1. Deer as a facilitator of exotic species invasion
in mature forests of Virginia
William McShea
Conservation Ecology Center, Smithsonian Conservation
Biology Institute, Front Royal, VA

2. Appalachian Mountains
/Ridge and Valley
• World-class temperate forest
both for diversity and extent
SNP & M,GW&J NFs
• Large blocks of public forest
• Primarily deciduous forest
• Mature 2° forest (>100 yrs)
• Close to urban centers

3. Stressors on eastern deciduous forests
• Forest loss, fragmentation, and parcelization
• Loss of critical species (American chestnut, wolves, cougars)
• Climate change (temperature, storm severity and frequency)
Invasive plant and animal species White-tailed deer
– you know the story – you know the story

4. Browsing by deer alters forest succession pathways and sustainability

5. When Should We Worry About “Overabundant”
Species
• Cause significant economic loss
• Lower diversity across the landscape
• Unsustainable demographics of rare species
• Alters pathways for productivity or succession

6. A species that, other than as a result of an introduction,
Native Species historically occurred, or currently occurs, in a particular
ecosystem.
Any species, including its seeds, eggs, spores or other
Exotic Species biological material capable of propagating that
species, that is not native to a particular ecosystem.
Invasive Species An exotic species whose introduction does, or is
likely to, cause economic, human health or
environmental harm.
In US – 20,000 native plant sp.; 4,000 alien plants; 400 invasive plants
Lets agree to worry about invasive (native or exotic) first & exotic later

7. Abundant ground cover – little of it native species

8. Hidden native species are
denied light but also invisible
to deer??

9. The problem – low recruitment and diversity
of native plants
• White-tailed deer prefer browsing native
vegetation compared to exotic species, so
native woody species not only compete with
invasive species for light, but must survive
preferential herbivory by deer.
The Solutions
• Remove invasives. But - when invasive plants are
removed - do plant populations increase or does herbivory
increase?
• Reduce deer numbers. But - when deer are removed -
do natives increase or do invasive plants respond more
quickly?

10. Direct consumption (-) (-)
(+) Competition for light
(-)
and nutrients
Can you increase recruitment
Predictions: of woody seedling or species richness
1) Reduced invasives of herbaceous plants by fixing only
will increase herbivory one
2) Reduced herbivory problem???
will increase invasives Are you promising something you can
not deliver when you try only one??

11. Project Details
• Co-Investigators – Norm Bourg, Chad Stewart
• C & O Canal and SCBI – 330 Plots
• 4 x 4 m plot with 4 1x1 m subplots within each
• ID and count all native herbaceous and woody plants
< 30cm high, within each sub plot. All saplings ( > 30
cm) within each plot. For grasses and ferns estimate
% cover.
• Identify all exotic species, count and estimate %
cover.
• Calculated species richness, species diversity
(Shannon index, H’), and number of individuals per
plot in 2005 (pre) and 2007 and 2009

12. Do Nothing
179 plots NN 53 plots PN
45 plots NF 49 plots PF

13. Measured all plots in summer 2005 and
select management category

14. Pulled Invasives twice
each year: may and august

16. Timeline
• 325 plots established 2005 (+ 8 in 2006)
• Invasives pulled twice each year & fences maintained
• Plots resurveyed in 2007 and 2009

17. After 4 years: Woody Species (> 30 cm)
14
Mean Number of Stems
12
10
Recommended
stocking rate for native (all)
8
seedlings native (trees)
6
invasives (all)
4
2
0
Control Pulled Fenced Pull/Fence
Treatments
2009 Sapling Data
Fencing (not pulling) increased native species (total or just trees)
Invasive species highest when deer excluded
Neither treatment achieved needed stocking rate after 4 years

18. 1
Red Maple
0.9
No treatments increased numbers
0.8
0.7
Number of Individuals/Plot
0.6
0.5
0.4
0.3
0.2
0.1
0
Control Fenced Only Pulled Only Pulled and Fenced
Treatment
2005 2009

19. 1
0.9 Quercus Species
Only combined treatment increased numbers
0.8
Number of Individuals/Plot
0.7 *
0.6
0.5
0.4
0.3
0.2
0.1
0
Control Fenced Only Pulled Only Pulled and Fenced
2005 2009 Treatment

20. Oak Saplings in 2009
Treatment N of Plots N of Saplings Density
Control 183 4 0.02/plot
Pulled 55 0 0.00/plot
Fenced 50 6 0.12/plot
Pull/Fence 48 16 0.33/plot

21. Forestry matters: decline of oaks in eastern forests
JWM 2007, McShea et al. based on FIA data
• Decline in proportion of intermediate-sized oaks in eastern
forests: 32% in 1989 down to 21% in 2000
•stem density of
maples doubled from
660 (+ 201) in 1989
1303 (+246) in 2000
• nosignificant change
in mast production yet
• maples are immune to
deer and invasives and
(lack of fire), while
oaks are not

23. Setting the Stage for this Study
Study took place on SIGEO Plot at SCBI
SIGEO Origins
Smithsonian Tropical Research Institute (STRI)
In 1980, Steve Hubbell and Robin Foster established a 50-
hectare (124-acre) forest plot in Panama. The survey
methodology was unprecedented in scale and scope.
Every tree greater than or equal to 1cm diameter was
identified, measured, tagged, and mapped. All trees are
re-censured every 5 years.
A “base layer” of tree community
is overlaid with multiple explanatory
and ancillary layers to understand forest
community structure
Barro Colorado Island

24. SCBI - SIGEO Plot Location
26 ha plot is created in 2008
With 20 x 20 m grid cells
with each post marked with row and column
Due to be resurveyed in 2013

25. Tree Measurements
- all stems > 1cm dbh measured, mapped, tagged & identified to species
Layers subsequently added: DEM, Downed woody debri; Soil nutrients and carbon;
Seedlings; Small mammals; Invasive worms; Invasive exotic plants

26. SCBI - SIGEO Forest Dynamics Plot
Initial census of 25.6 ha completed:
- 40,180 stems (29,914 living); 26 Families, 38 genera
- 62 species of free-standing trees & shrubs, 54 of which are native;
Composition:
- Mature secondary Eastern mixed deciduous forest – dominant species:
Canopy: Understory:
- Liriodendron tulipifera Asimina triloba
- Carya glabra Carpinus canadensis
- Carya tomentosa Cornus florida
- Quercus alba Cercis canadensis
- Q. rubra Amelanchier arborea
- Nyssa sylvatica
- Fraxinus americana Shrubs: Lindera benzoin (>17,000 stems)
- Succeeding to oak-hickory forest (8 spp. oaks, 4 spp. hickory + 2 Juglans spp.)

27. Added Twist to Plot
26 ha site includes 4 ha deer exclosure
erected in 1990
8 ft fence with 4 ft of American wire fencing
(set with larger mesh on bottom)
and 6 strands of high tensile wire (4 ft)
8 ft 2”x2” spacers with 6 slots (10o angle)
hold high tensile fence in place

28. Idea for study came mainly from
distribution of Microstegium in plot
relative to deer exclosure
4 ha deer exclosure erected in 1990 prior
to invasion of most exotic species
1) Are invasive plant distributions shaped
by distribution of deer
2) Underlying mechanisms for impact
Protocol for invasive species study
• All 20 x 20 m grid cells examined in 2010
• All invasive species recorded as present/absent
• All individual clusters counted except
Microstegium (5 abundance classes based on %)
• Distributions matched with data layers

29. Common invasive plants in forest
Wineberry Rubus phoenicolasius
Japanese barberry Berberis thunbergii

30. Common invasive plants in forest
Japanese stiltgrass Microstegium vimineum
Multiflora rose Rosa multiflora

31. Experimental Design
Four step process
1) Use canonical correlations to determine tree communities within each grid cell and select
section of grid (reference plot) that “matched” deer exclosure
2) Insure that the range of all parameters within deer exclosure and reference plot are
encompassed by the remaining squares (Phosphorus issue)
3) Permutation trees (conditional inference tree; party in R) were constructed using all
squares outside of deer exclosure and reference plot (p < 0.99 to prune tree)
4) Repeated process using significant variables identified in first tree - using gird cells from
deer exclosure and reference plot while adding “Fence” as variable

32. SIGEO study area (20 x 20 m2 quadrats)
Colors reflect community types,
created using a cluster analysis based
on basal area of the 10 dominant
tree species in each unit (80%).
Reference Plot (4 ha)
matching communities
Deer Exclosure (4 ha)
erected 1990

33. Norm Bourg
Jenny McGarvey and Xiaoli Shen

34. Min Max Mean SD
SPECIES ABUNDANCE
ROMU individual number (clumps) 0 33 1.01 2.96
BETH individual number (clumps) 0 138 6.44 11.79
RUPH individual number (clumps) 0 125 6.33 12.96
%MIVI cover in category
0 4 1.76 1.2
0 = absent; 1 = 1-25%; 2 = 26-50%; 3 = 51-75%; 4 = 76-100%
Comfrey individual number 0 116 10.99 18.83
PREDICTOR VARIABLES
No. of deer fecal pellet groups 0 52 1.93 4.99
Distance from quadrat center to forest edge (m) 21 523 282.89 115.5
Transformed aspect† -1 1 -0.008 0.72
Slope (degrees) 1.9 21.4 10.34 3.81
Topographic convergence index‡ 0 280.8 34.45 30.35
Woody species richness 3 20 10.16 2.85
No. of woody stem 7 582 60.37 71.22
pH 3.96 6.11 5.09 0.47
ECEC (estimated cation exchange capacity, cmol/kg) 6.98 41.26 18.13 5.65
Nitrogen (mg/kg) 2.13 9.09 4.3 1.16
Phosphorus (mg/kg) 10.31 35.05 20.1 5.82
% canopy openness (hemispherical photo) 3.69 20.89 9.07 2.16

35. Test Case – known deer-dispersed plant
Wild Comfrey Cynoglossum virginianum
11.39 1.17 38.49 4.48 4.15 0.79
21.79 2.20 6.21 1.71 0.01 0.01

36. Multiflora rose Rosa multiflora
More abundant in exclosure
Higher nitrogen levels increase abundance
1.00 + 0.15 4.58 + 1.01
0.29 + 0.10 1.55 + 0.43 0.22 + 0.05

37. Japanese barberry Berberis thunbergii
Soil cations important (organic content)
Twice as abundant outside of exclosure
2.17 + 0.39 5.32 + 0.80 11.16 + 1.0
3.26 + 0.25 1.80 + 0.33

38. Wineberry Rubus phoenicolasius
High nitrogen and low shrub density
increases abundance
- but in cells with low nitrogen more abundant
with deer
3.25 + 0.51 20.9 + 2.68 9.82 + 1.28
2.25 + 0.36 0.22 + 0.09 7.11 + 1.29

39. Japanese stiltgrass
Microstegium vimineum
Highest abundances found with low
density of shrubs and high pH or high
Levels of P and understory openness
Absence found almost only within
deer exclosure
0 = absent; 1 = 0-25%; 2 = 26-50%; 3 = 51-75%; 1.76+0.13 2.60+0.1 1.39+0.09 1.67+0.16 2.33+0.12
4 = 76-100%.
1.58+0.14 2.20+0.12 0.49+0.06

41. Hard Seed Crops Critical for Wildlife Populations in
Eastern Forests
• In order to produce seed we need mature trees
• In order to produce mature trees we need:
– Lower densities of deer
– Control of invasive plants
– Periodic light reaching forest floor – disturbance
• Fire, harvest, hurricanes, insect outbreaks
These are not problems with seedling establishment but
problems with the transition from seedling to sapling

42. A “Perfect” World
• Overall Lower Density of Deer
• Removal of invasive, exotic species
• Create Spatial and Temporal Heterogeneity
• Increase the Movement of Ungulates with
Respect to Resources (Predators)
• Increased Avenues for Flow of Productivity and
thereby Increased Biodiversity

43. Virginiathis all mean?
What does
Working
Landscapes
• Deer do play a role in establishment of some exotic species in this forest
• For one species (multiflora rose) the distribution of the plant was not
influenced by deer – bird-dispersed seeds
• Mechanism may not be the same for each exotic species
• Mechanisms for facilitation are not clear from this study
1 1
• Deer actively spread seeds through feces or on coat – possible but unlikely
Bill McShea , Maria Van Dyke , and James
• Deer activity changes soil characteristics and nutrient levels – possible (N, ECEC, P lower)
2
• Absence of deer reduces leaf litter disturbance - possible
Barnes
• Native plants established before arrival of most invasives (1990 fence) - possible
1. Smithsonian Conservation Biology Institute, Front Royal, VA
2. Piedmont Environmental Council, Warrenton, VA
Mission: To encourage the sustainable use of Virginia
landscapes for biodiversity
www.vaworkinglandscapes.org

44. Develop a Conservation Network:
Landowners

45. Grassland Research:
Measuring biodiversity on grasslands in the Northern
Shenandoah Valley and Piedmont Regions
1. Richness and Abundance of:
• Birds
• Pollinators
• Native Plants
2. Effects of Management programs on these three
biota
3. Conversion of introduced (CSG) to native grasslands
(WSG)

46. Wildlife WSG All Fields = 20 Acres
Not hayed
Not grazed
New and/or
Managed WSG
Hayed or
≤ 2 yrs old
Wildlife CSG
Not hayed
Not grazed
Managed CSG
Hayed or grazed

47. Citizen Science
Birds
Survey Protocol Techniques
Field Identification Training
Native Bees and Butterflies
Surveys Protocol Techniques
Ecology and Life History
Identification Training
Plants
Survey Protocol Techniques
Field and Microscope Identification

48. Fruit -eating
birds
Ground-nesting Under-story
birds seedlings
Non-mast
seeds
mesopredators
Rodents Humans
Ticks
Gypsy moths
Pathogens
Mast-eating Pathogens
birds DEER
Mast Production
Oak seedlings
Oak Trees
Fire
Sunlight Soil Nutrients Soil Moisture