Shovel logging is the term used to describe a type of log or whole-tree forwarding in which a “shovel”, “swing machine” or long reach hydraulic loader built for forestry advances stems toward roadside using a series of 2-3 “swings”. Figure 14.6 shows a shovel logging system in which Douglas Fir stems are being advanced to a log landing using a shovel logging machine on moderate slopes, alongside a cable logging operation on steeper terrain.

14.6.4 Chippers

Wood chippers may be disk or drum machines and are available in a variety of sizes, from small, trailer-mounted models able to handle small diameter branch material, to mobile, whole-tree chippers that can process large diameter stems with high throughput in industrial operations. Whole-tree chippers may be paired with a separate loader or may

be self-loading. Tracked machines are able to work in the woods in order to minimize slash forwarding with a forwarder or excavator. Stationary machines work at a landing or concentration yard. Figure 14.7 shows a full mobile chipping unit processing commercially thinned stems at a log concentration yard in north Idaho. In general, chipping tends to work most efficiently when stems have high moisture content (i. e., “green” wood).

Fuel chips are most commonly used for thermal applications, such as boiler fuel, and for power generation. The presence of bark and foliage in the chips is generally not problematic in these applications, assuming that the presence of inorganic material can be controlled to reasonable levels. In addition, certain biofuel conversion technologies can utilize fuel chips, notably the thermochemical processes that gasify biomass or utilize some form of pyrolysis to convert the solid material to a liquid or gas.