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 Area of Deer Exclosure Study 15 x 15 m each Fences exclude deer (and probably turkeys) but allow access by most other animals.
average pellet piles/ha Griffy Woods Deer Density Counted pellet piles in early spring 2011 Standard method for estimating deer densities 350 300 250 200 150 100 50 0 Moores Moores Griffy Woods Creek Lilly Dickey Lilly Dickey Woods Creek Woods 13 times more pellet piles at Griffy 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 vegetation contacts tape 140 cm 60 cm 20 cm
# Touches by Vegetation # Touches by Vegetation Vegetative Structure 20 16 12 8 4 0 P < 0.0001 P = 0.0003 Unfenced Fenced P = 0.0211 20 60 140 Height (cm) Vegetation is significantly more abundant inside exclosures at all heights within browse range. Data collected after 2-3 years of fencing. 300 250 200 150 100 50 0 Japanese stiltgrass is more abundant in controls than exclosures. Suggests interaction between deer and invasive species. Plots invaded by Stiltgrass Control Exclosure 20 60 140 Height Above Ground (cm)
Effects on Woody Plants open forest plot fenced forest plot 28 woody plants 7 species 204 woody plants 21 species
ash pawpaw multiflora rose spicebush privet hickory honeysuckle sassafras beech grape musclewood sugar maple viburnum barberry # new seedlings Tree and Shrub Seedlings 40 35 30 P = 0.0047 Outside exclosures: - No native trees are regenerating Control Exclosure 25 20 15 10 - Dominated by invasives and unpalatable species unpalatable invasive native trees 5 0 tree or shrub species
Growth Rate: - Tree seedlings grow faster inside exclosures - All types of woody plants grow faster in exclosures, especially invasive shrubs
Density Facilitation Inhibition? Time
Mean Species / Plot Species Richness of Spring Ephemerals 40 35 P = 0.017 Control 30 25 P = 0.046 P = 0.005 Exclosure 20 P = 0.2922 15 10 5 0 2009 2010 2011 2012
Total Mice Captured Effects on Forest Animals Live trapped mice and released in same location More mice inside deer fences. Juveniles found much more often in exclosures (none in controls 2011) 50 45 40 35 30 25 20 15 10 5 Control Exclosure P = 0.0012 0 ADULT JUVENILE image: http://www.cedarcreek.umn.edu/mammals/cricetidae.html with help from Evie Rynkiewicz
Mean Ticks / Plot Sample ticks with CO 2 traps Sampling period was very hot and after peak questing time. Ticks 2.5 2 P = 0.018 May be more indicative of environmental conditions than host availability 1.5 1 0.5 Dermacentor variabilis 0 Control Exclosure with help from Evie Rynkiewicz
soil compaction (kg/cm2) Soil Compaction 1.6 1.4 1.2 1 0.8 controls exclosures Soil inside exclosures is significantly less compacted than soil in control plots after only 2 years of fencing! 0.6 0.4 Treatment effect P < 0.0001 0.2 0 lowland ridge slope habitat Habitat effect P < 0.0001 with Jeremiah Henning & Peggy Schultz
Total Spore Abundance AMF Species Richness Mycorrhizal Diversity 40 35 30 control exclosure 5 4.5 4 3.5 control exclosure 25 3 20 2.5 15 2 10 1.5 1 5 0.5 0 0 0-5 cm 5-15 cm 0-5 5-15 Soil Depth Soil Depth (cm) 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 with Microstegium without 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
Fence No fence Potential Outcomes: Associational Resistance Mv no Mv Predator Refuge 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
Collaborators Peggy Schultz Jeremiah Henning Rich Phillips Burney Fischer (SPEA) Assistance 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 Acknowledgements Funding USDA Forest Service, Northern Research Station Indiana Hardwood Ecosystem Experiment Indiana Academy of Science