| | Cutblocks | Native Shelterbelts and Buffer Strips | Roads, Landings and Skid Trails | Surface Disturbance and Season of Logging | Utilization Standards | Debris Management
Cutblocks
The size and location of cutblocks will depend on your goal for the land and on a variety of other factors such as harvesting method and conservation issues.
Woodlot Management
In sustained yield timber management, mature timber is usually removed in two or more sequences of harvesting depending on the harvesting method.
For clearcutting, as a general rule, you should not clear more than half of the mature forested area at any given time. If you remove all the best timber in the first pass, then subsequent harvest sequences will be less economically viable. The uncut area should not be harvested until the vegetation on the original cutblocks has grown sufficiently to protect the watershed, guard against soil erosion and provide cover for wildlife. Forest cover greater than 3 m (10 ft) in height will achieve this.
With the selection method, you may be able to harvest a larger portion of the area at once without having as much impact. The other partial harvest systems (shelterwood and seed tree cuts) ultimately remove all the mature forest from a given area; therefore, these methods should employ the same general rule as clearcuts.
To minimize the effect of harvesting, keep cutblocks as small as possible. Bear in mind, however, that there are trade-offs between the size of individual cutblocks and the road or trail system required to access them. Roads significantly affect soil and water resources because they expose bare soil and may alter surface drainage patterns. Larger cutblocks may have less impact than smaller ones if you require less road to access them.
Some other considerations for designing cutblocks are as follows:
- Cutblock boundaries should follow natural terrain features, contours and timber types (similar species and age).
- Windfirm cutblock boundaries will reduce the effects of cutblocks on aesthetics, soil erosion and sediment loads in the watershed.
- Spruce blocks for natural regeneration by seedfall from adjacent stands should be laid out in narrow strips perpendicular to the prevailing winds. No part of the block should be more than 150 m (490 ft) from the seed source.
- Irregular boundaries will provide better wildlife habitat than straight boundaries (more edge and reduced line-of-sight).
- Leaving a few standing trees and old fallen logs will improve wildlife habitat. In particular, trees with existing nests should be identified and protected.
- Young, healthy trees should be protected from damage during harvesting. These trees can form the next crop, saving time and costs for reforestation.
Conversion to Agricultural Production
The size and shape of cutblock created when agricultural land is developed are determined by the pattern of arable soil, desirable size for each operating unit (field or pasture) and topographic constraints such as wetlands, watershed boundaries, watercourses or steep slopes. Where topography is not a limiting factor and the soils are arable, you may want to remove most of the forest cover in one harvest. This will increase the risks of soil erosion and flooding. Well-planned buffer strips and/or natural (native) shelterbelts can help reduce these risks.
Native Shelterbelts and Buffer Strips
Shelterbelts improve crop yields by reducing wind erosion and soil moisture loss, and by trapping snow for increased spring soil moisture. They also provide habitat and travel corridors for wildlife.
Native shelterbelts must be wide enough to provide reasonably continuous tree cover. A width of at least 5 to 10 m (15 to 30 ft) is usually required. Consider leaving an untilled area of equivalent width beside the shelterbelt. By encouraging natural regeneration in this area, you can ensure continued shelter when the trees in the original strip become over mature.
The area where crop yields benefit from a shelterbelt is a function of shelterbelt height. At a distance of about 20 times the height of the shelterbelt, conditions are similar to an unsheltered field. If trees in the shelterbelt are about 15 m (50 ft) in height, one shelterbelt every 300 m (1,000 ft) will ensure that all the cleared area receives some benefit.
Treed buffer strips along watercourses or other riparian areas create a barrier to equipment traffic, preventing soil disturbance. A cover of duff and vegetation protects against erosion and helps filter runoff before it enters the watercourse.
Buffers on riparian areas also provide important habitat and travel corridors for wildlife and enhance fish habitat by shading the watercourse. Wider buffer strips are recommended for larger water bodies because more wildlife is concentrated there.
Large permanent streams (streams with an unvegetated channel width greater than 5 m (15 ft)) should have undisturbed buffers at least 60 m (200 ft) wide on both sides of the streams. Smaller permanent streams should have 30 m (100 ft) buffers.
Ephemeral streams are vegetated channels or swales where water flows only during and immediately after rainfall and snowmelt. They can provide significant amounts of water (and sediment) to larger streams. Treed buffers are not required for ephemeral streams but the understorey vegetation should be left as undisturbed as possible.
Intermittent streams have well-defined channels that flow during wet periods but may dry up during drought. Intermittent streams should be treated as ephemeral streams or as small permanent streams depending on the slope and stability of their banks and adjacent soil conditions.
Buffers at least 100 m (300 ft) wide should be left along the shores of lakes greater than 4 ha (10 ac) in size. Seepage areas do not require buffer strips but heavy equipment should stay out of these areas except during dry or frozen periods.
Some additional guidelines for buffer areas are:
- No heavy equipment should be permitted within the buffer.
- Adjacent trees should be felled away from the buffer.
- No slash or other debris should be allowed to enter the watercourse; if debris does enter the watercourse, it must be removed immediately without equipment entering the watercourse.
- Where possible, breaks in topography should be used to define the boundaries of the buffer.
- If trees are not windfirm, a wider buffer may be required.
- Feathered edges (selectively logged transitions between clearcut areas and undisturbed buffers) may help reduce windthrow.
Selective logging within shelterbelts and buffers may be appropriate under certain conditions. Careful removal of diseased trees, over mature trees or trees susceptible to windthrow is acceptable provided the integrity of the shelterbelt or buffer is maintained. Fell such trees away from the shelterbelt or buffer. Winch or pull from the edge so heavy equipment does not enter the protected area. Take care that neither felling nor skidding damages other trees within the area.
Roads, Landings and Skid Trails
Wherever possible, roads, landings and skid trails should be located on level, well-drained areas within the cutblock. Avoid unstable areas, water source areas, springs and seepages. Minimize cuts and fills by following natural benches, moderate slopes and ridges.
Roads, landings and other bared areas should not be permitted within 100 m (300 ft) of the high water mark of lakes or permanent streams, within 30 m (100 ft) of intermittent streams, or within ephemeral streams or water source areas. Exposed soil surfaces should be revegetated as soon as possible. Do not allow runoff from bare areas to flow directly into watercourses. Carefully planned water bars (cross ditches) can be used to disperse runoff from skid trails and roads into undisturbed, vegetated areas.
Avoid stream crossings where possible. If a crossing is necessary, it should:
- be located on stable soils;
- allow for direct, gentle approaches;
- be at right angles to the watercourse;
- be located where the channel is well-defined, unobstructed and straight; and
- be at a narrow point along the watercourse.
At approaches to stream crossings, remove ground vegetation and duff only from areas requiring earthwork. Revegetate bared areas as soon as possible. Avoid disrupting the stream banks or channel, and keep debris out of the stream.
Surface Disturbance and Season of Logging
Logging should be conducted in a way that minimizes soil disturbance and water flow over exposed soil. Minimizing disturbance helps maintain a high infiltration rate and reduces the risk of erosion. However, if logging objectives include creating a seedbed for natural regeneration or broadcast seeding of forages, a controlled amount of surface disturbance may be desired.
Winter logging usually results in less disturbance of surface vegetation and the duff layer. To reduce surface disturbance during summer logging, choose low impact equipment and avoid travel on erodible soils or steep areas. Slopes over 45 per cent are usually considered too steep to harvest with conventional equipment; slopes over 30 per cent may require specially planned skid trails.
Soil compaction can reduce site productivity for many years after logging, particularly on clay or silt soils. Moist soils are more prone to compaction than dry soils. Logging when soil is frozen will minimize the risk of compaction. Summer logging is acceptable on well-drained soils but it may need to be temporarily halted during wet weather. Avoid or halt activities that cause ruts.
Aspen stands logged during winter will sucker more aggressively than those logged from mid-June to late August. Whether you wish to discourage or encourage aspen regeneration will influence the choice of logging season.
Utilization Standards
Utilization standards refer to the amount of the standing tree that is used for commercial purposes. These standards are important for two reasons:
- you don't get paid for what isn't used, and
- you may incur greater costs and site disturbance to remove debris left behind.
Utilization standards vary from species to species and according to the end use of the logs. In general, trees greater than 15 cm (6 in.) in diameter at the stump and more than 4.88 m (16 ft) in length to a top that exceeds 11 cm (4 in.) in diameter can be utilized. Logs with more than 50 per cent rot are usually left behind. When the butt section contains more than 50 per cent rot, 60 cm (2 ft) sections should be bucked off until a section containing less than 50 per cent rot is found. Long butting (cutting sections longer than 60 cm) can result in usable pieces being wasted.
Aspen and most coniferous species (except tamarack) are widely used by the forest industry. Use of black poplar, white birch and tamarack is limited to specialty users. If you are removing all the trees but cannot find a market for some species, consider having the unmerchantable species decked for use as firewood. Otherwise they may contribute a significant volume to the debris that must be removed.
The use of all merchantable stems will minimize the amount of debris left after logging. A high price per unit of timber may appear attractive; however, this price may not yield the best return per unit of area if the logger takes only the best timber. You are paid for a lower volume of timber and are left with more debris to clean up.
A good logger can keep stump heights to 30 cm (12 in.), and is often able to keep them lower than this standard unless the trees are very large. However, the best stump height will depend on the subsequent land use. Low stumps enhance livestock and equipment access but are difficult to remove with conventional land clearing equipment. Higher stumps provide better leverage for uprooting with clearing equipment, but they will impede access for years after logging if they are not removed. Uprooting stumps greatly increases site disturbance and is expensive. Determine whether you require complete removal of all stumps and adjust the stump height accordingly.
Debris Management
Logging debris (branches, tree tops, stumps and unmerchantable stems) interferes with equipment access, impedes livestock movement and may constitute a fire hazard requiring control measures pursuant to the Forest and Prairie Protection Act. On the other hand, the same debris can provide some protection from wind and water erosion and may provide shelter for small seedlings.
Eliminating all logging debris from a cutblock can be expensive. Uprooting stumps and pushing slash into piles disturbs the soil which increases the risk of erosion. Site disturbance and treatment costs increase with the area treated and the amount of debris handled.
Unless debris is excessive, spreading it evenly across the cutblock and/or crushing it with machinery is usually adequate for forestry purposes. In fact, this may be more desirable than removing the debris because the decomposing debris slowly releases nutrients back into the soil. For most other purposes, the debris should be removed.
Depending on the logging method, debris may be dispersed throughout the block or concentrated at roads and landings. Hand felling followed by topping and limbing at the stump results in slash dispersed throughout the cutblock. This practice is common in partial cutting or pine clearcutting where logging slash contains seed necessary for natural regeneration. On other clearcuts, a more common practice is to skid whole trees to roadsides or landings where they are topped and delimbed. This results in more debris near roads and landings, and less spread around the cutblock.
Debris is pushed into piles for disposal by burning. Usually a brush rake is used to pile debris. It has a toothed blade which moves debris but leaves soil relatively undisturbed. A straight blade (no teeth) can also be used, but the piles usually have more dirt and are more difficult to burn. (A straight blade may be effective for bunching heavy accumulations of slash such as those near roadsides.) Piles for burning should be located on mineral soil, not organic soil.
Attempting to burn logging slash without piling it first is not recommended. A fire intense enough to completely burn large debris will also degrade the site by destroying soil organic matter. The risk of the fire escaping is also significant.
Burning of any kind may require a burning permit from the local authorities.
Source: Conservation and Logging on Private Land in Alberta Agdex 581-2. |
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