Volume 21, numéro 2, september 2010

EN :

Volumetric productivity in harvesting varies as a function of the properties of the trees. Consequently, the harvesting price paid to the contractor tends to vary. However, pricing appears to depend not only on the properties of trees, but also on the division of any logging site into compartments. Such an effect depends on the statistical properties of any compartment. In the case of an exponentially distributed trunk volume, an upper incomplete gamma function appears to describe the relationship between the harvesting price and the productivity function. In the case of Weibull-distributed trunk volume, the relationship is given in terms of the ratio of two gamma functions. In the case of left-truncated Weibull-distribution, a ratio of two upper incomplete gamma functions appears. Exponential distribution may induce a deviation in excess of 10%, whereas a Weibull distribution with nonzero mode value induces at most 4%. Unification of compartments increases the harvesting price.

EN :

Time studies were carried out on a stump-to-mill multi-stem Eucalyptus harvesting and transport operation in Zululand, South Africa in 2007. A simulation model (System 1) of this system was subsequently built using a commercial simulation software package (Arena 9) and data from the time studies incorporated into the model. Following this, two hypothetical stump-to-mill multi-stem models (Systems 2 and 3) were built using Arena 9 and parameterized input data. All models were found to adequately represent reality. Simulated harvesting system balance was improved through normalization of machine utilization in Systems 2 and 3. Production improvements were predicted with simulated timber production per month increasing by 31.1% and 30.8%, from System 1 with three trucks, to System 2 with four trucks, and System 3 with four trucks, respectively. Cost reduction was predicted, with the cost per unit of timber decreasing by 12.5% and 4.1%, from System 1 with three trucks, to System 2 with four trucks and System 3 with four trucks, respectively. Beneficial operational techniques were also confirmed using the simulation models. In the studied conditions delimbing and debarking of full trees into tree lengths at roadside with delimber-debarkers before cross-cutting and loading with a slasher was predicted to be $0.65/m³ cheaper than delimbing, de-barking, and cross-cutting full trees into pulpwood with processors at the landing and then loading with a loader. Usability of Arena 9 in modeling forest harvesting operations was concluded as acceptable, but required detailed background logic inclusion.

EN :

The authors conducted a survey of mechanized harvesting and processing machinery in Italy, with the purpose of understanding if the close-to-nature small-scale forestry typical of this country may prevent a reasonably intense utilization of modern technology, or entail a significant increase of its operating cost. Despite the challenging work conditions offered by Italian forestry, modern forest technology has already made significant inroads, as witnessed by a small yet substantial harvester and processor fleet, counting more than 80 units, 75% of which are mounted on general-purpose carriers. Usage levels are lower than those reported for northern and central Europe, but still in excess of 1000 machine hours year, at least for the prime movers. Insurance, repair, and maintenance costs are significantly lower than generally reported in current literature. However, empirical data on machine costs is very scarce, and most studies report estimates rather than measured values. Such estimates are often obtained with the same basic methods derived from agriculture, thus raising the question of whether their adaptation to forestry use should be further refined.

EN :

Being sustainably available and CO2-neutral, woody biomass is becoming increasingly more important as an alternative energy source on a worldwide basis. However, despite broad acceptance of bioenergy plants in Austria, more and more neighboring residents are lodging a protest because of the noise and dust burden during wood-chipping operations. These circumstances force plant operators to utilize separate terminals for storing and chipping forest wood, in turn resulting in a redesigning of the forest fuel supply chains. The present paper focuses on the choice of spatial arrangement and the type of terminals used. For redesigning the forest fuels supply network, a Mixed Integer Linear Programming (MILP) model was developed and subsequently implemented for a study region. The network consists of direct supplies from the forest for combined heat and power facilities (CHP) and indirect supply lines via terminals. The MILP model provides a cost-optimal spatial arrangement of terminals by considering different terminal types with respect to spatial context, chipping technology, and the volume processed. Different scenarios are used to test the robustness of the network design. A simulation of a transportation cost increase shows that the optimal network design is stable within an increase of 20 to 50% and between 70 and 110%. At other levels of increase, the number of terminals used decreases. Furthermore, the number of terminals decreases as the domestic forest timber utilization rate increases. It was possible to demonstrate that industrial terminals offer considerable saving potentials. Therefore, the cooperation of CHP operators with a forest-based industry partner as a terminal provider is one of main management implications of the study results.