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Identifying persistent effects of exotic pasture grasses and their influence on rosemary scrub community and ecosystem r

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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Identifying persistent effects of exotic pasture grasses and their influence on rosemary scrub community and ecosystem r

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  1. 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

  2. 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’

  3. 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)

  4. 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)

  5. 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

  6. 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

  7. 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?

  8. 50m Experimental Design Subplot 1 3m 3m Control No crust addition Crust addition Herbicide - Restored 3m Subplot 2 3m

  9. Herbicide treatments: 1st application - Aug 2006 2nd application - Dec 2006 3rd application - spot treated Jan 2008

  10. Bahia pasture – Control Bahia pasture - Herbicide Natal scrub – Control Natal scrub - Herbicide

  11. 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

  12. 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

  13. 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

  14. 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

  15. Restoration treatment impacts on N-fixation

  16. Endemic herbaceous species introduced to all experimental sites • Eryngium cuneifolium • Hypericum cumulicola • Lechea cernua • Lechea deckertii • Paronychia chartacea • Polygonella basiramia Locally rare Locally abundant

  17. 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

  18. 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

  19. 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

  20. Thank you! Special thanks: Archbold Biological Station Plant Lab Hawkes Lab Funding: USDA Managed Ecosystems Program

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