Plow Power Requirements for Forestry Site Preparation
Abstract In this field study, data were collected to determine power requirements required by a trailing site preparation plow and the magnitudes of dynamic forces experienced by a plow during normal operation and during impact with stumps or other obstructions. Drawbar pull data were collected from five different tillage treatments on a recently harvested loblolly pine (Pinus taeda) site in central Alabama. The five treatments were: 1) a coulter, ripping shank, and four bedding disks; 2) a coulter, ripping shank, and two bedding disks; 3) a coulter and ripping shank; 4) a coulter alone; and 5) a ripping shank alone. A 330 kN [75 000 lb] capacity tension load cell was used to measure the drawbar load, a GPS receiver recorded tractor speed, four direct current displacement transducers (DCDT’s) monitored the depth of the disks, and two optical tachometers measured the speed of the tractor’s front and rear drive shafts. Each treatment produced significantly different drawbar loads (to alpha levels less than 0.001). The resulting mean loads were 46.0 kN [10 300 lb], 33.5 kN [7530 lb], 31.5 kN [7080 lb], 15.8 kN [3560 lb], and 43.4 kN [9760 lb] for treatments one through five, respectively. Maximum recorded drawbar load during a collision with a stump was 338.9 kN [76 188 lb].
Perspectives and drivers of modernisation of silviculture re-establishment in South Africa
Efficient and cost-effective re-establishment practices are important parts of any sustainable forest re-establishment programme. Re-establishment activities include residue management (post-harvest slash), preparation of a planting position, planting, fertilisation and vegetation management. In South Africa, these activities are largely labour intensive, time-consuming and relatively costly. Although mechanisation of site preparation during afforestation was achieved in the mid to late 1990s, plantation re-establishment operations in South Africa have remained manually oriented. However, there have been notable technology developments over the past decade. Semi-structured interviews were conducted with 66 experts (grower company specialists, foresters, contractors and machine manufacturers) to get their perspectives on modernisation of re-establishment activities in South Africa. Frequency distribution and chi-square test analysis found that two-thirds of the experts believed that re-establishment activities had progressed in terms of technology over the past decade. This development was reported as primarily due to the need to improve health and safety (91%), increase production whilst reducing costs (89%), improve stand productivity (quality) (86%), mitigate social (mainly labour) risks (80%) and reduce prevalent negative environmental impacts (50%). Key barriers to modernisation were identified as the capital cost of equipment (65%), reduction in employment opportunities (44%) and low utilisation of equipment due to seasonality of silviculture work (18%). Experts indicated that the efficiency of mechanised re-establishment equipment can be affected negatively by residues, high stumps and compaction of the site after harvesting. The results of this study will assist forestry stakeholders to make informed decisions when planning and implementing modernised silviculture operations.
Compaction of sandy forest soils by forwarder operations
Abstract Soil compaction by repeated passes of a loaded forwarder (a log-carrying vehicle with a gross weight of 26 tonnes) was measured on 2 coarse-textured soils in pine plantations under wet conditions. On soil that was previously undisturbed, the depth of wheel ruts increased linearly with the logarithm of the number of passes, up to 19 cm for 27 passes. On old tracks, which had been used previously only for thinning operations, new ruts were formed to a depth of 5 cm. Penetrometer resistance increased 2–3 fold in the previously undisturbed soil, but decreases in resistance were measured on the old tracks, where the initial values exceeded 5 MPa. Changes in the physical properties of the soil occurred to a depth of at least 70 cm. Soil bulk density increased under all tracks and reached about the same final value on the old tracks and on the initially undisturbed soil. A moderate decrease in saturated hydraulic conductivity and an increase in water retention at 10 kPa was measured. The compacted soil is likely to be restrictive to root growth. The possibility of reducing soil compaction by reducing ground pressure from the machine was assessed on the basis of laboratory measurements of soil strength and compressibility. It is argued from the results that the use of wider, low-pressure tyres would be beneficial on these unusual compactible sands, but this would have to be evaluated in further field trials.