Residual biomass recovery from fully-mechanized delayed thinnings on Spanish Pinus spp. plantations

In Spain, five million hectares of conifer plantations require thinning. As only a small part produces pulpwood, they are a major potential biomass resource. A time-study is performed on the recovery of logging residues in a Pinus plantation on gentle terrain in order to analyze the main factors affecting the productivity and cost of biomass and pulpwood harvesting. The first factor is the branches and tops piling method, either using the forest harvester head to bunch them along the strip road sides (method S) while processing the timber, or leaving them on the strip road centre (method C) and using a 175 HP bulldozer with a raking implement to pile them up afterwards. The second factor is the top diameter separating pulpwood and biomass, 8 or 10 cm. Mechanized felling-processing productivity is greater for the method C and the smaller diameter. Hauling biomass off with forwarder is also significantly more productive when piled by bulldozer. Productivity equations were fitted for pulpwood and biomass forwarding. The direct cost of biomass recovery ranged from €29.7 to €31.5 per green tonne (H = 51%). The roundwood and biomass effective yields – per hectare – were measured. This allowed evaluating the cost balance for roundwood/roundwood plus biomass harvesting, based on the net income per hectare. Under the 2013 Spanish market conditions, recovery of residual biomass is economically preferable to harvesting only roundwood in the studied stands. The greater net income balance corresponds to the piling method using the bulldozer (C) and the larger top diameter (10 cm).     

Regional woody biomass supply and economic impacts from harvesting in the southern U.S

Demand for woody biomass from the southern United States (US) is increasing because of its reliability in supply, recent developments in co-firing and biofuel conversion technologies, overseas pellet demand, and the expected economic impacts from reorienting the forestry sector towards energy feedstock production. This research examines the interaction between a set of woody biomass harvesting sources (logging residue, non-merchantable, and merchantable roundwood) and wood types (hardwood, planted softwood, and natural softwood), and the impacts harvest costs have on the extraction of these materials in the southern US. The expected woody biomass availability and its geographic distribution are determined with a cost minimizing linear programming model. The marginal cost of woody biomass supply is determined for different energy production targets, subject to satisfying conventional wood demand. Given derived industry supply curves, the economic impacts of the sector are analyzed using the IMpact analysis for PLANning model (IMPLAN) at the Bureau of Economic Analysis (BEA) level. The results suggest that forest biomass for energy production is projected to be available over a much wider price range with logging, residue, and non-merchantable and merchantable roundwood in these regions. Supply of hardwood and softwood biomass from merchantable roundwood is expected to increase if these materials can be harvested for non-conventional uses. Development of harvesting woody biomass from logging residue, non-merchantable, and merchantable timber has positive effects on local economies, bringing with it employment opportunities to some BEA regions.     

Productivity of harvesting dense birch stands for bioenergy

Marginal lands could be utilized for increasing energy biomass production independent of industrial roundwood procurement. Dedicated energy biomass production systems on such sites would be based on low stand establishment cost, clear-cutting at an early stage, and coppice regeneration. Harvesters designed for the processing of industrial roundwood are inefficient or too costly to use in small-diameter and dense stands, while insufficient cutting capacity and uneven space distribution of trees limit the use of modified agricultural harvesters developed for short-rotation woody-crop plantations (e.g. willow). We constructed time consumption models for clear-cutting and forwarding of whole trees from un-thinned, small-diameter stands. The data originated from naturally afforested downy birch-dominated stands located in a cutaway peat production area in northern Finland. Stand age varied from 14 to 29 years and stand density was 5150–160,250 trees per hectare. In clear-cutting, a medium-sized forest harvester equipped with an accumulating felling head fitted with a circular saw disc was used, and subsequent forwarding was done using a modified medium-sized forwarder. Cutting productivity was 3–11oven-dry tons (ODt) per effective hour (E₀-h), and was highly dependent on stand characteristics (e.g. mean whole-tree volume). At a distance of 300 m, for example, the productivity of forwarding in the time study plots was 6.7–10.4 ODt E₀-h⁻¹. Our study indicates that energy biomass can be harvested from young downy birch thickets efficiently by clear-cutting with appropriate machinery.     

Mechanized coppice harvesting with new small-scale feller-bunchers: Results from harvesting trials with newly manufactured felling heads in Italy

The revival of coppice management is being considered as one option to satisfy the increasing market demand for wood biomass. Commonly used harvesting systems in coppice forests (CF) are based on motor manual felling, but further mechanization of CF operations is desirable because of increasing labor costs and the high fatality rates associated with motor manual felling.The goal of this study was to determine the machine performance in terms of productivity, cost-effectiveness and cut quality of new feller-bunchers, when used on different types of CF. The study comprised of five tests on different sites in Italy, four of which represented a specific type of CF.Results showed that harvesting productivity varied from 3.1 to 8.6 dry t per scheduled machine hour (SMH) in multi-stem coppice stands (4.5–16 dry m³ SMH⁻¹). Productivity reached 16.2 dry t SMH⁻¹ in a short rotation forestry (SRF) control stand (39.4 dry m³ SMH⁻¹) and it increased with stump mass. Recorded productivities tested in conventional CF were not as high as achieved in single-stem SRF, or in the mechanized felling of comparable softwood stands, but still matched the requirements of commercial mechanized logging. Costs varied between 3.57 and 20.56 € dry t⁻¹ (1.47–14.17 € dry ${\text{m}}^{3^{\mathrm{-}1}}$). Lowest costs were reached in the SRF stand and highest cost in the Mediterranean CF growing on moderate to steep terrain. Shear heads produced poor cuts and single-action shears performed worst. The disc saw produced very low cuts with low damage levels, which might be acceptable even under current cut quality specifications.     

The long-term effects of logging residue removal on forest floor nutrient capital, foliar chemistry and growth of a Norway spruce stand

This study compared the nutrient capital of the forest floor, the nutrient status of trees, and the growth of a stand of Norway spruce (Picea abies L. (Karst.)) planted on a whole-tree harvesting treatment (needles left on site) with a conventional stem-only harvesting treatment 30 years after clearcutting. No significant treatment effects were detected in the amount of organic matter, the amounts of nutrients in the forest floor, or the concentrations of foliar nutrients. The results indicate that whole-tree harvesting with the needles left on the site did not reduce the long-term nutrient capital of the forest floor or the nutritional status of trees. Whole-tree harvesting significantly reduced the height of dominant spruce compared to stem-only harvesting, however the stem volume of dominant spruce did not differ between the harvesting treatments. The greater height growth of the dominant trees in the stem-only harvesting treatment could be attributed to indirect factors other than changes in site resource availability (e.g. protection against frost damage), and hence the effect of whole-tree harvesting on potential site productivity was inconclusive due to the confounding effect of site factors. In the whole-tree harvesting treatment, the total stem volume of the stand and, consequently, the actual site productivity, was lower when compared to stem-only harvesting due to the lower density of naturally regenerated seedlings.     

Forest management strategies for producing wood for energy from conventional forestry systems

The report reviews the current developments in forest management planning and practices to integrate the production of biomass for energy along with more conventional forest management goals. However, these have direct or indirect benefits on site preparation, planting and regeneration, stand improvement, and forest protection, soil compaction and disturbance, leaching and removal of nutrients maybe associated with increases in biomass harvesting.

Efforts are under way to adapt management practices and silvicultural treatments to biomass production. These begin at the planning stage with the development of management tools and more accurate forest inventory data. They include silvicultural treatments such as shelterwood thinning in mixed wood stands and the interplanting of various tree species with the dual purpose of producing energy wood and conventional forest products.

Three systems are available for recovering residues at time of final harvesting. The postharvest recovery of residues area is commonly used in Europe but is generally uneconomic in North America where the harvesting of small stems and integrated harvesting are favoured.

Future work is required to develop techniques for estimating the quantity of bioenergy resources available under different management strategies and to elucidate the long-term environmental impacts of producing wood for energy from conventional forestry systems.     

Sustainable use of eucalypt biomass grown on short rotation coppice for bioenergy

Bioenergy is one of the alternatives to reduce the dependence of global energy on fossil fuels. The short rotation coppice (SRC) of eucalypt species appears as an interesting option for forest biomass production in a short time. However, the harvesting of whole trees (included the crown) in SRC systems has implications on sustainable land use. More information is required on the increase of biomass as renewable energy resource to achieve the sustainability of these crops. The main objective of this research was to evaluate the sustainable use of biomass from very high-density eucalypt plantations, managed at tropical conditions for bioenergy. To accomplish this objective, the tree was fractionated into three fractions: stem, branches, and leaves, and there was determination of the dry matter, energy yield, and nutrients export. This experiment used a short rotation coppice, a hybrid clone of Eucalyptus urophylla × Eucalyptus grandis, of 2 years old. According to the results obtained, the density planting and fertilization levels have a greater influence on the dry matter yield, energy yield, and nutrient exports. The higher density planting reaches mean values of 30.9 tonnes of dry matter per hectare (t DM ha⁻¹) and 743.3 GJ ha⁻¹. Considering the biomass yield and nutrients export of short rotation coppice of eucalypt, the higher density planting with the lower dose of fertilization is more indicative of sustainable use. The leaves have an important participation in nutrients export and should be retained in the soil of forest.     

A new feller-buncher for harvesting energy wood: Results from a European test programme

In recent years, some manufacturers have developed new downsized feller-bunchers that are particularly suited to small-tree harvesting. One of these machines was tested in some of the most promising small tree resources of Europe, namely: Finnish young conifer forests, French hornbeam coppice and Italian sycamore plantations. The tests were conducted within the scope of a 3-year long European project, whose goal was to assess the suitability of this new technology to the production of wood biomass from silvicultural operations. Depending on site characteristics, the machine reached an average productivity between 4 and 8 green tonnes per net working hour, comparing favourably with other European shear-type felling heads and qualifying for deployment on a European scale.     

Biomass retention following whole-tree, energy wood harvests in central Maine: Adherence to five state guidelines

The expansion of the bioenergy industry in Maine has led to an increase in integrated roundwood and energy wood whole-tree harvesting. A better understanding of the amounts of logging residue left unrecovered on whole-tree harvested sites will enable the refinement of available forest residue estimates for Maine and the assessment of the potential effect of such harvesting on forest health. Several states have developed biomass harvesting guidelines in response to concerns generated from an expanding bioenergy industry. In this study downed wood and snags were inventoried on twelve sites in central Maine that had recently been whole-tree harvested for roundwood and energy wood. The percentage of harvested material retained as residue on the study sites was determined. On average, 45% of the energy wood generated during the harvest was left on site. This removal efficiency must be considered when developing forest residue availability estimates. Additionally, the volumes of logging residue were compared to measurable criteria from biomass and biodiversity guidelines of several states. We found that enough fine woody material (<15 cm diameter) remained on the harvest sites to meet the guideline criteria; however, the quantities of coarse woody material (≥15 cm diameter), large logs (≥38 cm dbh), and snags (≥25 cm dbh) were insufficient to meet the guideline criteria. These deficiencies likely resulted from prior forest practices rather than from the current energy wood removal. Retaining more trees of larger sizes in the future can address this concern.     

Modeling stump biomass of stands using harvester measurements for adaptive energy wood procurement systems

The value and volumes of industrial stump fuel supply are increasing for energy production. Accurate estimates of aboveground and belowground biomass of trees are important when estimating the potential of stumps as a bioenergy source. In this study two stump biomass equations were adapted and tested using them as calibrated stump biomass models computed as the cumulative sum by a local stand. In addition, variables derived from stem measurements of the forest harvester data were examined to predict stump biomass of a stand by applying regression analysis. The true stump yield (dry weight) was used as the reference data in the study. Both biomass models performed well (adjusted R² ˜ 0.84) and no advance was found in using other stem dimensions as independent variables in the model. The stand-level model can be used in innovative stump biomass prediction tools for increasing efficiency of energy wood procurement planning to stands within a certain area. In practice, wood procurement managers would need to adapt developed system and decide whether the degree of accuracy/precision provided by the models is acceptable in their local stand harvesting conditions.     

Suitability of published biomass equations for aspen in Central Europe—Results from a case study

Published biomass equations were applied to sample trees from an 18-year-old Populus tremula (L.)×P. tremuloides (Michx.) (Astria) stand in Germany and compared with the measured dry weights. Equations originally developed for quaking aspen did not perform better than equations derived from European aspen data. The complexity of equations also did not influence the mean percent deviation of calculated dry weights from measured dry weights. Equations derived from measurements in short-rotation coppice cultures grossly overestimated weights. The accuracy of the predictions of total tree biomass changed according to the gradient in height:diameter ratio of the sample trees of the original studies. Equations from trees with similar h/d ratio as the sample trees were more accurate than others. When equations from the literature are used to estimate biomass for given stands, equations that resulted from sample trees with similar height:diameter ratios should be preferred.     

A GIS-based analysis on the relationship between the annual available amount and the procurement cost of forest biomass in a mountainous region in Japan

The feasibility of utilization of forest biomass for energy in a mountainous region in Japan is discussed based on analyses with a geographic information system (GIS). In this study, ‘forest biomass’ denotes logging residues, thinned trees, and trees from broad-leaved forests. First, using the GIS, the distribution map of biomass resources was completed, and the topographical information of each sub-compartment was prepared. Second, harvesting and transportation systems were classified into six types by fraction of tree for energy (two types) and by topographical conditions (three types). Equations for cost calculation were developed and included the variables slope, skidding/yarding distance, and transportation distance. Finally, the relationship between the mass and the procurement cost of forest biomass in the region was analyzed. The results show that logging residues (the available amount was 4.035 Gg y⁻¹ on a dry-mass basis) were the least costly followed by broad-leaved forests (20.317 Gg y⁻¹) while thinned trees (27.854 Gg y⁻¹) were the most costly. The analysis may support operational planning, especially the decision of selecting sub-compartments to be felled. For instance, the amount of biomass needed to supply a power-plant covering 24.8% of the regional household need was calculated to 30.106 Gg y⁻¹. This amount of forest biomass could optimally be harvested from sub-compartments whose procurement costs were lower than 108.6 US$ Mg⁻¹.     

Biomass production from traditional coppice management in northern Italy

Traditional coppice stands cover millions of hectares throughout Europe and offer large amounts of biomass. The study analyzed 10 commercial coppice harvesting operations in northwestern Italy, where modern machines were deployed. Removals, prices, work, revenues and costs were carefully determined. Firewood was the main product, representing between 70% and 100% of the total product mass and value. Traditional coppice stands often yield over 200 m³ of energy biomass per hectare, at the time of cut. Cable yarding operations were better organized than ground-based operations, which explained why they incurred the same harvesting cost, despite the more challenging site conditions under which they were deployed. Mean harvesting cost was 45 € m⁻³, of which about 10% was needed for felling, 70% for extraction and processing, and the remaining 20% for loading and transportation. All operations accrued some profit, which varied between 13 and 43 € m⁻³ or between 1600 and 8600 € ha⁻¹, depending on operational efficiency, value recovery and stand yield.     

Woody biomass in the U.S. Cornbelt? Constraints and opportunities in the supply

The U.S. is clearly entering a new era of liquid fuel production; one that will be characterized by increasing degrees of renewable raw materials. Woody biomass is an especially compelling feedstock choice where available. Significant questions, however, exist regarding the potential of some landscapes to provide this feedstock. In an effort to answer these questions, we performed an exploratory spatial assessment of woody biomass production and supply capabilities in two-ecoregions Mississippi River corridor within the US Cornbelt. We used existing forest/timber inventories and conducted in-depth interviews with large regional sawmills to understand the accessibility of woody biomass from natural forests, availability of and general costs associated with woody biomass in the existing timber industry, and potential for production from short-rotation woody crop plantations. On an annual basis, taking into account only the annual net growth of non-sawlog species the Midwest Driftless Area currently produces 3.14 times the raw material required by a hypothetical facility using one-half million dry tons of woody biomass per year. Although allocated over a larger area, the Central Dissected Till Plain produces 3.94 times the required material. Throughout the entire region there would be an additional lower bound estimate of 107,000 dry Mg from easily transportable sawmill residues. The ecological state of US Cornbelt forests stand to gain from a developed market for woody biomass as proper woodland management to harvest trees, preserve wildlife, and reduce risk from disease, pests, and invasive species typically involves harvesting the low-value trees that will by and large drive the woody biomass system.     

Predictive models of forest logging residues in Romanian spruce and beech forests

Forest logging residues are systematically left after exploitation. In Romania, logging residues were traditionally used by population for fuel but have not been considered at large scale for industrialization. The estimation of the resource needed a more accurate assessment and the development of devoted biomass models for large-scale applications. Our study aims at estimating the amount of logging residues based on direct biomass measurements for the two main species of Romanian Carpathian forests: Norway spruce and beech. A country-scale field measurement campaign resulted in the sampling of 100 Norway spruce and 74 beech trees. Models of logging residues biomass were developed for both species. The amount of potential logging residues per tree was greater in beech than in Norway spruce. The models developed, nonlinear by essence, showed that diameter-based equations enable the evaluation of individual logging residues potential. Using tree height as an additional independent variable did not improve the models. The models fitted were applied to yield tables in order to estimate the resource potential in spruce and beech stands for each productivity class, and its dynamic during the production cycle. The calculations proved that the potential amount of logging residue is larger in spruce stands. The amount in beech is very sensitive to the productivity class, unlike in spruce stands. The potential biomass produced during early thinnings is however greater in beech stands than in spruce ones. A more systematic and organized collecting of residues could offer a fast answer to the need of increasing renewable energy share.     

Growth patterns and biomass productivity of two Salix species grown under short-rotation intensive culture in southern Quebec

Samples of two species of Salix, Salix discolor, which grows naturally in the northern half of North America and S. viminalis, which originated from central Europe, were studied to compare their productivity and their growth patterns under the short-rotation, intensive-culture system (SRIC). The study was conducted in the nursery of the Montreal Botanical Garden on former agricultural land. The plantation was established at a density of 27,000 trees per hectare from unrooted cuttings without any fertilizer or irrigation. Growth parameters were measured at regular intervals during summer of the two first years following planting. At the end of each growing season, after leaf drop, a part of each plot was cut down and the stems and branches were harvested and weighed to evaluate their annual growth rates and their biomass yields. For the first growing season, height growth in both species was greater than 2 m. Although S. viminalis grew more rapidly early in summer, S. discolor grew about three weeks longer and its total height at the end of the growing season was greater than the former. Meanwhile the stem-branch dry weight of S. discolor was similar to the one produced by S. viminalis. Two growing seasons after establishment, the total tree height was about 3.5 m for both species, while the biomass of stems and branches of S. viminalis was weakly superior in comparison to S. discolor and reached very high values-about 27 Mg ha⁻¹ for S. viminalis. The growth patterns and yields of the one-year-old coppice (one-year-cycle) were similar to those recorded at the end of the first year for trees developed directly from cuttings. Both species produced a comparable quantity of sprout biomass. The yield of the trees harvested two years after planting was about twice the total biomass harvested two times, at the end of each growing season, suggesting that a two-year cycle is more productive than a one-year cycle.     

Managing regrowth of an indigenous savanna tree species (Terminalia sericea) for fuelwood: the influence of stump dimensions and post-harvest coppice pruning

Most African savannas are subjected to harvesting of wood, especially for fuelwood, charcoal and construction timber. A key attribute of the resilience and productivity of savannas is the ability of damaged trees to regrow from the remaining stump. Survival of the cut stem and growth rate of the resultant coppice shoots is influenced by several factors, including size of the tree, cutting height and the root/shoot ratio after felling. Some of these can be manipulated to maximise subsequent regrowth, but this is little understood for most African savanna species. This study investigated the influence of original tree size, height of cut and post-harvest pruning on regrowth of Terminalia sericea. Regrowth was monitored as the number of coppice shoots, the mean coppice shoot length and the cumulative coppice shoot length per cut stump over four growing seasons. There was a positive relationship between cutting height and number of coppice shoots, but height of cut did not significantly affect mean or cumulative coppice shoot length. Larger stems produced more coppice and had greater mean and cumulative coppice shoot lengths than smaller stems. Post-harvest pruning increased the mean shoot length, but not the cumulative shoot length. After four growing seasons mean shoot length for the single shoot pruning treatment (one shoot left) was 54% greater than for the no prune treatment, whilst the double shoot pruning (two shoots left) was 40% greater. Extrapolated harvest intervals for fuelwood poles were 3–4 years for large stems, 4–5 years for medium-sized stems, and 4–9 years for small stems.     

Forests for carbon sequestration or fossil fuel substitution? A sensitivity analysis

Among the proposals for mitigating the increase of atmospheric CO₂ are the possibility of reforesting degraded lands to sequester C or of using sustainable forest harvests to displace fossil fuels. Storing C on-site in forests and harvesting forests for a sustainable flow of forest products are not necessarily conflicting options if we recognize that their relative merits in mitigating net emissions of C will depend on site-specific factors, such as forest productivity and the efficiency with which harvested material is used. Since the land available for reforestation or development of forest plantations is limited, the relative merits of the different mitigation strategies need to be considered. We use a mathematical model of C stocks and flows to compare the net effect on C emissions to the atmosphere for the two approaches over a range of values of forest productivity and the efficiency of product use. When sustainably-produced forest products are used inefficiently to displace fossil fuels, the greater C benefit is achieved through reforestation and protection of standing forests, and increasing the rate of stand growth yields little gain. However, when forest products are used efficiently to displace fossil fuels, sustainable harvest produces the greater net C benefits, and the benefit increases rapidly with increasing productivity.     

Above-ground biomass functions for Scots pine in Lithuania

This study presents biomass functions applicable to Scots pine (Pinus sylvestris L.) on Arenosols in Lithuania, and exemplifies the potential biomass removal from Scots pine stands during thinnings. Scots pine is the most common tree species on Arenosols in Lithuania. Stands of ages 10, 20, 40, 50 and 65 years were chosen for the biomass study. We sampled 5 Scots pine trees per plot (in total 25 trees) that were stratified according to the basal area. The sampling was performed in April 2003, before the vegetative period. The following components of each tree were sampled for the above-ground biomass measurements: (1) 5 stem discs, (2) 1 branch with needles from each whorl and (3) 1 dead branch per tree.Observed biomasses of above-ground components were examined using a non-linear regression model, using stem diameter (D), tree height (H) and D²H as independent variables.For stemwood biomass, the best approximation was D²H. However, D²H was not the best parameter for crown biomass because it does not allow evaluation of the opposite effects of diameter and height on crown biomass. The calculations at stand level showed that crown biomass changed insignificantly with the increase in stand age. However, the total stand biomass increased with age due to the growth of the stem. The removal of all logging residues from the Scots pine stand over a 100-year rotation could increase extraction of forest fuel by 15–20% compared with conventional harvesting.     

Criteria and indicators for sustainable forest fuel production and harvesting: A review of current standards for sustainable forest management

Forest biomass is increasingly being considered as a source of sustainable energy. It is crucial, however, that this biomass be grown and harvested in a sustainable manner.International processes and certification systems have been developed to ensure sustainable forest management (SFM) in general, but it is important to consider if they adequately address specific impacts of intensified production and harvesting methods related to forest fuels. To explore how existing SFM frameworks address sustainable forest fuel production, criteria and indicators (C&I) from 10 different international processes and organizations and 157 international, national and sub-national forest management certification standards under the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC) were reviewed. International processes include indicators that require identification or reporting of availability, harvested amounts, value, or share in energy consumption of forest fuels. Forest certification standards address several specific woodfuel issues, but not always in a consistent manner. It seems that developed countries more frequently address environmental consequences of harvesting residues or whole trees on soil fertility and biodiversity, while developing countries more frequently address social issues, such as local people’s access to firewood and working conditions in charcoal production. Based on findings, options to improve SFM standards for sustainable forest fuel production are discussed. These options include clarification of terminology, systematic inclusion of important management impacts unique to forest fuel production, coordination of efforts with other related governance processes, including tools promoting sustainability at more integrated levels, such as landscape, supply chain and global levels.