Survey of composition and diversity of herbaceous plants after a fire in Persian Oak forests of Southern Zagros

The Zagros forests, mostly located in semi-arid regions, are not safe from fire hazards, and fire affects these coppice forests continuously. Studying the change in the composition and quantity of vegetation in the areas exposed to fire can determine the extent of damage, and the potential of the region for reclamation. The aim of this study was to investigate the composition, diversity, and response of understory herbaceous plants to fire in the Persian oak forests in the Tulgahi region of Kohgilouyeh and Boyer-Ahmad province.
The fire took place in the summer of 2010. Four years after the fire, the characteristics of herbaceous vegetation, including composition and biodiversity of plants, were measured. Sampling of herbaceous plants was carried out within each main plot of 1000 square meters (designed to measure the forest parameters with systematic random sampling in a 50 by 100 meter grid), five subplots of one square meter were sampled in the center and four angles of main plots and the species type and cover percentage were recorded. In total, 200 subplots were measured in the fire and control regions (100 subplots at each region). The diversity indices were calculated in the PAST software, and plant species response to fire was determined with redundancy analysis (RDA) using Canoco 4.5.
The results showed that out of 72 herbaceous species identified, 22 species were exclusively found in the fire region, 9 species exclusively in the control region, and 41 species were shared between the two regions. The results of mean comparisons showed that among the study species, 17 species had a significant response to the fire in terms of canopy cover percentage. The fire caused the canopy cover percentage of Rubiaceae and Gramineae to increase significantly compared to control. The results of biodiversity indices revealed that no significant difference was found between the two regions in terms of biodiversity indices. The redundancy analysis (RDA) results showed that herbaceous species had different responses to fire, so that canopy cover species of Onobrychis sativa, Orobanche sp., Hordeum glaucum, Pimpinella sp., Bellevalia sp., Bromus donthoniae, Bromus tectorum and Chardinia orientalis were increased in the regions where fire occurred.
The results of this research showed that fire was an important and effective factor, causing to increase of grasses and annual forbs significantly after four years of its occurrence. In contrast, the presence of perennial grasses and forbs was decreased significantly by fire in the understory of Persian oak forests.