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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, [email protected]
• 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??
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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
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• 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
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• 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!
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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 ……
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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?
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• 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
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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
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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
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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
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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
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• 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
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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
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Sofie Sjögersten
Uppsala (‘DART’ Project)
University of Nottingham
Iain Hartley
Stirling (‘ABACUS’ Project)
University of Exeter
Mark Garnett
NERC Radiocarbon
Facility (Environment)
AcknowledgementsAcknowledgements
