| Sumario: | The most common yarding machine in Mexico is the jammer. This paper describes its parts, functioning and operation. Using time and movement data from 334 work cycles in a third entry coniferous forest in Michoacan, Mexico, regression equations were fitted to express the duration of each phase in a work cycle as a function of payload, residual stocking, yarding distance and topography. This set of equations allows the jammer’s performance to be estimated in terms of efficiency, both industrial and for the application of silvicultural treatments. Results provide evidence of this yarding system’s high productivity, and confirm its known drawbacks: high residual stand damage and high road construction requirements to keep average yarding distance under 70 m, despite its potential maximum distance of 400 m.
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