Fragmentation in Landscape -Review

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• EEES4760/6760
• Landscape Ecology
• Jiquan chen
• Feb. 25, 2009
• Fragmentation
• Island Biogeographic Theory (IBT)

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1km
50 m
1km
30 m
81 ha 69 ha 59 ha
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Case 7.2 (A) Degree of fragmentation of major
river basins of the world
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7.4 A fragmentation sequence
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7.8 A constellation of separate habitat patches
may be critical to the survival of individuals or
populations
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7.9 Many animals require a suite of different
habitats or resources to meet life history needs
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7.13 Roads can be significant barriers to the
movement of small vertebrates and invertebrates
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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

• Others
• Metapopulation dynamics
• Genetic inbreeding
• Size of disturbance patches
• Cumulative effects (rain, snow and flooding
  effects)

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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. (e-f) Pattern of cutting
at 50 point using single, four nucleus, and
aggressive-parallel cutting systems. (Franklin
Forman 1987)
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Creating Land Mosaics
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An old-growth patch surrounded by a long rotation
island that is cut in a programmed sequence such
( Harris 1984).
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• 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

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What do we want to know about fragmentation?

• What are the relationships among patch area,
  shape, isolation, edge, the interaction of these
  factors, and various population and ecosystem?
• How do various landscape elements (e.g.,
  corridors, linear networks, and matrix) affect
  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?

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Island Biogeographic Theory

• Early interest in habitat fragmentation arose
  from island biogeographic theory (MacArthur
  Wilson 1963 1967).

(MacArthur and Wilson, 1963)
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19.4 fish 1982
(Preston, 1962 Nilsson et al. 1988)
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19.3 mammal 1989
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• The equilibrium model of island biogeography by
  MacArthur and Wilson (1963)

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Manipulative and Mensurative Experiment- Two
Major Approaches -

• Manipulative experiment
• 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.
• An 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

• 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
• 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

• Landscape level study
• Isolation of a process
• Extinction threshold/ time lag/ synergisms
  between habitat area and configuration
• Inequity in the organismal focus
• Invertebrates, reptiles, and amphibians
• Replication / poorly controlled
• Spatial information