Introducing relative pollen productivity estimates for Iberian taxa: methodological insights and implications for landscape modelling in the Western Mediterranean

Abstract. Understanding the impact of ongoing global change on plant communities requires long-term quantitative reconstructions of past vegetation dynamics. Fossil pollen records offer one of the most powerful tools to reconstruct past landscapes, yet for their accurate interpretation it is important to take into account the differential pollen productivity of plant taxa. For southern Europe, and particularly for the Iberian Peninsula, estimates of pollen productivity remain scarce, limiting our ability to refine palaeoecological reconstructions. Here we present the first relative pollen productivity estimates (RPPs) for 21 common taxa in continental Spain. For that purpose, we used 1113 modern pollen samples from our own surveys and the Eurasian Modern Pollen Database (EMPD2), and vegetation data from the Spanish Forestry Map (MFE) and the Iberian and Macaronesian Vegetation Information System (SIVIM). RPPs were derived by applying an optimisation algorithm with the REVEALS model (REgional VEgetation Estimates from Large Sites). To test the reliability of our RPPs, we validated 8 arboreal taxa in 27 present-day coretops across Spain. We also compared the obtained RPPs with different studies across Europe, using a bias-free comparison framework. Our findings indicate that the dominant arboreal taxa (Pinus, evergreen and deciduous Quercus) are high pollen producers, whereas temperate forest, shrub and herbaceous taxa generally yielded medium to low estimates of pollen productivity. Validation of arboreal taxa from present-day coretops showed that REVEALS-based estimates perform better than raw pollen counts when compared with present-day vegetation cover. Comparison between different studies in Europe also showed that most of the Spanish RPPs are similar to those obtained in Europe, although notable differences emerged for some taxa. This study calculates, validates and compares the first RPPs in the Western Mediterranean, highlighting the value of quantitative palaeoecological data for Holocene landscape reconstructions. The findings of this paper would support that the Iberian Peninsula could have been home to a heterogeneous mosaic of open areas, conifers and broadleaf trees, offering new frameworks to improve both palaeoecological reconstructions and contemporary forest management strategies. Note: nomenclature and authority of the taxa in this paper were selected according to Flora Iberica (Castroviejo, 1986–2012).