The document summarizes research on understanding carbon dynamics in Arctic terrestrial ecosystems. It finds that the Arctic is experiencing widespread plant community and land cover changes, with wet sites changing more than dry sites. These changes can increase vegetation greenness as measured by NDVI, both by increasing plant biomass and through changes in surface water. While there is variability, climate change is creating more positive carbon feedbacks through effects like permafrost thaw and increased microbial respiration. Improving methods to scale ecosystem changes over time and integrating trace gas measurements is needed to better understand if the Arctic will become a carbon source.

1. The Arctic Carbon Bomb: Understanding the fate and transport of carbon in arctic terrestrial ecosystems Craig E. Tweedie PhD University of Texas at El Paso www.sel.utep.edu ctweedie@utep.edu With contributions From: Christian Andresen, Ryan Cody, John Gamon, Santonu Goswami, David Johnson, Mark Lara, David Lin, Steve Oberbauer, Sergio Vargas, Sandra Villarreal, Pat Webber, David Witt, and undergraduates

4. Slides: Greening of arctic BTF land cover change The Arctic is Greening but… Is there supporting evidence on the ground? What changes NDVI? Is the Arctic shifting from a long term sink to a source of carbon to the atmosphere? Bhatt et al. 2010 E. Interactions

5. Global relevance of tundra land area, Plant carbon, Net Primary Production, and soil carbon Standing Plant Carbon = 1 % Tundra Land Area = 6 % Deserts Grasslands Boreal Forest Temperate Forest Soil Carbon = 28 % NPP = 2 % Tropical Forest Lakes and Wetlands Croplands Ice (Adapted from WB GU, 1998)

8. Atmospheric GHGs Soil Processes CO2 CH4 4. Challenges to measuring NDVI Greenhouse warming CO2 CH4= 23 x CO2 CO2 2. Land-atmosphere CO2 and CH4 flux 3. Land cover change Albedo 1. Plant Community Change Aerobic Anaerobic

9. Picture of the arctic from space Our Arctic Field Sites…

10. Picture of the arctic from space Plant Community Change… Barrow (1972) Baffin Island (1962)

11. Baffin Island, Nunavut, Canada Barnes Ice Cap 300 km Study Area Davis Strait N Foxe Basin Hudson Strait Pat Webber 1963/2010

12. Lewis Glacier/Barnes Ice Cap Retreat 1961-2002 1961 Westernmost edge of Flitaway Lake 1961 RCAF aerial photography 2002 Landsat Image N N 1961 Terminus of the Lewis Glacier

13. Baffin Island 1964 2009 #172a

14. 1964 2009 #99a Baffin Island

16. 2009

17. X-axis site moisture gradient

18. Y-Axis productivity gradient

19. Drying and increased productivity

20. Wet sites changing more than dry sites

21. Time since glaciation does not explain changeHigh Cotton grass meadows Wet sedge meadows Pond margins Snow beds Productivity/ NDVI Mesic communities Dry stony slopes Barren, stony slopes Recent tills and sediments Low Soil Moisture Low High Non-metric multidimensional scaling (NMDS) ordination of seventy- nine sites sampled in 1964 and 2009. Points are mean axis scores for each plant community.

22. Barrow IBP Sites

23. Plant community change Barrow, AK Aquatic Moist Dry 1972 1999 2008 2010

25. Wet plant communities more dynamic than dry plant communities.

26. Little evidence of directional change in plant communities, except for wet plant communities which appear to becoming more similar to dry plant communities over time.

29. 1950-2010

30. Dramatic impact…Change in cover of plant functional types Years with Lemming highs

32. Herbivory maintains carbon sink activity????

33. Herbivory maintains high NDVIAlbedo Albedo

34. Picture of the arctic from space Land-Atmosphere CO2 and CH4 Flux…

35. Different plant communities demonstrate different capacities for CO2 uptake and CH4loss…

36. Modeling EcosystemFunction… PAR Tair LAI NDVI Dry Soil Standing H20 VWC Standing H20 Dry Soil VWC Wet Soil Tair NDVI NDSWI R2adj=0.71, P < 0.001, N = 566, RMSE=0.1364 R2adj=0.75, P < 0.001, N = 88, RMSE=0.1364 2002 20% increase 2008

37. Picture of the arctic from space Land Cover Change…

38. Barrow land cover change 1948 1955 2008 1200 meters 650 meters

39. Summary of land cover change for 7 Beringian sites extrapolated to 100 years using probabilistic modeling Alaska Chukotka, RU Coastal Inland

40. Summary of land cover change for 7 sites in Beringia (ca. 25km2) extrapolated to 100 years using probabilistic modeling Drier Wetter

41. Picture of the arctic from space Challenges to Measuring NDVI…

43. Nakamoto et al. In Press

44. Olivas et al. 2011.

45. Shiklomanov et al. 2011.Untreated N 300 m Tweedie et al. Submitted

47. 70% reduction in surface water can increase NDVI by 25%

48. Drying can increase greening

49. Are we missing the drying of the Arctic?

50. And/or are we under-estimating greening of the Arctic?NDVI decreases by almost 25% when surface water cover increases by 70%.

52. 70% reduction in surface water can increase NDVI by 25%

53. Drying can increase greening

54. Are we missing the drying of the Arctic?

57. Integrate land cover change assessments with trace gas flux studies to assess likely change in peak season carbon uptake potential and global warming potential (funded).

58. Use probabilistic modeling to forecast future vegetation states from plant community change assessments (funded).

59. Assess other disturbances (e.g. off road vehicle use, coastal erosion) (pending).

63. Acknowledgements SEL Lab postdoc, technicians, grad students and undergraduates Funding NSF x 7 In-kind Support GeoEye Foundation, Amazon, Student Support AGEP, NSF LSAMP, COS, UTEP Grad. School, NSF GK-12