Soil respiration and carbon stock responses to land use changes in the temperate forest of northern Iran

Land use change is one of the major sources of extra CO2 emission, which increasing in CO2 in the atmosphere leads to a global negative effect. Therefore, it is necessary to study the effect of land use change from forest to orchard and agricultural land on carbon stock, especially in developing countries, where its rate might be high, while reliable data are scarce. In this study, soil respiration and carbon stock of dense forests, open forests, as well as an orchard and arable land were considered as the common forms of land use in the Hyrcanian region, north of Iran. After field trip in the dense and open forests, circular plots (1000 m(2)) were employed systematically. The diameter at the breast height (D.B.H) of all the trees (D.B.H & GE; 12.5 cm) and total height (H-t) was recorded in each plot of dense and open forests, as well as in orchards. Soil physical-chemical properties were studied by taking samples (0-10 cm depth) from each land use. Soil CO2 efflux was measured with closed chambers and the root respiration measured using the root exclusion bag (2 mm size) method. The above-ground biomass of the trees (AGB) was calculated by allometric models of the Hyrcanian forest. The greatest above-ground biomass was observed in the dense forest (330 & PLUSMN; 13.16 t ha(-1)), followed by open forest (86 & PLUSMN; 6.49 t ha(-1)) and orchard (7 & PLUSMN; 2.11 t ha(-1)). The highest and lowest soil carbon stock was observed in dense forests and arable land. The highest and lowest soil microbial respiration was measured in the dense forest (51.40 & PLUSMN; 0.90 mol C h(-1) m(-2)) and arable land (38.28 & PLUSMN; 1.40 mol C h(-1) m(-2)). The root respiration was the highest in the orchard (16.69 & PLUSMN; 2.26 mol C h(-1) m(-2)). The total carbon stock of the orchard (50.77 & PLUSMN; 3.57 t ha(-1)) was not significantly different (p > 0.05) from that of the open forest and agricultural field. According to obtained results it can be stated that, due to the importance of reducing greenhouse gases along with the need for food, it seems that the introduction of multipurpose trees into the agricultural land or agroforestry systems would be a good practice for mitigating both important concerns.