Vegetation, land use and management of the inner-dune zone in the North-Holland D u n e Reserve, The Netherlands* F. W. van der Vegte I, J. Faber 2 & L. Kuiters T M l Provincial Waterworks o f North-Holland, Postbox 5, 2060 BA Bloemendaal, The Netherlands 2Biological 'Laboratory, Free University, de Boelelaan 1087, 1081 H V Amsterdam, The Netherlands

Keywords: Dune, Inner-dune grassland, Land use, Management, North-Holland, Vegetation development

Abstract The inner-dune zone between the villages of Bakkum and Egmond in the North-Holland Dune Reserve is one of the few remaining examples of the semi-natural boundary between the dunes and the polders. For several centuries this area has been used for various purposes, in particular for grazing. Large-scale excavating, especially after about 1900, has encroached upon the dunes. Vegetation and land-use history were studied and a provisional scheme on the vegetation development is presented. Management policies discussed are non-intervention, mowing in order to start natural processes such as rabbit grazing, and the continuation of traditional livestock grazing. Proposals for external management policies were made in order to maintain or enhance the original transition zone, based on comprehensive physical-geographical studies of the whole inner-dune zone.

Introduction The North-Holland Dune Reserve is an area of about 4 800 ha of Coastal dunes, owned by the Province of North-Holland and managed by the Provincial Waterworks of North-Holland. Its vegetation reflects a large variation in natural environment and human influences. The impact of men on the dunes has always been greatest around the old 'sea villages' and along the eastern, inland dunes. This inner-dune zone forms the semi-natural boundary zone between the dunes and the polders. In most parts of the Dutch mainland the inner-dune zone has been dug off for various purposes. Between the old villages of Egmondaan-Zee and Bakkum, large areas were excavated in the last century and converted into pastures and * Nomenclature follows van Ooststroom (1973). ** The authors are indebted to Mr D. K. J. Withrington, B.A. for correction of the English text and to the staff of the Waterworks for preparing the figures and typing the manuscript. Vegetatio 62, 449-456 (1985). © Dr W. Junk Publishers, Dordrecht. Printed in the Netherlands.

bulb fields. Fortunately, a large segment remained more or less in its original geomorphological state (180 ha out of a total of 240 ha). Comparable areas are rare in The Netherlands and virtually restricted to the former islands of Schouwen and Goeree in the south west. This paper outlines the history of the area, its present vegetation and former use and discusses the management of this zone in relation to the neighbouring, cultivated land.

Description of the study area The inner-dune zone as a boundary zone The inner-dune zone forms the natural boundary between two very different types of environment: the coastal dunes and the polders. The present dune landscape was formed in the second phase of the formation of the Younger Dunes in The Netherlands, from 800-1900 A.D. Climatic changes and

450 human activities both played an important role. The existing dune topography was mainly formed between 1400-1600. Blow-outs on a smaller scale have taken place since and have altered the topography in the eastern zone of the dunes. Geomorphologically, the inner-dune zone forms the transition between the high dunes with much relief and the low lying, flat polders to the east (Fig. I). There is also a hydrological transition. The dune massif gives rise to surface and underground run-off into th~ polders with their artificial drain-

age system. This moisture gradient has become less evident because of the drying out of the dunes, but there have been signs over the last ten years of a gradual recovery towards the natural hydrological situation. Summarizing it can be said that the original wide inner-dune zone of up to 2 km between the higher dunes and the polder has become much narrower over the years. The eastern limit of the higher dunes has been encroached upon by excavating and levelling. The soil transition zone between dune sands and the alluvial sediments of the polder has been negated to a great extent by the increasing intensity of agricultural practices. Nevertheless, the present surviving remnants of the inner-dune zone are highly valued, from a scenic and botanical viewpoint. Aspects o f the land use history

Although there had been previous habitation, the first agricultural settlements came into existence in the 8th century. The settlement of Arem (at present Bakkum) dates from this time. The 12th century saw the first reclamation of tidal fiats into polders. The first dike dates from ca. 1140. In the following centuries the dunes between Egmond and Bakkum were used for many different purposes: hunting, rabbit breeding, turf cutting (for use in stables, as fodder or as fuel), grazing, bleaching of linen, use of water for paper making and breweries, agricultural exploitation and, since 1930, for the production of drinking water (Jelles, 1968; Leermakers, 1980). Grazing is the oldest continuous form of use. Up to the beginning of this century extensive parts of the inner-dune zone were being used for grazing. The dunes were particularly useful when conditions were too wet in the polder. Considerable areas are still being grazed today, but large-scale excavating and conversion to arable land started after 1870 and reached its peak in the first half of this century (Fig. 2). Land use and vegetation within the Dune Reserve Fig. 1. Generalized map of the geomorphology and soils of the study area (after de Roo (1953) and Aris, W~ickerlin & van Waveren (1982)). Legend: Dh: High dunes, dune sand; DI: Dunes with low relief, dune sand; TI: Boundary zone with little relief, dune sand; Ts: Boundary zone, slightly sloping, dune sand; Pt: Polder, transition from sand to clay soils; Ps: Polder, alluvial sediments.

The present-day land uses within the reserve are summarized in Figure 3. The vegetation map is too complicated for reproduction here to be presented, but it reveals a strong correlation between land use and type of vegetation. The vegetation typology (Faber & Kuiters, 1982) is based on 140 Transley-

451

.

Fig. 2. Map of the study area in about 1900, showing the encroachment into the dunes. Legend." 1: Present-day border of natural dune topography; 2: Areas excavated since 1900; 3: Approximate borderline of cultivation in 1680.

relev6s o f quadrats, the size o f which being determined by the minimal surface-area of the vegetation (9 m 2 for c o m m o n grasslands, 25 m 2 for dune grasslands, and 225 m 2 for shrubland). The relev6s were supplemented with rare species occurring just outside the quadrats. C r y p t o g a m i c species were not included in the survey, since it was intended to acquire a fairly simple and easily recognizable t y p o l o g y on which a preliminary m a n a g e m e n t could be based. Recent vegetation studies did include cryptogamic species and after processing o f these data it is still possible to adjust m a n a g e m e n t if desired. Five main habitat

.

it

Fig. 3. Present-day land use of the inner-dune zone. Legend."

Dune grassland; 2: Dune grassland grazed by livestock; 3: Abandoned arable fields; 4: Cultivated fields; 5: Pastures with moderate grazing pressure; 6: Intensively used pastures; 7: Woodland.

types can be discerned: dune grassland, a b a n d o n e d arable field, pasture, shrubland and woodland. A total of 18 vegetation types were described. In Figure 4 possible routes of succession between these types are summarized on the basis of the main habitat types. In Table 1 the vegetation types are described in more detail. A floristic description is given together with main characteristics of the soil, based on indicator values of the occurring plant species. N o chemical soil analyses have been d o n e so far. F o r a s y n t a x o n o m i c description the (local) vegeta-

452

DUNE-

D U N E - ~

SCRUB

GRASSLAND PASTURE

with HAWTHORN, HF, HC, SSi, SC, Ro.

CO, KG, FG, AG, AC.

l'

I

WOODLAND

OAK and BIRCH.

i i I i

ROUGH-

FORMER ARABLE

GRASSLAND

FIELD

~C.

CE, CEG, CA, CAF.

Fig. 4. Scheme of the principal succession lines in the inner-dune zone (full line: succession; dotted line: regression). For a detailed description see text.

Table 1. Description of the main habitat types of the inner-dune zone zone. (Plots where spontaneous development to woodland occurs are still too small, so good descriptions of woodland types are not yet possible).

Habitat type

Vegetation types

Synecology

Syntaxonomy

Succession

Dune-grassland

Co: lichen steppe with Cor.vnephorus canescens and Sedum acre.

Dry dunes, poor in lime without humus,

Spergulo-Corynephoretum

KG: rabbit-grazed dunegrassland with Poa pratensis, Rubus caesius, Rhinanthus minor and Anthyllis vulneraria. FG: rabbit-grazed dunegrassland with Poa pratensis and Rubus caesius.

Soils relatively poor in lime and humus

Anthyllido-Silenetum nutantis

Soils relatively poor in lime and relatively rich in humus.

Festuco-Galietum maritimi.

Pioneervegetation; succession to type FG or KG under circumstances of no disturbance (digging, winderosion etc.) Rabbit-grazing stabilizes this type (Westhoff & den Held, 1969). Formation of more humus leads to type FG. Maintenance by rabbitgrazing (Westhoff & den Held, 1969). Reduced grazing pressure leads to establishment of scrub (Sloet, 1976).

AG: livestock-grazed dune-grassland with Agrostis tenuis and R u m e x acetosella.

Soils relatively poor in lime and rich in humus.

Local type with elements from: Festuco-Galietum maritimi and Lolio Plantaginetum.

Maintenance by livestockgrazing. Reduced grazingpressure leads to establishment of Salix repens scrub.

AC: rough dune-grassland with Poa pratensis, Rubus caesius, Agrostis tenuis, R u m e x acetosella, Linaria vulgaris and Daucus carota.

Soils relatively poor in lime, rich in minerals and organic matter, resulting from agricultural activities in the past.

Local type with elements from: GalioKoelerion, Arrhenatherion elatioris, Agropyro- Rumicion crispi, Silena-Allieturn vinealis.

Livestock-grazing will result in appearance of more dune-grassland species, type AG.

Characteristic species (species with a presence of more than 70% in the vegetation relev6s).

Festuca ovina Galium verum Plantago lanceolata Cerastium arvense Koeleria cristata

6 vegetation types are distinguished, connected with differences in: -lime content -minerals and humus -livestock- or rabbit grazing. Most of the vegetation is beyond the influence of the ground-water.

453

Table 1. (Continued). Habitat type

Vegetation types

Synecology

Syntaxonomy

Succession

RC: rough dune-grassland with Poa pratensis. Rubus caesius, Linaria vulgaris, and Daucus carota.

Disturbed soils, enriched with organic matter and rich in lime.

Local type with elements from: Arrhenatherion elatior&, Agropyro Rumicion crispi, Sisymbrion.

This type arises from all the other types (inclusive scrubtypes) after disturbance. Mowing will counteract this regression and will start succession-processes.

HF: Hippophae-scrub with d une-grassland species as Festuca ovina and Koeleria cristata.

Frequently occurring on dune-slopes, relatively poor in minerals.

Elements from: Hippophao-Sambucetum Hippophao- Ligustretum.

By formation of h u m u s this pioneer scrub will develop into a more species-rich scrub with Crataegus monoKvna and Quercus robur.

HC: Hippophae-scrub with rough-grassland species as Cirsium arvense and Galium aparine.

Occurring on abandoned arable fields on soils relatively rich in minerals and organic matter.

Elements from: Hippophao-Sambu-

Locally cutting makes a development possible to a more species-rich scrub with Crataegus monogyna and Quercus robur.

Characteristic .~pecies (species with a presence of more than 70% in the vegetation relev6s).

SSi: Salix repens-scrub with Sieglingia decumbens and Carex panicea.

Occurring in livestock grazed dunegrasslands on moist soils, poor in minerals and rich in humus.

Elements from: Salicion arenariae.

Continuing livestock-grazing holds the scrub in a stable situation. Reduced grazing-pressure will result in establishment of Crataegus monoKvna and Betula.

Salix repens Holcus lanatus A n t h o x a n t h u m odoraturn R u m e x acetosa Agrostis tenuis

SC: Salix repens-scrub with Calamagrostis epigejos and Festuca rubra.

Occurring in dunegrasslands sometimes mixed with Hippophae-scrub on soils only during the winter under the influence of the groundwater(?)

Elements from: Salicion arenariae.

Developments to a more species-rich scrub with Crataegus and Betula are possible.

Ro: dwarf scrub of Rosa pimpinellifolia with Festuca rubra and A n t h o x a n t h u m odoraturn.

Mainly on southexposed dune slopes, where mineralization is rather fast (Sloet, 1976).

Sub-association Koelerietosum of the association FestucoGalietum.

Rabbit grazing holds this type in a stable situation.

Dune-scrubland Characteristic species (species with a presence of more than 70% in the vegetation relev6s). Hippophae rhamnoides Rubus caesius Elytrigia repens Calamagrostis epigejos Urtica dioica.

celum.

2 types are distinguished, based on the understory vegetation, connected with the history of the soil.

2 types are distinguished, connected with moisture and mineral status. Characteristic species (species with a presence of more than 70% in the vegetation relev6s). Rosa pimpinellifolia Festuca ovina Plantago lanceolata Cerastium arvense Galium verum Only one type is distinguished

454 Table 1. (Continued). Habitat type

Vegetation types

Synecology

Syntaxonomy

Succession

Former arable field

CA: rough grassland with Agrostis tenuis, R u m e x acetosella, Vicia sativa ssp. angustifolia, Vicia hirsuta,

Soils relatively poor in lime, but rich in minerals,

Local type with ele ments from: Arrhenatherion elatioris, Agropyro-Rumicion crispi, Galio- Koelerion.

Mowing will introduce more dune-grassland species, type CAF, eventually leading to type AG.

CAF: regularly mown grassland with Agrostis tenuis, R u m e x acetosella, Festuca ovina and Rhinanthus minor.

Soils relatively poor in lime and minerals.

Local type with elements from: Festuco Galietum maritime.

Continued mowing will result in type AG. Rabbit grazing will enforce this process.

CE: rough grassland with Elytrigia repens and Linaria vulgaris.

Soils rich in lime and minerals.

Local type with eleelements from: Arrhenatherion elatioris, Agropyro Rumicion crispi, Galio- Koelerion.

Mowing will introduce more dune grassland species, type CEG, eventually leading to type FG.

Most of the vegetations within the influence of the groundwater.

CEG: regularly mown grassland with Elytrigia repens, Linaria vulgaris, Galium verum and Luzula campestris.

Soils relatively rich in lime but relatively poor in minerals.

Local type with elements from: Arrhenatherion elatioris, Agropyro Rumicion crispi, Galio- Koelerion.

Continued mowing will result in type FG. Rabbit grazing will enforce this process.

Pasture

Although developments to different types occur, no distinct types can be distinguished yet.

On excavated areas in the transition zone between the dunes and the polder, on soils rich in minerals.

Poo- Lolietum

Continuation of the management regime with a gradual reduction in the application of manure and in grazing intensity of livestock will lead to more dune grassland species, eventually to type AG.

Characteristic species (species with a presence of more than 70% in the vegetation relev~s). Poa pratensis Calarnagrostis epigejos Festuca rubra Plantago lanceolata Holcus lanatus

4 types could be distinguished, differences being related to a m o u n t of lime and minerals.

tion types are compared with the system of Westhoff & den Held (1969). Also, possible routes of succession are mentioned, based on local field observations, verbal communications of historic data and, whenever possible, on literature references. Growth form spectra were obtained for most of the previously described types. This was intended for use as a tool to monitor newly imposed management practices with emphasis placed on mowing and grazing. To arrive at a comprehensive growth form system, two existing systems for dune plants (Gimingham, 1951; van der Maarel, 1966) were combined and adjusted as needed. The synthesis was based on shoot morphology and propagation.

Vegetation and land use of a few characteristic areas In this section three areas with in the reserve (see Figs. 2 and 3) are examined in more detail, with regard to their land-use history, present vegetation and likely vegetational developments. 'De Bleek' This area has a natural relief of low dunes and shallow hollows. In places the land has been excavated for arable fields but most of them were abandoned between 1969 and 1976. History: In the 17th and 18th centuries three bleaching works existed here, but during the 19th century this industry disappeared (Jelles, 1968). Grazing occurred only with tethered goats. The arable fields were dug in the 19th and the beginning of the

455 20th century. During World War 11 turf cutting took place locally. Vegetation: The northern part of 'De Bleek' is covered with vegetation of type KG (see Table 1). This is also the main type of vegetation of the neighbouring high dunes, and it shows all the features of the so-called 'sea village landscape' (Doing, 1964). The rest of the area is dominated by vegetation type FG, which probably developed from type KG through the formation of more humus. The occurrence in many places of Corynephorus canescens and lichens (type Co) points to a poor soil which is probably the result of local turf cutting. Scrub development occurs in many areas. Further expansion will depend on the number of rabbits. The abandoned arable fields are now covered with a type of rough vegetation (type CE), which will probably develop into Hippophae scrub, type HC.

'De Westert' This area, which is situated not far from the village of Egmond-Binnen, is a complex of old, mostly abandoned, small arable fields. History: The western part of the area was probably already in use by the year 1700. The eastern part was excavated and levelled at the beginning of this century. Usually the fields are not larger than 0.6 ha and were dug out in several stages to a depth of 1 2 m, which was necessary to keep the fields within reach of the groundwater. Initially, potatoes were grown, alternating with carrots, French beans, beets and cornsalad (for its seeds). After 1945 bulbgrowing became popular, mainly tulips and gladioli, but also crocuses and other species. The culture of bulbs is rotated with the growing of vegetables. Along the edges around the fields, mounds of waste and sand developed. Most of the time the fields were dug yearly and manure or fertilizer was applied. Between 1969 and 1976 almost all the leases were cancelled and cultivation ceased as the area was to be designated for recreation. This policy was superseded in the latest regional plan and the area is now to be managed for nature conservation. Vegetation: The unmown plots are almost all overgrown with Hippophae scrub. On the mown fields type CA occurs. Here the structure of the vegetation is coarse: most of the species grow patchily. On several sites the vegetation appears to change towards dune grassland (well developed type CAF). Besides the regular mowing regime, the increase in rabbit grazing is of great importance in this process. The vegetation of the paths and verges between the fields belongs to type AC with many dune grassland species. This area can be compared with the Schurvelingen area on the isle of Schouwen. Here, extensive mowing of abandoned arable fields over a period of more than five years has led to similar developments in terms of establishment and propagation of many dune grassland species (Janzen, 1972). However, dune scrub developments are different, probably due to a lower lime content in the soil: the acidophilous shrub species Sarothamnus scoparius dominates here.

' Vennewater' The area called 'Vennewater" is rather extensive and varied, comprising pastures, hay meadows, abandoned arable fields and

grazed dune-grasslands with a low relief. It is situated south of 'Westert" and west of the village of Egmond-Binnen. History: Land use of this area has been constant tor several centuries (Fig. 2). Maps of 1680 already show sites which had been dug away or levelled. Other parts of the area remained the same up till now. Visually, the Vennewater area shows best the original, almost unspoilt transition from the dunes to the polders. Large parts are still traditionally grazed extensively by cows, sheep and horses. Rabbits and hares are also present, but not in great numbers. Vegetation: The vegetation of the grazed dune grasslands is quite uniform in appearance: type AG on the dryer parts and scrubtype SSi in the hollows. On closer inspection one can distinguish many gradients of moisture, exposure, trampling and grazing. Together, these create a finely grained vegetation mosaic. The pastures and hay meadows have also a long and continuous history of usage. Because of the dry soil conditions, these fields have never been used very intensively. The vegetation is probably transitional in character and shows some resemblance to trivial Poo Lolietum grassland (Westhoff& den Held, 1969). The present management policy aims at integrating these fields with neighbouring grazed dune-grasslands. Along the ditches in this area a vegetation rich in species occurs, including Rhinanthus species and orchids. The unique combination of environmental and historical factors causes difficulties in comparing vegetation and developments of livestock-grazed dune grassland with similarly managed areas elsewhere in The Netherlands. On the islands of Goeree and Schouwen livestock-grazed dune grassland vegetation is quite distinct from the Vennewater situation because of the elevated groundwater table in the latter caused by a clay layer under the superficial sand-layer. In these grasslands different plant communities prevail: the Airo Caricetum arenariae association (Westhoff et aL, 1961); elements of the Violion caninae and Nanocyperionflavescentis (Blom & Willems, 1971; kaumans, 1980).

Future management Management

of the vegetation

In order to decide of the most appropriate of management, vegetation

pattern

and to gain an insight into the

processes of vegetation reported

upon

form

it w a s n e c e s s a r y t o e s t a b l i s h t h e development.

in t h i s p a p e r

vegetation mapping, tory. In addition,

The studies

dealt not only with

but also with the land-use his-

the soils and hydrology

of the

area were studied and tables were drawn

up for

growth forms and for nitrophily of the plants (Fab e r & K u i t e r s , 1982). O n t h e b a s i s o f t h e s e d a t a a s well as data from the literature (Westhoff & den H e l d , 1969; S l o e t v a n O l d r u i t e n b o r g h , 1976) a p r o v i s i o n a l s c h e m e f o r v e g e t a t i o n d e v e l o p m e n t is p r e s e n t e d ( F i g . 5) a n d t e c h n i q u e s f o r t h e e v a l u a t i o n o f

456 FORME~ A~AeLE FIELDS

DUN£GRASSLAND

)

SCRUB

t , Ir _ _ L _ ,q ~):

z.[~:

°'

was to evaluate the possibilities for regeneration of the former landscape, management options were identified for each plot outside the nature reserve. As a result of this study, a successful effort has been made to incorporate the desirability of the conservation and regeneration of (parts of) the transition zone in the latest regional plan.

6

--

-To-

--

~;--

References ~

; S.1.6 , L ~ 1 6 3.8 I

7

I

2,7

' .3

g

Fig. 5. Provisional scheme of the lines of vegetation development (for symbols of vegetation types see text). Legend: Aspects of natural development and management measures: 0: Non-intervention; 1: Natural grazing; 2: Decrease of grazing; 3: Formation of humus; 4: Degeneration; 5: Mowing; 6: Grazing by livestock; 7: Stop grazing; 8: Soil disturbance; 9: Turf cutting.

management measures were proposed. Management options were put forward for each plot or field and compared with the general management objectives of the reserve. These objectives are firstly to further the natural development of communities and secondly to conserve the variety of landscapes which developed naturally or as a result of human usage. This policy leads to: (1) non-intervention in natural vegetation and removal of human abuses; (2) temporary management measures on the former arable fields to set in motion the natural development towards dune grassland or scrub; (3) continuation of grazing by livestock in certain areas and integration of the various fields into larger units. The m a i n t e n a n c e o f the i n n e r - d u n e z o n e as a transilion z o n e

Policies for preventing harmful influences on the nature reserve and for conserving the inner-dune zone as a whole were considered essential to complement the internal management measures. Thus physical-geographical studies have been carried out to determine the present properties and potentialities of the complete original transition zone between the dunes and the polder (Aris, W~ickerlin & van Waveren, 1982). One of the aims of this work

Aris, P., W/~ckerlin, J. & Waveren, E. van, 1982. De hoedanigheld en potenties van het afgegraven binnenduinlandschap tussen Castricum en Egmond aan den Hoef. Report, Dept. of Physical Geography, Univ. of Amsterdam. Blom, C. W. P. M. & Willems, R. J. B. M., 1971. De Westduinen op Goeree. Levende Natuur 74:219 225. Doing, H., 1964. Recreatie en Natuurbescherming in het Noordhollands Duinreservaat. Suppl. 2: Vegetatie. ITBONMed. 69C/1964. Engelberts, H. C. A., 1976. Vegetatiekundig onderzoek van de duinweilanden op Terschelling. Int. rapp. RIN. Faber, J. & Kuiters, L., 1982. De binnenduingraslanden tussen Egmond en Bakkum. Rep. Dept. of Nature Management, Agricultural University, Wageningen. Gimingham, C. H., 1951_ The use of life form and growth form in the analysis of c o m m u n i t y structure, as illustrated by a comparison of two dune communities. J. Ecol. 39:396 406. Janzen, R. W., 1972. lnventarisatie, evaluatie en beheer van de Schurvelingen bij Ouddorp op Goeree. Versl. Natuurbeheer. L H . Wageningen, 182. Jelles, J. G. G., 1968. Geschiedenis van beheer en gebruik van het Noordhollands Duinreservaat. ITBON Med. 87/1968. Laumans, P., 1980. De Springertduinen en de Westduinen op Goeree. Ontstaansgeschiedenis en vegetatie. Dokt. Versl. Vegetatiekunde en Plantenoecologie, Wageningen, 144 pp. Leermakers, C. J., 1980. Een landschapsoecologische kartering van het middengedeelte van Noord-Kennemerland. Rep., Dept. of Physical Geography, Univ. of Amsterdam. Maarel, E. van der, 1966. Over vegetatiestructuren, -relaties en -systemen, in het bijzonder in de duingraslanden van Voorne. Thesis Utrecht. Ooststroom, S. J. van, 1973. Henkels' flora van Nederland. Wolters-Noordhoff, Groningen. Roo, H. C. de, 1953. De bodemgesteldheid van Noord-Kennemerland. Vers]. Landb. Onderz. XI. Sloet van Oldruitenborgh, C. J. M., 1976. Duinstruwelen in het Deltagebied. Meded. Landbouwhogeschool Wageningen 76-8. Westhoff, V. & Held, A. J. den, 1969. Plantengemeenschappen in Nederland. Thieme en Cie, Zutphen. Westhoff, V., Leeuwen, C. G. van & Adriani, M. J., 1961. Vegetatie en fauna van Goeree. Utg. Stichting N a t u u r m o n u ment de Beer, Den Haag.

Accepted 6.10.1984.