Jansen, Andreas Johannes Maria

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   University of GroningenHydrology and restiration of wet heathland and fen meadow communitiesJansen, Andreas Johannes MariaIMPORTANT 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:2000Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Jansen, A. J. M. (2000). Hydrology and restiration of wet heathland and fen meadow communities. 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: 13-02-2023SummarySummaryThis thesis focuses on the restoration prospects of rvet heathland ecosystems within the con-text of their hydrological functioning. In The Netherlands these ecosystems are l imited to thePleistocene landscape, which is often rich in alt itudinal gradients, causing a large variation insite conditions within a short distance. Consequently, a variety of vegetation gradients coulddevelop, along which several endangered plant comnrunities may occur, such as dry heath-fands (all iance Calluno-Genistion pilosae), wet heathlands (all iance Ericion Ietralicis).smalf-sedge communities (all iance Caricion nigrae), fen meadows (all iance Junco-Molinion), communities of soft-water pools (class Littoreiletea) and dwarf-rush communi-ties (all iance Nonocyperion). Moreover, these communities harbour many endangered andprotected plant species. Despite their protection as nature reserves, these remnants of wetheathlands suffer from a loss in biodiversity, mainly as a consequence of desiccation. acidif i-cation and eutrophication. Therefore, their restoration is urgent from a nature conservationpoint  of  v iew.The major part of the research as been carried out in nature reseryes in the Pleistocenelandscape of the Twente region (eastem Netherlands), in which both degraded and well-developed plant communities of wet heathlands occur. Here, recently several measures havebeen carried out to restore degraded plant communities. In existing nature reseryes od cut-ting, hydrological measures or their combination have been applied, rvhereas in a former ag-ricultural f ield sod cutting down to the original top soil in combination with hydrologicalmeasures has been carried out. The successes and failures ofthese measures are discussed.Fen meadows are species-rich and characteristic of wet, slightly acid to neutral andlow-productive sites. The Iarger part ofthe remaining fen rneadows has severely deteriorated;norvadays only 30 ha of well-developed fen meadows remain. Therefore, recently severalprojects were launched to restore damaged fen meadows. In Chapter 2 the successes andfailures ofthese projects are reviewed in relation to the existing variation in hydrological sys-tems. Seven hydrological system types have been distinguished, rvhich all provide site condi-tions required by this community. Nowadays, the best developed fen meadows occur in thePleistocene landscape ofThe Netherlands, where they are dependent on base-rich groundwa-ter discharging from local or larger groundwater systems. Fen meadows of the low-lyingHolocene landscape usually occur in man-made surface water systems; almost all standshave severely deteriorated. Restoration of fen meadows in the Pleistocene landscape isprom-ising when the hydrology is only slightly disturbed or when hydrological measures are takenin combination with sod cutting. Restoration prospects of fen meadows in the Holocene Iand-scape are low. Until now a complete regeneration of fen meadows has not been realised. Res-toration measures failed to restore high pH values in the top soil. It is hypothesised that viableseeds ofmany target species are lacking in the soil seed bank. In addition, the dispersal ca-pacities of these species eem to be l imited.Successful restoration of fen meadows requires (l ) water tables that reach the soil sur-face during at least six months, and (2) discharging base-rich groundwater in the rooting zone(Chapter 3). Such conditions are still present in the l-emselermaten. In this nature reserye aneutrophicated fen meadow stand and a site with a former agricultural grassland and an aldercarr were sod-cut. Sod cutting ofthe former agricultural grassland and ofthe alder carr suf-fices to restore this plant community, whereas od cutting of the eutrophicated fen meadowSummarywas not successful.  The unsuccessful restorat ion ofthe eutrophicated fen meadow is attr ib-uted to the prolonged inundation result ing from the sod cutt ing. The chemical composit ion ofthe deep groundwater supplying the reserye has changed from base-rich and sulphate-poor tobase-rich and sulphate-r ich, due to the increased manure spraying by farmers in the catch-ment area. This change might have caused a higher nutr ient avai labi l i ty in the rooting zoneand therefore may have led to the eutrophication and subsequent degradation ofthe fornterfen meadow. This change might also negatively inf luence the restoration prospects of fenmeadows on the longer term, when a new organic top soi l  layer has bui ld up again.When hydrological nrechanisms are heavi ly disturbed, as in the nature reserveStroothuizen, restorat ion of former fen meadows on the sole basis of sod cutt ing was not suc-cessful (Chapter 4). This might be due to high phosphorus concentrat ions in the top soi l ,which possibly arise from high mineral isat ion rates as a result of the disturbance of crucialhydrological processes. Under such condit ions restoration of fen meadorvs is only prornisingwhen sod cutt ing is combined with hydrological measures that counter prolonged inundationand reinforce the discharge ofbase and iron-r ich groundwater. Further, lhe absence of(viableseeds ofl  characterist ic species might harnper complete restorat ion of the forrner fenmeadow. Sod cutt ing. however, did result in the restoration of wet heathlands, small-sedgemarshes and ephemeral dwarf-rush communit ies. The combination of sod cutt ing and hydro-logical measures, which was carr ied out in Staverden, a severely deteriorated nature reservein the central part of The Netherlands, resulted in the restoration of dry heathlands, small-sedge marshes and a species-r ich wet heathland. The successful restorat ion ofthis heathlandtype, which has several species in common with fen meadows, indicates that fen nreadowscan be restored when ( |  )  appropriate hydrological condit ions can be re-created and (2) targetspecies st i l l  occur in the vicinity ofthe restored site, as is the case in Staverden.The nature reserve Punthuizen is characterised by a complex vegetation gradient, inwhich fen meadows occur in the upslope part of the gradient (Chapter 5). The occurrence offen meadows in Punthuizen is determined by a local hydrological system, the features andlunctioning of rvhich are described. During the winter season a pool is formed as a conse-quence ofthe absence ofa superf icial outlet.  A concentrated f lux ofbase-rich groundwater isbrought up at the margin of the exfi l trat ion part of the pool, whereas dorvnstreanr inf i l t rat iontakes place. These processes, which cause a variety in site condit ions, and consequently alsoin plant communit ies. are phenomerra of a local groundwater system. A prerequisite for thefunctioning ofsuch a groundwater systern is the presence ofpools during the winter season.When summer groundrvater tables, which are being determined by regional features outsidethe reserve, but which determine the origin and the extension of pools, are too low, nleasuresoutside nature reserves have to be taken to restore high sumnrer water tables. In addit ion, suc-cessful restorat ion of degraded fen meadows determined by the local hydrological system re-quires sod cutt ing along the entire gradient. Since relat ively small  height dif ferences can re-sult  in groundwater f low, restoring local hydrological systems on former agricultural areasrequires f irst ofal l  restorat ion ofthe rel ief.In Chapter 6 the successes and fai lures of the restoration of endangered plant commu-nit ies of wet heathland ecosystems are discussed. Measures were carr ied out both in exist ingnature reseryes and in a former agricultural f ield in the Twente region. Sod cutt ing of de-graded sites appeared to be successful in the restoration of fen meadows, small-sedgemarshes and wet heathlands when groundwater regirne and base status of the soi l  rvere st i l lappropriate. Sod cutt ing in combination rvith hydrological measures led to the restoration of1 6 8the required site condit iestabl ished. both in an exmeasures improved the cwet heathland and a softonly temporari ly successcould valuable plant ccestabl ished. In addit ion, rt ic species in the soi l  seedstored sites. Life-forrn ansirni lar to their well-deveform composit ion rve areIn i t ia l l y ,  the  ab io t i rlogical processes and hydoughly discussed in Chalmunit ies are forntulated.for successful restorationtems requires f irst of al l  treserves, but also on fornrestoring suitable site conwith an unsuitable grountrestoration. The possiblestabl ishment of orchid s1ties of wet heathlands. t lshort- l ived soi l  seed banlyears afler carrying out rermeasures were carried ouing nature reserves the resremoving the organic toping late summer or early aprevents the complete renSpecies with a short- l ivecthe reserves. Apparently,species might be improvradequate management sclrequisite for the restoraticdrology. The Dutch pol ic 'disturbed wet ecosystemsI doubt whether pol icy grconservation several restcfol lowed in this study is t lof semi-natural landscapeshowed to be successful.d fen meadow is attrib-hemical composit ion ofich and sulphate-poor tory farmers in the catch-i l i ty in the rooting zonegradation of the fornrerlrat ion prospects of fenbu i ld  up  aga in .in the nature reservesod cutt ing was not suc-rtrat ions in the top soi l ,e disturbance of crucialldows is only promisinger prolonged inundation:r,  the absence of(viabletion of the former fenheathlands, snral l-sedgerfsod cutt ing and hydro-;eriorated nature reservef dry heathlands, srnal l-rrat ion of this heathlandicates that fen meadowsre-created and (2) targetr Staverden., vegetation gradient, iner 5). The occurrence of;ystem, the features andrl is formed as a conse->ase-rich groundwater isdownstream infi ltrations, and consequently alson. A prerequisite for theuring the winter season.egional features outsides, are too low. measures'tables. In addit ion, suc-hydrological system re-:ight differences can re-crmer agricultural areas.dangered plant comnru-ried out both in exist ing;ion. Sod cutt ing of de-meadows, small-sedge.tus of the soi l  were st i l lled to the restoration ofthe required site condit ions of conlmunit ies of the class Lit torel leteo, rvhich indeed re-establ ished, both in an exist ing nature reserve and in a forrner agricultural t leld. Hydrologicalmeasures improved the quali t l 'of snral l-sedge nrarshes. Sod cutt ing of a another degradedw.et heathland and a soft-water pool. where fornrerly the lsocto-l .obel ietunt occurred, wasonly temporari ly successful,  probably as a consequence of too low water tables. Not onlycould valuable plant comrnunit ies be restored. but also rnany endangered species re-establ ished. In addit ion, restorat ion was also favoured by the occurrence ofmany characteris-t i c  spec ies  in  the  so i l  seed bank  and by  the  presence o f these spec ies  in  the  prox imi ty  o f the  re -stored sites. Life-forrn and growth-form composit ion of the successful ly restored plots weresimilar to their well-developed references. Hence. by comparing spectra of l i fe- and growth-forrrr composit ion we are able to trace the origin of fai lures in restorat ion projects.In i t ia l l y ,  the  ab io t i c  requ i rements  o f  rve t  heath land p lan t  communi t ies  and the  hydro-logical processes and hydrological system tvpes which provide for these condit ions, are thor-oughly discussed in Chapter 7. Next, cr i ter ia for successful restorat ion of these plant com-munit ies are formulated. I t  appeared to be impossible to define one single objective cri terionfor successful restorat ion. Restoration of low-productive plant conrmunit ies of rvet ecosys-tems requires f irst ofal l  the re-creation ofappropriate site condit ions. Inside exist ing naturereseryes, but also on former agricultural f ields, the measures applied were often suff icient inrestoring suitable site condit ions of wet heathland plant comnrunit ies. Fai lures are associatedwith an unsuitable gror-rndrvater regirne. N4oreover, also other factors may hamper completerestoration. The possible absence of nrycosymbionts might explain the l imited re-establ ishment oiorchid species in restored fen meadows. Opposite to other plant communi-t ies of wet heathlands, the major part of the characterist ic species of fen meado"vs has ashort- l ived soi l  seed bank type. Nlany ofthe latter species have not re-appeared within tenyears after carrying out restorat ion r leasures. The best results were obtained when restorationmeasures were carr ied out in or ad.jacent to exist ing, well-developed fen meadows. In exist-ing nature reserves the results ofsod cutt ing as a restorat ion measure can be inrproved ( l)  byremoving the organic top soi l  precisely down to the mineral top soi l ,  (2) rvhen is sod-cut dur-ing late summer or early autumn and (3) by maintaining micro-rel ief.  Ihis way of 'sod cutt ingprevents the complete removal of the soi l  seed bank and st imulates the germination of seeds.Species with a short- l ived soi l  seed bank only re-establ ished when they were st i l l  present inthe reserves. Apparently, these species have l imited dispersal capacit ies. The dispersal ofspecies nright be inrproved by ( l)  connection of isolated nature reserves, (2) the design ofadequate management schemes and - as a last possible measure - (3) re-introduction. A pre-requisite for the restoration and sustainable conservation of wet ecosystems is a proper hy-drology. The Dutch pol icy is aimed at the substantial reduction of the area of hydrological lydisturbed wet ecosystenrs. Although wet ecosystems local ly have been restored successful ly,I  doubt whether pol icy goals on the restoration of these systems wil l  be reached. [n natureconservation several restorat ion strategies have been developed. In my opinion the approachfol lowed in this study is the most adequate one in centuries old, natural ly stabi le ecosystemsof semi-natural andscapes. Although i t  is an intensive, rather technological and costly one, i tshowed to be successful.  Therefore. the examole deserves to be fol lowed.169

Hydrology and restiration of wet heathland and fen meadow communities

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Hydrology and restiration of wet heathland and fen meadow communities

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