Interaction in Short Rotation Coppice willow,Salix viminalis genotype mixtures

Seven straight Salix viminalis genotypes with different levels of rust (Melampsora epitea) susceptibility were grown as mono-plots as well as being incorporated into a range of mixtures. Two 3-year harvests (2003 and 2006) were taken. Disease progress was followed on each of the individual genotypes throughout each growing season 2001–2006. In 2003 there were small but significant yield increases from the mixtures compared to the yield of individual components grown as mono-plots. These differences were not evident at the second harvest in 2006. No consistent effect of mixtures on reducing rust on the most susceptible genotype, Salix viminalis ‘77082’ were observed. In some years, e.g. 2003, at certain times during the growing season, significant reductions were observed on Salix viminalis ‘77082’ in certain 3-way mixtures compared to mono-plots. These, however, were not repeated consistently in subsequent years. It was concluded that the current commercial practice in many parts of Europe of planting mixtures as a disease control strategy will only be effective if there is sufficient genetic diversity between the Salix genotypes incorporated into the mixture.     

Biomass production of Salix viminalis in southern Finland and the effect of soil properties and climate conditions on its production and survival

Ten Salix viminalis clones were cultivated in 35 experimental plantations situated on privately-owned farms in southern and central Finland. Management instructions were given to the farmers who established and tended the study plots. The biomass production and survival of the clones were recorded by inventory every year during the first rotation period, which consisted of the establishment year and three following growing seasons. The greatest amount of biomass production exceeded 30 above-ground tonne of dry matter/3 years, but amounts varied greatly between the experimental plantations. The main reasons causing this variation were the low frost hardiness of most of the S. viminalis clones and unsuccessful weed control during the year the plantations were established. Early autumn frost in particular caused severe damage. S. viminalis grew rather well on a wide variety of soil types. Sufficient amounts of nitrogen, potassium and organic matter seem to be the properties which most clearly have an effect on the biomass production and survival of S. viminalis in mineral soils. A relatively small amount of manganese in wet and low oxygenic soils is recommended, because a high content may cause toxic effects. In this study S. viminalis clones only succeeded well in southernmost Finland, where properly managed plantations produced rather high biomass yields. In other parts of southern and central Finland more research work on frost resistance and the breeding of new clones is needed. To conclude, in the climatic conditions of Finland energy willow husbandry is a compromise between high biomass yield and frost hardiness.     

Allometric relationships from coppice structure of seven North American willow (Salix) species

Biomass yield and component coppice growth traits were assessed in up to 20 clones from seven native North American willow species, Salix amygdaloides (SAM), Salix bebbiana (BEB), Salix discolor (DIS), S eriocephala (ERI), Salix humilis (HUM), Salix interior (INT), and Salix nigra (NIG), established together in a clonally replicated common-garden field test. Aboveground mass, coppice stem number, stem length, and stem basal diameter measurements on up to 20 of the largest stems from 2-yr-old coppiced plants showed that ERI had the greatest aboveground mass, followed by INT, and then a close grouping of BEB, DIS, and HUM; the “tree” willows, AMY and NIG, had the lowest yields. The tree willows were not as prolific in coppice stem sprout production as were the shrub willows. The greatest number of stem sprouts was produced by ERI, with one coppice producing 67 2-yr-old stem sprouts, and ERI also showed an atypical, non-negative relationship between stem size and stem number; whereas the other six willows showed a varying but expected negative relationship between coppice stem size and stem number. Species differences in allometric relationships highlight the need to develop species-specific models for more accurate non-destructive biomass yield estimation.     

Combustion of Salix used for phytoextraction: The fate of metals and viability of the processes

Phytoextraction may reduce the environmental risk posed by contaminated sediments while simultaneously providing an economic return via bioenergy production. There is a lack of information on the combustion of metal enriched willows used for phytoextraction. This work aimed to determine the Cd phytoextraction efficiency of Salix on a case study in France and elucidate the distribution of metals in the end products of the combustion process. Three willow clones were cultivated in short rotation coppice (SRC) on a metal contaminated dredged sediment landfill site. Combustion assays were performed in a biomass boiler of 40 kW with a Zn and Cd enriched Salix wood ‘Tora’ harvested from a part of the SRC and a commercial ‘Tora’, for comparison. In a best-case scenario, phytoextraction could reduce total Cd burden of the sediment from 2.39 mg kg⁻¹ DW to 2 mg kg⁻¹ DW in 19 years. Combustion experiments showed that Cd and Zn occurred at the highest concentrations in the particulate fraction of the flue gas (flyash), rather than in the bottom ash. Combustion of ‘Tora’ from phytoextraction resulted in Cd and Zn concentrations in flue gas emissions that exceeded French regulation. This was also observed for Cd in the flue gas of the commercial ‘Tora’. Irrespective of the wood provenance, the use of industrial or collective boilers, equipped with efficient filters, is required to minimize air pollution. Given this constraint, wood produced during phytoextraction should be usable for bioenergy production. The possible uses of bottom ash are discussed.     

Development and validation of aboveground biomass estimations for four Salix clones in central New York

Commercial and research scale plantings of short-rotation woody crops require reliable and efficient estimations of biomass yield before time of harvest. Biomass equations currently exist but the accuracy and efficiency of estimation procedures at the level of specificity needs to be quantified for clones being used in North America. Diameter-based allometric equations for aboveground biomass for four clones of willow (Salix discolor, Salix alba, Salix dasyclados, and Salix sachalinensis), between two sites (Canastota and Tully, NY), and across four years (1998–2001), were developed using ordinary least-squares regression (OLSR) on log-transformed variables, weighted least squares regression (WLSR) on log-transformed variables, and nonlinear regression (NLR) methods and validated using independent data sets. Biomass estimations derived from clone, age, and site (Specific) using OLSR equations had highest R² and lowest percent bias (<2.3%) allowing for accurate estimations of standing biomass. Values for specific equations using WLSR were similar, but bias was higher for NLR (0.7–12.5%). However, the amount of time and effort required to develop specific equations, is large and in many situations prohibitive. Biomass estimates derived from clone and age, regardless of site (Intermediate), resulted in small increases in prediction error and a small increase in percent bias using OLSR (<0.4%) and WLSR (<1.7%). The increase in percent bias was larger (1.1–5.7%) for NLR equations. Intermediate models correspond to the loss of only a small amount of accuracy while gaining more efficiency in estimating standing biomass. Estimates of biomass derived from clone alone (general) equations, considering neither age nor site, had the weakest prediction abilities that may lead to large errors for biomass estimations using OLSR (7.0–9.5%), WLSR (1.1–21.7%) or NLR (31.9–143.4%).     

Frost-related dieback of willows. Comparison of epiphytically and endophytically isolated bacteria from different Salix clones,with emphasis on ice nucleation activity,pathogenic properties and seasonal variation

Swedish Salix plantations for biomass production have been suffering severe dieback during the past 10 years, possibly due to the combination of frost and bacterial disease. As opposed to summer and winter, spring and autumn are periods when epiphytic populations of ice nucleation active (INA) bacteria are generally high.The culturable bacterial floras from stems of diseased plants of four Salix viminalis clones were compared in spring and autumn. Both epiphytic and endophytic bacteria were isolated (i.e. from plant surface and from tissues beneath the bark, respectively), characterised and tested for ice nucleating activity and pathogenicity. Some strains were also identified with BIOLOG and 16S rRNA. Endophytically isolated communities were generally more stable than epiphytes, both in number of isolates and type of bacteria. More types were found in autumn than in spring the same year, although the total number of strains isolated was rather constant. In contrast, more strains (and a higher percentage of the total community) expressed ice nucleating activity in spring than in autumn. The overall number of pathogenic strains remained stable but their proportion among the community tested on plants increased. A close relationship was observed between the dieback rates in the field and the percentage of pathogenic strains found in the different clones. The dominating bacterial type isolated, Sphingomonas spp., also contained the highest percentage of ice nucleation active pathogenic strains.     

Willow clones with high biomass yield in short rotation coppice in the southern region of Tohoku district (Japan)

The present study was conducted to select willow (Salix spp.) clones with a high potential for use as biomass energy crops in the southern region of Tohoku district in Japan. Cuttings of 8 willow clones were planted on an abandoned farmland near Sendai (av. annual temp., 10.9 °C) in March 2006, grown throughout the year and cut back in late December 2006 to resprout from the remaining stools in March 2007. The biomass yield in December 2007, after the first growing season, was highest in Salix pet-susu clone KKD, followed by Salix pseudolinearis clone FXM and Salix sachalinensis clone SEN. The biomass yield on December 2008, after the second growing season, was again highest in clone KKD followed by clone FXM, S. pet-susu clone HB471 and S. sachalinensis clone SEN; the average annual yield of dry mass after the second growing season being 3.09, 2.58, 2.17 and 1.85 kgDM plant^?1 for the clones in this order. Plant growth form differed among the clones. Clones FXM and SEN had several shoots of almost uniform base diameter, whereas clones KKD and HB471 showed plagiotropic growth with one thick and several thin shoots. The calorific values of dried stem segments were similar among clones, ranging from 18.7 to 19.1 kJ g^?1. The dried stem segments contained 78.9–81.2 wt.% hollocellulose, 27.2–32.3 wt.% lignin and 2.1–4.0 wt.% extractives with ethanol-benzene, depending on clones. Based on these results, we could select four clones (KKD, FXM, HB471 and SEN) suitable for biomass production by SRWC in this area.     

Evaluation of the co-product pulp from Salix viminalis energy crops

Salix viminalis is among the species that are considered as promising for future energy crops in marginal lands throughout Canada. Whilst research conducted on Salix species is oriented, to a large extent, towards the hydrolytic production of sugars for fermentation, we have considered co-product fibre since it adds potential value to an integrated use of the biomass. In this study, extractives, lignin, hemicellulose, holocellulose and α-cellulose have been quantified using ASTM or TAPPI standard methods. Carbohydrates found in the hemicellulose were also quantified using HPLC. Hemicellulose comparison for one and three years old samples showed that the xylose content increases with age during this growth period. Kraft pulp has been produced at a bench scale (few kg range) using established pulping conditions. The pulp was tested following ATTPC standard methods. Pulp yields were of 29% and 34% for one and three years old samples respectively. The average fibre lengths were shorter for the younger samples, 0.35 mm, as compared with the older samples, 0.41 mm. Short fibres are not necessarily related to the species as much as to the fact that the samples used for the pulping were from young wood. When compared to industrial pulp, the basket willow pulp showed mechanical properties comparable to hardwood pulp which implies that this pulp could eventually be used in similar applications. Comparison with other energy crops shows advantages from the perspective of using this energy crop in Canada to co-produce pulp and, following suitable hydrolysis, sugars for fermentation to ethanol.     

Size matters? – The diverging influence of cutting length on growth and allometry of two Salicaceae clones

Short rotation coppices (SRC) are often established by inserting cuttings vertically into the soil. Longer cuttings are generally regarded as superior to establish plants on stress-prone sites. However, knowledge about above- and belowground biomass production, plant allometry and root characteristic of clones established through different lengths of cuttings is scarce.The experiment was performed with 2 common SRC clones (Populus clone Max 4, Salix clone Inger) and 2 cutting length (20 cm and 40 cm). Above- and belowground biomass and leaf and root morphology were determined after one growing season. Longer cuttings produce more biomass but have a diverging influence on the shoot:root allocation of both clones. Long cuttings of Populus cl. Max produce more aboveground biomass, mostly leaves, than 20 cm cuttings, while 40 cm Salix cl. Inger cuttings have more fine roots. Leaf and root morphology are only marginally influenced by cutting length.Choosing longer Populus cl. Max cuttings might not be a good strategy when considering SRC establishment on more stress-prone sites, since their larger above-ground biomass will e.g. increase transpirational demand. Because of the lower shoot:root ratio, longer Salix cl. Inger cuttings seem to be more suitable to establish SRC on fields with (partially) restricted water and nutrient supply than shorter cuttings. Thus, planting difficulties and higher costs of longer cuttings may be offset by higher survival and greater aboveground productivity only in some clones. In the future, optimal cutting lengths must be evaluated not only for different environmental conditions but also for different SRC species/clones.     

Biomass production,water use and photosynthesis of Salix clones grown in a wastewater purification system

An objective of the study was to identify leaf morphophysiological characteristics indicative of high aboveground woody biomass production of Salix clones growing in the vegetation filter of a wastewater purification system. It was hypothesized, that in these extra irrigated stands, the characteristics of photosynthesis are stronger determinants of the production than the characteristics of leaf water relations. The biomass production of the clones was correlated with numerous characteristics of leaf water relations and photosynthesis. Significant correlation was found between the biomass production and the following characteristics of top foliage leaves: daily decrease in water potential, stomatal conductance, stomatal sensitivity to increase in light intensity, and hydraulic conductance (positive); daily minimum and maximum water potentials, instantaneous water use efficiency, and stomatal sensitivity to decrease in leaf water potential (negative); maximum rate of photosynthetic electron transport, chlorophyll content, and the partitioning coefficient for leaf nitrogen into bioenergetics associated with electron transport (positive). In the most productive clones, the vertical gradient (through foliage) of values of almost all the characteristics was the smallest. The biomass correlated more strongly with the characteristics of photosynthesis light stage than with the characteristics of water relations. We conclude that the characteristics of photosynthesis light stage – high maximum rate of photosynthetic electron transport, high chlorophyll content, and also flat vertical gradient (through foliage) in values of the characteristics could be the strongest indicators of high biomass production of Salix clones growing in vegetation filter.     

Renewable energy in the Kujawsko-Pomorskie Voivodeship (Poland)

In this article we presented the current state and prospects for development of renewable energy in the Kujawsko-Pomorskie Voivodeship, in which the greatest amount of renewable energy in Poland is obtained. In this area there are 96 wind power plants, 103 water power plants, 7 biogas power plants, 4 biofuel producing plants, 3 big energy willow (Salix viminalis) plantations as well as numerous biomass boilers (mostly using wood). In the near future it is planned to further develop renewable energy based on wind, water and biomass.     

Effect of planting vertical/horizontal willow (Salix spp.) cuttings on establishment and yield

The conventional, commercial method of planting Short Rotation Coppice (SRC) willow is the use of a willow planter which delivers 20 cm hardwood cuttings vertically into the soil. On well prepared sites an establishment rate in excess of 90% is normal. Recently there has been interest in developing alternative planting protocols with the imminent launch of a ‘lay-flat planter’ which lays lengths of willow end to end at a depth of 8–10 cm. Small experimental plots were established in 2000 using two Salix spp. genotypes, ‘Olof’ and ‘V7534’ and three planting methods: conventional ‘cuttings’ (20 cm lengths planted vertically), ‘lay-flat’ rods (2–3 m lengths planted horizontally) and ‘billets’ (10 cm lengths planted horizontally). Two three-year harvests were taken in 2003/04 and 2006/07 when establishment, growth pattern and yield were assessed. While there were significant differences between the two genotypes, both responded in a similar way to the different planting protocols. Generally growth from billets was less than from either cuttings or lay-flat rods. The lay-flat system required almost three times more propagating material than either the cuttings or billets. Consequently for the system to be commercially viable significant savings must be made elsewhere, possibly through preparation of planting material, ground preparation or reducing planting costs.     

Geneti|c diversity of superior Salix clones selected for intensive forestry plantations

A number of willow clones are today in use in short rotation intensive culture plantations. The clonal nature of this crop makes it an easy target for pests and pathogens when grown in monocultures. This is a major concern as plantations of coppice must remain viable for up to 20 years to be profitable. In this paper the genetic diversity of 114 selected willow clones was examined and the possible solution of growing willows in multiclonal plantations is discussed. Forty five Salix eriocephala clones, 53 S. exigua clones and 16 clones of their inter-specific hybrid (12 S. eriocephala×exigua clones and 4 S. exigua×eriocephala clones), were evaluated. Starch gel electrophoresis was employed and 12 enzyme systems were used for the assessment of the genetic variation in the clonal material. A total of 29 loci and 57 alleles were revealed. Three measures of genetic diversity were used in order to evaluate the genetic base of the clonal set: average number of alleles per locus, percentage of polymorphic loci and mean heterozygosity. Results indicated that the genetic diversity within a species, is generally lower than the genetic diversity observed in natural populations or full-sib families of the same species. These results, however, are within the limits obtained from natural populations of the Salicaceae family. Heterozygosity values were found to be greater than similar values from poplar clonal material. In contrast to the results within species, inter-specific hybrid clones presented relatively high amounts of genetic diversity. The significance of these results in the management of clonal plantations is discussed from both the operational and conservation points of view.     

Long-term biomass productivity of willow bioenergy plantations maintained in southern Quebec,Canada

Maintaining the long-term productivity of short-rotation coppice plantations is very important to ensure the large-scale deployment of biomass as a renewable energy source. In Quebec (Canada), willow short rotation coppice has been studied since the early ‘90s, thereby allowing long-term analysis of the dynamic performance of several species and hybrids as well as management practices. In this study, we report on the long-term productivity of two trials maintained in southern Quebec and carried out to compare a) growth and biomass yield of willow Salix viminalis (cultivar 5027) grown for 15 years under fertilized and unfertilized conditions and b) growth of different willow cultivars over three successive rotations (10 years). The first trial showed that after four rotations, sludge-fertilized S. viminalis 5027 produced significantly more biomass, 19.2 odt ha⁻¹ yr⁻¹, whereas unfertilized plots yielded 13.8 odt ha⁻¹ yr⁻¹. The second trial showed that among the wide variety of commercial willow cultivars available, SX64 and SX61 along with some indigenous species (i.e. S25, S365, S546) were the most suitable for short-rotation forestry in southern Quebec.     

Biomass and energy production of catch crops in areas with deficiency of precipitation during summer period in central Bohemia

The biomass production dynamics of catch crops, volunteers and weeds in dependence on precipitation and air temperature, was studied in central Bohemia from 2004 to 2006. The cover of individual components of the growth was monitored during the same period. Also measured were energy and efficiency of utilization of global radiation by catch crops and volunteers. The catch crops included the following species: Brassica napus, Lolium multiflorum, Lolium perenne, Phacelia tanacetifolia, Sinapis alba, Trifolium incarnatum, Raphanus sativus var. oleiformis and Trifolium subterraneum. The highest biomass production and the highest cover of catch crops were observed in treatments with S. alba (1382.0 kg ha⁻¹, 47.8%). The average biomass production (sum of catch crops, volunteers and weeds) was highest in treatments with S. alba, R. sativus, and P. tanacetifolia and lowest in treatments with B. napus, L. multiflorum and L. perenne. It was demonstrated that an increase in the percentage share of volunteers caused a decrease in the biomass production of catch crops. The average energy production ranged from 0.31 to 2.37 MJ m⁻² in treatments with catch crops, and from 0.25 to 0.89 MJ m⁻² in treatments with cereal volunteers. The highest effectivity of global radiation utilization, was determined in treatments with S. alba (0.11-0.47%). Based on regression analysis the closest dependence between biomass production from all treatments on the experimental site and precipitation was observed from 1st May till the time of sowing and the average air temperatures from the sowing period till the time of the last biomass production assessment.     

Determination of biomass accumulation in mixed belts of Salix,Corylus and Alnus species in combined food and energy production system

Given the energetic, demographic and the climatic challenges faced today, we designed a combined food and energy (CFE) production system integrating food, fodder and mixed belts of Salix, Alnus and Corylus sp. as bioenergy belts. The objective was to assess the shoot dry weight-stem diameter allometric relationship based on stem diameter at 10 (SD₁₀) and 55 cm (SD₅₅) from the shoot base in the mixed bioenergy belts. Allometric relations based on SD₁₀ and SD₅₅ explained 90–96% and 90–98% of the variation in shoot dry weights respectively with no differences between the destructive and the non-destructive methods. The individual stool yields varied widely among the species and within willow species with biomass yield range of 37.60–92.00 oven dry tons (ODT) ha⁻¹ in 4-year growth cycle. The biomass yield of the bioenergy belt, predicted by allometric relations was 48.84 ODT ha⁻¹ in 4-year growth cycle corresponding to 12.21 ODT ha⁻¹ year⁻¹. The relatively high biomass yield is attributed to the border effects and the ‘fertilizing effect’ of alder due to nitrogen fixation, benefitting other SWRC components. On termination of 4-year growth cycle, the bioenergy belts were harvested and the biomass yield recorded was 12.54 ODT ha⁻¹ year⁻¹, in close proximity to the biomass yield predicted by the allometric equations, lending confidence and robustness of the model for biomass yield determination in such integrated agro-ecosystem.     

High yielding biomass genotypes of willow (Salix spp.) show differences in below ground biomass allocation

Willows (Salix spp.) grown as short rotation coppice (SRC) are viewed as a sustainable source of biomass with a positive greenhouse gas (GHG) balance due to their potential to fix and accumulate carbon (C) below ground. However, exploiting this potential has been limited by the paucity of data available on below ground biomass allocation and the extent to which it varies between genotypes. Furthermore, it is likely that allocation can be altered considerably by environment. To investigate the role of genotype and environment on allocation, four willow genotypes were grown at two replicated field sites in southeast England and west Wales, UK. Above and below ground biomass was intensively measured over two two-year rotations. Significant genotypic differences in biomass allocation were identified, with below ground allocation differing by up to 10% between genotypes. Importantly, the genotype with the highest below ground biomass also had the highest above ground yield. Furthermore, leaf area was found to be a good predictor of below ground biomass. Growth environment significantly impacted allocation; the willow genotypes grown in west Wales had up to 94% more biomass below ground by the end of the second rotation. A single investigation into fine roots showed the same pattern with double the volume of fine roots present. This greater below ground allocation may be attributed primarily to higher wind speeds, plus differences in humidity and soil characteristics. These results demonstrate that the capacity exists to breed plants with both high yields and high potential for C accumulation.     

Rapid biomass estimation using optical stem density of willow (Salix spp.) grown in short rotation

Quick and accurate biomass estimation of willow (Salix spp.) grown under short rotation intensive culture (SRIC) is essential for carbon accounting and management decisions. Currently, most estimates of tree biomass, including willow, rely on measurement of stem diameter. This is a suitable approach for single-stem species but for measurements of multi-stem species such as willow, there is an increase in the time and effort required as well as the need to include site, clone and age specific information. Therefore, we developed a new method which calculates optical stem density from digital photographs taken at predetermined locations and angles within a plantation during the fall or winter when the willow is without leaves. We then calibrated a mathematical model using destructive sampling to convert the measurements of optical stem density into estimates of biomass. The method produced very strong relationships (adjusted r² = 0.97) between the predicted and actual harvested biomass for the plots studied. Being new, the method still requires further testing and possibly adjustments for different planting designs and clones.     

Biomass and root stem production of a colony-forming willow (Salix interior) on highly disturbed,low fertility sites

This study describes biomass production, colony formation, and clonal spread via root stems (RS) of a wide-ranging North American willow species, Salix interior Rowlee (INT), one of the few willows that spread via vegetatively reproduced colonies, which can result in hundreds of upright stems arising from a shallow horizontal root network. Eight INT clones were tested in a common-garden experiment on two distinct site types (shale rock overburden and coarse gravel erosion sediments) with very low nitrogen and nutrients on a former coal mine site. Survival, height growth, aboveground biomass, and number of root stems (NRS) were quantified following 3 years of growth after establishment as rootless stem cuttings. Clonal differences were significant for survival and height at age 3. Survival was significantly greater on the coarse gravel outwash than shale rock overburden after the first and third year, but differences were only significant in the first year. There was a significant positive relationship between height growth and survival, both of which are indicators of plant vigor. Analysis of clonal variation in NRS showed an intermediate level of significance (P = 0.083), and a significant clone by site interaction (P = 0.024). On coarse gravel outwash, the more vigorous clones for height growth also produced more RS, indicating the absence of a potential trade-off in carbohydrate resource allocation between height growth of the ortet (mother plant) and its capacity for colony formation and spread via RS. It appears that RS quickly become independent sources of carbohydrate production. However, there was no relationship between clonal height growth and NRS on the rock overburden. Loose sand and gravel outwash deposits promoted a more rapid spread of the shallow horizontal root network than the less penetrable shale rock overburden that dominates this former coal mine site.     

Wood characterization for energy application proceeding from pruning Morus alba L., Platanus hispanica Münchh. and Sophora japonica L. in urban areas

Pruning urban forests generates significant amounts of lignocellulosic biomass every year. The energy potential of this biomass is unclear. The aim of this research was direct analysis of the gross calorific value (GCV), elemental composition and moisture content of Morus alba L., Platanus hispanica Münchh. and Sophora japonica L. by means of laboratory equipment. This analysis allowed for further development of indirect GCV prediction models which are economically attractive and less time consuming to direct analysis. These models presented high coefficients of determination (R² 0.66–0.96). It has been determined that the species with highest mean GCV is S. japonica L. (19615.68 kJ/kg-dry sample) whereas the one with the lowest is the M. alba L. (18192.87 kJ/kg-dry sample). Elemental analysis showed highest carbon (48.22%), hydrogen (6.17%) and nitrogen (1.16%) content in S. japonica L. in dry samples. Sulfur was constant at the level 0.05% for all analyzed species. Also percentage of bark and wood density were determined. Mean percentage of bark was highest for P. hispanica Münchh. (13.05%) while wood density was highest for S. japonica L. (0.86 g cm⁻³). This way the research has proven that the biomass produced by pruning urban forests appears to be an interesting source of renewable energy.