reciprocal influences of long-term beaver occupancy on landscape factors and forest structure...

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

Positive

NegativeBeaver

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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5

• 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

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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

Positive

Negative

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

Sel

ecti

vity

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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