Forest habitat diversity in the Cantabrian Mixed Forests ecoregion (NW Iberian Peninsula), a climatic refugium in western Europe

Abstract

Aims: (i) To classify forest habitat diversity in the Cantabrian Mixed Forests ecoregion, a putative biodiversity refugium in Western Europe, and (ii) to evaluate how the distribution of functional and ecological habitat types is explained by climatic drivers. Location: Cantabrian Mixed Forests ecoregion (northwestern Iberian Peninsula). Methods: We compiled a vegetation database for the ecoregion using data stored in the Iberian and Macaronesian Vegetation Information System (SIVIM). Then, we used the EUNIS Habitat Classification expert system, the modified Two-Way Indicator Species Analysis (TWINSPAN) and the semi-supervised k-means classification to classify all Forest plots into regionalised EUNIS habitat types. We determined the environmental space of each ecological forest type with bioclimatic and soil variables, and computed principal components analysis (PCA), generalised linear models (GLMs) and PERMANOVA to evaluate climatic differences among forests. Results: We identified 24 ecological forest habitat types (12 broadleaved deciduous, seven broadleaved evergreen and five coniferous), whose regional distribution is mainly driven by the oceanic influence and the amount and seasonality of annual precipitation. Most forest types had a specific climatic optimum, but there were also climatic overlaps in habitats traditionally favoured by human activities. Conclusions: The Cantabrian Mixed Forests ecoregion is a hotspot of forest diversity within the temperate deciduous forest biome in Europe, including multiple functional and ecological forest types. Such forest diversity is explained by present macro- and mesoclimatic heterogeneity, Pleistocene refugia, and the legacy of human intervention during the Holocene.