Ramon Pérez-Obiol

Mid-Holocene vegetation and climatic history of the Iberian Peninsula

The aim of this research is to study the climate and vegetation history in the western Mediterranean, in the Iberian Peninsula, during the middle Holocene through pollen analysis. The origin of the deposits varied from the most xeric to more mesic Mediterranean environments. The timing, extent, and progress of the establishment of the Mediterranean climate have a degree of variability depending on the biogeographical region. Analyses of several pollen sequences reveal climatic transformations in the flora and vegetation between 7000 and 4000 cal. yr BP. Pollen concentrations have been used in some sequences to evaluate the order of magnitude in biomass changes through time. Three main spatial and taxonomic responses could be assumed: (1) in littoral regions, deciduous broadleaf trees were frequently dominant and then replaced by sclerophyllous and evergreen forests; (2) in continental regions and sub-Mediterranean mountains, the dominance of pine throughout the whole Holocene signals a change of less magnitude; and (3) in southeastern semiarid Mediterranean regions, the main changes are reflected by alternation between steppe and shrub communities. The emplacement of the Mediterranean climate is reflected in an aridification process. A temporal first approach of Holocene climatic changes is proposed: a humid phase (12 000—7000 cal. yr BP), a transition phase (7000—5500 cal. yr BP) and an aridification phase (5500 cal. yr BP—Present). According to archaeological data, natural changes in the forests favoured the environments suitable for human settlements, farming and sheepherding.

Potential influence of Bond events on mid-Holocene climate and vegetation in southern Pyrenees as assessed from Burg lake LOI and pollen records:

Superimposed on the long-term climate variability attributed to orbital forcing, there are other modes of variability covering timescales from interannual to millennial throughout the Holocene. Their signatures in climate proxy archives can differ substantially because of their lower magnitude and regional diversity. However, if identified they can yield better understanding of the physical mechanisms regionally linking causes and effects. Here we describe a high-resolution record of organic matter accumulation in the sediments of Burg lake (Pyrenees, NE Iberian Peninsula), as assessed using loss on ignition (LOI), and compare it with the ice rafted debris (IRD) indexes from the North Atlantic. The LOI record indicates two main phases in the water body, a lacustrine phase as a shallow lake and a palustrine phase as a fen. The latter covers the period 2600—7200 cal. yr BP and within it there is a high coherence between LOI and IRD, which indicates submillennial climate fluctuations in the Pyrenees that can be related to the North Atlantic influence. The Burg’s LOI record suggests wetter (and occasionally colder) situations in the Pyrenees during high IRD in the Atlantic (Bond oscillations). These fluctuations would likely affect the snow covered period in the mountains (winter and spring seasons) the most, the period in which Atlantic westerlies currently have higher influence on precipitation over the Pyrenees. These climatic oscillations could have favoured Abies penetration during the mid Holocene, as evidenced by increased pollen percentages of this taxon during low IRD values (drier conditions). The pollen record also suggests potential relationships between climate and human activity as early as at mid Holocene, as human-related cereals increase during all the low IRD periods. The human signature (charcoal, cereals) becomes particularly evident at around 2800 cal. yr BP; in this oscillation Pinus overtake Abies in the conifer response to low IRD.

The Role of Environmental Geohistory in High-Mountain Landscape Conservation

Proper management of the perceived value of any geographic space requires the capacity to interpret research results from spatial, temporal, and environmental points of view, applying the principles of environmental geohistory. Basic concepts such as baseline, threshold, or resilience are discussed from a long-term ecological perspective, with examples that explain the dynamics of fir forests as well as the changes in agricultural cover. Studying the changes in the altitudinal limit of the forest and surveying the wetlands dynamics on the southern slopes of the central Catalan Pyrenees have been shown to be effective tools to develop appropriate management tasks. The arguments presented are useful to enrich the public debate over management policies for natural protected spaces in high-mountain areas.