Essay 9 assigned and due this Friday

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Essay 9 assigned and due this Friday Sunday
field trip. Meet 9 AM corner of McCaslin and
Coal Cr. Rd (south of Superior) Take HW 36.
Exit McCaslin at Superior. Go South up and over
the large hill. Park On west side of road at
intersection. Coalton Cr. Trail. We will go
off-trail (with permits) so cant take dogs.
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I can make the grass grow.
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Consumers as nutrient pumps.
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More data a biennial forb in the Southwest
Paige and Whitam, Am. Nat. 1987
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... grazing benefits many grasses and other
plants in grassland ecosystems Furthermore,
moderate grazing promotes the productivity of
many grasslands If these statements are not
true, then I believe the sun rises in the west,
Earth is flat, and water flows uphill
unaided. Sam McNaughton, 1993. Ecol. Appl. 3
17-20.
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Outcomes of herbivory If consumption has
negative effect on relative growth rate, (RGR)
then effect on NPP is ________________ If
consumption has NO EFFECT on RGR, then effect on
NPP is ____________________ If RGR increases at
a rate equal to biomass removal, then effect on
NPP is _____________ This is called
_______________________ If consumption greatly
enhances RGR, then the effect on NPP is
________________________ and this is called
________________________.
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Alaska was suggested to be more productive in the
Pleistocene than now!
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Chapter 13Temporal Dynamics
4/11

• Principles of Terrestrial Ecosystem Ecology
• Chapin, Matson and Mooney

The last component of the Jenny model (cl,o,r,p,t)
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Temporal dynamics

• Ecosystems are always recovering from past
  changes
• Never in equilibrium with current environment
• Time lags

(and the environment is changing)
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Dominant controls over ecosystem processes
depend on temporal scale
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Diurnal fluctuations

• Photosynthesis greater in morning than
  afternoon--even if environment is same
• but ecosystem ecology doesnt
• do much at this time scale.

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Seasonal fluctuations

• Plants grow rapidly in spring
• why?

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Seasonality in NPP Microbial activity and
mineralization can occur when plants are not
active Soils recharge with water during non-
growing season Thus, in the spring we have
light, water, and nutrientsHence rapid growth.
This also contributes to interannual variability
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Interannual variations

• Environment
• e.g., el. Nino
• Internal dynamics
• e.g., lemming or hare cycle
• Long-term directional changes (recovery
• from glaciation, global warming
• these challenge the steady state
  assumption)

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Climate, topography, parent material
Initial biotic community
regional pool of biota
(Jenny model)
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Biotic interactions with abiotic conditions
(changes in physical and chemical environment
for biota)
Climate, topography, parent material
new biotic community
Old community
regional pool of biota
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Classical Succession Pioneering species --gt
successional species --gt climax
species Dominant species traits are only able
to hog the resources under a given suite of
conditions The species themselves often change
this suite of conditions.
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disturbances
Climate, topography, parent material
Biotic interactions with abiotic conditions
(changes in physical and chemical environment
for biota)
Old community
new biotic community
regional pool of biota
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Ecosystem response to disturbance depends
on Resistance Tendency not to change Response
Magnitude of change Resilience Rate of return
to original state Recovery Extent of return to
original state
These concepts are perhaps no longer as
useful as they once were???
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Definition A
disturbance is a relatively discrete event that
destroys biomass and alters resource
availability. Picket and White 1985 (Watch
those cows create a disturbance!?)
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Problem with disturbance concept Is is
defined only after the fact? Fire, flood,
hurricane, volcanoes Extreme climatic
events Biotic events that are disturbances? Ins
ect outbreaks Vole (mice) eruptions
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NEW IN THE LATE 90s Making disturbance
ecology a predictive, generalized
concept Dont focus on the individual
event Focus upon the event within the context
of its probability or frequency of occurrence.
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Events (biotic, abiotic, climatic) can be
defined by their frequency and magnitude. Fire
return intervals Flood return intervals Avalanches
Climate events Insect outbreaks HISTORICAL
RANGE OF VARIABILITY (HRV)
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Spatial extent can be quantified On
averagethis point in the forest receives a
surface fire every ____ years and a canopy fire
every ____ years. ____ of the forest burns each
year. Or This area of the flood plain goes
under water on average once every ____ years.
(____ of flood plain goes under water every ___
years)
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Historical Range of Variation, Current
Conditions, and Desired Future Conditions NV
natural variablility (solid line), CC XX
current conditions, DFC desired future
conditions, dashed line)