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Overabundance of deer facilitate invasive species in Northeastern Forests. Joshua Grace. Roberta Stacy, http://homepage.mac.com/rstacy/. Today’s Presentation. Species background Feeding techniques Invasive plant facilitation Exotic seed dispersal Lower reproductive output of native species

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Overabundance of deer facilitate invasive species in northeastern forests l.jpg

Overabundance of deer facilitate invasive species in Northeastern Forests

Joshua Grace

Roberta Stacy, http://homepage.mac.com/rstacy/


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Today’s 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 germinated—47% 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 plots—veg. census each growing season.

    • Large-scale extension plot (exclusion)—same sampling regime

      • Percent cover

      • Proportion of reproductive plants—Native & 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 overabundance—Reason 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) 29:110-116.

  • Williams SC, Ward JS. Exotic seed dispersal by white-tailed deer in southern Connecticut. Natural Areas Journal (2006) 26:383-390.


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