In the late 1970s, the need for some type of machine to economically harvest small trees (under 5-inches D.B.H.) and forest residues was identified. Some machines and prototypes had been developed by industry and researchers to meet this need. These machines fell into four categories: portable chippers, mobile chipper forwarder, mobile chip harvester and mobile chip harvester forwarder (Sirois 1982a and Stokes and Sirois 1986b). Some of these machines could sever stems, while others relied on other equipment or manual chainsaws to fell stems for chipping. Some were self-propelled and others were trailer mounted for landing or roadside use.


From 1979 to 1982, researchers at the Forest Operations Research Unit tested a prototype swathe-felling mobile chipping machine, the Nicholson-Koch Mobile Chip Harvester. Some of the benefits expected from the use of this machine in harvested stands were improved aesthetics through removal of waste wood and slash, reduced scalping from traditional pile-and-burn operations, and reduced smoke management from windrow-and-burn operations. This was a large machine, mounted on an FMC tracked skidder which housed the felling bar mechanism and the chipper drum. The machine could sever standing trees and brush, and pick up large and small downed material. The total system included companion chip forwarders to collect the chipped material from the chipper spout. The chipped material was deposited in piles at roadside (Koch and Savage 1980). Later, the system was planned to have chips transferred directly from the forwarder into a chip van (Sirois 1982b). The 1979 initial field test was in an alder stand in Washington State (Koch and Savage 1980). The feller bar was modified and power requirements were analyzed in field tests in Alabama in 1980 and 1981 (Sirois 1981).


The results of the early 1980s studies (Sirois 1982a) of the Nicholson-Koch machine included chip quality and feed rates with the modified 3-knife system. The average production rate for the machine in early 1980 was one-acre per hour based on nearly flat terrain, firm soil, and an average D.B.H. of 6-inches. The biomass recovery rate was 76%, thus cleaning the test site enough to be planted without further site preparation. This production rate is not out of line with purpose-built mulching machines that are available on the market today.


Production of another chipper-forwarder was analyzed in a case study in central Georgia (Stokes and Sirois 1986b). The Purcell Chipper-Forwarder consisted of a chipper mounted on a salvaged military undercarriage. This machine chipped unmerchantable trees that were left in piles after a conventional harvest operation. Chips were collected in a large dumping hopper mounted on the rear of the unit and transported to roadside where the chips were dumped into an open-top chip van. Production, including travel and chipping elements, was determined and analyzed (Stokes and Sirois 1986b). The authors estimated that 5.54 bone dry tons per hour of small tree biomass was harvested at an average forwarding distance of 153 meters. Production rates are given for a range of forwarding distances. At a one-way forwarding distance of 500-feet, the production rate was 5.54 dry tons / hour. Cost per operating hour at that same distance was $13.54 - $22.56/dry ton/hour. A range of costs (based on an estimated purchase price and estimated owning and operating costs) were analyzed because the study was limited to eight cycles.


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