Landscape dynamics during the last 17,550 years in Cantabria, northern Iberian peninsulaapproaches from palaeoecology

Laburpena

The Cantabrian region (northern Iberian Peninsula) is an area of great palaeoecological interest. It is one of the European regions with the most documented archaeological sites, with multiple evidences of human presence since the Palaeolithic. From a botanical point of view, the area is of particular interest since it is located in the Eurosiberian biogeographical region yet is influenced by the Mediterranean. This thesis studied the evolution of the Cantabrian landscape over the last c. 17,550 years, with special emphasis on discerning the source of landscape changes, determining the role of fire and examining the various phases of mining activities. A multiproxy approach was adopted in a sedimentary record from La Molina peat bog (43.26º N, 3.97º W, 484 m a. s. l.; Puente Viesgo, Cantabria) that covers the last c. 17,550 years. Analyses were performed on organic matter content, sedimentary macrocharcoals (>150 µm), pollen and non-pollen palynomorphs for the whole period. Trace metal content (Cu, Ni, Zn, As, Cd and Pb) and Pb isotope ratios were analysed for the last c. 6740 years. For a better interpretation of the palynological record, calibration of the contemporary pollen rain of certain Cantabrian plant formations was performed based on the study of modern surface samples (mosses, n = 79). The fire regime was also explored in another Cantabrian peat bog, El Cueto de la Espina (43.06º N, 3.91º W, 1120 m a. s. l.; Corconte, Cantabria), through analysis of sedimentary macrocharcoals (>150 µm) over the last c. 5725 years. The results highlighted the importance of modern pollen rain calibration in interpreting palynological diagrams. In La Molina, there is no evidence of pine forests over the whole period. A steppe-like formation was revealed until the spread of Betula at c. 13,700 cal yr BP, which oscillated following climate variability until the onset of the Holocene. A mixed deciduous formation composed of Betula and deciduous Quercus was established in the region from that point onwards. In addition, a series of biomass pulses was detected during the early Holocene, probably linked to intervals of increased rainfall in the Cantabrian region. During the arid phases of the 9.3 and 8.2 ka events, the first significant fire episodes occurred which created open spaces and favoured the expansion of Corylus. Biomass pulses were no longer detected, revealing different behaviour from the Early Holocene. The charcoal record, however, rules out the use of fire to manage vegetation until the onset of the Neolithic. From that point onwards, cultural use of fire was deduced in La Molina with intervals of particular intensity during the arid phases of the Bond events 3 and 2 (c. 4200 and 2800 cal yr BP). The comparison between the two peat bogs allowed the identification of intervals with varying fire behaviour according to the degree of human pressure. Concerning the mining activities, trace metal contributions were identified from the Chalcolithic onwards, with intervals of particular relevance during the Iron Age, the Roman period, the Late Middle Ages and also related to the Cantabrian Zn-Pb deposit of Reocín, exploited during the 19th and 20th centuries CE. Overall, the composition of the Cantabrian landscape does not seem to have been repeated over the last c. 17,550 years. This kind of study provides insight into how the current landscape has been reached and helps to improve environmental management.