Variable responses of a California grassland to the reintroduction - - PowerPoint PPT Presentation

Variable responses of a California grassland to the reintroduction of tule elk

Brent Johnson - National Park Service

large mammalian herbivores

• consuming & trampling plants
• changing nutrient cycles

effects of large herbivores

• alter competition between plants
• modify successional processes

human impacts on herbivores

• altered distribution and abundance
• 10,000+ years in N. America
• negative impacts increased with the arrival
• f Europeans
• increased hunting and habitat loss
• conservation efforts
• species and habitat protection
• reintroductions are often necessary
• many herbivore populations are now

increasing

human impacts

• bison
• 1800: 30-60 million
• 1889: fewer than 1,000
• protection & reintroduction
• presently 5,000–6,000 in U.S
• still increasing

prevailing focus of reintroduction

• target species
• population size
• genetic diversity
• health of population
• less emphasis on recipient community

reintroduction into altered landscapes

• fragmented
• movement patterns changed
• reduction of predator populations
• transformed plant communities
• non-native species

Tule Elk (Cervus elaphus nannodes)

• endemic to California
• subspecies of North

American elk

tule elk through the years

• 1769 – 500,000 tule elk in California
• 1850 – <10 tule elk in California’s Central Valley
• 1873 – protected species
• 1905 – reintroduction efforts began
• 1970 – 500 tule elk throughout CA
• Present – 2,700 individuals in 22 sites
• 1978 – 13 tule elk to Tomales Point Elk Reserve

elk population on Tomales Point

100 200 300 400 500

1978 1981 1984 1987 1990 1993 1996 1999

Year Number of Elk

Tomales Point Elk Reserve

• Point Reyes National Seashore, Marin Co.
• 1030 ha enclosed reserve

Tule Elk in an altered landscape

• movements restricted to the point
• large predators absent
• transformed by introduced plant species
• unclear consequences

research questions

• Does an invasive grass avoid elk

herbivory by associating with a native shrub species?

• Do elk play a critical role in maintaining

grasslands by slowing the colonization of shrubs?

• How does herbivory by reintroduced elk

alter plant communities, and does this vary with habitat type?

experimental design

• large scale exclosure experiment
• established in 1998 by National Park Service
• 24 plots: 12 fenced and 12 unfenced
• 36 x 36 m

36 m

experimental plots on Tomales Point

N

P lo t L ayo u t

% B

a cc h aris

% Lu

p in us

% O

pe n 0.5 0.5 Kilometers

Baccharis

• pen

Lupinus

experimental plots on Tomales Point

N

P lo t L ayo u t

% B

a cc h aris

% Lu

p in us

% O

pe n 0.5 0.5 Kilometers

Baccharis

• pen

Lupinus

Baccharis grassland

experimental plots on Tomales Point

N

P lo t L ayo u t

% B

a cc h aris

% Lu

p in us

% O

pe n 0.5 0.5 Kilometers

Baccharis

• pen

Lupinus

Lupinus grassland

experimental plots on Tomales Point

N

P lo t L ayo u t

% B

a cc h aris

% Lu

p in us

% O

pe n 0.5 0.5 Kilometers

Baccharis

• pen

Lupinus

• pen

grassland

neighborhood effects

• Does an invasive grass avoid elk

herbivory by associating with a native shrub species?

• Holcus lanatus (velvet grass)
• non-native perennial grass
• invasive in California’s coastal

grasslands

• Baccharis pilularis
• native shrub
• widespread

neighborhood effects

• only in Baccharis plots
• abundance (2003) and

biomass (2002) of Holcus

elk excluded elk present

X X X X X X X X

10 20 30 40

neighborhood effects: abundance

shrub x elk interaction, p=0.0478

• pen

shrub

Association Holcus Abundance/m2/Plot

elk present elk excluded

200 400 600

neighborhood effects: biomass

shrub x elk interaction, p=0.0033

• pen

shrub

Association Holcus Biomass/Plot (g/m2)

elk present elk excluded

neighborhood effects

• native shrubs provide refuge for an exotic

grass by protecting it from elk herbivory

shrub cover

• Do elk play a critical role in maintaining

grasslands by slowing the colonization of shrubs?

20 40 60 80

shrub cover

p=0.083

Shrub Percent Cover/Plot

Baccharis Lupinus Open

Habitat Type

elk present elk excluded

community composition

• How does herbivory by reintroduced elk

alter plant communities, and does this vary with habitat type?

community composition

• 2002
• harvested aboveground living and dead

biomass

• 2003
• abundance (number of individuals)
• species richness

multivariate analysis

• complexity of community data
• reduce dimensionality of data set
• non-metric multidimensional scaling

(NMS or nMDS)

• multi-response blocked permutation

procedure (MRBP)

multivariate analysis

Axis 1 Axis 2

elk present elk excluded

stress=12.17

MRBP: A=0.35, p<0.0004 NMS

community: statistical analysis

• multifactorial MANOVAs & ANOVAs
• elk treatment (present or absent)
• grassland type (Baccharis, Lupinus, open)
• plot pair, nested within grassland type
• response variables

plant functional groups/life forms

• annual dicots
• native and exotic
• annual monocots
• exotic
• perennial dicots
• native and exotic
• perennial monocots
• native and exotic

200 400 600 800 1000 1200 1400 1600 1800 2000

total abundance

elk present elk excluded

Mean Abundance/m2/Plot

Baccharis Lupinus Open

Habitat Type

Exotic Monocot 250 500 750 1000 1250 1500 Exotic Dicot 20 40 60 80 20 40 60 80 100 Native Dicot

abundance: annuals

elk present elk excluded

Mean Abundance/m2/Plot p=0.002 p=0.071 p=0.048

Baccharis Lupinus Open

Habitat Type

Baccharis Lupinus Open

Habitat Type

Exotic Monocot 100 200 300 400 25 50 75 100 Native Monocot Exotic Dicot 50 100 150 200 5 10 15 20 25 30 Native Dicot

abundance: perennials

elk present elk excluded Baccharis Lupinus Open

Habitat Type

Baccharis Lupinus Open

Habitat Type Mean Abundance/m2/Plot p=0.77 p=0.83 p=0.46 p=0.34

10 20 30 40 50 60

total species richness

Baccharis Lupinus Open

Habitat Type

elk present elk excluded

Mean Species Richness/Plot

species richness: annuals

Exotic Monocot 2 4 6 8 10 Exotic Dicot 3 6 9 12 15 3 6 9 12 15 Native Dicot

Baccharis Lupinus Open

Habitat Type

Baccharis Lupinus Open

Habitat Type

elk present elk excluded

Mean Species Richness/Plot p=0.044 p=0.002 p=0.396

2 4 6 8 10 12 Native Dicot Exotic Dicot 1 2 3 4 5 6

species richness: perennials

Baccharis Lupinus Open

Habitat Type

Baccharis Lupinus Open

Habitat Type

elk present elk excluded

Exotic Monocot 1 2 3 4 5 2 4 6 8 10 12 Native Monocot Mean Species Richness/Plot p=0.343 p=0.152 p=0.021 p=0.0869

• A. Annual

50 100 150 200 250 300

• B. Perennial

100 200 300 400 500 600

biomass: annuals and perennials

p=0.008 p=0.0256

Baccharis Lupinus Open

Habitat Type Mean Aboveground Dry Biomass/Plot (g/m2)

elk present elk excluded

100 200 300 400 500 600

biomass: thatch

Mean thatch/Plot (g/m2)

Baccharis Open

Habitat Type

treatment x veg. type p=0.0045

elk present elk excluded

making sense of responses

• shrub cover
• richness [native perennial dicots]
• thatch biomass
• living biomass [perennials]
• biomass [annuals]
• richness [annuals] & [native per. monocots]
• abundance [annuals]
• Holcus lanatus

X

conclusions

• they’re back!
• complex
• elk have +/- effects on natives and exotics
• no easy answers
• potential solutions
• manage for mosaic of states

acknowledgements

advisor: Hall Cushman field assistants: Catherine Cumberland, Amy Nadell, Trisha Tierney National Park Staff: Natalie Gates, Michelle Coppoletta & Dave Schirokauer defense committee: Dan Crocker & David Stokes statistical advice and consoling: Karina Nielsen & Nathan Rank the Cushman lab: Michelle Cooper, Jim Coleman, Emiko Stevens, Melina Kazanitas & Jeff Amaral

Tomales Point Elk Reserve