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

effects of large herbivores • consuming & trampling plants • changing nutrient cycles • 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 of 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 500 400 Number of Elk 300 200 100 0 1978 1981 1984 1987 1990 1993 1996 1999 Year

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

Baccharis Lupinus open N P lo t L ayo u t % B a cc h aris % Lu p in us % O pe n 0.5 0 0.5 Kilometers experimental plots on Tomales Point

Baccharis Lupinus open Baccharis N grassland P lo t L ayo u t % B a cc h aris % Lu p in us % O pe n 0.5 0 0.5 Kilometers experimental plots on Tomales Point

Baccharis Lupinus open Lupinus grassland N P lo t L ayo u t % B a cc h aris % Lu p in us % O pe n 0.5 0 0.5 Kilometers experimental plots on Tomales Point

Baccharis Lupinus open open grassland N P lo t L ayo u t % B a cc h aris % Lu p in us % O pe n 0.5 0 0.5 Kilometers experimental plots on Tomales Point

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

neighborhood effects: abundance 40 shrub x elk interaction, p=0.0478 elk present Holcus Abundance/m 2 /Plot elk excluded 30 20 10 0 open shrub Association

neighborhood effects: biomass 600 shrub x elk interaction, p=0.0033 Holcus Biomass/Plot (g/m 2 ) elk present elk excluded 400 200 0 open shrub Association

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?

shrub cover 80 elk present p=0.083 elk excluded Shrub Percent Cover/Plot 60 40 20 0 Baccharis Lupinus Open Habitat Type

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 elk present NMS elk excluded Axis 2 stress=12.17 Axis 1 MRBP: A=0.35, p<0.0004

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

total abundance 2000 elk present 1800 elk excluded Mean Abundance/m 2 /Plot 1600 1400 1200 1000 800 600 400 200 0 Baccharis Lupinus Open Habitat Type

abundance: annuals 1500 Exotic Monocot elk present p=0.002 1250 elk excluded 1000 750 Mean Abundance/m 2 /Plot 500 250 0 80 100 Exotic Dicot Native Dicot p=0.071 p=0.048 80 60 60 40 40 20 20 0 0 Baccharis Lupinus Open Baccharis Lupinus Open Habitat Type Habitat Type

abundance: perennials elk present 400 100 p=0.83 p=0.46 Exotic Monocot elk excluded Native Monocot 300 75 Mean Abundance/m 2 /Plot 200 50 100 25 0 0 200 30 p=0.77 p=0.34 Native Dicot Exotic Dicot 25 150 20 100 15 10 50 5 0 0 Baccharis Lupinus Open Baccharis Lupinus Open Habitat Type Habitat Type

total species richness 60 elk present elk excluded Mean Species Richness/Plot 50 40 30 20 10 0 Baccharis Lupinus Open Habitat Type

species richness: annuals 10 p=0.002 elk present Exotic Monocot 8 elk excluded 6 Mean Species Richness/Plot 4 2 0 15 15 p=0.396 Native Dicot Exotic Dicot p=0.044 12 12 9 9 6 6 3 3 0 0 Baccharis Lupinus Open Baccharis Lupinus Open Habitat Type Habitat Type

species richness: perennials 5 12 p=0.343 Native Monocot Exotic Monocot 10 4 8 elk present 3 p=0.021 6 elk excluded Mean Species Richness/Plot 2 4 1 2 0 0 6 12 Native Dicot Exotic Dicot p=0.152 p=0.0869 5 10 4 8 3 6 2 4 1 2 0 0 Baccharis Lupinus Open Baccharis Lupinus Open Habitat Type Habitat Type

biomass: annuals and perennials 300 elk present A. Annual p=0.0256 250 elk excluded Mean Aboveground Dry Biomass/Plot (g/m 2 ) 200 150 100 50 0 600 B. Perennial 500 p=0.008 400 300 200 100 0 Baccharis Lupinus Open Habitat Type

biomass: thatch 600 elk present treatment x veg. type Mean thatch/Plot (g/m 2 ) elk excluded p=0.0045 500 400 300 200 100 0 Baccharis Open Habitat Type

making sense of responses - shrub cover - richness [native perennial dicots] - thatch biomass - living biomass [perennials] - biomass [annuals] - richness [annuals] & [native per. monocots] - abundance [annuals] X - Holcus lanatus

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