Soil Disturbance Effects from Tethered Forwarding on Steep Slopes in Brazilian Eucalyptus Plantations

Austin M Garren,Angelo C Moura,M Chad Bolding,Scott M Barrett,W Michael Aust

doi:10.3390/f10090721

Abstract

Traditional timber harvests on steep slopes have been conducted through labor-intensive and sometimes environmentally impactful methods, such as manual felling with chainsaws and extraction using bladed skid trails, winching, or cable yarding. Ground-based mechanized harvesting and primary transportation methods such as cut-to-length harvesters and forwarders have emerged in some parts of the world as low-impact, safe, and efficient alternatives to the aforementioned systems. However, when mechanized operations are used on steep terrain, problems such as poor stability, loss of traction, and increased soil disturbance can occur. Tethered or winch-assisted logging practices are being tested and applied in several countries to adapt to challenges associated with operating equipment on steep slopes while minimizing environmental impact. To better understand the feasibility of these systems, we conducted a designed experiment to quantify changes in soil properties and predicted erosion resulting from varying numbers of passes and payload levels by a forwarder operating on slopes ranging from 27 to 38 degrees. The machine was equipped with two different track configurations, tethered by either a machine-mounted or self-contained winch, in eucalyptus plantations in Brazil. On low slopes, bulk density significantly increased, but it did not increase on steeper slopes; this demonstrates traction winches’ effectiveness at reducing concentrated ground pressures. Rut depths were minimal and decreased with increasing slope classes due to reduced track slippage. Predicted erosion rates were high, primarily due to the extremely steep, long slopes and lack of adequate cover in some portions of the trail, illustrating the importance of proper erosion management practices on steep slopes.

Highlights

Logging operations on steep slopes often face more difficult challenges than those on gentler terrain
Between-track mean bulk density was significantly higher than off-track in low slope TWAGG but
Soil impacts resulting from the tethered logging operations overall were relatively light when compared with other steep slope ground-based methods requiring large road networks and bladed skid trails

Summary

Introduction

Logging operations on steep slopes often face more difficult challenges than those on gentler terrain. Chainsaw felling and choker-cable setting tend to be more physically taxing and dangerous for workers [3], while the use of bladed skid trails, winching, and cable yarding can be impactful to the environment and/or have reduced efficiencies when compared with ground-based mechanized operations on less challenging terrain [1,2,4]. Some modern purpose-built steep slope machines are capable of traversing grades up to 35 degrees while maintaining acceptable productivity [11,12]. Even highly specialized steep slope machines lose stability, traction, and productivity on extreme grades, weak soils and under adverse conditions, resulting in a practical slope limit of approximately 27 degrees for most machines [9]

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