Evaluating habitat suitability for the middle spotted woodpecker using a predictive modelling approach

This paper explores the influence of forest structural parameters on the abundance and distribution of potential habitats for the middle spotted woodpecker (Dendrocopos medius) in three different forest landscapes in Poland. We applied predictive habitat suitability models (MaxEnt) based on forest inventory data to identify key environmental variables that affect the occurrence of the species under varying habitat conditions and the spatial configuration of suitable habitats. All models had good discriminative ability as indicated by high AIX values (> 0.75). Our results show that the species exhibited a certain degree of flexibility in habitat use, utilizing other habitats than mature oak stands commonly associated with its occurrence. In areas where old oak-dominated stands are rare, alder bogs and species-rich deciduous forests containing other rough-barked tree species are important habitats. Habitat suitability models show that, besides tree species and age, an uneven stand structure was a significant predictor of the occurrence of middle spotted woodpecker. The total area of suitable habitats in the studied forests varied from 9% to 60%. Predictive habitat models identified several concentrations of suitable habitats (clusters) with the average distances between them ranging from 3.2 to 5.0 km. Although these distances lie within the species' dispersal ability, the migration of individuals between these sites might be difficult due to the necessity of travelling long distances through unsuitable forest types.