Changes in flora, life forms and geographical distribution of herbaceous plant species along an altitudinal gradient in oak forests, Iran

Intended to examine the effects of altitude on flora, life forms and geographical distribution of herbaceous species, this study was conducted in Kabirkouh forests of Darreshahr, located in Ilam Province, Iran, by selecting an area (circa 300 ha) in this forest. The study area was divided into three elevational classes and 63 systematic random plots were sampled (21 in each of the elevational classes). In order to record the herbaceous cover, the surface area of the plots was determined using the minimal area method. Then the herbaceous species and their percent coverage were recorded based on the Van der Marel criterion. A total of 109 herbaceous species belonging to 92 genera and 24 families were identified in the study area. The most frequent species were in the Asteraceae (23 species) and Poaceae (16 species) families. The results showed that in all three elevational classes, therophytes were the dominant life form of the area. The frequency of the therophytes in the first altitude class was higher than in the other classes. The second predominant life form was hemicryptophytes, whose frequency in the third class was higher than the other classes. Other life forms observed in the region were cryptophytes and chamaephytes, respectively which made up the least proportion of the area’s plant population. In addition, the results indicated that within all of the elevational classes, a high percentage of the existing plants of the study area belonged to the Irano-Turanian floristic region. Generally, the altitude had a significant effect on the distribution of the flora of the study area.