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Identifying persistent effects of exotic pasture grasses and their influence on rosemary scrub community and ecosystem restoration Sarah Hamman, Christine Hawkes University of Texas Eric Menges Archbold Biological Station Background

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Presentation Transcript
slide1
Identifying persistent effects of exotic pasture grasses and their influence on rosemary scrub community and ecosystem restoration

Sarah Hamman, Christine Hawkes

University of Texas

Eric Menges

Archbold Biological Station

background
Background
  • Over 1 million acres are used for grazing and pasture land in Florida
    • 10% of agricultural lands are abandoned each year (USDA, 2004)
  • Introduced pasture grasses can have long-term impacts on ecosystem dynamics
  • Restoring native species and ecosystem processes challenging due to exotic ‘legacy’
legacy effect
Legacy effect
  • Alteration of soil environment by non-native species that persists beyond their removal
    • Soil physical characteristics
    • Soil nutrient cycling
    • Soil microbial communities (fungi, algae, bacteria)
slide4

Central Florida-Lake Wales Ridge:

Ancient archipelago that supports one of the largest collections of rare organisms in the world

85% of dry uplands on Lake Wales Ridge have been used for cultivation, residential, or commercial development

Rare plants in these ancient sand dunes are adapted to very well-drained, low nutrient soils with unique biological soil crusts (algae and cyanobacteria)

land use history
Land Use History

Bahia pasture –Paspalum notatum

Natal scrub –Rhynchelytrum repens

Drought resistant, warm-season grass from South America

Roots can extend up to 8ft deep

Used extensively in lawns throughout Florida

Warm season grass from South Africa

Responds well to disturbance (fire)

Native scrub

land use history effects on soil
Land use history effects on soil

a

b

b

Significant differences between bahia and native scrub sites in all three variables

Bahia pastures – monoculture

Natal scrub – mixture of native and non-native species

a

a

b

b

b

a

major questions
Major questions
  • Are there legacy effects of the previous vegetation on soil biogeochemistry and soil microbial communities? If so, how long-lived are they?
  • How might these persistent effects impact and/or direct restoration efforts?
experimental design

50m

Experimental Design

Subplot 1

3m

3m

Control

No crust addition

Crust addition

Herbicide - Restored

3m

Subplot 2

3m

slide9

Herbicide treatments:

1st application - Aug 2006

2nd application - Dec 2006

3rd application - spot treated Jan 2008

slide10

Bahia pasture – Control

Bahia pasture - Herbicide

Natal scrub – Control

Natal scrub - Herbicide

slide11

Total inorganic N

  • Restoration treatment had no immediate impact on soil inorganic N pools
  • Flush of inorganic N in restored bahia pasture 4-14 months post-treatment
    • -No root uptake of soil N
    • -Remaining dead litter on site
  • No initial impact of herbicide on soil N in the natal scrub sites
  • Significant legacy impact of bahia grass on soil inorganic N pools
slide12

Soil fungi

  • 4 months post-treatment, soil fungi in restored sites close to native scrub levels
  • 10-14 months post-treatment, fungi increased beyond control levels in bahia sites
    • -Increased substrate for fungi (remaining litter on sites after restoration trt)
  • Legacy effect of both bahia and natal grass on soil fungi
  • Restored sites still tracking control patterns instead of native scrub
slide13

Active algae

  • Algae in native scrub and control pasture sites track soil moisture levels
  • Restoration treatment significantly decreased active algae in both pastures 4 months post-treatment
    • possibly from 2nd herbicide treatment
slide14

What role do biological soil crusts have in restoration of central Florida scrub?

  • Fix and retain nitrogen
  • Stabilize soil (increase aggregation)
  • Aid in germination of several sensitive species

Photo: Tom Eisner

Hawkes 2004

Hawkes 2004

endemic herbaceous species introduced to all experimental sites
Endemic herbaceous species introduced to all experimental sites
  • Eryngium cuneifolium
  • Hypericum cumulicola
  • Lechea cernua
  • Lechea deckertii
  • Paronychia chartacea
  • Polygonella basiramia

Locally rare

Locally abundant

slide17

Restoration success of 6 native species

Germination (1mo after seeding)

Establishment (6 mo after seeding)

  • NO germination in any control sites
  • Germination rates were 3-13x higher in native scrub than in the bahia/natal sites
  • Seedling establishment was 2-15x higher in native scrub than in bahia/natal sites
  • Overall, only about 50% of the germinated seedlings survived 6 months
conclusions
Conclusions
  • Bahia grass legacy on soil nitrogen, soil fungi, and soil algae
  • Natal grass legacy on soil fungi and algae
  • Residual above- and belowground litter likely mechanism behind legacy effects
  • Altered conditions greatly inhibit germination and establishment
adaptive management
Adaptive management
  • Removed litter from restored bahia sites
  • Applied crust inocula to sites
  • Continuing seasonal measurements of biogeochemical and microbial components
  • Conducting study to determine most effective way to decrease soil N content in pasture soils
slide20

Thank you!

Special thanks:

Archbold Biological Station Plant Lab

Hawkes Lab

Funding:

USDA Managed Ecosystems Program