Impact of mistletoe infestation on tree water status in Anatolian black pine trees in a semi-arid Mediterranean forest stand

Mistletoes can adversely affect the hydraulic functioning of their host trees by continuously extracting water and nutrients. This study investigated the effects of pine mistletoe (Viscum album subsp. austriacum) on water status in Anatolian black pine (Pinus nigra subsp. pallasiana) trees in a natural forest stand in Mediterranean Region, Türkiye, where mistletoe-infected and non-infected trees coexisted. Continuous stem radius change measurements were obtained throughout the 2024 growing period using automatic band dendrometers to compare maximum daily shrinkage (MDS) and tree water deficit (TWD) between infected and non-infected trees. Simultaneously, soil water potential was measured, and meteorological variables were recorded by a nearby station. Mistletoe-infected trees exhibited 92% higher TWD and 12% higher MDS compared to non-infected trees. In both groups, TWD and MDS were closely associated with meteorological variables. TWD showed significant correlations with soil water potential, global radiation, and vapor pressure deficit, while MDS was mainly related to air temperature, solar radiation, and soil water potential. Precipitation influenced MDS in non-infected trees but had no significant effect on infected trees. Moreover, correlation coefficients with environmental factors were consistently higher in infected trees. These findings indicate that pine mistletoe is associated with a marked deterioration in host water status, suggesting increased drought sensitivity and reduced physiological resilience under Mediterranean climatic conditions. Overall, this highlights the potential ecological risk posed by mistletoe infestation in drought-prone forest ecosystems.