Impact of Roadside Drying on Delivered Costs for Eucalyptus globulus Logging Residue and Whole Trees Supplying a Hypothetical Energy Plant in Western Australia Using a Linear-Programming Model

Australia’s large potential forest bioenergy resource is considerably underutilised, due largely to its high delivered costs. Drying forest biomass at the roadside can potentially reduce its delivered cost through weight reduction and increased net calorific value. There has been little research on the impact of roadside drying for Australian conditions and plantation species. This study compared delivered costs for three forest biomass types—Eucalyptus globulus plantation whole trees and logging residue (LR)-disaggregated (LR conventional) or aggregated (LR fuel-adapted)—and three roadside storage scenarios—no storage, ≤two-month storage and optimal storage—to supply a hypothetical thermal power plant in south-west Western Australia. The study was performed using a tactical linear programming tool (MCPlan). Roadside storage reduced delivered costs, with optimal storage (storage for up to 14 months) producing the lowest costs. Delivered costs were inversely related to forest biomass spatial density due to transport cost reductions. Whole trees, which had the highest spatial density, stored under the optimal storage scenario had the lowest delivered costs (AUD 7.89/MWh) while LR conventional, with the lowest spatial density, had the highest delivered costs when delivered without storage (AUD 15.51/MWh). For both LR types, two-month storage achieved ~60% of the savings from the optimal storage scenario but only 23% of the savings for whole trees. The findings suggested that roadside drying and high forest biomass spatial density are critical to reducing forest biomass delivered costs.

Predicting Logging Residue Volumes in Alaska

Alaska forest managers seek information on how timber harvesting practices change the creation of postharvest woody residues. To predict residue volumes, researchers investigated how residue ratios—growing-stock residue volume per mill-delivered volume—related to readily available data on logging site and tree attributes in Alaska. Residue ratios were not related to logging site-level variables but were related to individual tree variables with predictive models. Ratios varied widely by tree species and were predicted to increase with larger stump height and larger small-end used diameters and decline exponentially with increasing diameter breast height (dbh) to approximately 25 inches. Ratios were then predicted to increase progressively in larger dbh trees. Results from this study update previous findings in other US Northwest states and can be used to produce or improve residue prediction tools for Alaska land managers.

Logging Mats and Logging Residue as Ground Protection during Forwarder Traffic along Till Hillslopes

Forest soils in Northern Europe are generally trafficked by forest machinery on several occasions during a forest rotation. This may create ruts (wheel tracks), which could increase sediment transport to nearby surface water, reduce recreational value, and affect tree growth. It is therefore important to reduce soil disturbance during off-road forest transportation. In this study, rut depth was measured following forwarder traffic on study plots located along four harvested till hillslopes in Northern Sweden with drier soil conditions uphill and wet conditions downhill. The treatments included driving 1) using no ground protection, 2) on logging residue (on average, 38–50 kg m–2) and 3) on logging mats measuring 5×1×0.2 m. The hillslopes contain areas with a high content of boulders, stones, and gravel as well as areas with a significant content of silt. Six passes with a laden forwarder with four bogie tracks were performed. On the plots with ground protection, the application of logging residue and the application and removal of logging mats necessitated additional passes. Rut depth was measured using two methods: 1) as the difference in elevation between the interpolated original soil surface and the surface of the rut using GNSS positioning (Global Navigation Satellite Systems), and 2) manually with a folding rule from an aluminium profile, placed across the rut, to the bottom of the rut. The two methods generally gave similar results. Driving without ground protection in the upper part of the hillslopes generated ruts with depths <0.2 m. Here, the rut depth was probably modified by the high content of boulders and stones in the upper soil and drier soil conditions. In the lower part of the hillslopes, the mean rut depth ranged from 0.21 to 0.34 m. With a few exceptions, driving on logging residue or logging mats prevented exposure of mineral soil along the entire hillslope. Soil disturbance can thus be reduced by acknowledging the onsite variability in ground conditions and considering the need for ground protection when planning forest operations.

Trends and Perspectives in the Design of Mobile Wood Chippers

Mobile wood chippers represent a mature technology now available in a wide range of sizes and configurations. Different types exist, but the most widespread are disc and drum chippers. The latter have enjoyed wider popularity in recent years because they are best suited to processing logging residue and other low-quality wood. Drum chippers can be fitted with screens, designed to re-circulate oversize particles. In general, industrial chippers offer high productivity and high fuel efficiency, especially if settings are properly adjusted. Chippers are high-maintenance equipment and require proper care. Maintenance cost increases with machine age and can be predicted quite accurately, and so can chipping productivity and cost. Reliable models exist for estimating both maintenance cost and productivity, based on dedicated user-entered assumptions. All things being equal, there are no substantial productivity and maintenance differences between tractor-powered and independent-engine chippers.

Response of N2O emissions to logging residue piles of Norway spruce, Scots pine and silver birch

<p>Utilization of forest bioenergy is increasing; however, the overall environmental impacts of forest bioenergy utilization are not fully understood. Especially effects on N<sub>2</sub>O emissions in mineral soils are less studied. With current harvesting practices, either whole-tree-harvest or stem-only-harvest, piles of logging residues are left on the forest floor. As a result, soil nitrogen (N) cycling processes can be accelerated on clear cut area under the piles, especially net nitrification. When N is transformed to more mobile form, the risk for N losses via nitrous oxide (N<sub>2</sub>O) emissions from the forest floor may increase.</p><p>We studied how logging residue piles of three tree species, Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.), influence gaseous losses of N after clear-cut. A Norway spruce dominated mixed stand on a mineral soil site was clear-cut and N<sub>2</sub>O emissions were monitored. There were four treatments; three tree species treatments consisting of 40 kg m<sup>-2</sup> of fresh logging residues and control plot without residues as an additional treatment. Effects of logging residue piles on N<sub>2</sub>O emissions were monitored over 4 growing season with closed chamber technic. Simultaneously soil temperatures were recorded over 2 growing season. Soil denitrification activity and the contribution of nitrification and denitrification to N<sub>2</sub>O production were determined in laboratory experiments.</p><p>Logging residue piles lowered and balanced fluctuation of soil temperatures. N<sub>2</sub>O fluxes peaked under the piles during the second and third growing season after the establishment of the piles; however inconsistent fluxes tended to be low. The production of N<sub>2</sub>O was driven by both nitrification and denitrification processes, the proportion depending on the tree species. Our results indicate that logging residue piles accelerate N losses as gaseous form; however studies on the same field experiment shows that most of the N losses occur through soil percolation waters. Spruce residues tend to stimulate N<sub>2</sub>O emissions longer compared to other tree species. There was a positive correlation with net nitrification and microbial biomass C (Törmänen et al. 2018, FORECO). These results have implications for sustainable and productive forest management practices and nutrition of re-growing vegetation.</p>