Influence of forest road on tree and shrub biodiversity indices in Irano-Turanian forests (case study: Pasargad forests)

 Considering the importance of forest roads and their positive and negative effects on the forest ecosystem, in this study, the effects of a forest road on species diversity indices related to trees and shrubs in forests of Pasargad city were investigated.

 After field surveys, 30 plots of 400 square meters (20×20 m) were placed on both sides of the road perpendicular along the third-grade forest road with a distance of 100 meters in 0 to 20, 40 to 60 and 80 to 100 m intervals and the species of trees and shrubs were investigated. Then, richness and uniformity indices were calculated and the mean of each index was measured at similar intervals. Then, in SPSS software, the data were normalized by the Kolmogorov-Smirnov test as well as homogeneity analysis of variance using Leven's test. The effect of distance from the road on diversity, richness, and uniformity was determined using a one-way ANOVA method, and Duncan's test was also used to compare the multiple means.

 The results of the census of the trees in the study area showed that Amygdalus lycioides species had the highest and Ephedra foliate species had the least abundance in the plots. According to the results, the mean values of diversity, richness, and uniformity indices at different distances from the road showed no significant difference. Also, analysis of variance for values of diversity, richness, and evenness indices at specified intervals showed that there was no significant difference in the 95% confidence level between the values of these indices at different distances from the road.

 Light competition is one of the factors affecting the establishment of trees and shrubs. There was no light competition in the study area due to the long distances between trees and, therefore, the presence of roads in these conditions wouldn’t affect the light competition. On the other hand, the results showed that with increasing distance from the road, there were no significant differences between the density of trees and shrubs and species diversity indices. Third-grade forest roads are used during limited seasons of the year due to limited infrastructure and pavement, and so the adverse effects of human presence would be limited. Therefore, increasing the distance from third-grade forest road in the study area did not affect the richness, diversity, and evenness of tree and shrubs species.