study on the effect of soil chemical characteristics and crown canopy of ziziphus spina-christi l. on soil seed bank characteristics

this study was carried out to investigate the effect of crown canopy of ziziphus spina-christi on seed bank characteristics (density and similarity with above ground flora) in two sites with saline-alkaline and alkaline soils. in each soil, forty plots were established, half in and half outside of z. spina-christi cover. in each plot, soil sampling was done from 0-5 and 5-10 cm depths. paired and un-paired t-test were used to compare soil seed bank characteristics between the depths, between two different soils and between in- and outside the tree canopy. the results showed that the density of seed bank in 0-5 cm depths was significantly higher than 5-10 cm depths in both soils. the density of seed in both depths was significantly higher in saline-alkaline than alkaline soils. the similarity coefficient between soil seed bank and above-ground was significantly different between under tree canopy of two soils in 0-5 cm. soil seed density was highest under crown cover in both soils. the crown canopy of trees in dry rangelands can play an important role in reservation of soil seed bank. therefore, the conservation of individual trees in these areas should be concerned of the managers.