1. Estimates of carbon sequestration in European forest soils FP5 EU-project CNTER Per GUNDERSEN Danish Centre for Forest Landscape and Planning, Royal Veterinary and Agricultural University (KVL), Denmark N. Dise, B. Berg, C. Akselsson, B. Emmett, V. Gauci, J. Mol, A. Tietema, W. de Vries, L. Vesterdal, et al. Carbon - Nitrogen Interactions in Forest Ecosystems - CNTER

2. C sequestration (C sink) in soil? C sequestration in soil organic matter (SOM) is unknown and hard to measure CNTER try to develop methods to come up with qualified estimates

3. C-N interaction, basic idea C and N are bound together in organic matter Soil C and N accumulate together, thus from N retention we know the limits for C sequestration N saturated soils are C saturated

4. C seq. from N mass balance C seq  [N acc * C/N soil ], where N acc = [N input - (N tree accum +N out )]. Assumption N balance can be quantified soil C/N is not increasing

5. N-balance data IFEF database compiled from literature (Dise et al.) ICP Forest Level II monitoring (Van der Salm, de Vries...)

6. Soil C-sequestration (N-budget sites) Mean: 120 kgC/ha/yr Gundersen, Dise, Gauci et al. (in prep.)

7. Soil C-sequestration (N-budget sites)

8. Simple => possible to extrapolate C seq  [N imm * C/N soil ], where N imm = [N input - (N tree accum +N out )].

9. Soil C sequestration in Europe 6000 Level I plots 70 kgC/ha/yr or 16 Mt/yr 1/4 of wood C seq. (de Vries et al., 2006; GCB)

10. Limit value approach C seq = C litterfall (100 - limit value) limit value = f (N, Ca, Mn) For extrapolation: litterfall = f (AET) Berg et al. 2001 etc.

12. Cumulative CO 2 -emission from new and old soil organic matter Schmidt and Gundersen, unpublished CO 2 -emission weeks New SOM Old SOM N add 10 yr Control N add 10 yr Control Klosterhede, Denmark

13. Extrapolation to Sweden N-balance Limit value Direct measure 1961-2001 Akselsson et al. 200xAkselsson et al. 2005Berg et al. Mean = 96 kgC/ha/yrMean = 180 kgC/ha/yr

14. Since Iron Age 2500 years of change

15. Sitka spruce afforestation in Wales C-seq. from N-balanceN-balance Organic layer, DW

16. Soil C content in mineral soil 0-25 cm in spruce forest with time since planting on former farmland r 2 =0.75 r 2 =0.31 +23 -12 N retention 25% N retention 90%

17. Soil C sequestration estimates

18. Conclusions Forest soil C seq. is low (10gC/m2/yr) N retention and C/N stoichiometry  estimates of C sequestration  extrapolated to continental scales Indications that deposition N increased the organic layer C storage N saturated soils are probably also ‘C saturated’  soil C sink may fade Carbo-Nitro-EU measurements on the same sites may improve on this

19. Zzzzz …. … 200g N mobilised today means 5000g C … zzzzz C you in the future

20. Compare estimates of C sequestration Mol-Dijkstra et al. (in prep.) N-balance