seasonal variation of earthworm abundances and biomass in natural forests and plantations (north of iran)

soil productivity and plant growth are usually affected by biological activities of earthworms. the objective of this study was a comparative evaluation of earthworm abundances in 20-year-old plantations of alder, oak, maple and cypress with the adjacent natural mixed broad-leaved deciduous forest in the caspian region of iran. in this research one sample plot, each 1 ha; was selected in every plantation as well as in the natural stand, more over, in each plot, 10 microsample plots 10?10m were selected random systematically. to determine the seasonal variation of density and biomass with two methods, twenty samples were taken from each microsample plot. in the first method, 10 assigned soil pits of 100?100 cm and 30 cm depth were located among each treatment and adult earthworms were collected by hand counting. in the second method, 10 circular soil samples of 81cm2 to depth of 30 cm were taken in each treatment. the larves of earthworm extracted by using berlese funnel and were counted by binocular. finally in four seasons a total of 400 specimens were taken from 50 microsamples in different treatments. moreover, some site and treatment parameters were measured in each plot. the abundance and biomass of earthworms in the cypress plantation with 148.4 (n/m2) and 4.74 (g/m2) was significantly lower than other treatments, while the differences between other treatments were not statistically significant. the two important factors were extracted from eight variables in factore analysis. the analysis of fa showed that some treatment parameters and nutritional values of litter take an important role in seasonal variation of earthworm abundance at all the treatments.