1. Trade-offs between sequestration and bioenergy benefits Nicolas VUICHARD (1,2) Philippe CIAIS (2) Luca BELELLI (3) Riccardo VALENTINI (3) (1)CIRED – Nogent (France) (2)LSCE/IPSL – Saclay (France) (3)University of Tuscia – Viterbo (Italy) Growing biofuels over abandoned croplands in the former USSR

2. Abandoned cultivated lands are suitable candidates for bioenergy production (Field, 2008) ► Do not compete with food security ► Dot not induce a carbon debt Bioenergy competes with soil C sequestration but has a higher environmental impact Is there an optimal onset time to start biofuel cultivation, given future climate change and management practices?

3. The end of the USSR resulted into one of the largest crop abandonment of the 20 th century - 20 Mha Hurtt et al., 2006 20 Mha

4. Soil carbon changes are impacted by Crops Recovering grassland Natural grassland Soil carbon + Climate ++ Management + Climate ++ Land-use legacy 1950’s1990’s

5. A potential of 0.5 GtC could be sequestered into the abandonned 20 Mha of croplands New soil C data from abandonned crop fields in Russia

6. Goals Carbon benefit of sequestration by natural steppe recovery Carbon benefit of biofuel due to both: - biofuel can also sequester below ground C - biofuel harvest substitutes to Fossil Fuel Compare recovery vs. biofuel option -> Use a spatially explicit process-based model to address these questions

7. Model set-up

8. The ORCHIDEE global carbon-water-energy model ORCHIDEE SECHIBA energy & water cycle photosynthesis  t = 1 hour LPJ spatial distribution of vegetation (competition, fire,…)  t = 1 year STOMATE vegetation & soil carbon cycle (phénologie, allocation,…)  t = 1 day NPP, biomass, litterfall vegetation types LAI, roughness, albedo soil water, surface temperature, GPP rain, température, humidity, incoming radiation, wind, CO 2 meteorological forcing sensible & latent heat fluxes, CO 2 flux, net radiation output variables prescribed vegetation vegetation types

9. Including crops in ORCHIDEE Same Gridded climate and soil data STICS agronomic Model Library of ≠ crop varieties LUE growth Biomass allocation and yield Water and Nitrogen demand No soil C balance scale : field, months ORCHIDEE global model Generic ecosystem C dynamics with land-use disturbances scale : local => regional => global 1 year => 1000 years Brisson et al. (2002) LAI Root profile Irrigation needs Daily data assimilation of crop parameters into ORCHIDEE

10. Input (spatially explicit) land-use statistics FAO Including land-use change & land management Input N-fertilizer addition statistics USDA Simple agricultural parameterization Harvest -> grains + straw exported Tillage -> Mean Residence Time of soil C pools faster by 30% time 19511993 Recovery period 2000 Orchidee-Stics Orchidee Cultivation period on arable land of former USSR

11. Results

12. Croplands 100% instant. aband. If croplands all maintained after 1993 If croplands all abandoned in 1993 Realistic abandonment scenario gC m -2 yr -1 Sink regional mean Net Carbon Balance changes agriculture 19511993 recovering grassland 2000 Orchidee-SticsOrchidee

13. Sink spatial patterns Regional C gain from 1993 to 2000 373 gC per m 2 Some grid points in the south are net sources, because NPP of steppes is lower than soil carbon input from former crop fields -> we really need spatially explicit modelling

14. Towards realistic estimates Map of the C storage from 1993 to 2000 Abandoned cropland area from 1993 to 2000 C gain from 1993 to 2000 per m 2 64 TgC in 8 years over 17 Mha

15. Sensitivity tests No fertilization during cultivation period => +37% No tillage during cultivation period (no impact on soil decomposition) => -25% 10% of straw remained on plot => -15%

16. Biofuels on the steppe ?

17. Modelling Biofuel on the steppe Ethanol production from natural grassland biomass as in Tilman et al. (2006) ► 1 gC substitutes 0.42 gC Scenario: an abrupt switch to biofuels in 1990 Compare scenario with sequestration by calculating the crossing time t cross t cross = time at wich biofuels deliver more C benefits than sequestration

18. Biofuel production vs steppe recovery sequestration Soil C sequestration in natural steppe Total Bioenergy production Soil C sequestered with Bioenergy production t cross

19. t cross spatial patterns in yrs after 1990

20. Timing of bioenergy implementation If we wait 60-years after abandonment to install biofuels ? Trajectories change... but same t cross Soil C sequestration Bioenergy production Soil C released with bioenergy production t cross

21. Sensitivity to C initial stocks Condition: MRT must remain constant over time This condition could be challenged if Warming accelerates decomposition Tillage must be increased for cultivating biofuels Tilling t0=just after abandonment Tilling t0=60 years after abandonment Never tilled t cross

22. Conclusions Biofuel production looks suitable on abandoned croplands of former USSR Energy = 0.23 EJ per year (0.05% of world demand) Net Carbon balance of biofuels sink of 0.56 Gt C over 60 years - Carbon storage in biofuel soils = 0.08 GtC - Fossil carbon substituted = 0.48 Gt C Net Carbon Storage if steppe recovery sink of 0.3 Gt C over 60 years

23. Crossing date = 11 years, at which biofuels have a better carbon balance than steppe recovery Crossing date is relatively insensitive to timing of implementation under some conditions (no soil warming) Quick benefits

24. Perspectives Generalize to other ecosystems Priority = sugarcane in Brazil Calculate maps of carbon debt in the eventuality of forest clearing Welcome collaborations with real experts !