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Ignacio de la Torre [et al.].- Article first published online: 23 JUN 2015, Manuscript Accepted: 6 MAY 2015, Manuscript Revised: 26 APR 2015, Manuscript Received: 23 DEC 2014

The study of a pollen sequence obtained from a peat deposit in Hoyos de Iregua (Iberian Range, north-central Spain) has been carried out, revealing new information about the vegetation dynamics and climate changes since Late-glacial times. Pollen zones have been defined corresponding to successive phases in vegetation history during the end of the Late Wurm (Oldest Dryas, Late-glacial interstadial, Younger Dryas) and the Holocene. During the Oldest Dryas event, there was a sparse vegetation cover dominated by herbaceous taxa, with Pinus as the unique arboreal taxon with some importance. The vegetation landscape during the Late-glacial interstadial (13,000–11,000 yr BP) corresponded to coniferous forest and mixed forests, including the presence of evergreen Quercus . Between the Late-glacial and the Holocene, a brief cooler and drier phase occurred, the Younger Dryas event (11,000–10,000 yr BP). During this period an important reduction of the tree masses characterized the evolution of the landscape. The Holocene began with a period of increasing temperature that resulted in an expansion of the arboreal elements, which reached their highest representation during the Holocene Climatic Optimum. From 5060±90 BP a change to more arid conditions occurred, favouring the development of the mediterranean vegetation. Within the Late Holocene, clear evidence of the human impact on the environment are detected, being more accentuated towards the uppermost levels.

A palynological and lithological continuous record from La Mancha Plain (South-central Iberian Peninsula, Spain) is presented. The obtained results have permitted the reconstruction of the climatic evolution in the area since the Late-glacial/Holocene transition. The end of the Late-glacial was characterized by a cold and arid climate and it concluded at about 9890±180 yr BP. In the Early Holocene a slight climatic amelioration began, being interrupted by a more arid phase around 8500 yr BP. The Holocene Climatic Optimum started from ca. 8000 yr BP and was characterized by higher temperatures and more humidity. During the Mid-Holocene–Late Holocene times a stage of marked aridity occurred towards 5000 yr BP that preceded the development of a dry mediterranean climate. Under this new climate a short-time arid phase took place around 2500 yr BP after which the mediterranean conditions became accentuated, with an increasing dry climate. This climatic evolution has affected the characteristics of the marshlands of Las Tablas de Daimiel National Park, originating changes in the sedimentary environment. This environment was mainly fluvial until the end of the Holocene Climatic Optimum and became lacustrine–palustrine from the beginning of the more arid conditions.

Persistence of relict tree species in Mediterranean environments is becoming increasingly unlikely in view of ongoing and future global change. The variability in the Holocene climate and more recent anthropogenic impacts have driven many populations to fragmentation and isolation, and even to extinction. However, some have persisted to the present day. The understanding of their evolution requires long-term studies, in which pollen analysis is a key approach both for formulating hypotheses and supporting results from other disciplines. Mountain ranges have played and still play an essential role as both glacial and interglacial refugia during the Quaternary. The Spanish Central System harbors an exceptional diversity due to its geographical location and complex topography. Some cold-adapted species have survived here with significant proportions of their southernmost populations, often displaying striking adaptations to their changing environments. This work contains a comprehensive review of the palynological investigations conducted in the Spanish Central System, and reveals the distribution of genera such as Taxus, Betula, Fagus, Carpinus and Tilia throughout the Holocene. We also highlight the scarcity of well-dated and high-resolution works, which may contribute to a better understanding of their recent and future evolution.

Pollen data from three sequences (CH, PD and CbN) in the Gredos Range (Spanish Central System) have been presented. These data record the evolution of vegetation from the 7000 BP (Holocene). The most important results are summarized in the domain of the pine forest and the change in the local forest composition. Then, the forests of Betula and Corylus, developed until 3000 BP, are replaced by deciduous and evergreen Quercus. At this time and only in the sequence CH, presence of Cedrus and Fagus has been detected. From approximately 1000 BP, takes place an important decrease in arboreal taxa, mainly of Pinus associated with the expansion of Ericaceae and Poaceae, in response to an increase in both temperature and anthropogenic activities.

Correlations between ecological and cultural changes occurred during a short period between the end of Subboreal and the beginning of Subatlantic in the Amblés Valley (Ávila, central Spain) are analyzed, taking into account palaeopalynological and archaeological data. Plant dynamics from pollen analyses, both from archaeological sites and peat bogs, have been interpreted in relation to human settlements and the transformation of economic practices. These provided a comprehensive hypothesis on human/climate interactions at the beginning of the 1st millennium cal BC. There was an ecological crisis in the region that lasted for a century (ca. 850-760 cal BC). This was especially sharp due to both the geographical constraints of the area and its previous agrarian history. This event implied a sudden and abrupt climatic change from xeric and warm conditions (Subboreal) to more humid and cooler ones (Subatlantic). Environmental stress derived from climatic crisis could be an important factor in the explanation of the historical process, whose main consequences were both the origin of the Iron Age peasant villages and the end of the 'dehesa' type landscape. © 2008 Elsevier Ltd and INQUA.

Since the publication of the paper of , loss on ignition (LOI) has been widely used as a method to estimate the amount of organic matter and carbonate mineral content (and indirectly of organic and inorganic carbon) in sediments. The relationships between LOI at 550 °C (LOI550) and organic carbon (OC) content and between LOI at 950 °C (LOI950) and inorganic carbon (IC) content are currently accepted as a standard. However, the comparison of 150 analyses of samples of diverse lithologies, collected from a single core, reveals that these relationships are affected by sediment composition (presence of clays, salts, and the variable content of organic carbon). This results in an incremental error on the estimation of carbon content from LOI values that invalidates the use of LOI values as a quantitative method for estimating carbon content. Conversely, the general trends of LOI550 and LOI950 show a good correlation with carbon content (both organic and inorganic) allowing use of LOI as a qualitative test for carbon content. Similarly, in our case, LOI at 105 °C (LOI105) is a good qualitative proxy for the trends in gypsum content., Departamento de Estratigrafía, Universidad Complutense de Madrid, España, Departamento de Geología, Universidad de Alcalá de Henares, España, Dirección de Geología y Geofísica, Instituto Geológico y Minero de España, España, Dirección de Recursos Minerales y Geoambiente, Instituto Geológico y Minero de España, España, Dirección de Hidrogeología y Aguas Subterráneas, Instituto Geológico y Minero de España, España, Departamento de Geodinámica, Universidad Complutense de Madrid, España