Climate Change

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Climate Change Ecosystem Ecology

• Ecosystems as Energy Machines

In an ecosystem approach, we pay less attention
to individual organisms / species than to
system-wide properties
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• Ecosystems as Energy Machines
• Most energy enters ecosystems via sunlight
• Photoautotroph derives its energy from sunlight
• Heterotroph derives its energy from other
  organisms
• The energy can be measured as NPP, or g
  carbon/m2/yr

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• Large-scale NPP can be estimated with satellites.
  How?
• Satellites measure near infrared (NIR) and red
  (RED) reflectance from plants.
• NIR light is actively reflected by plants b/c it
  is too low-energy for photosynthesis. It just
  heats up the plant.
• RED light tends to be absorbed for
  photosynthesis.
• The ratio of NIR reflected to RED reflected is
  called the normalized difference vegetation index
  (NDVI)
• NIR RED / NIR RED
• NDVI correlates with NPP

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• See Fig. 25.15 for land-based NDVI estimates.

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• Using conversions you dont need to know,
  reflectance can be converted to NPP
• (See text, pp. 527-529)

http//earthobservatory.nasa.gov/Newsroom/NPP/Imag
es/psn.modis.seasonal.jpg
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• Change in N. Am. NPP, 1982-1998
• Based on satellite measurements

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• Over small areas, NPP (g carbon/m²/year ) can be
  measured on the ground as
• NPP ?B L G
• Where ?B biomass after biomass before
• L biomass lost by death of plants
• G biomass lost to herbivory

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• Biomass (grams dry weight) can be converted to
  energy (calories) in a bomb calorimeter.
• A simple calorimeter?
• Thermometer attached to an insulated container.
• Different plant parts need to be measured
  separately.
• Calorie energy needed to increase 1 g of water
  by 1 C. ( 4.185 Joules.)

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• Ecosystems as energy machines
• NPP can be converted to energy
• Sometimes this is done with fossil NPP
• e.g. coal, oil, natural gas
• Sometimes this is done with more recent NPP
• e.g. wood, biofuels

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• Trace all relevant impacts of biofuels on the
  carbon cycle

Fossil fuels needed to produce the biofuel
Energy output / energy inputs Land use changes
needed to produce the biofuel See FA_Land
Clearing Biofuel Carbon Diet
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• What factors might limit NPP?
• Amount of light entering the system
• Biomass of primary producers
• Photosynthetic rates of primary producers
• Respiration rates of primary producers
• Growth rates of primary producers
• Nutrient limitation

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• NPP limitation in terrestrial ecosystems
• Rosensweig 1968 NPP correlated with?
• actual evapotranspiration

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Rosensweig 1968
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• Evapotranspiration (ET) - the sum of evaporation
  and plant transpiration at a location.
• Transpiration is the loss of water as vapor
  through stomata.
• Potential evapotranspiration (PET) indicates
  the energy (solar radiation temperature)
  available to evaporate water, and the wind
  available to transport the water vapour into the
  lower atmosphere.
• Assumes moisture is unlimited

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Is this a dry or moist environment?
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Is this a dry or moist environment?
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How will changes in AET influence NPP globally?
Ecosystem-level question How will all components
of climate change interact to affect NPP (and
therefore carbon storage) globally?

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• Effects of climate on NPP are very hard to
  predict due to variable, interacting factors
• Global nitrogen levels are rising
• Precipiation rising in some places, falling
  others
• CO2 concentrations rising
• Simulated warming often increases decomposition
  more than NPP

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• How can this be studied experimentally?
• See SH_CO2 decreases plant growth
• Sometimes, experiments serve to raise more
  questions than they answer.