Temporal dynamics

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Temporal dynamics

• Part Ill Patterns
• Chapin, Matson, Mooney
• Principles of Terrestrial Ecosystem Ecology

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Temporal dynamics

• Ecosystems are always recovering from past
  changes
• Never in equilibrium with current environment
• Time lags
• Steady state no directional changes in ecosystem
  properties

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Diurnal fluctuations

• Photosynthesis greater in morning than
  afternoon--even if environment is same
• Plants are hungry for carbon in the morning

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Seasonal fluctuations

• Plants grow rapidly in spring
• Plants senesce in autumn
• In response to photoperiod

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Interannual fluctuations

• Environment
• e.g., e. Nino
• Internal dynamics
• e.g., hare cycle

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Lemmings influence abundance of preferred foods
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Long-term changes and legacies

• Climate

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Global to arctic
Mann et al.
Polar amplification
Chapman and Walsh
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Permafrost is warmer (Medium-term infrastructure
challenges)
Osterkamp and Romanovsky 1999
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Permafrost is thawing in many places, not just
southern margins
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Long-term changes and legacies

• Climate
• Vegetation
• Redwoods Relect of past climates
• Post-glacial migration still occurring

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Forests are expanding
Lloyd and Fastie
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Jorgensen
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1949
1949
Shrub density has increased
2000
Sturm
Chandler River, 50 miles S. of Umiat Sturm,
Racine and Tape Fifty Years of Change in Arctic
Alaskan Shrub Abundance
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Long-term changes and legacies

• Climate
• Vegetation
• Soils
• Agricultural abandonment in NE US
• Methane flux from Siberian lakes

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Thawing permafrost could increase CO2/CH4
release (potential surprise more warming)
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Thermokarst lakes Melting ice wedges Methane
emissions
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Walter et al. 2006
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Long-term changes and legacies

• Climate
• Vegetation
• Soils
• Disturbance regime
• Indian burning
• Black spruce migration
• Recent warming

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Lynch
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Area burned in W. North America has doubled in
last 20 years
Kasischki
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Rural communities have locations fixed by
infrastructure
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Peoples fine-scale relationship with fire has
changed over time

• Pre-contact Mobile family groups
• People adjust to fire regime
• Gold rush settlement Influx of population and
  fire
• People alter fire regime
• 1950s Consolidation in permanent settlements
• Fire affects communities
• 1980s Zonation for suppression
• Policy influences fire and communities

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Chapin et al. Submitted
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Communities differ in moose/caribou dependence
Nelson et al. In press
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Dominant controls over ecosystem processes depend
on temporal scale
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Properties of disturbance regime

• Severity is a measure of the physical
  change caused by disturbance.
• Intensity refers to the rate at which a
  disturbance produces (typically) changes in
  energy should be expressed in terms of
  temperature or heat yield.
• Frequency
• Type
• Size
• Timing

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Fire intensity and fire severity are not
synonymous and interchangeable Fire Intensity
refers to the rate at which a fire produces heat
at the flaming front and should be expressed in
terms of temperature or heat yield. Fire
severity, on the other hand, describes the
immediate effects of fire on vegetation, litter,
or soils. It is most commonly used to describe
fire's effects on the primary tree cover. Unlike
fire intensity, fire severity cannot be
expressed as a single quantitative measure that
relates to resource impact" (Robichaud et al.
2000). Instead, fires are typically ranked from
low to high severity based on the postfire
appearance of soil, litter, vegetation, or other
resource of interest.Fire severity depends not
only on the amount of heat generated along the
flaming front of a fire (i.e., intensity) but
also on the duration of the burn. Duration is a
function of the fire's rate of spread and
subsequent smoldering time. Both depend on
weather conditions and the nature of the forest
fuels. Rate of spread is additionally influenced
by topography and wind speed. A ground fire
smoldering in level terrain, for instance, may
travel only one foot in a week. At the other
extreme, a wind-driven crown fire can move
through 15 miles of forest in just one hour.
While a fast-moving, wind-driven fire may be
intense, a long-lasting fire that just creeps
along in the forest underbrush could transfer
more total heat to plant tissue or soil. In this
way, a slow-moving, low-intensity fire could have
much more severe and complex effects on something
like forest soil than a faster-moving,
higher-intensity fire in the same vegetation.
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Forest productivity often greatest in
mid-succession Declines following canopy closure
(maximum LAI) Several potential
explanations change in species and associated
growth traits decreased hydraulic conductance
as trees get larger decreased nutrient
availability as stands age changes in
allocation to different tissue types with age
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Common pattern of changes in plant carbon
pools Many patterns are possible NPP and plant
respiration about half of GPP Plant biomass
ceases to increase in late succession May reach
a plateau May decline (e.g., Alaskan forest
succession)
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Plant and soil carbon pools increase through
succession Disturbance causes decrease in plant
carbon pool Soil carbon pool can decrease (fire)
or increase (hurricane)
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Carbon fluxes change through succession NPP
maximal in mid-succession Decomposition lags
behind carbon inputs NEP is the balance between
NPP and decomposition
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Upland Secondary Succession
Topography controls vegetation succession and
production by controlling microclimate,
permafrost, soil temperature and moisture,
hydrology, and many other properties.
North-Facing Upland Slopes
South-Facing Upland Slopes
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Representative successional trajectories on
upland sites in interior Alaska along gradients
of soil temperature and soil moisture.
In general, self-replacement predominates in
extreme environments. Black spruce replaces
itself directly after fire in cold permafrost-domi
nated sites. Similarly, aspen replaces itself
directly after fire in warm dry sites without
other intervening tree species.
On intermediate sites, however, there is a
predictable replacement sequence of deciduous
species (aspen on southfacing slopes or birch on
cooler east- or west-facing slopes), followed by
white spruce after about 100 years. These
repeatable patterns of succession are a
consequence of competitive interactions over
multiple fire cycles that have sorted species
into those environments where they grow
most successfully.
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Tanana River Succession
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Floodplain Primary Succession
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Spruce succession, disturbance, and geomorphology
on the Tanana River floodplain
(Mann et al. 1995)
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Nutrient cycling changes through primary
succession
Mosses bind N
Low N availability
Moose speed cycling
N fixation by alders
Poplars cycle N rapidly
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Nodule respiration can be a significant fraction
of soil CO2 flux
Respiration of nodules is over an order of
magnitude greater than fine roots (per g of
tissue) Up to 2 µmole CO2 m-2 s-1 in early
successional stands
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2) How do changes in disturbance regimes interact
with legacies to affect biological
players? Effect of legacies of other things
(e.g., disturbance, other species) on the key
species How does browsing by moose and hares
influence alder, N fixation inputs and
potentially landscape evolution?
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Butler, L. G., and K. Kielland. in press.
Herbivore controls over plant demography,
vegetation composition, and succession in
riparian willow communities along the Tanana
River, interior Alaska. Journal of Ecology.
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Butler, L. G., K. Kielland, T. S. Rupp, and T. A.
Hanley. in press. Interactive controls by
herbivory and fluvial dynamics over landscape
vegetation patterns along the Tanana River,
interior Alaska. Journal of Biogeography.
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Yukon River
Tanana River
Delia Vargas-Kretsinger, M.S. student Vegetation
composition, structure and development during
early succession along the Yukon River near
Beaver, Alaska.
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Stands of Salix alaxensis along the Yukon River
near Beaver
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A. tenuifolia does well in browsing hot-spots
where the canopy is opened up
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FIRE
FIRE
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Life history parameters
Walker et al.
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Nutrient cycling in secondary succession

• Pulse of nutrient availability after disturbance
• Fate depends on retention mechanisms
• Plant uptake
• Microbial uptake
• Chemical fixation
• Changes in nutrient availability variable
• May remain high (e.g., temperate forests)
• May decline (boreal forests)

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Successional changes in nutrient cycling depend
on element Essential and limiting elements are
retained most strongly in mid-succession
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Runoff decreases after disturbance Less
transpiration More runoff (leftovers after plant
water uptake)
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Successional changes in boreal forest after fire
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Albedo increases after fire (more energy
absorbed) Herbaceous and deciduous vegetation
has high albedo
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Mid-successional vegetation transmits less heat
to atmosphere Higher albedo (less heat
absorbed) Higher evapotranspiration Less
sensible heat
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Permafrost response to climate warming involves
multiple ecosystem feedbacks that involve changes
in insulation by snow, moss, and the surface
organic mat
As permafrost recovers during post-fire
succession, an unfrozen layer (talik) forms
but disappears later in succession.
In a warmer climate, fire disturbance could lead
to persistence of a talik. In sloping terrain,
water drains laterally through the talik, drying
surface soils.
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Properties of disturbance regime

• Severity
• Intensity
• Frequency
• Type
• Size
• Timing

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Time
Negative Surface Energy Balance
Wetter Dryer
Seasonally frozen soil
Talik
Permafrost
Positive Surface Energy Balance
Seasonally frozen soil
Talik
Permafrost
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Nutrient cycling in secondary succession

• Pulse of nutrient availability after disturbance
• Fate depends on retention mechanisms
• Plant uptake
• Microbial uptake
• Chemical fixation
• Changes in nutrient availability variable
• May remain high (e.g., temperate forests)
• May decline (boreal forests)

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Successional changes in boreal forest after fire
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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