A harvester - forwarder system was studied in a selection harvest operation conducted in an interior forest stand composed of Douglas fir (Pseudotsuga menziesii), Ponderosa pine (Pinus ponderosa), and Grand fir (Abies grandis). A time-study analysis was used to develop models for predicting individual machine productivity over time for both the harvester and forwarder involved in the study. Analysis indicates that harvester productivity (13.85 m3 per SMH) closely matched forwarder production (14.10 m3 per SMH) during the study. Further analysis yielded models that can be used to predict system productivity across the range of stand values observed during the study. The results suggest that system productivity is balanced when operating in stands averaging 15 to 25 cm DBH. In stands of larger or smaller average diameter, productivity for the system becomes unbalanced and affects machine operation, particularly the forwarder. Further research is suggested to improve the developed predictor models and allow for prediction of system performance over a broad range of stand and site conditions.
Forest harvesting systems vary from place to place. This paper concentrates on the study of one of the most complex systems, multistage timber production, which is very popular in vast forest regions of China and Russia. Based on case studies from the Heilongjiang Forest Region, in the northeast part of China, optimal operation planning for forest harvesting, and the impact of harvesting on the forest environment, economic benefit and working safety, is carried using a multi-objective optimization model. The results of the case studies, optimizing operation time schedules, show that the models are quite applicable and helpful to practical operations.
Current wood-chip dumping systems consist of a platform, pivoted at one end, that is raised by expensive telescopic hydraulic cylinders with high energy requirements. A new concept for a self-tipping dumper is described that, theoretically, requires no energy to tip and empty a loaded B-Train Chip Van having a total mass exceeding 60 ts. The platform is pivoted near its centre and advantage is taken of the shift in centre of gravity between the loaded and empty vehicle to tip the platform to 60 degrees and then return it to the horizontal.
A series of dynamic loading tests were conducted on a small skyline logging system (15.8 mm [5/8 inch] skyline) operating in a second-growth Douglas fir stand. The tests included free vibration tests and logging tests with turns weighing from 1.5 to 9 kN [340 to 2050 lbs]. Natural frequency and damping were evaluated from free vibration tests, and the free vibration portion of logging tests. Dynamic load magnitude was evaluated for logging tests with natural and artificial breakouts of turns with a range in turn weights, and for a series of logging tests with the same turn. The natural frequencies of the guylines were in good agreement with simple cable theory. However, the presence of the carriage on the skyline resulted in measured natural frequencies significantly lower than simple cable theory would predict. Damping of the tailspar system and the skyline averaged about 10% of critical damping, but was highly variable from test to test. Dynamic load magnitude, whether expressed as the load peak produced by turn break-out, or the maximum cyclic load, was highly variable, with coefficients of variation ranging from 31 to 79%.
Even a series of logging tests with the same two-log turn produced maximum cyclic loads with a coefficient of variation of nearly 40%.
Forest land utilization is becoming an important disposal alternative for paper mill wastes. Interest in this disposal alternative for other organic solid wastes such as poultry litter and compost is likely to grow as well. Three main types of spreader mechanisms that have been tried for forest waste spreading operations are vertical impeller/blower units, horizontal-axis beater-type spreaders, and horizontal spinner-type spreaders. The main considerations in selecting equipment for forest spreading operations are the carrier, the type of spreading mechanism, hopper configuration, and self-loading capabilities (if the carrier is a forwarder). These considerations are discussed in terms of site/stand conditions as they affect manoeuvrability and access, the materials to be spread, costs, and the scale of the spreading operations.
An average yarding distance model for rectilinear skidtrail layout from a centralized landing is given. The model is appropriate to the evaluation of some row thinning designs in plantations. The theoretical basis for formulas used in the model is briefly described. The model was coded for computer solution and applied to a hypothetical example the results of which are presented.