Overabundance of deer facilitate invasive species in Northeastern Forests

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Overabundance of deer facilitate invasive species
in Northeastern Forests

• Joshua Grace

Roberta Stacy, http//homepage.mac.com/rstacy/
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Todays Presentation

• Species background
• Feeding techniques
• Invasive plant facilitation
• Exotic seed dispersal
• Lower reproductive output of native species
• Management Implications

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Species of Interest

• White-tailed deer
• Odocoileus virginianus
• Population on the rise
• Broad range

Nelson Davis
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Deer density map- QDMA

• Green ( less than 15 / sq mile)
• Light orange shades ( 15-45 /sq mile )
• Dark orange ( greater than 45 /sq mile )

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Odocoileus virginianus

• Herbivores
• Grazers by choice, browsers by necessity
• Feed by season

www.forestwonderer.com/id13.html
www.buckmanager.com
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Grazers ??

• Feed by season
• Spring/Summer
• herbaceous plants and woody foliage
• Fall
• Acorns and fallen fruits
• Winter
• woody stems
• Can be detrimental to single species
• Alter appearance and ecology of veg. communties

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Deer Impacts

• Population viability of individual understory
  species
• Regeneration failure in northern hardwood forest
  stands
• Drastic decrease in diversity as a whole
• Selective browsing
• Invasive introduction

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Exotic Seed Dispersal

• Williams Ward (2006)
• Examined role of deer in dispersal of exotic
  plants
• Seeds in scat
• Deer movement patterns
• Medium-density housing
• Connecticut, US

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Exotic Seed DispersalWilliams Ward (2006)

• Methods
• Selected a study area with high deer density
• 23 deer/km2
• Collected pellet groups (n 236)
• Placed in growing medium (6 months)
• 9 fitted GPS collars

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Results

• Seeds germinated47 of pellet groups
• 656 seedlings of 57 species
• 32 of these were non-native to CT
• Use of a Dispersal Index
• Herd on site
• 586-1046 seeds/day/km2 in 2002
• 390-696 seeds/day/km2 in 2003

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Results
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Lowering Reproduction Output of Native Species

• Knight et al. (2009)
• Quantified deer effects on native and exotic
  understory herbs
• Deer access vs. deer exclusion
• Pennsylvania, US

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Lowering Reproduction Output of Native
SpeciesKnight et al. (2009)

• Methods
• Created exclusion plotsveg. census each growing
  season.
• Large-scale extension plot (exclusion)same
  sampling regime
• Percent cover
• Proportion of reproductive plantsNative
  Non-native

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Methods
Knight et al. (2006)
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Results

• Initial Paired plots
• 46 herbaceous species
• Significant community composition divergence at 5
  year mark. Low native presence in access plots
• Exclusion plots- 25 fold increase in of
  flowering individuals.
• 10 hectare Extension Plot
• Similar results on a grander scale
• Native browsed 14 more than exotic (access plot)

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Results
Knight et al. (2006)
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Conclusions

• Deer overabundanceReason to worry!
• Three distinct ways deer facilitate exotic
  species.
• Increase available growing space for new
  seedlings
• Lower reproductive output of native species
• Dispersal of exotic seeds

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Literature Cited

• Knight TM, Dunn JL, Smith LA, Davis J, Kalisz S.
  Deer Facilitate Invasive Plant Success in a
  Pennsylvania Forest Understory. Natural Areas
  Journal (2009) 29110-116.
• Williams SC, Ward JS. Exotic seed dispersal by
  white-tailed deer in southern Connecticut.
  Natural Areas Journal (2006) 26383-390.