Fire effects on density and richness of soil seed bank (Case study: Haji-Ghoushan Rangelands of Gonbad Kavous)

Soil seed bank is important for range management because it contains propagules of species that may be considered desirable or undesirable for site colonization after management and disturbance events. However, human-caused fire can affect ecological processes related to soil seed bank and vegetation structure. In order to determine the effects of burning on the seed bank, we germinated soil samples from burned and unburned plots in Haji-Ghoushan located in the Northern part of Gonbad city (Golestan Province) where human-caused fires in September 2010. In controlled laboratory conditions the total number of seedlings, number of families and subfamilies found in the upper (0-5 cm) and lower (5-10 cm) layers of soil within burn and no burn plots were recorded. Our research indicated that the total seedling density was higher in first depth than in second depth, and lower in burned site than unburned site; however, differences were non-significant but the number of seedlings varied significantly with depth. Twenty-four species were identified in unburned site. The species numbers in the seed bank of burned site were 18. The majority of the family was Poaceace, which was common to the two treatments. In unburned site, Poa Bulbosa and Stellaria media accounted for 17.76 % and 12.69 %, respectively of the seedling population. In the burned site we found Stellaria media and Pao Bulbosa accounted for 18.44 % and 15.63%, of the seedling population respectively. The densities of soil seed banks were highest at first depth in unburned and burned site with 337.5 and 282.5 m2. In the deeper depth, the density of soil seed banks was 96 and 70 m2 in unburned and burned sites, respectively. Species richness and diversity were obtained higher in unburned site than burned site and were higher in the upper depth than the lower depth in both sites.ý