EDGEs in Forest Landscapes

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EDGEs in Forest Landscapes EEES
4760/6760 University of Toledo Jiquan Chen
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EDGE
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Ecological and physical processes near
beach front and clearcut boundaries
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(No Transcript)
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• Terminology
•  
• There is a lack of consistent terminology in the
  literature on forest edges. Following
  consideration of past definitions and common
  usage in the literature, as well as ecological
  relevance and usefulness of terms, we propose the
  following terms and definitions as standard.
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• Edges Relatively abrupt boundaries between
  different communities. Created edges form as a
  result of a natural or anthropogenic disturbance.
  Steep gradients in topography, soil type,
  microclimate and/or geomorphology result in
  inherent edges (Thomas et al. 1979).
• Forest edge Abrupt transition between forested
  and non-forested communities, or between two
  forests of contrasting structure or composition.
  In practice, a forest edge can be defined as the
  limit of the continuous canopy (Harper and
  Macdonald 2001) or the point of abrupt transition
  in canopy composition.
•  
• Forest interior Area within a forest landscape
  that shows no detectable edge influence. Interior
  conditions are typically characterized using
  samples located in large blocks of un-fragmented
  forest landscape or in the center of the largest
  patches available for study.
• Edge influence (EI) The effect of processes
  (both abiotic and biotic) at the edge which
  result in a detectable difference in structure,
  composition or function of the edge community, as
  compared to the ecosystem on either side of the
  edge (e.g. both interior forest and non-forested
  area). Both 'edge influence' (Chen et al. 1992,
  Harper and Macdonald 2001) and 'edge effects'
  (Harris 1984, Murcia 1995) have been used
  extensively and interchangeably in the
  literature.
• Significance of edge influence (SEI) The
  statistical significance of the edge influence
  (e.g. values at or near the edge, as compared to
  values in the interior forest, Saunders et al.
  1999).

(Harper et al. 2005).
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Terminology Cont.
(Harper et al. 2005).

• Magnitude of edge influence (MEI) A measure of
  the extent to which a given parameter differs at
  the edge, as compared to the reference non-edge
  ecosystem. Both 'significance of edge influence'
  (Chen et al. 1995) and 'magnitude of edge
  influence' (Harper 1999) have been defined this
  way. To avoid confusion, we propose using MEI and
  SEI to distinguish between ecological effect and
  statistical significance. We recommend
  calculating MEI as (e-i)/(ei) where e value of
  the parameter at the edge, i value of the
  parameter in the interior (non-edge) forest MEI
  thus varies between -1 and 1 and is equal to 0
  when there is no edge influence.
• Distance of edge influence (DEI) The set of
  distances from the edge into the adjacent
  community over which there is a significant edge
  influence (Chen et al. 1992). Distance of edge
  influence may be considered to represent a zone
  of edge influence that extends to both sides of
  the edge, in which structure or composition is
  different from either of the adjacent
  communities. This zone may actually begin some
  distance into the forest or in the adjacent
  non-forested area (Cadenasso et al. 1997, Harper
  and Macdonald 2001, 2002) effects are not always
  monotonic (c.f. Murcia 1995).
• Area of edge influence (AEI) The total area of a
  given landscape that is subject to significant
  edge influence an extension of DEI in two
  dimensions. Since DEI varies with edge
  orientation, edge contrast, surrounding
  topography and other factors, AEI typically
  appears as a belt of variable width surrounding
  all edges in the landscape.  
• Core area The total landscape area that is
  outside the zone of significant edge influence
  (e.g., total forested area - AEI).
• Patch contrast The difference in microclimate,
  structure, composition or function between
  adjoining ecosystems.

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Brief Review

• Game species (Leopold 1933)
• Biophysics in wind tunnels fields (50s-70s)
• Vegetation responses (50s present)
• Wildlife populations (30s present)
• Microclimate (late 80s present)
• Ecosystem processes very rare

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Brief Review

• Game species (Leopold 1933)
• Biophysics in wind tunnels fields (50s-70s)
• Vegetation responses 50s present
• Wildlife population (30s present)
• Microclimate (late 80s present)
• Ecosystem processes very rare

Create as much edge as possible because wildlife
is a product of the places where two habitats
meet. This has been the management principle for
both public private land owners until mid-90s.

• But increasing emphasis on plant and nongame
  wildlife conservation during the last 2 decades
  has revealed that many characteristics of edges
  and ecotones are now considered undesirable
  (Harris 1988).
• We must not conclude that creation of more edges
  in landscapes will always have a positive effects
  on wildlife . (Yahner 1988)

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Brief Review

• Game species (Leopold 1933)
• Biophysics in wind tunnels fields (50s-70s)
• Vegetation responses 50s present
• Wildlife population (30s present)
• Microclimate (late 80s present)
• Ecosystem processes very rare

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• Edge effects normally extend to 2-3 tree heights
  (Franklin Forman 1987)
• Neither empirical data, nor theoretical basis
  existed in the original FAO report.

Insert Raynor 1972
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Changes in light level from a south- and
east-facing edge into the forest
Edge exposure is a very important variable.
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Brief Review

• Game species (Leopold 1933)
• Biophysics in wind tunnels fields (50s-70s)
• Vegetation responses (50s present)
• Wildlife population (30s present)
• Microclimate (late 80s present)
• Ecosystem processes very rare

• Since Gysels publication in 1953, dozens of
  empirical studies have been conducted to examine
  gradual changes of plants as functional groups,
  populations, or communities across forest-open
  edges
• Each species/group responds to the same edge
  differently and some species are not affected at
  all.

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Canopy Cover ()
Seedling Population
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Brief Review

• Game species (Leopold 1933)
• Biophysics in wind tunnels fields (50s-70s)
• Vegetation responses (50s present)
• Wildlife population (30s present)
• Microclimate (late 80s present)
• Ecosystem processes very rare

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Brief Review

• Game species (Leopold 1933)
• Biophysics in wind tunnels fields (50s-70s)
• Vegetation responses (50s present)
• Wildlife population (30s present)
• Microclimate (late 80s present)
• Ecosystem processes very rare

• Significant differences in all microclimatic
  variables, but edge width varies greatly among
  variables, ranging from a few to 300 m in the
  Douglas-fir forest of the PNW.