Short rotation coppice (SRC) is coppice grown as an energy crop. This woody solid biomass can be used in applications such as district heating, electric power generating stations, alone or in combination with other fuels. Currently, the leading countries in area planted for energy generation are Sweden [1] and the UK.
SRC uses high yield varieties of poplar and willow. Typically willow species chosen are varieties of the common osier or basket willow, Salix viminalis. Poplar is generally planted for visual variation rather than being a commercial crop, although some varieties can outperform willow on suitable sites. [2]
Species are selected for their acceptance of varying climate and soil conditions, relative insusceptibility to pests and diseases, ease of propagation and speed of vegetative growth. To combat pests such as brassy and blue willow beetles, as well as the fungal pathogen Melampsora (a rust), planting a carefully selected mix of varieties is recommended. [3] The management of the plantations highly affects the productivity and its success. [4]
SRC can be planted on a wide range of soil types from heavy clay to sand, [5] including land reclaimed from gravel extraction and colliery spoil. Where used as a pioneer species the SRC yield may be smaller. Water availability to the roots is a key determinant for the success of the SRC. [6] [7]
Saplings are planted at a high density, as much as 15,000 per hectare for willow and 12,000 per hectare for poplar. [3] Willow SRC can be established according to two different layouts. In most North European countries (Sweden, UK, Denmark) and in the US, the most frequent planting scheme is the double row design with 0.75 m distance between the double rows and 1.5 m to the next double row, and a distance between plants ranging from 1 m to 0.4 m, corresponding to an initial planting density of 10,000–25,000 plants ha−1. [8] In other countries like Canada, a single row design ranging from 0.33 m between plants on a row and 1.5 m between rows (20,000 plants ha−1) to 0.30 m on the row and 1.80 m between rows (18,000 plants ha−1) is more common. [9] Planting takes place around March to take advantage of the high moisture of the soil in the spring and the amount of sunshine in the early summer. The most efficient planting machines plant four rows at a time and can plant a hectare in around three hours. Saplings are left to grow for one or two years and then coppiced.
The primary barrier to establishing plantations is the cost as there is no financial reward for four years from a large initial investment. However, in the UK grants are available to support establishment, [10] [11] and in Sweden an extensive scheme of subsidies was developed during 1991–1996, being reduced after that time. [12]
Harvests take place on a two- to five-year cycle, and are carried out in winter after leaf fall when the soil is frozen. The established root system and the nutrients stored in the roots and stumps guarantee vigorous growth for the shoots. A plantation will yield from 8 to 18 tonnes of dry woodchip per hectare per year. A plantation can be harvested for up to 20 years before needing to be replanted. [13]
When willow or poplar shoots are harvested as whole stems they are easy to store. The stems can be dried for combustion in a pile outdoors; the moisture content of the wood will decrease to about 30% on average until the next autumn. The stems can be cut further into billets that may not need to be chipped depending on use.
Where wood chip is being produced it is most efficient to use direct-chip harvesters. These are heavy self-powered machines that cut and chip the shoots on a loading platform. [13] Some can be attached to a normal tractor and a hectare can be harvested in around three hours. Direct chipping reduces costs as a separate chipping in the store will not be needed; however, the wood chip needs to be well stored to avoid it composting. Harvesting Poplar requires heavier machinery as it produces fewer and heavier stems.
The price of dry willow as a heating fuel is currently around 45 euro per tonne in most of Europe. This is not a relatively high-return crop, but it is low-maintenance and is a way of utilising difficult fields. Small-scale production can be combined with the production of material for wicker work. Correctly managed, there is little need for pesticides or treatments.
SRC has a low greenhouse gas impact as any carbon dioxide released in power generation will have been sequestered by the plantation over just a few years. Some carbon may also be stored in the soil, however the extent of this carbon storage is dependent on the carbon content of the soil to begin with. [14]
The carbon costs associated with SRC are: the planting, farming and chipping of the SRC plantation, generally done with fossil fuel powered machinery; the crops require herbicides during establishment, fertiliser throughout growth, and occasional pesticide treatment – these chemicals require substantial amounts of energy and potential fossil fuel usage through manufacture. In general, the environmental contribution of the short rotation plantations of willow can be considered positive towards the environment when compared to other agricultural options [15] even when alternative energetic uses are considered. [16]
Furthermore, willow and poplar SRC offer an alternative use to intense drained farm land. If the drainage of these sides would be decreased, this would support a positive impact on the CO2 balance. In addition, a use of moist location could avoid negative effects on the local water-balance as well as sensitive ecosystems. [17] [18]
Electricity or heat from SRC provides between three and six times the CO2 reduction per pound that can be obtained from bioethanol from cereal crops. However, the reduction in CO2 emissions is slightly lower than grass energy crops such as Miscanthus grass due to higher maintenance costs.
Good conservation management encouraging biodiversity can reduce the reliance on pesticides. Biomass crops such as SRC willow show higher levels of biodiversity in comparison with intensive arable and grassland crops. [19] SRC has a higher water consumption than agricultural crops. The root systems of SRC have a lower impact on archaeological remains than forestry but greater than agricultural crops such as wheat.
A power station requires around 100 hectares (1 km²) of SRC for 1 MW of power capacity. [20] The current nature of the power industry generally requires flexibility in energy supply which is incompatible with the long term commitment SRC requires; however, there is much interest in SRC due to the need to reduce fossil carbon emissions. Grants may also be available in some jurisdictions to further this type of land-use.
Enköping (Sweden) established a successful model that combines heat generation from biomass, SRC and phytoremediation. The municipality manages about 80 ha of willow plantations that are used in the district heating plant. At the same time, these plantations are used as a green filter for water treatment, which improves the functionality and the efficiency of the whole system. [21]
Biofuel is another option for using SRC as bioenergy supply. In the United States, scientists studied converting SRC poplar into sugars for biofuel (e.g. ethanol) production. [13] Considering the relative cheap price, the process of making biofuel from SRC can be economic feasible, although the conversion yield from SRC (as juvenile crops) were lower than regular mature wood. Besides biochemical conversion, thermochemical conversion (e.g. fast pyrolysis) was also studied for making biofuel from SRC poplar and was found to have higher energy recovery than that from bioconversion. [22]
Short-rotation coppice has recently gained importance in many countries as a means of providing additional environmental benefits. Some species, such as poplar and willow, have been successfully used for soil [23] and sludge [24] trace element phytoextraction, and for groundwater [25] and sewage wastewater [26] rhizofiltration.
Willows, also called sallows and osiers, of the genus Salix, comprise around 350 species of typically deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions.
Populus is a genus of 25–30 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar, aspen, and cottonwood.
Biofuel is a fuel that is produced over a short period from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. Biofuel can be produced from plants or agricultural, domestic, or industrial biowaste. Biofuels are mostly used for transportation but can also be used for heating and electricity. Biofuels are regarded as a renewable energy source. However, the use of biofuel has been controversial because of the several disadvantages associated with the use of it. These include for example : the "food vs fuel" debate, biofuel production methods being sustainable or not, leading to deforestation and loss of biodiversity or not.
Panicum virgatum, commonly known as switchgrass, is a perennial warm season bunchgrass native to North America, where it occurs naturally from 55°N latitude in Canada southwards into the United States and Mexico. Switchgrass is one of the dominant species of the central North American tallgrass prairie and can be found in remnant prairies, in native grass pastures, and naturalized along roadsides. It is used primarily for soil conservation, forage production, game cover, as an ornamental grass, in phytoremediation projects, fiber, electricity, heat production, for biosequestration of atmospheric carbon dioxide, and more recently as a biomass crop for ethanol and butanol.
Bioenergy is energy made or generated from biomass, which consists of recently living organisms, mainly plants. Types of biomass commonly used for bioenergy include wood, food crops such as corn, energy crops and waste from forests, yards, or farms. The IPCC defines bioenergy as a renewable form of energy. Bioenergy can either mitigate or increase greenhouse gas emissions. There is also agreement that local environmental impacts can be problematic.
Cenchrus purpureus, synonym Pennisetum purpureum, also known as Napier grass, elephant grass or Uganda grass, is a species of perennial tropical grass native to the African grasslands. It has low water and nutrient requirements, and therefore can make use of otherwise uncultivated lands.
The blue willow beetle, formerly Phyllodecta vulgatissima, is a herbivourous beetle of the family Chrysomelidae. It is dark with a metallic sheen that ranges from a blue color to bronze. It is distinguished from P. vitellinae by the latter more commonly displaying bronze coloration. European Phratora species can be distinguished based on morphology of female genitalia. The larvae undergo three instar stages from hatching to pupation. This beetle is found throughout Europe and Scandinavia, and occurs in China.
Pellet fuels are a type of solid fuel made from compressed organic material. Pellets can be made from any one of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and untreated lumber. Wood pellets are the most common type of pellet fuel and are generally made from compacted sawdust and related industrial wastes from the milling of lumber, manufacture of wood products and furniture, and construction. Other industrial waste sources include empty fruit bunches, palm kernel shells, coconut shells, and tree tops and branches discarded during logging operations. So-called "black pellets" are made of biomass, refined to resemble hard coal and were developed to be used in existing coal-fired power plants. Pellets are categorized by their heating value, moisture and ash content, and dimensions. They can be used as fuels for power generation, commercial or residential heating, and cooking.
Energy forestry is a form of forestry in which a fast-growing species of tree or woody shrub is grown specifically to provide biomass or biofuel for heating or power generation.
Energy crops are low-cost and low-maintenance crops grown solely for renewable bioenergy production. The crops are processed into solid, liquid or gaseous fuels, such as pellets, bioethanol or biogas. The fuels are burned to generate electrical power or heat.
Thlaspi arvense, known by the common name field pennycress, is a flowering plant in the cabbage family Brassicaceae. It is native to Eurasia, and is a common weed throughout much of North America and its home.
The Willow Biomass Project is a collaborative effort by members of the Salix Consortium to grow willow and other sustainable woody crops in upstate New York. The project, funded through the U.S. Department of Energy's Biomass Power for Rural Development Program, seeks to commercialize willow bioenergy crops as a renewable source of biofuel. To date, the project has planted willow on at least 465 acres (1.9 km2) of privately leased land and 25 acres (100,000 m2) of farmer-contracted land.
Biomass, in the context of energy production, is matter from recently living organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues including straw, and organic waste from industry and households. Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo. The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.
Miscanthus × giganteus, also known as the giant miscanthus, is a sterile hybrid of Miscanthus sinensis and Miscanthus sacchariflorus. It is a perennial grass with bamboo-like stems that can grow to heights of 3–4 metres (13 ft) in one season. Just like Pennisetum purpureum, Arundo donax and Saccharum ravennae, it is also called elephant grass.
Short rotation forestry (SRF) is grown as an energy crop for use in power stations, alone or in combination with other fuels such as coal. It is similar to historic fuelwood coppice systems.
Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.
Woodchips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, stumps, roots, and wood waste.
Rhizofiltration is a form of phytoremediation that involves filtering contaminated groundwater, surface water and wastewater through a mass of roots to remove toxic substances or excess nutrients.
The economic biomass potential of Turkey is 32 million tons of oil equivalent (Mtoe)/year. Total biomass production is estimated to reach 52.5 Mtoe by 2030. Arable crops in Central Anatolia and the Mediterranean have the most potential for electricity, and in 2021 biomass generated 7.6 TWh, which was 2.3% of the nation's electricity, from over 2 GW capacity. An estimated 6.5 million homes in Turkey use biomass as their main source of heating fuel.
Reinhart Jan Maria Ceulemans is an emeritus professor of Ecology and previous director of the Research Center of Excellence PLECO of the University of Antwerp. He has been vice-dean of the Faculty of Sciences at the University of Antwerp, and was a visiting professor at the University of Washington, Seattle, USA (1987-1988), at the Université Paris-Sud XI, Orsay and at the University of Ghent. He officially retired in October 2019 and is now a visiting professor at the University of Antwerp (Belgium), a researcher at CzechGlobe Academy of Sciences in Brno and an international consultant to the Slovenian Forestry Institute.
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