Transcript Edge influence

EDGE
Ecological and physical processes near beachfront and clearcut boundaries
Terminology
(Harper et al. in prep).
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 unfragmented 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. in prep).

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.
light
Structure
Influences
Growth
Mortality
Regeneration
Predation
Canopy
Physical
Env ironment
Damages
Community
Processes
Community
Processes
Energy Flow
Ev aportranspiration
Nutrient Cy cling
Soil respiration
Pollen & Seed dispersal
Horizontal energy f low
Inv asion
Aerosols dispersal
Sounds transf ormation
Density
Biomass
Snaps
CWD
Litter
Soil OM
Roots
Soil moisture
Air temperature
Productivity
Humidity
Habitat Quality
Diversity
Feedback
Direct
Changes
Community
Processes
Function
Direct and
indirect of
edge
influences on
ecological
pattern and
processes.
Forest
Exposure
Processes
What
properties
are really
affected?
Open
100
-100
-50
0
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-100
-50
0
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-100
-50
0
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-100
-50
0
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-100
-50
0
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40
-50
0
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-100
-50
0
50
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-100
-50
0
50
100
-100
-50
0
50
100
-100
-50
0
50
100
-100
-50
0
50
100
RUAL
0 20
60
VAAN
PRSE
HIER
PIBA
0
20
40
0
5 10
0 20
60
0 20
40
80
40
CAPE2
0
80
40
SAHU
0
VIOLA
10 20 30
0
10 15
5
0
ASSA
-100
10 20 30
Species abundance across a
jack pine edge in N. WI.
0
DASP
20
PRPU
0
50
60
0
20
ARUV
0 20 40 60
-50
0
COPE
-100
-100
-50
0
50
Distance from the Edge (m)
100
(a) Edge Species
Edge
Vs
Interior
Species
Distance from Edge
(a) Interior Species
Distance from Edge
So what?
Assuming the depth of edge
influence is 240 m, a 50 ha
(125 acre) forested patch
surrounded by open area
contains very little interior
environment. Indeed, 84%
of the forest is AEI.
Interior
Area of Edge Influence
(AEI)
(84%)
800 m
Management Philosophies
Leopold-Thomas-Harris/Yanher-Noss-…
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.
-- Aldo Leopold (1933)
The essential requirements of wildlife- food, cover, and
water- will be maintained so as to provide optimum ‘edge
effect’ and interspersion of habitat components in
important wildlife areas.
-- BLM Manual 1603 (1973)
The law of dispersion and interspersion work together to show the
forest manager how to increase wildlife populations associated with
edge.
-- Thomas et al. (1979)
But increasing emphasis on plant and nongame wildlife
conservation during the last two decades has revealed many
characteristics of edges and ecotones are now considered
undesirable.
-- Larry Harris (1988)
We must not conclude that creation of more edge in landscapes will
always have a positive effect on wildlife …
-- Richard H. Yahner (1988)