Sveriges lantbruksuniversitet
Institutionen för skogsteknik
Uppsatser och Resultat nr 277 • 1995
FOREST HARVESTING SYSTEMS FRIENDLY
TO THE ENVIRONMENT
I wan Wästerlund and Awatif E. Hassan
The Swedish University of Agricultural Sciences ISSN 0282-2377 Department of Operational Efficiency ISRNSUI-ST-UPPRLT--277--.SE S-776 98 Garpenberg
MASTER DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED Preface
The present report was presented at the 1994 ASAE Winter Meeting, Atlanta, Georgia, U.S.A. Since ASAE does not publish any proceedings, I decided to publish it as a Research Note at the Department of Operational Efficiency, Swedish University of Agricultural Sciences, Garpenberg, to increase the accessability.
Iwan Wästerlund Professor Paper No. 947512 An ASAE Meeting Presentation
FOREST HARVESTING SYSTEMS FRIENDLY TO THE ENVIRONMENT
by
Iwan Wästerlund, Assoc. Prof. Awatif E. Hassan, Prof. Swed. Univ. Agric. Sci. Col. of Forest Resources, S-776 98 Garpenberg North Carolina State Univ., Sweden Raleigh 27695-8002, USA
Written for presentation at the 1994 ASAE Winter Meeting Sponsored by ASAE
Atlanta Hilton & Towers Atlanta, GA, December 13-16, 1994
Summary: The trend in forestry practices today in Europe and USA in general, and Scandinavian countries in particular is towards adapting systems based on landscape planning. Thus common harvesting equipment available on the market will have to be replaced to meet these though demands. Environmentalists recommend that wood fiber should be harvested either by selection cutting or commercial thinning thus leaving the site "undisturbed" with no sign of machine traffic. This mandate will preserve ground water quality and assist in soil conservation. However, to meet the pulp and paper as well as saw mill industries, demand for wood from this method of cutting (selective or commercial thinning), requires a thorough examination of our harvesting systems and techniques. This paper will discuss present and future machines that are friendly to the environment. Hypothetical designs and improvements of existing machine systems will be addressed and recommendations will be made for future research activities.
Keywords: Harvesting, ecosystem, machine systems.
Th Abstract Introduction Silvicultural practices meeting environmental concerns Silvicultural strategies Potential methods of cutting in the Ecology Management (EM) Requirements for a friendly operation a. System requirements b. Road and terrain requirements c. Space/clearance requirements d. Handling requirements e. Acceptable degree of damage f. Environmentally friendly g. Cost efficiency Existing machine systems I. Harvesting II. Extraction III. Combined methods Evaluation of existing machine systems Conceptual designs for the future Conclusions References FOREST HARVESTING SYSTEMS FRIENDLY TO THE ENVIRONMENT1 Iwan Wästerlund and Awatif E. Hassan2 3 Abstract The trend in foresty practices today in Europe and U.S.A. in general and Scandinavian countries in particular, is towards adapting systems based on landscape planning. Thus common harvesting equipment available on the market will have to be replaced to meet these tough demands. Environmentalists recommend that wood fiber should be harvested either by selection cutting or commercial thinning thus leaving the site "undisturbed" with no sign of machine traffic. This mandate will preserve ground water quality and assist in soil conservation. However, to meet the pulp and paper as well as saw mill industries demand for wood from this method of cutting (selection or commercial thinning), requires a thorough examination of our harvesting systems and techniques. This paper will discuss present and future machines that are friendly to the environment. Hypothetical designs and improvements of existing machine systems will be addressed and recommendations will be made for future research activities. INTRODUCTION Forest machines are often developed on a trial-and-error basis to meet the industry need for forest operations. When the need for a certain task arises, design modifications of machine systems from the construction industry are adapted. Through that process, there are plenty of machine systems available for most forest operations and in particular for clearcutting. However, the use of efficient machinery for harvesting operations may be accomplished by changes in forestry practices towards sustainable forest silviculture and environ- mentally friendly systems. Thus, future machine systems for forestry operations might look quite different from the present ones, but the main task for tree cutting and extraction will remain the same. A number of harvesting system reviews have been conducted but with no evaluation of alternative systems that take into consideration the "new" silvicultural practices (cf. Jackson & Stokes, 1990; Reisinger & Aust, 1990). A more useful approach would be to examine the forestry operations, environ- 1 Paper No. 94-7512 presented at the 1994 ASAE International Winter Meeting, Atlanta, Georgia USA. 2The authors are, Iwan Wästerlund, assoc. prof., Swedish University of Agricultural Sciences, S-776 98 Garpenberg, Sweden, and Awatif E. Hassan, professor, North Carolina State University, Dept. of Forestry, Raleigh, N.C. 3 The use of trade names in this article does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar products not mentioned. mental requirements, existing machine systems, and future wood demand. Thus, the main objectives of this paper are to: (1) Define environmentally friendly operational systems, (2) Examine and evaluate existing machine systems that meet the above definitions, and (3) Recommend design modifications of existing systems and present new hypothetical concepts of future machines that are friendly to the environment. SILVICULTURAL PRACTICES MEETING ENVIRONMENTAL CONCERNS The pressure from environmentalists, politicians and the public about nature impose constraints on how we perform the harvesting operations as well as the silvicultural regimes. Treatment of the forest is considered to be a public issue whereas agricultural fields are the farmers' private business (Smith, 1978). It is also ironic that silviculture has been directed towards agricultural type of cultivation at the same time that minimum-tillage agriculture begins to appear as a mean of soil conservation. A new trend is that it has become fashionable to use recycabte mateiial such as wood but at the same time it has become more difficult to get allowances to cut trees! The most recent "green" dogma in Europe is that we should only use wood fibers coming from non-clearfelled areas for paper products because clearcutting is unnatural and destroys the environment. Recycling of paper is promoted but how many times can the wood fiber be recycled? A number of federal laws affect the forest management on private forest lands and a number of best management practices have been developed (Cubbage, 1993). The extent of these voluntary regulations on operational methods may increase in the future. The management of the national forestlands is more directed for a sustainable yield of several goods including water, wildlife, timber, recreation, and range. Biodiversity and sustainability are keywords for forest management all over the world and they are generally agreed upon (WCED, 1987) but still the practical interpretations are missing (Smith, 1993). Sustainabili- ty is defined by the Brundtland commission as a development that "meets the needs of the present without compromising the ability of future generations to meet their own needs" (WCED, 1987). The genemhpAtac has at present a very "romantic" view of the forest and want it to be "as Wfc» old days" but what does Jt mean? Should the forest look like it was yesterday or as it was 500 years ago? also not commonly recognized that the forest change appearance with age and if left alone, the dying and fallen trees may look unattractive to the public. Endangered species do often depend on old trees. They are endangered simply because the appropriate stands are getting more rare. On the other hand, even if spotted owls or woodpeck«R»would not need old-growth, the public still wants large trees. The existence of the "natural" forest itself is fundamental in the public concern. Schroeder and Daniel (1981) tried to find out an estimation of scenic beauty and big ponderosa pines got high scores whereas dead trees, slash, and small sized trees got negative scores. Here are conflicts with both traditional forestry as well as biodiversity. However, a stand with seed trees, young ingrowth and no dead standing trees could get rather high scores from a scenic beauty point of view and not be in conflict with an adapted forestry regime (Fig.1). Furthermore, it should be emphasized that not all forests should be old-growth since a number of species may gain by the access to different stages of the forest development. The objective is thus to have a balance between production, biodiversity and multiple use. The means are to have gocd silvicultural strategies. 250 T 200- 5 150' c 3 Ul co 100- 50- Young for Old for Shelter Selfregen Figure 1. Scenic beauty estimates (SBE) according to formulas given by Schroeder and Daniel (1981) for appearance of young forest, old forest, shelterwood and self-regeneration. Silvicultural Strategies There are a number of options for the silvicultural regimes and some are more likely to happen in the future. McQuillan (1994) suggested three forms of regimes (1) Old-growth left untouched, (2) Ecosystem management with both wood yield and multiple-use, and (3) tree farms. Boyce & McNab (1994) argued that the forestry regimes should be scheduled on a landscape level to produce the desired diversity, thus the above mentioned ecosystem management must be planned for large areas. Ecosystem management will probably need a "shift in silvicultural paradigm" (O'Hara et al., 1994). A silviculture to meet the requirements for biodiversity and multiple-use should include mixed species, two-aged and multicohort stand structures produced with flexibility and landscape perspectives and also meet the nontimber objectives with a small sacrifice of timber production (O'Hara et al., 1994). According to Holland et al. (1994) good harvest levels can be compatible with maintenance of diversity but the net values may be reduced. Another aspect is the need for good timber quality that partially has been sacrificed on behalf of maximized wood production (Bragg et al., 1994). Improvement of the timber quality by growing denser stand, may outweigh the reductions in net values when the market appreciate these qualities. The harvesting costs may have to increase for such systems but on f 9 other hand it may be balanced by the reduced regeneration costs. A scarce supply of high-value products could justify wide application of selection management (Seymour et al., 1976). To emphasize the growth of high quality sawlogs and veneer that yield high stumpage returns can work together with management objectives such as aesthetic values or protection against landslides (Smith, 1978). reased concern about erosion, leaching, and sedimentation problems may »nefit other systems than clearcutting not necessarily only on sensitive sites (cf. Cromack et al., 1978). According to Switser et al. (1978) the intensity of site disturbance varies initially among reproduction methods in the order: clearcut > seed trees > shelterwood > selection. A similar ranking between the methods is also given by Stone et al. (1978) when considering water yield and flow, nutrient loss, stream temperatures, and reduction in surface soil organic matter. Although a loss of nutrients or organic matter may not impact growth of trees in some areas (Allen et al., 1991). In summary, in the future it is likely to exist a change towards more diverse silvicultural regime practice. In some areas, the forest will be left more or less untouched as old-growth for different reasons. Here no harvesting operations will be done. In other areas, the tree farm concept w>M b*4|£.most suitable regime and here the maximum production goal can be fulfilled» a general fiber resource. The tree farms may have a hamMtkig system similar to present practices and the concept for machine and systems development will mainly be as rationalization. Based on ownership, Switzer et al. (1978) estimated that about 20-25 % of the forest land will be managed intensively in the South of U.S.A. This practice will leave about one third to half of the forested land to be potentially comitted to some kind of ecology management (EM). Do we have proper harvesting sysiems for the s.lvicultural regimes in these areas? The question first to be answered is what selection modes do we have and the answer determines what operations to be done. Potential Methods of Cutting in the Ecology Management (EM) Clearcutting, cutting of small patches or openings might be one of the alternatives in the future, especially for regeneration of shade intolerant species. Opening up the area could be necessary to start up a degenerated site. In principle, the commonly used equipment for ordinary clearfelling can be used. A technical problem might, however, raise as these areas would be small, which means that the machinery should be easy to move to next cutting place. Also, the clearing of small sized trees that have to be removed to prevent undesired ingrowth, might reduce machine productivity compared to conventional operations. Other cutting systems are (Seymour et al., 1S86; Megalos, 1994): Seed-tree selection: renewal of the stand by self-sowing from remaining selected seed-trees, which are left for that purpose and are thus rather few (80-120 trees per ha). Shelterwood: a stand left after cutting denser than for seed trees (150-250 trees per ha). Best for species that need partial shade and for protection of the young growth to sudden climatic changes. One-cut shelterwood: the removal of the overstory in a single operation and releasing advance growth without prior seed cuttings. Two-aged cut (irregular shelterwood): part of the overstory left in place until next rotation. Improvement cutting: early thinning to upgrade stand quality with control of stocking and removal of poor-quality trees and use of the harvested trees as fuelwood or chipped for pulp; mainly in hardwoods. Single tree selection: deliberates creation and maintainance of a balanced all- aged stand (Seymour et al., 1986) giving the stand a more natural, undisturbed appearance. The uneven-aged stand structures are typically defined in terms of basal area, maximum diameter, and others (Murphy & Shelton, 1994). The stand should have trees with a reverse J-shaped diameter structure where a maintenance can be made by a diameter-limit cut. Desired basal area for loblolly pines is 14-18 rrrVha with maximum 40 cm dbh. This method can only be used for tolerant species. Group-tree selection: cutting of a group of trees and creating larger openings than with single-tree selection. Precommercial thinning: precommerctat work to alter the composition and density of the stand. 8 An important step in the the silvicultural prescriptions is the identification of different sites and fitting the species composition to them (Smith, 1978). In the EM landscape, a number of different silvicultural regimes will be practiced and some of them can be done easily with present logging machinery and equipment like the seed-tree selection. However, with the one-cut shelterwood type, the damage levels of the residual stand (both aesthetic and quality) might be high (Bragg et al., 1994) and destruction of advance growth by logging system should be avoided (Seymour et al., 1986). The more moving around the remaining trees, the more damage will occur and the risk increases with increasing tree sizes and remaining basal area (Ostrofsky et al., 1986). According to Seymour etal. (1986), increased mechanization has made logging operations required by shelterwood cutting more difficult. However, the primary advantage of selective thinning over systematic row thinning is a larger, better, and potentially more profitable residual stand. Properly designed and managed selective thinning is cost competitive with row thinning (Stokes & Lanford, 1982). Another aspect is that it is most unlikely that we are going back to heavy labour intensive forestry work and the main issue must be to design proper mechanized operations suitable for EM; efficient machine system with minimum traffic and soil disturbance. In some areas, the harvesting system used should reduce and utilize the slash to prevent forest fires (cf. Covington & Moore, 1994). Requirements for a Friendly Operation The job to be done is thus a selection harvesting ranging from early conventional selective thinning (i.e. thinning from below) to single-tree selection management, primarily designed for working with smaiUimber holdings for private landowners. Preferably the system and machinery should be suitable for that broad range of operations to avoid heavy traffic associated with single function mMbines. A. System requirements. * The harvestinjjsystem could be shortwood, log length, or tree length without particular restriction. Tree chipping could be considered. Fulltree harvest might be restricted due to environmental considerations. Big slash piles should be avoided. * The system set up should be easy to move and install on next operating place since the cutting areas might be small. * The system must require a smalt taMcfing area since many operation sites might be involved. With a 2 % landing area, a small clearcut on one hectar should be limited to 200 m2 landing area but preferably less than that. * The mechanization level of the harvesting system should be more than 90 B. Road and terrain requirements. * The forest road network might have to be spaced and only second class roads may consitute 50 % of the main access roads, which would imply long extraction distances. The space for landings might also be a limiting factor. * The temporary roads should be winding to minimize the look of being man- made and access trails should be within normal tree spacing. This requirement might restrict the use of ground-based tree-length extraction due to its space demand when operating on curves. ' The harvesting system should be able to work on different ground conditions from hard to soft (e.g. wetlands), uneven terrain, and inclination up to 50 %. More severe terrain would require different systems. This requirement would favour wheeled machinery unless working on very wet sites and/or very steep terrain. o o o . O 0 • ° • 0*0* o • o 0 . 0 • O 0 • . o • • . o ° • o • . o.o. o . o o.o • • ° • • .,• 0 • O • O • ° Ä O O • q *3 ?m Figure 2. A forest stand showing tree distribution. Only the marked trees (black) should be removed in selection cutting. C. Space/clearance requirements. * A selective tree removal is the aim and hence, the system should be able to work without any forced cut of the selected trees, thus working within the selected tree spacing (Fig.2). * The density of the stand aftar the operation might vary between 1200 - 350 trees per ha, which gives a general spacing between the trees from 2.9x2.9 10 m to 5.3x5.3 meter. This density might not be a common strategy for coastal loblolly plantations with about 500 - 700 trees per ha after first thinning (Greene & Stokes, 1989; Rummer, 1993), but these plantations might be considered as the tree farm type of forestry. * The total width of the forest machine could then be maximum 2.5 - 3 m with at least 0.4 m on each side to minimize stem and root damage (O'Connor, 1991). However, for highway transportation, the maximum width may be restricted to 2.4 m. P. Handling requirements. * The system should be designed to handle up to almost the biggest trees. With cutting from above or a diameter-limit thinning, the machine should be able to handle trees up to 60 cm dbh, which means single trees of a total mass of 4,500 kg (Fig.3). * Trees should be sawn off and not sheared to reduce damage to the butt log (Gallagher, 1984, and Stokes & McNeel, 1990). 33 30 27 Tree height, meter Figure 3. Estimates of living tree mass a to formulas given by Rodriguez & Allen (1994) and Zobel et at. (1972). E. Acceptable degree of damage. * The machine system should be designed to limit damage to the remaining trees. Decay resulting from butt damage not only decrease the present value 11 of the trees, but also affect the growth rate of the trees in addition to the spread of the rot within the tree (Whitney, 1991). An EM stand will most likely have longer rotations times than optimal for fiber production and then butt damage will be more costly. Entries in the stand might be done in 10-20 year intervals. * Traffic should be reduced to a minimum (max. 20 % area trafficked) as to avoid rutting, root damage, and soil disturbance. In these EM stands, there would be rather small possibilities to repair soil damage such as site preparation or ripping, since the stand is depending on natural regeneration. However, there are situations where enrichment plantating could be desired to adjust species composition, improve the genetic qualities). * Damage to young trees within the stand should be as little as possible. Tree skidding should therefore be avoided. * To avoid soil compaction with ground-based machinery, the nominal ground pressure should be below 60 kPa and the machine mass should be below 10 tonne (Wästerlund, 1994). Tracks could be used on very soft ground (Murosky & Hassan, 1991) but then the trails should be as straight as possible. F. Environmentally friendly * The new harvesting system should be aimed to be environmentally friendly. (1) Environmentally sound (friendly): a degree of disturbance to the ecosystem due to the entry of some kind of human activity for the utiliza- tion of natural resources where the ecosystem functions can be recovered naturally within a reasonable part of its lifecycle. (2) Environmentally sound forest management: implementation of forestry and silvicultural regimes to increase production of goods and services while maintaining the ecosystem integrity and environmental quality. Webb (1994) stated: "Forest management operations should encourage optimal/efficient use of forests' multiple products/services, and to maintain critical ecological functions of forest and minmize adverse impacts on biological diversity, water resources, soils, nontimber resources and unique/fragile ecosystems/lands- capes". (3) Environmentally friendly forest harvesting operation: removal of selected trees or other products with minimal impact on the biodiversity, sustaina- bility, and aesthetic values of the forest ecosystem. Webb (1994) stated: "Forest management operations should maintain/enhance long-term social and economic well-being of forest workers and local communities". * It should be energy efficient and have low degree of emissions. Recycable materials, degradable oils, . etc should be used. G. Cost efficiency * The harvesting system should be cost effective to make it possible to perform the cuttings on an economical basis. 12 EXISTING MACHINE SYSTEMS I. Harvesting Feller-buncher Feller-buncher is a dual function machine which has gained considerable interest in the South. Different types of machines exist with shear heads, chain-bars or circular sawheads. In the beginning, the feller heads were mounted on excavators due to the size of old-growth forests but these tracked machines were found to be less suitable for thinning operations. Wheeled machines with frame mounted fellers were replaced by felling heads mounted on short booms to faciliate bunching. One popular machine for thinning applications is the three- wheeled shear feller-buncher Mor-Bell due to its small size and maneuverability. At fifth-row thinning operations, it can perform very well at low cost (Fig. 4). Later on other machines have been introduced based on the same concept. The drawback with this method is that the machine has to travel to each tree and at selection cutting the travel-to-tree time as well as travel-to-dump will increase considerably (equations given by Stokes et al., 1982 and Ashmore et al., 1983). The use of high flotation tires will decrease the foot print pressure but increase the width of the machine and make it difficult to handle in a selection cutting and resulting in increased stem damage (Ostrofsky et al., 1986 and Whitney, 1991). The alternative would be to mount the feller head on a long boom and lift out the whole trees. However, the whole tree is heavy (Fig. 3) and the branches would make it even more difficult to handle the felled tree between remaining standing trees. It would be easier in this case to fell, delimb, and buck the tree with a harvester. Tree processor and felling-delimbing-bucking machines (shortwood) A tree processor is a machine that can perform at least two operations but not felling. Farm tractor mounted processors are quite common among private landowners in the Nordic countries as an intermediate between delimbing- bucking with the chainsaw and a harvester. In the USA, grapple processors have been tested in pine plantations (Greene et al., 1984) but the productivity may hardly justify the third machine type between a feller-buncher and a skidder or a forwarder. Many different solutions for felling-delimbing and bunching have come and gone without making any success. One example is to delimb and top the tree standing, before felling it (see Staaf & Wiksten, 1984). However, the long boom to make this operation possible, made the machine very difficult to handle. 13 70- 60- Hydro-Ax / | 50- Tri-Trac Mor-Bell | 40- c 0 Norcar a 3o- /.•• Borberg CL 20- 10- 0.03 0.09 0.19 0.33 0.52 Volime per tree, rrO Figure 4. Compiled productivity data for feller-bunchers and harvesters. Feller- bunchers with shear head: Mor-Bell (Stokes, Lanford & Sirios, 1982); Hydro- Ax 411 (Ashmore, Stokes & Lanford, 1983); GafnerTri-Trac (Rummer, 1993). One-grip harvesters: Norcar (Brinker & Tufts, 1990); general Swedish data (Brunberg, Norden & Tosterud, 1989). Delimbing-bucking-bunching machines have found acceptance for work at the landings but not for in-wood operations (whole-tree systems). In general, a third machine between felling and extraction would increase cost with less improved production. Thus, for the environmentally friendly operation, the number of machines should be kept as few as possible and an extra machine for delimbing-bucking-bunching might not be a good approach. Tree harvester The integration of the feller-buncher and a mobile processor into a single machine was achieved with the development of the harvester (Andersson, 1984). Since most operations at that time dealt with clearfelling, the large tree size demanded a powerful machine that could fell the trees with a tool in the boom and positioned them into the chassis-mounted processor (two-grip harvester). The two-grip harvesters became very popular in the Nordic countries during the eighties and soon most of the clearfelling work was mechanized (Freij & Tosterud, 1989). Development of measuring devices for tree diameter and length faciliated computer-aided bucking. 14 ** Ii. i Figure 5. A small harvester for shortwood production. It fells, delimbs and sort the trees into sawlogs and pulpwood. The machine operates both on strip and access roads. One or two access roads could be used between the strip roads where the forwarder collects the wood. The two-grip harvester was, however, not very well suited for the thinning operations. In the middle of the eighties, the first attempt with boom-mounted one-grip harvester started. With this machine, the whole operation (felling- efelimbing-bucking and bunching) was completed from the first grip. Today it has surpassed the two*§rip harvester even in clearfelling operations, especially in stands with small tM$». A number of different machines exists as well as separate hawesting heads. The harvesting head sizes vary from 30 to 60 cm cutting dfarffeter with a mass of 300 to 1100 kg. Boom lengths can be 5.5 m for the smallest harvester and up to 10 m for larger machines. In thinning operation, the one-grip harvester would operate from the strip road extending the boom into the stand to fell the trees. Delimbing should be done in front of the machine to add slash on the strip road and in that way armouring and reducing soil disturbande. At the end of eighties, the small 5-tonne harvester was introduced and this narrow machine could work also within the stand on access roads (Fig. 5). Damage surveys showed that these small harvesters left almost unvisible tracks after passage and soil compaction from the wheels was minimal (Wilpert & Parbs, 1992; Jansson and Wästerlund, pers.comm). However, the acceptance 15 of the small harvesters has decreased due to its limited capability of cutting dimensions. General performance data are shown in Figure 4. It should be emphasized that the harvester did the delimbing in the wood and no cleaning-up of the landing was necessary - which in the case of feller-bunchers might be put on the skidder and decreasing its productivity with about 15-25 % (Stokes et al., 1982). Thus, the performance is comparable to feller-buncher operations. Soil and root damage levels are quite small but the large harvesters (> 10 tonne) may cause soil compaction even with the presence of debris (Jansson & Wästerlund, pers.comm.). The main limitations are: reduced ability to handle large trees, especially at distance, and the system is basically suited for shortwood. II. Extraction Helicopter logging Helicopter logging is not a very new invention and the system is described by Stewart (1978). The great advantage is the possibility to negotiate rough terrain and yarding distances can be long (up to 1.5 km) although the cycle time is dependent on flying distance (Hassan & Gupta, 1988). Production may be very high (130 m3 per hour, Stewart, 1978) for large helicopters (Sikorsky 65 Sky Crane). The helicopter prices have gone down considerably, but still it is a rather expensive yarding metod. Sloan et al. (1994) described the new type of helicopter, K-MAX, with dual counter rotating main rotors to be an alternative logging method for mountain forests giving a logging cost of about 33 USD m'3 at a hauling distance of 600 meter. The drawback is that the choking is done manually. Tree harvesting can be done with a feller-buncher (Kirk & Kellogg, 1990) but harvesters with delimbing devices are preferred in order to reduce transport weight. Sloan et al. (1994) calculated the lowest volume cut considered for the K-MAX to be 30-35 m3 per ha, which means the method would be better suited for a clearfelling operation with concentrated timber bunches rather than a selection operation. Noise and high fuel consumption make the helicopters less environmentally friendly although ground disturbance for extraction may be minimal. Balloon logging Balloon logging is a more labour intensive method than helicopter logging. The advantages of balloon logging are long yarding distances, minimum soil disturbance, less damage to remaining timber stand, minimum crew hazard and elimination of spar trees or steel towers (Stewart, 1978). Balloon logging with the pendulum-swing system is one improvement to get a more stable balloon, speed up the yarding cycle and decrease the required horsepower to run the system (Oisen et al., 1984). Balloon logging may be capable of harvesting isolated patches of windthrown and insect-infested timber (Oisen et al., 1984). 16 The system is clearly environmentally friendly but it is complex to set up and is weather dependent. Load per swing could be up to 5,000 kg. However, for the small harvesting volumes in an EM stand, the costs for set-up can outweigh the benefits of balloon logging. Cable yarding Cable yarding is commonly used for steep slopes and many different set-ups exist (Lisland, 1975; Kochenderfer & Wendel, 1978; Conway, 1982; Aulerich, 1990). It is a labour intensive method but when well done soil disturbance is least especially when with high lead cable logging (Stewart, 1978). The extraction method can fit both rough terrain conditions as well as steep slopes. However, the erection and logging in steep and bad terrain are hard work and expensive, and the time for erecting and dismantling increases rapidly ith cable length (Lisland, 1975), which means the forest road network should be dense and must be well planned with adequate landings. The extraction trails should be straight within corridors (Kochenderfer & Wendel, 1978). The costs of clearfelling may be about 15-19 USD m'3 (LeDoux & Baumgrass, 1990; and Sloan, pers. comm., 1994) and rise rapidly with increased number of landings per m3, decreased volume per tree, and yarding distance (Lisland, 1975), which means the system is not very suitable for selective cuttings. Economically, it is a heavy and dangerous work. Although a feller-buncher may be used, rigging of the cables and choking remains manual. yarding With a grapple hanging on wires between the grapple yarder and a haulback, trees or stems awrbe picked up and hauled to roadside. The method may work in clearfelling operations with greater concentrations of timber, but has not shown economic feasability (Peterson, 1986). The only advantage wittvthis method is the reduced traffic on the site and the possibility to transport stems across areas with low carrying capacity. Winching On ground pulling of stems or logs as an intermediate system between cable yarding and skidding. Winching is a lowcost extraction method with low efficiency, high pulling forces and often associated with high degree of damage to residual trees in a thinning operation. Skidding Skidding is the most commonly used method for timber extraction (Wästerlund, 1994). The grapple skidder is more cost efficient than the cable skidder (Kluender & Stokes, 1992). Extraction distance influences the productivity very .;** much (Fig. 6) and a skidding distance above 300 meter is not recommended. 17 JU ' 25- \ 20- \ \ ~" Forwarder Skidder ID- S' 0- 100 250 500 1000 2000 One way distance in meter Figure 6. Compiled principal data for two extraction methods: Forwarding based on data from Gullberg (1994) and skidding based on Roise & Hassan (1988). Skidding may also be the only alternative when considering large trees or logs with more than 4-5 tonne (Hendrison, 1990). However, in a number of reports (Cromack et al., 1978), the extraction by skidding is considered to be one of the major causes of soil disturbance due to the high skidding resistance forces (Hendrison, 1990). Jse of extra wide tires may reduce soil damage but also decrease the maneuverability of the machine on non-clearcut areas (Hassan & Gupta, 1988). Another possibility to reduce soil damage is to use a sulky (swing cart: see Southern Loggin1 Nov. 1994, p.45) to lift up the rear ends of the trees. A drawback is that the machine carry small loads (4-5 m3) per turn, which means more intensive ground traffic. Tree length is preferred but the long stems influence road planning towards straight and wide skid trails similarly. Shortwood increases the traffic and decreases the productivity. Clam-bunk skidders can take large loads and are efficient on long distances but have in principle the same drawbacks as ordinary skidders. Forwarding Forwarding is mainly used in Canada and the Nordic countries. The main advantage is that the machines carry the load, which means less skidding resistance, jess soil particles on the timber, and less soil damage. However, its performance will depend on the machine design and the tire sizes and arrangement. The forwarder is often equipped with bogies both front and rear 18 to reduce ground pressures, increase traction, and improve the comfort. On the other hand, bogies cause side skidding forces when operating on cross grades and curves. Studies have shown less soil damage with forwarding compared to skidding {Wronski 1984; Lanford et al., 1991; Thompson, 1991). Forwarding works best with shortwood systems and due to loading and unloading time, it can only compete with skidders on long extraction distances (Fig. 6). Another benefit is that the area required for roads and landings for temporary storage of the timber is much smaller than for skidding (Kellogg & Bettinger, 1994). Horses and oxen Extraction with the help of horses and oxen and proper equipment (trailer with loader or sulkies) have gained some new interest. The benefits are the low investments, adaptability to stand conditions and with low number of passes little soil damage. However, the method is labour intensive and productivity is low (Staaf & Wiksten, 1984). Air-cushion vehicles Air-cushion vehicles have been considered for log transportation but due to their almost absent contact with ground, the sideslope negotiation is also absent. Soil damage can be reduced to near zero but instead dust problems may arise. Chutes Transportation of logs in chutes or tubes downhill has been tested in the Appalachian mountains in the beginning of the century. The V-shaped log slides can be up to four km long along the valleys in the mountains (Weal, 1993). The set up of the system is labour intensive and to be efficient the method needs fcjpjih a concentration of timber and steep slopes. Friction can be dimished with help of water transportation in the tubes or low friction material in the chutes (Warkotsch, pers. comm). An environmentally friendly extraction method when properly done but the method is depenttent on having rather steep slopes and is potentially unsafety. Railroad Railroads were the only way to transport the logs out from the foroatto the mill in the old time (Weals, 1993). With old-growth forests, the sizes of the logs demanded heavy equipment. Railroad haujjrjö was best suited to these high volumes, high tonnage, and hauls exceeding 500-600 km (Conway, 1982). With present density of forest roads, the costs for building of railroads can never be justified. III. Combined Methods Feller-forwarder One way to reduce the traffic on the site is the use of multi-purpose machinery. 19 One concept is the machine that can fell the trees and transport them to the landing. The multi-function aspect:~> accomplished with minor complexity than a feller-buncher (cf. Conway, 1982). It offers a high man/day productivity and a tidy operation (Kurelek, 1984) but these statements may be questionned. Koehring feller-forwarder is the most known type. The drawback of the method is when high volumes are to be cut on long forwarding distances which means a low utilization of the felling head. In principle, the method can be very useful for selection operations with low cut volumes, especially at places with short forwarding distances. For selection cutting with winding roads, the stem lengths can be a problem. Preferably the slash are kept on site, partially to reinforce the strip road, which means the machine is to be equipped with a delimber head. Feller-skidder The feller-skidder is, in principle, the same concept as above (Staaf & Wiksten, 1984, p.91). Usually it is equipped with a clambank for the trees and for improving machine stability. This machine type may have a further disadvantage in the selection cutting by dragging the trees and thus damaging the residual trees more than the feller-forwarder. Harvester-forwarder In the beginning of the nineties the Nordic company Valmet introduced a harvester-forwarder, aiming to reduce the number of needed machines and for small operations. Time studies on the machine showed, however, that at normal forwarding distances, the harvesting head was under-utilized and not really beneficial. The question of the suitability of this machine for selection cuttings is not yet proven. The same conclusions concerning the feller-forwarder above, are valid for this machine type too. Experiments with this machine type is on- going in the Nordic countries. In-woods chipping Chipping at roadside has been of interest since the seventies (Plummer, 1981). Early developments were associated with production of fuel-wood. Many systems have been tried and the main drawback has been the problems for pulp mills to accept chips with bark contamination. Lately, mobile delimber-debarker- chipping machines have been developed to produce chips of high quality for pulp mills. Cost analysis of such systems, considering all costs to ready chips at the mill, show that chipping at landing can compete successfully with roundwood systems especially with small diameter trees (Favreau, 1992). However, frequent moves will increase the costs and chipping at landing can therefore be of less interest for selection cutting. A benefit with whole tree chipping is a higher degree of utilization of the wood fiber resources (Herrick, 1982). Studies on off-road chippers carried on forwarders have shown a reduced 20 productivity (but not necessarily higher costs) compared to chipping at roadside and with a shuttle, the production may increase but not necessarily reduce the costs (Richardson, 1986). With frequent relocation, a mobile off-road chipper is more economic than a landing type, because of low set-up time (Richardson, 1986). The mobile chipper can also be used to clean-up the area and reduce fuel for forest fires. However, whole tree utilization may be restricted in some areas for EM. Another drawback with off-road chippers is their weight. Without a slash mat an extensive rutting can occur (Richardson, 1986) and means to reduce weight of the machine and to increase the flotation is necessary. In Sweden a delimber-debarker-chipper with a chip hopper has been developed to be mounted on a farm tractor (see p. 198 in Staaf & Wiksten, 1984). It is designed forsmall diameter trees and to work in first thinnings. Chip quality has been found to be good but the economy is not always acceptable. The main advantage with inwood chipping is a better recovery of wood fibers. However, transport costs for wood chips may be high since the material has low density. Some kind of compaction of the material is necessary to improve transport economy (Hassan, 1977). Still, the present system need a pre-felling and bunching of material. Direct feeding with a felling head has been tested but appeared to be time-consuming with low utlization of the complicated and expensive machine. Fire hazard is reduced through the removal of combustible material from the wood (Richardson,1986). EVALUATION OF EXISTING MACHINE SYSTEMS An attempt to evaluate harvesting and transporting machines is summarized in Table 1. The evaluation is based on the assumed suitability for application in ecology management according to the requirements stated in the section above, and accounting the best machines/methods in each category that exist today. The scores are subjective and each category has the same weight. In reality, the cost efficiency should havQj&auble weight, which in turn would favour for instance the feller-buncher afRHkidding system. Our evaluation shows that no machine or method recieved maximum scores for all aspects. However, the addition of all scores (column 9 in Table 1) could make it easier to get an overview of the machine performances. The suitability of the listed machines and methods for an EM operation can be classified as: scores 18-21 recommended scores 14-18 acceptable scores < 14 unacceptable 21 Table 1. Summary of the evaluation of the different methods to extract and harvest the timber in an ecology management silviculture regime. Legends: 3 = good; 2 = average; 1 = poor A B C D E F G Total scores Harvesting Fell-bunch 3 2 1 3 1 2 3 15 Processor 2 3 1 2 2 2 1 13 Harvester 3 3 3 1 3 3 2 18 Extraction Helicopter 2 3 2 3 3 1 1 15 Balloon 1 3 2 3 3 3 1 16 Cable yard. 1 3 3 3 3 3 1 17 Grapple y. 1 3 1 3 3 2 2 15 Winching 2 3 2 3 1 2 2 15 Skidding 3 2 2 3 1 2 3 16 Forwarding 3 3 3 2 3 3 2 19 Animals 2 2 3 2 2 3 1 15 Air-cushion 2 1 2 2 3 1 1 12 Chutes 1 2 3 2 3 3 1 15 Railroad 1 1 1 3 1 3 1 11 Combined Feller-forw 2 3 2 2 2 2 1 14 Feller-skid 2 2 2 3 1 2 1 13 Harv-forw. 3 2 3 2 3 3 2 18 Chipping 3 2 2 2 2 1 2 14 Table footnotes: D: Tree handling requirements A: System requirements E: Acceptable degree of damage B: Road and terrain requirements F: Environmentally friendly C: Space/clearance requirements G: Cost efficiency 22 The evaluation shows that some of our present methoos, such as shortwood with the use of a harvester and a forwarder, could be recommended and that all recommended machines and methods are ground-based. Harvesters are better than feller-bunchers mainly due to the long reach of their boom. The boom-mounted head, together with the shortwood method will reduce the traffic in the stand and provide slash residues on the roads. Although the feller-buncher can have a low ground pressure, the number of passes to approach the trees will increase the load on the soil (Wronski & Humphreys, 1994). The drawback with the harvesters are the lack of capability to handle big trees, which partly depends on the machine stability and strength of boom. The exception from already commonly used machines in the list, is the harvester-forwarder. This machine type got high scores for the single machine operation, which means also easy to move and suitability for low volume operations. The most used types of machines and methods today are found acceptable. Cable yarding is still the main alternative for steep terrain operations. The conclusion from our evaluation is that we do have acceptable systems but improvements seem necessary for future successful operations. It is obvious that future development should continue with ground-based machinery. CONCEPTUAL DESIGNS FOR THE FUTURE As shown by Stokes et al. (1992), a selection cutting operation would decrease the productivity of an ordinary method and put a demand on improving the technique. The system should be ground-based and work without permanent roads. Light and multi-purpose machines would be preferable, although it may be difficult to handle big trees with sueh machines. Further improved tires for low ground pressure and good traction, and application of variable tire pressure inflation (VTP/CTI) - as proposed by Zealley (1990) - could be one of the ways to decrease soil disturbance by heavy machinery. Further, the machine should have a boom or crane for multi-purpose tasks: felling, processing, loading, piling, spacing operations, site preparation and planting by simply attaching the right tool to the boom. For selection cuttings a one-grip harvester head would be preferred because of the small space requirements. Delimbing of trees could then be done in the stand and preferably in front of the machine and thereby spreading out the slash in the stand. Piles of logging residues can otherwise be a problem (McKenzie & Garret, 1994). Preferably the harvesting head should b%j0to to handle multiple stems to increase productivity when working with smalt trees (Brunberg et al., 1989). The base machine should have hydrostatic transmission drive which might increase its cost. However, the machine versatility should increase giving more 23 freedom for alternative designs. A traction/slip control could be of advantage (Mohr & Eriksson, 1993). The wheels could be assembled on hydraulic controlled pendulum arms (Fig. 7), thus eliminating the traditional axles and allowing operation on uneven terrain. This type of machine could have articulated steering without the use of pivoting joint, which will increase machine stability. Skogsjwi487SochXL Z780 (med 700»34j Figure 7. A conceptual machine for a one-grip harvester. Boom length 10 m and lifting capacity of 160 kN. Machine mass 12 tonne. The machine has hydrostatic transmission with independent wheel motors and the wheels are placed on hydraulic controlled pendulum arms for operating on uneven terrain. With maximum 20 % trafficked area, the harvesting machine should have 9 - 10 m boom to reach out between the trails. The capability to lift large trees would be reduced as the reach distance increased. Theoretical calculations on the harvester shown in figure 7, show that the machine with a weight of 120 kN is unstable at loads above 25 kN for a boom reach of 10 m when lifting at the front of the machine (Fig.8). At 90 degrees angle the stability is less and max 9.1 kN can be lifted. From those values the weight of the felling head (10-11 kN) should be subtracted. A comparison with the tree weights in Figure 3 shows that only small trees can be handled with this long boom reach (h reality the gross lifting capacity of 160 kN on that machine will be limiting when working 24 O X (O 200 160 120 Machine weight, 80 kN Boom length, m Figure 8. Theoretical calculation of the maximum lifting capacity when lifting in the front direction with a boom of different length without turning over. The principal model for calculations is the machine presented in figure 7 and the mass of the boom is assumed to be 1500 kg. straight forward). Tractor excavators have supporting arms for increased stability and similar ones could also be used on forestry machines, e.g. arms that are automatic extended to increase the machine stability with a certain load on the boom. Calculations show that automatic arms extending only 1 m would increase the maximum load for stability in the front direction to 46.6 kN and at 90 degrees to 27.2 kN. Thus, a simple device will have a great effect. Boom construction and strength are another area for development. The present booms are rigid to allow easy handling but actually an elastic one may be able to handle larger weights. Computer-aided boom control has been developed (Löfgren, 1989) without common acceptance. However, a computer-controlled elastic boom would be very difficult to develop. ^ •mm Machinery for extraction has operated on the same princips since inception in the early sixties. Machine extraction productivity has not changed very much during the last decade. One way to improve both comfort and travel speeds could be to supply these machines with semiactive/active suspension and chock absorbars.The technology is available but will demand R & D for forestry applications. At long extraction distances, the "Rattler" technique could be used. 25 The Rattler is a wheeled toy with a number of powered units connected to each other with pivoting finks. If the base machine is equipped with hydrostatic transmission, additional loading units (trailers) could be attached with pivoting steering connection, thus creating an off-road train. As mentioned earlier, the harvester-forwarder concept can be of value for selection cuttings. The main drawback is the low ulitization of the harvester head. One idea that could be worthwhile to test, is to combine that machine with a separate chipper/hopper. The harvester-forwarder fells, delimbs and bucks only the sawlogs, thus working with valuable products that benefits from separate handling. The low value pulpwood is piled along the strip road which in turn will improve the capacity of the inwood chipper. If the slash is to remain on site, the chipper can be equipped with a delimber and debarker to produce clean pulpwood chips. The machines should of course have biodegradable hydraulic oils. It is commonly used in new machines for the Swedish market. Some problems existed but with improvements, the new oils provided lower temperatures in the hydraulic system. Finally, we have taken the man off the ground, so why not continue and liberate man from the machine. Robots are becoming more capable to make outdoor orientation and within 10 years, some prototypes may be working in forestry. Meanwhile, some components should be utlized on the present machines (e.g. boom control). One conceptual machine is presented in the table of content (Gellerstedt, 1994). The base machine for the robot can be designed as wheeled, tracked or walking beam. A wheeled version could very well be based on the Quadractor concept. The Quadractor was developed during the seventies by an airplane designer and has a very intelligent wheel suspension system, among other interesting concepts (Sarna, 1978; Stevens & Smith, 1978). For timber transport of timber, the designer proposed a grapple under the chassis, which is genious since the more load it takes, the lower the center of gravity it gets. Some few walking machines exist and one type has been tried out for forestry applications (Stuart et al., 1992). In many forestry operations, a walking machine can fit very well, in harvesting, spacing and planting. A walking machine uses considerably less energy for movements than a wheeled machine, since it lacks the rolling resistance. It can operate on uneven terrain and can move sideways. The latter aspect makes that machine very easy to position. Walking machines may be too expensive and fragile for forestry work but they provide basic platforms for future forestry robots. 26 CONCLUSIONS A general trend in the world is to cut down on machine R&D for forestry operations, implying that new machines are not needed. However, the new silvicultural trends towards ecological management of the forest will demand some other machine concepts than the present ones. Some ideas are presented here but we need to know how to handle large trees in selection cuttings in a smart way. Robotic technique will come but it needs high R&D input to get self- controlling robots well working in a forestry operation. Another aspect is where to handle and sort the trees: in the forest, at the landing, or at final destination. If the goal is transport of valuable products, then proper handling should be done in the forest with good technique to avoid lowering the values. Acknowledgement Appreciation is extended to the Nicholson Trust for sponsoring Iwan Wästerlund, Swedish University of Agricultural Sciences, visit to North Carolina State University. REFERENCES Allen, H.L., Morris, L.A. & Wentworth, T.R., 1991. Productivity comparisons between successive loblolly pine rotations in the North Carolina Piedmont. In: W.J. Dyck and CA. Mees (ed.). Long-term field trials to assess environmental impacts of harvesting. Proc. IEA/BE T6/A6 workshop, Florida, USA, February 1990. IEA/BE T6/A6 Report No. 5. Forest Res. Inst. Rotorua, New Zealand, FRI Bulletin No. 161. pp. 125- 136. Andersson, S., 1984. Forces and obstacles in the mechanization of forest operations in Sweden. In: Cocoran, T.J. & Gill, D.R. (eds). Proc. of the C0FE/IUFRO3 meeting. University of Maine at Orono. Society of American Foresters. SAF Publication No. 84-13. pp. 115-119. Ashmore, C, Stokes, B.J. & Lanford, B.L., 1983. Thinning performance of the Hydro-Ax 411 in fifth-row thinning. ASAE Paper No. 83-1604. Aulerich, S.P., 1990. Wetland harvesting with cable systems. A.S.A.E. Paper No. 90-7574. Boyce, S.G. & McNab, W.H., 1994. Management of forested landscapes. Simulations of three alternatives. J. Forestry, 92(1):27-32. Bragg, W.C., Ostrofsky, W.D. & Hoffman, Jr., B.F., 1994. Residual tree damage estimates from partial cutting simulation. Forest. Prod. J., 44(7/8): 19-22. Brinker, R.W. & Tufts, R.A., 1990. Economics of a cut-to-length harvesting system in second- thinning. In: Managing Forestry Operations In A Changing Environment. Proc. of the 13th Annual Meeting of the Council on Forest Engineering, August 12-16,1990, Outer Banks, N.C. pp. 84-88. Brunberg, B., Norden, B. & Tosterud, A., 1989. Flerträdshanterande engreppsskördare kan 27 sänka kostnaderna. The Forest Operations Institute of Sweden. Resultat No 18, 1989. (In Swedish) Conway, S., 1982. Logging practices. Principles of timber harvesting systems. Revised edition. Miller Freeman Publications, Inc. Covington, W.W. & Moore, M.M., 1994. Southwestern ponderosa forest structure. Changes since Euro-American settlement. J. Forestry, 92(1):39-47. Cromack, Jr., K., Swanson, F.J. & Grier, C.C., 1978. A comparison of harvesting methods and their impact on soils and environment in the Pacific Northwest. In: Youngberg, C.T. (ed). Forest soils and land use. Proc. of the 5th North American Forest Soils Conference, Colorado State University, August 1978. Fort Collins, CO. p. 449-476. Cubbage, F., 1993. Federal environmental laws and you. Forest Farmer, 52(3):15-18. Favreau, J., 1992. In-woods chipping: A comparative cost analysis. FERIC, Technical Rep. No. TR-105. Freij, J. & Tosterud, A., 1989. Systems and methods used in large scale forestry - logging, silviculture and roads. The Forest Operations Institute of Sweden. Report No. 6, 1989. Gallagher, T.V., 1984. Evaluating the impact of shear damage on southern pine sawlogs. A.S.A.E. paper No. 84-1611. Gellerstedt, S., 1994. Att gallra med skogsmaskin [To work with a machine in thinning operations]. Swedish University of Agricultural Sciences, Uppsala. Skogsfakta Nr 6-1994. (In Swedish) G eene, W.D. & Stokes, B.J., 1989. Use of wide spacings and heavy thinnings in the Southeastern United States of America. In: New Approaches to Spacing and Thinning in Plantation Forestry. Proc. of IUFRO Conference 1989 April 10-14, Rotorua, New Zealand. Ministery of Forestry, Forest Research Institute, pp. 54-57. Greene, W.D., Lanford, B.L. & Stokes, B.J., 1984. Productivity of the Valmet 940 GP grapple processor in southern pine plantation thinning. In: Cocoran, T.J. & Gill, D.R. (eds). Proc. of the COFE/IUFRO3 meeting. University of Maine at Orono. Society of American Foresters. SAF Publication No. 84-13. pp. 105-108. Gullberg, T., (1994). Comparative experimental studies of farm tractor with grapple-loader trailer and small forwarder. Swedish University of Agricultural Sciences, Dept. of Operational Efficiency, Garpenberg. (manuscript). Hassan, A.E., 1977. Compaction of wood chips - energy cost. Transactions of the ASAE, Vol. 20(5):839-842. Hassan, A.E. & Gupta, R., 1988. Evaluation of wetland hardwood harvesting systems. A.S.A.E. Paper No 88-5032. Hendrison, J., 1990. Damage-controlled logging in managed tropical rain forest in Suriname. Wageningen Agricultural University, Wageningen. Diss. Herrick, O.W., 1982. Estimating benefits from whole-tree chipping as a logging innovation in northern U.S. forests. For. Prod. J., 32(11/12):57-60. Holland, D.N., Lilieholm, R.J, Roberts, D.W. & Gilles, J.K., 1994. Economic trade-offs of managing forests for timber production and vegetative divesity. Can. J. For. Res., 24:1260-1265. Jackson, B.D. & Stokes, B.J., 1990. Low-impact harvesting systems for wet sites. In: S.S. Coleman & D.G. Neary (eds). Proc. of the 6th biennial southern silvicultural research conference, 1990, October 30-November 1, Memphis, TN. U.S.D.A., Forest Service, Southeastern Forest Experiment Station. Gen. Tech. Rep. 70, Vol. 2:701-709. Kellogg, L.D. & Bettinger, P., 1994. Thinning productivity and cost for a mechanized cut-to-length system in the Northwest Pacific coast region of the USA. J. 28 For. Eng., 5(2):43-54. Kirk, R.J. & Kellogg, L.D., 1990. Mechanized felling on a cable yarding operation. In: Managing Forestry Operations In A Changing Environment. Proc. of the 13th Annual Meeting of the Council on Forest Engineering, August 12-16, 1990 Outer Banks, North Carolina. pp 168-174. Kochenderfer, J.N. & Wendel, G.W., 1978. Skyline harvesting in Appalachia. U.S.D.A., Forest Service Paper NE-400. Kuralek, J., 1984. The feller forwarder concept and its application. In: Cocoran, T.J. & Gill, D.R. (eds). Proc. of the COFE/IUFRO3 meeting. University of Maine at Orono. Society of American Foresters. SAF Publication No. 84-13. pp. 191-194. Lanford, B.L., Wilhoit, J.T. & Curtin, D.T., 1991. Forwarder system development for non-industrial private forest (NIPF) applications. ASAE Paper No 91-7509. Lisland, T., 1975. Cable logging in Norway. A description of equipment and methods in present use. Oregon State University, Corvallis, Oregon. 52 p. LeDoux, C.B. & Baumgrass, J.E., 1990. Cost of wetland protection using cable logging systems. In: Managing Forestry Operations In A Changing Environment. Proc. of the 13th Annual Meeting of the Council on Forest Engineering, August 12-16, 1990 Outer Banks, North Carolina, pp 38-43. Löfgren, B., 1989. Boom-tip control. Forest Operations Institute of Sweden, Kista. Meddelande No 18. (Engl. summary). McKenzie, D.W. & Garret, S., 1994. Steep slope logging slash treatment. USDA, Forest Service. Technology & Development Program, San Dimas. Report 9451 1206-SDTDC. McQiullan, A.,1994. National public tree farms. Toward a spectrum of designations. J. Forestry, Megalos, M.A., 1994. Forest stewardship: Planning for beauty and diversity. North Carolina Cooperative Extension Service, NCSU, Raleigh. Woodland Owner Notes 28. Mohr, E. & Eriksson, U., 1993. Traction forces and torque distribution on an 8WD forwarder. Proc. 11th International Conference of the ISVTS, Lake Tahoe, USA, September 27-30, 1993. Vol. II: 803-812. Murosky, D.L. & Hassan, A.E., 1991. Impact of tracked and rubber-tired skidders traffic on a wetland site in Mississippi. Transactions of the A.S.A.E., Vol. 34 *"**"*'" (1):322-327. Murphy, P.A. & Shelton, G.A., 1994. Growth of loblolly pine stands after the first five years of uneven-aged silviculture using single-tree selection. South. J. Appl. For., 18(3): 128-132. O'Connor, P.R., 1991. Advantages and implications of forwarding cut-to-ength wood. A.S.A.E. Paper No. 91-7571. OHara, K.L, Seymour, R.S., Tesch, S.D. & Guldin, J.M., 1994. Silviculture and our changing profession. Leadership for shifting paradigms. J. Forestry, 92(1):8-13. Ostrofsky, W.D., Seymour, R.S. & Lemin Jr., R.C., 1986. Damage to northern hardwoods from thinning using whole-tree harvesting technology. Can. J. For. Res., 16:1238-1244. Peterson, J.T., 198S. Comparison of three harvesting systems in a coastal British Columbia second-growth stand. FERIC, Technical Rep*J00. TR-73. Plummer, G.M., 1981. The state of whole-tree harvesting. Tappi. Vol. 64(4):71. Reisinger, T.W. & Aust. W.M^»jA90. Specialized equipment and techniques for logging wetlands. A.S.A.E., paper No. 90-7570. 12 pp. Richardson, R., 1986. Evaluation of Bruks off-road chippers. FERIC, Technical Rep. No. TR-71. 29 Rodriguez, M. & Allen, L.H., (1994). Comparison of biomass and nutrient content estimates of three southeastern United States loblolly pine plantations. Manusc- ript. Roise, J.P. & Hassan, A.E., 1988. Comparative simulation of forest harvesting systems. ASAE Paper No. 88-7519. Rummer, B., 1993. Thinning with the Gafner Tri-Trac feller/buncher: A case study. USDA, Forest Service. Research Paper SO-273. Sarna, R.P., 1978. Quadractor. American Pulpwood Association. Technical Release No. 78-R-49. Schroeder, H. & Daniel, T.C., 1981. Progress in predicting the perceived scenic beauty of forest landscapes. Forest Sci., 27(1):71-80. Seymour, R.S., Hannah, P.R., Grace, J.R. & Marquis, D.A., 1986. Silviculture; The past 30 years, the next 30 years. J. Forestry, 84(7):31-38. Sloan, H., Tollenaere, J. & Croft, C, 1994. Technology advances in helilogging: A case study of the K-MAX in Appalachian hardwoods. In: Advanced Technology in Forest Operations:Applied Ecology in Action. Proceedings of the 17th Annual meeting of COFE/IUFRO Div 3, held July 24-29 1994, Portland/Corvallis, Oregon USA. pp 237- 245. Smith, D.M., 1978. Implications for silvicultural management in the impacts of regeneration systems on soils and environment. In: C.T. Youngberg (ed). Forest soils and land use. Proc. of the 5th North American Forest Soils Conference, Colorado State University, August, 1978. Fort Collins, CO. p. 536-545. Smith, L.G., 1993. Impact assessment and sustainable resource management. Longman Scientific & Technical, Harlow. Staaf, K.A.G. & Wiksten, N.A., 1984. Tree harvesting techniques. Martinus Nijhoff/Dr W. Junk Publishers, Dordrecht. 371 pp. Stevens, D.C. & Smith, N.R., 1978. Wood for energy: Skidding firewood with small tractors. A report on two field trails. Department of Forests, Parks and Recreation, Vermont. Misc. Stokes, B. & Lanford, B.L., 1982. Patterns and equipment for selective thinning. In: Stephenson, E.H. (ed). Proc. of a workshop on thinning southern pine plantations. Forestry and Harvesting Training Center, May 24-26,1982. Long Beach, Miss. p. 105- 118. Stokes, B.J., Lanford, B.L. & Sirois, D.L., 1982. Mor-Bell thinning system: Feller buncher, skidder and loader. ASAE Paper No 82-1590. Stokes, B.J. & McNeel, J.F., 1990. Wood damage from mechanical felling. U.S.D.A., Forest Service. Research paper SO-258. Stokes, B.J., Kluender, R.A., Williams, R.A. & Klepac, J.F., 1992. Assessment of costs and impacts for alternative harvesting methods in mixed stands. In: J.C. Brissette (ed). Proc. of the 7th biennial southern silvicultural research conference; 1992 November 17-19, Mobile AL. USDA, Forest Service, Gen. Tech. Rep. SO-93:655-662. Stone, E.L., Swank, W.T. & Hornbeck, J.W., 1978. Impacts of timber harvest and regeneration systems on stream flow and soils in the eastern deciduous region. In: C.T. Youngberg (ed). Forest soils and land use. Proc, of the 5th North American Forest Soils Conference, Colorado State University, August 1978. Fort Collins, CO. p. 516-535. Stuart, W.B., Aust, W.M., Lacki, H. & Andrews, L., 1992. Evaluation of an adaptive suspension vehicle. J. For. Engineering, Vol 3(2):45-55. Switzer, G.L., Moehring, D.M. & Terry, T.A., 1978. Clearcutting vs alternative timber harvesting - stand regeneration systems: Effects on soils and environment of th& south. In: Youngberg, C.T. (ed). Forest soils and land use. Proc. of the 5th North 30 American Forest Soils Conference, Colorado State University, August 1978. Fort Collins, CO. p.477-515. Thompson, M.A., 1991. Thinning northern hardwoods with chain saws and forwarders. N.J.Appl.For.. 8(4):149-153. WCED (World Commision on Environment and Development), 1987. Our future common. Oxford University Press, Oxford. Weals, V., 1993. Last train to to Elkmont. A look back at life on Little River in the Great Srr.oky Mountains. Olden Press, Knoxville, TN. Webb, L., 1994. Green purchasing: Forging a new link in the supply chain. Resource, Vol. 1(6):14-18. Whitney, R.D., 1991. Quality of eastern white pine 10 years after damage by logging. Forestry Chronicle, 67:23-25. Wilpert, K. von & Parbs, J., 1992. Flächenbedeutung von Bodenschäden bei der Erstforstung mit kombiniertem Miniharvester-Forwarder-Einsatz. Forsttechnische Informationen, Vol. 44(4):25-28. Wronski, E.B., 1984. Impact of tractor thinning operations on soils and tree roots in a karri forest, Western Australia. Aust. For. Res., 14:319-332. Wronski, E.B. & Humphreys, N., 1994. A method for evaluating the cumulative impact of ground-based logging systems on soils. J. For. Engineering, Vol. 5(2):9-20. Wästerlund, I., (1994). Environmental aspects of machine traffic. J. Terramechanics, Vol. 31 (5):265-277. Zealley, H.E., 1990. Operation bigfoot: The development and application of variable tire pressure/central tire inflation technology for the national forests of the United States. In: Managing Forestry Operations In A Changing Environment. Proc. of the 13th Annual Meeting of the Council on Forest Engineering, August 12-16, 1990 Outer Banks, North Carolina, pp 147-153. Zobel, B.J., Kellison, R.C., Matthias, M.F. & Hatcher, A.V., 1972. Wood density of the southern pines. North Carolina Agricultural Experiment Station, NCSU, Raleigh. Tech. Bui. No. 208, 56p. NEN FÖR SKOGSTEKNIK (Pris: 50 kr + moms, om inte annat anges): LIST OF "UPPSATSER OCH RESULTAT" PUBLISHED BY THE DEPARTMENT OF OPERATIONAL EFFICIENCY FROM 1994 ONWARDS (Price: SEK 50 unless otherwise stated): 1994 Nr 264. Uppgård, R. Tidsstudier av mobila sågverk - Laimet 120 - och Wood-Mizer LT 40 HD. (Under utgivning). Nr 265. Nordfiell, T. Studier av framkomlighet och lastbärande förmåga för små terrängfordon. Studies of mobility and load capacity of small terrain vehicles. ISRN SLU-ST-UPPRLT-265-SE Nr 266. Nordfiell, T. Framkomlighet i snö med små terrängfordon och häst. Mobility in snow with small terrain vehicles and horses. ISRN SLU-ST-UPPRLT-266-SE Nr 267. Nordfiell, T. Jämförande tidsstudie av gallring med miniskotare. Metod, tidsåtgång, arbets- belastning och ekonomi. Comparative time study of thinning with mini-forwarder. Method, production, work load and economy. ISRN SLU-ST-UPPRLT-267-SE Nr 268. Johansson, J. Översikt av erfarenheter av anläggningsmaskiner som basmaskiner i skogsbruket. Eanh-moving equipment as base machines in forest work - an overview. ISRN SLU-ST-UPPRLT-268-SE Nr 269. Liden. E. MASKINENKÄT -93 - maskiner, volymer och ägandeformer i storskogsbruket i Sverige utfall 85/86, 92/93 samt prognos för 97/98. MACHINE INQUIRY -93 - harvesting systems, ownership and volumes in Swedish forest enterprises outcome 85/86 and 92/93 and prediction for 97/98. ISRN SLU-ST-UPPRLT-269-SE Nr 270. Bertilsson, L. & Synwoldt, U. Småskalig torvproduktion. Del 1. Driftsuppföljning och maskin- studier. Small-scale peat production. Part 1. Operational studies and machine performance. ISRN SLU-ST-UPPRLT-270-SE Nr 271. Synwoldt, U. Småskaligt torvproduktion. Del 2. Beräkning av produktionsresultat för olika maskinsystem. Small-scale peat production. Part 2. Calculated production for different machine systems. ISRN SLU-ST-UPPRLT-271--SE Nr 272. Johansson. J. Lantbrukstraktor som basmaskin - Ford 276 Versatile med engreppsskördar- aggregat samt griplastare och vagn. Farm tractor as base machine - Ford 276 Versatile with a single-grip hatvester head and grapple loader and wagon. ISRN SLU-ST-UPPRLT-272-SE 1995 Nr 273. Liden, E. Inquiries into Harvesting Systems, Quantities, and Machine Ownership in Swedish Industrial Forestry - status 1985/86 and 1992/93 and prediction for 1997/98. ISRN SLU-ST-UPPRLT--273--SE Nr 274. Liden, E. Attrition in Swedish Forestry Work 1986-1990 - Extent and Causes. ISRN SLU-ST-UPPRLT-274-SE Nr 275. Miring, B. Utvärdering av skogsbränslesystem med träddelsterminaler - Projektutvärdering och metodutveckling. Evaluation of forest fuel systems with tree-section terminals - Project evaluation and method development ISRN SLU-ST-UPPRLT-275-SE För den som är intresserad att ta del av tidigare utgivna publikationer i institutionens för skogsteknik serier "Stenciler (1974-1984) respektive "Uppsatser och Resultat" (1984-) kan en publikationsförteckning rekvireras med hjälp av nedanstående talong. For those interested in studying previous publications in the series "Stenciler" (1974- 1984) and "Uppsatser och Resultat" (1984- )from the Department of Operational Efficiency, there is a list of publications available, which can be ordered by using the form below. Härmed rekvireras ett exemplar av institutionens publikationsförteckning. Please, send me a copy of the list of publications from the Dept. of Operational Efficiency. Namn: Name: Adress: Address: Sänds till: Margareta Nyström Mail to: Sveriges lantbruksuniversitet Inst för skogsteknik S-776 98 GARPENBERG Sweden Distribution från Ansvarig utgivare A vailable from Responsible for the publication Sveriges lantbruksuniversitet Inst. för skogsteknik S-776 98 GARPENBERG Pris: 50 kr Tel:0225-26000 Price: 50 SEK