Ministry of Forests
Forest Practices Branch
Procedures
Manual
SITE PREPARATION
Mechanical
1 Background
Many environmental factors affect seedling performance in planting spots, or in
seedbeds prepared for natural or artificial seeding. Of prime importance are
temperature, moisture, soil aeration, soil physical characteristics (texture and
structure), soil nutrients, light, vegetation, frost, insects and diseases, and small
damaging mammals. Changes in one of these factors may affect others, causing a
chain reaction. It is, therefore, important to recognize the interaction of cause and
effect relationships. The following is an overview of some of the important
relationships.
1.1
Soil Temperature
Low soil temperature limits the survival and growth of tree seedlings in the cool
climates of northern latitudes and upper elevations. The forest floor commonly builds
to a considerable thickness because low temperatures reduce the rate of decomposition. The soil beneath a thick forest floor is insulated from the sun’s rays and
therefore remains cool. Removal of the forest floor to expose mineral soil allows the
soil to warm up. Roots grow faster in warm soil than in cold soil and also absorb
nutrients more readily. In cold climates, the lower roots of planted seedlings may die
10 to 15 cm below the soil surface.
Various methods of site treatment can remove the surface duff layer, however,
excessive scalping should be avoided (see “5, Site Degradation,” this section).
Although the effects of exposing mineral soil are generally beneficial, exposure
of fine-textured mineral soil can result in frost heaving and reduced availability
of nutrients.
1.2
Soil Water
In warm, dry climates, such as the Interior Douglas-fir Zone, vegetation depletes soil
water so that newly planted seedlings are exposed to drought stress. By controlling
competing vegetation, more soil water is available to the tree seedlings.
Scarce soil water may be conserved in dry climates by creating sunken planting
spots. Snow and rain will accumulate in these depressions.
In wet climates, or in water accumulating habitats in drier climates, excess soil water
occupies space in the soil which should be occupied by soil air. Raised planting
spots, subsoiling and drainage ditches can increase the amount of soil air around
seedling roots. Roots require adequate oxygen in the soil to grow and to absorb water
and nutrients, therefore, early performance can be enhanced by providing a welldrained planting spot.
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Excess soil water can also exacerbate problems of low soil temperature, as wet soil
requires more energy to warm than well-drained soil.
1.3
Soil Air
To grow and absorb nutrients, roots require adequate oxygen in the soil. Pore space
must be sufficient for roots to grow and penetrate the soil, and for water to filter
through. Compacted soils are more poorly aerated and also have a greater risk for
runoff and surface erosion. Site preparation treatments, such as mixing and
subsoiling, tend to loosen the soil and increase soil air.
1.4
Soil Texture and Structure
Both very fine-textured and very coarse-textured soils can have adverse effects on
seedling performance. Seedling roots grow through compact, fine-textured soils with
difficulty. When the planting spot is exposed, fine-textured soil, access to soil water
and nutrients may be restricted and the risk for frost heaving is increased.
Conversely, very coarse-textured soils drain rapidly so that seedlings may suffer
moisture stress. Very coarse-textured soils also generally lack adequate amounts of
soil nutrients.
A compact layer close to the soil surface restricts the volume of soil seedlings can
use. Consequently, care should be taken not to reduce further the effective rooting
depth of shallow soils by deep scalping. To allow deeper root penetration, the
compact layer can be broken up by subsoiling. This will also improve drainage, and
may relieve the problem of a high water table restricting root penetration.
1.5
Soil Nutrients
In most soils, the surface organic matter and the uppermost mineral soil horizon
contain most of the nitrogen used by seedlings. Removal of these horizons by
mechanical site preparation treatment leaves the nutrient-poor subsurface soil as the
growing medium. In medium to moderately coarse-textured soils, where root growth
is not restricted, the increase in soil temperature resulting from exposure of mineral
soil can more than make up for initial nutrient deprivation. With increased soil
temperature further contributing to growth, roots can readily extend to the nutrients
of surface layers at the edge of scalped patches.
However, in fine-textured soils roots cannot quickly reach the nutrients in
surrounding undisturbed soil and overall seedling growth is restricted. In this case, or
when scarce nutrients overlay a coarse-textured soil, a treatment such as mixing,
which retains soil nutrients in close proximity to the seedling roots, is preferred.
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Procedures
Manual
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In soils where organic matter and nutrients extend deeper into the soil profile,
removal of the uppermost horizons by site treatment may have little adverse effect on
nutrient supplies.
1.6
Competing Vegetation
In wet climates and habitats, tree seedlings may be smothered when surrounding
shrubs, herbs, grasses and ferns are flattened by snow. Competing vegetation may
also reduce the heat and light available to seedlings to suboptimal levels. In drier
climates, competing vegetation deprives seedlings of soil water. When attempting to
control competing vegetation by scalping surface soils to remove plant roots,
consideration should be given to soil texture.
In some cases, a competing vegetation problem may be introduced to a site where
treatment stimulates rhizomes or creates seedbed at an inappropriate time of the year.
1.7
Light
Tree seedlings can be deprived of adequate light by surrounding competing
vegetation. Research has shown that seedling growth is retarded at levels below 50%
shading. Removal of shading vegetation is therefore an important objective of site
treatment, but should be carried out using methods appropriate to the site.
1.8
Air Temperature
Frost during the growing season can be harmful to seedling performance. Buds may
be killed and growth distorted or set back. Frost later in the season can damage
succulent growing shoots causing appreciable growth reduction. Less damage by
frost may occur where seedlings are growing in exposed mineral soil or on raised
planting spots (mounds). Seedlings growing on raised planting spots may escape frost
damage if the pool of cold air in a frost pocket is shallow. Sufficient heat may be reradiated by exposed mineral soil during the night to keep seedlings warm enough to
avoid the effects of frost. Small patches of exposed mineral soil will not re-radiate
sufficient heat to affect frost damage. Planting spots with partial or no disturbance to
the duff can be very susceptible to growing season frosts, especially in low lying frost
pocket locations. Frost pocket locations treated with herbicide that removes
surrounding vegetation without exposing mineral soil can be especially prone to
growing season frost damage. Seedlings planted on mounds may be more susceptible
to chinooks and to damage from early spring frosts.
High temperature at the soil surface may damage the stems of the tender germinants
of natural regeneration in hot climatic zones. Some species are more susceptible to
damage than others. The succulent stems of recent germinants are most susceptible to
damage by high soil surface temperatures.
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High temperatures combined with low relative humidity can desiccate seedlings even
if moisture is available in the soil. When the rate of transpiration is faster than the
rate at which the seedling can replenish the moisture, the seedling will suffer drought
stress. Non-living shade, such as cull logs, stumps or shade cards, unlike shade from
other plants, cools the seedling without depleting soil moisture.
1.9
Insect, Disease and Animal Damage
The spruce weevil (Pissodes strobi) can have a devastating effect on established
spruce plantations. This weevil prefers vigorous, open-grown saplings and causes
terminal dieback of at least two years’ growth. Since some protection may be
afforded by a canopy of hardwoods, site preparation methods that completely exclude
a hardwood canopy can make spruce susceptible to weevil damage. Contact the
regional entomologist to identify where a hazard of spruce weevil exists.
Phellinus and armillaria root rots spread when the roots of the newly established
forest contact infected stumps of the previous stand. Removal of infected stumps has
been used to control re-infection of the new stand. However, stump removal is
expensive and caution must be taken to avoid unacceptable site disturbance.
Mistletoe on residual Douglas-fir or lodgepole pine may be controlled by a site
preparation method that damages the infected residual seedlings sufficiently for them
to desiccate and die and provides sufficient soil disturbance to allow subsequent
regeneration from pine cones on the ground. Drum choppers are suitable for this
treatment.
On sites with sufficient vegetation cover to protect the snowshoe hare from predators,
browsing damage may delay indefinitely regeneration of species such as interior
spruce. This is also true for mice and voles that girdle seedling stems. Vegetation
cover reduction through site preparation gives the seedlings time to grow to a height
where small mammal damage is less inhibiting. Caution must be used when
prescribing row-type treatments, such as disc trenching, which can actually increase
browsing by ungulates and trampling by domestic cattle. Seedling damage may also
increase in the vicinity of slash piles, which provide cover for small mammals.
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Procedures
Manual
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Mechanical
2 Methods of Microsite Formation
Mechanical treatment can readily modify surface organic and soil layers of many
forest sites. Changes in these layers can influence seedling performance (survival and
growth). Additionally, the rearrangement of slash loads and the preparation of
planting spots can reduce hazards and improve planter access and reduce the time
taken for planting spot selection, thereby reducing costs.
Surface layers can be modified by scalping, mixing, and inverting. Suitability of each
method will vary according to depth and quality of organics, soil texture, and other
factors limiting seedling growth.
Seedbeds or planting spots formed by these methods may be level, raised above, or
depressed below the original ground level. Also, treatments may cover the whole site,
be in continuous or intermittent strips, or in discontinuous patches or spots.
2.1
Scalping
Removal of excessive, loose surface organic layers exposes the underlying rich
decomposed organic layers and mineral soil. Exposed mineral soil warms more
rapidly and reaches higher subsurface temperatures than does undisturbed soil. In wet
climates where high surface temperatures threaten stems of tender germinants,
exposed mineral soil conducts heat down, away from the soil surface.
On exposed mineral soil, seedlings are initially deprived of nutrients, because the
fertile surface layers are removed by scalping. However, when scalping is conducted
on appropriate sites, seedling roots stimulated by increased soil temperature, extend
quickly beyond the scalped area to reach nutrients in surrounding mixed or
undisturbed areas. The optimum area of exposed mineral soil varies with site.
2.2
Mixing
Mixing incorporates surface organic layers with the underlying mineral soil, making
nutrients available to newly planted seedlings. The surface of well-mixed soils is
essentially mineral in character, which enhances soil temperature much as scalping
treatments do.
For fine-textured soils, mixing may be more satisfactory than scalping. Mixing
organic matter with the mineral soil creates planting spots which are not as compact,
so the problem of restricted root growth is avoided. If sufficient amounts of organics
are incorporated, seedling susceptibility to frost heaving is also reduced.
Competing vegetation can be controlled by intense mixing, which is most easily
achieved on fine-textured, relatively stone free soils. Partial or coarse mixing is
suitable only where there is little competing vegetation. Mixing rarely eliminates
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vegetation for prolonged periods and may result in a change from one competing
vegetation complex to another.
Where the forest floor (duff) is deep, mixing may not incorporate sufficient mineral
soil. In such cases, the risk of seedling dessication is increased.
2.3
Inverting
Planting spots consisting of overturned surface organic matter covered by mineral soil
may provide several potential benefits for seedlings. Seedling roots can proliferate
with the warm soil temperatures provided by the exposed mineral soil cap. Also,
seedlings have immediate access to nutrients in the buried surface organic layers.
If deep enough, the mineral soil capping suppresses the resprouting of competing
vegetation and retains moisture. Shallow mineral soil capping, on the other hand, may
not suppress competing vegetation and mounds are at a greater risk of drying out.
Mineral soil cappings are prone to desiccation during dry periods and, therefore,
seedlings with roots only in the cap may experience moisture stress. Seedlings
should be planted deep with roots extending well into the humus layer. While the
use of long-rooted seedlings has been tried to alleviate this potential problem, the
logistics of growing and planting proved to be infeasible.
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3 Elevation of Prepared Planting Spots
3.1
Raised Planting Spots
Raised planting spots improve drainage and aeration on wet sites and result in
improved seedling performance. Well-drained soil warms faster than waterlogged
soil. In zones with cool temperatures, the enhanced soil temperature of raised
planting spots may improve seedling performance even on mesic sites. In
comparison, raised planting spots may desiccate more than planting spots level with
the original soil surface on sites with seasonal moisture deficits.
Raised planting spots may be formed as discrete mounds, as continuous or
discontinuous ridges, or as berms.
While all types of raised planting spots enhance soil temperature and aeration, their
effectiveness in providing adequate soil water, nutrients, vegetation control and light
varies with forest site series.
Inverted Humus Mounds or Ridges with Mineral Soil Capping
Mineral soil capped inverted humus mounds or ridges are particularly useful when
soil textures are fine. Seedling roots proliferate in the mineral soil/humus interface
because soils are friable, warm, and well supplied with nutrients.
It is important that the configuration and position of the mound is conducive to roots
growing beyond the raised area. Roots of some species experience difficulty in raised
planting spots with vertical sides, and in mounds surrounded by scalped soil. Trees
with root systems confined to a ridge and extended in only two directions are
susceptible to blow down.
When deep mineral soil cappings are required to control competing vegetation, it is
important that seedling roots are planted well into the inverted surface organic matter,
even if this means planting seedlings below the root collar. Seedlings should not be
planted close enough to the edge of the mound to be shaded by surrounding
vegetation or susceptible to snow press.
The double organic layer beneath the mineral soil cap can act as an impediment to
planting seedling roots straight and deep. J-rooted seedlings with root systems
confined to the mineral soil capping are prone to drought stress.
Mineral Mounds
Heaps of mineral soil dropped on bare mineral soil may be favorable for seedling
growth in dry but cool climates. Soil temperature is enhanced, but the absence of
surface organic layers below the mound favors the transfer of moisture from the
ground to the mound. When the mineral soil in the mound is medium-textured (loam
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to sandy loam), root extension is promoted and nutrients (especially nitrogen) from
undisturbed soil surrounding the mound may be reached soon after planting. Mineral
soil on mineral soil mounds is not appropriate on fine-textured soils.
Mixed Humus and Mineral Soil Mounds
Raised planting spots consisting of mineral soil and humus elevate soil temperature,
avoid possible problems of capillary discontinuity, improve aeration, and provide
accessible nutrients in humus fragments. Where competing vegetation is not a
problem, coarsely mixed, raised planting spots can be favorable for seedling
performance. However, coarse mixing does not generally control vigorous
competing vegetation.
Peat Mounds and Ridges
Creating mounds or ridges in deep peat soils may be the only way of increasing soil
temperature, improving drainage, and controlling competing vegetation. The
frequency of chlorotic seedlings during the first few years after planting suggests that
peat mounds have a poor nutrient status. However, as the peat mineralizes, seedling
color improves. Seedlings should be planted deeply to avoid the possibility of
drought stress.
For further information on raised microsites, refer to the video Mounding: A Site
Preparation Technique in Review [1990], FRDA Memo 100 [Haeussler 1989],
FRDA Memo 160 [Coates and Haeussler 1990], FRDA Report 178 [von der Gönna
1992], and FRDA Report 105 [Örlander et al. 1990].
3.2
Depressed Planting Spots
Planting spots below the general soil surface level are generally favorable for
seedling performance in dry zones or sites. Snow and rainfall will accumulate in
depressions and can extend the period of moisture availability. Seedlings may also be
sheltered from desiccating winds.
Depressions in fine-textured soils may accumulate moisture and result in
waterlogged seedlings.
3.3
Level Planting Spots
The mineral soil covered inverted humus planting spot, more or less level with the
surrounding terrain (e.g., a plowed field), is a favorable planting spot for relatively
dry climates (e.g., BWBSmw1). Seedlings are not as exposed to drying winds as
when they are planted on raised spots and planting may be easier.
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4 Continuity of Treatment/Planting Spots
Planting spots may be formed by: treatments that cover the whole site (such as
windrowing slash); treatments that are in continuous or intermittent strips; or,
treatments in discrete patches or spots. The target number of plantable spots/ha and the
desired spacing must be considered, especially when using intermittent strip or spot
treatments. For row-type treatments (e.g., disc trenching, Bräcke patch), fixed
equipment settings or difficult site conditions may make uniform spacing impossible.
Under such conditions, the total number of prepared planting spots may still be created
if “in-row spacing” is adjusted to compensate for wider spacing between rows.
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5 Site Degradation
The role of site preparation in British Columbia’s reforestation program has increased
significantly in the past several years. During the period from 1981 to 1990 over
1.2 million hectares of Crown forest land were site prepared. The diversity of
forest conditions and management objectives has lead to a wide variety of site
preparation methods.
All site preparation disturbs the site to some extent. Soil disturbance can range from
beneficial to detrimental depending on the nature of the site and the severity and
extent of the disturbance. Site disturbance that leaves the site more suitable for
regeneration and that does not impair the site productivity is clearly beneficial.
Disturbance from site preparation is considered to be excessive when the long-term
site productivity is lowered resulting in diminished stand growth. The application of a
site treatment method to achieve early growth and survival should not be at the
expense of long-term productivity.
When considering long-term productivity, mechanical site preparation (MSP) is
particularly topical. The recent increase in MSP on sites which have traditionally
been treated by fire has heightened the concern for site productivity.
5.1
Guidelines
At present, soil conservation guidelines for harvesting are in place on the coast and in
the interior. Under the Forest Practices Code, guidelines are covered by the following
guidebooks: Soil Conservation, Site Preparation, and Hazard Assessment Keys for
Evaluating Site Sensitivity to Soil Degrading Processes. Guidebooks for soil
conservation surveys, fire management and rehabilitation are currently under
development.
5.2
Rehabilitation
Soil compaction, either naturally occurring or introduced by harvesting, may exceed
optimum levels for forest growth. Site preparation has long been seen as a means of
reducing compaction. The effectiveness of ripping as a means of alleviating soil
compaction depends upon the type of ripper being employed, as well as the type of
soil being treated. Winged subsoilers are more effective in reducing compaction than
standard rock rippers or brush rakes. Generally, ripping is more effective on coarsertextured, non-cohesive soils. On sites where organic matter has been severely
depleted, the benefits of subsoiling are often temporary and nutrient levels remain
low. In such cases, subsoiling must be supplemented by some form of organic matter
management, such as seeding legumes.
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Soil density may also be reduced by other methods of site preparation, which mix
organic matter with mineral soil. The Madge rotoclear and Eden relief bedding plow
have both provided excellent mixing and compaction reduction, however, operational
use is limited by site and cost.
For detailed information on rehabilitation, see Appendix 2, Selected References.
Guidelines on rehabilitation are being developed.
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6 Prime Movers
Once a site preparation method has been chosen (e.g., spot mixing), the appropriate
implement and prime mover must be selected. Generally, prime movers such as
wheeled skidders, forwarders, crawler tractors, or excavators are used, however, farm
type tractors and flex track equipment (FMCs) have also been used. The type of
prime mover selected will usually depend upon limiting/restricting site factors,
special requirements of the site preparation implement chosen and cost. Restricting
site factors include slope, ground roughness (including frequency and size of
obstacles, and frequency and size of stumps), soil bearing capacity, slash loading, and
evenness of terrain. Special requirements of the site preparation implement include
factors such as drawbar pull requirements, hydraulic requirements, weight and
balance considerations, travel speed limitations, and special attachments to raise and
lower implements for turning or travel between treatment areas.
In the past, skidders or crawler tractors were simply taken from harvesting operations
and used for prime movers in site preparation. This was most often the case for
contractors who logged in the winter and did site preparation in the summer.
Unfortunately, due to differences in the nature of the duty cycle, this was often a
costly and unsuccessful decision. The site preparation duty cycle differs from
harvesting in the following respects: necessity to cover 100% of the ground,
continuous operation under load, heavy loads with high peak forces, frequent end-ofpass turning, on-road travel between sites, constant start and stop operation, push/pull
requirements, slow steady working speeds, and necessity to carry a load. Common
problems included overheating and not having sufficient power at low speeds.
Contractors dedicated to site preparation have dealt with many of these problems by
purchasing equipment with specifications suited for site preparation work. Duty cycle
considerations for prime movers are outlined in the following sections.
6.1
Skidders
Wheeled skidders are the most common prime mover for site preparation. They are
generally used to pull light implements but can also be used in heavier applications
such as powered disc trenching. Skidders are limited to relatively easy terrain and
light slash conditions. Some contractors have modified their skidder blades or have
replaced them with light rakes for clearing and aligning slash. It is recommended that
skidders be limited to slopes of 15% or less for contouring and 25% for downslope
operation. Skidders equipped with wide tires have greater stability on side slopes,
however, they are more prone to slipping when slash is wet. Wide tires also cause
increased wear on the drive train and are expensive to purchase. Good chains are
essential and they must be checked regularly to ensure that they are tight.
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John Deere 740 skidder with V-rake and powered
disc trencher.
Skidders used for site preparation often have extra oil coolers for their hydraulic
system and have transmissions designed for operation at slow travel speeds. Specialty
skidders, such as the Franklin and SK250, have been designed specifically for site
preparation.
6.2
Forwarders
Forwarders have also been used as prime movers for site preparation. Forwarders are
more powerful than skidders and are better designed for carrying a load (such as an
auxiliary engine). Six- or eight-wheel drive forwarders having one or two sets of
bogies generally have higher floatation than skidders equipped with standard tires.
Forwarders also offer greater stability on slopes, and with their bogies, will ride over
obstacles more easily than skidders, thereby reducing the jarring to the operator.
Forwarders are more expensive to operate than skidders and have therefore seen
limited application.
Rottne SMV Rapid with powered-disc trencher.
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6.3
Procedures
Manual
Ministry of Forests
Forest Practices Branch
Crawler Tractors
Crawler tractors are better-suited for “pushing” than skidders and in the past have
been used primarily for piling heavy accumulations of slash or for blading treatments.
Recently, they have been used for disc trenching operations where the need to part
heavy slash or to traverse rough terrain has called for extra power. Crawlers can
contour on slopes up to 35% and can work downhill up to 45%. However, crawlers
are slower and cost more to operate than skidders.
International TD20 crawler with V-plow and
powered-disc trencher.
6.4
Excavators
Excavators are the most versatile of all prime movers. Unfortunately they are the
slowest and most expensive to operate. Excavators are used for spot treatments on
broken terrain or slopes, and for mounding or ditching on wet sites. Excavators can
work on slopes up to 50%, and can treat small steep pitches given access such as skid
trails. Excavators can be equipped with a variety of attachments and offer complete
operator control over microsite creation and spacing. When choosing an excavator
for site preparation, ensure that it has been properly guarded for bush applications
and that it is equipped with the proper track pads and grousers for the job.
Hitachi Ex 200 excavator.
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For additional information on excavators and their use in silviculture, see the video
Excavators: Silvicultural Attachments and Treatments [1993].
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7 Site Preparation Implements
A wide range of site preparation implements is available. Each implement can
prepare one or more types of planting spot or seedbed. The first step in choosing the
most appropriate implement is to decide what site factors should be modified to
produce the optimum planting spot or seedbed for the ecosystem which must be
treated. Having identified what is needed, an implement that can prepare the required
planting spot can then be selected. See Appendix 3, Equipment Comparison: Costs
and Productivity, for a listing of comparative costs of many implements.
7.1
Brush Blades and Rakes
Brush blades and rakes were once the most common implements for preparing
scarified strips. The recent availability of more specialized implements has lead to
brush blades being used primarily for the re-arrangement of slash for hazard
abatement (windrowing or piling and burning), and to improve planter access where
slash loading is very heavy.
Standard brush rake.
When pushing slash, care must be taken to float the blade above the ground to avoid
creating excessive soil disturbance. Tilting (4- or 6-way) blades are especially useful
on sloped ground. The use of retractable-toothed rakes can reduce the amount of soil
disturbance associated with windrowing slash. These rakes have also been used to
break up and knock down slash and create seedbed for natural regeneration. When
slash loads are very heavy, brush rakes can be used to facilitate subsequent passage
of more microsite-specific implements.
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FMC with 6-way slash rake.
Eden rake.
Raumfix slash rake.
For additional information on blades and rakes, see Maxwell [1989] and FRDA
Handbook 002 [Coates and Haeussler 1987].
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Excavators equipped with wide rakes have also been used for windrowing slash.
Excavators are a good choice for sensitive sites as a swath the width of the reach of
the boom on either side can be prepared in one pass.
Five-tine excavator slash rake.
For additional information on excavator rakes, see FERIC Technical Note TN-180
[von der Gönna 1992].
7.2
Front-Mounted V-Blades and V-Rakes
Front-mounted V-blades and V-rakes can be used as a first-pass treatment to clear
aside slash and facilitate operation of a microsite-specific implement, or to improve
planter access. The advantage of V-blades compared to brush blades is that the
forward movement of the prime mover need not be interrupted to unload the blade.
On medium to relatively coarse-textured soils, V-blades can be used to remove
competing vegetation. The resulting strips of exposed mineral soil may remain free
from vegetation for some years. V-blades are also useful for the reduction of deep
duff layers. V-blading has the potential to cause significant site degradation and,
therefore, it should be used only with great caution, particularly on fine-textured
soils.
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Sanders V-blade.
7.3
Rear-Mounted Plows and Rippers
In wet areas where summer access is poor, rear-mounted plows, capable of digging
deeply, can be used on frozen ground. A deep trench and roughly overturned berm
are formed. On wet sites in cold climates, the trench may not provide suitable
planting spots. The berm, being better drained and warmer, forms favorable planting
spots unless the site has the potential of developing dense competing vegetation.
On dry sites, the trench formed by smaller rear-mounted plows can provide favorable
planting spots because scarce soil water is conserved in microsites below the general
ground level.
Rear-mounted ripper plow.
Agricultural breaking plows provide overturned furrow slices which have a mineral
soil layer covering the inverted organic matter. Seedlings generally perform well in
such planting sites. When furrow slices are laid one in contact with another,
vegetation may be controlled for several years.
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Triple-bottom breaking plow.
Winged subsoilers are used to break up compact subsurface horizons to improve
drainage and to increase effective rooting depth. Subsoilers are limited by slash and
stumps, and are generally limited to landing and skid road rehabilitation.
Winged subsoiler.
Close up – winged subsoiler.
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For additional information on the winged subsoiler, see FERIC TN-146 [De Long
et al. 1990] and FERIC Field Note No. Silviculture-36 [Rasmussen 1991].
7.4
Drag Scarifiers
Drag scarification is used primarily on lodgepole pine sites to create seedbed,
distribute cones and provide conditions for cone opening. Serotinous cones remain
closed until they are warmed sufficiently. Exposed mineral soil provides a suitable
seedbed for the survival of germinants. Drag scarifiers are most suitable when slash
is light and stumps are low.
There are two basic types of drag equipment: anchor chains with tines welded across
the links, and drums with “fins” welded spirally along the surface (sharkfin barrels).
These may be used separately or together to achieve certain objectives. Sharkfin
barrels are heavier than the anchor chains and are used on sites where brush, slash
and depth of humus render the lighter anchor chains unsatisfactory. The drums do not
move as freely as the anchor chains and therefore tend to produce limited seedbed or
planting sites as opposed to the random mixing and exposure achieved with the
anchor chains.
Sharkfin barrels.
For additional information on drag scarification, see Appendix 4, Treatment Guide
for Anchor Chains and Sharkfin Drums, FRDA Handbook 002 [Coates and Haeussler
1987] and Drag Scarification in B.C. [Glenn 1979].
7.5
Shear Blades, Downing Chains and Roller Drum Choppers
This equipment is used primarily to flatten vegetation, snags, stagnated or residual
lodgepole pine and aspen. Soil disturbance is slight when the ground is frozen. If
required, planting spots can be prepared by additional mechanical or motor manual
treatment or by burning.
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Marden chopper.
7.6
Patch Scarifiers
Patch scarifiers create three distinct microsites: a scalped, depressed patch; a low
mound of inverted surface organic matter generally covered by a thin layer of mineral
soil; and the level to slightly raised hinge position at the interface between the
scalped patch and the mound. On dry sites with medium-textured soils, the depressed
patch is the preferred planting spot because scalping increases soil temperature and
improves soil water availability. The low mound has improved access to soil
nutrients compared to the patch but is more prone to drought. On many sites, the
slightly raised hinge position provides the optimum compromise between moisture
and nutrient availability. Patch scarifiers are generally unsuitable where competing
vegetation is aggressive. In B.C., patch scarification is accomplished with the Bräcke
patch scarifier and the Leno, and with excavators equipped with rakes.
Two-row Bräcke patch scarifier.
For additional information on the Bräcke and Leno, see FRDA Handbook 002
[Coates and Haeussler 1987] and Maxwell [1989].
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For additional information on excavators, see FERIC TN-180
[von der Gönna 1992].
7.7
Disc Trenchers and Cone Scarifiers
Disc trenchers and cone scarifiers create pairs of continuous or intermittent trenches
(furrows) and berms providing a range of planting positions. The exposed mineral
soil trench is preferred where moisture conservation is required. The berm, composed
of irregularly overturned surface organic matter and mineral soil, is usually too loose
to form a suitable microsite for planting. It does, however, act as a mulch, warming
the soil below and providing a good environment for root growth. The hinge provides
an intermediate planting position and is favored in most situations.
The trench profile can be adjusted by changing the disc angle, rotation speed, downpressure, and travel speed. A disc angle more perpendicular to the direction of travel
produces a wider, flatter trench, while a disc angle more parallel to the direction of
travel produces a deeper, narrower trench. By increasing the down-pressure and
decreasing the travel speed, a deeper trench and a well-formed berm are produced.
Silva Wadell cone scarifier.
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TTS powered-disc trencher.
For more information on disc trenching, see FRDA Memo 099 [Beaudry 1989], the
video Disc Trenching: A Site Preparation Technique in Review [1991] and FRDA
Report 178 [von der Gönna 1992].
7.8
Mounders
Mounders prepare raised microsites for planting. For additional information on the
reasons for mounding, see “3, Elevation of Prepared Planting Spots” in this chapter.
In B.C., the majority of mounding is done by excavators equipped with buckets or
specialty mounding rakes. The excavator is best suited to difficult or sensitive sites
and mounds can be tailored to the specific needs of the site.
Excavator mounding rake.
For additional information, see FERIC TN-180 [von der Gönna 1992] and FERIC
TN-131 [Dorion 1989].
The Bräcke mounder has been used in B.C. since 1984. It is a two-row mounder
having two hydraulically operated spades. The spades dig into the scalp and deposit
mineral soil on the upper slope of the scalp or on the inverted surface material.
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Bräcke mounder.
For additional information on the Bräcke mounder, see FRDA Handbook 002
[Coates and Haeussler 1987] and Maxwell [1989].
The Donaren 870H is a Swedish-built mounder. This mounder uses the same base
assembly and hydraulics as the Donaren 180 and 280 disc trenchers. On the mounder,
the traditional discs are replaced by two ripper wheels, each fitted with three toothed
rippers. In 1992, the Donaren 870H was used opertionally in Alberta and was also
demonstrated in B.C.
Donaren 870 mounder.
For more information on the Donaren 870H, see FERIC TN-200 [Hunt 1993].
The ministry spot mounder is a prototype mounder developed by the B.C. Ministry of
Forests. The digging blades of the mounder, mounted on the ripper parallelogram, are
hydraulically activated and electronically controlled. The digging cycle involves
forcing the digging blades into the ground, raising the blades after a predetermined
period and flipping the blades to invert the mound.
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Ministry of Forests spot mounder.
For additional information on the ministry spot mounder, see FERIC TN-183 [Parker
1992] and Maxwell [1989].
7.9
Mixing
Appropriately executed mixing can control competing vegetation, increase soil
temperature and aeration, decrease soil bulk density, improve soil water relations,
and retain nutrients stored in surface organic layers making them immediately
available to crop seedlings. However, inadequate mixing can stimulate competing
vegetation and introduce air pockets.
Coarse Mixing Implements
Coarse mixing is accomplished using large discing implements that heap clods of
surface organic and mineral soil layers into a bed. Coarse mixing provides little
control of competing vegetation, but is beneficial where low soil temperatures and/or
high soil water tables inhibit seedling growth.
On sites with high competing vegetation potential, coarse mixing must be followed
by planned brushing treatments.
Coarse mixing can only be undertaken on relatively clean sites so much of the forest
land in B.C. is unsuitable for this treatment. The Eden bedding plow has been used as
a second-pass treatment on backlog sites in north central B.C. The plow consists of
six large hydraulically controlled concave discs that are arranged three to a side, each
offset and with the concave side of the discs facing inward. The bedding plow creates
a continuous raised bed.
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Eden bedding plow.
For additional information on the Eden bedding plow, see FERIC
TN-149 [De Long 1990], and Maxwell [1989].
Fine Mixing Implements
Fine mixing is used on sites with high potential for competing vegetation, where a
high rotation speed is required to chop propagating plant parts into pieces sufficiently
small to prevent them from resprouting. Fine mixing requires slow travel speeds to
allow sufficient time to chop up the soil and vegetation.
Fine mixing is suitable on fine-textured soils, with few cobbles or boulders. It is
unsuitable on sites with the following conditions:
stony or bouldery soils;
coarse-textured soils with a thin humus layer;
wet sites (unless they can be subsequently bedded or mounded).
Fine mixing will result in shrubby vegetation complexes, such as willow or aspen,
being replaced by herbaceous vegetation and grass. This shift in vegetation complex
may not be desirable on certain ecosystems.
The Madge rotoclear is designed for high-speed mixing. The Madge is a selfpowered machine pulled behind a prime mover. It drives a toothed rotor (width 2.3
m) up to 360 RPM. The rotor pulverizes and mixes the forest floor. The Madge is
limited to sites that are relatively free of slash and stones.
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Madge rotoclear.
For more information on the Madge rotoclear, see Maxwell [1989].
Spot Mixing Attachments
Spot mixing is prescribed for sites where mixing is biologically appropriate, but
where slash, stumps, or other obstacles prohibit use of strip mixing implements. Spot
mixing is also used on sites where minimal soil disturbance is required.
Spot mixing implements are usually mounted on excavators, as excavators are able to
work on a wide range of sites.
Two excavator attachments, the VH mulcher and the Hytest tilling mounder, have
been specifically designed for mixing. For additional information on these attachments, see:
FERIC Field Note 40 [von der Gönna 1992],
FERIC Field Note 45 [Hunt 1992], and
the video Excavators: Silvicultural Attachments and Treatments [1993].
Hytest tiller.
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VH mulcher toolplates: the “screefer,” the “nine-tooth
ripper,” and the “egg beater.”
7.10 Motormanual Scarification Attachments
Various attachments have been developed for use with brush and chain saws. Most
create small scalped patches, somewhat below the general ground level. The chain
saw mounted Hawk Scarifier can make small, mixed mounds as well as scarified
patches. Penetration to mineral soil with brush saw attachments may be difficult
when roots are concentrated near the soil surface. For more information, see Maxwell
[1989].
Hawk scarifier.
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8 Planning and Implementing the Site Preparation Project
Initial planning for mechanical site preparation is conducted at the Pre-harvest
Silviculture Prescription (PHSP) stage. The PHSP will state whether or not site
preparation is required to achieve free growing stocking standards and other
reforestation objectives. If the choice of mechanical site preparation has been made,
the treatment type (e.g., scalping, mounding, or mixing) should be stated in general
terms. Consideration should have been given to the costs and benefits of the various
treatments (see Appendix 3, Equipment Comparison: Costs and Productivity, for
comparative cost figures). If planting will be required, regional stocking standards
and the number of acceptable naturals will determine the number and spacing of
plantable spots to be prepared. If site preparation is for naturals, the amount and a
definition of suitable seedbed should be stated.
Following harvest, the appropriateness of the PHSP can be checked using the FS 117
form. This process fine-tunes the prescription since conditions present after harvest
may not match those that were anticipated in the PHSP. Once the prescription has
been confirmed and the treatment and equipment selected, the project is ready to be
implemented. For additional information, refer to “Project Management” and
Appendix 1, Forms Management.
8.1
Operational Considerations
Timing Treatments to Minimize Site Disturbance
The majority of mechanical site preparation is carried out during the summer and fall
months, once sites have dried out sufficiently to allow machine traffic. The wetter the
soil, the greater the risk of causing compaction and rutting damage. It is important to
be aware of the compaction hazard of the site and to monitor soil moisture. At times,
treatments such as shearing and piling should be carried out only after the ground is
partially frozen. For more information, see Curran et al. [1993].
Treatment Pattern
There are two main types of treatment patterns: back-and-forth and concentric. The
concentric pattern is used to minimize the time spent turning, or when turning is
difficult, for example, during drag scarification. When working in a concentric
pattern, the operator begins along the outer edge of the cutover and continues to go
around and around until the whole area is treated.
The back-and-forth pattern is used when other considerations, such as planter access
or aspect, take priority over machine productivity. The operator begins at one end of
the cutover and drives back and forth in parallel runs, usually perpendicular to the
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road. The runs should be longer than 150 m to ensure that time spent turning is
appropriate relative to the total working time.
The treatment pattern may also have to be modified to accommodate site factors such
as slope, bedrock, wet pockets or natural regeneration.
Special Considerations
On some sites, integrated resource management may result in areas requiring
modified treatment. Two examples are given below:
Yew – The discovery of a cancer treating agent in yew bark has resulted in the
protection of yew trees being a high priority. If yew trees are left on a block to be
treated following harvesting, ensure that the site preparation contractor is aware of
this at the pre-work conference.
Wildlife Trees – The protection of wildlife trees has received considerable attention
recently. Such trees, protected through harvesting, should be identified and should
not be disturbed by site preparation operations. Such trees may have modified work
zones flagged out where machine traffic is not allowed, or where it may not be safe
for ground workers. In any case, designated wildlife trees should be pointed out to
the site preparation contractor or operator at the pre-work conference. For further
information, see Wildlife tree management in British Columbia [Backhouse 1993].
Safety
Safe operating techniques and procedures are always important. In site preparation,
unlike harvesting operations, the contractor is usually operating in isolation from
other equipment or activities. Therefore, it is desirable to operate equipment in pairs
whenever possible. Prime movers should always be equipped with a two-way radio
or mobile telephone. Fire safety is also a concern, especially during periods of dry
weather. Sparks can fly from the prime mover, or implements, and can ignite ground
vegetation or logging debris. Welding, cutting, and metal grinding should not be
performed in the cutover. During periods of high fire hazard, personnel with
firefighting equipment should be posted to watch over the workplace after treatment
has ended, and after machine repair work has been completed. Site preparation
operations should be equipped with safety and firefighting equipment as specified by
the ministry. Complete directions for firefighting must be supplied by the
supervisory staff.
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