One of the most important micro engineers of the terrestrial ecosystems, especially in the arid areas is the harvester ants due to their activity in the soil through nest building; they can make major changes while influencing the surface and subsurface in the rangeland soil. The purpose of this study was to investigate the effects of harvester ants (Messor spp.) on some soil properties in Roodshoor Steppe rangeland in Saveh, Iran. Soil samples in four depths (0-10, 10-20, 20-30, and 30-40 cm) were taken in three treatments of active and non-active nests and control area. Soil infiltration test was carried out over ants' nest and control site in dry and wet seasons by double rings method. The results showed that the Messor spp. soils had lower pH and higher concentration of organic matter, total carbon, N, P, K, Mg+2, Ca+2, Ec and sand percent in comparison with the control site. The soil infiltration rate regarding the nests was significantly higher than the control area in both dry and wet seasons. In the same habitat, nutrient concentrations did not change along the vertical gradient in contrast to control plots where soil nutrients decreased with depth. This showed homogeneity of different soil layers by ants. On the other hand, investigating the chemical and physical properties of soil did not show a significant difference between the dead nests and the control area. This can be the expression of effects created as the result of the presence of ants in modifying soil in the active nests. These effects disappeared with the passage of time after they left their nests. Therefore, the role of the ants in changing soil properties should be considered, especially in the arid and semi-arid area in which the soil is poor. The presence of ant colonies and their activity in this climate can improve soil conditions and increase soil fertility in most parts of the ground. پرونده مقاله

Harvester ants are known as one of the most renowned bio-disturbances in the arid and semi-arid ecosystems that affecte vegetation by collecting seeds and harvesting plants. It seems that physiognomy of plant association in steppe shrub land of Roodshoor, Saveh, Iran has been highly changed by harvester ants’ activities that caused to conduct this research. The study was carried out on active and inactive nests and control site from June to August 2012. Diversity indices and functional groups such as vegetative form, longevity, and photosynthesis type were analyzed as compared to criteria in three sites. Results showed that richness, diversity, and vegetation cover in the ant colonies through increasing the annual forbs and rare species (Campanula stricta and Lepidium vesicarium) were more than the control site. For evenness index, however, there was no significant difference between the control and nest sites. In contrast, the function of plant community in the active nests due to the decrease of dominant shrub frequency of the area that is Artimisia siberi by Messor spp. was less than the control site. Low diversity, richness, plant function, and high vegetation cover in inactive nests were also observed as the results of the presence and activities of the ants in the active nests. Hence, the ant activities in the active and inactive nests can bring out micro sites with different plant associations so that regarding high density and quantity of the ant nests in all the area, it can decrease the key plants and change their functions. It therefore will debilitate the stability and function of this rangeland ecosystem. پرونده مقاله