Download Edges and Edge Effects

10/7/2010
A.Defined
Edges known to be most productive (hunters,
birdwatchers).
Edges
g & Edge
g Effects
Edge effect - apparent increase in wildlife where
2 habitats meet
Many spp frequent edges more commonly
than interior areas.
1. Attraction of simultaneous access to more than
one environmental need – food, cover, water etc.
Exact mechanism unknown
2 Hypotheses
2. A greater variety of vegetation including
species common to each type of habitat plus
some plants characteristic of edge only.
B. Types
1. Inherent edges
Natural edges, caused by changes in soil,
topography
eastern North America – deciduous, coniferous
edge
grasslands, woodland edge along rivers
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2. Induced edges
May occur where floods or fires have reversed
succession
May occur where humans have created
patchwork of tilled land interspersed with
fencerows and wood lots
Edge effects on deer
Williamson and Hirth 1985. An evaluation of edge use by
White-tailed Deer. Wildlife Soc. Bulletin 13:252-257.
Browsing by WTD in clear cuts adjacent to
h d
hardwood
d forests
f
t
Clearcutting – stimulates abundant regeneration of
woody sprouts of value as deer browse.
Availability of browse was homogenous
throughout clear cut stand but deer preferred
feeding near edge.
Exception – 2 spp. highly sought after browse
Which edge hypothesis do these results
support?
Deer moved as far as 100m into opening for
preferred browse (red maple, pincherry)
Level of nutrition provided by browse offset
additional predation risk??
Management Recommendation
Large clearcuts in which the centers are more
than 100 m from shelter would be less useful for
deer
Represents
p
case where 2 resources occur
in proximity instead of reflecting larger
diversity of species near edge.
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Grouse – greater hunting pressure on those
along edges
Paradox –
Gates and Gysel (1978) found that nest densities
higher on both sides of forest – field edge
compared to interior
But…
Desired mix of aspen (stands 3 age classes)
creates lots of edges.
How can one minimize?
Nest parasitism and predation higher on nests
along edges!!!
Why do birds select fragmented or edge sites???
Ecological Trap Hypothesis
Ecological Trap
Ecological Trap
1) Areas that have all the cues which trigger
animals to perceive it as its habitat and settle but
some critical resource is missing or in short supply
so that
th t survival
i l or reproductive
d ti success is
i reduced.
d
d
2) Areas that have all the cues and resources of
high quality habitat but some feature, event or
organism is present that causes increased
mortality
t lit or d
decreased
d reproduction.
d ti
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Edge effects on birds
TIPS FOR EDGE MANAGEMENT
• When harvesting timber, make several
small, irregularly shaped cuts to increase
the amount of edge
• Retain strips of forest along streams for
water protection and for wildlife travel lanes
TIPS FOR EDGE MANAGEMENT
TIPS FOR EDGE MANAGEMENT
• Leave about 5% of recently harvested areas
untreated to provide brushy edges
• Allow native vegetation to take over
fencerows, terraces, roadsides, and field
borders
• When possible, allow fingers of native
vegetation to creep out into open areas
• Plant trees and shrubs to speed
p
up
p the
development of cover along edges
• Plant wildlife travel lanes (corridors) or
hedgerows to connect large forested areas
where edge is limited
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TIPS FOR EDGE MANAGEMENT
• Create brush piles in pastures, clearcuts, and
other open areas
• Cut and leave large trees on field edges to
provide cover
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