Recovery rates of logging residue harvesting in Norway spruce (Picea abies (L.) Karsten) dominated stands

A significant amount of logging residues is available for recovery in clear-cut areas. The forest residues’ potential has usually been estimated using biomass models. In Norway spruce (Picea abies) dominated stands, a large share of material is left on site especially due to dropping of needles as residues are left on site to dry in small heaps. In this study, we compared the measured dry weight of logging residues at a power plant with the potential biomass estimations made at a stand level. The study was performed in eight Norway spruce dominated stands, three of which were located in eastern Finland (North Karelia region) with the remainder being in Central Finland. The dry weights of branches, needles and stem tops were estimated using biomass models developed for individual trees by Repola et al. [1]. These dry weights were also compared with Swedish biomass models produced by Marklund [2]. The diameter and tree height information of each harvested tree served as input data in these model-based computations. Tree diameter information was obtained straight from the harvester’s stem value files, while the height information was obtained from models using the data from the stem value files as input. Inventory data before logging was used as a control material for harvester based estimates to spot possible measurement errors on the harvester measurement data. In addition, inventory data were used to get the crown height information, which was not available in the harvester measurement data. It was found that the average recovery rate was approximately 62% when applying Repola’s et al. [1] models and 61% when applying Marklund’s [2] models. However, variation between the logging sites was high. According this study, at least a third of the residues remains on the logging site if they are seasoned during the spring and summertime in small heaps.     

Impacts of changing the minimum diameter of roundwood on the accumulation of logging residue in first thinnings of Scots pine and Norway spruce

The aim of this study was to examine the impacts of different minimum top diameters of roundwood on the accumulation of logging residue in first thinnings of Scots pine and Norway spruce. The aim was also to compare estimates of residue accumulation calculated by tree-specific models with field measurements from thinnings. Felling experiments were performed in young pine and spruce stands to evaluate the model calculations. The felling was performed by a harvester with a single-grip harvester head. Sample trees were felled and processed to a minimum diameter of 12, 10, 8 and 6 cm and the delimbed branches and stem wood between these cutting points were weighed. The mean relative masses of the tree tops of spruce were nearly doubled with each increment of 2 cm in the top diameter. Respectively in pine, the mean relative tree top mass was increased by 50-60% when the top diameter was increased by 2 cm. The mass of total residue (tree top and all delimbed branches) was similarly increased, but the differences were not as large. Compared to pine, smaller variation in the crown mass of the spruce sample resulted in a more accurate model prediction of the mass of tree tops and total residue. The results of this study suggest that the biomass quantity and distribution of a small amount of trees cannot be predicted very reliably, but when these results are generalized to stand-level, the model predictions can be improved to a practicable level.     

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.     

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).     

The carbon sequestration potential of unmanaged forest stands in Finland under changing climatic conditions

Changes in stand-level carbon (C) storage and C flows in biomass, litter and soil organic matter in the humus layer were studied under current and changing climatic conditions in Finland with the help of a gan-type simulation model. The changing climate scenario assumed increases in mean annual temperature of 0.4°C per decade for the first one hundred years and 0.2°C per decade for the second hundred years. Warming was assumed to be larger during the winter than during the other seasons.

In southern Finland, the long term average (over 200 years) net forest ecosystem production (NEP) at the stand level was 0.4–1.0 Mg C/ha/a under the current climatic conditions, and 0.1–0.9 Mg C/ha/a under changing conditions, depending on the tree species. Under the climate change scenario, NEP decreased in Scots pine, Norway spruce and Pubescent birch stands, but increased in Pendula birch stands. During the first 25–50 years, however, NEP was found to be larger both in Scots pine and Pubescent birch stands. In northern Finland, the long term average NEP increaed, regardless of tree species, from 0.3–0.8 Mg C/ha/a to 0.4–1.0 Mg C/ha/a. The biggest changes took place in Norway spruce and Pendula birch stands.

During the early and late phases of stand development, the stands were C sources, since emissions from decaying litter and soil organic matter in the humus layer exceeded the growth of vegetation. Stands became C sources earlier under the changing climatic conditions than under the current conditions. In southern Finland, the long term average C storage was 107–201 Mg C/ha under the current climatic conditions, and 88–142 Mg C/ha under the changing conditions, depending on tree species. In northern Finland, the long term average C storage was 77–151 Mg C/ha under the current climatic conditions and 89–177 Mg C/ha under the changing conditions.     

Available residual biomass obtained from pruning Morus alba L. trees cultivated in urban forest

Large quantity of residual biomass with possible energy and industrial end can be obtained from management operations of urban forests. The profitability of exploiting these resources is conditioned by the amount of existing biomass within urban community ecosystems. This research was focused on direct and indirect quantification of lignocellulosic waste from urban tree pruning of Morus alba, which is widely deployed as ornamental vegetation in Mediterranean countries. The mean quantity of dried pruned biomass obtained in street and park location was 31.67 kg/tree and 77.78 kg/tree with standard deviation 16.88 kg/tree and 29.51 kg/tree, respectively. Mathematical models for predicting the available amount of pruning residues for this species were developed from easily measurable dendrometric parameters, such as diameter at breast height, crown diameter and total tree height. The best functions were obtained when several variables were combined in quadratics models. R² was 0.96 for topping type of pruning practice and street location, and 0.88 in maintenance pruning applied in park areas. Good results were also found when correlating apparent crown volume with kilograms of yielded residues. These models can be used for urban inventories and the application of logistic models. The analysis indicates that an abundant amount of residual biomass originating from pruning operations of ornamental species can be used to achieve ecological and energy targets.     

A study of bonding and failure mechanisms in fuel pellets from different biomass resources

Pelletization of biomass reduces its handling costs, and results in a fuel with a greater structural homogeneity. The aim of the present work was to study the strength and integrity of pellets and relate them to the quality and mechanisms of inter-particular adhesion bonding. The raw materials used were: beech, spruce and straw, representing the most common biomass types used for fuel pellet production, i.e. hardwoods, softwoods and grasses, respectively. The results showed that the compression strengths of the pellets were in general higher for pellets produced at higher temperatures, and much higher for wood pellets than for straw pellets. Scanning electron microscopy of the beech pellets fracture surfaces, pressed at higher temperatures, showed areas of cohesive failure, indicating high energy failure mechanisms, likely due to lignin flow and inter-diffusion between adjacent wood particles. These were absent in both spruce and straw pellets. Infrared spectroscopy of the fracture surfaces of the straw pellets indicated high concentrations of hydrophobic extractives, that were most likely responsible for their low compression strength, due to presence of a chemical weak boundary layer, limiting the adhesion mechanism to van der Waals forces. Electron micrographs indicating interfacial failure mechanisms support these findings. Infrared spectra of the fracture surface of wood pellets, pressed at elevated temperatures, showed no signs of hydrophobic extractives. It has been shown that both temperature and chemical composition, i.e. the presence of hydrophobic extractives, have a significant influence on the bonding quality between biomass particles during the pelletizing process.     

Energy and greenhouse gas balance of the use of forest residues for bioenergy production in the UK

Life cycle analysis is used to assess the energy requirements and greenhouse gas (GHG) emissions associated with extracting UK forest harvesting residues for use as a biomass resource. Three forest harvesting residues were examined (whole tree thinnings, roundwood and brash bales), and each have their own energy and emission profile. The whole forest rotation was examined, including original site establishment, forest road construction, biomass harvesting during thinning and final clear-fell events, chipping and transportation. Generally, higher yielding sites give lower GHG emissions per ‘oven dried tonne’ (ODT) forest residues, but GHG emissions ‘per hectare’ are higher as more biomass is extracted. Greater quantities of biomass, however, ultimately mean greater displacement of conventional fuels and therefore greater potential for GHG emission mitigation. Although forest road construction and site establishment are “one off” events they are highly energy-intensive operations associated with high diesel fuel consumption, when placed in context with the full forest rotation, however, their relative contributions to the overall energy requirements and GHG emissions are small. The lower bulk density of wood chips means that transportation energy requirements and GHG emissions are higher compared with roundwood logs and brash bales, suggesting that chipping should occur near the end-user of application.     

Dissolution of granulated wood ash examined by in situ incubation: Effects of tree species and soil type

Wood ash recycling to forests may counteract nutrient losses caused by biomass harvest, since most nutrients except nitrogen are largely retained in the ash. Raw wood ash has an alkaline reaction with water and contains easily soluble as well as resistant compounds. Ash can be treated to ease handling and to avoid undesired effects on vegetation and leaching of nutrients. Forest ecosystems with different tree species and soils provide variable conditions for mineral dissolution with respect to pH, amount of organic ligands and humidity in the forest floor and the top soil. To study the effects of tree species and soil type on wood ash dissolution, granulated wood ash with particle size 2–4 mm was incubated in situ for 7 years in polyamide mesh bags. The bags were placed under the organic horizon of beech, oak, Norway spruce and Douglas-fir on a nutrient poor soil (typic Haplorthod) and a nutrient-rich soil (oxyaquic Hapludalf) in Denmark. After 7 years of incubation, the weight loss of the wood ash granulates was 20% in both soil types. Nutrient losses determined by total element analysis were about 35% for calcium, magnesium and potassium and 19% for phosphorus, regardless of tree species or soil type. Incubation for 7 years could not demonstrate possible effects of tree species and soil type on the dissolution of granulated wood ash incubated in mesh bags. The missing effect of tree species and soil type is suggested to be an effect of the incubation method and the pre-treatment of the ash tested here using cement as a binder. Across this broad range in chemical weathering environment the granulated wood ash dissolved at a rather slow rate, suggesting that this ash will have a negligible impact on the soil environment.     

Quality properties of pelletised sawdust,logging residues and bark

The dominant raw material for wood pellet production in Sweden is sawdust, planer shavings and dry chips. However, other types of biomass, such as bark and logging residues, are also interesting raw materials due to the large volumes available. These alternative raw materials differ from stemwood with regard to physical characteristics and chemical composition. In order to produce high-quality pellets of such materials, it is necessary to understand the role of these variations. Nine pellet assortments, made of fresh and stored sawdust, bark and logging residues (a mixture of Norway spruce and Scots pine) were tested for moisture content, heating value and contents of ash, sulphur, chlorine and Klason lignin. Dimensions, bulk density, density of individual pellets, durability and sintering risk were also determined. The heating value was highest in logging residue pellets. The ash content was highest in the bark and logging residue pellets, implying higher sintering risk compared with sawdust pellets. The results showed that bark pellets had the highest durability, whereas sawdust pellets had the lowest. Pellet density had no effect on durability, unlike lignin content which was positively correlated. It is concluded that bark and logging residues are suitable raw materials for pellets production, especially if the ash content is controlled.     

Performance of two shear heads for harvesting biomass in hardwood stands in France

The increasing demand for energy wood in Europe is accompanied by the development of new harvesting tools to mobilize forest biomass, notably hardwood biomass. Two logging operations are targeted more specifically: the first thinnings in regular high forest, and the clear cuttings of traditional coppices and of high productive short rotation coppices. The challenge is to find efficient and sustainable harvesting tools for hardwood trees that are very common in central and southern Europe.Two French manufacturers have recently developed shear heads dedicated to hardwood: Jacquier C360 and Sève S350. Nowadays, many logging companies are investing in these tools, as they are relevant to the whole tree system that has been adopted for harvesting woody biomass.The performance of these shear heads was determined on 3 logging sites in the North East of France. A regression analysis was run in order to evaluate models for cutting productivity of each machine, considering significant factors influencing productivity: tree size and stand type (high forest/coppice).The two shear heads were more productive at high forest than at coppice. The stand type had a significant effect only on the C360’s productivity. At high forest sites with small diameter trees, the C360 was 11.8% more productive than the S350. However, at coppice site, the S350 was 15% more productive than the C360 for harvesting big clumps. Results showed that working in coppice forest requires a head that must be very powerful and have a wide opening.     

Optimum stand density of Leucaena leucocephala for wood production in Andhra Pradesh, Southern India

Leucaena leucocephala is widely used as raw material for the manufacture of paper and packaging material and in biomass based power plants in the state of Andhra Pradesh, Southern India. Experiments were conducted to study the affect of tree density on the growth, biomass partitioning and wood productivity. Six treatments 1 × 1 m, 1.3 × 1.3 m, 3 × 0.75 m, 3 × 1 m, 5 × 0.8 m and 3 × 2 m corresponding to a tree density of 10,000, 6666, 4444, 3333, 2500 and 1666 were evaluated with leucaena variety K636. At 51 months after planting, spacings significantly influenced tree height, diameter at breast height (DBH), number of branches and biomass partitioning. Wider tree rows resulted in greater tree height and diameter growth resulting in higher per plant productivity. At harvest, 70% of trees in 3 × 2 m attained a diameter of more than 7.5 cm, while 35% of the trees attained the same DBH in 1 × 1 m spacing. Increased spacing levels decreased the relative amount of growth allocated to the bole of the tree. Marketable biomass yield was highest with 1 × 1 m spacing. Spacing of 3 × 0.75 m produced marketable biomass comparable to that of 1 × 1 m and greater proportion of stems with more than 5 cm diameter. Leucaena can be grown at 3 × 0.75 m spacing either for pulpwood or fuelwood depending on the prevailing market prices and demand.     

Enhancement of bioenergy estimations within forests using airborne laser scanning and multispectral line scanner data

Forest biomass is a substantial source of renewable energy and is becoming increasingly important due to environmental and economic reasons. In Germany, several studies have assessed the bioenergy potential for large areas, e.g. for an entire Federal state. However, in most cases it was not possible to provide detailed maps showing the biomass and the sustainable energy potential for individual forest stands. Thus, the aim of this study was to develop a new and robust method that provides detailed information regarding the spatial distribution of biomass and forest residues as a potential energy resource using a combination of remotely sensed and in situ data. A case study was carried out in a mixed forest in Southern Germany. First, regression analyses were applied to identify relationships between field measurements with several remote sensing metrics to estimate timber volume, mean stem diameter and age. Cross-validation yielded relative root mean square errors (RMSEs) of 30.20% for volume, 27.92% for diameter and 28.81% for the estimation of the age. The absolute RMSEs were smaller than the standard deviation of the observed variables. Next, the regression equations were used to compute attributes for individual forest stands. Stand attributes were then used to model forest residues. To estimate the sustainable annual potential, the actual harvest volume, as defined by forest management planning, was included in the model. Different model parameters were analyzed and an average potential from 0.993 to 1.181 t ha⁻¹ a⁻¹ was computed. The results were compared to previous studies in Germany.     

Quantification of the residual biomass obtained from pruning of trees in Mediterranean olive groves

This research quantified the available residual biomass obtained from pruning olive trees. The additional biomass quantified could be used as a source of energy or as raw material for the wood industry and would provide additional income for fruit producers and also a more sustainable system. Several factors were analyzed: Variety, aim of the pruning, age of the plants, size of the plantation, crop yield and irrigation. Regression models were also calculated to predict the weight of dry biomass obtained per tree and tonnes of dry biomass obtained per hectare according to the significant factors. These equations could implement logistic planning as the Borvemar model, which defines a logistics network for supplying bio-energy systems. Olive tree varieties were classified into two groups for annual pruning: high residual biomass productivity (average yield 10.5 kg dry biomass tree⁻¹) and low productivity (average yield 3.5 kg dry biomass tree⁻¹). Some varieties are in transition between the two groups. There are no differences in biennial pruning, reaching an average residual biomass of 33 kg tree⁻¹. This means that in Mediterranean areas the residual biomass from olive pruning reaches an average 1.31 t ha⁻¹ in annual pruning and 3.02 t ha⁻¹ in biennial pruning.     

Future production and utilisation of biomass in Sweden: Potentials and CO2 mitigation

Swedish biomass production potential could be increased significantly if new production methods, such as optimised fertilisation, were to be used. Optimised fertilisation on 25% of Swedish forest land and the use of stem wood could almost double the biomass potential from forestry compared with no fertilisation, as both logging residues and large quantities of excess stem wood not needed for industrial purposes could be used for energy purposes. Together with energy crops and straw from agriculture, the total Swedish biomass potential would be about 230 TWh/yr or half the current Swedish energy supply if the demand for stem wood for building and industrial purposes were the same as today. The new production methods are assumed not to cause any significant negative impact on the local environment. The cost of utilising stem wood produced with optimised fertilisation for energy purposes has not been analysed and needs further investigation. Besides replacing fossil fuels and, thus, reducing current Swedish CO₂ emissions by about 65%, this amount of biomass is enough to produce electricity equivalent to 20% of current power production. Biomass-based electricity is produced preferably through co-generation using district heating systems in densely populated regions, and pulp industries in forest regions. Alcohols for transportation and stand-alone power production are preferably produced in less densely populated regions with excess biomass. A high intensity in biomass production would reduce biomass transportation demands. There are uncertainties regarding the future demand for stem wood for building and industrial purposes, the amount of arable land available for energy crop production and future yields. These factors will influence Swedish biomass potential and earlier estimates of the potential vary from 15 to 125 TWh/yr.     

Assessment of potential biomass energy production in China towards 2030 and 2050

The objective of this paper is to provide a more detailed picture of potential biomass energy production in the Chinese energy system towards 2030 and 2050. Biomass for bioenergy feedstocks comes from five sources, which are agricultural crop residues, forest residues and industrial wood waste, energy crops and woody crops, animal manure, and municipal solid waste. The potential biomass production is predicted based on the resource availability. In the process of identifying biomass resources production, assumptions are made regarding arable land, marginal land, crops yields, forest growth rate, and meat consumption and waste production. Four scenarios were designed to describe the potential biomass energy production to elaborate the role of biomass energy in the Chinese energy system in 2030. The assessment shows that under certain restrictions on land availability, the maximum potential biomass energy productions are estimated to be 18,833 and 24,901?PJ in 2030 and 2050.     

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.     

Biomass equations and estimation for Gmelina arborea and Nauclea diderrichii stands in Akure forest reserve

Biomass estimation was carried out for even-aged stands of Gmelina arborea and Nauclea diderrichii in Akure forest reserve. Linear and allometric regression equations for biomass prediction were developed for trees of both species. The yield of each species and total above-ground biomass (TAGB) were estimated and compared. The various equations developed were assessed based on high coefficient of determination (R²), significant F-ratio, and small Furnival index (FI) to select appropriate equation for prediction. The t-test shows a significant difference when the total volume and total dry weight of both species were compared, Gmelina arborea having a greater value than Nauclea diderrichii in both cases. The total volume of Gmelina arborea per hectare was 721.40 m³ and 265.18 m³ for Nauclea diderrichii. The TAGB for Gmelina arborea was 264,762 kg/ha and 88,293 kg/ha for Nauclea diderrichii.     

Importance of biomass energy sources for Turkey

Various agricultural residues such as grain dust, crop residues and fruit tree residues are available in Turkey as the sources of biomass energy. Among the biomass energy sources, fuelwood seems to be one of the most interesting because its share of the total energy production of Turkey is high at 21% and the techniques for converting it to useful energy are not necessarily sophisticated. Selection of a particular biomass for energy requirements is influenced by its availability, source and transportation cost, competing uses and prevalent fossil fuel prices. Utilization of biomass is a very attractive energy resource, particularly for developing countries since biomass uses local feedstocks and labor. Like many developing countries, Turkey relies on biomass to provide much of its energy requirement. More efficient use of biomass in producing energy, both electrical and thermal, may allow Turkey to reduce petroleum imports, thus affecting its balance of payments dramatically. Turkey has always been one of the major agricultural countries in the world. The importance of agriculture is increasing due to biomass energy being one of the major resources in Turkey. Biomass waste materials can be used in Turkey to provide centralized, medium- and large-scale production of process heat for electricity production. Turkey's first biomass power project is under development in Adana province, at an installed capacity of 45 MW. Two others, at a total capacity of 30 MW, are at the feasibility study stage in Mersin and Tarsus provinces. Electricity production from biomass has been found to be a promising method in the nearest future in Turkey.     

Woody energy crops in the southeastern United States: Two centuries of practitioner experience

Forest industry experts were consulted on the potential for hardwood tree species to serve as feedstock for bioenergy in the southeastern United States. Hardwoods are of interest for bioenergy because of desirable physical qualities, genetic research advances, and growth potential. Yet little data is available regarding potential productivity and costs. This paper describes required operations and provides a realistic estimate of the costs of producing bioenergy feedstock based on commercial experiences. Forestry practitioners reported that high productivity rates in southeastern hardwood plantations are confined to narrow site conditions or require costly inputs. Eastern cottonwood and American sycamore grow quickly on rich bottomlands, but are also prone to pests and disease. Sweetgum is frost hardy, has few pest or disease problems, and grows across a broad range of sites, yet growth rates are relatively low. Eucalypts require fewer inputs than do other species and offer high potential productivity but are limited by frost to the lower Coastal Plain and Florida. Further research is required to study naturally regenerated hardwood biomass resources. Loblolly pine has robust site requirements, growth rates rivaling hardwoods, and lower costs of production. More time and investment in silviculture, selection, and breeding will be needed to develop hardwoods as competitive biofuel feedstock species. Because of existing stands and fully developed operations, the forestry community considers loblolly pine to be a prime candidate for plantation bioenergy in the Southeast.