The fight against climatic change has introduced a new dimension to Finnish forestry. Renewable forest fuels play an important role in the national climate strategy, which is aimed at reducing the greenhouse gas emissions in accordance with Finland's international commitments. According to the Action Plan for Renewable Energy Sources, 5 million solid m3 forest chips or 0.9 Mtoe energy is to be derived annually from low-quality forest biomass by 2010: two thirds from logging residues from final fellings and one third from small trees from early thinnings.
The production of fuel chips from early thinnings is a challenge, but provides the opportunity to improve the tending of young forests. To make the use of chips competitive, the cost of harvesting must be reduced, and the yield of biomass per hectare must be increased. Therefore, in industrial operations the chips are produced from whole trees rather than delimbed stems. The intensive recovery of biomass can result in the accelerated loss of nutrients from forest soils, and this has to be taken into account in site selection and system development.
In 1999, the National Technology Agency Tekes launched a five-year Wood Energy Technology Program to develop efficient procurement systems for large-scale production of forest chips from residual forest biomass. The ongoing program is reviewed in this paper from the viewpoint of early thinnings. Among the topics discussed are the resource and its biomass composition, background problems, cost of production, silvicultural impacts, benefits from the program, and future prospects.
The felling and bunching of small diameter trees in Finland is still largely carried out manually using a chain saw and clearing saw. The felling of small diameter trees has been developed and mechanized. In addition to the high felling costs of small trees, the move towards mechanized harvesting is also caused by a shortage of professional lumberjacks, the possibility of all-year-round mechanized energy wood harvesting, and an increasing demand for energy wood.
The research investigated the productivity, costs and silvicultural result of the guillotine blade equipped, multi-tree-processing Naarva-Grip 1600-40, for small diameter energy wood harvesting. Work-studies were carried out in six young stands at the first thinning stage.
In mechanized energy wood harvesting with the Naarva-Grip 1600-40, an average of 73% of the trees felled were multi-tree-processed. The multi-tree-processed proportion increased to 96% in dense Scots pine (Pinus sylvestris L.) sites with small trees. One bunch consisted of approximately 3.2 trees. The average density and volume of removal had the greatest effect on the productivity of the felling-bunching work. Felling-bunching was carried out on the sites at a rate of 106-422 trees per effective hour (E0, excluding delay times). Productivity on the different sites varied from 3.0 to 7.2 m3/E0, giving an average of 4.7 m3/E0 (weighted by felling volume) with an average tree size on the site of 32 dm3.
When the size of the felled trees was under 20 dm3, the felling-bunching costs were over 20 US$/m3. When the average tree size on the site increased to 50-70 dm3, the felling-bunching costs approached the 10 US$/m3 level. During the research, the Naarva-Grip 1600-40 proved to be competitive compared to the other multi-tree-processing, energy wood felling heads on the market. In order to keep the felling-bunching costs at a reasonable level, mechanized harvesting should be targeted at sites where the average size of the trees removed is over 30 dm3, and the energy wood volume at felling over 30 m3/ha.
A comparison is made of energy usage and the contribution made to the global warming potential (GWP) by present (1997) and past (1972) forestry operations (including secondary haulage) in Sweden. The results are expressed in units of one cubic metre (solid u.b.) of harvested timber.
The results indicate that, since 1972, improvements in fully mechanized forestry operations, particularly logging, have led to a reduction in total energy use from 1972 (236 MJ). In fact, the energy used by today's (1997) mechanized logging systems (147-200 MJ) is roughly the same as that used by motormanual systems back in 1972 (156-177 MJ). The same is true as regards the contribution made to global warming potential: more fossil carbon was released in mechanized forestry (22 GWP) in 1972 than in 1997 (13-17 GWP). What's more, the contribution to GWP in 1997 is on the same level as that made by motormanual systems in 1972 (15-16 GWP).
It is accepted that forest management in Sweden mitigates the global warming potential. This is because the resulting sequestration effect in forest biomass is greater than the level of emissions from forestry operations.
Cut-to-length harvesting systems offer an alternative to conventional mechanical systems for thinning mixedwood stands. We evaluated the performance of a single-grip harvester and forwarder in a poplar-dominated mixedwood stand in Southern Ontario to quantify the effect of tree size and tree form on harvester productivity and harvesting cost, and to assess the damage caused by the harvesting operation to advance regeneration and residual trees. A single-tree selection silvicultural system was used. Individual trees were assigned a form index based on their visual estimates of limb size and stem form. The cut-to-length harvester produced 23.1 m3 per productive machine hour (PMH). Forwarder productivity was 17.2 m3/PMH. The results indicate a significant and positive relationship between harvester productivity and tree size (dbh) and tree form. Tree size (dbh) has the greatest influence on the unit cost of harvesting. At an average 27 cm dbh and extraction distance of 200 m, the stump-to-landing cost was approximately 10 US$/m3. As tree size increased, the unit cost of wood produced decreased. Damage to residual trees and advance regeneration was minimal. The results suggest that single-grip cut-to-length harvesting systems can be effective in managing poplar-dominated mixedwood stands.
In Finland, many bio power and heating plants have been recently built and existing power plants have been improved to allow increased energy production. To meet the increasing demand of solid fuel at bio power plants, a large transportation fleet is needed and both the logistics of solid fuel transportation and power plant fuel reception must be improved. This study investigated fuel truck arrival and unloading processes at a power plant which produces heat for the city of Kuopio and electricity for the national grid. The aim of this study was to minimize fuel truck queuing times, and balance the use of two delivery bays by improving the logistics of fuel handling at the receiving station and by distributing truck arrivals at the power plant more uniformly throughout the day. Discrete-event simulation was implemented as a method for analyzing the system. To balance the utilization of both delivery bays at the power plant and shorten the queuing times, the most feasible solution was for more effective control of truck interaction with the delivery bays: having the shortest queue and faster fuel flow from delivery bay to combustion by arranging fuel transport with a new conveyor to the boiler. Adaptable scheduling of truck arrivals was found to be feasible during the morning to smooth out the peaks of the truck arrivals in cold periods when fuel consumption at the power plant is at its highest.
A silvicultural project encompasses tasks such as site-level planning, regeneration, harvest, and stand-tending treatments. An essential problem in managing silvicultural projects is to efficiently schedule the operations while considering project task due dates and costs of moving scarce resources to specific job locations. Transportation costs represent a significant portion of the total operating cost. The main difficulty in developing such a management system is finding an optimal transport schedule while handling complicated constraints, such as precedence and temporal relations among project tasks, project due dates, truck routing, weather, and other operational conditions. It is well known that finding an optimal solution to these types of problems involves high computational complexity. They are usually NP-hard. For this reason, we propose to use simulated annealing -a meta-heuristic optimization method- that interacts with a network simulation model of the system in which the precedence and temporal relations among project tasks and logistics are explicitly accounted for. The approach has been tested using data provided by a silvicultural contractor located in Alabama. The results obtained solving one instance of a small size problem with five worksites showed that the best solution could be found in less than four minutes using a personal computer with a processor Pentium III (1 GHz). A good solution for a larger problem with twenty worksites was found in thirty minutes. Also a resource analysis is performed to evaluate the impact of each resource on the best solution.
The grabbing forces of log grapples were modeled and analyzed mathematically under operating conditions when grabbing logs from compact log piles and from bunch-like log piles. The grabbing forces are closely related to the structural parameters of the grapple, the weight of the grapple, and the weight of the log grabbed. An operational model grapple was designed and tested to validate grabbing forces of the mathematical models while grabbing logs from five alternative diameter classes under two different working conditions. The working conditions and log sizes affected the grabbing forces significantly. Validation results suggest that the mathematical models developed can be used to estimate the grabbing forces required in the design process of log grapples. The results can be used by equipment manufacturers and researchers involved in the engineering design of grapples used in harvesting operations.