Post-Harvest Evaluation of Soil Physical Properties and Natural Regeneration Growth in Steep-Slope Terrains

Hadi Sohrabi,Farzam Tavankar,Rodolfo Picchio,Meghdad Jourgholami,Rachele Venanzi

doi:10.3390/f10111034

Hadi Sohrabi, Farzam Tavankar + Show 3 more

Open Access

https://doi.org/10.3390/f10111034

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Abstract

Protection of forest soils during harvesting operations is necessary to reduce damage and accelerate recovery time. The current study aims to evaluate soil physical properties, natural regeneration, and its recovery process in treatments including slope gradient, traffic intensity and skid trail after long periods of time, after ceasing the timber harvesting operations. The most recent skidding operations within each 5 years recovery period were studied for a chronosequence of 20 years. Soil samples were taken in abandoned skid trails and data were recorded on naturally regenerated species and density. The results revealed that most soil disturbances occurred on the slopes >20%, as well as the highest levels of traffic intensity. Bulk density and penetration resistance were still higher than the control area, with a significant difference between them, while total porosity was partially recovered. Twenty years after the skidding operation, soil bulk density and penetration resistance were 13.2% and 23.7% higher than the control area, while total porosity was 9.78% lower the than value of the control area. Seedlings of 50–150 cm and >150 cm in height on skid trails had significantly lower density than those in the control. The number of seedlings per m2 was less than the control area in all skid trails and for all height classes. The proportion of seedlings present in low traffic intensity was higher than in medium and high traffic intensities. The findings confirmed that full recovery rates are lengthy, and more time than 20 years is required to fully recover, especially with regards to penetration resistance.

Highlights

The use of heavy machinery in timber harvesting operations leads to increase soil disturbance and degradation [1,2,3]
Machine traffic on forest soil leads to increased soil compaction, reduces soil porosity, and condenses the pore connectivity, which results in an increase in soil bulk density and penetration resistance [4,5,6,7]
Results showed that the recovery period, traffic intensity and the slope of the skid trail have a significant effect on bulk density, penetration resistance and total porosity

Summary

Introduction

The use of heavy machinery in timber harvesting operations leads to increase soil disturbance and degradation [1,2,3]. Machine traffic on forest soil leads to increased soil compaction, reduces soil porosity, and condenses the pore connectivity, which results in an increase in soil bulk density and penetration resistance [4,5,6,7]. Soil strength and soil porosity are often considered as the most direct quantitative measurements of soil compaction [1,4,8,9,10]. Increases in bulk density or soil strength often coincide with decreasing total aeration, which adversely affects the air and water exchange and the microbial activity in topsoil layers [4,7]. A small increase in soil bulk density and soil strength can cause a considerable reduction in soil porosity, macroporosity

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