The effect of windthrow disturbances on biochemical and chemical soil properties in the northern mountainous forests of Iran.

Abstract: Land degradation as a result of wind (aeolian processes) is one of the most significant causes of soil loss in northern Iran. In order to gain a broader understanding of the specific effects of aeolian disturbance on soils in this region, research was conducted to evaluate soil microbial respiration and nitrogen mineralization in places where differences in microtopography occur due to the uprooting of trees by windthrow events, thereby causing variations in microtopography hereby referred to as “pit–mound positions”. A twenty-hectare study site situated within the Tarbiat Modares University Experimental Forest Station located in the Mazandaran province of northern Iran was chosen for this research, with thirty-four uprooted trees selected for detailed study. A classification of five microsites was developed to distinguish differences in microtopography in the immediate vicinity of these uprooted trees: mound top, mound wall, pit bottom, pit wall and closed canopy. Soil was sampled in the 0–15, 15–30 and 30–45cm depths at all microsites using a core soil sampler with an 81cm2 cross section. Soil reaction, organic carbon, total nitrogen, carbon-to-nitrogen ratio, moisture, abundance and biomass of earthworms, soil microbial respiration and net N mineralization for all samples were measured in the laboratory. Statistical comparisons revealed that the highest soil microbial respiration and net N-mineralization occurred in pit bottoms. Mound tops showed the lowest levels of soil microbial respiration and net N mineralization. Measurements of soil microbial respiration and net N mineralization were shown to decrease in relation to increased soil depth, with significant differences depending on soil depth. Indications of aeolian processes indicate that windthrow events create different microsites, thereby influencing the specific micro-scale soil characteristics. These micro-scale characteristics should be taken into account when performing forest soils surveys and to inform forest management practices. [Copyright &y& Elsevier]