Mistletoe (Viscum album L.) is a semi-parasitic plant and in moderate abundance it does not pose a lethal threat to a tree. However, recent droughts have made heavy impact on forests and mistletoe in recent years began to appear on a larger scale in regions and in places where it has never been a threat before.

The main purpose of this research was to carry out large-scale mistletoe inventory in Central Poland for assessing the number of mistletoe on individual trees and in the stands as well as to test new inventory method adapted to Polish conditions. It is based on random sample plots, each consisting of 15 trees on which impact of mistletoe is assessed.

On every sample plot the mistletoe occurrence, location in the crown, estimate of the percentage within the crown and the number of mistletoe on a tree is assessed. In addition, for further analysis, information on stand (forest habitat type, site index) as well as measured trees (age, diameter, Kraft class, crown length, loss of assimilation apparatus, crown type) levels is recorded.

Research undertaken in Kozienice Forest (100 km south from Warsaw) had taken into account 300 sample plots on which 4500 trees were assessed. Preliminary results show that about 10% of trees are infected by mistletoe, more than 80% of which were infected heavily by more than 6 specimen.