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What is the problem with our dune grasslands

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Dynamic Dunes Congress 2015
Keynote: Annemieke Kooijman - What is the problem with our dune grasslands

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What is the problem with our dune grasslands

  1. 1. What is the problem with our Dune grasslands? Interactions between high N-deposition, geology and soil organic matter content, and loss of natural regeneration capacity Dr. Annemieke Kooijman University of Amsterdam
  2. 2. Grass-encroachment Foto’s: Rienk Slings
  3. 3. High atmospheric N-deposition Nitrogen deposition 1500-2004 0 500 1000 1500 2000 2500 3000 3500 4000 1500 1600 1700 1800 1900 2000 (mol/ha) NH3 NOx total N • Especially in 1990s • Decreasing, but still too high
  4. 4. Present situation Lime-rich Grey dunes Lime-poor Grey dunes
  5. 5. 2030: no real improvement Lime-rich Grey dunes Lime-poor Grey dunes
  6. 6. Response to N depends on soil • Wadden district • lime-poor and iron-poor sand • no chemical P-fixation • grass-encroachment everywhere • Renodunaal district • lime-rich and iron-rich sand • P-fixation possible • grass-encroachment local Wadden district Reno- dunaal district
  7. 7. Renodunaal district: zonation Lime-rich Foredunes Decalcified Middle dunes Lime-poor Hinterdunes
  8. 8. Grass-encroachment 1990-2008 Foredunes 1990 tall grass open Foredunes 2001 tall grass open Foredunes 2008 tall grass open Middle dunes 1990 tall grass open Middle dunes 2001 tall grass open Middle dunes 2008 tall grass open Hinterdunes 1990 tall grass open Hinterdunes 2001 tall grass open Hinterdunes 2008 tall grass open
  9. 9. Important to management • decrease grass- encroachment in fore and hinter dunes • still increase in middle dunes • although less fast • differences in soil are relevant increase in tall grass vegetation -3 -2 -1 0 1 2 3 4 5 %tallgrassindunegrasslandsperyear fore dunes middle dunes hinter dunes ungrazed grazed
  10. 10. N in soil not important • N-mineralization • many experiments in lime-rich and lime-poor soil • higher, lower or no difference • Soil community • expected to differ between lime- rich and lime-poor soil • only small differences • Accumulation of N in OM • 15N added as ammonium • very rapid nitrification • no storage in stable OM • P as regulating factor?
  11. 11. Lime-rich Foredunes • relatively fortunate • higher critical load: 15 kg/ha yr • lower grass-encroachment • P-fixation in calcium phosphate • high natural regeneration capacity • (potentially) high rabbit density • more blow-outs • danger • acidification – loss of lime-rich species • dissolution calcium phosphate – increase biomass production
  12. 12. High N:P ratio Carex arenaria N:P ratio van de vegetatie 0 5 10 15 20 25 30 35 alle vaatplanten zandzegge N:Pratio(g:g) TPL TPH DHL DHHP-limitation in lime-rich soil by Ca-phosphate Plant without mycorrhiza Kooijman et al. 2014
  13. 13. Decalcified Middle dunes • very unfortunate • high biomass production – (extra) dissolution of calcium phosphate – increase biomass production – increase N-mineralization 2 4 6 8 0 100 200 300 400 500 livingbiomass 2 4 6 8 pH-CaCl2 Ah -300 -200 -100 0 100 200 300 P-mineralization 2 4 6 8 0 2 4 6 8 N-mineralization
  14. 14. Acidification in Lime-rich soil • Natural acidification • dissolution of CaCO3 • soil with 4% lime – 6-9 cm decalcification per century – 12-18 mm in 20 years • Accelerated acidification • 20 years of increased decalcification • soil with 4% lime – extra decalcification of 4.3 -11.1 mm – almost as high as natural levels
  15. 15. Dissolution of calcium phosphate • higher acidification • extra dissolution of calcium phosphates • per mm soil: 60 mg m-2 P • per mm decalcification – release of 60 mg m-2 P • with 8 mm extra decalcification – appr. 500 g m-2 extra biomass – grass-encroachment – shrub-encroachment – Prunus serotina
  16. 16. Accelerated succession Fujita et al. 2015
  17. 17. Lime-poor Hinterdunes • relatively unfortunate • low critical load: 10 kg/ha yr • iron-rich soils • but only with low OM – P-fixation in iron phosphates • soils with high OM – weak P-binding to Fe-OM complexes • low regeneration capacity • low rabbit density • low aeolian activity • added problem • the moss Campylopus introflexus
  18. 18. Added problem: Campylopus introflexus • Decrease, but mainly transformation to tall-grass 1993 2007
  19. 19. Response to N depends on soil • Wadden district • lime-poor and iron-poor sand • no chemical P-fixation • grass-encroachment everywhere • Renodunaal district • lime-rich and iron-rich sand • P-fixation possible • grass-encroachment local Wadden district Reno- dunaal district
  20. 20. High grass-encroachment Wadden Figuur 1. Verschuiving van het aandeel van lage, open en vergraste vegetatie in duingrasland in vier verschillende duinzones. R-voorduin = Renodunaal district, kalkrijke voorduinen; R-midden = Renodunaal district, ondiep ontkalkte middenduinen; R-achterduin = Renodunaal district, diep ontkalkte achterduinen; Wadden = Wadden district, onkalkte, ijzerarme bodems. Gegevens uit het Renodunaal district zijn gebaseerd op luchtfotointerpretaties (Mark van Til, ongepubliceerde resultaten). Gegevens uit het Wadden district zijn gebaseerd op vegetatiekarteringen (Kooijman & de Haan 1995). R-voorduin 1990 vergrast open vegetatie R-midden 1985 R-achterduin 1990 Wadden 1986 R-voorduin 2001 R-midden 2001 R-achterduin 2001 Wadden 1992
  21. 21. Wadden district • very unfortunate • lime-poor and iron-poor soil • no lime-rich soils – no P-fixation in calcium phosphate • no iron-rich soils • Fe only in Fe-OM complexes – no P-fixation in iron phosphate – high net P-mineralization – very sensitive to N-deposition – strong grass-encroachment • low regeneration capacity • low rabbit density • only few blow outs IJzer in de bodem 0 4 8 12 16 20 Reno- dunaal Wadden ijzer(mmol/kg) mineraal organisch P-'m ineralisatie' 0 100 200 300 400 500 R eno- dunaal W adden P-mineralisatie(mg/m2april-oktober)
  22. 22. What is wrong with our dunes? • N-deposition still too high • Lime-rich dunes relatively fortunate • but keep soils lime-rich • Lime-poor dunes more problematic • but restoration measures possible – grazing helps – keep soils ‘young’ » low OM: P-fixation in iron phosphates » low OM: relatively high pH and species richness

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