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

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. Grass-encroachment
Foto’s: Rienk Slings

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. Present situation
Lime-rich Grey dunes Lime-poor Grey dunes

5. 2030: no real improvement
Lime-rich Grey dunes Lime-poor Grey dunes

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. Renodunaal district: zonation
Lime-rich Foredunes
Decalcified Middle dunes
Lime-poor Hinterdunes

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. 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. 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. 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. 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. 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. 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. 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. Accelerated succession
Fujita et al. 2015

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. Added problem: Campylopus introflexus
• Decrease, but mainly transformation to tall-grass
1993 2007

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. 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. 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. 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