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Abstract

The hemiparasite European mistletoe (Viscum albumL.) adversely affects growth and reproduction of the host Scots pine (PinussylvestrisL.) and in consequence may lead to tree death. Here, we aimed to estimate mistletoe-induced losses in timber yieldapplying the process-based forest growth model 4C. The parasite was implemented into the eco-physiological forest growthmodel 4C using (literature-derived) established impacts of the parasite on the tree’s water and carbon cycle. The amended modelwas validated simulating a sample forest stand in the Berlin area (Germany) comprising trees with and without mistletoe infection.At the same forest stand, tree core measurements were taken to evaluate simulated and observed growth. A subsample of treeswere harvested to quantify biomass compartments of the tree canopy and to derive a growth function of the mistletoe population.The process-based simulations of the forest stand revealed 27% reduction in basal area increment (BAI) during the last 9 years ofheavy infection, which was confirmed by the measurements (29% mean growth reduction). The long-term simulations of the foreststand before and during the parasite infection showed that the amended forest growth model 4C depicts well the BAI growth pat-tern during>100 years and also quantifies well the mistletoe-induced growth reductions in Scots pine stands.