Forest trees demonstrate different distribution patterns, depend on their living condition (Such as pest infestations). Forest density and epidemic pest concentration are hypothetically among the most influential factors. The current study was carried out on distribution pattern of the orchard ermine (Yponomeuta padella) infested hawthorn trees (Crataegus monogyna) in Bazoft river watershed in Central Zagros. Nine sites were selected with different infections. The site selection was based on pollution and position (North or South) it. Pollution, density of trees and coordinates (X , Y) were recorded for each tree. Eberhart and Ripley’s K functions were used to elucidate the infested and non-infested tree distribution. The results showed a clumped distribution of the trees in sound sites and in infested sites with high hawthorn density. Trees in low-dense infested sites had a tendency toward more random and even uniform population distribution.