The effect of tree covers on topsoil biological indices in a plain forest ecosystem

Soil, as an important part of the ecosystems, are affected by tree species with differences aboveground and underground biomass, canopy structure, liter quality and quantity under the same field condition. Regarding to the importance of recognizing and studying of biological properties, appropriate indices to assess the soil quality and health, the variability of topsoil fine root biomass, earthworm density/biomass and CO2 emissions for each species of native broadleaf species (Carpinus betulus, Pterocarya fraxinifolia, Quercus castaneifolia and Acer velutinum) in plain areas of northern Iran is studied.
After field trip in a plain forest area located in Noor city, groups (spots) of the pointed broad-leaved species were recongnized and five replications of each species were considered in same dimatere class. Litter and soil samplings were carried out under each tree in northren way. Samplings were taken from two positions (near and away from the main stem) in the growing season (July) with microplots of 30×30×15 cm.
Analysis of variance for litter quality, soil physical (except clay and moisture) and chemical properties showed statistically significant differences among studied tree species. Greater amounts of soil fine root biomass were significantly measured under Pterocarya fraxinifolia (92.79 g m-2) whereas the species of Acer velutinum (71.46 g m-2), Carpinus betulus (62.21 g m-2) and Quercus castaneifolia (31.44 g m-2) were next in the ranking. The most earthworm density was significantly recorded under Carpinus betulus (2.50 n m-2), Acer velutinum and Pterocarya fraxinifolia (1.90 n m-2) and Quercus castaneifolia (0.7 n m-2) respecively. The lower values of earthworm biomass were significantly found under Quercus castaneifolia (8.61 mg m-2), Acer velutinum (24.21 mg m-2), Pterocarya fraxinifolia (24.66 mg m-2) and Carpinus betulus (29.59 mg m-2) respecively. The highest soil CO2 emission were significantly observed under Carpinus betulus (0.47 mg CO2-C g soil-1 day-1), Acer velutinum (0.44 mg CO2-C g soil-1 day-1), Pterocarya fraxinifolia (0.32 mg CO2-C g soil-1 day-1) and Quercus castaneifolia (0.27 mg CO2-C g soil-1 day-1) respectively. According to results, litter quality and soil properties were no affected by sampling positions. The finding of correlation is indicating that soil biological indices are more influenced by litter quality and soil chemistry.
The result of this research is showing that forest trees have significantly different effects on soil biological indices, as well as physico-chemical and litter quality properties. Our findings can be used by forest managers due to priorities of broad-leaved species to restore of degraded areas of the northern plains of Iran.