Beyond Top Diagram the Corylus-Percentage Decreases Rapidly; Nevertheless It in the Whole Keeps Occurring Largely (40%) Profile up to 25 Cm

Untersuchungen an Niederländischen Mooren.

K Westerwolde .*).

Researches of bogs in Westerwolde, province of Groningen

H.J. Eshuis (Utrecht).

of S. E. The bogs Groningen are part of the great peat-marshes

from E. Drente inclusive. extending S. as far as N.W. Germany

So far as the territory of Westerwolde is concerned, people have off the begun digging very early. According to map by Krayen- hoff in 1816 nearly the whole peat-marsh westward from the line been few Blijham—Termaarsch had already reclaimed, only a parts still covered with the being original peat-layer (cf. map, fig. 1).

The digging off east of the above line commences at the beginning of the the borderland of and Drente. 19th century on Groningen in Borings were performed three places and the samples pollen- analytically and stratigraphically examined.

I. „Veenhuizer slukken”.

The first profile is from the ,,Veenhuizer stukken” north of Peat has been off for the in Termaarsch. dug greater part here, some

down to the sand. The still is about places bog existing 1,5:0 m this been thick, bigness probably having greater: the stratigraphic established investigations that probably a portion has already been dug off.

The of Pinus is at the percentage (cf. diagram I) very great com- mencement of the pollen-diagram (98%), Betula hardly occurs The extension of is and (2%). Corylus already very great (71%) increases maximum the of the at once to a (140%). Beyond top diagram the Corylus-percentage decreases rapidly; nevertheless it in the whole keeps occurring largely (40%) profile up to 25 cm

below the surface and then it descends to 20%. the decline As soon as Corylus-curve begins to after its maximum,

*) See Recueil dcs Travaux neerlandais Vol. XXIX botaniques (1932), p. 1 XXXII in het Botanisca and Vol. (1935) p. 430, also Mededeclingen van Museum Herbarium d. Utredht and en v. Rijksuniversiteit te no. 1, 23 24. 689

Fig. 1.

the of Pinus also falls off and it continues percentage very quickly

to with deviations round of to move slight an average j % up the surface.

Meanwhile Alnus has augmented and as in most of the N.W.

European profiles, Alnus also here has the greatest percentage of the het of the pollen in younger layers bog. Although in post-

glacial times Alnus has been a tree greatly coming to the front in these it is in characteristic of definite parts, not general a period. Diagram I: „Veenhuizer stukken”.

= = = 2 = Erica; = 1 Wood; Andromeda; 3 Calluna; 4 5 Monocotyle-

6 = 8 = = dones; = Scheuchzeria; 7 Rhynchospora; Hypnaceae; 9 Sphagnum. 691

Its extension in Central Europe is not nearly so great as in these regions (Rudolph 1930) and therefore the authors who have examined the of bogs N.W. Germany (Koch, Overbeck & Schubert and do take Schmitz, others*) not a separate Alnus period for granted. For the growth of Alnus is determined

by edaphic factors. Tiixen (1931) pointed to the fact that Alnus is with a tree typical demands of standing-place. Especially it

on a wet soil. The alder-marsh is grows very poor in plant nutri- tious matter, it furnishes, however, good pasture-ground and therefore most of the Alneta which have existed have changed into

most of grass-land. Along the brooks of Westerwolde Alnus is sure have to had a great extension, the nature of the soil which was for its Soon after its necessary growth being present. appearance Alnus has spread maximally (81%). The percentage decreases when the surface it is 61. approaching where yet Of the components of the Quercetum mixtum Quercus and Tilia the the appear at same time, in second place also Ulmus. Tilia

and Ulmus are found only in small quantities, Quercus is the

principal component of the Quercetum mixtum. A short time after

the of the mixtum in appearance Quercetum Fagus appears very small which quantities only, quantities, however, increase quite the surface. There also near appears Carpinus. In the same time the have Ericaceae a maximal development (380%); Betula origi- in small nally occurring quantities only at last also somewhat in-

creases. The whole profile practically includes only two periods:

1. a Pinus-Corylus-period, which terminates at the beginning of the diagram; Pinus and have a Alnus Corylus maximum, appears.

2. a has Quercetum mixtum-Corylus-period; Alnus a great later also extension, Fagus appears, on Carpinus; at the end of the diagram Alnus and Corylus decrease, Betula increases. the classical of the Though terminology postglacial climate by & Blytt Setnander has been waved aside by Von Post

( 1 93°)j Grosz K. Bertsch and (1930), (1935) others, we may use their nomenclature without the climatological connotation.

Von Post pointed to the fact that the terminology established

& Serna by Blytt nder, originally only meant for Scandi-

navia, however to other of conveyed regions Europe, is now even obsolete for Sweden too. In the first place because neither in Sweden nor elsewhere the sole definite border-line between its the subboreal-subatlantic periods, limit, was a turning point for forest-evolution in the for same degree as it was bog-stratigraphy, 692

while the terms boreal, atlantic etc. were also inadequate for the other stages of development. Secondly, because more recent investigations, especially in Sweden, have shown that the changes of climate had been considerably more complicated than the old scheme suggested. of tihe As division Von Post - a general postarctic epoch pro posed in accordance with the main features of European forest- of three development a system periods:

i. The stage of the approach of the warm period, characterized tihe and the first increase of by appearance relatively heat-loving

trees of different kinds.

The the of these forest-elements. 2. stage of culmination The of the decrease of the characteristic of the 3. stage trees

and the the return of the warm period appearance or predominant

forest-constituents of the present day. Summarizing the research of the last and best developed profile

we will trace how far the division of Von Post is useful here.

If we use the terminology of Blytt & Sernander only as

a division of time, therefore without the climatological connota-

Tree-stumps, found in the peat. (photo A. Pulle) 693

after with the of the tion, we may suppose comparison results investigation of neighbouring German bogs that the Pinus-Cory- lus-period is boreal, the Quercetum mixtum-Corylus period, the falling past crossing of the Pinus- and Alnus-curves, atlantic. As the has we were saying peat been dug off down to the sand in have some places. Fairly many tree-stumps come out the and during process, obviously originating from Pinus having forms. One two kind (on the right side of the photo) has a normal vertical whose there root-system, among parts are great clods of The of the other kind side of the sand. tap-root (on the left photo), has been the however, reduced and lateral roots have developed

horizontally; often the roots have curbed upwards partly. This latter kind of contains tree-stump peat among the roots. the from the sand is the Evidently stump coming older one,

it stood in the diluvial underground. When the soil became wetter and the peat began being formed, tap-root remained rudimentary and the lateral roots have strongly developed, that the roots should find sufficient for their existance. oxygen form the of The conic of stumps Pinus in the bog is striking.

Their origin will have been as follows; The foot of the tree getting surrounded also the horizontal in be- by peat, roots the long run short of and the died. The came oxygen finally tree atmosphere

and the acted most the border-line of air and water now upon and this decreases peat (at A in fig. 2) process gradually down to the lower end of the in When the has tree (B fig. 2). decay pro-

Fig. 2 Fig. 3

ceeded far off of enough the tree snaps on the border-line peat and air, and the conically formed lower end sticks with the roots the the influence of the in soil, thus being no longer open to The which weather (cf. fig. 3). tree keeps lying on the peat decays

totally and this explains why mostly only tree-stumps and seldom

whole trees are found in the peat. This, however, principally 694

holds good for Pinus; of Quercus often stems are found and no roots.

It is evident from the preceding, that the „Veenhuizer stukken” found their origin in the fact, that the soil of a forest changed into In a marsh. Germany this is called „Versumpfungsmoor”.

As to the further stratigraphic research, this has produced little that of Of the elements of the in the older is value. principal peat

wood and to be layers only Monocotyledones prove recognizable; in a nearer classification, however, was impossible general. Excep- tions to this are offered by Scheuchzeria and Rhynchospora; the

its former was easily to be recognized by fibrous structure, of the latter fruits found. The were whole, however, gives an impression of wood-peat; gradually the trees must abandon the contest against the growth of the bog. More in the first and upwards, atlanticum, Sphagnum appears next Ericaceae (twigs, leaves and flowers of Calluna and Erica, of a seed Andromeda): so the peat-formation has become from These old meso- oligotrophic. layers belong to the peat, which from the of appears high degree weathering; young Sphagnum- all the of the peat fails over. Perhaps upper part peat already the the the belongs to border-layer, i.e. peat underlying Grenz-

Horizont of Ericaceae is is (the percentage great here); it not however. We take it for that the clear, must granted young

Sphagnum-peat, if it has ever been present, has been dug off all over.

II. „Hoornder veen”.

The second bored in the km profile was ,,Hoornder veen”, 3

of Wedde. Here too the whole has been off west nearly peat dug and the land has been made fit for agriculture. The remaining above the like part rises surroundings an island.

The pollen-analytic research brought to the light that this profile is older than the it in the preceding one; begins preboreal. Just

as the Veenlhuizer stukken” the lies on sand. The bottom- „ bog is in of the other hand sample very poor pollen trees, on many

Cyperaceae-pollen were found: in onze preparation 2 Betula-, 2 and but Pinus-, 4 Corylus-, 65 Cyperaceae-pollen (cf. diagram II). conclude that this there From this we might at time were no forests (cf. Firbas 1935). The late-glacial, i.e. the time which passed between the recession of the ice from the inmost Baltic final-moraine and the second Finnish Salpausselka, was divided by Firbas into three periods: which characterized 1. an arctic period, is by forestlessness. Diagram II: „Hoornder veen”.

Vaccinium = = Calluna; 1 — Charcoal; 2 = Oxycoccus; 3 Erica; 4

= = 5 Andromeda; 6 — Monocotyledones; 7 Eriophorum vaginatum;

8 = Rhynchospora; 9 = Sphagnum. 696

subarctic in which Betula- and 2. a period, pure Pinus-forests

are found.

in which found the first 3. a proper preboreal period, we of the Alnus the appearance more demanding trees; Corylus, and the mixtum. components of Quercetum In the researched profile the first period is clearly to recognize.

The second period, however fails; in the research, at least, it has been found. The of this be die distances not cause may too great between the researched samples; for in the sandy bottem-layers each much than in the cm represents a longer period higher parts of that the distance the bog, so proportionally in deeper layers the

between the samples must be much smaller. When the pollen-diagram begins, Betula and Pinus still dominate

and though Betula still prevails, this tree already is decreasing.

For a short time Pinus still rises, then reaches a maximum (71%) and afterwards is the whole present during profile, just as Betula, but in lower percentages.

Meanwhile the heat-loving trees, which at the beginning of the

diagram already were found in small quantities, have increased

greatly: Alnus soon reaches a high value (67%) and keeps moving round this value the further same as an average during development of the bog. The boreal, which has begun about the Pinus-top, has its ending

at the crossing of the Pinus- and Alnus-curves and is succeeded the atlanticum. The rises maximum of by Corylus-curve to a 91 % and further the the surface with remains in profile up to an value the lies average of 31%. In „Hoornder veen” a Corylus-top about the middle of the atlanticum; in the „Veenhuizer stukken” lies this top still in the boreal. Koch (1929) found in the

Miinsterland in general a Corylus-top in the boreal and in the

atlanticum a secondary rising of Corylus, which sometimes was

Van greater than the first maximum. Raalte & Wassink found Meer (1932) in Zwarte now a top in the boreal, now in

the atlanticum, now in both. Van Dobben (1932) found in

the bog of Valthermond a Corylus-top in the atlanticum. Evidently the the other fail. It is now one, now top may possible too that

of both is not found account of distances one tops on too great between the samples.

Before Corylus has its maximal value, the Quercetum mixtum

reaches a As to the order of of the already top. appearance com-

ponent parts of the Quercetum mixtum this must be thought a« follows; first then Ulmus and Tilia. Quercus appears, finally reaches with the Quercus first a top (and together Quercus Quer- 697

cetum mixtum), then Tilia and finally Ulmus. Two with the the of other tops concur Corylus-top: group

Varia has a maximum of 42%, the Ericaceae even exceed 650%. At that time the have been wooded. surroundings may thinly and Even before the Grenz-Horizont now again Fagus appears small the Grenz-Horizont rises in percentages; only passed Fagus

above 10%, be it only for a short time. Then also the first

Carpinus appears. The of the forests be resumed here follows: history may as

1. a forestless period.

2. a short Betula-Pinus-period succeeded by in which Alnus imme- 3. a Quercetum mixtum-Corylus-period diately has a high value, Quercus, Tilia, Ulmus, and Corylus in

turns reach maxima, Betula sometimes occurs in still important

percentages and Fagus begins to appear.

A Fagus-period such as the German bogs mostly show and

such as Ten Houten (1935) found in the „Korenburger veen”

also, does not occur here. the other the research Just as with two profiles, stratigraphic has been done less when aim thoroughly, because we at getting acquainted with the forest-history, it is of less importance than the pollen-analytic research.

In the preboreal and in the boreal only remnants of Monoco-

tyledones are found. Shortly after the crossing of the Pinus- and

Alnus-curve, in the atlanticum therefore, Sphagnum begins to in the formation of the Later it is Erio- help peat. on especially phorum vaginatum and Calluna (twigs, leaves and flowers) and Erica some less important Ericaceae (Vaccinium Oxycoccus, and that the bulk of The main Andromeda) compose the samples. constituent is old Sphagnum-peat. Remarkable of which be found is the occurrence charcoal, may the atlanticum the Grenz-Horizont. The Grenz-Horizont from up to is and lies below the surface. The easily observed, at 17 cm upper of full of of 7 cm the peat have greatly decayed and are roots the recent vegetation.

III. „Veeler veen”.

The last bored in the km profile was „Veeler veen”, 6 east of Wedde. drew At the time when Krayenhoff his map of these regions were totally consisting bog yet. Little by little large fragments have been reclaimed, indeed, but still there is

original bog, which is being worked until the present day. The basins formation of the peat has begun in mossdiags, great 698

in the ground from to to 20 m diameter. When these moss-hags

had been filled, the bog kept growing in an upward direction,

at the same time the between the overgrowing space moss-hags, last soil covered with of so that at the whole was a layer peat

By sounding it was possible to find the middle of a moss-hag, so that a profile of 4,38 m could be bored. The A bog lies on sand. typical forestless period with high

values for the Cyperaceae was not found, alas. The diagram

Diagram III: „Veeler veen”.

= = 1 2 = Wood; Monocotyledones; 3 = Andromeda; 4 — Calluna; 5

6 = Erica; Menyanthes; 7 = Viola palustris; 8 = Myriophyllum; 9 =

= Betula Nuphar; 10 = Batrachium; 11 nana; 12 = Eriophorum vaginatum;

= = = 16 = 13 Potamogeton; 14 Scheuchzeria; 15 Scirpus; Carex; 17 =

18 = Bryales; Hypnaceae; 19 = Sphagnum imbricatum; 20 = Sphagnum

= spec.; 21 Selaginella. 699

(cf. diagram III) begins at the time of the subarctic Betula- and

Pinus-forests, the second period of F i r b a s. As remnants of the

former tundra-vegetation in these layers were found Selaginella

selaginoides (microspores) and Betula nana (leaf-fragments). In

the „Soesterveen” Selaginella was found In the first, forestless

of F i b in the at the rise of period r a s; same period and the

subarctic forests also Betula nana. In the „Veeler veen” both are found found somewhat later. Probably they in the bog a refuge, which their demands the best The of Vrie- met in way. research

zenveen („Bruine Haar”) by Florschiitz & W a s s i n k (1935),

where Selaginella is found as late as the Pinus-Corylus-period, that also later be found. proves on Selaginella may

which first with an value of far Betula, at average 90% exceeds Pinus, decreases after some time and is then almost

completely crowded out by Pinus. Near this change of domination the a maximum of the Cyperaceae is found. This does not attain

100% but points to a smaller density of forests during a short time of Carices. or to a stronger growth Now there in succession and appear Quercus, Corylus Alnus, of b The so here the third period F i r a s is reached. preboreal ends less when the reaches In the more or Pinus-curve a top. boreal of Pinus in- a rise Corylus appears. soon declines, Alnus and in the former the atlanticum with creases, as profiles begins the crossing of the Pinus- and the Alnus-curve at about 40%. Of the of the mixtum components Quercetum only Quercus is

a rather important element. Tilia and Ulmus have a small share in the of the the of Tilia composition forests; greatest percentage

of Ulmus The mixtum reaches a with isi 3, 4. Quercetum top Corylus. Except as for Fagus, the diagram has a normal course.

Fagus, however, is to be found here in the atlanticum already

at of below the maximum a depth 1,75 m surface soon finding a of reduced and extension there; next it is soon again to nought

until below surface it In not 0,75 m the appears again. general

Fagus begins in the Netherlands shortly before or after the Grenz- least with somewhat 1 Horizont, at important percentages (F o r- schiitz others Wassink & 1932, Florschiitz & 1935,

Ten Bouten 1935). An exception to this is the bog of „Boe- which rendijk” (Vriezenveen), was explored by Florschiitz

& Wassink. The authors to have settled suppose Fagus during the atlanticum here and there the that on sand, so only at the

outskirts it sent pollen into the bog.

Vermeer—Louman (1934) also mentions some finds of

In Fagus from old layers. a boring near Sloten (province of 700

N. Holland) she found the empirical limit of Fagus-pollen (i.e. the beginning of the cohesive curve) in the boreal. In the atlanticum attains of the total of the Fagus 4% at a depth 4 m; then percentage gets low again. The rational limit of the pollen (i.e. the

of tihe continued rise of the lies at the beginning curve) 2,35 m, bottom of the young Sphagnum-peat. Polak (1929) too found already regularly Fagus in the old Sphagnum-peat of the „Riekerpolder”. who also noticed the fluctuation the Ernst (1934) great in empirical and the rational limit of Fagus-pollen, distinguishes three of of with the Grenz- types curves Fagus-pollen regard to Horizont:

while 1. the Fagus-curve begins below the Grenz-Horizont, the absolute, empirical and rational limit coincide. The curve rises without a minimum to a top. sub while also the 2. the Fagus-curve begins as 1, absolute, rational limit coincide. The makes empirical and curve a top immediately, but soon falls again, after which only above the

Grenz-Horizont a maximum is formed. the and rational 3. absolute, empirical pollen-limits are sepa- rated distances. above the the for- by great Only Grenz-Horizont of mation a top begins.

Ernst points to the fact that Fagus must have spread irregu- larly and that at first only here and there it has obtained a foothold. factors will have here. The dis- Edaphic played a part tribution by animals and men, which according to Ernst possibly has contributed to the spreading of Fagus, probably is of little importance. What factors, however, cause the minimum with the second which the of the veen’ type, to present case „Veeleer belongs, Ernst does not point out. As Fagus according to

F. Bertsch (1935) occurs only in a specific climate (Fagus oceanic and shuns the continental wants an climate), we might here of climate. The three of expect a change types Ernst, found divided almost dis- however, are not regionally but in all tricts explored, from the Ems as far as in the north-east of Denmark close together. So a factor of climate is impossible.

Though we cannot indicate a further distinct cause for the the of the second evident that minimum in Fagus-curve type, it is the importance of the Grenz-Horizont, at least with regard to the of appearance Fagus is only slight. in the veen’': Summarizing we may distinguish „Veeler

1. a Betula-Pinus-period. which 2. a Pinus-Betula-period, during Quercetum mixtum, 701

and Alnus Corylus begin to appear. in which has 3. a Quercetum mixtum-Corylus-period, Alnus a

great extension and Fagus a small top. the 4. a Quercetum mixtum-Corylus-Fagus-period, during which quantity of Fagus increases for the second time, but in small density.

Distinguishing the climate-periods according to Von Post in this with difficulties. The first the diagram meets period, approacn of the with the and the first extension warm period appearance of the in the far the heat-loving trees goes diagram nearly as as Pinus-Betula-period inclusive. This period is succeeded by the

Quercetum mixtum-Corylus-period in which both Quercus and culmination therefore of Corylus show a top, a heat-loving trees, which is typical of the second period of Von Post. Limiting

the third period, however, is more difficult. For a typical decrease

of the characteristic trees of the second period (components of the

Quercetum mixtum and Corylus) does not actually occur. Perhaps

it is right to draw this line between the Quercetum mixtum-Cory-

lus-period and the Quercetum mixtum-Corylus-Fagus-period as

according to F. Bertsch Fagus might point to the fact that the climate became rather atlantic.

The research the that the stratigraphic brought to light peat in

the moss-hag is caused by the change of a pool into land. From the

sand far found which to this as as 3,20 m Hypnaceae are point fact. Further seeds of Potamogeton, Nuphar luteum, Myriophyllum alterniflorum, Batrachium, Scirpus and Menyanthes. Also Carex

and Scheuchzeria were found in rather large quantities. Remark- is the of in the first able, however, presence Sphagnum eutrophic vegetation. finds be mentioned: From 3,20 m up to i,jj m as principal may Scheuchzeria, Carex, Scirpus and other Monocotyledones which

could not be determined. Above this layer begins the old peat all of but for which, however, is not composed over Sphagnum, the of indeterminatae. Rather there greater part Bryales soon appear

Ericaceae, first Erica, next Calluna.

Between and there of water in the 1,40 m 1,30 m was a layer bog, hence the interruption of Erica and Bryales.

A distinct border-layer cannot be distinguished; this proceeds

from the old which ends at where the unobservably peat 1,10 m, The latter consists of not-determined young peat begins. Sphagna

and especially of Sphagnum imbricatum. There are to be found Ericaceae (Erica, Calluna and Andromeda) and especially Erio- phorum vaginatum. 702

To conclude short follow of the a comparison may profiles

researched here with the bogs that are nearest; the bog of Val- thermond (Van Dobben 1932) and the bogs of Emsland

(Koch 1934 a, b, c). On most points these researches exhibit resemblance with the Westerwolde. a great outcomes at

The bog near Valthermond has developed in about an equal

the veen”. thickness as „Veeler Of both the forest-history mav be retraced far the The further as as in preboreal. development of the forests is nearly the same with both of them, with these exceptions, however, that Van Dobben found the absolute limit of the Fagus-pollen only after the Grenz-Horizont, and that decline the he observed a of Corylus-percentage after the subboreal-

subatlantic contact. The stratigraphic research brought to the light that far the limit of boreal and the atlanticum the as as the peat was

formed This of to the by Hypnaceae. way originating points change of a pool into land, so the same as happened with the formation

of the „Veeler veen”. Here this was more evident, however, through the finds of Potamogeton, Nuphar, Myriophyllum and Batrachium.

Koch, on the other hand, nowhere found as origin of the

peat-formation the change of a pool into land but always the of forest change a into marsh, probably by the rising of the in the has been described ground-water; same way, therefore, as veen” as to the „Veenhuizer stukken” and the „Veeleer outside

the The of K h’s moss-hags. bottom-layers o c bogs always are wood-peat.

K o c h’s most fully developed profiles begin in the preboreal,

in the subarctic period, in which no Selaginella was found indeed,

but where Betula nana was shown by pollen-statistical numera-

tions. The exactness of this method to demonstrate Betula nam called of is in question, however; at any rate leaf-fragments are

more importance and these where not found by Koch. Koch’s oldest profile which is from the „Walchumer Moor”

(8 —10 km S.S.E. of Boertange) shows in the preboreal and the boreal repeatedly change of domination between Betula and Pinus. Possibly these changes would have been found in the „VeeIer veen” and the if the distances between the ,,Hoornder veen” too, researched had been taken shorter. With Koch these samples are 5 cm,

with the researches cm. present 15 for the further of the this As process forest-history agrees espe- with that of the which is cially „Veeler veen”, so to say part of the bogs of Emsland. in of the before Grenz-Horizont Fagus most profiles appears the 703

and then takes an extension (e.g. in the ,,Walchumer Moor”) of

6 to 7% in the atlanticum and subboreal (in the „Veeler veen” 10%). After the Grenz-Horizont Fagus reaches values of 25%, found Westerwolde. percentages not at Valthermond nor at Any- is old how, in S.E. Groningen Fagus already a very tree.

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