Analysis of earthworm's patchy distribution and variability of soil biochemical properties under single -tree influences

The forest soils can be strongly influenced by tree species. Many studies have addressed the effects of monocultures on forest soil biochemical and earthworms, but few have examined the effects of varying ratios of species within stands. The validity of the concept of "single tree influence circles" was tested in a forest dominated by beech (Fagus orientalis Lipsky) and hornbeam (Carpinus betulus L.) on steep slopes in the Alborz Mountain, Hyrcanian forest of Iran. Due to, twenty hectare areas of Experimental Forest Station of Tarbiat Modares University was considered. The positions of trees with diameter at breast height more than 45cm were recorded by Geographical Position System (GPS). Three single -trees (trees with canopy cover separated from other trees and covered distinguished space) considered for soil sampling from every tree species and diameter class as three replications. All of soil samples were excavated in north aspect and at the nearest point to tree collar for more precision. Soil samples were taken at 0 -15, 15 -30 and 30 -45cm depths using auger soil sampler with 81cm² cross section. Soil moisture, pH, organic matter, total nitrogen, C/N ratio, N mineralization, microbial respiration, earthworm number and biomass measured in the laboratory. Significantly statistical differences were found in the most studied characters. N mineralization, microbial respiration, earthworm number and biomass were significantly greater under hornbeam single -trees than in beech. These results indicate that single -tree influence on soil properties is detectable even in mixed stands on steep slopes and the soil landscape may be considered a mosaic of profiles reflecting the occurrence and chemical characteristics of the ground cover vegetation and of individuals of the various tree species present.