Mistletoe-induced growth reductions at the forest stand scale

Area of Science:

• Forest Ecology
• Plant Pathology
• Ecosystem Modeling

Background:

• European mistletoe (Viscum album L.) is a parasitic plant that negatively impacts Scots pine (Pinus sylvestris L.) health, growth, and reproduction, potentially causing tree mortality.
• Quantifying the economic impact of mistletoe infestation on timber yield is crucial for forest management and conservation strategies.

Purpose of the Study:

• To estimate mistletoe-induced losses in timber yield of Scots pine stands.
• To validate and apply the process-based forest growth model 4C, incorporating the effects of mistletoe infection.

Main Methods:

• The eco-physiological forest growth model 4C was enhanced to include established impacts of Viscum album on the host tree's water and carbon cycles.
• Model simulations were validated using data from a sample Scots pine forest stand in the Berlin area, Germany.
• Tree core measurements and biomass quantification of harvested trees were used to evaluate simulated growth and derive a mistletoe growth function.

Main Results:

• The enhanced 4C model simulated a 27% reduction in basal area increment (BAI) over a 9-year period of heavy mistletoe infection.
• Field measurements confirmed a mean growth reduction of 29% in infected Scots pine trees.
• Long-term simulations demonstrated the model's ability to accurately depict BAI growth patterns over 100 years and quantify mistletoe-induced reductions.

Conclusions:

• The validated 4C model effectively quantifies mistletoe-induced growth reductions in Scots pine stands.
• Viscum album significantly impacts forest productivity, highlighting the need for effective management strategies to mitigate its effects on timber yield.