Relationship between abundance/infection intensity of dwarf mistletoe (Arceuthobium oxycedri (DC.) M. Bieb.) and qualitative and quantitative characteristics of the host tree, physiographic conditions, and soil erosion

Dwarf mistletoe (Arceuthobium oxycedri) has a worldwide range of distribution amongst the dwarf mistletoe species. To investigate the effects caused by dwarf mistletoe infection on juniper trees, this study was conducted in an area of 400 hectares in the Parvar protected area, Semnan Province. Sampling was carried out using 60 quadratic plots with the area of 20×20 m2 in a randomly-systematic manner. The discriminant analysis showed that the characteristics of herb canopy cover, individual gender, slope (%), and even aspect direction are not substantially deterministic for infection intensity of dwarf mistletoe. In contrast, the highest correlation was observed in traits like root exposure, collar diameter, crown area, altitude, and tree height. The lowest frequency of infected individuals and the lowest severity of infection were observed in upper elevation class (2500-2700 m a.s.l.), low rate of soil erosion, and trees without root exposure. Moreover, the proportion of infected individuals to total trees are little on the 30-60% slopes and in north and west slope aspects. The results suggest that trees with broader canopy, higher collar diameter, and taller height are more prone to this parasite. In addition, the maximum severity of the infection is observed on larger trees, especially if the trees are located at lower elevations, faced with the degraded ecosystem and soil erosion that leads to root exposure and tree weakness. Therefore, in the case of the continuation of the spread of dwarf mistletoe in juniper forests and the lack of a non-destructive strategy to control the population of this parasitic herb, these communities would be expected to be partly degraded in the near future especially, for the higher sensitivity areas (such as lower habitats of juniper communities.