CASE STUDIES OF CABLE YARDING ON SENSITIVE SITES IN MINNESOTA

Transcription

1 CASE STUDIES OF CABLE YARDING ON SENSITIVE SITES IN MINNESOTA Michael A. Thompson, James A. Mattson, John A. Sturos, Rick Dahlman, and Charles R. Blinn 1 ABSTRACT. Site and stand impacts from tree harvesting can be responsible for serious declines in timber quality and productivity. Alternatives are needed for harvesting timber with less impact to residual trees and sensitive soils. Skyline cable yarding systems have the potential to minimize site and stand impacts on sensitive sites. These systems yard logs to a landing using long cables supported by adjacent trees. If the system is laid out properly, soil impacts are minimal because the logs are partially or fully supported by the cable and the site is not traversed by heavy equipment. Careful corridor layout and choker setting can also minimize the damage to residual trees. Two case studies of skyline cable yarding were done in Minnesota - one on steep ground and one on a flat, wet site. In this paper, we report the estimated productivity, cost, and impacts associated with these case studies. The method used to harvest timber can have serious adverse impacts on timber quality and forest productivity. Forest machines and processes can damage residual trees, advance regeneration, and other vegetation directly or can reduce regeneration and growth by affecting soil quality. Soil quality can be reduced by the inadvertent soil compaction and displacement that often occurs while harvesting timber. Methods of removing timber from the forest with less damage to residual vegetation and the soil are needed. Skyline cable yarding is a timber harvesting method that, if properly applied, can result in less site and stand impacts than conventional ground-based systems. This method consists of a yarder with three large powered winch drums one carrying the skyline, one carrying the mainline, and one carrying the haulback line. The yarder also has a tall, guyed spar through which these winch lines are run to provide lift to the logs. The skyline is pulled out and fastened to a tailhold, which is usually a large, guyed tree at the end of the yarding corridor. A carriage runs along the skyline carrying the mainline with chokers out to the logs. Logs are pulled to the yarder using the mainline winch. The haulback line is used to pull the carriage back out to the logs when the slope of the skyline is adverse (i.e., too level or yarding downhill). When yarding uphill, the haulback line is not needed because the carriage returns by gravity. This system normally lowers impacts to the site because heavy machines do not traverse the site to remove the logs. Heavy machinery is normally used only at the landing unless a mechanized feller is used. Felling machines used are usually tracked excavator-type machines with low ground pressure that do very little soil damage. These are used because of better stability and flotation on steep, uneven, and soft ground. Another factor resulting in less soil disturbance is that logs are usually transported to the landing with at least one end off the ground. This reduces the amount of soil disturbed by the logs digging in while being dragged. In some cases, the log is fully suspended above the ground during yarding. Aside from being a low-impact harvesting method, skyline cable yarding is uniquely suited to harvesting timber on difficult sites, such as steep slopes and unstable soils. There are many sites in the Lake States where operability is severely limited using conventional harvesting techniques due to either steep slopes or soft, wet soil. Operating conventional ground-based equipment in these areas is often unproductive, costly, and results in undesirable environmental impacts. The use of low impact harvesting systems, such as skyline cable yarding, will reduce the negative impacts associated with harvesting, permit better use of forest resources, and help maintain sustainable forest ecosystems. LITERATURE REVIEW 1 The authors are, respectively, General Engineer, Project Leader, and Mechanical Engineer (retired), USDA Forest Service, North Central Research Station, Houghton, MI; BMP Program Coordinator, Minnesota Department of Natural Resources, Division of Forestry, St. Paul, MN; and Professor/Extension Specialist, Department of Forest Resources, University of Minnesota, St. Paul, MN. The skyline cable yarding system is commonly used on steep slopes in the western mountain regions, but has not been used extensively in the east since the early 1900 s (Peters 1984). It was discontinued in the east after most of the old-growth timber was harvested. Increasing log sizes and environmental concerns have brought renewed interest in cable yarding in the east for harvesting difficult sites.

2 Matics (1980, 1982), Keesee (1982), and Norton (1982) report the use of cable yarding by the forest industry in the southeast. Research by the Forest Service and others shows the level of interest in cable yarding in the southeast (Fisher and Peters 1982). Cable yarders studied include the Ecologger (Fisher et al. 1980a), the Urus yarder (Fisher et al. 1980b), the Clearwater yarder (Koten and Peters 1985, Sherar and Tillman 1984), the Koller K- 300 yarder (Stuart and Rossi 1984), the Appalachian Thinner (Biller and Fisher 1984), and the Bitterroot Miniyarder (Cubbage and Gorse 1984, Baumgras and Peters 1985). All of these studies were done in steep slope applications. Very little work has been done on skyline cable yarding systems in the Lake States. Conditions closest to those found in the Lake States occurred in a study in Upstate New York (Koten and Peters 1985). It is generally believed that the Lake States has very few sites that justify the use of cable yarding systems. However, Ziemer (1980) estimates that the potential area available for cable yarding is about 4.4 million acres, which includes both steep terrain and flat, wet sites. Cable yarding could help ensure compliance with best management practices (BMP s) and promote ecosystem management on these problem sites. OBJECTIVE The purpose of this research was to provide case studies of the productivity, cost, site impacts, and residual stand damages associated with cable yarding on steep slopes and flat, wet sites in the Lake States. STEEP SLOPE CASE STUDY Several study sites totaling 29 acres were selected on Minnesota Department of Natural Resources (DNR) land in southeastern Minnesota. The stands contained mostly oak on steep terrain carved out by tributaries of the Mississippi River. Slopes ranged from 20 to 70%, averaging 46%, and were an average of 300 feet long. The stands had an average diameter of 10.4 inches, an average basal area of 111 ft 2 per acre, and an average volume of 16 cords per acre [1 cord = 500 bd ft (Miyata et al. 1981)]. The stands were marked for partial or clearcutting as prescribed by DNR foresters. Marked trees on each site were chainsaw-felled in early fall prior to yarding by the local cooperating logger. The felled trees were yarded uphill to a landing using a Clearwater 2 2 The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. It does not constitute an official endorsement or approval of any product or service by the United States Department of Agriculture to the exclusion of others that may be suitable. double-drum cable yarder owned by the USDA Forest Service. Yarded stems were extracted from the corridor with a crawler tractor. The performance of the yarding operation was evaluated using continuous time study techniques. In addition to the detailed timing data collected, corridor yarding distance, lateral yarding distance, number of stems per turn, and individual log measurements were recorded. Post-harvest site disturbance was assessed on five cable-harvested sites and two similar, nearby sites that were harvested with conventional ground-based equipment (crawler tractors for these steep slopes). Disturbance data were collected using 40-m line transects at random azimuth orientations from a uniform grid of points. The length of each type of soil disturbance occurring along each transect was recorded. Soil disturbance severity was noted as low, moderate, high, or none. The cause of disturbance was noted as winching, skidding, or felling. The soil layer exposed was classified as organic or mineral, and rut depth (if rutted) was measured. The understory disturbance was classified as low, moderate, or high, and the slash cover was rated as light, moderate, or heavy. Residual stand damage was determined by conducting a 100% survey of all remaining trees in the partial cut cable-yarded and crawler-skidded areas. The following information was collected: location on the slope, distance to the skid trail or yarding corridor, tree dbh, tree species, cause of the damage, location on the tree, scuff size, height and diameter of broken branches, and other types of tree damage (uprooted, pinned, broken, or leaning). Productivity and Cost The productivity, cost, and other attributes observed in this study of steep slope yarding in Minnesota are presented in table 1. Average cycle time was about 9 minutes with an average volume per cycle of about 0.6 cords [1 cord = 85 ft 3 (Miyata et al. 1981)]. This translates to an average productivity of about 4.0 cords per hour, which is similar to that observed in other studies of this equipment (Koten and Peters 1985, Courteau and Heidersdorf 1991, Richmond et al. 1991). Average cost for yarding (not including other activities) was about $20 per cord. Site Disturbance The total amount of soil disturbance by cable yarding was less than that caused by crawler tractor skidding. Soil disturbance on the five cable-yarded sites ranged from 1.5 to 10.5% and was mainly a function of land form (greater log suspension resulted in less soil disturbance). Soil disturbance on the two crawler tractor sites, on the other hand, was consistent and ranged from 18.5 to 20.5% of the area.

3 Table 1. Productivity, cost, and other attributes associated with cable yarding steep slopes in southeastern Minnesota. Attribute Value Total volume 190 cords Total cycles 315 Ave. volume per cycle 0.6 cords Total # of pieces 405 Volume per piece 0.47 cords Ave. # of pieces per cycle 1.3 Ave. yarding distance 298 ft Ave. corridor distance 238 ft Ave. lateral distance 60 ft Ave. time per cycle 9.0 minutes Productivity Hourly system cost* Yarding cost 4.0 cords per hour $80.27 per hour $20.07 per cord * The hourly system cost is for the yarder and three operators, it does not include felling, log preparation, log extraction from the corridor, loading, or hauling costs. Costing assumptions are provided in the Appendix. The amount of organic soil exposed was only slightly more for the crawler tractor sites (average of 3.7% of the area) than for the cable-yarded sites (average of 1.8% of the area). However, crawler skidding caused significantly more mineral soil to be exposed (average of 15.8% of the area) than cable yarding (average of 6.0% of the area). This difference can be attributed to the trafficking by the crawler tractor and the higher incidence of dragging as trees were transported to the landing. This difference is significant relative to the impact soil disturbance has on sedimentation, water quality, and timber productivity on these highly erosive slopes of southeastern Minnesota. Residual Stand Damages Partial cut operations were conducted with both a skyline cable yarding system and a crawler tractor skidder system on similar, nearby sites. A primary consideration in partial cut harvests is the amount of residual stand damage caused by the logging system. Both felling and yarding/ skidding damages were assessed on these sites. There were 4.3 trees per acre damaged by cable yarding and 4.9 trees per acre damaged by ground skidding. This difference was not significant. These damage rates were considered low relative to normal damage rates in partial cutting. FLAT, WET SITE CASE STUDY A flat, wet aspen stand was selected on DNR land in eastcentral Minnesota. The stand contained mostly aspen with some spruce, fir, and maple. The soils were poorly drained. The trees were clearcut with a JD 653E tracked feller buncher having 24- by 122-inch tracks and an 18- inch capacity circular sawhead. Trees were delimbed and topped by chainsaw in early fall, then yarded to the landing with a Koller K501 Yarder and pulled from the corridor with a John Deere 748E grapple skidder. The performance of the yarding operation was evaluated using continuous time study techniques. In addition to the detailed timing data collected, corridor yarding distance, lateral yarding distance, number of stems per turn, and individual log measurements were recorded. Post-harvest disturbance was assessed on both the cable-harvested site and similar, nearby sites that were harvested with either a cut-to-length (CTL) or a mechanized feller buncher/ grapple skidder system. Disturbance data were collected using 50-foot line transects at random azimuth orientations from a uniform grid of points. The length of each type of soil disturbance occurring along each transect was recorded. Soil disturbance classes were adapted from Turcotte et al. (1991). Productivity and Cost The productivity, cost, and other attributes observed in this study of flat, wet site yarding in Minnesota are presented in table 2. Overall average cycle time was about 11.7 minutes per cycle with an average volume per cycle of about 0.5 cords. This translates to an average productivity of about 2.6 cords per hour, which is similar to that observed in other studies of this type of operation (Meek 1997). Average yarding cost was about $36 per cord. Site Disturbance The results of the site disturbance assessment are presented in table 3. The total amount of soil disturbance by cable yarding (9.2% of the area) was significantly less than that caused by CTL (31.1%) or grapple skidding (60.5%). A much larger portion of the CTL area was slash-covered, which generally has a protective effect for the soil (Jakobsen and Moore 1981, McDonald and Seixas 1997, McMahon and Evanson 1994). Aside from the higher incidence of soil impacts on the grapple skidder sites, impacts to the soil on these sites were also more severe. The grapple skidder sites had an average of 42.9% of the area with mineral soil exposed, while the CTL had 17.3% and the cable-harvested site had 2.8%. Organic soil exposure was 17.6%, 13.8%, and 6.4% for the grapple-skidded, CTL, and cable-yarded sites, respectively.

4 Table 2. Productivity, cost, and other attributes associated with cable yarding flat, wet sites in east-central Minnesota. Attribute DISCUSSION Value Total volume 69.5 cords Total cycles 139 Ave. volume per cycle 0.5 cords Total # of pieces 581 Volume per piece 0.12 cords Ave. # of pieces per cycle 4.2 Ave. yarding distance 327 ft Ave. corridor distance 271 ft Ave. lateral diistance 56 ft Ave. time per cycle 11.7 minutes Productivity Hourly system cost* Yarding cost 2.6 cords per hour $94.82 per hour $36.47 per cord * The hourly system cost is for the yarder and three operators, it does not include felling, log preparation, log extraction from the corridor, loading, or hauling costs. Costing assumptions are provided in the Appendix. The productivity of steep slope cable harvesting (4 cords per hour) is quite a bit higher than that for flat, wet site cable harvesting (2.6 per hour). This difference can be attributed to several factors. First, the trees at the wet site were much smaller than at the steep slope site, making it necessary to choke several per turn to get a decent load. Second, the haulback of the carriage to the stump area was much slower when done with a winch drum than when allowed to descend by gravity. Last, and probably most importantly, rigging was much more time-consuming and less reliable on wet sites than on steep slopes. This can be attributed to the need for intermediate supports to get the necessary lift on the skyline and the lack of well-rooted guy and tailhold trees. Trees in wet areas tend to have shallow rooting, making them prone to uprooting when used as a tailhold, intermediate support, or guy tree. Cable operations in wet areas should consider use of mobile tail holds (Fraser and Robinson 1998a, Fraser and Robinson 1998b). Also, corridors should be pre-rigged with a separate rigging crew to keep the yarder working. This would increase overall costs, but reduce the cost per cord by about $3 due to the higher yarding productivity. The results of the soil disturbance assessment clearly show that skyline cable yarding results in less soil impacts than other common systems for steep slope and flat, wet site harvesting. This is a logical result because the site is not trafficked by heavy equipment during harvesting. It would also be logical to assume then that less soil erosion, sedimentation, and timber productivity impacts would occur on cable-yarded sites than on sites harvested with ground-based systems. Access to sites with very sensitive soils is also more feasible throughout the year with cable yarding systems than with ground-based systems. Unfortunately, this access and lower impacts come at a higher harvesting cost than conventional systems. This cost was estimated at between $245 and $490 per acre in another study (LeDoux and Baumgras 1990). SUMMARY Ground-based forest operations can cause adverse impacts to the soil and residual stand. Skyline cable yarding is a harvesting technology that can lessen impacts on steep slopes and flat, wet sites. The purpose of this study was to evaluate the productivity, cost, residual stand impacts, and site impacts associated with skyline cable yarding on steep slopes and flat, wet sites in the Lake States. The Clearwater skyline cable yarder averaged 4 cords per hour at a cost of $20 per cord on steep slopes in Minnesota. The Koller skyline cable yarder averaged 2.6 cords per Table 3. Percent of area in different disturbance classes for cable yarding, CTL, and grapple skidding. Disturbance class Yarding CTL Grapple Undisturbed Organic mound Organic rut Mineral scarified Mineral mixed Mineral mound Mixed rut side Mineral rut Slash Stumps

5 hour at a cost of $36 per cord on flat, wet sites in Minnesota. Cable yarding was no less damaging to the residual stand than crawler skidding on steep slopes, but was substantially less damaging to the soil on both steep slopes and flat, wet sites. Although steep terrain is not usually associated with Lake States forests, there is a considerable area (100,000 acres) on slopes greater than 45% (Ziemer 1980). There is an additional 4.3 million acres of flat, wet sites. The conventional method of harvesting these sites with ground-based equipment can cause significant impacts to the soil if done when the soils are not frozen. Skyline cable yarding is a harvesting alternative that minimizes impacts to the soil resource, extending the logging season and maintaining timber productivity. LITERATURE CITED Baumgras, J.E.; Peters, P.A Cost and production analysis of the Bitterroot miniyarder on an Appalachian hardwood site. Res. Pap. NE-557. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 32 p. Biller, C.J.; Fisher, E.L Whole-tree harvesting with a medium capacity yarder. ASAE Pap St. Joseph, MI: American Society of Agricultural Engineers. 16 p. Courteau, J.; Heidersdorf, E Cable yarding in eastern Canada - 5 case studies. Technical Note TN Forest Engineering Research Institute of Canada. 16 p. Cubbage, F.W.; Gorse, A.H., IV Mountain logging with the Bitterroot miniyarder. In: Proceedings, Mountain logging symposium. Morgantown, WV: West Virginia University: Fisher, E.L.; Peters, P.A Analysis of eastern United States cable harvesting operations. ASAE Paper No St. Joseph, MI: American Society of Agricultural Engineers. 27 p. Fisher, E.L.; Gibson, H.G.; Biller, C.J. 1980a. Production and cost of a live skyline cable yarder tested in Appalachia. Res. Pap. NE-465. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 8 p. Fisher, E.L.; Gochenour, D.L.; Biller, C.J. 1980b. Significant factors affecting performance of a Urus cable yarder. Transactions of the ASAE. 27(4): Fraser, D.; Robinson, D. 1998a. Excavator mobile anchoring methods. LIRO Report. 23(4): 6 p. Fraser, D.; Robinson, D. 1998b. Tractor mobile anchoring methods. LIRO Report. 23(5): 7 p. Jakobsen, B.F.; Moore, G.A Effects of two types of skidders and of a slash cover on soil compaction by logging of mountain ash. Australian Forest Research. 11: Keesee, K.C Small tree steep slope harvesting. In: Proceedings, Harvesting small timber: waste not, want not; 1981 April 28-30; Syracuse, NY. Proc. P Madison, WI: Forest Products Society: Koten, D.E.; Peters, P.A Cable yarding on environmentally sensitive areas in New York State. In: Proceedings, 8th Annual council on forest engineering meeting; 1985 August ; Tahoe City, CA: LeDoux, C.B.; Baumgras, J.E Cost of wetland protection using cable logging systems. In: Proceedings of the 13th Annual council on forest engineering meeting; 1990 August 12-16; Outer Banks, NC: Matics, H.E Why Westvaco uses cable yarders in the Appalachians. In: Proceedings, Cable yarding conference. Asheville, NC: Tennessee Valley Authority: Matics, H.E Westvaco cable logging program, the future situation. In: Proceedings, Appalachian cable logging symposium. Blacksburg, VA: Polytechnic Institute: McDonald, T.P.; Seixas, F Effect of slash on forwarder soil compaction. Journal of Forest Engineering. 8(2): McMahon, S.; Evanson, T The effect of slash cover in reducing soil compaction resulting from vehicle passage. LIRO Report. 19(1): 8 p. Meek, P Preliminary trials of wood extraction by cable yarding on soft soils. Forest Engineering Research Institute of Canada, Field Note No.: Cable Yarding p. Miyata, E.S.; Steinhilb, H.M.; Coyer, L.A Metric conversions for foresters. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Research Station. 4 p. Norton, D Owens-Illinois cable logging program. In: Proceedings, Cable logging symposium. Blacksburg, VA: Polytechnic Institute:

6 Peters, P.A Steep slope clearcut harvesting with cable yarders. In: Proceedings, Harvesting the south s small trees; 1983 April 18-20; Biloxi, MS. Proc Madison, WI: Forest Products Society: Richmond, A.P.; Sampson, G.R.; Gasbarro, A.F Cable yarding a shelterwood overstory in white spruce timber. Northern Journal of Applied Forestry. 8(1): Sherar, J.R.; Tillman, D.A The Clearwater yarder. In: Proceedings, Mountain logging symposium. Morgantown, WV: West Virginia University: Stuart, W.B.; Rossi, M.K Production study of the Koller K-300 cable yarder operating in the mountains of Virginia. In: Proceedings, Mountain logging symposium. Morgantown, WV: West Virginia University Turcotte, D.E.; Smith, C.T.; Federer, C.A Soil disturbance following whole-tree harvesting in northcentral Maine. Northern Journal of Applied Forestry. 8(2): Ziemer, I Preliminary study to establish the feasibility of cable yarding in the Lake States. Final report for Cooperative Agreement (FS-NC ). 42 p. On file with: USDA Forest Service, 410 MacInnes Drive, Houghton, MI

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8 SITE DISTURBANCE ASSESSMENT SYSTEM The method consists of three levels of assessment that answer three main questions: What is visible on the soil surface? What happened here? Is this part of a larger feature in the landscape? Each question corresponds to an evaluation column in the scheme as follows: Visible Layer Evaluation Feature Litter Undisturbed Main Trail Organic Soil Trafficked Secondary Trail Mineral Soil Scarified Skyline Corridor Muck Gouged-depth Landing Area Slash Rutted-depth Decking Area Stump Mounded-height Service Area Rock Covered-height Road Water Unknown Stream, Pond, Marsh Visible Layer - The visible layer defines what is on the soil surface at that point. Litter is the largely undecomposed organic debris, such as leaves, twigs, and other plant remains, that covers most forest soils. Organic soil is defined as the uppermost soil layer just below the litter containing largely decomposed organic matter (humus and O horizons) and is generally darker in color than the mineral soil below. Mineral soil is defined as the soil layer just below the organic soil composed of material of predominantly mineral origin (A and B horizons). If litter, organic soil, or mineral soil are mixed, the point is classified as the predominant component of the mix. Muck is completely saturated richly organic soil. Slash is woody debris covering the soil surface that is too thick to allow classification of what happened to the soil at that point. A slash designation is only used if the observer cannot see the soil surface beneath the slash to evaluate it. Stumps are only classified as stumps when remaining in place. If a stump has been uprooted from the ground and the soil surface cannot be evaluated beneath it, it should be classified as slash. Rocks and stumps are usually considered undisturbed because driving or dragging things over them does not affect site quality in general. Water should only be recognized if it is a permanent or semi-permanent feature of the landscape (i.e., vernal pond, intermittent stream, etc.). Occasional puddles should not be considered water. Different layers should only be recognized if measuring 30 cm across or larger. Measurements should be taken to the nearest 10 cm along transects (if used) and to the nearest 3 cm for a height or depth measurement. Evaluation - This column is an evaluation of what happened to the soil surface at the point in question. Undisturbed means nothing happened. Trafficked means there is evidence that the tires or tracks of a machine passed over the soil surface. Scarified means there is evidence that something was dragged across the soil surface with no associated trafficking. Gouged means there is evidence the soil layers were gouged by something other than the tires or tracks of a passing machine. Rutted means there is evidence of ruts caused by the passage of tires or tracks on a machine. Mounded implies disturbance of the original soil layers into a mound and is normally found adjacent to ruts. Covered implies no disturbance of the original soil layers, only a fresh layer of disturbed soil on top (normally found adjacent to a gouge). Unknown is a designation that should only be used in conjunction with slash because this is the only case where the observer will not be able to evaluate the soil surface. The only other evaluation that should be used with slash is trafficked if there is clear evidence that the slash over the soil surface had been trafficked. The hole left by an uprooted stump should be considered a gouge. Feature - This is a less important part of the classification scheme used to evaluate larger features in the landscape and their relative abundance. Any major feature of interest on the site could be added to this list, or this column could be disregarded.