The ‘Bandicoot’ Spot Mounder
An Assessment by DPI Forestry, Qld

Spot mounding with excavators has been adopted as an appropriate second rotation site preparation technique for poorly drained and highly erodible soils within exotic pine plantations in southeast Queensland. Spot mounding allows the plantation manager to cultivate these sensitive sites without needing to employ intensive clearing and surface drainage engineering. This avoids the use of site damaging conventional tracked or wheeled machines. The DPI Forestry Bandicoot spot mounder was developed through a joint venture between the Queensland Forestry Research Institute Silviculture Developm. Group, Gympie and Savannah Equipment Ply Ltd over the period 1998 99.

The two prototypes built have since treated over 300 hectares within the Tuan Toolara exotic pine plantation estate.

Machine Description and Operation

The Bandicoot spot mounder is comprised of a flat base plate, under which are mounted two heavy-duty arms carrying 90 centimetre (36 inch) diameter offset discs. A six pronged debris rake is attached to the forward edge of and at a slight angle to the base plate. A quick hitch attachment suitable for the make and model of excavator is bolted to the top of the base plate. The design also allows for the attachment of a short, forward-mounted winged cultivating tine under the base plate.  

Prior to forming a mound, the rake is used to clear logging residue from the mound site in order to limit incorporation of excess vegetation material in the mound. To form a mound, the Bandicoot is drawn horizontally through the ground for approximately two metres, at a depth of about 20cm. This action results in the two discs throwing up a rectangular shaped mound over a centrally cultivated section made by the tine (if fitted). In operation the excavator travels forward straddling a premarked line and constructing three rows of spot mounds at predetermined spacings as it proceeds.

New 'Bandicoot' Spot Mounder: the rake clears the surface debris and the two 36" disks cultivate the soil into a well-defined mound

Average mound size produced is 2.0 metres long, 1.25 metres wide and 0.35 metres high. Total ground disturbance is approximately two metres square. Being a single pass implement, the Bandicoot can generally only cultivate to a primary stage. Therefore the quality of mounding is usually determined by site factors such as soil type and moisture content, amount of logging residue and by the presence of surface root masses.

The sandy wallum soils are easier to work and to form into a well shaped and cultivated mound. However  subsurface horizons of some hard setting soils, which are characterised by their high silt and fine sand content, have the ability to 'set like concrete' when inverted, particularly if worked in excessively wet condi­tions. These soils require secondary cultivation to amelio­rate the situation and allow satisfactory planting. Obviously a second cultivation is impractical. Therefore planting on these sites is best achieved by waiting until significant rainfall softens the mound.

Again, heavy masses of surface roots associated with swamp sedges and blady grass can adversely affect mound construction. Unsatisfactory mounds on these sites are comprised of large clods of soil bound together by root mat, which remains alive and competes with the planted tree. It is recommended that an effective glyphosate treatment be carried out prior to mounding to avoid this problem. Strip control of these grasses would also eliminate the task of line pegging.

Operational trials indicate a base production rate of a little more than three hours per hectare for the Bandicoot mounted on a 13 tonne excavator, and a little less than three hours per hectare when mounted on a 22 tonne machine. These rates translate to approximately $300 per hectare with the smaller excavator being slightly more economical. To this base cost should be added those of line pegging and a hire cost for the Bandicoot (estimated at $15 per hectare). Trials indicated that the effort required by an excavator to form a mound with the Bandicoot was significantly less than with previously used spot mounders, which typically required the power and weight of a 22 tonne machine. Therefore excavators as small as 13 tonnes are now being successfully employed.  

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Job quality and efficiency are adversely affected by the presence of excessive remnant or regenerated vegetation and by unevenly distributed logging residue. When working in these conditions, excavator operators can waste time in locating and sighting pegged lines, accurately estimating mound placement and clearing residue from mound sites. Chopper rolling of dirty sites is an efficient way of improving spot mounding production through enhanced visibility and access.

Conclusions

The Bandicoot spot mounder is a robust, economical and effective excavator-based implement, suitable for mound construction on poorly drained and environmentally sensitive sites. It can create three rows of mounds per pass, to a primary cultivation standard on poorly drained or environmentally sensitive exotic pine plantation sites, where conventional tractor-mounted mounding machinery cannot operate or has proven inappropriate. Costs have decreased by 30% since the introduction of the Bandicoot.

by John Grimmett, DPI Forestry, QLD