Investigation of the Relationship between Altitude and Aspect with Plant Diversity: A Case Study from Nawa Mountain Ecosystem in Zagros, Iran

Mountain ranges cover around one-half of Iran, and Zagros ecosystem is considered as one of an important biological site in Iran. Physiographic factors such as altitude and aspect have an important role in plant species distribution. This study was conducted in the Nawa mountain ecosystem in the western side of Zagros ranges, located in the western zone of Iran in 2016. The experiment aim was to reveal the influences of altitude and aspect on features of plant biodiversity. Hence in the each main aspect regarding to gradient, transect-lines were established with distance 100 m into another and perpendicular to gradient from the elevation of 1200-2400 m a.s.l. Four plots (1 m²) were randomly located along each transect; generally, 208 plots were drown. The Shannon– Wiener index for α-diversity was calculated, and field data were analyzed using two-way ANOVA. There were 158 identified plant species belonging to 104 genus and 27 families based on the results. Altitude and aspect had a significant effect on the plant diversity and species richness (p<0.01). The highest values of the Shannon–Wiener index and species richness (2.58 and 1033 respectively) were seen in lower elevations (from 1200-1400 m a.s.l.). Results also showed that the highest and lowest values of the plant diversity and species richness for the southern aspect were 2.51 and 8.9 and for eastern aspect 1.20 and 3.63, respectively. Interaction effects of environmental variables were only significant on the species richness. There was a negative correlation between the plant diversity and species richness with altitude in all main aspects, too. Along the altitudinal belts, the highest species diversity and richness belonged to low and mid-elevational zones of the Nawa mountain.