A palaeoecological approach to the last 21 000 years in the pyrenees: The peat bog of Freychinede (alt. 1350 m, Ariege, South France)

Local palaeoclimatic and palaeoecological reconstructions in the Ariège Pyrenees were applied to palynological and sedimentological investigations of the Freychinède peat bog (alt. 1350 m), complemented by a geomorphological study of the neighbouring area. Correlations are possible between local glacial evolution, deposition in the lake and the history of the vegetational cover for the period from about 21 300 B.P. to 13 000 B.P. The altitude of the cirque floors indicates mean July temperatures probably ranging between 6.5°C and 8.5°C from 21 300 B.P. to 15 000 B.P.; 7°C and 9°C from 15 000 B.P. to 13 150 B.P.; 7.5°C and 9.5°C from 13 150 B.P. to the beginning of the final transitional phase. Based on the comparison of the palynological data with the modern plant communities of the area, especially with the subalpine and alpine communities, the local climate would have been favourable to the development of Boreo-arctic plants at the altitude of the lake during the cold phase. The Postglacial period begins near 10 650 B.P. with the extension of Quercus. Abies spread at about 7000 B.P. followed by Tilia cordata. From 5000 to 3900 B.P., Fagus spread moderately, but its strongest development occurred after about 3900-3800 B.P., when human activity began on the mountain forest and many beech—fir forests developed. Middle Ages, in many valleys of Ariège, the mountain and subalpine forests were destroyed. The modern landscape has large treeless zones with scattered recent populations of beech where fir is beginning to develop.