Effects of Climate Change on Effects of Climate Change on Tundra Ecosystems Tundra Ecosystems

Greg Henry, University of British Columbia

Philip Wookey, University of Uppsala

Climate Change and Tundra Climate Change and Tundra EcosystemsEcosystems

• IntroductionIntroduction

• Conceptual issues: time and Conceptual issues: time and space scales, processesspace scales, processes

• Evidence of change: Evidence of change: observationsobservations

• Experimental results: ITEXExperimental results: ITEX

• Research needsResearch needs

• CO2 ‘fertilization’ effect (‘-factor’);

• Regional differences in global warming: greater than average warming at high northern latitudes;

• Increased deposition of airborne N-containing compounds;

• Stratospheric O3 depletion increased UV-B fluxes at the surface.

Environmental change has multiple facets

• “The past as a key to the future” Yes, but with caution!

Shaver et al., (2000) BioScience

Herbivores

Climate ChangeSnow cover

Veg

eta

tion

Oth

er

Soils

migration and invasion

disturbance regime herbivores

SOM development

species w/in initial community

litter mass, quality microbes, fauna

N availability

allocationLeaf Ps, Rs

1 day 1 yr 10 yr 100 yr 1000 yr

TIME-SCALE OF RESPONSE

Key issues – time scalesKey issues – time scales

[from Shaver et al.. (2000) BioScience]

“Typical” study length

Need to understand long-term effects

Key issues – time scalesKey issues – time scalesEcosystem C balanceEcosystem C balance

NetC uptake

bysystem

C

E

D

A

B

Time

NetC loss

toatmosphere

Harvard forest (A,B)Toolik Lake (C,D)Great Dun Fell (D,E)Colorado subalpine (C)Abisko (C)

[from Shaver et al. (2000) BioScience]

0

Vegetation cover

Soil organic matter

Nutrient stock

Unoccupied space

Cryo-processes??

Temperature gradient(30º latitude & 10º temp)

Warmer Colder

Key issues - spatial scalesKey issues - spatial scales

Geological & topographic influences - cross-cutting (regional and local scales)

Low Arctic High Arctic

Schematic comparison of low- and high-arctic Schematic comparison of low- and high-arctic tundra response to warmingtundra response to warming

Permafrost table

Water table

Organic matter(and nutrient pool)

Mineral ‘soil’or regolith

• Lateral spread• Immigration• Vertical development

• Vertical development• Community shifts

LOW ARCTIC TUNDRA

Mesic Shrub Tundra

HIGH ARCTIC TUNDRA

Polar Semi-Desert

(= + and -)

(= + and -)

Deeper active layer

2

2

14a

3

4b

55Semi-permanentsnow drift

Prevailing wind

1. Dry exposed ridges2. Mesic zonal sites3. Wet meadows4. Snowbeds a. well-drained, early-melting b. poorly-drained,

late-melting5. Streamside sites

1. Dry exposed ridges2. Mesic zonal sites3. Wet meadows4. Snowbeds a. well-drained, early-melting b. poorly-drained,

late-melting5. Streamside sites

Key issues - spatial scalesKey issues - spatial scales

[From Walker D.A. (2000) GCB]

Relations between topography and tundra plant communities

Evidence of changes in tundra Evidence of changes in tundra vegetationvegetation

• Increased abundance of shrubs – Alaska

• positive feedback with snow accumulation

• Increased growth rates of trees at treeline

• leading to greater seed production and treeline advance (?)

• Results from experimental manipulations

• International Tundra Experiment (ITEX)

International Tundra Experiment - www.itex-science.net

Experimental approaches ITEXExperimental approaches ITEX

12 years progress (ITEX Resolution, 5th December, 1990) sites in 1992;

Straightforward approach designed to encourage broad international participation;

Manipulation, monitoring, modelling (synthesis), mapping;

Bottom-up (‘ITEX species’)

Toolik Lake, Alaska

Alexandra Fiord, Ellesmere Island, Canada

Magerøya, Norway

ITEX and related experiments

Temperature/Position in range

Pro

cess

rate

North

South

Net PS

Intensity of competition

Experimental approaches –Experimental approaches –Experiments along gradientsExperiments along gradients

Alexandra Fiord, Ellesmere Island, Canada

ITEX Meta-analysis: leaf bud breakITEX Meta-analysis: leaf bud break

Arft et al. 1999

ITEX Meta-analysis of vegetative growthITEX Meta-analysis of vegetative growth

Arft et al. 1999

Short-term effects differ by growth form

ITEX synthesis II - ITEX synthesis II - Community Community responsesresponses

Deciduous shrubs

4

All shrubs

Graminoids

4

6

Bryophytes

4

Lichens

2

Litter

3

COVER CANOPY HEIGHT3

4

2

DIVERSITY (Shannon)

42

1.0

-1.0

0

-0.5

0.5

Effect-size (d)

Walker et al. Figure 3

Walker M.D. et al. (2004)

Meta-analysis

ITEX results – synthesis IITEX results – synthesis I

WarmingWarming experiments confirm sensitivity of cold region vegetation in general (e.g. Rustad et al. 2001): ITEX provides detail for tundra plants;

Growth increasedGrowth increased in general - variation among growth forms;

Phenological shiftsPhenological shifts consistent – earlier flowering;

Geography is importantGeography is important; (e.g. low vs high arctic)

Plant communities exhibit detectable detectable

responsesresponses to warming in only 3-4 3-4

years;years;

The most significant changes are: increasesincreases in deciduous shrubdeciduous shrub cover & height decreasesdecreases in cryptogamcryptogam cover decreasesdecreases in (apparent) species species richnessrichness;

ITEX results – synthesis IIITEX results – synthesis II

• effects on soil microorganism diversity effects on soil microorganism diversity and processes?and processes?

• negative feedback of increasing C:N ratio negative feedback of increasing C:N ratio (low quality litter) and stimulation by (low quality litter) and stimulation by warmth?warmth?

• use of organic vs mineral N sources by use of organic vs mineral N sources by plants and microbes: how will this change?plants and microbes: how will this change?

• effects of combined factors: COeffects of combined factors: CO22, heat, , heat, moisture, nutrients, light, season lengthmoisture, nutrients, light, season length

• Long-term changes in NEP and Carbon Long-term changes in NEP and Carbon balance?balance?

Continuing questions:Continuing questions: