Reciprocal Influences of Long-Term Beaver Occupancy on Landscape
Factors and Forest Structure (Adirondack Mountains, NY)
Dr. John StellaAnna Harrison
19th September 2011
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Question 1: What landscape factors maintain suitable habitat for beaver in the long-term?
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Potential site influences on long-term occupancy
Maintenance Cost
Dam Volume
Number of Dams
Cross Valley Slope
Landscape Capacity
Down Valley SlopeForage AreaPond Area
PositiveNegative
Beaver Occupancy Duration Resource Quality & Quantity
Hardwood basal area
Softwood basal area
Total basal area
Expected Relationships
• Huntington Wildlife Forest
• 30-year beaver occupancy dataset
• 14 sites stratified by occupancy rate:1. Located on stream
reach or wetland2. Open-canopy
wetlands3. Evidence of dam4. One active colony
only5. Sites are discrete
land areas
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• Forage Area• Pond Area• Dams and Dam
Volume• Upland Forest
Vegetation– 5-m wide belt
transects– Inventory of tree
community
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Field Sampling
12 4
3
9
Landscape Capacity
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Can calculate total beaver habitat area from pond area
Resource quantity and quality
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Conceptual Model Summary:Strongest relationships with long-term
occupancy
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Landscape Capacity
Pond Area
Forage Area
Down Valley Slope
Cross Valley Slope
Maintenance Cost
PositiveNegative
Highly Significant
Beaver Occupancy
Hardwood basal area
Softwood basal area
Resource Quality & Quantity
Total basal area
Cross Valley Slope
Down Valley Slope Forage
Area
Hardwood basal area
Beaver Occupancy30 year dataset
Forage Area
Hardwood basal area
Number of Dams
Dam VolumeDam Volume
Pond Area
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Question 2: How do forest impacts by beaver vary with distance from the pond?
Known selection processes and beaver preferences
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• Variety of documented forage preferences– Aspen, willow, cottonwood,
and alder (Denny 1952)
• Preferred sizes: <10cm diameter (Pinkowski 1983, Haarberg & Rosell 2006 Raffel et al. 2009)– Allows for multiple uses
(Barnes and Mallik 1997)
• Increase selectivity with increased distance from pond (Raffel et al 2009)
Josh Cousins
Photo: Josh Cousins
Species selectivity by stem and basal area
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Selectivity = cut / cut + live (Gallant et al. 2004, Raffel 2009)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Stem
Basal Area
Woody tree species
Sele
ctiv
ity
STM; 5%
AB; 29%
WA; 1%YB; 8%
SM; 7%RM; 10%
RS; 17%
BH; 4%
BF; 15%
Live Stem Relative Density
Size selectivity along a gradient
Multi-stemmed growth habit
Large area + concentrated impact on forest communities
Large area + concentrated impact on forest communities
Potential landscape area impacted by beaver at HWF
Implications
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• Broad landscape controls on beaver behavior
• Fine-scale foraging impacts of beaver
• Results in changes to forest composition and abiotic environment
• Extensive areas with intense foraging could alter forest composition
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