polar ecosystems arctic/antarctic contrasts tundra - the physical template (climate, landforms,...

Polar ecosystems Arctic/Antarctic contrasts Tundra - the physical template

(climate, landforms, soils) Tundra plant and animal communities Winter survival Population cycles Management issues Responses to future climate change

Arctic(a) vs. Antarctica

land: 8 X 106 km2 (30% ice)

substantial terrestrial food

land mammals

herbivorous & insectivorous birds

land: 14 X 106 km2 (97% ice)

no terrestrial food

no land mammals

no herbivorous or insectivorous birds

Arctic(a) vs. Antarctica not

geographically isolated

glacial refuges ice-free coastal

zone in summer relatively high

plant and animal diversity

geographically isolated

no? glacial refuges

v. restricted ice-free coastal zone in summer

low plant and animal diversity

Tundra ecosystems

“tundra” = treeless barrens

Global distribution of tundra

Arctic ecosystems in Canada

N.Arctic = polar desert

S.Arctic = tundra

Tundra ecosystems

Tundra ecosystems are associated with areas of extreme near-polar climate which operates either directly, or through a series of environmental forcings (primarily thaw-layer dynamics) to limit productivity and biodiversity.

Tundra ecosystems

Low species diversity may promote instability. This is expressed by highly cyclic behaviour.

Arctic communities are geologically-recent developments in the planetary biome landscape.

Day-length and insolationat top of atmosphere

Equator

40°N

60°N

90°N

Inso

lati

on

(w m

-2)

0

100

200

300

400

500

600

daylength (North Pole) 0h 12h 24h 12h 0h

J M J S D

Tundra climate stations

Barrow

Churchill

IqaluitSvalbard

Tiksi

Gulf Stream

Treeline

60°N

75°N

Mean monthly temperatures,tundra climate stations

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-5

0

5

10

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J F M A M J J A S O N D

Barrow,AK

Churchill

Iqaluit

Svalbard

Tiksi

Mean monthly precipitationtundra climate stations

J F M A M J J A S O ND

Barrow,AK

Tiksi

ChurchillIqaluit

Svalbard0

10

20

30

40

50

60

70

Barrow,AK

Tiksi

Churchill

Iqaluit

Svalbard

Synoptic climatology(after Reid Bryson)

Treeline

Mean position of Polar Front (July)

ARCTIC airmass

Bering Sea ice

Frost-free days

Treeline

Mean annual snowfall (mm)

Treeline

Permafrost distribution(note transect lines

and presence of sub-sea

permafrost)

Alaska

Siberia

Boreal forest Tundra

Permafrost

patchy discontinuous continuous

120 30 mean #d >10°C

mean locationPolar FrontJulyJan

150 240 mean #d <0°C

treegrowth

pollen/seedviability

150 60 frost-free days

The critical thaw period

Data from Barrow, AK

~70 d

~40 d

Microclimatology: slope and aspect

Aspect Flat South-facing North-facingSlope (°)Ground-Sunangle (°)0 10 20 40 10 20 4045 55 65 85 35 25 5210Direct-beam radiation, solar noon, summer solstice, 68.5°N

forest?

Vigorous tree growth on south-facing slopes near

treeline

Polar montane environments:

freeze-thaw weathering -

felsenmeer and talus cones

Polar uplands:

thaw-layer dynamics

and solifluction

Polar lowlands

Cryoturbation and patterned ground

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

dwarf shrubs,grasses

sedges,lichens

Frost polygons: note unvegetated ‘boils’ and standing water in cracks

Tundra floras(product of late Tertiary cooling and landbridges during glacial phases?

Centre-of-origin?

Davis Strait “gap”(major floristic contrast)

Plio-Pleistocene

migration

Plio-Pleistocene

migration

Alpine highlandsof NE Asia

Topography Tundratype

Flora Thawdepth(m)

Organiclayer (m)

rocky, well-drainedridges

Heath evergreenshrubs

>2 <0.1

gentlyrolling

Tussock Eriophorum 0.3-0.5 <0.3

flatlowlands

Wetsedge

graminoids 0.2-0.3 0.1-0.5

well-drainedalluvialsites

Shrub deciduousshrubs

>1 thin?

Tundra vegetation-soil catenas

Sedge Shrub Sedge Tussock Heath

0 organics

sandysoil

permafrost

rockysoil

silty soilsilty soil

Depth (m)

1

2

Felsen-meer

Felsenmeer vegetation dominated by lichens

Evergreen heath tundra

Dominated by Ericaceae (heaths), such as Cassiope

Heath tundra is floristically more diverse than other tundra types

Tussock tundra

(dominated by Eriophorum)

[cotton grass]

Wet sedge tundra:

dominated by graminoids (e.g. Carex, Dupontia)

Animal life

Surviving winterStrategy Organisms

Distant migration Local migration Above snow-pack

heavy insulation

protective colouring

Below snow-pack Hibernation Dormant phase

birds caribou

ground squirrelsplants, insects

muskox, polar bear

lemmings, voles

arctic fox, ptarmigan

Are cyclical population dynamics

(~4 yr period)a product of simple food

webs?(note difference in time

scales)

Vole data: N. FinlandLemming data: N. Norway

Lemming distribution

The tundra phosphorus cycle

lemmings/ha 2-12 2-12 40-50 180-200 jaegers uncommon uncommon breeding breeding(pairs/km2) no breeding no breeding 10 40-50snowy owls scarce scarce breeding breeding(pairs/km2) no breeding no breeding 0.1 0.2shorteared absent absent 1 record 10/km2

owls

Active layer

Permafrost

CaCa

Ca

CaN

NN

N

P

PP

P

K KK

K

Forage (%P) 0.2 0.2 0.3 0.6quality

•• ••••Litter layer thin thick

Caribou dynamics

The ANWR debate

Porcupine herd migrations: radio-collared females at calving grounds on

Arctic Alaska coastal plain

Winter feeding grounds in Yukon, Porcupine caribou herd (1998-99)

300 k

m

Snow goose dynamics

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Lesser snow goose flock

~4 M geese breed in the marshes of the

Canadian Arctic

birds

devegetatedarea

Jeffries et al., 2006. J. Ecol. 94, 234-242.

Impacts of snow goose overgrazing

drying ofsurface soil

increasedsoil salinity

reduced graminoid

growth

reducedgraminoidbiomass

Intense grubbing andgrazing by snowgeese

Effects of snow goose grazing and grubbing (James Bay)

Salicornia

Puccinellia

Potential effects of climate change

Is climate change occurring in Arctic environments? - climate records short - biotic data fragmentary

Simulation modelsField experiments

Recent (post-1950) climate change in polar regions

Arctic:• Reduction in sea ice extent and thickness• Northward treeline shifts (e.g. E. coast Hudson Bay)• Increased lake productivity (e.g. Ellesmere Island)• Range expansions (e.g. dragonflies - Inuvik - 2000)Antarctic:• Ice shelf disintegration (e.g. N. Larsen & Wordie

Shelf)• Spread of flowering plants (e.g. Antarctic hairgrass

has expanded its range 25-fold since 1964)• New lichen species colonizing recently deglaciated

areas

Climate change

Climate change in the western Canadian arctic

Data: Environment Canada

Inuvik, NWT

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10

20

30

1950 1960 1970 1980 1990 2000 2010

Year

Temperature (°C)

Monthly Max. Temp. (°C)Mean Ann. Temp. (°C)Monthly Min. Temp. (°C)

Climate change in the western Canadian arctic

Data: Environment Canada

Inuvik, NWT

0

50

100

150

200

250

300

350

400

1950 1960 1970 1980 1990 2000 2010

Year

Precipitation (mm)

Total Precip. (mm)

Snow (mm; water equivalent)

Climate change in the eastern Canadian arctic

Iqaluit, Nunavut

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-20

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0

10

20

1940 1950 1960 1970 1980 1990 2000 2010

Year

Temperature (°C)

Monthly Max Temp (°C)Mean Ann. Temp. (°C)Monthly Min Temp (°C)

Data: Environment Canada

Climate change in the eastern Canadian arctic

Data: Environment Canada

Iqaluit, Nunavut

0

100

200

300

400

500

600

700

1940 1950 1960 1970 1980 1990 2000 2010

Year

Precipitation (mm)

Total Precip. (mm)

Snow (mm; waterequivalent)

Source: www.metoffice.gov.uk/.../ images/figure5.jpg

Sea-ice extent, Arctic

and Antarctic oceans

Source: Arctic Climate Impact Assessment website

The Arctic of the future

Field experiments:

ITEX sites

Impacts of climatic warming (ITEX results [1997])

inc. seedweight and

viability

increasedgraminoidabundance

reduced evergreen shrub competitiveness

increasedplant

productivity

Increased airtemperature

reducedplant diversity