Infection of juniper trees (Juniperus excelsa M. Bieb.) to juniper dwarf mistletoe (Arceuthobium oxycedri (D.C.) M. Bieb.) in forests of Miankouh Tash protected area, Shahroud

Juniper stands, renowned for their ecological role, are facing a recent threat from the proliferation of a parasitic plant known as the juniper dwarf mistletoe, scientifically named Arceuthobium oxycedri. The primary objective of this study is to assess the extent of this disease among juniper trees in the Miankoh Tash region.

A 250×250-meter grid was systematically established, comprising 65 square-shaped sample plots, each measuring 20×20 meters. Within each sample plot, various quantitative characteristics of juniper trees, such as tree height, crown diameter, collar diameter, canopy coverage percentage, and the presence of branch dieback, were meticulously measured. Furthermore, habitat factors, including elevation, slope, geographical direction, soil erosion status beneath the juniper crown (classified into four categories), and tree root exposure (classified into three categories), were meticulously documented. The collected data underwent analysis utilizing both univariate and discriminant analysis techniques.

Our results suggest that the gender of the host individuals, slope percentage, and geographical direction had no significant impact on the severity of infection. However, infected host trees displayed higher average values in tree height (5 meters), crown diameter (3.7 meters), collar diameter (54.7 cm), and crown area (12.8 square meters) compared to healthy junipers (3.1 m, 2.1 m, 24.1 cm, and 4.1 m², respectively). Moreover, the frequency of branch dieback, a common symptom of dwarf mistletoe invasion, was notably higher in infected trees. Discriminant analysis identified several key indicators of juniper dwarf mistletoe severity, including the severity of erosion under the canopy, root exposure, collar diameter of trees, collar diameter of trees per hectare, crown diameter, and tree height.

The study concludes that larger, and thus older, trees are more susceptible to juniper dwarf mistletoe infection. Additionally, juniper trees with increased root exposure and soil erosion on their canopy surface, indicative of livestock overgrazing, exhibit a heightened susceptibility to parasitic plant invasion. This underscores the compounding effects of livestock grazing pressure on host trees. Therefore, prioritizing non-destructive methods to control juniper dwarf mistletoe, particularly in areas with old and large juniper trees, is recommended.