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The effects of ground-based harvesting on coastal British Columbia soils : mitigating the negative consequences Trommel, Steve Apr 6, 2013

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        The effects of ground-based harvesting on coastal British Columbia soils: Mitigating the negative consequences     FRST 497 Graduating Report Faculty of Forestry        April 6, 2013 Steve TrommelThe effects of ground-based harvesting on coastal British Columbia soils                                                    i  Abstract The recent downturn in British Columbia?s coastal forest industry, together with an increased proportion of timber harvest from second growth stands has increased pressure on harvest operations to reduce costs. Using ground-based harvest methods, primarily with skidders and hoe-chuckers, harvest operations can lower costs compared to cable yarding. Skidders and hoe-chuckers have the potential to negatively affect future site productivity and natural hydrological processes. The complexity of factors influencing the amount of soil disturbance resulting from skidder and hoe-chucker use makes the interpretation of research results difficult. The strongest factors are soil moisture at time of harvest and soil texture. Short term research on seedling growth has found a decrease in growth on machine trails of 20 to 53 percent (Senyk & Craigdallie, 1997). The difference in growth between machine trails and undisturbed areas decreases over time. Increased growth on the margins of machine trails has been shown to partially offset losses to growth on trails. Direct hydrological impacts from ground-based machinery have not been researched in great depth as hydrological processes are also complex. Case studies have shown the potential of ground-based harvesting to change water flow patterns resulting in mass wasting and drainage structure failures. The negative of consequences of ground-based harvesting can be mitigated by reducing harvest during very wet periods and through the use of designated trails, rehabilitating trails, proper equipment choice and operator training.    Key words: Ground-based harvesting, soil disturbance, site productivity, forest hydrology, skid trail rehabilitation, coastal British Columbia   The effects of ground-based harvesting on coastal British Columbia soils                                                    ii  Table of Contents 1. Introduction .......................................................................................................................................... 1 2. Coastal British Columbia ....................................................................................................................... 2 3. Ground-based equipment used in coastal British Columbia ................................................................ 3 3.1 Skidders ......................................................................................................................................... 3 3.2 Hoe-chuckers ................................................................................................................................ 6 3.3 Operator influence ........................................................................................................................ 7 4. Site conditions influencing soil degradation ......................................................................................... 7 4.1 Soil Moisture ................................................................................................................................. 7 4.2 Soil texture and organic matter .................................................................................................... 8 4.3 Terrain ........................................................................................................................................... 9 5. The effect of ground-based harvesting on forest productivity ............................................................. 9 5.1 Skidders ......................................................................................................................................... 9 5.2 Hoe-Chuckers .............................................................................................................................. 10 6. The affects of ground-based harvesting on forest hydrology. ........................................................... 10 6.1 Skidders ....................................................................................................................................... 11 6.2 Hoe-chuckers .............................................................................................................................. 11 7. Reducing the negative consequences of ground-based harvesting ................................................... 12 7.1 Scheduling the harvest ................................................................................................................ 12 7.2 Selecting the right equipment for the site .................................................................................. 12 7.3 Designated machine trails ........................................................................................................... 13 7.4 Deactivating built trails ............................................................................................................... 13 8. Conclusion ........................................................................................................................................... 14 9. References .......................................................................................................................................... 15  Index of figures and table Figure 1. Grapple skidder picking up a log .................................................................................................... 3 Figure 2. Tire chains with stiff cross-members mounted on a rubber-tired grapple skidder . ..................... 4 Figure 3. Steel-tracked grapple skidder used for winter logging near Harrison Lake. .................................. 5 Figure 4. A hoe-chucker moving a log. .......................................................................................................... 6 Table 1.. Soil compaction and puddling key???????.????????????????????????..???..8 Figure 5. Failure below block harvested using ground-based methods ..................................................... 11 The effects of ground-based harvesting on coastal British Columbia soils                                                    1   1. Introduction The system used to move logs from the site where a tree is felled to a collection site, known as primary transport, often factors strongly into the economic viability of harvesting a stand. Ground-based harvesting is often the most cost efficient method of harvesting logs where conditions allow for ground-based equipment to be used. Equipment travels over the ground to felled logs before carrying or dragging the logs to a landing site. Conditions allowing for the use of ground-based harvesting are described by the Forest Engineering Research Institute of Canada (FERIC) as ?terrain that is not too steep or broken and soils strong enough to support the machine? (MacDonald, 1999, p. 50). Terrain in coastal British Columbia is varied between steep mountains and gentler valley bottoms, resulting in the use of various methods of primary transport. In a survey of 59 tenure licensees, with annual harvest rates ranging from 20,000 cubic meters to over 1 million cubic meters per year, FERIC found the percentage of total harvest done using ground-based methods to be between 11 and 25 percent for 49 percent of respondents (Morford, Moshenko, Proteau, & Thomson, 2004).  Lower log values associated with second growth timber harvest resulted in an increase in ground-based machinery use to lower logging costs and make second growth harvest profitable (Rogers & MacDonald, 1989). The recent downturn in British Columbia?s forest industry, from 2007 till 2012, has also factored into an increase in ground-based primary log transport.   There has been increased concern o the environmental impact and sustainability of forest harvesting since the late 1980?s. Currently, under the Forest and Range Practices Act (FRPA), licensees operating on Crown land are required to maintain key resource values, including soils, timber and water, values that can be affected by ground-based harvesting (Province of British Columbia, 2013). The Forest Practices Code (FPC) guidebook for assessing soil degradation lists three major soil degrading processes (British Columbia Ministry of Forests, 1999). The processes are: ? soil compaction, ? soil displacement (exposure of unfavourable subsoil or changes to hydrology) and  ? soil erosion (exposure of mineral soil). Many factors affect the degree of degradation ground-based equipment causes. Soil, topography, climate machine selection and operator experience can strongly influence the amount of soil degradation. Excessive soil disturbance has been found to lower site productivity and increase surface water flow by increasing soil density, decreasing soil aeration and decreasing water permeability The effects of ground-based harvesting on coastal British Columbia soils                                                    2   (Douglas & Courtin, 2001). Excessive ground compaction can severely decrease the pore space in soil, leading to the reduced ability to hold water. This process, known as puddling, can persist for a long time. Displacement of soil increases rates of soil erosion and can decrease the productive area of a block.   The affects ground-based machinery has had on site productivity have been well researched around the world, with some research specific to coastal British Columbia. Research has been performed using the most commonly used ground-based harvesting equipment in coastal British Columbia, skidders and hoe-chuckers. The hydrological effects of ground-based harvesting have not been researched in much detail. Some case studies have been done showing how machine trails may have the same consequence as roads, negatively affecting the hydrological processes of an area. This paper examines available research to determine if mitigation measures are necessary to maintain site productivity and hydrological processes and to examine some specific mitigation measures that may be useful.  2. Coastal British Columbia Coastal British Columbia is the furthest west portion of British Columbia, stretching from Washington State to the State of Alaska. The area is dominated by the Insular Mountains on Vancouver Island and the Coast Mountains on the mainland. Much of the terrain is steep and rugged. The climate is variable, dependant mostly on elevation and if a site is on the windward or leeward side of mountain ranges. Most of the coast receives large amounts of precipitation and has low seasonal temperature differences compared to other regions. The majority of precipitation occurs in the fall, winter and spring. The summers can be dry as high pressure weather cells can extend from the North Pacific over the coast (Jungen & Lewis, 1986).   The geology is mainly igneous rock. The Coast Mountains are mostly intrusive batholiths. Large portions of the Insular Mountains are comprised of folded and faulted volcanic and sedimentary rock. The resistance of intrusive rock to weathering results in coarse textured parent material for soils (Jungen & Lewis, 1986, p. 101). The dominant process of soil development has been glaciation.   Coniferous trees blanket much of the coast, primarily consisting of Western hemlock, Amabilis fir, Western red cedar and Douglas-fir. Harvesting conifers has been an important part of the economy in British Columbia since the 18th century.   The effects of ground-based harvesting on coastal British Columbia soils                                                    3   3. Ground-based equipment used in coastal British Columbia There is a long history of ground-based harvesting in coastal British Columbia. Horses and oxen were first used to drag logs to water where they could be easily transported. Steam powered winches, commonly known as steam donkeys, were developed in the late 19th century to transport logs by winching them with cables (Wilma, 2003). Primitive track-based bulldozers were used on all sites under many conditions from the 1930?s until the 1950's (Senyk & Craigdallie, 1997). As the remaining un-harvested terrain became steeper, the majority of harvest on the coast trended towards mobile cable yarders. An economic downturn and transition towards the harvest of second growth timber in the 1980's led to the increased use of ground-based equipment. This essay will focus on skidders and hoe-chuckers, the most commonly used equipment for ground-based harvesting in coastal British Columbia.  3.1 Skidders  The term skidder describes equipment which travels to felled logs through a block and drags the logs to a landing site. Skidders are classified by their use of rubber tires or steel tracks for traction and the use of either a grapple or cable for holding logs. One end of a turn, one or more logs moved at one time, is suspended above the ground. The other end of the turn is dragged along the ground to the landing. The cost of skidding is a function of yarding distance. Skidders with cables, known as line skidders, have the advantage of not needing to travel directly adjacent a log. This can reduce the amount of ground travelled on in a block. Line skidders also have higher payloads decreasing the number a passes made over a skid trail (MacDonald, 1999, p. 52). Hooking up and releasing logs with chokers takes more time than hook-up and release of logs with a grapple, decreasing productivity and making line skidders less economical in most cases. Grapple skidders can be productive with yarding distances under 300 meters (p. 52). Grapple skidders lift one end of turns higher than line skidders resulting in less Figure 1. Grapple skidder picking up a log.                                                                                                                                          (photo credit: Private Forest Landowners association, www.pfla.bc.ca)  The effects of ground-based harvesting on coastal British Columbia soils                                                    4   soil disturbance from the dragging logs. Many new skidders have both a cable and grapple to take advantage of both systems (Forests and Rangelands, 2013).  Rubber-tired skidders are articulated machines that can operate on slopes up to 35% (MacDonald, 1999). Different wheel configurations can be used to increase traction and decrease soil disturbance. A loss of traction can quickly cause soil displacement. Wide, low ground pressure tires can be used to decrease compaction (McDonald & Stokes, 1995). Many skidders currently operating on the coast use wide, low ground pressure tires wrapped in chains to increase traction. Stoilov recommends using tightly installed chains in mountainous terrain to increase traction without strongly increasing the rolling resistance of the tires (2007). Using newer, more tightly linked chains with stiff cross-members can further increase traction while reducing ground pressure (McDonald P. , 2012).  Figure 2. Tire chains with stiff cross-members mounted on a rubber-tired grapple skidder (source: forestnet.com).  Steel-tracked skidders are similar to bulldozers. Steel tracks offer more traction than rubber tires allowing for operation on slopes up to 50% (MacDonald, 1999). Steel-tracked skidders are usually only used for difficult terrain, as the equipment is less productive and more costly to operate than rubber tired skidders (p. 64). Although steel tracks produce lower static ground pressure compared to rubber tires, research has shown little difference in compaction caused by rubber-tired or steel-tracked machines (Sheridan, 2003). The risk of rutting is low but soil displacement can still be high where the machine turns. Soil displacement is variable over a machines path. The effects of ground-based harvesting on coastal British Columbia soils                                                    5    Figure 3. Steel-tracked grapple skidder used for winter logging near Harrison Lake.   The use of steel-track and rubber-tire machines with hydrostatic drive-trains can decrease the amount of soil disturbance caused by yarding. The system uses a complex system with hydraulic fluid to power wheels or tracks allowing power to be distributed better between wheels or tracks resulting in better traction (MacDonald, 1999).  The amount of soil disturbance caused by ground-based harvesting has been well researched. Rollerson (1990) researched the soil disturbance caused by a skidder using 1.12 meter wide tires. The skidder caused increases in bulk soil density, a measure of soil compaction, mostly ranging from 5 to 20 percent with a high of 35 percent. Most of the compaction was found to occur over the first 10 to 20 passes.  Rutting, the displacement of some soil while exposing other mineral soil, was also caused by skidder traffic. Depth of rutting was a factor of soil moisture and number of passes.   The building of bladed skid trails, often necessary on steep slopes, increases the severity of soil disturbance. Built trails can expose mineral soil, divert subsurface flow and decrease plantable spots if not rehabilitated. Logs dragged on steep slopes can also divert water flow (MacDonald, 1999).   Skidders are often favoured because they are relatively inexpensive to maintain and operate. On many sites skidders are less expensive to operate then hoe-chuckers. This has led an increase in the use of skidders on the coast during the recent downturn in the forest industry. The effects of ground-based harvesting on coastal British Columbia soils                                                    6   The previous experience of an operator also factors into the choice made when considering the use of skidders and hoe-chuckers. 3.2 Hoe-chuckers Hoe-chuckers, also called loader-forwarders or hoe-forwarders, were introduced  in the late 1980?s to decrease the level of soil disturbance caused by ground-based yarding while keeping costs lower than cable yarding (Douglas & Courtin, 2001). Hoe-chuckers are similar to hydraulic log loaders but modified to operate on more challenging terrain (Douglas & Courtin, 2001, p. 1). Modifications include: ? a raised and widened carriage to clear stumps and debris, ? a lengthened boom to increase reach,  ? widened tracks to increase stability and floatation and ? increased fuel capacity.   Hoe-chuckers transport logs by passing them across the length of its reach. The machine starts at the back line of a cutblock, usually travelling parallel to the road, passing logs toward the road. On steeper terrain hoe-chuckers may travel directly up and down slopes. Logs starting at the backline may be moved in several steps before reaching the road. The cost of using hoe-chuckers is a function of the number of passes needed to move logs to the collection area. Using this method each path the machine takes is often travelled only once. Mats of tree tops and branches can be placed on the machine path to reduce soil disturbance. Carrying, rather than dragging logs, reduces soil disturbance compared to skidding. Hoe-chuckers can operate on more rugged terrain than skidders as the boom can be used to stabilize the machine. Hoe-chuckers can cause soil compaction and displacement. Operating on steep slopes, traveling over a location several times and turning a machine can increase the disturbance caused by a hoe-chucker (Douglas & Courtin, 2001; Douglas & Brown, 2009).  Figure 4. A hoe-chucker moving a log (Douglas & Courtin, 2001). The effects of ground-based harvesting on coastal British Columbia soils                                                    7   3.3 Operator influence The influence the equipment operator has on soil disturbance is often not described in research articles. Where it is mentioned, it is seen as a critical factor in level of disturbance caused by ground-based equipment. McDonald and Stokes describe operator experience as having a strong effect on soil disturbance (1995, p. 41). Operator experience should be included more often in ground-based soil disturbance research.  4. Site conditions influencing soil degradation Site conditions strongly affect the amount of disturbance caused on a site by ground-based harvest. The location and soil conditions at the time of harvest can affect the feasibility of harvest operations constrained by soil disturbance limits. Conditions also affect the operability of a cutblock. The complex interaction of factors influencing soil degradation and high variability of conditions over small areas can make relationships between ground-based harvesting and soil disturbance difficult to understand.  4.1  Soil Moisture Early in the trend from cable logging to ground-based logging, operations were only done in dry, favourable conditions. However, for investment in new ground-based equipment to be possible, ground-based harvesting operations were expanded into wet conditions, common during much of the year on the coast. The affect moisture has on soil strength is seen as a primary factor in the severity of soil disturbance caused by ground-based harvesting. Laboratory compaction tests have shown the shear strength of soil to decrease with increased water content (Rab, Bradshaw, Campbell, & Murphy, 2005). Although compaction is not as severe as lab testing may suggest, field research has found compaction from ground-based equipment to increase with moisture levels in most cases. Murphy is cited by Rab et al. to have ?found three times as much deep disturbance on the wetter of two logging sites in western Oregon that were both stocked with Douglas-fir, had the same soil type, and were thinned by the same tractor? (p. 5). In some cases other factors may decrease the influence of moisture. Smith et al. found the compaction of a sandy loam to be almost independent of soil moisture (Rab, Bradshaw, Campbell, & Murphy, 2005, p. 28).  Lower soil strength from increased soil moisture can decrease the load bearing capacity of soils. Wet soil is more easily displaced by wheels or tracks resulting in deeper rutting (Williamson & Nielson, 2000).   The effects of ground-based harvesting on coastal British Columbia soils                                                    8   4.2  Soil texture and organic matter The texture and density of soil at the time of harvest influence the resilience of soil to disturbance. Coarse soils are more resistant to compaction than fine textured soils. Coarse fragments in soil also resist compaction and add strength to soil structure. Fine soils more easily disturbed and displaced by rutting. Soils with organic horizons less than 20 centimeters are seen as more resistant to disturbance than soils with organic horizons greater than 20 centimeters. This is likely because thick organic horizons are easily rutted and offer little traction for machinery, especially when wet. Very low amounts of organic matter also increase risk of soil disturbance. Organic matter increases the ability of a soil to absorb water, resist deformation and increases soil elasticity (Rab, Bradshaw, Campbell, & Murphy, 2005).  The B.C. Ministry of Forests summarized soil compaction and puddling hazard in the following table published in a Forest Practices Code Guidebook (1999, p. 5), Table 1. Soil compaction and puddling key (British Columbia Ministry of Forests, 1999).  The effects of ground-based harvesting on coastal British Columbia soils                                                    9   4.3  Terrain As equipment is operated near its limit concerning terrain, more soil disturbance is caused. Research performed by Agherkalki found soil disturbance from skidders to be intensified on slopes greater than 20 percent (2010). Skid trails on steep side slopes need to be built like a simple road to maintain machine stability. This soil displacement increases the percentage of a block disturbed. Sidle and Drlica found adverse skidding to increase soil disturbance (Sidle & Drlica, 1981).   Similar to the sequence of the first harvest through the coastal British Columbia landscape, second growth harvest is moving from more gentle, low elevation terrain, to more challenging, rugged terrain. Using ground-based machinery close to its operating limits will continue to become more common.     5. The effect of ground-based harvesting on forest productivity The most studied consequence of soil disturbance is site productivity. Land managers and researchers are concerned the current use of economical harvesting methods may result in lower future yields for the next rotation. Soil disturbance can affect the performance of seedlings by: ? reducing ground permeability, ? restricting root space and ? causing poor aeration (Maynard & Senyk, 2004).  Soil disturbance can restrict root growth and decrease the amount of nutrients roots can take up. Microbial organisms need good aeration to decompose organic matter into nutrients seedlings can use. The diversion of ground water can lead to water shortages for some seedlings and excessively wet conditions for other seedlings. 5.1 Skidders Research examining decreases in site productivity from skidders compare seedling growth on skid trails to undisturbed control areas in the block. The amount of area covered by skid trails is quite variable between sites. Off-road cutblock coverage up to 40 percent has been observed in blocks where skidder operators are not restricted to designated trails (Garland, 1997). Seedlings growing directly on the tracks show the highest decreases in growth. Seedlings in between and The effects of ground-based harvesting on coastal British Columbia soils                                                    10   just outside the tracks usually show little differences in growth. Senyk found decreases in Western hemlock and Douglas-fir height after one year from 20 to 53 percent, mostly dependant on the level of traffic at a location (Senyk & Craigdallie, 1997). After seven years, on the more heavily used trails, the difference in height ranged from 6 to 33 percent. Skid trails used less than five times exhibited increases in tree height compared to undisturbed locations. Decreased growth on skid trails is sometimes compensated by increased growth on trail margins leading to little net effect to growth (Rollerson, 1990). Excessive decrease in growth is often associated with a high level of soil disturbance caused by heavy skidder traffic and wet harvesting conditions (Maynard & Senyk, 2004; Senyk & Craigdallie, 1997).    5.2 Hoe-Chuckers Research on differences in seedling growth between hoe-chucker tracks and undisturbed soils have shown differing results. In a study done on North Vancouver Island, seedling growth was lower on tracks where competing salal was not a factor. Growth was stronger on tracks where the disturbance reduced salal competition (Douglas & Courtin, 2001). A second research project near Woss, on Vancouver Island, found seedlings on undisturbed ground had put on considerably more volume than trees planted on tracks after 15 years. There was little difference found in seedling growth between seedlings planted in undisturbed areas in the plantation and the area flanking and between machine tracks (Douglas & Brown, 2009). Hoe-chuckers often have less detrimental affects to site productivity compared to skidders because they travel over less ground in the block and travel on the same trails less frequently. The ability to travel on mats of tree branches and tops can greatly mitigate damage in sensitive sites.  6. The affects of ground-based harvesting on forest hydrology.  Ground-based harvesting can change the hydrological processes of an area. Compaction can reduce soil infiltration capacity increasing surface runoff (Adams & Froehlich, 1981). Machine trails can divert surface runoff or ground water flow to roads with drainage structures insufficient to handle increased flow. Ground-based harvested blocks are often located on gently sloped terrain above steep slopes. Slope failures have been found below blocks where old trails have diverted subsurface water flow onto trails before releasing accumulated diverted flow onto unstable steep slopes below (Jordan, et al., 2010). Slope failures can have long lasting, serious impacts on downhill resources such as fish streams, roads, buildings and forest productivity. The risk of hydrological impacts is also high where trails are The effects of ground-based harvesting on coastal British Columbia soils                                                    11   located on steep slopes where soil disturbance is intensified and water flows faster with more erosive power. Increased erosion can remove growing medium from a site and scour streams resulting in simplified stream morphology and increased sedimentation in streams.   Figure 5. Failure below block harvested using ground-based methods likely resulting from "subtle changes to slope hydrology" (Jordan, et al., 2010). 6.1 Skidders Skidders pose a greater threat to hydrological processes than hoe-chuckers. Bladed trails can have the same effect as roads, with decreased infiltration strongly increasing surface runoff (Jordan, et al., 2010). Skid trails often run directly to roads, potentially carrying water to roads. Higher levels of soil compaction, deeper rutting and increased trail coverage over a block also contribute to more hydrological changes as a result of skidder activity compared to Hoe-chucking. 6.2 Hoe-chuckers Hoe-chuckers lower ground pressure and different yarding techniques decrease hydrological impacts. The use of debris on trails can slow the flow of water on trails. Trails running parallel to road systems divert less surface runoff to roads. There is still high risk for consequence on steep ground, where water flows faster and more soil disturbance is caused. Trails on steep ground often run perpendicular to slope contours accelerating the flow of water.   The effects of ground-based harvesting on coastal British Columbia soils                                                    12   7. Reducing the negative consequences of ground-based harvesting Methods of mitigating the negative effects of ground-based harvesting have been used since the 1980s. Different management methods are still being explored to maintain productivity while not causing unacceptable soil degradation. Four methods of managing soil disturbance are the scheduling of harvesting, selecting the best equipment for the site, designating machine trails and rehabilitating machine trails.  7.1 Scheduling the harvest Many researchers recommend restricting the use of ground-based machinery to dry conditions (Rollerson, 1990; Rab, Bradshaw, Campbell, & Murphy, 2005; Douglas & Courtin, 2001). Restricting skidder use to dry conditions can decrease rutting and soil displacement (Rollerson, 1990, p. 29).This is often not feasible in Coastal B.C. due to long periods of high soil moisture. Using a hoe-chucker in wet conditions can mitigate disturbance if tree branches and tops are used to protect the underlying soil.  7.2 Selecting the right equipment for the site Picking the right equipment can decrease soil disturbance while providing good production rates. In some cases, high risk of soil disturbance will restrict harvesting to the use of hoe-chuckers or even more costly methods of yarding, such as cable yarding. The operability limits of equipment must be considered when choosing equipment. Operating machinery over its limit is unsafe, causes excessive disturbance and often results in low productivity.  Using a combination of a hoe-chucker and a grapple skidder for yarding can often maintain production while minimizing soil disturbance. FERIC monitored the logging of two similar blocks on Vancouver Island while collecting productivity, cost and soil disturbance data (Kosicki, 2003). One block was harvested using only a hoe-chucker and the other with a combination of a hoe-chucker and skidder. Using the combination of equipment was found to be less expensive and offer higher productivity while maintaining acceptable soil disturbance levels (p. 14). Using both types of equipment together takes advantage of the strengths of both machines. Hoe-chuckers can move logs from areas of a block more sensitive to disturbance, steeper portions of a block or where the logs need to be yarded uphill (adverse), to a trail where skidders can operate without causing excessive soil degradation. The high productivity of skidders allow for longer yarding distances (p. 14). Hoe-chuckers can also clean landing sites of The effects of ground-based harvesting on coastal British Columbia soils                                                    13   debris so skidders can drop off turns faster. Some difficulties of using this system, especially for small logging contractors, is the need to purchase and maintain more equipment. Another challenge is the specialized experience of logging contractors. Contractors, experienced working on the Coast, often prefer to only use hoe-chuckers while contractors from the interior prefer skidders.  7.3 Designated machine trails Marking machine trails before harvest and restricting machines to trails can decrease the coverage of skid trails on a cutblock from 20 to 35 percent to less than 10 percent (Adams & Froehlich, 1981). Most soil compaction has been found to occur over the first ten turns so restricting the area of skidder traffic can decrease the area of soil disturbed (Sidle & Drlica, 1981; Rollerson, 1990). By using key designated, built trails, and allowing skidders to leave the trail for short distances to pick up turns, skidding can be safely done on steep slopes (Thibodeau, 2002). A challenge of restricting skidders to designated trails is the difficulty operators may have following marked trails after a block is felled. Displaying skid trails on logging plan maps can be helpful.  7.4 Deactivating built trails Deactivation of designated, built trails is very important to achieve acceptable levels of soil disturbance (Thibodeau, 2002). Rehabilitating disturbed areas mitigates negative hydrological impacts. De-building excavated trails and mounding or water barring trails on slopes can slow the flow of water and prevent surface water from reaching streams. The affect of trail rehabilitation on site productivity has been found to vary by site. Miller found trail rehabilitation did not to have a significant effect on site productivity (Miller, Scott, & Hazard, 1996). Trail rehabilitation done in very wet conditions was found to have a strong negative effect to seedling growth (Douglas & Brown, 2009). Mitchell found rolling topsoil back on to built skid trails to be sufficient to make seedling growth on trails equal to seedling growth in the rest of the plantation (2009). Rehabilitating trails immediately after harvest, while machinery is still present, can reduce costs and potential impacts of disturbance. Avoiding planting on poor, difficult to rehabilitate, micro-sites can decrease losses in site productivity (Rollerson, 1990). Higher planting densities near poor micro-sites can compensate for the lost area.   The effects of ground-based harvesting on coastal British Columbia soils                                                    14   8. Conclusion The amount and severity of soil disturbance resulting from ground-based harvesting is affected by many complex factors. Site specific information on terrain, soil characteristics and possible ranges of soil moisture at time of harvest should be gathered to properly plan harvest operations. Planning logging during expected dry periods should be attempted, although it is often not feasible on the coast.  Choosing the right equipment for harvesting can help reduce disturbance while maintaining productivity. Using skidders and hoe-chuckers together on a block can maintain productivity and mitigate soil disturbance. The strengths of both machines can be managed by: ? using skidders on easier ground and built trails to increase yarding distance and ? using hoe-chuckers on more difficult and sensitive terrain to increase the land base operable by ground-based harvesting. Soil disturbance caused by ground-based harvesting has been shown to cause short term losses to site productivity on machine trails. Longer term results have shown the affects of ground-based harvesting on site productivity to diminish over time. The continuation of studies should be performed to explore site productivity over a rotation. Restricting equipment to designated trails, with the exception of allowing machines to leave trails to pick up turns, can decrease the percentage of a block disturbed. On heavily used, built trails, rolling back topsoil can mitigate decreases in seedling growth.  Although much of the research involving site degradation has focused on site productivity, the affects of ground-based harvesting on hydrological processes have the potential of causing more damage through slope and drainage structure failures. Higher precipitation rates and steep slopes contribute to higher slope failure risks in coastal British Columbia (Jordan, et al., 2010). More research, specific to coastal British Columbia, should be done examining the relationship between ground-based harvesting and hydrology. Ground-based primary log transport plays an important role in Coastal British Columbia, allowing more stands to be economically viable for harvest. Increased awareness of the potential soil degradation resulting from the use of ground-based machinery is important for equipment operators and forest managers. Through proper management practices soil disturbance can be mitigated while keeping logging costs down. As research projects continue, more long term effects on site productivity will be understood.   The effects of ground-based harvesting on coastal British Columbia soils                                                    15   9. References Adams, P., & Froehlich, H. (1981). Compaction of forest soils. Corvallis: Pacific Northwest Extension. Agherkalki, B., Najafi, A., & Sadeghi, S. (2010). Ground based operation effects on soil disturbance by steel tracked skidder in a steep slope of forest. Journal of Forest Science, 278-284. British Columbia Ministry of Forests. (1999). Hazard assessment keys for evaluating site sensitivity to soil degrading processes guidebook. Victoria: Forest Practices Branch. Douglas, M., & Brown, K. (2009, March). Soil disturbance effects of hoe-forwarding on tree growth and site productivity: 15-year results at the Woss study site. Nanaimo, B.C. Douglas, M., & Courtin, P. (2001, March). Impacts of hoe-forwarding on site productivity. Nanaimo, British Columbia. Forests and Rangelands. (2013, March 6). Forest Operations Equipment Catalog: Skidders. Retrieved March 20, 2013, from Forests and Rangelands : http://www.forestsandrangelands.gov/catalog/equipment/skidders.shtml Garland, J. (1997). Designated skid trails minimize soil compaction. Corvallis: Oregon State University. Jordan, P., Millard, T., Campbell, D., Schwab, J., Wilford, D., Nicol, D., & Collins, D. (2010). Forest management effects on hillside processes. In R. Pike, T. Redding, R. Moore, R. Winkler, & K. Bladon, Compendium of Forest Hydrology and Geomorphology in British Columbia (pp. 275-329). Victoria: British Columbia Ministry of Forests and Range. Jungen, J., & Lewis, T. (1986). The soil landscapes of British Columbia. Victoria: British Columbia Ministry of Environment. Kosicki, K. (2003). Evaluation of a Timberjack 660D grapple skidder working on moderately steep slopes in coastal British Columbia. Vancouver: Forest Engineering Research Institute of Canada . MacDonald, A. (1999). Harvesting Systems and Equipment in British Columbia. Vancouver, British Columbia, Canada: Forest Engineering Research Institute of Canada. Maynard, D., & Senyk, J. (2004). Soil disturbance and five-year tree growth in a montane alternative silvicultural systems (MASS) trial. The Forestry Chronicle, 573-582. McDonald, P. (2012, January). Eco-Wheel tracks deliver traction on B.C.'s steep slopes. Retrieved from Logging & Sawmilling Journal: http://www.forestnet.com/LSJissues/Jan_12/Eco_wheel.php McDonald, T., & Stokes, B. (1995). Soil physical property changes after skidder traffic with varying tire widths. Journal of Forest Engineering, 41-50. Miller, R., Scott, W., & Hazard, J. (1996). Soil compaction and conifer growth after tractor yarding at three coastal Washington locations. Canadian Journal of Forest Research, 225-236. The effects of ground-based harvesting on coastal British Columbia soils                                                    16   Mitchell, J. (2009). Soil productivity on rehabilitated roads, skid trails, and landings . Vancouver: Forest Engineering Research Institute of Canada. Morford, S., Moshenko, D., Proteau, E., & Thomson, A. (2004). An assessment of the reseach and technical information needs of forestry operators in British Columbia. Vancouver, British Columbia. Province of British Columbia. (2013). About the FRPA resource values. Retrieved March 20, 2013, from FRPA resource values: http://www.for.gov.bc.ca/hfp/frep/values/index.htm Rab, A., Bradshaw, J., Campbell, R., & Murphy, S. (2005). Review of factors effecting disturbance, compaction and trafficability of soils with particular reference to timber harvesting in the forests of South-west Western Australia. Kensington, Western Australia. Rogers, R., & MacDonald, A. (1989). Ground skidding second growth timber in Coastal British Columbia: A case study. Vancouver: Forest Engineering Research Institute of Canada. Rollerson, T. (1990). Influence of wide-tire skidder operations on soils. Journal of Forest Engineering, 1913-2200. Senyk, J., & Craigdallie, D. (1997). Ground-based wet weather yarding operations in coastal British Columbia: Effects on soil properties and seedling growth. Victoria: Canadian Forest Service. Sheridan, G. (2003). A comparison of rubber-tyred and steel-tracked skidders on forest soil properties. Australian Journal of Soil Research, 1063-1075. Sidle, R., & Drlica, D. (1981). Soil compaction from logging with a low-ground pressure skidder in the Oregon Coast ranges. Soil Science Society of America Journal, 1219-1224. Stoilov, S. (2007). The improvement of wheel skidder tractive performance by tire inflation pressure and tire chains. The Croatian Journal of Forest Engineering, 137-144. Thibodeau, F. (2002). An alternative ground-skidding method for reducing soil disturbance on steep slopes. Vancouver: Forest Engineering Research Institute of Canada. Williamson, J., & Nielson, W. (2000). The influence of forest site on rate and extent of soil compaction and profile disturbance of skid trails during ground-based harvesting. Canadian Journal of Forestry Research, 1196-1205. Wilma, D. (2003, March 1). John Dolbeer invents the donkey engine and revolutionizes logging in 1881. Retrieved from HistoryLink.org: http://www.historylink.org/index.cfm?DisplayPage=output.cfm&File_Id=5331  

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