Topography is the most factor that has the greatest impact of all factor that affect the distribution.To study the diversity of trees and shrub species in the Perc forest situated in Khorramabad,Lorestan,140 circular plots of 1200 m~2 in a grid of 300 m 9 250 m were surveyed,using a systematic random sampling method.In each plot,the Margalef richness index,Shannon–Wiener diversity index,Hill’s N_1 and Simpson indices and the evenness index of Simpson and Smith-Wilson were calculated and ordered on the basis of different classes of elevation,exposition and slope.The results indicated that slope did not have any significant effect on the indices.Exposition and elevation classes significant impacted the richness and diversity indices,but did not influence evenness.In general,the highest plant diversity was observed for slopes less than 15 %,northern aspects,without geographical direction,and elevations of 2100–2200 m.This information can be very useful in achieving the goals for sustainable management of forests.In addition to greater protection for regions with high diversity and reforestation(compatible species) in degraded area,we can help increase diversity in forests. Topography is the most factor that has the greatest impact of all factor that affect the distribution. To study the diversity of trees and shrub species in the Perc forest situated in Khorramabad, Lorestan, 140 circular plots of 1200 m ~ 2 in a grid of 300 m 9 250 m were surveyed using a systematic random sampling method. Each plot, the Margalef richness index, Shannon-Wiener diversity index, Hill’s N_1 and Simpson indices and the evenness index of Simpson and Smith-Wilson were were and ordered on the basis of different classes of elevation, exposition and slope.The results indicated that slope did not have any significant effect on the indices.Exposition and elevation classes significant impacted the richness and diversity indices, but did not affect evenness ..In general, the highest plant diversity was observed for slopes less than 15%, northern aspects, without geographical direction, and elevations of 2100-2200 m. This information can be very useful in achieving the goals for susta inable management of forests.In addition to greater protection for regions with high diversity and reforestation (compatible species) in degraded area, we can help increase diversity in forests.