Recent dynamics of arctic tundra vegetation: Remote sensing, field observations, and modeling

Transcription

1 Recent dynamics of arctic tundra vegetation: Remote sensing, field observations, and modeling Howard E. Epstein (University of Virginia) M.K. Raynolds, D.A. Walker, U.S. Bhatt, C.J. Tucker, J.E. Pinzon G.V. Frost, Q. Yu, G.J. Jia, and H. Zeng International Polar Year Montreal, April 2012 (Photo H.E. Epstein)

2 The Arctic Tundra Biome Southern boundary of the mapped area is tree line.! Tundra is defined as being treeless but not absent of woody plants.! Largest expanses in Russia and Canada, with some in U.S., Scandinavia, and Greenland.! Note the close proximity of all parts of the biome to perennially or seasonally frozen seawaters.! Walker, D. A.. et al The Circumpolar Arctic Vegetation Map. Journal of Vegetation Science.

3 Bhatt et al. (2010)

4 From Raynolds et al. 2012

5 North American Arc.c Transect Subzone E (Shrub) Subzone E (Tussock) Subzone D Subzone C Subzone B Subzone A (Photos D.A. Walker and H.E. Epstein)

6 Yamal Arc.c Transect Forest Tundra (Forest) Forest Tundra (Tundra) Subzone E Subzone D Subzone C Subzone B Subzone A (photos by D.A. Walker and H.E. Epstein)

7 Aboveground Total and Shrub Biomass along both transects Total Aboveground Biomass (g/m²) y = e x r² = SWI ( C months) YAMAL Aboveground Shrub Biomass (g/m²) y = e x r² = SWI ( C months)

8 (Raynolds et al. 2012)

9 Total ~0.40 Pg C increase in tundra vegetation over 28-year period Epstein et al. (2012) up to ~0.2 Pg C sequestered per year.

10 Climate warming () and grazing (-) effects on aboveground biomass as simulated by the ArcVeg tundra vegetation dynamics model Yu et al. (in prep. presentation 1600, this session)

11 Percent (%) Greenland Ice Cap A B C D E Percent of pixels with significant change in biomass

12 Increased length of the growing season Zeng et al. (2011)

13

14 Map showing southern Yamal region and location of Kharp study site in northwest Siberia. Comparison of 1968 (Corona) and 2003 (QuickBird) showing area of recent alder expansion. Areas with new shrub cover are marked in red. Kharp landcover change summary Changes in alder cover are readily detected using Corona imagery as baseline Alder cover increased by 8% (52 ha) during Frost et al. (in prep.)

15 Feedbacks between shrubland development and permafrost in the northwest Siberian Low Arctic Gerald V. Frost Friday, 10:15 AM Room 520A Session Environmental Consequences of Change

16 ArcVeg Arctic tundra vegetation dynamics model Total Soil Organic Nitrogen Climate / Grazing Current plant biomass Plant a2ributes (Herbivory/Senescence/Mortality) Tundra Vegetation Dynamics Climate (mineralization) Plant Nitrogen by Functional Type Plant- Available Nitrogen Climate Current plant biomass Plant a2ributes (Plant uptake/growth) (Epstein et al. 2000)

17 Yamal Peninsula, northwestern Siberia, Russia Nenets reindeer herders Photo: D.A. Walker

18 132 model simulations Five climate zones, with grazing intensity and climate change scenarios each point is a multivariate vegetation community (a) Ax i s 2 Gr az i ng Lati tude Text ur e Wa r mi n g SON Si tes- Texture Kr enkel - l oamy Kr enkel - s andy Os t r ov Bel y y - l oa my Os t r ov Bel y y - s a ndy Khar as avey- l oamy Khar as avey- s andy Vas ki ny Dac hi - l oamy Vas ki ny Dac hi - s andy Laborovaya- l oamy Laborovaya- sandy (b) Ax i s 2 Total Biomass LI CH FORB RUSH LOWS EPDS MOS S DPDS GRAS EEDS DEDS TUSS Temperature (c) Subzone Ax i s 1 Relative Biomass FORB RUSH (d) Gr a z i ng (0.1,25%) (0.5,25%) (0.1,50%) (0.5,50%) Ax i s 1 Tot al SEDG GRAS MOS S LI CH Ax i s 2 Grazing explains 13% of the variability in plant community structure, buffers positive responses to warming, and alters plant community composition Yu et al. (2011) Ax i s 2 EPDS EEDS TUSS Ax i s 1 Tot al LOWS SEDG DEDS DPDS Grazing Tot al bi omass Ax i s 1 r =.469 tau =.364 Ax i s 2 r = tau = Ax i s 1

19 Biomass (g m -2 ) Biomass (g m -2 ) Warming effects on PFT biomass Control Transient warming Equilibrium warming FORB MOSS LICH TUSS SEDG GRAS RUSH HADS LADS LAES HAES TALL Control Transient Warming Equilibrium warming High Arctic Low Arctic FORB MOSS LICH TUSS SEDG GRAS RUSH HADS LADS LAES HAES TALL Graminoids - - Shrubs -

20 Low Grazing effects on PFT biomass High Biomass(g m -2 ) Biomass(g m -2 ) FORB MOSS LICH TUSS SEDG TALL FORB MOSS LICH TUSS SEDG TALL High 140 Arctic Low 300 Arctic GRAS HADS LADS LAES HAES RUSH GRAS HADS LADS LAES HAES RUSH Evergreen shrubs

21 Conclusions General widespread greening of arctic tundra, but greater increases in vegetation seen in southern tundra subzones. Approximately 0.40 Pg C difference in vegetation over past 28 years. Shrub expansion appears to be accounting for a substantive fraction of the greening circumpolarly, particularly in the southern tundra. Grazing may buffer the responses of vegetation to warming, and interactions among grazing and warming are likely to alter plant community composition in tundra.

22 Acknowledgments Funding sources NASA/NEESPI Land Cover Land Use Change Initiative, Grant No. NNG6GE00A NSF Grant No. ARC , part of the Synthesis of Arctic System Science initiative (Greening of the Arctic) NSF Grant No. ARC , part of the Changing Seasonality of Arctic Systems initiative Department of Environmental Sciences, Univ. of Virginia