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Effects of Climate Change on
Tundra Ecosystems
Greg Henry, University of British Columbia
Philip Wookey, University of Uppsala
Climate Change and Tundra Ecosystems
• Introduction
• Conceptual issues: time and
space scales, processes
• Evidence of change:
observations
• Experimental results: ITEX
• Research needs
Environmental change has multiple facets
• CO2 ‘fertilization’ effect (‘-factor’);
• Regional differences in global warming:
greater than average warming at high
northern latitudes;
• Increased deposition of airborne Ncontaining compounds;
• Stratospheric O3 depletion  increased UVB fluxes at the surface.
• “The past as a key to the future” Yes, but
with caution!
Herbivores
Snow cover
Climate Change
Shaver et al., (2000) BioScience
Key issues – time scales
Need to study
understand
“Typical”
lengthlong-term effects
Other
migration and invasion
disturbance regime
 herbivores
Vegetation
Soils
SOM development
 litter mass, quality
 microbes, fauna
N availability
 species w/in initial community
allocation
Leaf Ps, Rs
1 day
1 yr
10 yr
100 yr
TIME-SCALE OF RESPONSE
[from Shaver et al. (2000) BioScience]
1000 yr
Key issues – time scales
Ecosystem C balance
Net
C uptake
by
system
C
A
0
Harvard forest (A,B)
Toolik Lake (C,D)
Great Dun Fell (D,E)
Colorado subalpine (C)
Abisko (C)
B
D
Net
C loss
to
atmosphere
E
Time
[from Shaver et al. (2000) BioScience]
Key issues - spatial scales
Low Arctic
High Arctic
Warmer
Colder
Temperature gradient
(30º latitude & 10º temp)
Vegetation cover
Soil organic matter
Nutrient stock
Unoccupied space
Cryo-processes??
Geological & topographic influences cross-cutting (regional and local scales)
Schematic comparison of low- and high-arctic tundra
response to warming
• Vertical development
• Community shifts
• Lateral spread
• Immigration
• Vertical development
Organic matter
(and nutrient pool)
() = + and
-)
Water table
() = + and
-)
Mineral ‘soil’
or regolith
Permafrost
table
Deeper active
layer
LOW ARCTIC
TUNDRA
HIGH ARCTIC
TUNDRA
Mesic Shrub Tundra
Polar Semi-Desert
Key issues - spatial scales
Relations between topography and
tundra plant communities
1
2
4a
Prevailing wind
4b
Semi-permanent
snow drift
[From Walker D.A. (2000) GCB]
1. Dry exposed ridges
2. Mesic zonal sites
3. Wet meadows
4. Snowbeds
a.
well-drained,
early-melting
b. poorly-drained,
late-melting
5. Streamside sites
2
3
5
5
Evidence of changes in tundra vegetation
• 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)
Experimental 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’)
International Tundra Experiment - www.itex-science.net
Toolik Lake, Alaska
Magerøya, Norway
Alexandra Fiord, Ellesmere Island, Canada
ITEX and related experiments
Experimental approaches –
Experiments along gradients
Process rate
Intensity of competition
Net PS
North
Temperature/
Position in range
South
Alexandra Fiord, Ellesmere Island, Canada
ITEX Meta-analysis: leaf bud break
Arft et al. 1999
ITEX Meta-analysis of vegetative growth
Short-term effects differ by growth form
Arft et al. 1999
COVER
ITEX synthesis II Community responses
All shrubs
Effect-size (d)
1.0
CANOPY HEIGHT
3
4
0.5
0
-0.5
-1.0
4
4
Deciduous shrubs
6
Meta-analysis
2
Graminoids
4
DIVERSITY (Shannon)
Bryophytes
2
4
3
Lichens
2
Walker M.D. et al. (2004)
Litter
Walker et al. Figure 3
ITEX results – synthesis I
 Warming experiments confirm sensitivity of
cold region vegetation in general (e.g.
Rustad et al. 2001): ITEX provides detail for
tundra plants;
 Growth increased in general - variation
among growth forms;
 Phenological shifts consistent – earlier
flowering;
 Geography is important; (e.g. low vs high
arctic)
ITEX results – synthesis II
 Plant communities exhibit detectable
responses to warming in only 3-4 years;
 The most significant changes are:
 increases in deciduous shrub cover &
height
 decreases in cryptogam cover
 decreases in (apparent) species
richness;
Continuing questions:
• effects on soil microorganism diversity
and processes?
• negative feedback of increasing C:N ratio
(low quality litter) and stimulation by
warmth?
• use of organic vs mineral N sources by
plants and microbes: how will this change?
• effects of combined factors: CO2, heat,
moisture, nutrients, light, season length
• Long-term changes in NEP and Carbon
balance?