Epsilon Archive for Student Projects

Abstract

Forest enterprises have always searched for ways to improve efficiency. For the past few
years there has been an emphasis on stock-keeping levels. Increased demand for fresh
round timber and the need to decrease the amount of tied-up capital has made the forest
industry reduce its inventory levels. This has brought on a higher demand on the timber
supply from the forest management districts concerning both delivery in time and
assortment output. As a result, the flow of timber has fluctuated a lot with serious
consequence for the timber supply during 1994. One reason was unexpected weather
conditions which lead to transportation stops.
This MSc thesis deals with the planning of logging operations and the problems that are
involved in that process for SCA Forest and Timber. This study was initiated by the
wood procurement and transportation department, Virke syd, and Strömsund's forest
management district within SCA. The purpose is to formulate a flexible and optimizing
model for decision-support in short-term planning and follow-up of logging operations.
The decision-support involves linear programming in order to minimize the cost of cross­
cutting losses, delivery bonus-losses and moving the logging machines from on logging
unit to another. The aim is to increase the adaptability between timber request and
logging result on assortment level. A seeond objective is to make a survey offactors that
influence the possibility for forest management districtsto achieve a continuous timber
yield in time and assortment output.
The validity of the model in this paper is limited to the planning techniques and
philosophy used within SCA and their short-term planning routine. The linear
programming model involves:
• a planning horizon of one to two months
• optimization of logging unit selection regarding rnachine resources in the ranger
district
• five assortments; pine and spruce timber, pulpwood of softwood, fresh cut spruce and
hardwood
• four cross-cutting alternatives; minimal top-diameter of timber; 12, 14, 16, 18 cm.
A result from an optimization gives a logging unit selection that minimizes the costs,
earlier mentioned, for periods extending from a couple of days up to two months. The
main thesis is that decision concerning resource allocation is to be taken "just in time".
The advantage with this procedure is that the decision maker has the latest information
regarding the actual wood flow and can make more accurate decisions.
To improve management and the linear programming model a continuously increasing
delivery bonus system has been constructed to allow the forest managementdistrictsto
equalize their logging operation costs with the bonus. To refine the decision basis,
harvester measurement of timber volume has been used in the decision-support system,
to make simple yield forecast for logging units.
Results from the decision-support system run on material from Strömsund's forest
management district have involved a large amount of moving logging resources between
logging units. This is mainly due to a relatively large difference between pulp wood and
timber prices. U sing the current timber and pulp wood prices the marginal cost for cross­
cutting adjustments usually exceeded the cost for shifting a logging unit. This is also
related to the size of the logging unit, whereas larger logging units have a low shifting
cost per cubic meter.
Major conclusions:
• Output estimations used within SCA short-term planning routines suffer from bias
and random errors. The most serious are the area estimation and the assortment
output functions. This makes it difficult to maintain a continuous timber yield in time
and assortment output in shorter periods.
• The decision support model that this study focuses on can be used on a practical basis
hut there is a substantial risk for suboptimization if the planning period is shorter
than a month andfor the wood flow demands are set too high.
• The use of "intelligent" computer based planning routines such as the model
constructed in this study could improve decision-making if the decision-maker fully
understood the fundamentals in economic optimization and the use of computers. The
key is to use common sense with computer-based planning.
• The use of harvest measurement, instead of wood measurement at milis, would
improve both planning and foliow-up with more accurate, daily based logging unit
related measures. This would refine the decision basis for the planner and make it
possible to do yield forecasting.
• Increase the logging team's influence and co-operation especialiy in areas concerning
wood flow planning and follow-up. This would not only give interesting task's for the
logging team's, it could also give faster more pliable solutions in the area of interest.
• Search for unconventional solutions in keeping a good wood flow; for example aliocate
more than one logging team to a logging unit, move logging resources to logging units
that give a more appropriate wood flow, change cutting form, etc.