Timber Provision on Soft Soils in Forests Providing Protection Against Natural Hazards: A Productivity and Cost Analysis Using the Koller 507 in the Horizontal Yarding Direction in Switzerland

Abstract

Forest soils can be sensitive to traffic for various reasons, such as a high water table and the absence of sturdy ground, both of which can lead to fragile ground conditions under wet weather conditions. Extracting timber from such stands is a challenge, and cable-based systems might be the best option. While damage to the remaining stand and to the soil during extraction is not always avoidable, the use of cable-based systems completely eliminates ground-based traffic in the case of fully suspended loads and at least reduces soil compaction, soil surface damage and erosion. From a technical viewpoint, cable-based systems can be applied in most forest types and at almost any time if they are equipped properly and with an appropriate configuration (e.g. with all-terrain cable yarders). However, only a few previous studies have been focused on the productivity and related costs that can be expected when cable-based systems are used in flat and environmentally sensitive areas. Therefore, we evaluated a forest operation using a Koller tower yarder with the aim to develop a productivity model that makes it possible to predict the productivity of comparable yarding operations beforehand and estimate related costs. In June 2021, we collected data from 473 cubic metres over bark (m3ob) during 104.25 h of commercial operation. We analysed the resulting 276 work cycles using ordinary least squares regression models. We categorised the work steps into felling (28.3%), yarding (68.0%) and piling (3.7%). The average yarding cycle time was 10.77 ± 5.40 min and resulted in an average yarding productivity of 9.95 m3ob PMH15−1. The variable payload, which was suboptimal in the analysed case, was the predictor with the greatest impact on productivity. Production costs were 86.65 CHF m3ob−1 at roadside, corresponding to 80.59 € m3ob−1.