Plant Ecology - Chapter 14

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Plant Ecology - Chapter 14

• Ecosystem Processes

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Ecosystem Ecology

• Focus on what regulates pools (quantities stored)
  and fluxes (flows) of materials and energy in
  abiotic and biotic components

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Ecosystem Ecology

• Turnover time - how rapidly does it move through
  the system
• Retention time - how long does it reside in a
  component

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Ecosystem Ecology

• Pools, fluxes connected together into
  biogeochemical cycles
• Biology, geology, chemistry interconnected

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Ecosystem Ecology

• Plants under the influence of some cycles,
  influence others
• Water, oxygen, carbon, nitrogen, phosphorus,
  sulfur, potassium

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Water Cycle
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Water Cycle

• Terrestrial plants are only living things to have
  significant effect on water cycle
• Evapotranspiration from plants can provide huge
  proportion of moisture in atmosphere - affect
  rainfall patterns

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Water Cycle

• Cutting rainforests can result in decreased
  evapotranspiration, decreased rainfall, increased
  air temperatures at ground surface

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Water Cycle

• Since plants intercept rainfall, reduce its
  impact on ground, removing vegetation can alter
  infiltration/runoff relations

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Water Cycle

• Even removing vegetation in semi-arid regions can
  reduce rainfall, increase soil temperatures,
  induce onset of desertification

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Water Cycle
Flux differences among, within biomes
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Water Cycle

• Potential evapotranspiration (PET) - water lost
  via this process if water is freely available and
  plant cover is 100
• Actual evapotranspiration (AET) - precipitation
  minus runoff and infiltration
• PETgtAET in dry climates
• PETAET in intact tropical rain forests
• AET linked to productivity, decomposition

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Carbon Cycle
Primary productivity - rate of transfer of
inorganic C from atmosphere into organic C in
plants via photosynthesis
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Carbon Cycle
NPP - dry metric tons/ha/yr
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Productivity
Different forests - latitude, climate, elevation
Different ecosystems - related to leaf biomass
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Productivity
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Estimating Productivity

• Standing biomass after a growing season
• Drawbacks destructive, and ignores belowground
  productivity (can be majority in some plants)

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Estimating Productivity

• Indirect measures develop formulae for relating
  plant size changes to biomass changes
• Allometric relationships used by timber
  companies, forest ecologists
• Drawback formula needed for each species

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Estimating Productivity

• Indirect measures use relation between
  productivity and AET
• Fairly good estimates of productivity over broad
  range of climates
• Drawback poor predictor of productivity where
  precipitation and temperature are both high

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Estimating Productivity

• Remote sensing - use reflectance of light
  wavelengths by chlorophyll to estimate
  productivity
• Normalized difference vegetation index (NDVI) -
  good correlation between NDVI and NPP ground
  measurements

NDVI NIR-VIS NIRVIS
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Decomposition
Dead stuff becomes soil organic matter, then
via mineralization becomes inorganic nutrients,
CO2, water, and energy
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Decomposition
- Saprophytic fungi are the major decomposers of
dead leaves, plant litter - Bacteria also
essential, but only in latter stages
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Decomposition
Root decomposition of soft and hardwoods

• Decomposition largely an aerobic process - very
  slow in waterlogged, cold soils
• Physical, chemical characteristics also affect
  rate of decomposition

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Net Ecosystem Production

• NEP is net accumulation of carbon per year by
  ecosystem
• Positive during growing season, negative during
  non-growing season

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Net Ecosystem Production

• Undisturbed ecosystems usually show small,
  positive accumulations of C each year
• Accumulation of woody tissue in long-lived plants

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Soil Carbon Pools and Fluxes
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Nitrogen Productivity
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Nitrogen Cycle

• Rapid flux through living organisms
• Large global pool with slow turnover

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Phosphorus Cycle

• Does not have major atmospheric
• pool like other cycles
• Mostly recycled in organic form
• through other living organisms

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Calcium Cycle

• Sedimentary cycle
• Needed by plants for chemical (growth, stress
  regulation), structural (support) roles
• Largely lost in leaf fall - must be replaced each
  year

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Calcium Cycle

• Calcium depletion occurring in many forests today
• Acid deposition displaces soil calcium, logging
  removes it
• Decreased growth, higher mortality (more
  susceptible to pathogens)