The incidence and distribution of white mistletoe(Viscum albumssp. abietis) on Silver fir (Abies alba Mill.) stands from Eastern Carpathians

Abstract

In Romania Viscum album ssp. abietis is one of the most significant biotic factors that affect Silver fir situated on Eastern border of its natural area. The aim of our research is to assess the incidence and distribution of mistletoe in representative Silver fir stands from the Eastern Carpathians (at four forest districts level - Gura Humorului, Vaduri, Manastirea Casin and Agas). According with this purpose a statistical inventory of Silver fir stands based on 2 x 2 km grid was performed. At the intersection of the gridlines, stands older than 70 years were searched for on a distance of 500 m around. Each Silver fir stand chosen in this way represents a sample plot. In each plot 30 dominant Silver fir trees were chosen. For all this trees, the mistletoe infection degree was quantified using a 4-class rating system: no infection, low infection, moderate infection and heavy infection. The incidence of Silver fir was presented according to the damage degree. The site and stand parameters - elevation, exposure and canopy closure - were analysed to establish whether correlation between these parameters and mistletoe incidence exists. The volume of dead trees (due to the mistletoe infection) in 2004 - 2007 was also compared with mistletoe incidence in order to establish the correlation between these variables. Silver fir trees infected by mistletoe have been found in 55% of all 86 sample plots. Within the studied area 22% out of 2147 Silver fir trees were infected by mistletoe (42.2% - 1st infection class, 32.7% - 2nd class and 25.1% - 3rd class). The highest percentage of infected trees was found in the forest district Manastirea Casin where 42% of examined trees were infected, mostly of the trees being in the 2nd and 3rd infection classes. There was a significant negative correlation between the elevation and mistletoe incidence. Up to 600 m, the most of the trees are heavily infected, while above 800 m the trees are incipiently infected. Regarding the canopy closure, sample plots with understocked and sparsely closed stands have shown a high level of infection compared with plots with closed stands. A significant correlation has been found between the volume of dead Silver fir tees and mistletoe incidence. The highest mistletoe infection was registrated in Silver fir stands at the eastern border of the Eastern Carpathians. There was noticed a decrease of mistletoe infection from the East to the West.