Impact of Deer Management Inaction on Natural Ecosystems. Anne Hairston-Strang, Ph.D. Forest Hydrologist MD DNR Forest Service

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1 Impact of Deer Management Inaction on Natural Ecosystems Anne Hairston-Strang, Ph.D. Forest Hydrologist MD DNR Forest Service

2 Maryland 39% forested Oak-hickory dominant type Fire-tolerant: strong root sprouting, thick bark Acorns and buds important food for large and small mammals in winter Host for many insects, food for migratory birds Tight nutrient cycling Trend is fewer young oaks Fire suppression Deer population much higher Intermediate shade tolerance and limited harvests Need young oaks in understory and midstory to regenerate Maryland Forests

3 Maryland Forest Trends USFS Forest Inventory and Analysis Data Number of Live Trees on MarylandTimberland by Forest Type and Diameter Class Number of Trees (thousands) 160, , , ,000 80,000 60,000 40, ,000 0 Oaks Red Maple Oaks Red Maple 1 to 3 inch class 5 to 7 inch class

4 Watershed Forests Forest conditions for watershed protection Resistant to disturbances Diverse species Diverse ages Complex structure Resilient following disturbances Multiple layers Actively regenerating for future healthy forest

5 Where s the next forest? Reservoir Forests- understory plots % plots no regen Loch Raven Prettyboy Tridelphia Liberty Rocky Gorge

6 Forest Layers-Patuxent Reservoirs Forest Layers Canopy Closure (%) Midstory (%) % cover Rocky Gorge Triadelphia Shrub Cover (%) Ground Cover (%) Multiple layers usually present Shrub layer low

7 Effects of Deer on Forests Forest Succession Fewer seedlings, can prevent regeneration (Oswalt et al. 2006, Russell et al. 2001) Change species composition, shifts from oak, hemlock (Cote et al. 2004, Rooney and Waller 2003, Ruzicka et al. 2010) Plant Diversity Loss of spring wildflowers, incl. Trillium (Augustine & French 1998) Ginseng (McGraw & Furedi 2005) Lower diversity (Asnani et al. 2006) Increase in invasive plants (Eschtruth and Battles 2009) Increase in grass, sedge, rush, some ferns (Horsley et al. 2003) Wildlife Habitat Quality Loss of layers and diversity (McShea et al. 1997) Impact on songbirds, esp. shrub nesters, mid-canopy nesters, low canopy foragers (DeCalesta 1994, Allombert et al. 2005, Tymkiw 2010) Water Quality Species shifts away from oak/hickory (Lovett et al. 2002) Increase in N mineralization with some invasive species Changes in biomass and carbon sequestration

8 Deer Exclosure Studies Baltimore City Reservoirs 20 sites, established ft x 8 ft Measured annually by Baltimore City staff Methods in Baltimore Reservoir Forest Conservation Plan (after McWilliams, USFS) MD National Capital Park & Planning-Montgomery Co. 9 sites, established m x 20 m Measured sites remeasured 2005 Methods after Storm and Ross 1992 (NPS, USFWS)

9 Near Loch Raven Boat Ramp/Fishing Area

10 All species and seedling sizes Tree Regeneration at Loch Raven Forests with 90% confidence interval, sample SD Seedlings/acre Browsed-LR Exclosure-LR

11 Oak or Hickory only Oak Hickory stems/ac, all sizes, Baltimore Reservoirs Seedlings/acre Browsed-All Exclosure-All Significantly different, p=0.01

12 Seedlings over 1 foot (2500/acre desired, over 4.5 ft preferred) Seedlings/acre over 1 ft, Loch Raven with 90% confidence interval for 8 sites Tree seedlings/acre Browsed-LR Exclosure-LR Year Significantly different, p<0.01

13 Effect of bow hunting Seedings > 1 ft/acre by Reservoir Seedlings/acre Browsed-PB Exclosure-PB Browsed-Lib Exclosure-Lib Browsed-LR Exclosure-LR Loch Raven not hunted during this period. Prettyboy and Liberty Reservoir Forests open to bow hunting. Deer density estimates from infrared survey on Loch Raven in 1999 averaged 39/sq. mi., compared to 10-25/sq. mi. to avoid moderate to heavy damage to vegetation.

14 Percent Cover, 1-ft intervals MNCPPC Deer Exclosures Exclosure-05 Exclosure-96 Browsed-05 Browsed

15 Deer Browse and Invasive Species cumulative number stems Japanese Stiltgrass Exclosure Browsed Control AHFP NWVSP RCRP MNCPPC Park Selective browsing alters species composition Unpalatable species like Japanese stiltgrass (Microstegium) are dense outside of MNCPPC deer exclosures after 10 years Stiltgrass was absent at beginning of study and remains sparse inside exclosures

16 Palatable Invasives Other invasives, like honeysuckle, can increase in exclosures Japanese Honeysuckle Overall, areas outside deer exclosures have more species and greater extent of invasive plants and no tree regeneration % plot covered Exclosure Browsed Control See Eschtruth and Battles 2009, Rossell et. al AHFP NWVSP RCRP MNCPPC Park

17 Interactions and the new ecology of the forest?

18 Conclusions Heavy deer browse reduces tree seedlings and can change species composition in forests, with implications for: Plant diversity Wildlife habitat Water Quality Deer can accelerate invasive species spread, further reducing native tree regeneration The longer the heavy browse, the greater the effects (browse line becomes loss of mid-canopy)

19 Opportunities Forests are long-lived, leaving a large but diminishing window of opportunity. A diversity of native species remains in most forests. Many management options are available for trees and deer, IF we choose to use them.