Biocomplexity of Arctic Patterned Ground:ecosystems

Photos: Ina Timling and D.A. Walker

A tale of cracking, heaving, and smothering

Biocomplexity of Arctic Patterned Ground:ecosystems

Photos: Ina Timling and D.A. Walker

A tale of cracking, heaving, and smothering

Co-authors:

Donald Walker1, Ronnie Daanen1, Howard Epstein2, William Gould3, Grizelle Gonzalez3 Anja Kade1, Alexia Kelley2, William

Krantz4, Patrick Kuss1, Gary Michaelson5, Corinne Munger1, Dmitri Nickolsky1, Rorik Peterson1, Chien-Lu Ping5, Martha Raynolds1,

Vladimir Romanovsky1, Charles Tarnocai6, and Corinne Vonlanthen1

1IAB, University of Alaska Fairbanks, 2 Univ.Virginia, 3USDA Inst. Trop. Forest., San Juan, PR, 4Dept. Chem. Mater. Eng., Univ. Cincinnati, 5UAF Ag. And Forestry Exp.

Sta., Palmer, AK, 6Ag. and Agri-Food Canada, Ottawa, CAN

Funding:NSF Biocomplexity in the Environment, OPP Grant #0120736

Howe Island, AK.Photo; D.A. Walker

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?

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.

North American Arctic Transect

Dalton Highway (7 locations)

Isachsen

Green Cabin

Mould Bay

Inuvik

A B CDE

Arctic Bioclimate Subzones

Transect Study Sites>12Forest

9-12E

7-9D

5-7C

3-5B

<3A

Mean July Temperature

(˚C)

Sub-zone

North American Arctic Transect

Dalton Highway (7 locations)

Measurements

• 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

Maps of vegetation, active layer and snow

• Posters (Raynolds et al. and Munger et al.)

Munger et al. 2006

Photo Active Layer

Vegetation Snow Depth

Subzone A: Isachsen

Subzone C: Green Cabin

Subzone E: Happy Valley

Conceptual model of patterned-ground trends along the Arctic bioclimate gradient

Sub-

zone: A B C D E

Drawings modified from Chernov and Matveyeva 1997

Cracking Heaving Smothering

Cracking• Small non-

sorted polygons (Washburn 1980).

• Desiccation cracking or seasonal frost cracking (Washburn 1980).

• Very important in the High Arctic, but poorly understood.

Isachsen, Howe Island

Mould Bay

Photos: D.A. Walker

Heaving

• Non-sorted circles and earth mounds

• Caused by differential frost heave.

• Most common in the Mid-and Low Arctic (subzones C and D).

• Several models.

Earth mounds, Mould Bay, Nunavut. Earth mound, Inuvik, NWT

Non-sorted circles, Howe Island, AK, .

Photos: D.A. Walker

Vegetation succession

Vegetation and organic soils:

• Insulate the surface.

• Stabilize the soil.

• Mask cracking and heaving.

Drawing: Nadya Matveyeva. Photo: D.A. Walker

The effects increase toward the south.

Summer warmth index along the transect

0

5

10

15

20

25

30

35

Isachsen Mould Bay West Dock Deadhorse Franklin BluffsSagwon Hills Happy Valley

Sum

mer

War

mth

Inde

x (ū

C m

o)

Air Surface of patterned-ground feaSurface between PG features

• 5x increase in total summer warmth (red bars).

• Surface temperatures are generally warmer than air temperatures.

• Barren patterned ground features are warmer than the adjacent tundra.

Sub-zone: I A I B I C I D I E I

Courtesy V. Romanovsky and R. Daanen

August Thaw Depth on 10x10-m Biocomp

0

10

20

30

40

50

60

70

80

90

100

Isac

hsen

- 1

Isac

hsen

- 2

Isac

hsen

- 3

Mou

ld B

ay- 1

Mou

ld B

ay- 2

Wes

t Doc

k

Howe

Isla

nd

Green

Cab

in- 1

Green

Cab

in- 2

Green

Cab

in- 3

Deadh

orse

Fran

klin

Blu

ffs- 1

Fran

klin

Blu

ffs- 2

Fran

klin

Blu

ffs- 3

Sagw

on N

onac

idic

- 1

Sagw

on N

onac

idic

- 2

Sagw

on A

cidi

c

Happy

Val

ley-

1

Happy

Val

ley-

2

Happy

Val

ley-

3In

uvik

Th

aw

Dep

th (

cm)

20002001200220052006

Subzone: I A I B I C I D I E IBFI

August thaw depth at 10 x 10-m grids

Each bar represents the mean of at least 121 probes at each grid.

The active layer does not follow the air-temperature gradient.

• Deepest thaw in subzones C and D.

• Thaw at Happy Valley (subzone E) was comparable to that at Isachsen (Subzone A).

Plant cover strongly affects the thaw layer.

Average August 2006 Thaw Depth for Patterened-grouand Between Features

0

10

20

30

40

50

60

70

80

90

100

Isac

hsen

Mou

ld B

ayHow

e Is

land

Green

Cab

inDea

dhor

seFr

ankl

in B

luffs

Sagw

on- N

onac

idic

Sagw

on- A

cidi

cHap

py V

alle

y

Inuv

ik

Th

aw

Dep

th (

cm)

Barren centers of Pattern-ground featuresVegetated areas between pattern-ground fe

Subzone: I A I B I C I D I E I BF I

• End of Aug thaw is about 10-20 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).

0

100

200

300

400

500

600

700

800

Isachsen Mould Bay GreenCabin

Deadhorse FranklinBluffs

SagwonNonacidic

SagwonAcidic

HappyValley

Bio

mass

(g

/m

2)

Deciduous shrubEvergreen shrubForbGraminoidLichenMoss

Data represent the means of 5 20x50-cm plots in each vegetation type.

Biomass responds dramatically to

warmer temperatures.

Patterned-ground features

Zonal vegetation

Sub-zone: I A I B I C I D I E I

• 5-fold increase on zonal sites.

• 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.

Above-ground Biomass

0

100

200

300

400

500

600

700

800

1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2

Isachsen Mould Bay Green Cabin Deadhorse FranklinBluffs

SagwonNonacidic

SagwonAcidic

HappyValley

Bio

mas

s (g

/m^2

)Deciduous shrubEvergreen shrubForbGraminoidLichenMoss

1- Patterned-ground features2- Between paterned-ground feature

Biomass affects NDVI along the transect.• 2-fold increase of the

NDVI on zonal surfaces.• NDVI of patterned-

ground features increase more rapidly than that of the adjacent tundra areas.

• Barren:zonal ratio decreases toward the south and affects circum-polar NDVI patterns.

y = 0.0079x + 0.2298R2 = 0.6526

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35

Summer Warmth Index (°C)

NDV

I

y = 2320.8x - 459.23R2 = 0.7166

y = 1452.4x - 326.35R2 = 0.5267

y = 817.29x - 198.18R2 = 0.4576

0100200300400500600700800900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

NDVI

Abo

vegr

ound

Bio

mas

s (g

/m²) Total AG

Vascular

Shrubs

Random hand-held NDVI of zonal tundra along the temperature gradient

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

PG

F

Tu

nd

ra

PG

F

Tu

nd

ra

PG

F

Tu

nd

ra

PG

F

Tu

nd

ra

PG

F

Tu

nd

ra

PG

F

Tu

nd

ra

PG

F

Tu

nd

ra

Isachsen MouldBay

GreenCabin

FranklinBlfs

SagwonMNT

SagwonMAT

HappyValley

ND

VI

NDVI of patterned-ground features and nearby tundra along the gradient

Courtesy of Howie Epstein and Alexia Kelley

I A I B I C I D I E I

Vegetation removal and transplant experiment (Anja Kade)

Control Vegetation removal (barren)

Transplant moss carpetTransplant sedges

Effects of vegetation on summer and winter soil surface temperatures.

Mean Summer Temperaure:Vegetation removal: +1.5˚C (+22%)Moss addition: -2.8 ˚C (-42%)

Mean Winter Temperature:Vegetation removal: -0.9̊C (-6%)Moss addition: +1.3˚C (+7%)

•The sedge treatment had a similar response as the barren treatment.

Kade and Walker in press

Summer

Winter

Mosses

Barren

Control

MossesControl

Mosses

Effects on thaw depth and heaveThaw:

Vegetation removal: +5 cm (+6%)Moss addition: -11 cm (-14%)

Heave:Vegetation removal: +3 cm (+24%)Moss addition: -5 cm (-40%)

Kade and Walker in press

Maximum Thaw Depth

0102030405060708090

Bareground

Sedges Mosses Control

Treatment

Th

aw

dep

th (

cm)

Fros

02468

1012141618

Bareground

Sedges Mosses Control

Treatment

Heave (

cm)

Frost Heave

0 0.2 0.4 0.6 0.8 1 1.20

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Hea

ve (m

)

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.

Displacement of the ground surfaceNo additional insulation

2 cm4 cm

6 cm8 cm

10 cm

Non-sortedcircle

Vegetated inter-circle

area

Thermo-mechanical model of frost-heave: vegetation interactions (D. Nickolsky et al.)

Sequestered carbon at depth caused by cryoturbation.

Carbon-rich horizon at base of non-sorted circle

•Movement of carbon from margin of circle to the base of circle via cryoturbation.

•2x previous estimates of soil carbon in subzones D and E.

Photos courtesy of Gary Michaelson.

Recent Findings (Ping et al., 1992-2005)

0

10

20

30

40

50

60

A B C D EArctic Bioclimate Subzone

C-S

tore

s (k

gOC

m3 )

Active LayerPermafrost

Effects on soil nitrogen

• 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.

Courtesy of Alexia Kelley, in prep.

Pools of available nitrogen

Nitrogen mineralization and immobolization

Sub-zone: I E I D I C I B I A I

A B EC D BF

Stre

ngth

of e

ffect

3

2

1

Cracking

Bioclimate SubzoneA B EC D BF

3

2

1

Heaving

A B EC D BF

3

2

1

“Smothering”

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.

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.