In recent years, many factors such as climate change and drought have changed the Zagros forests in western Iran. Also, unsuitable use of the forest is now threatening the long-term survival of Zagros forests by local natives. The municipal solid waste (MSW) disposal of Ilam city (in the west of Ilam province) is located in the Zagros forests. In this study, the effects of the Ilam landfill on soil and Oak tree (leaf) contamination with heavy metals (HMs) were investigated. 31 points around the landfill (at different distances from the landfill) were considered for sampling, and also 6 points were selected in forest areas that are far away from pollution sources as control areas. The forest soils and oak leaves were randomly collected from the control area and landfill. The soil and tree leaf samples were analyzed for cadmium, chromium, cobalt, copper, iron, lead, nickel, magnesium, and zinc using atomic absorption spectrophotometry. Several pollution indices, the Kriging method, and principal component analyses were applied for evaluating the contamination level spatial distribution, and possible sources of heavy metals. The concentrations of chromium, cobalt, and nickel in landfill soils were 531.6, 43.87, and 408.8, respectively, which were 5–10 times higher than the United States Environmental Protection Agency (USEPA) standards. The concentrations of chromium and nickel in oak leaves were 2.83 and 5.91, respectively, which are higher than the permissible limit. The results showed that there were statistically significant differences (p < 0.05) in metal soil concentrations between (lead, cobalt, zinc, and copper) the control area and landfill (with was 2 times higher than in the control). Higher values of soil pollution indices were obtained for the landfill sites than for the control sites. The findings of the spatial distribution confirmed that the heavy metals from the landfill significantly affected the soils of the Zagros forest. The presence of heavy metal
