Fire effects on composition, density and species diversity vegetation and soil seed bank (Case study: Kangavar rangelands)

Abstract Background and objectives: Fire as a frequent phenomenon in rangelands and because of its complicated and different effects on natural ecosystems, has great importance. Awareness of such fire effects on vegetation cover in point of rangeland management after fire is important and helps better Understanding and sustainable management of rangelands. Changing in plant structure and composition and site  situations is on of the most clear effects of fire on natural ecosystems especially in arid and semi-arid areas. Fire effects on soil seed bank is a fundamental subject in ecology and phytosociology. These seeds have a vital role in maintenance and reclamation of deteriorated rangelands and also in plant composition improvement in plant communities. This study was conducted to evaluate the effect of fire on vegetation and soil seed bank in Sarkhalaj rangelands of Kangavar (middle Zagros). Methodology: In current research, one year after the fire, in two areas of the control (Grazing exclosure) and fire, percentage of canopy cover and soil seed bank were sampled on transects with a systematic-random approach. Soil was sampled on these transects in two depths of 0-5 cm and 5-10 cm. After greenhouse cultivation, germinated seeds were identified and the composition and density of soil seed bank were determined. In order to comparing of biodiversity, we used species richness index, species diversity index (Shannon- Wischmeier) And evenness index (Pielou). Also similarity index (Jacard) between ground and underground vegetation cover in exclosure and fire area using formula. Mean comparison of biodiversity indices performed by LSD test. Also, biodiversity indices calculation of plant communities based on two viewpoints: ground and soil seed bank plant composition was done andsignificancy of differences of functions of biodiversity of ground and soil seed bank under treatments (fire and control area) compared via T-test. Raunkiaer life-form system was used to Plant categorizing. Results: The results of this study indicated that after one year fire the diversity, richness and evenness indexes were significantly reduced. Assessment of soil seed bank in depth of 0 – 5 cm showed that fire decreased the diversity and species richness indexes. However, it did not significantly affect the evenness index. Moreover, in depth of 5-10 cm fire had no significant effect on diversity indexes. Plants life form classification changed after fire and Cryptophytes  and Hemicryptophytes species decreased 8% and 6 %, respectively which resulted in domination of annuals in plant composition. Also, seed amounts decreased greatly in soil surface layer (0-5 cm.).  Conclusion: Overall, considering the results of this study, it could be said that by changing the site conditions, both in terms of the space required for the establishment of new species and by changing the soil properties, the fire has caused a change in the composition and diversity of species and finally the life form of existing species in the area.