Viscum album in French forests: Distribution, environmental drivers and impacts on tree health and growth

The European mistletoe ( Viscum album ) is represented in France by three subspecies and plays a dual role in ecosystems. While it provides essential food and habitat for numerous animal species, it also reduces the economic value of timber and weakens trees, making them more vulnerable to biotic and abiotic stressors. This study leveraged the French National Forest Inventory dataset, comprising observations from over 737,000 trees across more than 80,000 plots, to investigate the environmental factors shaping mistletoe distribution and assess its impacts on tree health and growth performance. Our findings revealed that mistletoe distribution is not random within the range of its host species but is significantly influenced by climate and soil conditions, as well as by the history of forest use. V . a . album was primarily constrained by soil properties, whereas V. a. abietis and V. a. austriacum were strongly affected by isothermality. Additionally, mistletoe was more frequently observed on trees with a higher crown dieback and, for Scots pine and silver fir, trees with a high level of infestation exhibited a growth reduction of 23–34 % compared to non-parasitized individuals. Fir and pine mistletoe occurrences were significantly lower in species-rich stands and in younger forests compared to older ones. With the ongoing impacts of climate change, implementing fine-scale monitoring of mistletoe populations could help foresters mitigate mistletoe-induced economic losses while simultaneously supporting biodiversity conservation efforts. • The spatial distribution of mistletoe depends on environmental and tree-level factors. • Isothermality, temperature and soil factors are key drivers of mistletoe distribution. • Mistletoe is less frequent in fir and pine stands with high species diversity. • The likelihood of mistletoe infestation is highest in trees with severe canopy dieback. • Mistletoe-infested Scots pine and Silver fir trees show significant growth reductions of 23–34 %.