A Long Term Perspective of Landscape Evolution in a Coastal Interface: Case Studies from the Portuguese West Coast, Near the Aveiro Lagoon

Abstract

Based on data from different disciplines, such as Archaeology, Palaeobotany and History, the key moments of landscape evolution in the coastal stretch surrounding the Aveiro Lagoon are identified and interpreted in a broad diachronic perspective. In the southern part of the region, just north of the Lower Mondego River Valley, we find a broad flattened area, where the predominant sandy soils overlap deposits from ancient Pleistocene beaches. The wide and complex chronology of these deposits and the characteristics of its components suggest that during their development, environmental constraints, such as climate and vegetation, imposed severe limitations on human settling, as testified by the absence of archaeological remains in the lower deposits, extending westwards, which survey was facilitated by various sand quarries. This evidence contrasts with the presence of Acheulean assemblages in Mealhada, nearby the Cértima valley, in deposits which some authors considered to be equivalent to some of the Pleistocene beaches indicated.

Later on, in the end of the Pleistocene, the extensive dune formations that cover the previous Pleistocene deposits was associated with a severe episode of aridity that affected the entire region. Represented by a covers and extremely aeolised, this formation was currently named Areias da Gândara. Recent studies allow more precise chronology and also reinforce their similarity to the Landes formations, in France.

Lack of data from the Pleistocene-Holocene transition does not allow us to characterize the coastal landscape in this phase. Still, it is clear that in the Mid-Holocene extensive pine and oak forests were found in the region. As in other western Iberian coastal areas, during the Bronze, human activities led to a significant decrease in forest areas, marking a new phase of landscape evolution. These seem to be connected with changes in human societies, agriculture and settlement. This trend became clearer in later periods, following major changes in the strategies of occupation and exploitation of the territory. It is clear, from this stage, the expansion of heathland presumably as a result of the increase in animal husbandry.

These were already predominant in Roman times.

Agricultural and grazing signs continue to be important drivers of change throughout Medieval and Modern times. These and the climate changes related to the Little Ice Age led to a progressive destruction of vegetation cover and subsequent sand accumulation. This scenario which affected several areas of the Portuguese coast has been intensively studied further north in the Aveiro Lagoon.

That is exactly what was happening across the Gelfa, the medieval name assigned to the sandy spit developed from the South of Espinho that closed the large bay formerly localized in the area of the current Aveiro lagoon. Until the nineteenth century no permanent human occupation was found in the sandy cordon, probably due to lack of suitable agricultural fields and the risk of piracy. Such areas were only used for pasture as well as a starting base for sea fishing with the art of xávega, further developed by the implementation of the canning industry (eighteenth century). This scenario only changed with the forest stands for dune fixation initiated during the twentieth century.

Whether climatically induced or anthropogenic, changes in vegetation are an important variable for the understanding of the trends in human settlement in the region in a long-term perspective.

However, it is necessary to increase our knowledge of the diachronic, regarding such multiplicity of factors. Only then will we be able to fully understand the characteristics and the intensity of such changes.