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EDGEs in Forest Landscapes
EEES 4760/6760
University of Toledo
Jiquan Chen
EDGE
Ecological and physical processes near beach:
front and clearcut boundaries
Terminology
(Harper et al. 2005).
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.
•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).
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)/(e+i) 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.
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
Brief Review
• Game species (Leopold 1933)
Create as much edge as possible because wildlife is a product
places where
two habitats
meet.
This has
been the
•of the
Biophysics
in wind
tunnels
& fields
(50s-70s)
management principle for both public & private land owners
until mid-90s.
• Vegetation responses 50s – present
 But increasing emphasis on plant and nongame wildlife
conservation
during the last
2 decades
has revealed that
• Wildlife
population
(30s
– present)
many characteristics of edges and ecotones are now
considered undesirable (Harris 1988).
• Microclimate (late 80s – present)
 We must not conclude that creation of more edges in
landscapes will always have a positive effects on wildlife ….
• Ecosystem
(Yahner 1988)processes: very rare
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
• 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
Changes in light level
from a south- and eastfacing edge into the forest
Edge exposure is a
very important
variable.
Brief Review
•Game species (Leopold 1933)
•Biophysics in wind tunnels & fields (50s-70s)
•Vegetation responses (50s – present)
 Since Gysel’s publication in 1953, dozens of empirical
•Wildlife
population
(30s –topresent)
studies have
been conducted
examine gradual changes
of plants as functional groups, populations, or
communities across
edges;
•Microclimate
(lateforest-open
80s – present)
 Each species/group responds to the same edge differently
and some species
are not very
affected
at all.
•Ecosystem
processes:
rare
Canopy Cover (%)
Seedling Population
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
Brief Review
Changes inspecies
major (Leopold 1933)
•Game
microclimatic
variables from
•Biophysics
in wind tunnels & fields (50s-70s)
edges into
mature forests in
the PNW.
•Vegetation
Adopted by the responses (50s – present)
FEMAT team.
•Wildlife population (30s – present)
•Microclimate (late 80s – present)
 Significant differences in all microclimatic variables, but
edge width processes:
varies greatly among
variables, ranging from a
•Ecosystem
very rare
few to 300 m in the Douglas-fir forest of the PNW.