Relationship between pine mistletoe infestation severity and tree size in even-aged Scots pine stands

Abstract

Pine mistletoe (Viscum album subsp. austriacum) is increasingly reported in managed Scots pine (Pinus sylvestris) stands in Central Europe. The relationships between crown mistletoe severity and stem diameter at breast height (DBH) and total height were evaluated across a broad age gradient in central Poland using a field-practical severity scale based on counts of visible mistletoe clusters. Mistletoe severity was associated with lower DBH, with the clearest differences occurring in the youngest and oldest stands, whereas height varied less consistently across severity categories. Ordinal modelling indicated that older trees were more likely to occur in higher-severity categories, and DBH was inversely associated with severity after accounting for other predictors. These inventory-based relationships support prioritising mistletoe monitoring and management planning in compartments where severe categories are frequent, particularly in older Scots pine cohorts.

Key words: Viscum album subsp. austriacum; Pinus sylvestris; diameter at breast height; stand age; ordinal logistic regression; forest health monitoring