Spatial determinants of mistletoe dispersal in Scots pine dominated forests: Are more complex forest stands less prone to invasion?

Mistletoe ( Viscum album ssp. austriacum ) is an increasingly prevalent parasitic plant in European pine forests. It raises concerns among forest managers due to its negative impacts on tree health and timber production. This study investigates the spatial and structural determinants of mistletoe infestation in Scots pine ( Pinus sylvestris ) stands within the Kozienicka Forest in Central Poland, using a combination of intensive spatial sampling in field surveys, LiDAR data, and satellite imagery. We analyzed 423 plots using generalized additive models to identify key variables influencing mistletoe presence. Our results show that older and larger trees were most likely to be infested, and these were associated with increased defoliation, while dense, young, even-aged pine stands offer some resistance. Increased shrub cover in the understory and proximity to the forest complex edge significantly elevated infestation likelihood, suggesting bird-mediated seed dispersal is critical. The presence of old-style orchards in the forest's complex surroundings and the proximity to the Vistula River, an important bird migration corridor, may also enhance mistletoe spread. These findings highlight the complex interactions between forest structure, birds' behavior, and mistletoe dynamics, offering valuable insights for forest management strategies to mitigate mistletoe invasion. • Young, dense, even-aged pine stands offer structural resistance to mistletoe. • Regions close to the forest complex edge are more prone to infestations by mistletoe. • Bushy under-canopy increases the chance for mistletoe to spread in Scots pine stands.