The central issue of this thesis is the identification of key factors controlling the occurrence of basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea
islands. ...

Zie: Summary

Lammerts, Evert Jan.,

Lammerts, Evert Jan

University of Groningen

   University of GroningenBasiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islandsLammerts, Evert JanIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1999Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Lammerts, E. J. (1999). Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands.Groningen: s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019t a zSUMMARYThc central issuc of this thesis is the identi l icat ion of key factors control l ing theoccurrence of basiphi lous pionee| vegctat ion in dune slacks on the Dutch Wadden Scaislands. Such vegetation harbours many rare and protected plant species, among whichare several orchids, rushes and sedges. ln most of North West Europe the characteristicplant communit ies of natural and semi-natural landscapes are only prcsent in rdegenerate lbrm, i.e. the characteristic species are absent or seriously threatened. On theWadden Sea islands, however, the perspectives for conservation and restoration ofseveral plant communit ies are comparatively good. This study focuses on a thoroughunderstanding of the necessary habitat conditions for basiphilous species; in particular,thc f'actors which control such conditions: i.e . the key factors.Initially, in chaptcr 2, the identification of key variables indicating the presenceof a buffèr mechanism capable of maintaining the soi i-pH above 6.0 (which is general lyconsidered a minimum value for rnost basiphi lous species) is discussed. Chloride andcalcium contents of shal low groundwater and the CaCO: content of the mineral soi lappeared to be key variables. When at least one of these three variables exceeded acertain threshold value, the neccssary buffel status appeared to be guaranteed.Moreover, the values of the three key variables together gave information on the type ofactive buffer mechanism responsiblc for the environmental control of basiphilouspioneer vegetation: ( i)  high Ct-and Car* concentrat ions indicatc periodical inf low ofbrackish water, ( i i )  high CaCO: vulues und Calt concentrat ions indicate the presence ofl ime-rich mineral soi l  at the sr.rrface, ( i i i )  high Ca2* concentrat ions combined with lowCaCOr values and low Cl concentrations mark the influence of seepage of mineral richwater originating fron"r larger hydrological systems. The longevity of basiphilous pioneervegetation appeared to depend on the type of buffer mechanism. For priniary duneslacks, on l ime-rich soi ls and/or periodical ly inf luenced by brackish water, l i fe spanestimates ranged from 30-50 years without a mowing regime to 100-150 years with amowing regime. If hydrological systems supplied calcareous and iron rich groundwaterto slacks, their magnitude and strength determined the l i fe span of basiphi lous pioneerve-qctation: cstimates varied between 20 and 200 years.The analysis of a hydrological data set from dune slacks on the Dutch WaddenSea islands Arncland, Terschelling, Vlieland and Texel revealed three variablesdescribing site-specif ic hydrological condit ions (chapter 3), i .e. variables adequarelyidentifying diffèrcnces in local hydrological conditions between sites. They wereinferred by filtering the inÍluences of climatological fluctuations. The site-specificity ofthe variables could be confirmed by a good fit o1'modelled (based on these variables in(Ícshaos lolra(Frbtrel olcranl l l ispesttors control l ing thc)utch Wadden Scacies, among which'e the characteristiconly present in athreatened. On theand restoration oflses on a thorough:cies; in part icular,cating the presence(which is general lyssed. Chloride andrf the mineral soilriables exceeded ato be guaranteed.rtion on the type ofrol of basiphilouseriodical inÍlow of:ate the presence of:ombined with lowage of mineral-r ichbasiphilous pioncerFor primary dunesh water, liÍè span0-150 years with an rich groundwaterrasiphi lous pionecrthe Dutch Wadden:d three variablesuiables adequatelysites. They weree site-specificity ofr these variables inSummary t f , Jcombination with precipitation surplus data) with measured hydrological regimes' Twoofthe variables, the local drainage lcvel (á.1 and the yield-Ínctor (u), appeared to indicatesulficiently the suitability of dune slacks for basiphilous pioneer vegetation. They are,therelbre, considered to be key variables representing the hydrological components ofenvironmental control of basiphi lous pioneer vegetation in dune slacks.The oligotrophic character of natural dune slack habitats of basiphilous pioneervegetation is generally caused by nitrogen deficiency (chapter 5). In a successionalchronosequence (comprising c. 80 years) in the Koegelwieck (Terschell ing), including astage with basiphi lous pioneer vegetrt ion, nitrogen pools increased with age (chapters 4and 6). The fairly constant annual supply of nitrogen from its main source, atmosphericcleposition. corresponded to the annual storage in organic n'ratter while net nitrogenrnineralization was extremely low in all chronosequential stages. This suggested thatnitrogen availability for plant growth will be almost constant during early successton.However, i'ertilization experiments in the Koegelwieck chronosequence showed that thetype of nutrient limitation not only diÍlèrs between species but also changes during earlysuccession. Highly competitive grass species appeared to be suppressed not only bynitrogen clef iciency but also by phosphorus deficiency in the earl iest stages, whilebasiphi lous spccies themselves only showed nitrogen l imitat ion; they probably growvery wcl l  at extremely low phosphorus supplies. In later stages, where tal ler vegetationstructures had developed and basiphilous pioneer species had almost completelydisappcared, only species clominating the top layer of the vegetation still showed somenitrogen l imitat ion. The other species did not show any nutr ient l imitat ion. Some of thedisappearing, or less vital, species in this stage were probably outcompeted by tallerspecies in the struggle for light.The above results suggest that control of basiphilous pioneer vegetation at thehabitat level rs not only governed by a low avai labi l i ty of nitrogen but also by a lowavailabi l i ty of phosphorus. The negative effects of CaCOr addit ion on the productivi tyof phophorus-limited species (grasses and dwarf shrubs dominating the latersuccessional stages in the Koegelwieck) probably indicated the most importantoperational efïects of any buffer mechanism: fixation of inorganic phosphorus inmineral phosphates. The almost complete absence of phosphorus-limited species in theacidified stages of the Koegclwieck corroborates this supposition'The importance of seed avai labi l i ty in restorat ion sites is i l lustrated in chapter 7.From the case study on this subjcct (again in the Koegelwieck chronosequence) tt maybe concluded that basiphilous pioneer species can still be found in the seed bank ofrelatively old successional stages. Seeds of pioneer species in general have a greaterIongevity than seecis of species dominating older successional stages. An estimate oflongevity could only be given for a f'ew of these pioneer species: somewhere between 40and U0 years. Basiphilous spccics not found in the seed bank must spread by somemeans of diaspore dispersal. The tussock sedge Schoenus nigrican's, not only a characterspecies of basiphilous clune slack vegetation but also possibly facilitating theestablishment and growth of other basiphilous species, apparently spreads by waterSummarydispersal of i ts seeds during winter inundation. This, of course, is only possible whensome tussocks are present in the close vicinity of newly developing pioneer stands. [nconclusion, dispersule availability is an important factor for the development ofbasiphilous pioneer vegetation in suitable habitats.Conclusions on environmental control of basiphilous pioneer vegetation maydepend on the successional stage under study. In the earliest stage of the Koegelwieckchronosequence there were large annual fluctuations in vegetation composition while nodirectional changes were identified. In the most optimal stage (with most characterspecies) on the contÍary, annual fluctuations wcre small while directional changes,indicating a gradual development to succeeding communities, were obvious (chapter8). It was also observed that species "at the edge of the characteristic community"fluctuated much more in response to differences in weather conditions thancharacteristic species.Ways to use the kcy variables, identified in the present work, for decisionmaking in the design and execution of restoration projects, are described in chapter 9.On the basis of the present investigations, combined with some general considerations,it is concluded that on the Wadden Sea islands priority shouid be given to restorationprojects involving secondary dune slacks, especially those which are fed by calcareousgroundwater from relatively large hydrological systems. Dune slack research for the useof nature restoration and management should give priority to: (i) the identification ofspecific threshold values of the new hydrological key variables for different basiphilousplant communities and the incorporation of these variables in hydrological modelling,(ii) investigating the role of diaspore availability and dispersal mechanisms in theestablishment of basiphilous pioneer species in young dune slacks, (iii) assessing therelationships between geomorphological patterns and processes and the occurrence ofbasiphilous pioneer communities in areas where water and wind driven dynamics have(re-)established.(ttIb((lrut;(cJ

Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands

ARTS repository - University of Groningen

   University of GroningenBasiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islandsLammerts, Evert JanIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1999Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Lammerts, E. J. (1999). Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands.s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 06-06-2022t a zSUMMARYThc central issuc of this thesis is the identi l icat ion of key factors control l ing theoccurrence of basiphi lous pionee| vegctat ion in dune slacks on the Dutch Wadden Scaislands. Such vegetation harbours many rare and protected plant species, among whichare several orchids, rushes and sedges. ln most of North West Europe the characteristicplant communit ies of natural and semi-natural landscapes are only prcsent in rdegenerate lbrm, i.e. the characteristic species are absent or seriously threatened. On theWadden Sea islands, however, the perspectives for conservation and restoration ofseveral plant communit ies are comparatively good. This study focuses on a thoroughunderstanding of the necessary habitat conditions for basiphilous species; in particular,thc f'actors which control such conditions: i.e . the key factors.Initially, in chaptcr 2, the identification of key variables indicating the presenceof a buffèr mechanism capable of maintaining the soi i-pH above 6.0 (which is general lyconsidered a minimum value for rnost basiphi lous species) is discussed. Chloride andcalcium contents of shal low groundwater and the CaCO: content of the mineral soi lappeared to be key variables. When at least one of these three variables exceeded acertain threshold value, the neccssary buffel status appeared to be guaranteed.Moreover, the values of the three key variables together gave information on the type ofactive buffer mechanism responsiblc for the environmental control of basiphilouspioneer vegetation: ( i)  high Ct-and Car* concentrat ions indicatc periodical inf low ofbrackish water, ( i i )  high CaCO: vulues und Calt concentrat ions indicate the presence ofl ime-rich mineral soi l  at the sr.rrface, ( i i i )  high Ca2* concentrat ions combined with lowCaCOr values and low Cl concentrations mark the influence of seepage of mineral richwater originating fron"r larger hydrological systems. The longevity of basiphilous pioneervegetation appeared to depend on the type of buffer mechanism. For priniary duneslacks, on l ime-rich soi ls and/or periodical ly inf luenced by brackish water, l i fe spanestimates ranged from 30-50 years without a mowing regime to 100-150 years with amowing regime. If hydrological systems supplied calcareous and iron rich groundwaterto slacks, their magnitude and strength determined the l i fe span of basiphi lous pioneerve-qctation: cstimates varied between 20 and 200 years.The analysis of a hydrological data set from dune slacks on the Dutch WaddenSea islands Arncland, Terschelling, Vlieland and Texel revealed three variablesdescribing site-specif ic hydrological condit ions (chapter 3), i .e. variables adequarelyidentifying diffèrcnces in local hydrological conditions between sites. They wereinferred by filtering the inÍluences of climatological fluctuations. The site-specificity ofthe variables could be confirmed by a good fit o1'modelled (based on these variables in(Ícshaos lolra(Frbtrel olcranl l l ispesttors control l ing thc)utch Wadden Scacies, among which'e the characteristiconly present in athreatened. On theand restoration oflses on a thorough:cies; in part icular,cating the presence(which is general lyssed. Chloride andrf the mineral soilriables exceeded ato be guaranteed.rtion on the type ofrol of basiphilouseriodical inÍlow of:ate the presence of:ombined with lowage of mineral-r ichbasiphilous pioncerFor primary dunesh water, liÍè span0-150 years with an rich groundwaterrasiphi lous pionecrthe Dutch Wadden:d three variablesuiables adequatelysites. They weree site-specificity ofr these variables inSummary t f , Jcombination with precipitation surplus data) with measured hydrological regimes' Twoofthe variables, the local drainage lcvel (á.1 and the yield-Ínctor (u), appeared to indicatesulficiently the suitability of dune slacks for basiphilous pioneer vegetation. They are,therelbre, considered to be key variables representing the hydrological components ofenvironmental control of basiphi lous pioneer vegetation in dune slacks.The oligotrophic character of natural dune slack habitats of basiphilous pioneervegetation is generally caused by nitrogen deficiency (chapter 5). In a successionalchronosequence (comprising c. 80 years) in the Koegelwieck (Terschell ing), including astage with basiphi lous pioneer vegetrt ion, nitrogen pools increased with age (chapters 4and 6). The fairly constant annual supply of nitrogen from its main source, atmosphericcleposition. corresponded to the annual storage in organic n'ratter while net nitrogenrnineralization was extremely low in all chronosequential stages. This suggested thatnitrogen availability for plant growth will be almost constant during early successton.However, i'ertilization experiments in the Koegelwieck chronosequence showed that thetype of nutrient limitation not only diÍlèrs between species but also changes during earlysuccession. Highly competitive grass species appeared to be suppressed not only bynitrogen clef iciency but also by phosphorus deficiency in the earl iest stages, whilebasiphi lous spccies themselves only showed nitrogen l imitat ion; they probably growvery wcl l  at extremely low phosphorus supplies. In later stages, where tal ler vegetationstructures had developed and basiphilous pioneer species had almost completelydisappcared, only species clominating the top layer of the vegetation still showed somenitrogen l imitat ion. The other species did not show any nutr ient l imitat ion. Some of thedisappearing, or less vital, species in this stage were probably outcompeted by tallerspecies in the struggle for light.The above results suggest that control of basiphilous pioneer vegetation at thehabitat level rs not only governed by a low avai labi l i ty of nitrogen but also by a lowavailabi l i ty of phosphorus. The negative effects of CaCOr addit ion on the productivi tyof phophorus-limited species (grasses and dwarf shrubs dominating the latersuccessional stages in the Koegelwieck) probably indicated the most importantoperational efïects of any buffer mechanism: fixation of inorganic phosphorus inmineral phosphates. The almost complete absence of phosphorus-limited species in theacidified stages of the Koegclwieck corroborates this supposition'The importance of seed avai labi l i ty in restorat ion sites is i l lustrated in chapter 7.From the case study on this subjcct (again in the Koegelwieck chronosequence) tt maybe concluded that basiphilous pioneer species can still be found in the seed bank ofrelatively old successional stages. Seeds of pioneer species in general have a greaterIongevity than seecis of species dominating older successional stages. An estimate oflongevity could only be given for a f'ew of these pioneer species: somewhere between 40and U0 years. Basiphilous spccics not found in the seed bank must spread by somemeans of diaspore dispersal. The tussock sedge Schoenus nigrican's, not only a characterspecies of basiphilous clune slack vegetation but also possibly facilitating theestablishment and growth of other basiphilous species, apparently spreads by waterSummarydispersal of i ts seeds during winter inundation. This, of course, is only possible whensome tussocks are present in the close vicinity of newly developing pioneer stands. [nconclusion, dispersule availability is an important factor for the development ofbasiphilous pioneer vegetation in suitable habitats.Conclusions on environmental control of basiphilous pioneer vegetation maydepend on the successional stage under study. In the earliest stage of the Koegelwieckchronosequence there were large annual fluctuations in vegetation composition while nodirectional changes were identified. In the most optimal stage (with most characterspecies) on the contÍary, annual fluctuations wcre small while directional changes,indicating a gradual development to succeeding communities, were obvious (chapter8). It was also observed that species "at the edge of the characteristic community"fluctuated much more in response to differences in weather conditions thancharacteristic species.Ways to use the kcy variables, identified in the present work, for decisionmaking in the design and execution of restoration projects, are described in chapter 9.On the basis of the present investigations, combined with some general considerations,it is concluded that on the Wadden Sea islands priority shouid be given to restorationprojects involving secondary dune slacks, especially those which are fed by calcareousgroundwater from relatively large hydrological systems. Dune slack research for the useof nature restoration and management should give priority to: (i) the identification ofspecific threshold values of the new hydrological key variables for different basiphilousplant communities and the incorporation of these variables in hydrological modelling,(ii) investigating the role of diaspore availability and dispersal mechanisms in theestablishment of basiphilous pioneer species in young dune slacks, (iii) assessing therelationships between geomorphological patterns and processes and the occurrence ofbasiphilous pioneer communities in areas where water and wind driven dynamics have(re-)established.(ttIb((lrut;(cJ

English

   University of GroningenBasiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islandsLammerts, Evert JanIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1999Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Lammerts, E. J. (1999). Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands.s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 16-07-2023t a zSUMMARYThc central issuc of this thesis is the identi l icat ion of key factors control l ing theoccurrence of basiphi lous pionee| vegctat ion in dune slacks on the Dutch Wadden Scaislands. Such vegetation harbours many rare and protected plant species, among whichare several orchids, rushes and sedges. ln most of North West Europe the characteristicplant communit ies of natural and semi-natural landscapes are only prcsent in rdegenerate lbrm, i.e. the characteristic species are absent or seriously threatened. On theWadden Sea islands, however, the perspectives for conservation and restoration ofseveral plant communit ies are comparatively good. This study focuses on a thoroughunderstanding of the necessary habitat conditions for basiphilous species; in particular,thc f'actors which control such conditions: i.e . the key factors.Initially, in chaptcr 2, the identification of key variables indicating the presenceof a buffèr mechanism capable of maintaining the soi i-pH above 6.0 (which is general lyconsidered a minimum value for rnost basiphi lous species) is discussed. Chloride andcalcium contents of shal low groundwater and the CaCO: content of the mineral soi lappeared to be key variables. When at least one of these three variables exceeded acertain threshold value, the neccssary buffel status appeared to be guaranteed.Moreover, the values of the three key variables together gave information on the type ofactive buffer mechanism responsiblc for the environmental control of basiphilouspioneer vegetation: ( i)  high Ct-and Car* concentrat ions indicatc periodical inf low ofbrackish water, ( i i )  high CaCO: vulues und Calt concentrat ions indicate the presence ofl ime-rich mineral soi l  at the sr.rrface, ( i i i )  high Ca2* concentrat ions combined with lowCaCOr values and low Cl concentrations mark the influence of seepage of mineral richwater originating fron"r larger hydrological systems. The longevity of basiphilous pioneervegetation appeared to depend on the type of buffer mechanism. For priniary duneslacks, on l ime-rich soi ls and/or periodical ly inf luenced by brackish water, l i fe spanestimates ranged from 30-50 years without a mowing regime to 100-150 years with amowing regime. If hydrological systems supplied calcareous and iron rich groundwaterto slacks, their magnitude and strength determined the l i fe span of basiphi lous pioneerve-qctation: cstimates varied between 20 and 200 years.The analysis of a hydrological data set from dune slacks on the Dutch WaddenSea islands Arncland, Terschelling, Vlieland and Texel revealed three variablesdescribing site-specif ic hydrological condit ions (chapter 3), i .e. variables adequarelyidentifying diffèrcnces in local hydrological conditions between sites. They wereinferred by filtering the inÍluences of climatological fluctuations. The site-specificity ofthe variables could be confirmed by a good fit o1'modelled (based on these variables in(Ícshaos lolra(Frbtrel olcranl l l ispesttors control l ing thc)utch Wadden Scacies, among which'e the characteristiconly present in athreatened. On theand restoration oflses on a thorough:cies; in part icular,cating the presence(which is general lyssed. Chloride andrf the mineral soilriables exceeded ato be guaranteed.rtion on the type ofrol of basiphilouseriodical inÍlow of:ate the presence of:ombined with lowage of mineral-r ichbasiphilous pioncerFor primary dunesh water, liÍè span0-150 years with an rich groundwaterrasiphi lous pionecrthe Dutch Wadden:d three variablesuiables adequatelysites. They weree site-specificity ofr these variables inSummary t f , Jcombination with precipitation surplus data) with measured hydrological regimes' Twoofthe variables, the local drainage lcvel (á.1 and the yield-Ínctor (u), appeared to indicatesulficiently the suitability of dune slacks for basiphilous pioneer vegetation. They are,therelbre, considered to be key variables representing the hydrological components ofenvironmental control of basiphi lous pioneer vegetation in dune slacks.The oligotrophic character of natural dune slack habitats of basiphilous pioneervegetation is generally caused by nitrogen deficiency (chapter 5). In a successionalchronosequence (comprising c. 80 years) in the Koegelwieck (Terschell ing), including astage with basiphi lous pioneer vegetrt ion, nitrogen pools increased with age (chapters 4and 6). The fairly constant annual supply of nitrogen from its main source, atmosphericcleposition. corresponded to the annual storage in organic n'ratter while net nitrogenrnineralization was extremely low in all chronosequential stages. This suggested thatnitrogen availability for plant growth will be almost constant during early successton.However, i'ertilization experiments in the Koegelwieck chronosequence showed that thetype of nutrient limitation not only diÍlèrs between species but also changes during earlysuccession. Highly competitive grass species appeared to be suppressed not only bynitrogen clef iciency but also by phosphorus deficiency in the earl iest stages, whilebasiphi lous spccies themselves only showed nitrogen l imitat ion; they probably growvery wcl l  at extremely low phosphorus supplies. In later stages, where tal ler vegetationstructures had developed and basiphilous pioneer species had almost completelydisappcared, only species clominating the top layer of the vegetation still showed somenitrogen l imitat ion. The other species did not show any nutr ient l imitat ion. Some of thedisappearing, or less vital, species in this stage were probably outcompeted by tallerspecies in the struggle for light.The above results suggest that control of basiphilous pioneer vegetation at thehabitat level rs not only governed by a low avai labi l i ty of nitrogen but also by a lowavailabi l i ty of phosphorus. The negative effects of CaCOr addit ion on the productivi tyof phophorus-limited species (grasses and dwarf shrubs dominating the latersuccessional stages in the Koegelwieck) probably indicated the most importantoperational efïects of any buffer mechanism: fixation of inorganic phosphorus inmineral phosphates. The almost complete absence of phosphorus-limited species in theacidified stages of the Koegclwieck corroborates this supposition'The importance of seed avai labi l i ty in restorat ion sites is i l lustrated in chapter 7.From the case study on this subjcct (again in the Koegelwieck chronosequence) tt maybe concluded that basiphilous pioneer species can still be found in the seed bank ofrelatively old successional stages. Seeds of pioneer species in general have a greaterIongevity than seecis of species dominating older successional stages. An estimate oflongevity could only be given for a f'ew of these pioneer species: somewhere between 40and U0 years. Basiphilous spccics not found in the seed bank must spread by somemeans of diaspore dispersal. The tussock sedge Schoenus nigrican's, not only a characterspecies of basiphilous clune slack vegetation but also possibly facilitating theestablishment and growth of other basiphilous species, apparently spreads by waterSummarydispersal of i ts seeds during winter inundation. This, of course, is only possible whensome tussocks are present in the close vicinity of newly developing pioneer stands. [nconclusion, dispersule availability is an important factor for the development ofbasiphilous pioneer vegetation in suitable habitats.Conclusions on environmental control of basiphilous pioneer vegetation maydepend on the successional stage under study. In the earliest stage of the Koegelwieckchronosequence there were large annual fluctuations in vegetation composition while nodirectional changes were identified. In the most optimal stage (with most characterspecies) on the contÍary, annual fluctuations wcre small while directional changes,indicating a gradual development to succeeding communities, were obvious (chapter8). It was also observed that species "at the edge of the characteristic community"fluctuated much more in response to differences in weather conditions thancharacteristic species.Ways to use the kcy variables, identified in the present work, for decisionmaking in the design and execution of restoration projects, are described in chapter 9.On the basis of the present investigations, combined with some general considerations,it is concluded that on the Wadden Sea islands priority shouid be given to restorationprojects involving secondary dune slacks, especially those which are fed by calcareousgroundwater from relatively large hydrological systems. Dune slack research for the useof nature restoration and management should give priority to: (i) the identification ofspecific threshold values of the new hydrological key variables for different basiphilousplant communities and the incorporation of these variables in hydrological modelling,(ii) investigating the role of diaspore availability and dispersal mechanisms in theestablishment of basiphilous pioneer species in young dune slacks, (iii) assessing therelationships between geomorphological patterns and processes and the occurrence ofbasiphilous pioneer communities in areas where water and wind driven dynamics have(re-)established.(ttIb((lrut;(cJ

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 University of Groningen
Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands
Lammerts, Evert Jan
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
1999
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Lammerts, E. J. (1999). Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands
Groningen: s.n.
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
number of authors shown on this cover page is limited to 10 maximum.
Download date: 10-02-2018
t a z
SUMMARY
Thc central issuc of this thesis is the identi l icat ion of key factors control l ing the
occurrence of basiphi lous pionee| vegctat ion in dune slacks on the Dutch Wadden Sca
islands. Such vegetation harbours many rare and protected plant species, among which
are several orchids, rushes and sedges. ln most of North West Europe the characteristic
plant communit ies of natural and semi-natural landscapes are only prcsent in r
degenerate lbrm, i.e. the characteristic species are absent or seriously threatened. On the
Wadden Sea islands, however, the perspectives for conservation and restoration of
several plant communit ies are comparatively good. This study focuses on a thorough
understanding of the necessary habitat conditions for basiphilous species; in particular,
thc f'actors which control such conditions: i.e . the key factors.
Initially, in chaptcr 2, the identification of key variables indicating the presence
of a buffèr mechanism capable of maintaining the soi i-pH above 6.0 (which is general ly
considered a minimum value for rnost basiphi lous species) is discussed. Chloride and
calcium contents of shal low groundwater and the CaCO: content of the mineral soi l
appeared to be key variables. When at least one of these three variables exceeded a
certain threshold value, the neccssary buffel status appeared to be guaranteed.
Moreover, the values of the three key variables together gave information on the type of
active buffer mechanism responsiblc for the environmental control of basiphilous
pioneer vegetation: ( i)  high Ct-and Car* concentrat ions indicatc periodical inf low of
brackish water, ( i i )  high CaCO: vulues und Calt concentrat ions indicate the presence of
l ime-rich mineral soi l  at the sr.rrface, ( i i i )  high Ca2* concentrat ions combined with low
CaCOr values and low Cl concentrations mark the influence of seepage of mineral rich
water originating fron"r larger hydrological systems. The longevity of basiphilous pioneer
vegetation appeared to depend on the type of buffer mechanism. For priniary dune
slacks, on l ime-rich soi ls and/or periodical ly inf luenced by brackish water, l i fe span
estimates ranged from 30-50 years without a mowing regime to 100-150 years with a
mowing regime. If hydrological systems supplied calcareous and iron rich groundwater
to slacks, their magnitude and strength determined the l i fe span of basiphi lous pioneer
ve-qctation: cstimates varied between 20 and 200 years.
The analysis of a hydrological data set from dune slacks on the Dutch Wadden
Sea islands Arncland, Terschelling, Vlieland and Texel revealed three variables
describing site-specif ic hydrological condit ions (chapter 3), i .e. variables adequarely
identifying diffèrcnces in local hydrological conditions between sites. They were
inferred by filtering the inÍluences of climatological fluctuations. The site-specificity of
the variables could be confirmed by a good fit o1'modelled (based on these variables in
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combination with precipitation surplus data) with measured hydrological regimes' Two
ofthe variables, the local drainage lcvel (á.1 and the yield-Ínctor (u), appeared to indicate
sulficiently the suitability of dune slacks for basiphilous pioneer vegetation. They are,
therelbre, considered to be key variables representing the hydrological components of
environmental control of basiphi lous pioneer vegetation in dune slacks.
The oligotrophic character of natural dune slack habitats of basiphilous pioneer
vegetation is generally caused by nitrogen deficiency (chapter 5). In a successional
chronosequence (comprising c. 80 years) in the Koegelwieck (Terschell ing), including a
stage with basiphi lous pioneer vegetrt ion, nitrogen pools increased with age (chapters 4
and 6). The fairly constant annual supply of nitrogen from its main source, atmospheric
cleposition. corresponded to the annual storage in organic n'ratter while net nitrogen
rnineralization was extremely low in all chronosequential stages. This suggested that
nitrogen availability for plant growth will be almost constant during early successton.
However, i'ertilization experiments in the Koegelwieck chronosequence showed that the
type of nutrient limitation not only diÍlèrs between species but also changes during early
succession. Highly competitive grass species appeared to be suppressed not only by
nitrogen clef iciency but also by phosphorus deficiency in the earl iest stages, while
basiphi lous spccies themselves only showed nitrogen l imitat ion; they probably grow
very wcl l  at extremely low phosphorus supplies. In later stages, where tal ler vegetation
structures had developed and basiphilous pioneer species had almost completely
disappcared, only species clominating the top layer of the vegetation still showed some
nitrogen l imitat ion. The other species did not show any nutr ient l imitat ion. Some of the
disappearing, or less vital, species in this stage were probably outcompeted by taller
species in the struggle for light.
The above results suggest that control of basiphilous pioneer vegetation at the
habitat level rs not only governed by a low avai labi l i ty of nitrogen but also by a low
availabi l i ty of phosphorus. The negative effects of CaCOr addit ion on the productivi ty
of phophorus-limited species (grasses and dwarf shrubs dominating the later
successional stages in the Koegelwieck) probably indicated the most important
operational efïects of any buffer mechanism: fixation of inorganic phosphorus in
mineral phosphates. The almost complete absence of phosphorus-limited species in the
acidified stages of the Koegclwieck corroborates this supposition'
The importance of seed avai labi l i ty in restorat ion sites is i l lustrated in chapter 7.
From the case study on this subjcct (again in the Koegelwieck chronosequence) tt may
be concluded that basiphilous pioneer species can still be found in the seed bank of
relatively old successional stages. Seeds of pioneer species in general have a greater
Iongevity than seecis of species dominating older successional stages. An estimate of
longevity could only be given for a f'ew of these pioneer species: somewhere between 40
and U0 years. Basiphilous spccics not found in the seed bank must spread by some
means of diaspore dispersal. The tussock sedge Schoenus nigrican's, not only a character
species of basiphilous clune slack vegetation but also possibly facilitating the
establishment and growth of other basiphilous species, apparently spreads by water
Summary
dispersal of i ts seeds during winter inundation. This, of course, is only possible when
some tussocks are present in the close vicinity of newly developing pioneer stands. [n
conclusion, dispersule availability is an important factor for the development of
basiphilous pioneer vegetation in suitable habitats.
Conclusions on environmental control of basiphilous pioneer vegetation may
depend on the successional stage under study. In the earliest stage of the Koegelwieck
chronosequence there were large annual fluctuations in vegetation composition while no
directional changes were identified. In the most optimal stage (with most character
species) on the contÍary, annual fluctuations wcre small while directional changes,
indicating a gradual development to succeeding communities, were obvious (chapter
8). It was also observed that species "at the edge of the characteristic community"
fluctuated much more in response to differences in weather conditions than
characteristic species.
Ways to use the kcy variables, identified in the present work, for decision
making in the design and execution of restoration projects, are described in chapter 9.
On the basis of the present investigations, combined with some general considerations,
it is concluded that on the Wadden Sea islands priority shouid be given to restoration
projects involving secondary dune slacks, especially those which are fed by calcareous
groundwater from relatively large hydrological systems. Dune slack research for the use
of nature restoration and management should give priority to: (i) the identification of
specific threshold values of the new hydrological key variables for different basiphilous
plant communities and the incorporation of these variables in hydrological modelling,
(ii) investigating the role of diaspore availability and dispersal mechanisms in the
establishment of basiphilous pioneer species in young dune slacks, (iii) assessing the
relationships between geomorphological patterns and processes and the occurrence of
basiphilous pioneer communities in areas where water and wind driven dynamics have
(re-)established.
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Basiphilous pioneer vegetation in dune slacks on the Dutch Wadden Sea islands

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