Studies in the Vegetational History of S. W. Spain. IV. Palynological Investigations of a Valley Mire at El Acebron, Huelva

Abstract

The peat and pollen stratigraphy of a valley mire site in the south-west of Spain was examined by means of a transect of borings. Pollen analysis and radiocarbon dating reveals that at the time of mire initiation (approximately 4500 BP), Pinus was by far the most important tree in the area, but was undergoing destruction at the hands of Bronze age/Copper age man. Quercus was more prominent during the subsequent recovery of the vegetation, but there is evidence of continued disturbance, both in the form of charcoal inwash into the site and in the frequency of pollen from indicators of burning (such as Cistus-type) and soil disturbance (such as Loeflingia-type, Echium, Plantago and Rumex). The biostratigraphic and lithostratigraphic evidence reveals a major episode of vegetation destruc- tion and burning which resulted in a complete layer of mineral sediment and charcoal being deposited across the entire valley. Only in recent times (about the last 100 years) has Pinus recovered fully in the area, and this is probably the result of planting, for it is accompanied in the pollen record by Eucalyptus, which has been extensively planted in the last 80 years. Vitis vinifera pollen is found in a series of three peaks, the earliest dating from 4340+80 BP, and some attempt is made to interpret these in the light of a number of surface samples taken in a transect across the carr vegeta- tion of the mire, where Vitis currently occurs as a liane. One of the three peaks is associated with high values of carr taxa, such as Salix, and could be accounted for by the local growth of wild vine in carr vegetation, but the other two peaks are associated with evidence for soil disturbance and are likely to have resulted from viticulture. Peat stratigraphic studies of the mire suggest that the first development of peat at the site resulted from hydrological changes induced by vegeta- tion destruction in the catchment. Subsequent forest clearance and burn- ing has had considerable influence on the development of the mire and may have been a prime factor in the establishment of Fraxinus angustifolia in the margins of the present carr.