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In the usa
Over the years, the forests of southern New England have seen several different timber and wood/pulp harvesting systems. Until the advent of the internal combustion engine, all felling and bucking was done with axes and hand saws; all skidding was done with horses or oxen. In the 1930's, chainsaws and crawler tractors (bulldozers) began to replace axes, handsaws, and draft animals. In the 1960's, 4-wheel-drive, rubber-tired skidders began to replace crawlers. Now fully mechanized harvesting systems are beginning to replace chainsaws and skidders. The following will describe and discuss these harvesting systems, all of which (except axes and handsaws) are still in use in this area.
Horses or Oxen
Logs are loaded onto a low-to-the ground sled or attached at one end with choker chains to a 2-wheel forecart which are pulled by the horses/oxen. The animals are specially bred and have been trained for their work. Some are capable of skidding from stump to log landing and back unassisted.
The main advantage of horse/oxen skidding is the very low level of damage to the residual trees and the forest soils. The main disadvantage is the low limit on skidding distance for which draft animals are economical. Uphill skidding on grades steeper than 10% is generally not feasible.
Crawler Tractors
Crawlers run on metal tracks which give them excellent traction and maneuverability. They most often have a cable winch attached to the rear end with several log choker chains attached to the cable. The chains may be attached to logs (or whole stems) lying close to each other. When the cable is winched in, the logs come together to form a hitch which is then skidded out to the log landing.
The main advantage of crawlers is that they compact the soil less than rubber-wheeled skidders because their weight is spread out over a much larger tractive surface area. They are also able to do road construction work with their blades, and their manueverability can help avoid damage to residual stands. The main disadvantage for crawlers, as for draft animals, is the cost factor. Tracks require more maintenance than wheels and they limit the speed of the machine. Some land is too rocky to operate with crawlers because rocks can damage tracks and the low-slung undercarriages of crawlers.
Date: 2015-07-02; view: 486; Нарушение авторских прав; Помощь в написании работы --> СЮДА... |