The leaf area index (LAI) as an ecological index has a great importance in the study of the health of the trees as well as vegetation stress in the forest. In this case study, we investigate the effects of industrial dust on the health of forest plants in Hyrcanian forests of the north of the country. For this purpose, a hemispherical photography method has been used to estimate leaf area index. A total of 8 sample lines were collected in two directions around the industrial dust area with an attitude up to 600 meters For data analysis, variance
1 analysis method was used. There was a significant difference between the mean leaf area index at three levels of distance from the contamination center (p <0.05). The results of the Post Hoc Test, to pair-wise comparison of leaf area index in different distances from dust center using the Tukey index, showed that the average of leaf area index was less than 150 m and a significant difference in a distance of more than 300 meters was revealed . Regression analysis was used to eliminate the effect of varieties of plant species and dominant wind direction on leaf area index. The results of the hierarchical regression of leaf area index showed that the variables of the type of plant species and the dominant wind direction affect the prediction of the leaf area index value. In the following, the correlation between distance classes of industrial dust and the average of leaf area index at Land acquisition points was investigated. The results showed that the best correlation between the two above variables in the east direction of this center and along the dominant winds was observed. The amount of R
2 was 0.847 with positive power function
