Forestry Branch

Site Preparation for Artificial Regeneration: mechanical chemical prescribed burning

 

Site preparation for artificial regeneration is carried out to create a good environment for the efficient establishment and growth of seeds and seedlings. Manitoba administers site preparation activities through contractual agreements or rental agreements.

Site preparation methods depend on the physical and biological characteristics of the area requiring treatment. Therefore, site inspections and specific evaluations must be done prior to harvest or immediately following harvest, for proper assessment.

Physical attributes which influence site preparation techniques, include:

• soil type
• rockiness
• slash volume
• size and frequency of stumps
• slope
• depth of duff layer, and
• ground vegetation

whereas the biological factors include:

• weed species
• disease or insects
• seed supply
• residuals
• advance regeneration, and
• organic material.

The development of The Forest Ecosystem Classification For Manitoba (1995)has helped to further define treatment responses as well as identify the limitations regarding treatment options.

Site preparation can influence several of the forest production factors which affect the growth and survival of seedlings.

These include above ground factors including:

• solar radiation humidity and temperature

and below ground factors such as:

• water availability, oxygen content, soil temperature, nutrient availability and soil density.

Site preparation methods are grouped into the following categories:

• mechanical
• chemical (see: Vegetation Management)
• prescribed burning, or a
• combination of these methods.

The method chosen will depend on site specific factors, such as the amount of debris present and terrain features, and the proposed regeneration method. Seedbed and/or microsite requirements for the regeneration species is the prize consideration.

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Mechanical Site Preparation

Mechanical site preparation can greatly influence the moisture conditions around seedling roots. The aim of the treatment is to provide the planting spot with relatively high, secure moisture availability, without risk of oxygen deficiency. The favourable effect of site preparation and soil temperature on seedling survival and growth has been clearly demonstrated in many studies. Removal of the humus layer increases soil temperatures, and other methods such as mounding can improve moisture conditions, aeration, and soil temperature.

The biological effectiveness of different treatment methods varies according to soil texture and climate. Soil depth is an important consideration. Scalping-off uppermost soil layer on medium to coarse textured soils generally provide better micro-sites by eliminating competition for light and moisture. Scalping should not be too severe as it may necessitate planting in less fertile soil (i.e. C horizon). Mixing or inverting fine textured soils increase root penetration and soil moisture availability.

Powered-disc trenching is preferable to patch scarification on operationally difficult sites (i.e. those with a thick duff layer and a high frequency of stones, slash) . Patch scarification should be used where harsh site preparation is best avoided, such as on dry or thin humus sites, where the probability of creating plantable microsites with patches is high.

In addition to the biological improvements, mechanical site preparation for planting can offer more control over seedling spacing, provide better access for planters, and reduce planting costs. Spaced plantations will be less costly to carry out future stand maintenance and perhaps reduce harvesting costs with mechanical harvest techniques.

Some of the site preparation equipment used in Manitoba are:

• Anchor Chains with or without Shark-finned Barrels
• The Bräcke Scarifier (with or without Vegetation Management attachments)
• The Bräcke Mounder
• Disc Trenchers (both powered and conventional (with or without Vegetation Management attachments))
• Shear Blade
• Ripper Tooth, and
• 7 and 8 foot Drum Choppers.

A wide variety of additional equipment has been tested and used over the past 70 years.

Most of the site preparation in Manitoba is implemented through contractual agreements with equipment operators supervised by Regional Operations staff.

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Prescribed Burning

The practice of using regulated fires to reduce the incorporated organic matter of the forest floor and undesirable vegetation is called prescribed or controlled burning. Burning is conducted under such conditions that the size and intensity of the fires are no greater than necessary to achieve a clearly defined purpose of forest renewal. A successful prescribed burn is one that is executed safely, burns under control, accomplishes the prescribed treatment, and attains the land and resource management objectives for the area involved.

Highly productive sites with an abundance of fuel (e.g. slash, heavy shrub/hardwood vegetation, thick duff layers, and fine fuels) and scattered residuals are ideal candidates for prescribed burning. Fire boundaries (breaks), which are an essential component of any prescribed burn, may be comprised of lakes, streams, lowland spruce, swamps or marshes, and gravel roads or harvest areas cleared down to mineral soil. The entire area within burn boundaries should be eligible for burning due to the difficulty in protecting small patches, such as wildlife areas within the burn boundary.

The information required for prescribed burn planning is as follows:

• Physical and biological characteristics of the site to be treated.
• Land and resource management objectives for the site to be treated.
• Known relationships between pre-burn environmental factors, expected fire behaviour, and probable fire effects (fire regime).
• The existing art and science of applying fire to a site for example Forestry Canada, US Forest Service, and the North West Ontario Technical Development Unit (NWOTDU).
• Previous experience from similar treatments on similar sites.

The cost of implementing a prescribed burn is difficult to predict due differences between each site. Other variables would include the costs associated with preparing each site, the experience of the planning team and implementing teams, the costs for staff wages and other costs such as advanced weather monitoring equipment, communications equipment, and emergency suppression capability on standby.

Some of the favourable attributes of prescribed fire include the following:

• can be used on difficult terrain
• doesn't compact the soil
• increased soil temperature and release of nutrients previously unavailable in duff layers
• can improve growth and survival of planted seedlings, and
• can eliminate or retard competing vegetation.
  
  
• Prescribed burning can also be an especially effective treatment on larger sites, greater than 100 hectares (larger = more cost effective), that are difficult to treat by methods of mechanical site preparation.

The reduction of fire hazard by burning top piles or woodpiles at landings (which also act as insect and disease habitat) can therefore have an additional benefit of reduced long-term risk to silvicultural improvements.

Disadvantages, which may be associated with fire, are:

• risk of escape
• prescription objectives may not be achieved
• may result in loss of soil nutrients (on coarse textured soils), and
• may adversely effect physical and chemical soil properties at higher burn intensifies.

The reduction of organic matter and nutrients in surface soils after burning is the result of loss from ignition and leaching, and this is more evident in coarse textured soils.

Sites where prescribed burning should be avoided include areas with:

• coarse textured soils
• low productivity
• no fire boundaries present (natural or manmade)
• high value sites requiring protection, and
• critical wildlife or fisheries habitat.

Prescribed burns can produce different results depending on the method and type of fire implemented. Light spring burns usually called head fires (i.e. move in same direction as wind) burn quicker and consume less fuels. Hot summer burns usually called back fires (i.e. moves into the direction of the wind) burn slowly and consume a large amount of fuel. Duff reduction is a prime objective with any site preparation for planting or seeding, and requires hot burns on sites with thick duff layers.

In the future, operational guidelines for prescribed burning may be developed for use in Manitoba. The development of fire management guidelines for prescribed burning will be a joint effort by silviculture, forest protection, and forest operations sections in conjunction with industry. The use of prescribed fire has long been considered a useful site preparation tool, however the dangers associated with its use has restricted implementation, especially with the explosive wildfire history in Manitoba.