Jackie Mitchell provided this description of tehtered logging and example photos of the equipment :
This is all considered ground based logging. Untethered has the exact same effects as our typical tractor logging however our tractor systems are not allowed to operate on slopes greater than 40% slope. Untethered systems, because they have a more evenly distributed weight across their suspension, can operate untethered (on certain soil types) up to 50%. They will tether to a tree stump and operate on steeper slopes when needed.
When tethered they operate more like a skyline system. They require corridors where they must remove all the trees within a 12-14 foot distance to allow for the equipment to lower directly down the slope. There are some photos included showing this. When tethered, they can harvest slopes up to approximately 80% slope.
They utilize a cut-to-length (CTL) harvest method which is different than our typical Whole Tree Yarding method. CTL is when the Harvester first fells and removes the limbs of the tree. It then cuts the logs directly at the site of harvest and decks them in centralized locations throughout the unit. The branches and tops (slash) are then used as matting on the ground surface for the equipment to drive over as an added barrier/cushion protecting the soil underneath.
Since the slash is kept inside the units rather than brought to a central location at a landing, there is a difference in fuel loading on the landscape. However in most cases, because the slash is compacted due to equipment driving over it, the height remaining is limited and meets our standards for lop and scatter. The need for pile burning would be extremely minimal using these systems.
Once the Harvester has the trees felled and decked, a Forwarder comes in behind and collects the logs to be loaded directly into the back of the Forwarder. There are many photos showing logs stacked in the piece of equipment I am referring to. This Forwarder transports the logs directly to the truck loading site, not unloading the logs at a separate location. This is why there is no need for landings as they are not decking the logs twice, just once after harvest in the unit.
Because of the methods used for harvest and transport, there is no need for the construction of landings or temp roads. The equipment travels through units in the same way we analyze for skids trails. They take a minimal number of passes, harvesting very few trees to do so (unless they are tethered). The equipment is no wider than the skidders we already utilize so they do not need more than a width of 12-14 feet to pass and swerve through the stand.
The equipment minimizes ground disturbance by utilizing the slash mats and is also aided in the fact that the equipment does quite a bit less compaction than standard logging equipment. Unloaded the PONSEE Harvesters & Forwarders are approx. 6 pounds per sq. inch (PSI). Loaded they can get up to approx. 10 PSI. A typical skidder unloaded is around 14 PSI. Their longer frames and better weight distribution are what create the lessened PSI.
The equipment can be both tracked and rubber tired depending on the needs of the sale objectives or unit requirements. In the photos attached you will see both examples. The equipment is standard rubber tired but the tracks can be added on top of the tires to aid in grip and stability on steeper slopes.
This type of harvesting is currently being done out in Sun Valley on Bald Mountain. There are some photos included from those operations.
The main difference here is the end visual result after tethered systems are used, as the corridors do remain visible for some years after, until the understory regenerates or seedlings establish.