Positive effects of site preparation on nutrients availability

A primary objective of mechanical site preparation is to strike a balance between enhancing short-term nutrient availability for seedlings and preserving the longer-term nutrient capital of the site.  Nutrient availability can be enhanced with the following techniques:

Removing or reducing the insulating effect of the organic layer.

Mixing, inverting and trenching, for example, all enhance soil warming, and consequently nutrient mineralization.  Results from studies in Sweden and Finland show that the mineralization of nitrogen, potassium, and phosphorus is increased for at least three years after site preparation.  Warming the soil also promotes tree root growth, which allows roots to quickly reach the adjacent organic material. (This assumes that the cleared areas are relatively small).

Mixing the organic surface layer with the underlying mineral soil.

Mixing may further enhance nutrient availability in soils of low fertility by encouraging the spread of myccorrhizae into the mineral soil.  (The effect of site preparation on mycorrhizal fungi needs to be better defined by researchers.) Cultivation can also improve aeration and assist microbial activity in soils that either suffer from compaction or have impenetrable layers.

Raising and cultivating (loosening) the soil. Bedding or mixed small mounds, as practiced in the southern United States can enhance nutrient uptake for many years in soil that suffer from poor water movement and aeration.

Reducing competing vegetation on a site.  This serves to reduce competition for soil nutrients and, as a result of increased light, enhances carbon uptake for crop trees.

Mechanical site preparation has an impact on the nutrient reserves of a site primarily through the displacement or redistribution of the reserves stored in logging debris and in the organic and upper soil layers, and through the increased availability of nutrients as a result of mineralization.  Unfortunately, neither newly germinated tree seeds nor planted stock are initially able to use all of the large nutrient reserves made available as a result of site preparation.   Consequently, nutrient loss by leaching may result.  The following techniques have been employed to preserve the site's nutrient capital:

Spot scarifying only the small area in which an individual seedling will be planted.  This will minimize losses due to leaching and will also conserve the nutrient reserves in the undisturbed organic layer and in logging debris close to the growing seedling.  The incidence of erosion, another source of nutrient loss, is also reduced.

Mixing the more fertile surface organic layers and the underlying mineral soil, instead of completely remove the organic layer.  This will preserve the longer-time nutrient status of the site and can enhance tree growth by slowing the mineralization of soil nutrients during the initial years of plantation development,  and may preserve these nutrients until crop trees are older and better able to exploit available nutrients.  Mixing that incorporates the surface organic materials deep into the mineral soil can have a moderate effect on the rate of mineralization of nutrients by avoiding the temperature extremes commonly observed on the exposed surface organic layers.  Buried wood and bark can also conserve soil fertility, as the microbial activity that accompanies their decomposition can temporarily immobilize nutrients.

Reducing the depth of removal of the organic and mineral soil horizons.  This will help conserve nutrients, which can be particularly important when the subsoil is infertile.

Negative effects of site preparation on nutrient availability.

In terms of overall net losses of site productivity, the negative consequences of mechanical site preparation have not been well defined for most forest conditions.  Researchers in Sweden have recommended that "harsh" site preparation methods. (continues disc trenching or tilt plowing) be avoided on poor site types with thin humus layers, dry or coarse-textured soils, in favor of   "milder" treatments such as spot preparation.

Other studies are less definitive.  Results from the southern United States suggest that on sites low in organic matter and where large nitrogen deficiencies occur, nitrogen availability and plantation productivity may eventually be reduced by treatments that remove or displace large amounts of nitrogen (such as burning).  On the basis of results from past studies on seedling growth following mechanical site preparation in British Columbia, windthrowing appears to result in the most consistent reduction of tree growth, compared with less severe forms of mechanical disturbance.  After summarizing the effects of various forms of mechanical site preparation on vegetation and the growth of spruce in the north-central British Columbia, this study concluded that although blade scarification reduced competing vegetation, it also decreased spruce performance for up to 13 years following treatment.   Another study found that scalping of the forest floor temporarily eliminated the mycorrhizae-forming fungi and resulted in short-term deficiencies in phosphorus uptake.

In Ontario, studies have shown how duff removal on infertile sites before planting has a negative effect on tree growth between 8 and 19 years.   The question of which site preparation methods are harsh or detrimental should be considered within the context of soil and site fertility and the relative degree of disturbance.

Extremely shallow soils have limited store of nutrients and are sensitive to disturbance,  as are coarse-textured, excessively well drained soils, whose limited nutrient reserves reside principally in the surface organic layer and in logging debris.  Any treatment of such sites should retain as much of the organic layer and any logging debris as possible, or mix the organic and mineral soil layers together.

Changes to the VH Mulcher                                                                           Nothing stays the same forever.

Since the first design in 1989 the VH Mulcher has undergone three major redesigns.  The latest structural changes were completed in 1992 with only peripheral changes since.

As knowledge of our mechanical abilities and performance of the excavators and contractors became substantiated, a concentrated effort to train operators to the forest companies preferences increased our popularity.

As acceptance by Forest companies increased so did the contractors performance. We learned together.  When foresters gained knowledge of what they should consider doing and learned that a VH Mulcher did exist, and little about what it could do......we found ways of doing what they wanted, expeditiously.

The design of the VH Mulcher was based around the 20 ton excavator, the most versatile in the forest industry in Canada and U.S.A. (It can be used as a roadbuilder, processor, loader, small feller buncher, small forwarder etc.).  Competition in the market has made all the 20 Tonne excavators near equal.  Owners in North America generally will buy the brand of excavator which best serves their particular needs.  Operator ergonomics are important.  Excavators, like automobiles, have option sheets, air conditioning can improve productivity when the operator is sitting for long hours behind glass in the sun on a warm day.  Operator Roll over and Falling Object Protection for forestry work is required by law in most countries.  The optional Long Track is critical for stability when countering weight forces of the attachments, working steep slopes, or traversing uneven terrain and slash. Optional wide track pads 32 inches (street pads) reduces ground pressure to 4-5 lb. PSI and can be important on wet or boggy ground or where compaction or disturbance of soft ground is a concern.  Optional single grouser pads, cleets, or corks welded to the pad increase traction on steep, hard, or heavy slash covered terrain.   This option can, in the right conditions, greatly increase productivity and operator safety.

Larger machines have been used: 22 Tonne, 25 Tonne and 30 Tonne machines have been used successfully.  The hourly pay rate required for larger machines is a deterrent. 22 Tonne and 25 Tonne machines may be optimum on harder, dry, steep ground.

15 Tonne and 19 Tonne machines: In 1997 there are few machines with long carriage in this class.  To my knowledge, although hydraulically capable, installation and use of the smaller machine with a VH Mulcher has not been done nor is it recommended.  These machines may be capable of working on easier ground conditions: gentle slopes, light slash loads where the optional and detachable thumb is not required or installed on the excavator.   Durability of lighter machines used in severe conditions such as found commonly in British Columbia is questionable.  A new 1997 series available in long carriage in the 16 Ton range may offer a viable alternative.

Site Factors: When approaching a new cutover for the first time, VH Mulcher/Excavator assessment would include:

Soil description          -textured, sand, loam, clay, silt, coarse, rocky (each type can affect                                    productivity)

Slope and Aspect      -slope less than 35% or greater (terrain affects costs)

Slash Load                 -excavators can handle extremely heavy slash loads although costs rise.                                    Being "on target" for required spots per hectare / acre can be critical                                    in obtaining a financially viable site preparation option.

Block Size, Accessibility and Uniformity                                                                                      

                                 -as costs are always critical, small, remote trial blocks can be the most                                     expensive and may not represent average costs.  These high costs will                                     affect feasibility of doing larger more cost effective projects.

Obstacles impeding the movement of the excavator

                                 -Stumps- height, diameter number per hectare/ acre.  Excavators can work                                     through virtually any logged area.  Stumps are only a cost per hectare/acre                                     consideration.   Stumps under 12 inches in height generally do not effect                                     pricing.   Large diameter (48 inches) stumps over 18 inches tall, can increase                                     costing by 20%  or more.  Normally, a reduction in the number of                                     prescribed spots per hectare/acre is the best way to offset higher costs of                                     reaching full target spacing.  Obtaining 80% of the target spacing may save                                     50% of the cost.