Effects of mistletoe infestation on the decline and mortality of Abies cephalonica in Greece

Abstract

In recent decades, stands of Greek fir (Abies cephalonica Loudon) are declining and high tree mortality has been observed in some years. The exact causes of fir decline and mortality have not been established although many have been proposed (drought, climatic change, air pollution and attacks by pathogens or insects). This study has focused on the effects of mistletoe (Viscum album L.) on fir crown condition by assessing the mistletoe infestation level and its effects on fir defoliation. In the fir forests of Central Greece, the tree crown condition and the extent of mistletoe infestation were assessed and their relationships with tree height, altitude and aspect were investigated. The role of mistletoe on overall fir mortality was investigated by assessing standing trees that had died recently. The leaf water potential and chlorophyll fluorescence of mistletoe and fir were also measured during one growth season. The results showed that mistletoe infestation is related to crown defoliation. Altitude and tree height were not related with mistletoe infestation while infestation levels were lower on northern exposures. Mistletoe showed significantly lower water potentials and higher photochemical efficiencies than fir branches.