Dave1949,
The industry has changed a lot here in the last 20 years and what you suggest might become economical in some situations in the future, but prices for the raw material would have to get pretty high.
We hardly ever see skidders any more. They cause too much site damage, mostly in compaction which leads to erosion and site quality degradation--Douglas-firs don't like compacted soil, but they do like sun. Now, the machine of choice is an excavator, or better yet, if the logger can afford it, a processor. The processor is a glorified, computerized excavator and chainsaw. The machine goes to the tree, grabs onto it, cuts it near ground level. If the tree isn't too big, it holds the tree horizontally, rollers run the tree left to right through a yoke and in doing so the rollers break off the limbs while the machine measures the diameter, length and taper. With current log prices programmed into the machine, it computes where to buck it and makes the cuts. All in about a minute. Then it stacks the logs for later removal. Skidders are sometimes used following a processor, but because the processor stacks the logs in an organized manner, skidders travel on a very small portion of the site.
Larger trees are felled in the traditional way with fallers. Once limbed and bucked, the excavator picks up the log and swings it around to set it down toward the landing. Does that with all the logs within reach, then moves around the stack and repeats the procedure until they get to the landing. Sounds inefficient, but it's really cheaper than skidders and cats. The excavator has about 2-3 psi ground pressure and operates on the slash and there are no skid roads. Very little soil disturbance and virtually no compaction. Cats have about 8 psi and skidders go up to 12-15.
The excavator, once the logs are out of the way, then piles the slash for burning. In a stand of small trees, there may be no need to pile the slash; we can plant right thru it. Yes, the slash is disposed of for fire concerns.
On my place, we had a lot of slash, as the trees were too open grown which gave them large crowns with lots of large limbs. We only logged about 3 1/2 acres. To remove the slash, we would have had to have a place to put it and whenever the dump truck arrived, the machine would have had to stop where it was and go load the truck with low value product. Space was limited, we only used 2 landings and there was undisturbed forest between most of the logged area and the road, so we would have had to haul all that low value product thru the forest to pile somewhere by the road. That means taking down some trees to make space to pile the slash--trees that would otherwise be left to grow and develop value.
Now, a log or a few logs you can pick up and move. The
grapple on the excavator grabs at one point and the log sticks out 30-40 feet beyond, so picking it up in one spot, you pick up a lot of material. Now imagine a
grapple looking like your thumb and forefinger picking up a mass of limbs. To move an equal weight of material, you would have to pick up several loads of slash. Each time with a machine costing a couple hundred or more per hour.
Logs can be moved efficiently, slash can not.