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Overabundance of deer facilitate invasive species in Northeastern Forests

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

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  1. Overabundance of deer facilitate invasive species in Northeastern Forests Joshua Grace Roberta Stacy, http://homepage.mac.com/rstacy/

  2. Today’s Presentation • Species background • Feeding techniques • Invasive plant facilitation • Exotic seed dispersal • Lower reproductive output of native species • Management Implications

  3. Species of Interest • White-tailed deer • Odocoileus virginianus • Population on the rise • Broad range Nelson & Davis

  4. Deer density map- QDMA Green ( less than 15 / sq mile) Light orange shades ( 15-45 /sq mile ) Dark orange ( greater than 45 /sq mile )

  5. Odocoileus virginianus • Herbivores • Grazers by choice, browsers by necessity • Feed by season www.forestwonderer.com/id13.html www.buckmanager.com

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. Results

  12. 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

  13. 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

  14. Methods Knight et al. (2006)

  15. 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)

  16. Results Knight et al. (2006)

  17. 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

  18. 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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