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Landscape perspective: Dynamics of terrestrial ecosystems
in the face of climate and environmental change
(importance of ecosystem feedbacks)
Phil Wookey, University of Stirling, pw9@stir.ac.uk
• Biosphere, atmosphere and hydrosphere
are strongly coupled:
� Environmental change affects ecosystem
structure, functioning and distribution;
� Ecosystem responses, in turn, can
feedback on further environmental change
by altering:
Impacts and feedbacksImpacts and feedbacks
• surface energy and water balance, and
• net exchange of radiatively forcing
(greenhouse) gases (of biogenic origin).
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Biosphere/Ecosystems/Soils
Atmosphere
Lithosphere CryosphereHydrosphere
Coupling between biosphere and atmosphereCoupling between biosphere and atmosphere
CO2 CH4
Carnivore 2Carnivore 1Herbivore
Detritus
Decomposers
CO2
Inorganic
nutrients
Plant
subsystem
Herbivore
subsystem
Decomposition
subsystem
Recycling
[from Swift, Heal & Anderson (1979)]
Carbon dioxide fluxes in ecosystem contextCarbon dioxide fluxes in ecosystem context
POC, DOC, DIC??
3
COCO2 2 is not the only GHG of interestis not the only GHG of interest
Environmental controls
on CH4 fluxes are
complicated!!
Coupling between biosphere and atmosphereCoupling between biosphere and atmosphere
Incoming short-wave solar radiation
4
• CO2 ‘fertilization’ effect (‘β-factor’);
• Greenhouse effect (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.
We also need to remember that environmental We also need to remember that environmental
change has change has multiple facetsmultiple facets
• “The past as a key to the future” (Adams &
Woodward 1992) - Yes, but with caution!
• Ecosystem CO2 fluxes and ‘acclimatory’
processes through time
• Biotic cascades and feedbacks in northern
ecosystems: The ‘domino effect’ of
changing vegetation composition
• Ecosystem CH4 budgets and the role of
topography
3 case studies 3 case studies
5
• Oechel et al. 1993. Recent changes of Arctic tundra
ecosystems from a net carbon dioxide sink to a
source. Nature 361:520-523.
• Oechel et al. 2000. Acclimation of ecosystem CO2
exchange in the Alaskan Arctic in response to
decadal climate warming. Nature 406:978-981.
North Slope Alaska and net CONorth Slope Alaska and net CO22 fluxesfluxes
Nature paper 1993!
6
Why should ecosystems become a Why should ecosystems become a
source of COsource of CO22 with warming?with warming?
Temperature
Process
Rate
PS
Respiration
Svante August Arrhenius
1859 – 1927
Nobel Prize 1903
the dependence of the rate constant k of
chemical reactions on the temperature T
(in absolute temperature, such as Kelvin or
Rankine) and activation energy Ea
Arrhenius Arrhenius ……
7
Temperature
Process
Rate
PS
Respiration
Carnivore 2Carnivore 1Herbivore
Detritus
Decomposers
CO2
Inorganic
nutrients
Plant
subsystem
Herbivore
subsystem
Decomposition
subsystem
Recycling
[from Swift, Heal & Anderson (1979)]
What are the What are the ecosystemecosystem consequencesconsequences
of accelerated decomposition?of accelerated decomposition?
8
• Ecosystem CO2 fluxes and ‘acclimatory’
processes through time
• Biotic cascades and feedbacks in northern
ecosystems: The ‘domino effect’ of
changing vegetation composition
• Ecosystem CH4 budgets and the role of
topography
3 case studies 3 case studies
• Shifts in plant communities will result
in a complex series of biotic cascades
and feedbacks which are
supplemental to the direct responses
of ecosystem components to the
primary global change drivers
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Vegetation
Other
Soils
migration and invasion
disturbance regime
∆ herbivores
SOM development
∆ species w/in initial community
∆ litter mass, quality
∆ microbes, fauna
N availability
allocation
Leaf Ps, Rs
1 day 1 yr 10 yr 100 yr 1000 yr
TIME-SCALE OF RESPONSE[from Shaver Shaver et al.et al. (2000) (2000) BioScienceBioScience]
Direct effects on organisms
Cascades and feedbacks
Key issues Key issues –– timescales and cascadestimescales and cascades
• Global environmental change, related to climate
change and the deposition of airborne N-
containing contaminants, has already resulted in
substantial shifts in plant species composition in
arctic and temperate alpine regions:
� how will key ecosystem processes be altered by
these transformations?
� what are the biological cascades and feedbacks
that may result?
� what are the potential consequences for
ecosystem ‘emergent’ properties
10
Tape et al. (2006)
The evidence for shrub
expansion in Northern
Alaska and the Pan-
Arctic. GCB 12: 686-
702.
• New colonization;
• Patch in-filling;
• Individuals getting
larger
Photo credit: Ulf Molau
Latnjajaure, Sweden: Latnjajaure, Sweden: pointpoint quadratingquadrating
Photo by permission of Ulf Molau
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Photo by permission of Gus Shaver
Photo by permission of Gus Shaver
12
ITEX synthesis II ITEX synthesis II --
Community responsesCommunity responses
Walker M.D. Walker M.D. et al.et al. (2006)(2006)
Feedbacks:
• energy budget
• trace gases
13
Global Change Drivers
� SHRUBS
�Woody litter
�CRYPTOGAMS
(& graminoids?)
Growth & allocation
� ECM or ERC
� shading
� N availability
� summer N availability
� winter N availability
-
� Height & LAI
� Snow
? -
+
+-
IPY ABACUSIPY ABACUS
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Tundra heath
Mountain birch
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2.43.910.1Tundra heath
2.01.36.3Mountain birch forest
JoatkaAbiskoDovrefjell
Carbon storage (kg mCarbon storage (kg m--22) in the ) in the
soil organic horizon in forest and soil organic horizon in forest and
tundra sitestundra sites
Note: CPMAS 13C NMR analysis suggests tundra SOM is also more labile
Sjögersten S & Wookey PA (2009) Ambio 38, 2-10
• Use of ‘bomb’ 14C peak (late 1950s to early 60s) in soils to investigate SOM turnover (Iain Hartley with Mark Garnett, NERC RCF)
• IPY ABACUS Project
NERC Radiocarbon Facility (Environment), East Kilbride
16
Data compiled from ORNL, TN
• Early indications that mountain birch might be involved in ‘priming’ the decomposition of older SOM: labile litter or rhizodeposition?
14C (%Modern)
100
102
104
106
108
110
112 Soil
Understorey
May July September
100
102
104
106
108
110
112 Soil
Eco
(a) BIRCH
(b) HEATH
17
• a comparison of total ecosystem C storage in forest and tundra in the Abisko area (based on the soil organic layer, understorey vegetation, and mountain birch C pools) suggests a shift in tree line could result in a loss of 18.9 t C ha-1 (1.89 kg C m-2) to the atmosphere:
�Positive feedback on global warming.
• Ecosystem CO2 fluxes and ‘acclimatory’
processes through time
• Biotic cascades and feedbacks in northern
ecosystems: The ‘domino effect’ of
changing vegetation composition
• Ecosystem CH4 budgets and the role of
topography
3 case studies 3 case studies
18
Controls on CHControls on CH44 fluxes are complicated!fluxes are complicated!
CHCH44 at two hydroat two hydro--topographical topographical
gradients in Abiskogradients in Abisko
0 0.2 0.4 0.6
Soil moisture content (m3 m-3)
-0.1
0
0.1
0.2
mg CH4 m-2 h-1
Tundra site
R2 = 0.31
0 0.2 0.4 0.6Soil moisture content (m3 m-3)
-0.1
0
0.1
0.2
mg CH4 m-2 h-1
Forest site
R2 = 0.66
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Schematic diagram of CHSchematic diagram of CH44 fluxesfluxes
(+)
Methanogenesis
(–)
Methanotrophy
Soil volumetric water contentSwitching
Switching
zone
zone
Desiccation
Desiccation--
sensitive zone
sensitive zone
2.2. 3.3.
Increasingly anaerobic
Net CH4flux
1.1...
0
2
2
14a
3
4b
55
Late-melting
Snow driftPrevailing wind
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
Challenges Challenges ––
‘‘spacespace’’ (scaling(scaling--up from plots to landscapes) up from plots to landscapes) ……
Adapted from D.W. Billings
20
Sofie Sjögersten
Uppsala (‘DART’ Project)
University of Nottingham
Iain Hartley
Stirling (‘ABACUS’ Project)
University of Exeter
Mark Garnett
NERC Radiocarbon
Facility (Environment)
AcknowledgementsAcknowledgements
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