Trade-offs between sequestration and bioenergy benefits

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

2. Abandoned cultivatedlands 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 startbiofuel cultivation, given future climate change and management practices?

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

4. Soil carbon changes are impacted by + Climate + Climate ++ Management + Climate ++ Land-use legacy Soil carbon Natural grassland Crops Recovering grassland 1950’s 1990’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 meteorological forcing output variables sensible & latent heat fluxes, CO2 flux, net radiation rain, température, humidity, incoming radiation, wind, CO2 ORCHIDEE SECHIBA energy & water cycle photosynthesis Dt = 1 hour LAI, roughness, albedo soil water, surface temperature, GPP STOMATE vegetation & soil carbon cycle (phénologie, allocation,…) LPJ spatial distribution of vegetation (competition, fire,…) vegetation types Dt = 1 day Dt = 1 year prescribed vegetation NPP, biomass, litterfall vegetation types

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

10. Including land-use change & land management • Input (spatially explicit) land-use statistics FAO Orchidee Orchidee-Stics time Recovery period Cultivation period 1951 1993 2000 • Input N-fertilizer addition statistics USDA on arable land of former USSR • Simple agricultural parameterization Harvest -> grains + straw exported Tillage -> Mean Residence Time of soil C pools faster by 30%

11. Results

12. Sink regional mean Croplands 100% instant. aband. Net Carbon Balance changes Orchidee-Stics Orchidee agriculture recovering grassland 1951 1993 2000 If croplands all maintained after 1993 If croplands all abandoned in 1993 Realistic abandonment scenario gC m-2 yr-1

13. Sink spatial patterns Regional C gain from 1993 to 2000 373 gC per m2 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 64 TgCin 8 years over 17 Mha C gain from 1993 to 2000 per m2 Map of the C storage from 1993 to 2000 Abandoned cropland area from 1993 to 2000

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 timetcross • tcross = time at wich biofuels deliver more C benefits than sequestration

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

19. tcross 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 tcross tcross Bioenergy production Soil C sequestration Soil C released with bioenergy production

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 Never tilled Tilling t0=just after abandonment Tilling t0=60 years after abandonment tcross tcross tcross

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 of0.3 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 !