Pieter Bruegels, Hunters in the Snow

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Pieter Bruegels, Hunters in the Snow
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1895
1980
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Disturbance any relatively discrete event in
time that disrupts ecosystem, community, or
population structure and changes resources,
substrate availability or the physical
environment.
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Quantifying Disturbance Regimes
Frequency-number of occurrences per unit
time   Patch size- area over which a disturbance
event occurs   Severity-degree to which the
disturbance alters the ecological system
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Frequency none
Frequency 250-500 yrs Severity high Size large
Frequency 50-90 yrs Severity low Size small
Fire Disturbance Regimes in the PNW
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Wildfire and Logging (1, 2) disturbance regimes
expressed in three dimensions.
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Fire history of the Yellowstone Plateau. From
Romme 1972.
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Fire-dependent Species
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Landscape Dynamics
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Types of Landscape Dynamics
Nonequilibrium - The case where an attribute
(e.g. distribution of seral stages) of a
population, community, or landscape deviates
unpredictably over time. Shifting Steady-State
Mosaic - A landscape where the characteristics of
individual patches are out of phase but the
collective behavior of patches displays
equilibrium.
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Windthrow in Southeast Alaska