Steep terrain solutions for mechanised ground-based silviculture equipment

It is well understood that working on steep terrain (>35%) is more complex than level and gentle slopes. This is mainly because when equipment is used on steeper terrain the stability and traction of the machine is reduced. This creates a high safety risk for the machine operator and the likelihood of machine tipping over is increased. Furthermore, the potential for significant soil damage is higher when working on steep slopes if adequate precautions are not taken. Silvicultural activities have traditionally been conducted manually on steep terrain; however new solutions are being introduced to improve the terrain handling abilities of existing silvilcultural equipment.

Unlike harvesting were cable yarding systems as well as specialized ground-based equipment have been developed to harvest and extract timber from the site, very little equipment is currently available to work on steep slopes in silviculture. The complexity in silviculture is that equipment working on steep slopes not only has to perform the work required (e.g., planting) in a safe and efficient manner but, it needs to handle resources (e.g., seedlings, water, fertilizer, chemical) which is required to successfully carry out the operation. The handling and replenishment logistics become complex because a suitably adapted machine needs to deliver the resources to the machine or the machine performing the task needs to regularly stop operating and go to a point where it can be replenished. The additional costs and viability of steep slope work is a genuine concern when considering the application of advance steep terrain technologies in silviculture operation. In most cases manual labour is still used to tackled steep terrain silviculture work.

Tracked machines are known to have better slope handling abilities than wheeled machines. Therefore, when performing silvicultural activities tracked machines may be a preferred option. Purpose built, tracked machines with arrow tracks and single deep grousers will have better traction abilities compared to conventional excavators with wider tracks and triple grousers. Levelling upper structures also improve the operator’s ability to sit at a level position thereby carrying out the activity unobstructed. Most existing excavator-based soil preparation and planting machines are conventional excavators configured with tailswing to work on level and gentle terrain. When looking at tracked machines, another option is to consider using tracked crawler type tractors to work on steep slopes where necessary.

In silviculture, agriculture and forestry type tractors are commonly used to draw implements on relatively flat terrain because of their slope limitation. However, forwarder and skidder-based carriers are able to deal with more steeper areas, more especially if the equipment has bogey axles and traction aids like band tracks and wheel chains which facilitate better traction.

The purpose of the winch assist systems is to improve traction and stability of the machine on steep slopes. According to Safe (2022) Traction aid is where the rope is added to reduce machine slip, but the supported machine is both stable and still able to move on the slope without support from the rope whilst winch assist gives access to terrain that could not otherwise be operated without the support of a winch and wire rope. Winch or cable assist technologies have been adopted widely in harvesting (e.g. Twinch, Timbermax, Herzog) and can potentially be adopted in silvilcultural equipment as well. The steep areas where trees are harvested with winch assist technologies need to be replanted and tended, therefore consideration needs to be made on how similar technology can be used to regenerate the same forest stands. Collaborative work is stilled required between silviculture machine and winch assist attachment manufacturers to make this technology more noticeable in the market.

                                                                                                            Image source: Ecoforst - Twinch

Silvicultural tools used on ground-based equipment can also be adapted to function optimally on steep terrain. One such solution is the Bracke P12.b planting head which has a tilt levelling function which enables the planting head to plant upright and well positioned seedlings on steep slopes even though the carrier machine maybe on working on an incline. This ensures good quality planting of seedlings.

                                                                                                                                           Image source: Bracke Facebook

As harvesting technology continues to pursue safety and more efficient ways to extract timber on steep slopes, it is only a matter of time before similar systems are used on modern silviculture equipment. Throughout the world, various modern silviculture equipment is being developed and tested. As machine manufacturers and foresters become more attuned with the functionalities of the new silviculture machines, the terrain handling abilities will be integrated to enhance the equipment’s ability to work on steep slopes. Even though technology can be used to overcome steep terrain challenges to a certain extent, it important to ensure that operators are well trained, experienced and supervised when working on steep terrain. In conclusion, manual and ground-based equipment are the primary ways in which silviculture activities are performed however, other operation specific technologies such as the use of UAVs (drones) can be used.

Safetree. 2022. New Zealand Winch-Assisted Harvesting Best Practice Guide. (online) https://safetree.nz/resources/winch-assisted-harvesting-bpg/  (Accessed March 2023)