The Holocene tree limit history and stomata analysis

 

 

Holocene tree limit history in the northern French Alps stomata and pollen evidence

by David F. (1997)

Fernand David

in Review of Palaeobotany and Palynology 97(3-4): 227-237 – ISSN :0034-6667 –

https://www.infona.pl/resource/bwmeta1.element.elsevier-4cc2ec84-1075-3711-8f3f-f6accb544942

Abstract

Certain aspects of the Holocene tree limit history in the northern French Alps are inferred from both pollen and stomata analysis conducted in a subalpine marsh (2080 m a.s.1.). The proposed chronology is based on 1 4 C AMS dating of terrestrial plant macrofossils. In the area, Betula invaded this altitudinal level at the beginning of the Holocene prior to 9100 yr B.P., whereas the first occurrence of Pinus stomata is recorded much later at around 7000 yr B.P.

Afterwards five periods of stomata accumulation are recorded (6480-6130, 5600-4990, 4730-4470, 3200-2870 and 2680-2300 yr B.P.). The low pollen influx in the first four periods and the occurrences of Artemisia at the beginning of these periods indicate that stomata accumulation resulted from a reduction of the tree cover.

The climatic and/or anthropogenic origin of these stomata accumulations is discussed. A good correlation appeared with five of the nine phases of Holocene climatic deterioration described in the Swiss and Austrian Alps.

In this study, the combination of pollen influx and stomata determination proved to be a useful tool for understanding the tree limit history. Moreover, discrepancies in the occurrence of Pinus in an adjacent area imply it is difficult to find universal indicators of tree line fluctuations even in a small area.

This warrants methodological discussion.

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L’etude du contenu en pollen et stomates d’un petit site de l’etage subalpin asylvatique de la zone intermediaire des Alpes francaises du nord permet de proposer un schema de l’evolution holocene de la limite superieure des arbres dans cette aire et une chronologie basee sur 8 datations AMS de macrorestes vegetaux terrestres. Le bouleau colonise ce niveau altitudinal des le debut de l’holocene (avant 9100 yr B.P.) et precede les pins dont les premiers stomates sont enregistres autour de 7000 yr B.P. Cinq niveaux d’accumulation de stomates sont ensuite enregistres jusqu’aux deboisements de la periode romaine (6480-6130, 5600-4990, 4730-4470, 3200-2870, 2680-2300 yr B.P.). La diminution des flux polliniques dans 4 de ces niveaux et la reapparition d’Artemisia au debut de ces periodes soulignent la relation entre ouverture du milieu et accumulation de stomates. L’origine climatique ou anthropique de ces phases est discutee et une correlation apparait avec 5 des neuf phases holocenes de pejoration climatique decrites dans les Alpes suisses et autrichiennes. La combinaison des comptages de pollen et de stomates est un bon outil pour decrire les fluctuations de la limite des arbres si l’on considere les flux polliniques et non les seules frequences relatives. Cependant les differences chronologiques entre regions dans l’apparition des pins soulignent la difficulte a definir des indicateurs universels des fluctuations de la limite des arbres.

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Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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