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Climate change, grass invasions, and woody plant dynamics in semi- arid savannas

Jake Weltzin Department of Ecology and Evolutionary Biology University of Tennessee. Climate change, grass invasions, and woody plant dynamics in semi- arid savannas. NASA. Clay - Pleistocene. Sand - Holocene. >100. 80. 60. 40. 20. %. 0. -20. -40. -60. -80. -100.

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Climate change, grass invasions, and woody plant dynamics in semi- arid savannas

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  1. Jake Weltzin Department of Ecology and Evolutionary Biology University of Tennessee Climate change, grass invasions, and woody plant dynamics in semi-arid savannas

  2. NASA

  3. Clay - Pleistocene Sand - Holocene

  4. >100 80 60 40 20 % 0 -20 -40 -60 -80 -100 Precipitation regimes: wither the future? HadCM2 CGCM1 NAST 2000

  5. Recruitment of woody plants Seed • Climate • -precipitation • -temperature • -[CO2] • Microclimate • Soil • -water • -texture • -nutrients • Fire • Grass neighbors • -identity • -interactions • -density • Herbivory • -direct • -indirect • Seed availability • -production • -predation • -dispersal Seedling emergence Seedling survival Mature plant

  6. Climate • -precipitation • -temperature • -[CO2] • Microclimate • Soil • -water • -texture • -nutrients • Fire • Grass neighbors • -identity • -interactions • -density • Herbivory • -direct • -indirect • Seed availability • -production • -predation • -dispersal Recruitment of woody plants Seed Seedling emergence Seedling survival Mature plant

  7. Experimental design • Grass neighborhood • No grass (bare) • Native grass (Heteropogon contortus) • Non-native, invasive grass (Eragrostis lehmanniana) • Summer precipitation • - Wet (LTM + 50%) • Dry (LTM - 50%) • Soil texture • Sand (Holocene) • Clay (Pleistocene) • Mesquite (Prosopis velutina) demography • - Seeds planted August 2002 • - Seedlings monitored through June 2004

  8. Irrigation mimics intra-annual variation (daily, seasonal) Annual 409 mm 34 events

  9. Soil types respond differently to irrigation Clay Sand

  10. Irrigation controls seasonal soil moisture Clay

  11. Grass presence and identity control soil moisture Clay

  12. Eragrostis depletes soil moisture faster than Heteropogon Clay June 2002 Sand Time since pulse (days) Huxman et al.

  13. Emergence facilitated by grasses, esp. in wet plots Sand & Clay

  14. Under grasses, soil moisture inversely related to emergence Sand & Clay Heteropogon Bare Eragrostis

  15. Grasses do not reduce soil temperature English et al.

  16. ns 0 Sand: grass identity not important, irrigation not important Sand

  17. Clay: grass identity not important, irrigation is important WxP: P = 0.008 ns 0 Clay

  18. Sand Clay Seedlings in bare plots largest on wet, clay soil

  19. Seedlings in summerless water-stressed on clay than on sand Low Water stress High Sand Clay Fravolini et al.

  20. Most summer rain events are small Summer rain events Summer rain event size class (mm) Fravolini et al.

  21. Sand Clay Small rain events are transparent to mature mesquite on clay soil Use of isotope-labeled water (%) Time since pulse (days) Fravolini et al.

  22. Recruitment ultimately depends on soil moisture • Seed-seedling conflict mediated by grasses • Facilitation ---> Competition • Presence/absence of grass most important • Ultimately, identity of grass unimportant • Importance of summer precipitation depends on soil type • Seedling dem./phys. inconsistent with landscape patterns • Seedling-adult conflict mediated by ppt regime and soil • Landscape pattern controlled by interactions between life-history stage and environment

  23. Acknowledgments USDA NSF University of Tennessee Santa Rita Experimental Range Josh Avey Coleen Brown Deborah Angell David Williams Travis Huxman Nathan English Mike Mason Bill Cable Steve Archer Brian Enquist Mitch McClaran Guy McPherson Don Post Susan Schwinning NCEAS PrecipNet Participants Alessandra Fravolini Leigh Thomas Daniel Potts Philip Allen Michael Andregg Enrico Brugnoli Dayna Burns Jessica Cable Janet Chen Alex Eilts Rico Gazal Robbie Hannawacker Kevin Hultine Danielle Ignace Dan Koepke Charles Price Josh Polacheck Lara Souza Lisa Sturdivant Sam Waskow

  24. PrecipNet Improving understanding of precipitation effects on ecosystems through cross-disciplinary research networks http://precipnet.ucsc.edu/index.html

  25. PrecipNet Improving understanding of precipitation effects on ecosystems through cross-disciplinary research networks PrecipNet Goals • Research coordination, communication, and integration • Regional comparisons of precipitation change and its effects • Fostering multidisciplinary activities • Promoting skill development and technology transfer • Participants

  26. Participants

  27. CABI Bioscience (3 sites) 9 sites (VULCAN / CLIMOOR) 25 sites 5 sites (GLOWNET Network) Osvaldo Sala Participating sites and networks

  28. http://eeb.bio.utk.edu/weltzin/

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