Quaternary Science Journal - Patterns of Late Glacial vegetation in The Netherlands by Geozon Science Media

Eiszeitalter

Gegenwart

78 — 88

Hannover

8 Abbildungen

1997

Patterns o f Late Glacial vegetation in The Netherlands WIM Z. HOEK*) W e i c h s e l i a n Late Glacial, v e g e t a t i o n a l d e v e l o p m e n t , climate, T h e N e t h e r l a n d s

A b s t r a c t : T h e W e i c h s e l i a n Late G l a c i a l ( c a . 1 3 , 0 0 0 - 1 0 , 0 0 0

v e r s c h i e d e n e n Instituten untersucht. Z u r K o m p i l a t i o n v o n

y e a r s B P ) m a r k s t h e transition from t h e c o l d W e i c h s e l Late

m e h r als 2 5 0 P o l l e n d i a g r a m m e n w u r d e d i e E t i r o p e a n P o l

Pleniglacial t o t h e w a r m e r H o l o c e n e .

During this p e r i o d

len D a t a b a s e s t r u k t u r g e n u t z t . Datierte V e r ä n d e r u n g e n im

t h e c l i m a t e rapidly c h a n g e d a s d i d t h e v e g e t a t i o n a n d t h e

a r b o r e a l e n P o l l e n b e s t a n d b i l d e n die G r u n d l a g e d e s r e g i o

abiotic landscape. T h e vegetational development o f the

n a l e n Z o n i e n i n g s s c h e m a s . Mit Hilfe d i e s e r D a t e n w u r d e n

W e i c h s e l i a n Late G l a c i a l in T h e N e t h e r l a n d s is d e t e r m i n e d

I s o - P o l l e n - K a r t e n d e r w i c h t i g s t e n T a x a für v e r s c h i e d e n e

firstly b y t h e l a r g e - s c a l e c h a n g e s in climate a n d in t h e s e

Zeitfenster d e s Weichsel-Spätglazials konstruiert. D i e h o h e

c o n d p l a c e b y l o c a l v a r i a t i o n s in lithology, g e o m o r p h o l o g y

B e o b a c h t u n g s d i c h t e p a l y n o l o g i s c h e r D a t e n in d e n N i e d e r

a n d h y d r o l o g y . P o l l e n d i a g r a m s from different a r e a s , e m

landen

b r a c i n g t h e s a m e time-stratigraphical interval, often s h o w

P o l l e n - K a r t e n für d e n b e t r a c h t e t e n Zeitraum. E s g i b t e i n e

c l e a r variations in v e g e t a t i o n history, w h i c h c a n n o t b e e x

klare B e z i e h u n g zwischen d e n b e o b a c h t e t e n Iso-Pollen-

plained on climatological grounds alone.

M u s t e r n u n d d e m Landschaftstyp. E s s o l l t e n u n m ö g l i c h

In T h e N e t h e r l a n d s o v e r 4 0 0 p a l y n o l o g i c a l s e c t i o n s , c o v e r

sein, k l a r e r z w i s c h e n k l i m a t i s c h e n u n d a b i o t i s c h e n F a k t o

ing a part o r t h e w h o l e o f t h e W e i c h s e l i a n Late Glacial,

ren

h a v e b e e n investigated b y s e v e r a l institutes. F o r t h e c o m p i

steuern.

erlaubte die Konstntktion hoch auflösender

unterscheiden,

Iso

d i e die V e g e t a t i o n s e n t w i c k l u n g

lation o f t h e data from o v e r 2 5 0 p o l l e n diagrams, u s e w a s m a d e o f t h e E u r o p e a n P o l l e n D a t a b a s e structure.

Dated

Introdution

shifts in t h e a r b o r e a l p o l l e n c o n t e n t constitute t h e basis o f a regional z o n a t i o n s c h e m e . W i t h t h e h e l p o f this, iso-pol

The

l e n m a p s o f m a i n taxa w e r e c o n s t r u c t e d for different t i m e -

b e t w e e n t h e c o l d W e i c h s e l i a n Late P l e n i g l a c i a l a n d

w i n d o w s within t h e W e i c h s e l i a n Late Glacial. T h e d e n s e

t h e w a r m e r H o l o c e n e . T h e climate c h a n g e

n e t w o r k o f p a l y n o l o g i c a l o b s e r v a t i o n sites in T h e Nether lands p e r m i t t e d t h e drafting o f h i g h - r e s o l u t i o n i s o - p o l l e n m a p s o f the period considered. A clear relationship c a n b e r e c o g n i z e d b e t w e e n t h e i s o - p o l l e n patterns a n d t h e land s c a p e type. T h u s , it s h o u l d b e p o s s i b l e t o distinguish m o r e

W e i c h s e l i a n Late Glacial m a r k s t h e

transition

during

this transition c a u s e d t h e vegetation a n d t h e a b i o t i c c o m p o n e n t o f the l a n d s c a p e to c h a n g e rapidly.

g r e a t n u m b e r o f p a l y n o l o g i c a l data c o n s i d e r i n g the Late G l a c i a l have b e e n c o l l e c t e d in N W - E u r o p e a n d

clearly b e t w e e n climate a n d other abiotic a g e n c i e s o f the

e s p e c i a l l y T h e N e t h e r l a n d s during t h e last d e c a d e s .

environment which affected vegetational development,

T h e r e f o r e , the g e n e r a l v e g e t a t i o n d e v e l o p m e n t for this p e r i o d is well k n o w n .

[Spätglaziale Vegetationsverteilung

At t h e e n d o f the W e i c h s e l i a n Late P l e n i g l a c i a l t h e r e

in d e n Niederlanden]

w a s in T h e N e t h e r l a n d s a sparse v e g e t a t i o n c o v e r comprising

Gramineae,

Cyperaceae

and

Betula

K u r z f a s s u n g : Das Weichsel-Spätglazial (ca. 13.000-10.000

nana,

J a h r e v o r h e u t e ) markiert d e n Übergang v o m kalten späten

r o u n d 1 3 , 0 0 0 years B P h e r b a c e o u s plant c o m m u n i t i e s

Weichsel-Pleniglazial z u m wärmeren dieser Periode änderten

Holozän.

Während

s i c h Klima, V e g e t a t i o n u n d d i e

a b i o t i s c h e Landschaft s e h r r a s c h . D i e V e g e t a t i o n s e n t w i c k lung i m W e i c h s e l - S p ä t g l a z i a l d e r N i e d e r l a n d e w i r d in e r s t e r

and

m a n y p l a c e s w e r e altogether b a r e . F r o m a-

dwarf bushes

developed due

temperature

rise. D u r i n g the A l l e r i 0 d interstadial r a t h e r o p e n tula

a n d later o n Pinus

w o o d s occurred. T h e colder

Linie d u r c h langfristige K l i m a ä n d e r u n g e n u n d a n z w e i t e r

Late D r y a s stadial interrupted a r o u n d 1 0 , 9 5 0 B P the

Stelle d u r c h V e r ä n d e r u n g e n d e r Lithologie, G e o m o r p h o l o

development to a m o r e dense vegetation cover. T h e

gie u n d Hydrologie gesteuert. Pollendiagramme aus ver

Pinus

s c h i e d e n e n R e g i o n e n , d i e d a s g l e i c h e stratigraphische In

b a c e o u s plant c o m m u n i t i e s c o m p r i s i n g

tervall u m f a s s e n , z e i g e n oft d e u t l i c h e V a r i a t i o n e n in d e r

nigrum,

V e g e t a t i o n s g e s c h i c h t e , d i e n i c h t allein mit k l i m a t i s c h e n

( 1 0 , 1 5 0 years B P ) Betula

V e r ä n d e r u n g e n erklärt w e r d e n k ö n n e n . Ü b e r 4 0 0 Profile, d i e T e i l e o d e r d a s g e s a m t e W e i c h s e l Spätglazial u m f a s s e n , w u r d e n in d e n N i e d e r l a n d e n v o n

a n d Betula

w o o d s d i m i n i s h e d in s i z e a n d her

d e v e l o p e d . At t h e start o f t h e

Empetrum Holocene

a n d later o n Pinus

woods

e x p a n d e d again a n d b e c a m e m o r e d e n s e a s a result o f t e m p e r a t u r e rise. T h e r m o p h i l o u s t r e e s a s Quercus,

Tilia,

Ulmus

a n d Alnus

Corylus,

a p p e a r e d later in

the H o l o c e n e a n d are s u p p o s e d to h a v e b e e n a b s e n t *) Anschrift d e s V e r f a s s e r s : D r . W . Z. H o e k , T h e Nether lands C e n t r e for G e o e c o l o g i c a l R e s e a r c h ( I C G ) , F a c u l t y o f Earth S c i e n c e s , Vrije Universiteit A m s t e r d a m , D e B o e l e l a a n 1 0 8 5 , 1 0 8 1 H V A m s t e r d a m , T h e Netherlands.

during the Late Glacial in T h e Netherlands. T h i s g e n eral v e g e t a t i o n d e v e l o p m e n t c a n b e r e c o g n i z e d in m o s t o f t h e p o l l e n d i a g r a m s from T h e N e t h e r l a n d s .

Patterns o f Late Glacial v e g e t a t i o n in T h e N e t h e r l a n d s

figure 1. I lie continental position of The Netherlands during die Weichselian Late Glacial (modified after JELGERSMA, 1 9 7 9 and LANG, 1 9 9 4 ) .

Abb. 1: Die kontinentale Lage der Niederlande während des Weichsel Spätglazials (modifiziert nach JELGERSMA 1979 und LANG 1994)

H o w e v e r , pollen diagrams from different areas in T h e Netherlands s h o w clear variations in pollen c o m p o s i t i o n during t h e Late Glacial. Palaeogeographical approach For T h e Netherlands it is to b e e x p e c t e d that there w e r e o n l y small spatial differences in climate during the W e i c h s e l i a n Late Glacial due to the small area a n d relatively large distance to the f o r m e r coastline. As s e a l e v e l w a s b e t w e e n 9 0 and 65 m e t e r s b e l o w the p r e s e n t date level (JELGERSMA, 1 9 7 9 ) , the coastline w a s m o r e than 2 0 0 kilometers away a n d any climate gradient induced b y the sea can b e n e g l e c t e d for T h e Netherlands during the time under investigation. Fig ure 1 s h o w s the relative continental position o f T h e Netherlands during the Weichselian Late Glacial (modified after JELGERSMA, 1979 and LANG, 1994). In t h e classical a p p r o a c h , single l o c a t i o n s are the m a i n basis for p a l a e o c l i m a t e reconstructions. It is o b v i o u s that climate parameters derived from single pollen diagrams will represent certain local influen ces. T h e main reason for this is the fact that not o n l y the large scale c h a n g e s in climate determined the v e getation d e v e l o p m e n t in for instance t h e W e i c h s e lian Late Glacial. Also m o r e local variations in lithology, g e o m o r p h o l o g y and geo-hydrological c o n d i tions h a v e influenced the vegetation d e v e l o p m e n t

a n d patterns. P a l a e o c l i m a t e reconstructions b a s e d o n single pollen diagrams will therefore give a w r o n g picture o f the regional climate. With a p a l a e o g e o g r a p h i c a l a p p r o a c h the vegetation patterns and c h a n g e s in the patterns c a n b e compar e d with g e o l o g i c a l / g e o m o r p h o l o g i c a l maps. As s o o n as the relations b e t w e e n the palaeovegetation a n d the abiotic c o m p o n e n t s o f the landscape are k n o w n , the relations b e t w e e n vegetation and cli m a t e will be m o r e clear. This a p p r o a c h requires a d e n s e network o f palynological s e c t i o n s in an area with a well k n o w n g e o l o g y a n d g e o m o r p h o l o g y . The

Late Glacial abiotic l a n d s c a p e o f The Netherlands

T h e Late Glacial landscape is a landscape with chang ing g e o m o r p h o l o g y a n d vegetation. During the W e i c h s e l i a n Late Glacial g e o m o r p h o l o g i c a l p r o c e s ses w e r e active, but the abiotic c h a n g e s w h e r e not as large as during the preceding Pleniglacial. Morpholo gical features related to permafrost that had existed at the e n d o f the Pleniglacial d i s a p p e a r e d due to the c h a n g e s in climate towards t h e H o l o c e n e . Per mafrost disappeared, although d e e p seasonal frost m a y have occurred during the Late Glacial (VANDENBERGHE, 1 9 9 2 ) . T h e vegetation d e v e l o p m e n t initiated soil formation a n d stabilized the substratum. T h e

WIM Z. HOEK

Figure 2. R e c o n s t r u c t i o n o f t h e l a n d s c a p e t y p e s in T h e N e t h e r l a n d s d u r i n g t h e W e i c h s e l i a n Late Glacial ( m o d i f i e d

after

Zagwijn, 1986). Abb. 2: Rekonstruktion der Landschaftstypen in den Niederlanden während des Weichsel Spätglazials (modifiziert nach ZAGWIJN 1986) main landscape types that existed during the Late Glacial in T h e Netherlands are formed b y glacial, flu vial a n d aeolian p r o c e s s e s . F o r T h e Netherlands in general five larger l a n d s c a p e regions existed during the Late Glacial. 1 T h e till region in the northern Netherlands w a s form e d as a result o f the Saalian glaciation. Glacial tills

form the substratum in a gently undulating scape. In this region hundreds o f Pleniglacial remnants o c c u r ( D E GANS, 1 9 8 1 ) . From t h e s e remnants, formed after melting o f the p i n g o s e n d o f the Pleniglacial, m a n y pollendiagrams been obtained.

land pingo pingo at the have

2 T h e ice-pushed region in the central Netherlands

Patterns o f Late Glacial v e g e t a t i o n in T h e N e t h e r l a n d s

includes the e n d m o r a i n e s o f the Saalian ice-sheets. T h e hills rise up to a hundred meters a b o v e the surrounding river deposits a n d are built o f

older river deposits. B e t w e e n the i c e - p u s h e d ridges deposition o f c o v e r s a n d s t o o k p l a c e during the Weichselian Pleniglacial and Late Glacial (MAARLE-

WIM Z. HOEK

During t h e Late Dryas stadial a layer o f c o v e r s a n d was d e p o s i t e d over soils a n d peats, indicating the landscape w a s m o r e o p e n than in the p r e c e d i n g A l l e r 0 d interstadial. T h e organic deposits in this area consist o f peats and shallow lacustrine deposits forme d in t h e depressions b e t w e e n coversand ridges. 5 'Ehe c o v e r s a n d region in the southern Netherlands is characterized by a gently undulating t o p o g r a p h y . T h e c o v e r s a n d s are mainly deposited during t h e W e i c h s e l i a n Pleniglacial (SCHWAN, 1988). In t h e w e s tern part, Early P l e i s t o c e n e clayey deposits o c c u r at shallow depth. Like in t h e eastern c o v e r s a n d r e g i o n , organic deposits in this area consist o f p e a t s a n d shallow lacustrine deposits formed in the d e p r e s sions b e t w e e n coversand ridges. S o m e smaller p i n g o remnants o c c u r (KASSE & BOHNCKE, 1992). In figure 2a reconstruction o f the landscape in T h e Netherlands during the W e i c h s e l i a n Late G l a c i a l is given (modified after ZAGWIJN, 1986).

Available palynological data

Figure 4 : Regional Late G l a c i a l p o l l e n diagram o f t h e m a i n taxa for T h e Netherlands.

Abb. 4: Regionale spätglaziale Pollendiagramme der wichtig sten Taxa für die Niederlande. VHi.D & VAN DER SCHANS,

1961). As the

ice-pushed

ridges consist mainly o f well-drained gravels and sands, only a few w e t b a s i n s o c c u r w h e r e organic deposits c o u l d b e preserved. 3 T h e river region in t h e central Netherlands is main ly formed b y the rivers R h i n e a n d Meuse. As the ri vers c h a n g e d their patterns and m o r p h o l o g y b e t w e e n braiding a n d m e a n d e r i n g d u e t o climate c h a n g e , t h e a b a n d o n e d river channels form the basins w h e r e organic deposits could b e preserved. Under dry conditions during t h e s e c o n d p h a s e o f the Late Dryas stadial, sand w a s b l o w n out o f t h e braid e d river b e d s , forming riverdunes in the surrounding vegetation c o v e r (BOHNCKE et al. 1993). T h e river l a n d s c a p e during the Late Glacial has b e e n d e s c r i b e d b y KASSE et al. (1995) and BERENDSEN et al.

In T h e Netherlands over 4 0 0 palynological s e c t i o n s have b e e n investigated b y several institutes during the last d e c a d e s , covering part or w h o l e o f the Weichselian Late Glacial. Most o f the investigated sections are unpublished and the original data are stored as counting sheets in archives o f the G e o l o g i cal Survey, Soil Survey a n d different universities. As a first step in this study, t h e pollen countings w e r e gathered a n d inserted into a computer. B y n o w 2 5 0 of these sections are available in digital format. T h e data a r e stored in a relational database, using t h e E u r o p e a n P o l l e n D a t a b a s e structure. T h e spatial d e n s i ty o f available pollen data decreases in w e s t e r y di rection, directly related to the depth o f the Late Gla cial deposits below the present day surface. I n the most w e s t e r n part o f T h e Netherlands the Late Gla cial deposits are c o v e r e d with up to 15 m e t e r s o f H o l o c e n e fluvial sediments, marine s e d i m e n t s a n d peat. T h e r e f o r e , Late Glacial deposits are difficult to collect. Nevertheless, t h e spatial resolution is high, as c a n b e s e e n in figure 3. T h e locations o f t h e pol len diagrams which are stored in the d a t a b a s e are p r e s e n t e d as b l a c k dots, while the other l o c a t i o n s are p r e s e n t e d as o p e n circles. With this d e n s e pat tern o f palynological investigated locations a r e c o n struction o f the vegetation patterns in different time w i n d o w s during the W e i c h s e l i a n Late Glacial c a n b e made.

Preparation o f the palynological data

(1995). 4 T h e c o v e r s a n d region in t h e eastern Netherlands is characterized b y thick layers o f c o v e r s a n d formed during t h e Weichselian Pleniglacial (SCHWAN, 1988). In this region Saalian i c e - p u s h e d ridges o c c u r also.

For t h e construction o f the pollen diagrams from the pollen countings a uniformous pollen s u m w a s u s e d to calculate percentages, s o the diagrams c a n b e c o m p a r e d . In the pollen s u m only n o n - t h e r m o -

P a t t e r n s o f Late G l a c i a l v e g e t a t i o n in T h e N e t h e r l a n d s

Mekelermeer

Uddelermeer

Daarle

Middelbeers

100

F i g u r e 5: P o l l e n d i a g r a m s with s e l e c t e d taxa from 4 s m a l l b a s i n s in different r e g i o n s . a M e k e l e r m e e r (BOHNCKE et al., 1 9 8 8 ) ;

b U d d e l e n n e e r (BOHNCKE et al., 1 9 8 8 ) ; c D a a r l e (BIJLSMA & DE LANGE, 1 9 8 3 ) ;

d M i d d e l b e e r s (KOELBLOED, 1 9 6 9 ) .

Abb. 5: Pollendiagramme ausgewählter Taxa aus vier kleinen Becken in verschiedenen Regionen. a Mekelermeer (BOHNCKE et al., 1988); d Middelbeers (KOELBLOEO. 1969).

b Uddelermeer (BOHNCKF et al,

1988);

c Daarle (BIILSMA & DE LANGE,

1983);

philous trees, s h a i b s and dry h e r b s are included, r e Juniperus in zone Ic reaches the highest values up to gional taxa sensus JANSSEN ( 1 9 7 3 ) . T h e local p o l l e n 3 0 % in the diagram from the eastern coversand region taxa, aquatics a n d riparian h e r b s including C y p e r a (c) and 1 5 % in that from the central Netherlands ( b ) . c e a e , as well as thermophilous tree pollen a n d During the following zone 2a, the highest values for spores w e r e e x c l u d e d from the pollen sum. T h e m a Juniperus, up to 3 0 % are recorded in the diagrams jor shifts in the main pollen taxa, radiocarbon d a t e d from the central Netherlands and 1 0 % in the southern in several pollen diagrams distributed o v e r T h e coversand region (d). Netherlands, a r e used to construct a regional zonatiDuring zone 2 b Pinus has the highest value round on ( H O E K , in prep.). In figure 4 t h e zonation is p r e - 5 0 % in the diagrams from the till region, the central sent-ed as a generalized Late Glacial pollen diagram Netherlands a n d t h e eastern c o v e r s a n d region. T h e for T h e Netherlands o n an uncalibrated r a d i o c a r b o n values for Pinus in the diagram from the southern timescale. B a s e d o n the zonation, a zone c o d e h a s coversand region remain b e l o w 2 0 % . b e e n assigned to t h e analyzed levels from t h e p o l l e n T h e percentages o f Ericales, including Empetrum ni diagrams in t h e database. If a n y uncertainties a p grum, during z o n e 3 are the highest in the diagram peared, for instance in the c a s e o f a pollen s u m less from the northern Netherlands till region with values than 100, indications for reworking o r c o n t a m i n a up to 2 5 % . T h e diagrams from t h e central Nether tion, n o z o n e c o d e was assigned to that level. I n fig lands and the eastern c o v e r s a n d region s h o w values ure 5a-d four pollendiagrams with selected taxa a r e up t o 1 0 % a n d 7 % respectively. F o r e a c h pollen dia presented. T h e pollendiagrams are derived from gram in the database the m e a n a n d m a x i m u m values small (former) lakes, pingo remnants from the north o f the main taxa h a v e b e e n c o m p u t e d for the distin ern Netherlands till region ( a ) , t h e central Nether guished z o n e s . lands ice - p u s h e d region ( b ) a n d the eastern ( c ) a n d Construction o f the iso-pollen m a p s southern ( d ) coversand region. In these d i a g r a m s the differences b e t w e e n the percentages o f JunipeFor three z o n e s within the Late Glacial iso-pollen rus, Pinus and Ericales can b e s e e n . T h e higher p e r maps w e r e constructed showing t h e highest percen centages o f Pinus and Ericales at the, m i n e r o g e n i c , tages o f the distinctive taxa in that z o n e . Z o n e Ic a n d l o w e r part o f s o m e o f the diagrams are c a u s e d b y the base o f z o n e 2a are characterized b y high values reworking from older deposits. of Juniperus communis (Juniper), a s p e c i e s spread

WIM Z. HOEK

50 _|

100 __]

150

200

2 5 0 km

Figure 6: Iso-pollen map for the maximum values of Juniperus between 1 2 , 1 0 0 - 1 1 , 5 0 0 BP (zone Ic/2al). Abb. 6: Iso-Pollen-Kaite f端r Maximalwerte von Juniperus zwischen 12.100 und 11.500 BP (Zone Ic/2al). by birds a n d favoured b y the p r e s e n c e o f a b a r e sandy substratum. Z o n e 2 b is characterized b y high values o f Pinus sylvestris ( S c o t s p i n e ) w h i c h migrat-

e d around 1 1 , 2 5 0 B P from the south-east, presumably distributed along the river Rhine course. Z o n e 3 is characterized by high values o f Ericales, e s p e c i a l -

P a t t e m s o f Late Glacial v e g e t a t i o n in T h e N e t h e r l a n d s

100

150

200

250 km I

Figure 7: Iso-pollen m a p for the m a x i m u m values o f P i n u s b e t w e e n 1 1 , 2 5 0 - 1 0 . 9 5 0 B P ( z o n e 2 b ) . Abb. 7: Iso-Pollen-Karte f端r Maximalwerte von Pinus zwischen 11.250 und 10.950 BP (zone 2b).

ly in the s e c o n d part o f this zone. Empetrum nigrum (Crowberrry), the m a i n constituent o f the Ericales during this z o n e is spread by birds. It can b e d e m -

onstrated that the p e r c e n t a g e s o f t h e characteristic pollen taxa o f e a c h z o n e vary with the landscape type, HUNTLEY & BIRKS ( 1 9 8 3 ) presented iso-pollen maps

WIM Z. HOEK

ESS O-

50 _j

100

150

200

250 km i

Figure 8: Iso-pollen map for the maximum values of Ericales between 1 0 , 9 5 0 - 1 0 , 1 5 0 BP (zone 3 ) . Abb. 8: Iso-Pollen-Karte f端r Maximalwerte von Ericales zwischen 10.950 und 10.150 BP (zone 3). which show large s c a l e patterns in pollen p e r c e n t a g e over E u r o p e . T h e spatial resolution o f t h e s e maps o f E u r o p e is unavoidably l o w and

these m a p s can not b e u s e d for regional a n a l y s e s , For t h e construction o f the iso-pollen m a p s in this study, t h e locations with their m a x i m u m v a l u e for

Patterns o f Late Glacial v e g e t a t i o n in T h e N e t h e r l a n d s

the specific taxa within their distinct z o n e were re trieved from the database. Iso-pollen m a p s w e r e constructed using a squared inverse distance inter polation with a search radius o f 2 0 kilometers. T h e search radius is in a c c o r d a n c e with the possible s o u r c e area o f the regional pollen record. In areas w h e r e n o data w e r e available within the search ra dius the o u t c o m e has automatically b e e n blanked. T h u s n o extrapolations towards areas without data have b e e n made. T h e data points used in the inter polation are displayed as black dots. For z o n e Ic and the b a s e o f z o n e 2a, the time-win d o w from 12,100 - 11,500 BP, the highest p e r c e n tages o f Juniperus are plotted in figure 6. T h e p r e s e n c e o f Juniperus pollen during these z o n e s is r e c o r d e d in 8 2 pollen diagrams in the database. For zone 2b, the time-window from 11,250 - 10,950 BP, the ltighest percentages o f Pinus are plotted in figure 7. The presence o f Pinus pollen during pollen z o n e 2 b is r e c o r d e d in 113 pollen diagrams in the database. For z o n e 3, the time-window from 10,950 - 1 0 , 1 5 0 B P , the highest p e r c e n t a g e s o f Ericaes (mainly Empet rum nigrum) are plotted in figure 8. T h e pre s e n c e o f Ericales pollen during pollen z o n e 3 is r e c o r d e d in 114 pollen diagrams in the database.

Relationship between the iso-pollen patterns and the abiotic landscape T h e highest percentages Juniperus during z o n e Ic and 2a with values up to 3 0 percent are related to the ice-pushed ridges in the central and eastern Nether lands and the southern Netherlands coversand re gion. T h e s e areas consist o f the m o r e sandy welldrained sediments. T h e growth oi Juniperus commu nis is favoured by a bare sandy substratum and is therefore likely to have been growing in the coversand areas. Lower percentages are recorded in the river val leys and the northern Nedterlands till region, areas with higher groundwater levels and a less sandy substratum. T h e highest values o f Pinus during z o n e 2 b are re c o r d e d in the central Netherlands river region. T h e l o w e s t values are recorded in the eastern part o f the southern Netherlands coversand region. T h e r e s e e m s to b e no south-north gradient in the p e r c e n tage o f Pinus as suggested by several authors. As Pi nus sylvestris is at present growing on drier l o c a tions, it is s u p p o s e d that Pinus w a s not inhabiting the river valleys but g r e w on the higher parts o f the terraces along the river valleys. T h e high p e r c e n tages o f Pinusin the central Netherlands river region may also b e a result o f a more o p e n h e r b a c e o u s vegetation type, suggesting Pinus is o v e r r e p r e s e n t e d clue to king distance transport. T h e iso-pollen m a p for the m a x i m u m values o f Eri cales during z o n e 3 (figure 8 ) , s h o w s the high val ues, o v e r 2 0 % , linked to the poorly drainage a n d

l e a c h e d soils in tills situated in the northern Nether lands. In the ice-pushed region o f the central Nether lands and western part o f the southern Netherlands c o v e r s a n d area p e r c e n t a g e s a b o v e 1 0 % occur, pre sumably related to the o c c u r r e n c e o f a clayey sub stratum at shallow depth. Pollen diagrams from the c o v e r s a n d area a n d the nutrient rich river area s h o w values b e l o w 5% for Empetrum during z o n e 3. T h e high o c c u r r e n c e o f Empetrum nigrum is often used as an indicator for oceanity, based o n higher preci pitation rates. At present, a higher o c c u r r e n c e o f Em petrum indicates a l o w nutrient availability o r acid soils, a situation occurring already in the till region during the time u n d e r investigation. Empetrum is a b l e to g r o w in areas with an active aeolian sedimen tation, a situation that occurred during the s e c o n d p h a s e o f the Y o u n g e r Dryas (BOHNCKE et al., 1993). Conclusions Not only climatic c h a n g e s (temperature and precipi tation) influenced the vegetation d e v e l o p m e n t . Also m o r e local variations in lithology, g e o m o r p h o l o g y a n d geo-hydrological conditions influenced the ve getation and especially the vegetation patterns. As the vegetation in T h e Netherlands, a n d other areas, will not have b e e n uniformous during the Late Gla cial o n e has to b e careful with deriving the climate signal from single pollen diagrams. As T h e Netherlands o c c u p i e d a relative continental position during the Weichselian Late Glacial, it is not feasible that differences in the pattern o f Ericales dur ing the Late Dryas stadial are c a u s e d by a climatic gradient over T h e Netherlands. T h e r e will, h o w e v e r have occurred a climatic event causing the great e x pansion o f Empetrum nigrum in the areas favour able for this s p e c i e s . Acknowledgements T h i s study forms part o f the project: P a l a e o g e o g r a phy o f Late Glacial vegetations: analysis in time and space. Aim o f this project is to reconstruct the Late Glacial vegetation in the northwest-european lowland in re lation to climate a n d the abiotic c o m p o n e n t s o f the landscape. T h e project is s p o n s o r e d by T h e Netherlands Orga nization for Scientific Research ( N . W . O . - G.O.A.) and is incorporated in the research program o f T h e Netherlands Centre for G e o - e c o l o g i c a l Research ( I C G ) . Supervisor o f the project is Prof. Dr. W. H. Zagwijn, w h o is a c k n o w l e d g e d for his valuable c o m m e n t s on the text. T h e palynological data used in this study w e r e kind ly provided b y the following institutes; T h e Nether lands Geological Survey ( R G D ) , D L O Staring Centre, W a g e n i n g e n , Laboratory for P a l a e o - e c o l o g y and Landscape-evolution (University o f Gent, Belgium),

WIM Z. HOEK

H u g o d e Vries Laboratory (University o f Amster d a m ) , Laboratory for P a l y n o l o g y a n d P a l e o b o t a n y (University o f Utrecht), Institute for Prehistory (Uni versity o f Leiden) a n d t h e Faculty o f Earth S c i e n c e (Vrije Universiteit A m s t e r d a m ) . References BERENDSEN H.J.A., HOEK, WZ. & SCHORN, E.A. (1995): Late Weichse

lian and Holocene river channel changes of the rivers Rhine and Meuse in the Netherlands (Land van Maas en Waal). Paliäoklimaforschung Palaeoclimate Research, 14, 151-171. BIJLSMA, S. & DE LANGE, G.W. ( 1 9 8 3 ) . Geology, palynology and age

of a pingo remnant near Daarle, province of Overijssel, The Netherlands. Geologie en Mijnbouw, 62, 563-568. BOHNCKE, S.J.P., WLJMSTRA, L., VAN DER WOUDE, J . & SOHL, H. (1988).

The Late-Glacial infill of three lake successions in The Nether lands: Regional vegetational history in relation to NW Euro pean vegetational developments. Boreas, 17, 385-402. BOHNCKE, S.J.P., VANDENBERGHE, J.F. & HUIJZER, A.S. ( 1 9 9 3 ) : Perigla

cial Paleoenvironments during the Late Glacial in the Maas Valley, The Netherlands. Geologie en Mijnbouw, 72, 193-210. DE GANS, W. (1991): Location, age and origin of pingo remnants in the Drentsche Aa valley area (The Netherlands). Geologie en Mijnbouw, 61, 147-158. HUNTLEY, B. & BIRKS, H.J.B. ( 1 9 8 3 ) : An atlas of past and present pol

len maps for Europe: 0-13,000 years ago. Cambridge Universi ty Press, 667 pp. JANSSEN, CR. (1973): Local and regional pollen deposition. In: Birks, H.J.B, and West, R.G. (eds), Quaternary Plant Ecology, pp. 3 1 42, Blackwell Scientific Publications, Oxford.

JELGERSMA, S. (1979): Sea-level changes in the North Sea basin. In: Oele, E., Schüttenhelm, R.T.E. and Wiggers, A.J. (eds), The Quaternary History of the North Sea, pp. 233-248, Acta Universitas Uppsala, 2, Uppsala. 249KASSE, C & BOHNCKE, S.J.P. ( 1 9 9 2 ) : Weichselian Upper Pleniglacial

Aeolian and Ice-cored Morphology in the Southern Nether lands (Noord-Brabant, Grootc Peel). Permafrost and Periglacial Processes, 3, 327-342 KASSE C, VANDENBERGHE, J.F. & BOHNCKE, S.J.P. (1995): Climate change

and fluvial dynamics of the Maas during the late Weichselian and early Holocene. Palaoklimaforschung Palaeoclimate Research, 14, 123-150.

KOELBLOED, K.K. (19Ö9): Pollen diagram Middelbeers meerven. In tern rapport van de Stichting voor Bodemkartering, afdeling palaeobotanie, 2 pp. LANG, G.H. (1994): Quartäre Vegetationsgeschichte Europas. Gu stav Fischer Verlag, Jena. 4 6 2 pp. MAARLEVELD, G.C. & VAN DER SCHANS, R.P.H.P. (1961): De dekzand-

morfologie van de Gelderse Vallei. Tijdschrift van het Koninklijk Nederlands Aardrijkskundig Genootschap, 7 8 , 22-34. SCHWAN, J. (1988). The structure and genesis of Weichselian to Ear ly Holocene aeolian sand sheets in Western Europe. Sedimen tary Geology, 55, 197-232. VANDENBERGHE, J.F. (1992): Periglacial Phenomena and Pleistocene

Environmental Conditions in the Netherlands - An Overview. Permafrost and Periglacial Processes, 3, 363-374. ZAGWIJN, W.H. (1986): Nederland in het Holoceen. Rijks Geologi sche Dienst, Haarlem, The Netherlands, 4 6 pp. Manuskript e i n g e g a n g e n a m 17. 0 5 . 1 9 9 6