The Effect of Living and Non-Living Safe Sites on the Species Diversity of Limestone Outcrops in the Rainfall Gradient

Safe sites are microhabitats that provide the basic requirements for seed dormancy breaking, germination, and seedling establishment. They reduce threats from seed predators, herbivores, pests, and competitors. We identified and assessed living and non-living safe sites in the rocky outcrops and their effects on species diversity at six sites along a rainfall gradient in the north of Iran. Four dominant plant species were considered as living safe sites, but crevices and rocks were attributed as the non-living safe sites. Ten transects of 10 meters long were established at each site, along the rainfall gradient. Plant abundance and canopy cover were measured for all species along the transects. Soil physiochemical properties, moisture and temperature were recorded at the safe sites along the transects and their adjacent open areas. Rainfall had a significant effect on species diversity in non-living and living safe sites. Abundance and evenness increased in all safe sites; diversity indices increased in living safe sites and decreased in non-living safe sites. Soil nitrogen, carbon, potassium, and clay were significantly higher under the nurse shrubs. Results of this research indicate the crucial role of safe sites in maintaining the diversity of plant species under the harsh conditions of stressful environments on the limestone outcrops.