforestation ratio 1990 = DEFORESTATION 1990 /(FOREST AREA 1990 *AGRICULTURAL AREA 1990) [1/(km²*Year) ]

deforestation ratio after 1990 = ANNUAL DEFORESTATION AFTER 1990 /(FOREST AREA 1990 *AGRICULTURAL AREA 1990) [1/(Year*km²) ]

deforestation ratio = IF THEN ELSE(Time <= 1990, deforestation ratio 1990,

deforestation ratio after 1990) [1/(Year*km²) ]

deforestation = forest area *agricultural area *deforestation ratio [km²/Year]

degradation rate = IF THEN ELSE (Time <= 1990, LAND DEGRADATION RATE 1990, LAND DEGRADATION RATE AFTER 1990) [1/Year]

degradation = agricultural area *degradation rate [km²/Year]

increase of agricultural area = deforestation -degradation [km²/Year]

agricultural area = INTEG (increase of agricultural area, 5e+006) [km²]

CO2 release by degradation = degradation *CO2 sequestration difference between fallow and farm land [tCO2/Year]

CO2 sequestration by reforestation = reforestation and regeneration *CO2 sequestration difference between forest and fallow land [tCO2/Year]

CO2 release by deforestation = deforestation *CO2 sequestration difference between farm and forest land [tCO2/Year]

CO2 increase = -(CO2 release by deforestation +CO2 release by degradation +CO2 sequestration by reforestation) /1e+009 [GtCO2/Year]

cumul CO2 from land conversion = INTEG (CO2 increase, 0) [GtCO2]

net CO2 release from land conversion = CO2 increase [tCO2/Year]

CO2 sequestration difference between fallow and farm land = CO2 SEQUESTRATION IN FALLOW LAND -CO2 SEQUESTRATION IN FARMLAND [tCO2/km²]

CO2 sequestration difference between forest and fallow land = CO2 SEQUESTRATION IN FOREST LAND -CO2 SEQUESTRATION IN FALLOW LAND [tCO2/km²]

CO2 sequestration difference between farm and forest land = CO2 SEQUESTRATION IN FARMLAND -CO2 SEQUESTRATION IN FOREST LAND [tCO2/km²]

Simulation time parameters

INITIAL TIME = 1900 [Year]

FINAL TIME = 2100 [Year]

TIME STEP = 0.25 [Year]

6. Simulation results

The development of forest area, agricultural area and degraded land area in tropical forest regions, calculated for the period between 1900 and 2100 with the default parameter settings is shown in Figure Z304b. Annual deforestation and reforestation as well as annual net CO2 release from land conversion and cumulated CO2 from land conversion are shown in Figure Z304c. Figures Z304d and e show how strongly the key quantities forest area and cumulated CO2 from land conversion depend on scenario assumptions about the annual deforestation after 1990

7. Exercises

1. Use the model to examine the spectrum of possible developments for plausible choices of parameters and scenarios.

2. Compare the results for the rates of CO2 release with the results of the global model Z303 “CO2 dynamics”. Which relative contribution does the destruction of tropical forests make to the complete CO2 balance?

3. Using simulations, determine which forest, agricultural and settlement policy measures should be applied to tropical forest areas after the year 2000 to reduce the net emission of CO2 from tropical forest areas to zero as quickly as possible and to possibly use these areas even as CO2 sinks.

8. References

Deutscher Bundestag 1990: Schutz der tropischen Wälder – Eine internationale Schwerpunktaufgabe. 2. Bericht der Enquête-Kommission "Vorsorge zum Schutz der Erdatmosphäre". Zur Sache 10/1990, Deutscher Bundestag, Bonn.

=== End of the extract from Bossel (2007) System Zoo Z605 Miniworld ===

9. Model diagram

Simile model diagram

11. Model equations

Compartment agricultural area :

Initial value = 5e+006 (real)

Rate of change = + increase of agricultural area

Compartment cumul CO2 from land conversion :

Initial value = 0 (real)

Rate of change = + CO2 increase

Compartment forest area :

Initial value = 3.5e+007 (real)

Rate of change = + increase of forest area

Flow CO2 increase :

CO2 increase = -(CO2_release__by_deforestation+CO2_release_by_degradation+CO2_sequestration_by_reforestation)/1e+009 (real)

Flow increase of agricultural area :

increase of agricultural area = deforestation-degradation (real)

Flow increase of forest area :

increase of forest area = if forest_area>100000 then reforestation-deforestation+regeneration else 0 (real)

Variable Annual reforestation after 1990 :

Annual reforestation after 1990 = 10000 (int)

Variable CO2 release by deforestation :

CO2 release by deforestation = deforestation*CO2_sequestration_difference__between_farm_and_forest_land (real)

Variable CO2 release by degradation :

CO2 release by degradation = degradation*CO2_sequestration_difference_between_fallow_and_farm_land (real)

Variable CO2 sequestration by reforestation :

CO2 sequestration by reforestation = reforestation_and__regeneration*CO2_sequestration_difference_between_forest_and__fallo_land (real)

Variable CO2 sequestration in farmland :

CO2 sequestration in farmland = 25000 (int)

Variable CO2 sequestration difference between fallow and farm land :

CO2 sequestration difference between fallow and farm land = CO2_sequestration_in__fallow_land-CO2_sequestration_in_farmland (int)

Variable CO2 sequestration difference between forest and fallo land :

CO2 sequestration difference between forest and fallo land = CO2_sequestration_in__forest_land-CO2_sequestration_in__fallow_land (int)

Variable CO2 sequestration difference between farm and forest land :

CO2 sequestration difference between farm and forest land = CO2_sequestration_in_farmland-CO2_sequestration_in__forest_land (int)

Variable CO2 sequestration in fallow land :

CO2 sequestration in fallow land = 5000 (int)

Variable CO2 sequestration in forest land :

CO2 sequestration in forest land = 100000 (int)

Variable Recover time of degraded soil :

Recover time of degraded soil = 200 (int)

Variable TOTAL AREA :

TOTAL AREA = 4e+007 (real)

Variable agricultural area 1990 :

agricultural area 1990 = 2e+007 (real)

Variable annual deforestation after 1990 :

annual deforestation after 1990 = 250000 (int)

Variable deforestation :

deforestation = forest_area*agricultural_area*deforestation__ratio (real)

Variable deforestation 1990 :

deforestation 1990 = 250000 (int)

Variable deforestation ratio :

deforestation ratio = if time<=1990 then deforestation_ratio_1990 else deforestation_ratio_after_1990 (real)

Variable deforestation ratio 1990 :

deforestation ratio 1990 = deforestation_1990/(forest_area_1990*agricultural_area__1990) (real)

Variable deforestation ratio after 1990 :

deforestation ratio after 1990 = annual_deforestation_after_1990/(forest_area_1990*agricultural_area__1990) (real)

Variable degradation :

degradation = agricultural_area*degradation_rate (real)

Variable degradation rate :

degradation rate = if time<=1990 then land_degradation_rate_1990 else land_degradation_after_1990 (real)

Variable degraded land area :

degraded land area = TOTAL_AREA-forest_area-agricultural_area (real)

Variable forest area 1990 :

forest area 1990 = 1.8e+007 (real)

Variable land degradation after 1990 :

land degradation after 1990 = 0.005 (real)

Variable land degradation rate 1990 :

land degradation rate 1990 = 0.005 (real)

Variable net CO2 release from land conversion :

net CO2 release from land conversion = CO2_increase (real)

Variable reforestation :

reforestation = if time<=1990 then reforestation__1990 else Annual_reforestation_after_1990 (int)

Variable reforestation 1990 :

reforestation 1990 = 10000 (int)

Variable reforestation and regeneration :

reforestation and regeneration = reforestation+regeneration (real)

Variable regeneration :

regeneration = degraded_land_area*regeneration_rate (real)

Variable regeneration rate :

regeneration rate = 1/Recover_time_of__degraded_soil (real)

Variable time :

time = time(1) (real)

12. The model itself

Simile model

Simile native format (.sml) download

This is what you get when you save a model in Simile.

To use this model, download it, then open the file up in your version of Simile.

Important note: If you are a visitor to this site, please see this page regarding getting hold of Simile in order to view and run this model.

Similette model

Not currently available

13. Simulation results, including comparison with original results

14. Conclusions

Download fil