Pollen analysis of post glacial peats and deposits in France for the period 1939?1946
✍ Scribed by Dubois, Georges
- Publisher
- Springer-Verlag
- Year
- 1948
- Tongue
- English
- Weight
- 576 KB
- Volume
- 1
- Category
- Article
- ISSN
- 1573-5052
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✦ Synopsis
Special care was given to pollen analysis on the surface of peat bogs and forest humus of the present day, and to peaty soils in the mountains of Auvergne, research being made by G. L e m 6 e and by G. and 1VIme C. D u b o i s . T h e y have confirmed the w e l l -k n o w n fact that pollen of P i n u s disseminates m o r e easily and in a greater radius than other pollens, e v e n those of A b i e s and P i c e a. At the surface of the peat bogs of the Montagne Bourbonnaise and the Monts-Dore (G. L e m 6 e, 1941, 1942), and even in the humus of present-day forest soils, far a w a y f r o m pine-barrens, at the v e r y heart of n a t u r a l or planted clumps of F a g u s , A b i e s and P i c e a , in the Cantal (G. and C. D u b o i s in ~. D ub o i s 1946), one n e a r l y always discovers 10--30 % of P i n u s pollens, sometimes e v e n t h e y reach 50--68 %.
The investigations of M m e M. V a n C a m p o -D u p 1 a n (1945) m a d e in Paris at the Bois de Boulogne about pollen-fall in the course of two spring days, also r e v e a l a superrepresentation of P i n u s pollens, but at the same time of A e s c u 1 u s which w e r e in blosom at the time at which the experience took place.
In the Monts-Dore d ' A u v e r g n e G. L e m 6 e (1942) stated that in wooded country, the trees growing on peat bogs or in their immediate vicinity, are represented, with regards to their pollens, w i t h the utmost frequence, especially in the direction of p r e d o m i n e n t winds; in bare country, on the other hand, the most anemochoric trees and those which produce the greatest quantity of pollen are over-frequent.
Besides, it becomes evident through the research of G. L e m 6 e (1942) in the Monts-Dore, and of G. and C. D u b o i s (in G. D u b o i s 1946) in the Cantal and in the Alps, that the spots whose altitude is above the natural or artificial forest limit, receive a pollen contribution which is fairly representative of the average forest composition of the slopes which they are overhanging.
The analysis of peaty mountain soils in the Cantal, on spots which are above the present-day forest limit, between 1500 and 1858 m, made it possible for G. and C. D u b o i s and F. F i r t i o n (1944 a and b), to demonstrate that these soils do not belong to, the present day in their full depth, bu~ that they h a v e a certain historical and e v e n prehistorical ancientness. They are the result of a slow accumulation of chiefly eolian n a t u r e of tiny m i n e r a l particles, joined together by means of a peaty substance due to the slow humification of the vegetal carpet, u n d e r the influence of the cold and damp climat6j of mountanous regions. W h e n it reaches a thickness of several decimeters, several thousand years have been r e q u i r e d to accumulate that mass.
A certain n u m b e r of conclusions d r a w n f r o m G. and C. D u b'o i s ' papers on different peat-bogs in mountains or plains refer to questions of general scope. A p p l y i n g to occidental Europe the postglacial geochronology of D e G e e r, in correlation w i t h the synchronism generally admitted of forest evolution, the authors take for granted that the m e d i u m g r o w t h in thickness of the evoluated peat is about 0.5--0.6 m m in the mountains and in most of the valleys. This m e d i u m growth is often m u c h less. It is sometimes more considerable, for instance in the peat-bog of the P u y de l'Enfer or d'Espinasse (Chain of the Puys, A u v e r g n e ) (G. and. C. D u b o i s and F. F i r t i o n 1945), wher e it reaches up to 2.14 mm. In the l o w e r valleys and the estuaries the annual speed of peaty accumulation is bound to be linked to that of the m e d i u m sealevel in the course of the Flandrian transgression, a glacio-eustatic event resulting f r o m the W u r m glacial recession; thus the pollen analysis allows to m a k e sure that this moderate speed of ascension scopes f r o m one to a f e w m m per a n n u u m (G. and C. D u b o i s 1943 a and b).