Transcript Document

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.
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
•Biophysics
windwhere
tunnels
fieldsmeet.
(50s-70s)
product of thein
places
two &
habitats
This has
been the management principle for both public & private
land owners until
mid-90s. 50s – present
•Vegetation
responses
But increasing emphasis on plant and nongame
wildlife conservation
during
last 2 decades has
•Wildlife
population
(30s the
– present)
revealed that 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
•Ecosystem
processes:
very
rare effects on
wildlife …. (Yahner 1988)
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
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
•Wildlife
population
(30sconducted
– present)to examine
empirical studies
have been
gradual changes of plants as functional groups,
populations, or communities
across forest-open edges;
•Microclimate
(late 80s – present)
Each species/group responds to the same edge
•Ecosystem
processes:
very
differently and
some species
are rare
not affected at all.
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)
Many excellent studies. See presentation today
•Microclimate (late 80s – present)
from Drs. Rolf Koford & Stanley Temple.
•Ecosystem processes: very rare
Brief Review
Changes species
in
•Game
(Leopold 1933)
major
microclimatic
•Biophysics
variables from in wind tunnels & fields (50s-70s)
edges into
mature forests responses (50s – present)
•Vegetation
in the PNW.
Adopted by the
•Wildlife
population (30s – present)
FEMAT team.
•Microclimate (late 80s – present)
Significant differences in all microclimatic variables, but
edge width varies
greatly among
•Ecosystem
processes:
veryvariables,
rare ranging from a
few to 300 m in the Douglas-fir forest of the PNW.
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)
But see Tom Hayes’s presentation today
•Vegetation responses (50s – present)
Productivity of tropical forests declined by about
36% as a result of edge creation (Laurance et al. 1997,
•Wildlife
Science) population (30s – present)
•Microclimate (late 80s – present)
•Ecosystem processes: very rare
News From LEES Lab
Euskirchen et al. (2001)
High
edge
(a) Edge Species
The maximum
edge effect does not
always occur at 0 m.
1
Relative Abundance
Edge effects of two
sides are not
sympatric;
2
Low
3
High
edge
(b) Interior Species
2
3
4
1
Low
Distance from Edge
(a) Edge Species
Edge
Vs
Interior
Species
Distance from Edge
(a) Interior Species
Distance from Edge
News From LEES Lab
Within the area-ofedge influence (AEI),
most areas are under
multiple edge effects!
Distribution of area-of-edge
influences (AEI) around older
clearcut, showing a complex AEI
composition.
Composition of AEI around 4 patch types in the CNF
Proportion of AEI (%)
60
Proportion of AEI (%)
Mixed hardwood
Jack Pine
40
20
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t
cu
r
a
le
ld
C
re
O
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Proportion of AEI (%)
60
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Proportion of AEI (%)
Old Clearcut
40
40
20
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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