Effect of repeated fire on understory plant species diversity in Saravan forests, northern Iran

Fire usually causes changes in the composition and diversity of herbaceous species. The present paper aimed to study the effect of repeated fire incidents on understory species diversity in the Saravan forests of Guilan Province located in the north of Iran. To do so, three 50-hectare areas with identical physiographical conditions and overstory (hand-planted softwood Pinus taeda) were selected. Seven fire incidences occurred for the 10-year period in one of the areas and the other area experienced three fire incidents within the same period. The area with no fire incidents was considered as the control area. All the fire incidents were surface ones. The systematic random method with a sample size 100 × 200 m was used for collecting data. Based on the above, 25 samples were determined in each area. The whole coverage of the understory was taken into consideration using Whittaker’s method and the Domain criterion so as to calculate species diversity indices. The results showed that Shannon-Wiener diversity and Menhinick’s richness in the regions which experienced 3 and 7 fire incidents were maximum and minimum, respectively, whereas no significant difference was seen between the regions with regard to Smith and Wilson’s evenness index