Seminars

1
Seminars

• EECB seminar Thurs 400 PM OSN 120. Dr. Larry
  Stevens, Grand Canyon Wildlands Council.
  Biogeography of the Grand Canyon, and Colorado
  River Management.

2
Reading

• Textbook Chapter 12 and 13
• Sparrow, A., M. Friedel, and D. Tongway. 2003.
  Degradation and recovery processes in arid
  grazing lands of central Australia part 3
  implications at landscape scale. Journal of Arid
  environments 55 349-360.

3
Outline

1. Case study identifying communities and relating
   to environmental conditions
2. Student case studies
3. Productivity plants and ecosystems
4. GPP, NPP, and Efficiency
5. Global and environmental patterns of NPP
6. Production in forest VS rangeland
7. Factors influencing productivity fire,
   herbivory, nutrient pulses, etc.
8. Climate change, CO2 accumulation, and carbon
   sequestration

4
Identification and interpretation of community
patterns

• Using classification (TWINSPAN) to identify wet
  meadow communities
• Relate community classification to environmental
  (hydrologic and geomorphic) variables
• Interpret impact of stream incision on vegetation
  communities

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Humboldt-Toiyabe National ForestCentral
NevadaSan Juan Creek
Reese River
Birch Creek
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Reach-scale vegetation patterns
Below-fan Intermediate valley characteristics Woo
dy riparian, mesic dry meadows
Above-fan Broad valley bottom Wet meadows
At-fan Narrow valley bottom Woody riparian
and upland vegetation
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Objectives Hydrologic Component

• Determine the dominant vegetation types their
  species associations within Kingston Meadow
• Examine relationship of vegetation types to the
  current hydrologic regime within Kingston Meadow
• Evaluate any changes in vegetation associated
  with a different hydrologic regime following
  meadow restoration activities

8
Sampling Scheme

• Determine the composition, ground cover, and
  biomass of the vegetation associated with each
  piezometer or nested well across a hydrologic
  gradient within the meadow
• 14 cross-valley transects (10 with
  piezometers/wells 4 more to adequately sample
  vegetation)
• 55 sampling points (45 nested piezometers 10
  additional sampling points)
• 110 sample plots (2 subsamples per sampling
  point)

9
Terrace Height TWINSPAN
From unpublished data and Henderson, 2001 Stream
cross-sections
10
Meadow GroundwaterCharacteristics
Meadow Type
From Linnerooth Chambers, 2000
11
Vegetation Types- Hydrology Plots
Dominate Species Wetland Status Present in Geomorphic Plots
Carex rostrata Carex rostrata OBL
Carex nebrascensis Carex nebrascensis OBL ?
Mesic Graminiod Poa pratensis Juncus balticus FACU OBL ?
Dry/Planted Bromus inermis Cardex douglasii Agropyron cristatum NONE FACU NONE ?
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Current System Dynamics

• Climate changes that occurred over 2000 years ago
  are still influencing system dynamics
• Recent incision began at the end of the Little
  Ice Age about 290 years ago
• The rate and magnitude has undoubtedly been
  increased by human disturbance

16
Stream Incision Causes

• Overgrazing in riparian zone and upland areas
  within the watershed
• Roads (crossings, captures)
• Sediment starvation due to long-term climate
  effects

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Stream Incision Causes
Barrett Canyon
Corral Canyon
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Stream Incision Causes

• Overgrazing in riparian zone and upland areas
  within the watershed
• Roads (crossings, captures)
• Sediment starvation due to long-term climate
  effects

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Stream Incision Consequences

• Lowers water table in the riparian zone
  (threshold event)
• Stream flow becomes isolated from former
  floodplain
• Development of inset terraces
• Invasion of more-xeric species
• Narrowing of riparian zone and loss of riparian
  habitat

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Barley Cr. (Monitor Range)
San Juan Cr.
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Cottonwood Creek
1998
1994
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Gaining Systems
Non-Incised Meadow
Ground Surface
Water Table Surface
Incising Meadow
Ground Surface
Water Table Surface
Losing Systems
Ground Surface
Water Table Surface
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Your turn

• List management issues/projects you know of in
  range and forest ecosystems.
• Which of the ecological processes or interactions
  we have discussed so far do you need to
  understand?
• Can you make predictions or recommendations based
  on your understanding of the ecological systems?

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Productivity

• Energy captured by autotrophs.
• GPPtotal solar radiation fixed into chemical
  energy via photosynthesis
• NPPGPP-respiration
• Textbook Figure 12.1 energy pathways at primary
  trophic level. Solar energy is reflected,
  emitted, assimilated, respired, consumed by
  herbivores, turned into detritus, or stored in
  standing crop/biomass.

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Efficiency

• Proportion of energy converted into plant
  material. Three components
• Exploitation efficiency ability to intercept
  light. GPP/solar radiation X 100. Affected by
  LAI, leaf orientation, latitude, topographic
  location.
• Assimilation efficiency ability to convert
  absorbed light into photosynthate. GPP/absorbed
  radiation X 100. Affected by CO2 absorption,
  temperature, light and water availability.
• Net production efficiency capacity to convert
  photosynthate into growth/reproduction rather
  than respiration. NPP/GPP X 100. Depends on
  temperature and amount of non-photosynthetic
  biomass supported.

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Net Primary Production

• Difficult to measure accurately on large scale
  because requires measures of photosynthetic and
  respiration rates.
• Usually use changes in biomass over time
• NPP (wt1- wt) D H
• Where (wt1- wt) is change in biomass over time
• D biomass lost to decomposition
• H biomass lost to herbivores

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Net Primary Production

• Can also use allometric means changes in plant
  size use regression to assess.
• Allometry provides measure of root production
  (mini-rhizotron images)
• Global scale
• Models based on climate, precipitation,
  evapotranspiration
• Also remote sensing data

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Carbon balance

• NPP-decomposition/loss to herbivores
• Essentially change in standing crop over time
• Important in assessing impact of vegetation on
  CO2 emissions under Kyoto Protocol etc.

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Relationship of biomass to productivity

• BAR biomass accumulation ratio
• Ratio of dry weight biomass to annual NPP.
• Higher for plant communities with more long-lived
  structure (woody plants)

Plant community BAR
Annual 1
Desert 2-10
Grassland 1.3-5
Shrubland 3-12
Forest 20-50
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Forest biomass and NPP

• Productivity often strongly related to soil
  fertility or texture (eg N mineralization rate in
  eastern US)
• As community ages, ANPP changes
• Immediately following disturbance ANPP rapid and
  biomass accumulates quickly
• Maximum NPP and living biomass at 50-100 yrs
• Leaf biomass is maximal just before canopy
  closure
• Older forests have lower carbon balance
  decomposition and respiration/maintenance of
  nonphotosynthetic tissues

33
Rangeland biomass and NPP

• Higher biomass not necessarily related to higher
  NPP
• In dense grasslands removal of dead or decadent
  biomass may stimulate productivity
• Indication of coevolution of herbivores and
  grasses? Ability of grasses to re-grow
  photosynthetic tissue after removal herbivore
  tolerance
• Grazing lawns rapid nutrient cycling and high
  productivity caused by repeated grazing

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Factors affecting NPP

• Light, temperature
• Water (precipitation, evapotranspiration)
• Carbon dioxide (high concentrations more
  influential for C3 than C4)
• Nutrient availability (see handout and text P326)
• Herbivory can stimulate (by reducing
  competition for light) or decrease (by removing
  photosynthetic tissue)
• Fire usually stimulates release of nutrients,
  removal of competition for light and water

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Variable resources

• Resources are not constant in time or space
• Ecosystems are limited by a variety of resources
• Transient Maxima Hypothesis TMH
• Explains patterns of productivity for
  non-equilibrium systems.
• E.g. tallgrass prairie at equilibrium, light is
  limiting (soil resources not utilized to maximum)
• When disturbed, light not limiting, productivity
  increases to utilize available resources (hence
  increase in productivity with fire or herbivory)

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Global carbon cycle

• Atmospheric carbon flux strongly affected by
  human activity
• Combustion of fossil fuels and clearing of forest
  releases sequestered carbon into atmosphere
• Substantial changes in CO2 since industrial
  revolution (from 280 ppm to gt350 ppm)
• Productivity of vegetation affects CO2
  concentration in atmosphere