Effects of overabundant deer in the lower Midwest on native biodiversity and interactions with invasive species Keith Clay, Daniel Johnson, Angie Shelton, Luke Flory and Cynthia Huebner
Causes of High Deer Populations – improved forage from agriculture – elimination of natural predators – increase in edge habitat – supplemental feeding – warm winters – hunting biased towards bucks Images from Fairfield County, Conn. Deer Management Alliance. www.deeralliance.com
History of Deer Population in Indiana • early 1900s: Deer eliminated from Indiana by hunting and habitat destruction • 1930s: Deer reintroduced to state • 1950s: Populations re-established and modern hunting programs begun • 1990s - present: Historically high deer populations • Today: Forest vegetation in Bloomington area more visibly affected by deer than nearby areas
Shelton, A.L ., J.A. Henning, P. Schultz and K. Clay. 2014 . Effects of abundant white-tailed deer on vegetation, animal communities, mycorrhizal fungi, and soils. Forest Ecology and Management 320: 39-49. Johnson, D. J., S. L. Flory, A. Shelton, C. Huebner and K. Clay. 2015 . Interactive effects of a non‐native invasive grass Microstegium vimineum and herbivore exclusion on experimental tree regeneration under differing forest management. Journal of Applied Ecology 52: 210-219.
Deer Exclosure Study at IU ’ s Griffy Woods Griffy Lake Region • 15 fenced exclosures and 15 unfenced controls • Constructed 2005 – 2010 • 15 x 15 m each Area of Deer Exclosure Study Fences exclude deer (and probably turkeys) but allow access by most other animals.
Griffy Woods Deer Density • Counted pellet piles in early spring 2011 • Standard method for estimating deer densities 350 average pellet piles/ha 300 250 200 13 times more 150 pellet piles at 100 Griffy Woods 50 0 Griffy Woods Moores Creek Moores Lilly Dickey Woods Lilly Dickey Griffy Woods Creek Woods
Questions: - What are effects of exclosures on native vegetation? - On invasive plant species? - On animals? - On soil properties?
Vegetative Structure • Run tape at 3 heights above ground level • Count number of times 140 cm vegetation contacts tape 60 cm 20 cm
Vegetative Structure 20 Unfenced P < 0.0001 # Touches by Vegetation 16 Japanese stiltgrass is more Fenced abundant in controls than exclosures. 12 Suggests interaction between P = 0.0003 deer and invasive species. 8 P = 0.0211 4 Plots invaded by Stiltgrass 300 # Touches by Vegetation Control 0 250 20 60 140 Exclosure 200 Height (cm) 150 100 Vegetation is significantly more abundant inside exclosures at all heights within 50 browse range. Data collected after 2-3 0 20 60 140 years of fencing. Height Above Ground (cm)
Effects on Woody Plants open forest plot fenced forest plot 28 woody plants 204 woody plants 7 species 21 species
Tree and Shrub Seedlings 40 P = 0.0047 Outside exclosures: Control 35 - No native trees are Exclosure 30 regenerating 25 - Dominated by invasives and # new seedlings unpalatable unpalatable species 20 invasive 15 native trees 10 5 0 ash pawpaw multiflora rose spicebush privet hickory honeysuckle sassafras beech grape musclewood sugar maple viburnum barberry tree or shrub species
Growth Rate : - Tree seedlings grow faster inside exclosures - All types of woody plants grow faster in exclosures, especially invasive shrubs
Facilitation Inhibition ? Density Time
Species Richness of Spring Ephemerals 40 35 Control P = 0.017 Exclosure 30 P = 0.046 Mean Species / Plot P = 0.005 25 P = 0.2922 20 15 10 5 0 2009 2010 2011 2012
Effects on Forest Animals • Live trapped mice and released in 50 same location Control 45 • More mice inside deer fences. Exclosure 40 • Juveniles found much more often in Total Mice Captured P = 0.0012 35 exclosures (none in controls 2011) 30 25 20 15 10 5 0 ADULT JUVENILE with help from Evie Rynkiewicz image: http://www.cedarcreek.umn.edu/mammals/cricetidae.html
Ticks • Sample ticks with CO 2 traps 2.5 • Sampling period was very hot P = 0.018 and after peak questing time. 2 • May be more indicative of Mean Ticks / Plot 1.5 environmental conditions than host availability 1 0.5 0 Control Exclosure Dermacentor variabilis with help from Evie Rynkiewicz
Soil Compaction 1.6 • Soil inside exclosures is controls 1.4 soil compaction (kg/cm2) significantly less exclosures 1.2 compacted than soil in 1 control plots after only 2 years of fencing! 0.8 0.6 Treatment effect P < 0.0001 0.4 0.2 Habitat effect P < 0.0001 0 lowland ridge slope habitat with Jeremiah Henning & Peggy Schultz
Mycorrhizal Diversity 40 5 control control 4.5 35 exclosure exclosure 4 30 Total Spore Abundance 3.5 AMF Species Richness 25 3 20 2.5 2 15 1.5 10 1 5 0.5 0 0 0-5 cm 5 - 15 cm 0-5 5-15 Soil Depth (cm) Soil Depth No significant effect of treatment. Some effect of plot and depth. With Jeremiah Henning and Peggy Schultz
Conclusions : - Exclosures resulted in increases in spring ephemerals, native tree seedlings and invasive shrubs - Increased growth rate of woody plants - Increased abundance of mice and ticks but no effects on salamanders or earthworms - Decreased soil compaction and trend for increased mycorrhizal diversity and abundance
How do abundant deer and invasive species interact to affect forest regeneration? Microstegium vimineum , an invasive annual grass
Six sites – three with no timber harvest for > 20 yrs, three with timber harvest w/i 3 yrs 1m 1m 1-2m without Microstegium with Microstegium Blocks with two paired plots (x10 per site) Herbicide sprayed to remove Microstegium (pre-emergent sprayed year 2)
Half of each plot fenced to exclude deer and other vertebrate herbivores 1m 1m 1-2m with Microstegium without Microstegium
20 tree seedlings of five species planted per plot 1m 1m 1-2m with Microstegium without Microstegium Followed growth and survival ( Acer saccharum, Prunus serotina, Quercus alba, Q. rubra and Q. shumardii) for two years
Potential Outcomes : Associational Resistance Fence No fence Mv Predator Refuge no Mv Interspecific Competition
Tree Seedling Survival Factor P Removal <0.0001 Exclosure <0.0013 Species <0.027
Seedling Biomass Factor P Removal <0.0001 Management <0.0013 Species <0.0001 R x M <0.032
Conclusions : - Removal of Microstegium improved seedling performance - Excluding herbivores also improved seedling performance but less than removal - No removal x exclosure interactions - Management history affected biomass, and interacted with removal - Variation among species. Removal especially good for oaks
Acknowledgements Collaborators Funding • Peggy Schultz • • Jeremiah Henning USDA Forest Service, • Rich Phillips Northern Research Station • Burney Fischer (SPEA) • Indiana Hardwood Ecosystem Experiment Assistance • Indiana Academy of Science • Michael Chitwood and IURTP staff • Evie Rynkiewicz and Clay Lab Group • ISCC: Thomas Jackson & Xuefu Wang • Curtis Conrad, Katherine Zaiger, Nathan Wells, Julia Ferguson, Rachel Maranto, Elizabeth Ridens, Barrett Goodale, Sean Fox, Eric Menigat, Piotr Madej, Hannah Milano, Alicia Cooley, Environmental Biology students
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