Northern Iberia, especially on coastal areas, was also patched with populations of tree species, and this is not only documented by palaeobotanical data (pollen, charcoal) but also postulated by phylogeographical models.

We present a new stratigraphic (pollen and nonpollen microfossils and charcoal particle) sequence with five AMS dates, covering about the last 9000 yr, of a core collected from the Spanish northern meseta, one of the territories of the Iberian Peninsula for which little paleobotanical information is available. The results support the hypothesis of the permanence of the pine forests, in more or less pure masses or large timber stands, during the Holocene in some Iberian continental zones. The typical substitution in postglacial dynamics of heliophyllous species, such as pines or Cupressaceae, by broadleaf trees did not occur in this inland region. Presumably, factors linked to the substrate, in this case very deep sand dunes covering vast areas, may have contributed to the scarce local competitiveness of the broadleaf trees, which would account for the hegemony of pines in this region. Based on the dynamics of aquatic plants and nonpollen microfossils, an initial phase previous to 7500 14C yr B.P. of high levels in the lake can be identified by high percentages of hydrophytes. A progressive increase in helophytes and the gradual infilling of the lake over the last 5000 yr appear to indicate a phase of aridification similar to those established for the western Mediterranean. Study of charcoal particles, more abundant in the last 2500 yr, has given rise to certain hypotheses regarding the incidence of recurring fires of a local or regional nature.

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Summary Pinus nigra Arn. forests dominated over extensive areas of the Northern IberianPlateau (Spain) during the Holocene, but a strong decline during the historical period (c. 1300-700 cal. BP) led to the present fragmented populations. This demise has been generally attributed to land-use changes or climate, but the specific roles of disturbance regimes such as fire variability and grazing on the long-term are not fully understood yet. 2.We combine multi-proxy palaeoecological data (fossil pollen, spores, conifer stomata, microscopic and macroscopic charcoal) together with quantitative analyses (ordination and peak detection) from a high-resolution sedimentary sequence (Tubilla del Lago, 900 m a.s.l.) to assess the causes of pine forests demise. A new microscopic charcoal record from an additional sequence (Espinosa de Cerrato, 885 m a.s.l.) is used to assess burning and pine decline at a more regional (100 km radius) scale.

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Most unsuccessful palynological work is never published. As a consequence, pollen analysts waste time re-processing sterile sediments, and the available literature exhibits a uniformly positive record of success in pollen extraction. Here we report failures with Quaternary pollen analyses in the Iberian Peninsula; that is, case studies where it was not possible to extract palynomorphs for pollen counting. Both totally sterile and partially sterile sites are considered. Sites and perspectives for future studies are suggested. The majority of the failed studies are openair archaeological and palaeontological sites, caves and rockshelters, but there are prominent cases of success. Peat bogs have provided positive results, but only with sequences formed under continuous sedimentation processes in marshy environments. Lakes are often successful sites, but a multi-core strategy, following the facies change along a transect from the shore to the depositional centre, is recommended for saline lacustrine deposits, salt marshes and lagoons, especially when there is evidence of temporary desiccation. Cave and rockshelter infills should be considered case-by-case, and these sites definitely require a palyno-taphonomical approach to post-depositional processes. Indurated deposits are sometimes surprising in their high pollen concentration, but one must be prepared for sterility. Coprolites have been insufficiently exploited, and offer a great potential, especially those of Pleistocene Crocuta. This article shows that venturing into sediments assumed a priori to be 'difficult', like fluvial terraces, slope deposits, speleothems, cave travertines, and palaeosols, may nevertheless be successful. A

No abstract

Palaeoecological evidence indicates that highland pines were dominant in extensive areas of the mountains of Central and Northern Iberia during the first half of the Holocene. However, following several millennia of anthropogenic pressure, their natural ranges are now severely reduced. Although pines have been frequently viewed as first-stage successional species responding positively to human disturbance, some recent palaeobotanical work has proposed fire disturbance and human deforestation as the main drivers of this vegetation turnover. To assess the strength of the evidence for this hypothesis and to identify other possible explanations for this scenario, we review the available information on past vegetation change in the mountains of northern inland Iberia. We have chosen data from several sites that offer good chronological control, including palynological records with microscopic charcoal data and sites with plant macro-and megafossil occurrence. We conclude that although the available longterm data are still fragmentary and that new methods are needed for a better understanding of the ecological history of Iberia, fire events and human activities (probably