In the late 1970’s, 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
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.