The incidence of mistletoe (Viscum album ssp. abietis) on silver fir (Abies alba) in Croatia

The research on incidence of mistletoe ( Viscum album ssp. abietis ) on silver fir ( Abies alba ) was carried out in natural fir stands in Croatia. In the area of Gorski Kotar 32.8 % of the examined dominant fir trees were infected with mistletoe. The mistletoe incidence was presented according to the damage degrees of silver fir from 0 (healthy trees) to 4 (dead trees), rated by the crown defoliation and needle discoloration. With the increase of incidence, mistletoe spreads more onto more vital, i.e. less damaged trees. In the Dinaric Alps 28.6% of the examined fir trees were infected, this percentage amounting to 27.1% for the mountainous regions between the Sava and Drava rivers. The site and stand parameters (exposure, elevation, site quality, forest community and crown closure) were analysed in order to establish whether there was a correlation between these parameters and mistletoe incidence. There was a negative correlation between the elevation and mistletoe incidence. Among the compartments with a closed stands there were considerably less compartments with higher mistletoe incidence than among compartments with a sparsely closed and understocked stands. The other analysed site and stand parameters individually had no significant influence on mistletoe incidence. The correlation of silver fir mortality in 2004 and mistletoe incidence in 2002/03 was analysed, and their strong correlation was established. Mistletoe could be considered as a bioindicator of silver fir decline, and probably a significant contributor to that decline. In the areas where mistletoe incidence is great it can be presumed that silver fir is significantly damaged.