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The effects of groundwater availability on Kiawe ( Prosopis pallida ) physiology and growth

The effects of groundwater availability on Kiawe ( Prosopis pallida ) physiology and growth . Bruce Dudley, Flint Hughes, Rebecca Ostertag , Susan Cordell. Kiawe history in Hawaii. Introduced in 1828 Spread and planted throughout leeward Hawaii during the 19 th century

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The effects of groundwater availability on Kiawe ( Prosopis pallida ) physiology and growth

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  1. The effects of groundwater availability on Kiawe (Prosopispallida) physiology and growth Bruce Dudley, Flint Hughes, Rebecca Ostertag, Susan Cordell

  2. Kiawe history in Hawaii • Introduced in 1828 • Spread and planted throughout leeward Hawaii during the 19th century • Farmed as cattle feed • By 1900 Kiawe was the dominant lowland tree species on western coasts • Currently covers 58,766 ha (3.55% of the total land area of the Hawaiian islands)

  3. Potential negative effects • Reduction in regional groundwater levels • Reduction in habitat for native species (by shading) • Reduction in anchialine pond habitat and water quality

  4. Potential positive effects • Potentially increases water and nutrient availability in surface soils • Prosopisseed pods can be made into beer

  5. Research questions • What proportion of water used by kiawecomes from deep (aquifer) and shallow (rainfall events) sources? • How does water availability alter kiawe growth and productivity? • How does water availability alter kiawe N inputs to soil and groundwater

  6. Lighter… δ18O = - - - -X‰ Lighter… δ18O = - - -X‰ Lighter… Deep groundwater includes high altitude rainfall - Isotopically lighter δ18O = - -X‰ δ18O = -X‰ Surface water - Isotopically heavier Sea δ18O = zero

  7. Kiholo Bay Lowland Upland Lowland Upland

  8. Water sources – December 2010 Upland rain -7.73‰ Lowland rain -7.77‰ Aquifer -7.16‰ Summer rain / shallow soil water (From Cordell and Sanquist 2008) ~ +1.5 to -1‰

  9. Water potential This will tend to decrease with water availability

  10. Photosynthetic efficiency Pre-dawn (PD) yield in healthy plants typically around .83 (83%) This will tend to decrease in (water-) stressed plants

  11. Leaf chemistry

  12. Soil Chemistry

  13. Work still to do… Assess N inputs and losses from upland and lowland soils Continue water availability and plant physiology measurements at 3 month intervals for 21 further months.

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