Stockmarr (Geological S11rvey of Demnark)
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RETROGRESSI VE FOREST DEVELOPMENT, AS REFLECTED IN A MOR POLLEN DIAGRAM FROM MANTINGER BOS, DRENTHE , THE NETHERLANDS ]. Stockmarr (Geological S11rvey of Demnark) , CONTENTS PREFACE AIM OF THE INVESTIGATION SOIL FORMATION . ABSOLUTE DATING 44 POLLEN DIAGRAM . 44 The mu/L phase . 45 First human interference 4 5 The amphimull Jorest 4 5 Second human interf erence . 45 Third human interference 47 CONCLUSION 47 REFERENCES 47 APPENDIX H. T. Waterbolk: The human occupation of rhc Mantingerbos area . J. STOCKMARR PREFACE bleached sand was a former mull. At the transition from sand to mor Querrns and Betula usually In 1970, Johs. Iversen and H. T. Waterbolk visited increased at the expense of Alnus, Tilia and Cory the small forest Mantingerbos in central Drenthe, Lus (plus Ulmus when the transition was old the Netherlands (fig. l ) , which is known as an enough). The present lower mor, which contains a almost pure !lex grove. Iversen discovered that the considerable amount of sand, should be explained soil was a mor "thicker than a pencil is long" and, as a former amphimull (see below). therefore, could be excellent for pollen analysis. In Iversen described five important events in the 1971, I visited the forest and collected material for mor diagrams. The first was the neolithic land pollen analysis. nam, probably 4,500 B.P. It was followed by weak Unfortunately, Iversen never saw the total pol traces of local clearings and catt!e browsing. The len diagram, and after his death in 1971 I decided next event was the re-immigration of !lex. In to publish it. Draved, !lex was found in Atlantic time, and after The pollen analytical work has been carefully an absence, for still unknown reasons, during a done by Mr. C. Vang Nielsen. Dr. Waterbolk and period of l ooo to l 5 oo years, it returned in la te Dr. van Zeist assisted in the interpretation, and Subboreal time. Iverseri estimated that the climate Dr. Waterbolk has been very hospitable during my perhaps was unsuitable for !lex in the intervening visits to the Netherlands. Kirsten Andersen made period. However, it is also clear that in the late the drawings. My sincere thanks are due to them. Iron Age !lex was favoured by catt!e browsing. The third event was the Iron Age clearing (1800- AIM OF THE INVESTIGATION 1900 B.P.), which favoured the expansion of the recently immigrated Fagus. The greatest clearing It is now more than 2 5 years since Iversen found ( the fourth event) was the Viking Age one ( l l oo that the Draved area in S. Jutland contains some B.P.). Parts of the forest were clear-cut and they of the most original mixed deciduous woods of became covered by grasses or Calhma. It took a Denmark. Draved is situated in a isolated area and long time before the forest was able to take pos was originally surrounded by moorlands. Except session again of the cleared areas ( the fifth change for some minor areas, human activity in the forest in the diagrams). has been rather low until the last centuries. During the work at Draved, Iversen got an in The soils in the forest are almost unchanged by timate knowledge of the forest dynamics, of which human activity. In some parts very thick mor he published only a minor part before his untimely layers (> 30 cm) were discovered. Iversen (1964) death. has demonstrated that mor layers are suitable for The study of the Mantingerbos soil was started pollen analysis. ci·1 determinations suggest that because Iversen hoped that by tracing !lex back to the fossil mor in Draved is very old, more than the Atlantic or at least to early Subboreal time, it 6000 radiocarbon years (Iversen 1969). During the could help to elucidate the phenomenon of the past 20 years many mor profiles have been ana early Subboreal absence of the tree in Draved. lysed, elucidating the vegetational history of Dra The Mantingerbos (bos= forest) is only 400 m ved forest (Iversen 1958, 1964, 1967, 1969, 1973), in diameter and lies on the fringe of the old village The diagrams give a very local picture, but the fields. Today, the forest consists of a ringshaped same type of vegetational development may be expected in other places where thick mor layers are present. In Draved Iversen worked on prob Fig. r. The location of Mantingerbos in Drenthe, the Nether lems concerning the soil development and es lands. The scale of the map is r : 30.000. The arable fields pecially on the interplay of soil, vegetation and are situated t0 the south of Mantinge, and between Gar human activity. minge and 13alinge. Mantingerbos (Mantinger Bosch) is standing on rhe fringc of the pasture area (with ditches). Iversen demonstrated that in the bleached sand See also fig. 6. Thc position of the section, from which below the mor Tilia and Corylus were the most thc samples of thc pollen diagram wcrc takcn, is indicated common tree pollen types, indicating that the by a white dot. Retrogressive forest development, as reflected m a mor pollen diagram ' ( . pc=:ø ) / "' 0 20 l V' " . I I . I ;' \ " . I '\ I \ \ km. · · I . · ,_ ... .... - I :,; ' . '<:' ' () i ""' ' , . " . .; ' " :·r ( ' \ .... '\ • ' ·' .... \ I Assen I ;.. I ' '\ / -.. ..._ / I 1 / _ I / l· ..... ......, , ' X ) Mantingerbos• , ,.I ( , • . " ...... Meppel....._ -- Emmen Ii """'"""\ f' ''<.-·-·--·....... • -.. --1 . ' ,-• 39 J. STOCKMARR llex forest with 3 or 4 great old Fagus trees and 5 5 - 70 cm dark brown humus pan some old Quercus trees. It is from this part of the 70 ->85 cm red- and yellow-brown humus forest that the pollen diagram is made. The central hard pan, not penetrated. part of the forest consists of middle-aged Quercus The words copromor and mycomor, which are trees with some Sorbus and a few young !lex trees. adopted from Iversen's unpublished notes, re This part is surrounded and intersected by dikes fer to mor dominated by arthropod droppings and and ditches. When this area went into forest is fungal hyphae respectively. unlmown. To explain the soil profile it is first necessary !lex is one of the most shade-tolerant trees in to describe the development of a forest podsol. northwestern Europe, but it is very susceptible P. E. Miiller (1879) writes that the biologically to cold winters (Iversen 1944). In closed forest active layers, the mul! and the "upper ground" it grows as a shrub with many suckers and mo (the submull), are usually 0.5-1.0 m, and same derate flowering. It could be a terrible weed in the times even l.5 m thick. When a mull changes into 19th century forest (Vaupell 1863). !lex has a a mor these layers become a pod sol (Miiller l 8 8 4, poor pollen dispersal and its pollen is not com Havinga 1963, 1968). monly found in lake and bog sediments, but in In the mul! stage the litter on the soil surface mor deposits it may be found in small amounts. is mixed with material from lower layers, frag !lex is susceptible to fire, but suckers will rise mentated and digested mainly by earthworms. Also quickly in great amounts if the soil was not heated nematods, protozoa, bacteria and fungi play an too much. Also forest clearing, especially when it important role in the decomposition of the organic is followed by cattle grazing, seems in some cases matter both befare and after digestion by worms. to favour !lex, and then it may become a tree of Even the pollen exine, the outer part of the pollen medium height. wall, which forms the basis for the pollen analysis, is decomposed. In time the soil becomes more and SOIL FORMATION more acid because of the high production of car bon dioxide, during the decomposition of organic Mantingerbos stands on holocene brooksand (Geo!. matter. Carbon dioxide in aqueous solution is acid map of the Netherlands no. 17, III, l: 50,000) at and together with the organic acids, it dissolves an elevation of approximately l 5 m above sea first lime, and later other minerals. level, and its topography is very smooth. In the When the mull becomes too acid the earthworms forest a profile was opened up alongside a low disappear, first the larger species and later the bank from where the following description was small ones. The more superficially working arthro made on moist material (see also fig. 4). pods take over the main role in the rotation of the upper soil. The other mull fauna and flora is o - 4. 5 cm mycomor, brown partly replaced by enchytraids and new fungi 4. 5- 9. 5 cm fossil mycomor, chocolate brown species, while the remaining bacteria are not able 9.4- 14·5 cm fossil mor, brown with sparse to break down the pollen exines. This is the tran sand, transition from fossil cop sitional stage from mull to mor, called amphimull romor to mycomor (Lafond 1952). The change may go faster if man 14.5- 22.5 cm fossil copromor with some sand, helps by cutting, burning and cropping the wood dark brown without manuring or fertilizing. 22.5- 29.5 cm greasy humus sand or fossil cop During the degradation, the submull at a deeper romor with sand, blackish brown level is isolated and mineralized, and through 29.5- 35.5 cm humus sand, grey-blackish leaching it will change into bleached sand. In the brown amphimull stage the organic debris is not totally 35.5- 39·5 cm sand, grey with !ittle humus (up mineralized and some insoluble humus will remain per bleached sand) in the soil. Also the pollen exines begin to remain 39.