Biocomplexity of Arctic Patterned Ground: ecosystems

Transcription

1 Biocomplexity of Arctic Patterned Ground: ecosystems A tale of cracking, heaving, and smothering Photos: Ina Timling and D.A. Walker

2 Biocomplexity of Arctic Patterned Ground: ecosystems A tale of cracking, heaving, and smothering Photos: Ina Timling and D.A. Walker

3 Co-authors: Donald Walker 1, Ronnie Daanen 1, Howard Epstein 2, William Gould 3, Grizelle Gonzalez 3 Anja Kade 1, Alexia Kelley 2, William Krantz 4, Patrick Kuss 1, Gary Michaelson 5, Corinne Munger 1, Dmitri Nickolsky 1, Rorik Peterson 1, Chien-Lu Ping 5, Martha Raynolds 1, Vladimir Romanovsky 1, Charles Tarnocai 6, and Corinne Vonlanthen 1 1 IAB, University of Alaska Fairbanks, 2 Univ.Virginia, 3 USDA Inst. Trop. Forest., San Juan, PR, 4 Dept. Chem. Mater. Eng., Univ. Cincinnati, 5 UAF Ag. And Forestry Exp. Sta., Palmer, AK, 6 Ag. and Agri-Food Canada, Ottawa, CAN Funding: NSF Biocomplexity in the Environment, OPP Grant #

4 Central Questions How do biological and physical processes interact to form small patterned- ground ecosystems? How do these systems change across the Arctic climate gradient? Howe Island, AK. Photo; D.A. Walker

5 Why focus on small patterned-ground features? They are interesting. Formation processes not well understood. Important to biogeochemical cycling, and other ecosystem processes. Ideal system to study the effects of disturbance across the Arctic climate gradient.

6 North American Arctic Transect Arctic Bioclimate Subzones Subzone A B C D E Forest Mean July Temperature ( C) < >12 Isachsen Mould Bay Green Cabin Dalton Highway (7 locations) A B C D Inuvik E Transect Study Sites

7 Measurements North American Arctic Transect 21 Grids and maps Active layer Vegetation Snow Climate /permafrost Met station Soil temperatures Frost heave Soils Characterization Nitrogen mineralization Decomposition Remote sensing NDVI Biomass Dalton Highway (7 locations)

8 Maps of vegetation, active layer and snow Photo Vegetation Active Layer Snow Depth Posters (Raynolds et al. and Munger et al.) Subzone A: Isachsen Subzone C: Green Cabin Subzone E: Happy Valley Munger et al. 2006

9 Conceptual model of patterned-ground trends along the Arctic bioclimate gradient Subzone: A B C D E Cracking Heaving Smothering Drawings modified from Chernov and Matveyeva 1997

10 Cracking Mould Bay Small nonsorted polygons (Washburn 1980). Desiccation cracking or seasonal frost cracking (Washburn 1980). Very important in the High Arctic, but poorly understood. Isachsen, Howe Island Photos: D.A. Walker

11 Heaving Non-sorted circles and earth mounds Caused by differential frost heave. Non-sorted circles, Howe Island, AK,. Most common in the Midand Low Arctic (subzones C and D). Several models. Earth mounds, Mould Bay, Nunavut. Earth mound, Inuvik, NWT Photos: D.A. Walker

12 Vegetation and organic soils: Insulate the surface. Stabilize the soil. Mask cracking and heaving. Vegetation succession The effects increase toward the south. Drawing: Nadya Matveyeva. Photo: D.A. Walker

13 Summer warmth index along the transect Summer Warmth Index (ūc mo) Air Surface of patterned-ground fea Surface between PG features 5x increase in total summer warmth (red bars). Surface temperatures are generally warmer than air temperatures. 0 Subzone: I A I B I C I D I E I Isachsen Mould Bay West Dock Deadhorse Franklin BluffsSagwon Hills Happy Valley Courtesy V. Romanovsky and R. Daanen Barren patterned ground features are warmer than the adjacent tundra.

14 The active layer does not follow the airtemperature August thaw depth at 10 x 10-m grids gradient. Deepest thaw in subzones C and D. August Thaw Depth on 10x10-m Biocomp 100 Subzone: I A I B I C I D I E IBFI Thaw Depth (cm) Thaw at Happy Valley (subzone E) was comparable to that at Isachsen (Subzone A) Isachsen- 1 Isachsen- 2 Isachsen- 3 Mould Bay- 1 Mould Bay- 2 West Dock Howe Island Green Cabin- 1 Green Cabin- 2 Green Cabin- 3 Deadhorse Franklin Bluffs- 1 Franklin Bluffs- 2 Franklin Bluffs- 3 Sagwon Nonacidic- 1 Sagwon Nonacidic- 2 Sagwon Acidic Happy Valley- 1 Happy Valley- 2 Happy Valley- 3 Inuvik 0 Each bar represents the mean of at least 121 probes at each grid.

15 Plant cover strongly affects the thaw layer. End of Aug thaw is about cm deeper on barren patterned ground features than in the adjacent tundra areas. Contrast much greater at the beginning of the thaw season (not shown). Thaw Depth (cm) Average August 2006 Thaw Depth for Patterened-grou and Between Features 0 Subzone: I A I B I C I D I E I BF I Isachsen Barren centers of Pattern-ground features Vegetated areas between pattern-ground fe Mould Bay Howe Island Green Cabin Deadhorse Franklin Bluffs Sagwon- Nonacidic Sagwon- Acidic Happy Valley Inuvik

16 Biomass (g/m^2) Deciduous shrub Evergreen shrub Forb Graminoid Lichen Moss Above-ground Biomass Zonal vegetation Biomass responds dramatically to warmer temperatures. 5-fold increase on zonal sites. Biomass (g/m 2 ) Isachsen Mould Bay Green Cabin Deadhorse Franklin Bluffs Deciduous shrub Evergreen shrub Forb Graminoid Lichen Moss Patterned-ground features Isachsen Mould Bay Green Cabin 1- Patterned-ground features 2- Between paterned-ground feature Deadhorse Franklin Bluffs Subzone: I A I B I C I D Sagwon Nonacidic Sagwon Nonacidic Sagwon Acidic Sagwon Acidic Data represent the means of 5 20x50-cm plots in each vegetation type. Happy Valley Happy Valley I E I 30-fold increase on patterned-ground features. Shift in dominant growth forms with temperature on zonal sites. Different suite of plant growth forms on the patterned-ground features.

17 Biomass affects NDVI along the transect. NDVI y = x R 2 = Random hand-held NDVI of zonal tundra along the temperature gradient Summer Warmth Index ( C) 2-fold increase of the NDVI on zonal surfaces. NDVI of patternedground features increase more rapidly than that of the adjacent tundra areas. Barren:zonal ratio decreases toward the south and affects circumpolar NDVI patterns. NDVI 0.8 NDVI of patterned-ground features and 0.7 nearby tundra along the gradient PGF Isachsen Tundra PGF Mould Bay Aboveground Biomass (g/m²) Tundra PGF Green Cabin Tundra PGF Franklin Tundra PGF Sagwon Tundra PGF Sagwon I A I B I C I D I E Courtesy of Howie Epstein and Alexia Kelley Tundra y = x R 2 = Blfs0.1 MNT0.2 MAT0.3 Valley NDVI PGF Happy I Tundra Total AG Vascular Shrubs y = x R 2 = y = x R 2 =

18 Vegetation removal and transplant experiment (Anja Kade) Control Vegetation removal (barren) Transplant sedges Transplant moss carpet

19 Effects of vegetation on summer and winter soil surface temperatures. Summer Barren Control Mean Summer Temperaure: Vegetation removal: +1.5 C (+22%) Moss addition: -2.8 C (-42%) Mosses Winter Mosses Control Mosses Mean Winter Temperature: Vegetation removal: -0.9 C (- 6%) Moss addition: +1.3 C (+7%) Kade and Walker in press The sedge treatment had a similar response as the barren treatment.

20 Thaw depth (cm) Bare ground Effects on thaw depth and heave Maximum Thaw Depth Sedges Mosses Control Treatment Thaw: Vegetation removal: +5 cm (+6%) Moss addition: -11 cm (-14%) Heave (cm) Bare ground Fros Frost Heave Sedges Mosses Control Heave: Vegetation removal: +3 cm (+24%) Moss addition: -5 cm (-40%) Treatment Kade and Walker in press

21 Thermo-mechanical model of frost-heave: vegetation interactions (D. Nickolsky et al.) Heave (m) Displacement of the ground surface Non-sorted circle No additional insulation 2 cm 4 cm 6 cm 8 cm 10 cm Vegetated inter-circle area Distance from the center of a circle, m Differences in heat flux drive the movement of water necessary for differential heave. Vegetation removal, as occurs with many types of disturbance, causes cryogenic activity to increase. Adding a thick vegetation mat, as occurs with vegetation succession, reduces frost heave and other cryogenic processes.

22 Movement of carbon from margin of circle to the base of circle via cryoturbati on. 2x previous estimates of soil carbon in subzones D and E. Sequestered carbon at depth caused by cryoturbation. C-Stores (kgoc m 3 ) Recent Findings (Ping et al., ) Active Layer Permafrost A B C D E Arctic Bioclimate Subzone Carbon-rich horizon at base of non-sorted circle Photos courtesy of Gary Michaelson.

23 Effects on soil nitrogen Pools of available nitrogen Nitrogen mineralization and immobolization Strong differences in nutrient pools between patterned ground features (short bars) and the surrounding tundra (long bars). Nutrient pools and N- immobilization are greatest in subzone D, the region with the warmest soil temperatures. Subzone: I E I D I C I B I A I Courtesy of Alexia Kelley, in prep.

24 Conclusions: 1. Cracking, differential heave and vegetation succession all interact to affect pattern-ground morphology along the Arctic climate gradient. Each of these processes has its dominant effect in a different part of the climate gradient. Strength of effect Cracking Heaving Smothering A B C D E BF A B C D E BF Bioclimate Subzone A B C D E BF

25 Conclusions 2. Our study and models focused on the combined effects of differential heave and vegetation succession. New models will be needed to incorporate cracking. 3. Strong thermal contrasts between the centers and margins of heave features drive the movement of water and the development of frost heave. 4. The presence of patterned ground affects most ecosystem processes at small spatial scales. How these small-scale processes scale up to large regions still needs to be described. 5. Experimental manipulation of small-patterned ground features, such as that of Anja Kade help elucidate the response of these features to disturbance.