Agri 2022

Effects of different harvesting treatments on soil, nitrogen, and phosphorus losses in the surface flow in Kheyrud forest


Sarakarami, Speaker at Agriculture Conference 2022
Tehran University, Iran (Islamic Republic of)
Title : Effects of different harvesting treatments on soil, nitrogen, and phosphorus losses in the surface flow in Kheyrud forest


Forest degradation and manipulation caused to disturbed water cycle, which in turn, has negatively impacted runoff and sediment production. As forests have an important role in mitigating runoffs, decreasing erosion and improving overall water quality, soil erosion and its consequences have become a new environmental and forest management challenge that seriously threaten water and soil resources. In general, it should be said that the type of land use and erosion are closely related to each other, and if the land is used improperly, the rate of erosion will increase sharply.This study aims to measure the effects of different forest harvesting methods on runoff, soil loss and nitrogen and phosphorous levels in surface runoffs in Kheyrud forest. Rainfall data was measured in 2 square meter samples over a 3-year period, and in each year, 3 replications of the experiment were conducted for increased accuracy. Measurements were done in parcel 320 of Ghazbon district of Kheyrud forest with treatments including single and group selection methods, skid trails and undisturbed area (as control). Results revealed that runoff, sediment yield, and concentrations of NO3-N and PO4-P peaked at the first year after treatments. In the first year following forest harvesting, runoff in the skid trail (7.36 mm) were higher than the group selection, single selection, and unharvested treatments by 1.15-, 5.63-, and 48.1-fold, respectively. Results showed that sediment yield (3.85 g m−2) and concentration nitrate (2.89 mg l−1) and phosphate (0.221 mg l−1) were at highest level in the skid trail in 2014. Nitrate and phosphate concentration in the skid trail, group and single selection didn’t recover within three years after treatment compared to unharvested treatment. However, phosphate in the group and single selection methods returned to the unharvested level over a 3-year period. A close relationship between runoff, sediment yield, and concentrations of nitrate and phosphate and amount of rainfall was observed especially in the first and second year after forest harvesting at all treatments. According to the results of current study, it can be concluded that silvicultural treatments such as single selection show the lowest impacts on hydrological characteristics that can be rapidly recovered within a few years. It can also be used during different periods by selecting appropriate methods and machines and designing accurate and permanent skid trails and cutting trees in the proper direction, prevent unnecessary movement of machinery and skidding equipment in the forest area in order to maintain the natural soil conditions and prevent or reduce soil and element loss during different time periods.

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