Transcript Landscape Equilibrium & Mgmt

Equilibrium and Landscape
Management
Lecture 17
April 19, 2005
Disturbance and Landscape
Equilibrium
Note: All definitions of equilibrium depend on the focal
spatial/temporal scale of interest and measurement.
State variables
Regional Scale Equilibrium - Climate always changing at
long time scales.
Local scale Equilibrium - More affected by shorter-term,
stochastic events.
Normal
multiple
states
operating
range
Disturbance
Recovery
Time
Landscape Equilibrium: Definitions
Stability: The tendency of a system to move away from a
stable state (i.e., a constant range of variation).
State variables
Persistence: The length of time a system remains in a defined
state (or range of states).
Normal
multiple
states
operating
range
Disturbance
Recovery
Time
Landscape Equilibrium: Definitions
State variables
Resistance: The ability of a system to absorb or dissipate
disturbances and prevent them from growing into larger
disturbances.
Normal
multiple
states
operating
range
Disturbance
Recovery
Time
Landscape Equilibrium: Definitions
Resilience: “persistence of relationships within a system and
is a measure of the ability of these systems to absorb
changes… and still persist” Hollings 1973.
A.H. Perera and L.J. Buse 2004
Emulating Natural Forest Landscape Disturbances
Columbia University Press
Landscape Equilibrium: Types
Shifting mosaic steady-state: the landscape maintains a constant
proportion in each patch type through time, as the random
creation of patches by disturbance is balanced by the maturation
of old patches through succession.
Typical of the northeastern US forests.
Very stable over long periods of time.
Landscape
state
Time
Landscape Equilibrium: Types
Stationary process: the landscape is composed of a series of
processes whose distributions do not change in time or space.
Example: river flow peaks in the spring, lowest in autumn.
Very stable of long periods of time.
Landscape
state
Time
Landscape Equilibrium: Types
Bounded equilibrium: the landscape exhibits random changes
over time in response to stochastic disturbance events, but
remains within bounds.
Example: Vegetative carbon in a prairie is relatively low
(‘bounded’) due to fire and grazing. If fire or grazing
removed, it may convert to forest with high carbon.
The mean and variance are very sensitive to scale (spatial and
temporal). Often very non-stationary.
Landscape
state
Time
Managing Landscape Equilibrium
Managing Landscape Equilibrium
Why?
Promote Stability and Resilience:
All ecosystems are adapted to a native disturbance
regime.
Therefore, maintaining the composition (flora and
fauna) and functioning of that ecosystem may
require the maintenance of the natural landscape
equilibrium or Range of Natural Variation.
Managing Landscape Equilibrium
Why?
Two common human alterations to landscape
equilibrium:
Too much disturbance
e.g., clearcutting in the Cascades
Too little disturbance
e.g., lack of fire in the BWCA
e.g., lack of flooding in the Colorado River
Managing Landscape Equilibrium
Why?
Promote Sustainability:
The ability of an ecosystem to maintain ecological processes
and functions, biological diversity, and productivity over time.
Sustainable vs. Nonsustainable Disturbances
a. non-sustainable
frequency.
b. non-sustainable rate of
recovery.
c. non-sustainable
severity.
A.H. Perera and L.J. Buse 2004
Managing Landscape Equilibrium
Why?
Promote Conservation:
Maintain genetic variation and fitness.
Maintain viable species populations, particularly those
dependent upon patch type and patch configuration
(metapopulations).
Maintain species richness: dependent upon natural landscape
equilibrium.
Some species may be adapted to a particular disturbance
type for reproduction
e.g., fire dependent tree species
e.g., Colorado River fish species
Managing Landscape Equilibrium
Why? Promote Conservation
Example: Maintain the Minimum Dynamic Area (MDA)
The smallest area with a natural disturbance regime which
maintains internal recolonization sources and hence
minimizes extinctions (Pickett and Thompson 1978).
i.e., what’s the smallest sized landscape that will allow
enough disturbance to maintain diversity?
Dependent upon disturbance magnitude, variance, frequency,
duration.
versus
Windthrow gap
Northeastern US
Fire in
Yellowstone Ntl Park
Managing Landscape Equilibrium
How? Disturbance Emulation
What is Emulation?
Emulation is not duplication.
Emulation is not restoration to pre-European conditions.
Emulation is generally very goal oriented. Example, if we
want to preserve species X, that requires Y amount of open
space, then we need to create Y amount of open space regardless of how that space is created.
Therefore, emulation usually means re-creating one or two
dimensions of a natural disturbance regime.
Managing Landscape Equilibrium
How? Disturbance Emulation
Question: Emulate what
dimension(s) of a disturbance?
Spatial:
Mean area/size
Spatial distribution
Temporal:
Frequency
Recurrence interval
Return interval
Rotation period
Magnitude:
Intensity - energy released
Severity - mortality caused
from A.H. Perera and L.J. Buse 2004
Managing Landscape Equilibrium
How? Current Emphasis
Emulate Legacies - Jerry Franklin, U
Washington
common in natural disturbances
promote faster recovery to
previous state
Emulate Landscape Pattern
should clearcuts be dispersed or
aggregated?
Emulate Temporal Patterns
reintroducing spring floods into
rivers through dam release
West Chilcotin
Forest Products Ltd.
Managing Landscape Equilibrium
Emulation Tools: Experimentation
Experimentation
terrestrial: generally small scale
larger scale on rivers
Example: Goal = rebuild sand bars and breeding habitat
for Humpback Chubs on Colorado River
Results: Number of chubs declined!
Colorado River during
release
Colorado River after
release
Managing Landscape Equilibrium
Emulation Tools: Modeling
Proportional landscape
dominance
0.8
0.6
Black spruce
Aspen/birch
Red pine
Other
White cedar
Fire Rotation Period
= 50
White spruce/fir
White pine
0.8
0.4
0.2
0.2
0.0
0.6
FRP = 100
0.6
0.4
0.0
0
Proportional landscape
dominance
Jack pine
50
100
150
200
250
300
FRP = 300
0
0.8
50
100
150
200
250
300
150
200
250
300
No Fire
0.6
0.4
0.4
0.2
0.2
0
0.0
0
50
100
150
200
Simulation Year
250
300
0
50
100
Simulation Year
Examples of
Disturbance Emulation
Question: how to emulate fire
patterns in the NWWisconsin Pine Barrens?
Large open patches are crucial
for grassland birds (e.g.
sharp-tail grouse).
Extensive crown fires
provided large open patches
at pre-settlement times
Radeloff et al. 2000
Restoration Ecology 8: 119126
Examples of
Disturbance Emulation
Small restoration areas not
sufficient to maintain openhabitat species.
Aggregated clear-cuts appear
to be suitable to provide the
habitat structure necessary
for open habitat species.
Simulation modeling used to
test alternatives.
Radeloff et al. 2000
Restoration Ecology 8: 119126
Managing Landscape Equilibrium
How? Disturbance Emulation
However, managers must often
work with incomplete or imprecise
information.
Adaptive Management:
Adaptive Mgmt
Mgmt System
(treatment)
Why? Emulation requires more
resources than not emulating.
A system for testing effectiveness
of disturbance emulation
Requires that meaningful indicators
are monitored.
But! Adaptive Mgmt = $
Response/Outcome
Monitor/Measure
Indicators
Managing Landscape Equilibrium
Negative Consequence of Emulation
Reduced resource extraction:
lower forestry yield
lower electrical yield
resource use displacement?
Negative public perceptions:
large clearcut sizes
lower lake levels, ‘muddy’ rivers
introduced fires: ugly burns, smoke and haze
Loss of recreation value
less jet skiing
lower game populations?
May not be sensitive to rare species
Managing Landscape Equilibrium
Summary
Assumptions:
Disturbance history is an appropriate model for
ecosystem mgmt.
Disturbance is integral to maintaining biodiversity.
We understand all the requisite processes. We
don’t.
An emulated disturbance approximates a real
disturbance.
There is excess capacity for disturbance emulation.
Managing Landscape Equilibrium
Summary
The emulation of the natural landscape equilibrium or ROV is
currently very popular with management and conservation
groups. A significant shift from resource extraction first!
However, it is still a new and somewhat unproven concept.
Landscape equilibrium happens at long time scales!
Assumption: we know what the natural disturbance regime
was and that it was constant!
Assumption: the natural disturbance regime is appropriate
for future conditions.
Past disturbance regimes may not be compatible with future
climates, species, nutrient deposition, etc.
Managing Landscape Equilibrium
Ecological Challenges
Lack of knowledge about disturbances across scales and
disturbance interactions -> Disturbance Complexity
Terrestrial:
Emulating disturbance severity, nutrient releases
Rivers:
Emulating water flows at the appropriate water temperatures
Managing Landscape Equilibrium
Institutional Challenges
Institutional inertia
Emulation at the proper scales is impeded by multiple land
owners.
Overcoming public perceptions of desired goals, safety.