Transcript Fragmentation in Landscape -Review & Methods-

Fragmentation and
Management of Landscape
 How
many red spots make a
white cow red?
 How many clearing make a
forest, prairie?
 A threshold reached?
(Forman and Godron 1986)
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Where was it from?
 Origins
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& Definitions
Where we are?
 Problems
– Case Studies
 Importance of fragmentation.
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Where to go?
 Achievements
& Necessities
Island Biogeographic Theory
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Early interest in habitat fragmentation arose
from island biogeographic theory (MacArthur
and Wilson, 1963 & 1967).
(MacArthur and Wilson, 1963)
19.4 – fish 1982
(Preston, 1962; Nilsson et al. 1988)
19.3 – mammal 1989
The equilibrium
model of island
biogeography by
MacArthur and
Wilson (1963)
Definitions
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Broad Definition: transformation of original
continuous forest landscape into small and
isolated remnant patches of plantation or nonforest habitat. It is simply the disruption of
continuity.
Narrow Definition: Breaking up of a habitat
or land type into smaller parcels
Examples – Fragmentation
Fragmentation: Habitat Loss
Miombo
Africa
Maraba
Africa
NE China
Bayfield
(WI)
From Dar Roberts, CA
Fragmentation: Subdivision of habitat
Rondonia, Brazil
(1986)
(1993)
(1999)
Fragmentation: Patch Isolation
Observed reproductive rates were low enough for some species in the most fragmented
landscapes to suggest that their populations are sinks…. Conservation strategies should consider
preservation and restoration of large, un-fragmented “core” areas in each region.
Fragmentation:
Edge Effects
1972
2001
The forested areas of Warwickshire, England (shown in black) (Wilcove et al. 1986)
1km
50 m
1km
30 m
81 ha
69 ha
59 ha
The Checkerboard Landscape
Patterns of
clearcutting
development under
various models(a-c)
Progression of
clearcutting using
the dispersed patch
model in which
areas are selected
for cutting so as to
be distributed
regularly across the
landscape: shown
are 25, 50, and 75%
cutover points. (ef) Pattern of cutting
at 50% point using
single, four
nucleus, and
aggressive-parallel
cutting systems.
(Franklin &
Forman 1987)
Susceptibility
of forests in
the Douglasfir region to
various
damaging
agent along a
landscape
cutting
gradient as
shown by the
checkerborad
model.
(Franklin &
Froman 1987)
EFFECTS OF FRAGMENTATION
Landscape structure
 Patch density
 Patch size
 Inter-patch distance
 Connectivity
 Boundary length
 Interior/edge ratio
 Maximum of core (interior forest)
 Total interior
 Stepping stones
 Corridors
Species
 Isolation
 Number of generalist
 Exotic species
 Nest predation
 Extinction rate
 Dispersal of interior species
 Large-home-range species
 Richness of interior species
Others
 Metapopulation dynamics
 Genetic inbreeding
 Size of disturbance patches
 Cumulative effects (rain, snow and
flooding effects)
Creating
Land
Mosaics
An old-growth patch surrounded by a long rotation island
that is cut in a programmed sequence such. ( Harris 1984)
Conclusions
The number, size, and arrangement of the patches in a
mosaic created by forest managers strongly influence the
degree to which management objectives are fulfilled.
Two recommendations are: (1) reduce the emphasis on
dispersing small clearcut patches through the forest landscape,
and (2) identify and reserve large patches of primeval forest in
the landscape for maintenances of interior and amenity values.
SLOSS debate
What do we want to know about fragmentation?
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What are the relationships among patch area, patch shape,
patch isolation, edge, the interaction of these factors, and
various population and ecosystem?
How do various landscape elements, such as corridors, linear
networks, and matrix, affect various ecosystem processes and
the connectivity of populations in fragmented landscapes?
How do pattern-process linkages function in spatially and
temporally dynamic landscapes across the range of spatial
and temporal scales?
What levels of habitat loss and fragmentation does population
viability decline drastically?
How long does it take population and ecosystem processes to
respond to physical changes in the landscape associated with
fragmentation?
Manipulative and Mensurative
Experiment - Two Major Approaches
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Manipulative experiment
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Physically manipulates some attribute of the system
in a controlled manner, while holding all other
attributes constant.
Mensurative experiment
Simply observes or measures the system at different
locations or times
 The treatment is the different conditions in space or
time.
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Generally, manipulative experiments lead to
stronger inferences and therefore more reliable
knowledge than mensurative experiments.
A Ideal Manipulative experiment requires
The similarity among landscape minimizes the
experimental error
 The size of the landscape are functionally relevant to
the process/organism(s) under consideration
 Areal extent and configuration manipulation is
needed to assess independent and interactive of
processes
 Replication and Random
 Temporal and Spatial Controls (Natural Variability)
 Observing the delayed effect
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Mensurative Experiment
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Can overcome some of the important
limitations
The practical and logistical difficulties of
implementing large-scale treatment
 No practical limit to the spatial or temporal scale of
the study system
 Flexibility in time lag effect
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Still problems …
Additional sources of variation associated with
inconsistent and uncontrolled past perturbations
 Lack in pretreatment control – owing to substituting
space for time – inherent variability and
autocorrelation
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Lack in …
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Landscape level study
Isolation of a process
Extinction threshold/ Time lag/ synergisms
between habitat area and configuration
Inequity in the organismal focus
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Invertebrates, reptiles, and amphibians
Replication / Poorly controlled
Spatial information