Impact of mistletoe attack (Viscum album ssp. abietis) on the radial growth of silver fir. A case study in the North of Eastern Carpathians

Viscum album ssp. abietis (Wiesb.) Abrom L. is one of the three subspecies of Viscum album L that is frequently encountered in Romanian forests. The mistletoe has notoriously negative effects on trees and forests health. The mistletoe infections not only reduce both height and diameter growth, it can also cause partial or total die-back of the trees. The present study on the incidence of mistletoe (Viscum album ssp. abietis) on silver fir (Abies alba) increments was carried out in natural stands of the Forest District Gura Humorului (one permanent plot P ltinoasa and one experimental plot Voronet), because this location (400-1000 m elevation) is characteristic for pure silver fir stands that can be found on the border of Carpathians Mountains at the contact zone with Suceava plateau. Four classes describing the level of infection were distinguished: no infection, low, moderate and strong infection.As only a few of healthy trees (class 0) were found, the comparison was made on the trees from the 1st class of attack. In parasited silver trees development were distinguished 3 phases: i) phase 1 - from 1920 till 1945 when the trees that nowadays are falling into the 2nd and 3rd class had similar growth with the ones recorded in the 1stclass; ii) phase 2 - from 1946 till 1976-1977; during this period the trees had been reducing their growth. The growth of silver fir trees that fall into the 2nd and 3rd classes of parasitism represents 80% of the average growth of 1st class trees; iii) phase 3- from 1977 till 2007 (with a couple of episodes) when trees growths from 1st,2nd and 3rd classes of parasitism were clearly differentiated.