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.
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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