Air pollution from industrial areas is environmental stress on trees that can seriously endanger the future of forests. Ancient Persian oak trees (Quercus brantii Lindl.) in the semi-arid forests of the Zagros are exposed to various environmental stresses such as air pollution from the Ilam gas refinery, which causes many challenges in forest regeneration and afforestation, thus jeopardizing forest sustainability or restoration. This study aimed to investigate the effect of toxic pollutants emitted from a gas refinery operation on seed germination and morphological characteristics of seedlings from maternal trees that are located at different distances (1000, 1500, 2000, 2500, and 10000 m) and directions (east and west) from the facility. The results showed that oak seedlings grown from acorns collected at a distance of 10000 m had the highest values in various seed germination and seedling developmental measures and morphological traits such as leaf and root mass, number and length compared to other distances of 1000, 1500, 2000 and 2500 m from the gas refinery. The highest values in seed germination and seedling emergence and growth occurred at distances furthest from the refineries. Also, direction from the refinery significantly (p <0.05) affected root growth, with larger seedlings occurring from acorns collected west of the refinery. The results of principal component analysis and discriminate analysis showed that various seed germination traits were most sensitive to gaseous toxic pollutants emitted from this source. Based on all studied traits, seedlings from acorns collected at 10,000 m from the facility were easily distinguished from seedlings of acorns collected at closer distances. It can be concluded that refinery toxic pollutants caused significant adverse changes in germination and seedling growth from acorns collected from oak trees located near (less than 10000 m) to the source of air pollution. It is recommended that such pollution sources should be established far away from forest areas, and if constructed, be equipped with appropriate technologies such as flare gas recovery (FGR) to reduce emission of toxic pollutants and other emissions such as sulfur dioxide (SO2) and hydrogen sulfide (H2S) from the gas refinery. It is also strongly recommended that acorns collected for restoration measures come from maternal trees growing at a distance >10000 m, and especially to the west of gas refineries
