Perennial Energy Crops: Growth and Management M

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To cite this chapter M. Weih, (2009), PERENNIAL ENERGY CROPS: GROWTH AND MANAGEMENT, in Soils, Plant Growth and Crop Production, [Ed. Willy H. Verheye], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net] PERENNIAL ENERGY CROPS: GROWTH AND MANAGEMENT M. Weih Swedish University of Agricultural Sciences, Uppsala, Sweden Keywords: Agriculture, biomass production, biodiversity, breeding, energy crops, environment, Miscanthus, Salix, willow. Contents 1. Introduction 2. Types of Energy Crops 3. Species 4. Production Systems and Management 5. Breeding 6. Environmental Aspects 7. Conclusions Related Chapters Glossary Bibliography Biographical Sketch

Summary The production of biomass for energy purposes on agricultural land is an important way to generate renewable energy, and energy crops will probably be grown on a significant and increasing fraction of agricultural land in Europe and worldwide. Among the energy crops, particularly perennial grasses and trees could contribute substantially to alleviation of global problems in climate change and energy security, if high yields can be achieved. Miscanthus and Salix are frequently regarded as front-runners in the search for commercially viable perennial energy crops as they are high yielding, can cope with a range of soils and climate conditions, and have a productive life of 15 to 20 years. This chapter briefly describes growth, management and breeding aspects of perennial energy crops, in particular Miscanthus and Salix. In addition, environmental aspects including influence of perennial crops on soil and biodiversity are discussed. 1. Introduction Energy consumption worldwide has increased much faster than the increase in population size. Global problems due to climate change and energy security have greatly increased the interest for renewable energy including energy crops grown on agricultural land. In addition, economic evaluations have revealed that energy crop cultivation has the potential to offer farmers a profitable alternative to frequently declining returns from conventional land use. Thus, a significant and increasing fraction of agricultural land in Europe and worldwide is likely to be dedicated to the culture of energy crops in the near future. There is a great challenge and concern, that cultivation of energy crops might reduce land availability for feed and food production. However, experience shows that energy crop production for existing markets does not necessarily come at the expense of food crops and that it even may contribute to improve food security (FAO 2008).

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2. Types of Energy Crops 2.1. Annual and Perennial Energy Crops Today, annual crops, i.e. crops grown for one growing season such as maize and wheat, contribute greatly to bio-energy worldwide, but yields of these crops are highly dependent on high N inputs into soils. In contrast, perennial grasses and tree crops, i.e. crops with a life span of more than 2 yr, can achieve higher biomass yields with relatively lower inputs of nitrogen fertilizer and are regarded as most efficient nitrogen users. This difference greatly affects energy balance, i.e. energy input per harvest, and life-cycle analyses of bio-energy chains for the different crops, because the production of nitrogen fertilizers is very energy intensive. Energy crops are generally grown for two different markets, i.e., solid bio-fuels for heat and power generation on one hand, and liquid transport fuels on the other hand (Figure 1). Regarding the transport sector, so-called first-generation bio-fuels such as bio-diesel and bio-ethanol (mainly produced from annual crops such as oilseed rape and cereals) dominate the bio-fuel sector today. A shift towards second- generation bio-fuels, produced from mainly lingo-cellulosic biomass (mostly perennial crops such as Miscanthus and Salix grown in short rotation), is expected for the future. This shift will greatly affect not only agriculture, but also industry. For example, the development of perennial biomass crops has been stated to be the major driver for the cellulosic ethanol industry.

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2.2. Perennial Crops for Warm and Cool Climates The greatest potential for high biomass yields of perennial energy crops is in areas with warm and humid climatic conditions supporting rapid plant growth, e.g., many warm-temperate, sub-tropical and tropical climates. Most appropriate crop species to be grown under these climate conditions are perennial grasses such as Miscanthus and sugarcane, but also fast-growing trees such as eucalypts and poplars. Also cool-temperate and boreal floras include fast-growing perennial species that are suitable for energy plantations in high-latitude regions, where particularly the frequent occurrence of frost during winter sets limits for the culture of many otherwise high-yielding crops. Particularly tree species of Populus and Salix, but also grasses such as reed canary grass are suitable crops under these conditions, and they are used as energy crops in northern Europe and North America. Miscanthus and Salix are often regarded as front-runners in the search for commercially viable perennial biomass crops, as they are relatively high yielding, can cope with a range of soils and climate conditions, have relatively few pests and have a productive life of around 15 to 20 yr. Miscanthus and Salix represent two different growth habits and life forms, i.e., grasses and trees, which has major implications for the choice of production system and management. For example, harvest of grasses is often performed with mowers that are common in conventional agriculture, whereas tree harvest often requires specialized machinery (see Section 4.2 below). Among the energy crops currently discussed for large-scale biomass production on agricultural land in many regions of the world, Miscanthus and Salix are selected here to represent the two major groups of perennial energy crops, i.e. grasses and trees. This chapter briefly characterizes mainly these two species they may stand for many other crops of similar life form and appearance with respect to their potential use as energy crops on agricultural land and gives an outline of the appropriate production systems and management actions required to achieve high biomass yields. In addition, breeding issues of these perennial crops and critical environmental concerns associated with their culture are addressed.

3. Species There are a number of perennial plants (grasses and trees) with a great potential as energy crops and with regionally greater potential compared to Miscanthus and Salix. The most prominent example is probably sugarcane (species of Saccharum), which is the basis for the production of liquid transport fuels (ethanol) in Brazil. Several other C4 perennial rhizomatous grasses, e.g. switchgrass (Panicum virgatum L.), species of Cyperus and Spartina and - not least - fast-growing bamboos (various species within the family Poaceae) are interesting alternatives for biomass production in warm-temperate and tropical regions. Reed canary-grass (Phalaris arundinacea) is an example for a robust perennial C3 grass, widely grown across temperate regions of Europe, Asia and North America, where it is currently tried as energy crop on agricultural land in some regions, like in Sweden and Finland. Among the trees, some species can be grown in short rotation on agricultural land and are therefore potentially interesting energy crops for agriculture. Apart from Salix, poplars and aspens (species of Populus) have a great potential as energy crops in temperate and boreal agriculture, whereas fast-growing eucalypts (species of Eucalyptus) are sensitive to frost and therefore confined to warm-temperate and tropical agriculture. Only Miscanthus and Salix are presented here more in detail, but production systems and general management issues for many other energy crops are not principally different from these two species. For example, poplars and aspens are currently much more important for biomass production than willows in many regions of Europe and North America, but production systems and management of poplars for energy purpose is very similar to willow, especially when grown in short rotation.

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3.1. Miscanthus Miscanthus species are tropical and subtropical grasses native to southeastern Asia, China, Japan, Polynesia and Africa. Cultivars of M. sacchariflorus, M. sinensis, their hybrids, and other Miscanthus species are frequently grown as ornamental crops. The genotype with the greatest biomass potential is a sterile hybrid (Miscanthus x giganteus), likely of M. sacchariflorus and M. sinensis parentage. Miscanthus species are similar in appearance to some types of bamboo, although they are more closely related to sugarcane. They produce a new canopy of tall canes each year. In their region of origin, the canes can reach a height of 7 to 10 m, whilst in Europe heights of around 4 m are more common (Fig. 2). They have a rigorous root and rhizome system that can penetrate to depths of 1 m or more. The very high potential yield of Miscanthus is due partially to its C4 photosynthetic pathway, which is similar to other plants of tropical origin such as maize, sugarcane and sorghum. Compared to the C3 photosynthetic pathway, which is common for most agricultural crops native to the temperate zone (e.g. wheat), the C4 photosynthetic pathway typically enables the plants to employ a more efficient carbon fixation process, particularly when grown under warm and droughty conditions.

Although having evolved in regions experiencing warm temperatures and high precipitation, Miscanthus has been grown successfully in temperate regions and has demonstrated an above ground tolerance for light frost conditions. Leaves and shoots are destroyed below approximately -5oC, but the plants can overwinter as rhizomes at considerably lower temperatures. In comparison to most crops native to temperate climates, the temperature requirements to break winter dormancy of the tested Miscanthus genotypes are very high, which strongly limits productivity in temperate regions by means of greatly delayed spring emergence and growth. Delayed spring growth in combination to frost sensitivity are likely to be the major limiting factors for Miscanthus culture in environments with short growing seasons and cold winters.

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In Europe and North America, Miscanthus cropping was tried since the late 1990s in field experiments to investigate agronomic problems such as plant establishment, nutrient supply, yield development and biomass properties. Mean harvestable biomass yields over several harvest years are frequently reported at around 10 to 15 tons ha-1 yr-1, although figures beyond 20 tons ha-1 yr-1 were also reported. Compared to many annual crops, Miscanthus cropping has also been reported to enhance the nutrient cycling in the plant soil system. For example, as a result of high inputs of leaves, rhizomes and roots, increased concentration of organic carbon and total nitrogen have been demonstrated.

3.2. Salix Willows (species of Salix) are trees or shrubs distributed throughout the northern hemisphere with only a few species native to the southern hemisphere. Shrub willows (Salix viminalis in Europe and S. eriocephala in North America) are considered most suitable as biomass crops. The vast majority of species is native to Asia, North America and Europe. Many species are highly frost tolerant during winter and therefore suitable as energy crops also at high latitudes. Salix is a difficult genus to identify at the species level, because there is considerable individual variability and inter-specific hybridization. Products from Salix have been used traditionally in many parts of the northern hemisphere (basket making, fencing, ornamental use, etc.), but the cultivation of willows was performed at a rather small scale until the early 1990s, when the potential of willow as an energy crop came into focus. Willows are C3 plants like most other trees of the temperate zone, but can achieve a considerably greater photosynthetic rate and light-use efficiency, when well supplied with water and nutrients. In addition, fast-growing varieties of Salix partition a great fraction of the assimilated biomass to stem parts, rather than roots, and are able to utilize a greater part of the growing season for growth, compared to other tree species. A specific feature of many willows is their ability to re-sprout from omnipotent cells at very old nodal areas such as stumps or stools even after repeated harvesting. Unlike grasses, most trees reach their maximum growth rate after several decades of growth. However, Salix has an ability to rapidly reach its maximum growth rate within only a few years. The great initial growth rate in combination with the ability to vigorously re-grow after harvesting of above-ground biomass, and to tolerate high planting densities, makes Salix a very suitable energy crop. In parts of Europe, major research initiatives and test trials on willows for the purpose of biomass production were already initiated in the 1980s. For example in Sweden, the typical design of the willow production system (see section 4) was developed, and willow cultivation as a source of biomass for energy purpose expanded from a few hectares of test trials around 1970 to about 16 000 ha of commercial willow plantations by the end of the 1990s (Fig. 3). Biomass production rates of more than 20 tons ha-1 year-1 were reported after 3 to 5 yr of growth in fertilized (experimental) willow stands grown in Sweden and Canada. However, such high production figures have been achieved only in small-scale experimental plantations and biomass yields in commercial willow plantations grown in southern and central Sweden are usually in the range 5 to 15 tons ha-1 year-1. Similar compared to Miscanthus, increased concentrations of soil organic carbon and total nitrogen have been reported in willow plantations compared to annual agricultural crops.

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4. Production Systems and Management Production systems for perennial crops are rather different from annual crops, but similar within the two groups of perennial crops presented here, i.e. grasses and trees. As usual in agriculture, site conditions are important to achieve high yield, and warmer climate along with fertile soils may generate higher yields than cold climate and infertile soils. Sandy ground, light or medium clays or even heavy clays may be suitable for perennial energy crops, and soil pH should be between 5.5 and 7.5. Manuals and guidelines for the culture of Miscanthus, Salix and some other perennial crops are available (Larsson et al. 2007, DEFRA 2008). Similar to other agricultural crops, energy crops require good management in order to achieve high yields. In contrast to annual crops, perennial crops and particularly woody species ask for a long-term investment from the farmer, need great initial costs for the establishment of the plantation, and economic returns, i.e. biomass harvests, appear only after several years. Therefore, a failure in the first year(s) greatly affects biomass yield from perennial crops and economic benefits of the plantation during the subsequent years. Consequently, the most important step for achieving high yield in the long term is the successful establishment of the crop, and this requires, for instance, effective weed control prior to plantation. After establishment of the crop, nutrients need to be added to the soil by fertilization in order to replace the nutrients exported by biomass harvests. Apart from planting and harvesting of some perennial crops, most management measures can be performed using standard agricultural machinery and methods. 4.1. Miscanthus Experimental plantations of Miscanthus have been established in many countries since the late 1990s (Fig. 4). The genotypes currently used as energy crops (mostly Miscanthus x giganteus) are sterile hybrids, which produce no seed and must be established vegetatively by planting divided rhizome pieces. This process results in high establishment costs relative to crops produced from cuttings or seeds. The cropping period can be more than 20 yr and can be divided into an establishment phase and the phase of main use.

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Preparation of the planting site is performed by using conventional agricultural machinery and methods. Miscanthus is established by planting mechanically divided rhizomes (rhizome cuttings) or plantlets micro-propagated in tissue culture in spring at a density of 10 000 to 20 000 plants ha-1. The establishment phase is characterized by an increasing biomass from year to year and constant development of the below-ground storage system (rhizomes and roots). Biomass yields in the first year after establishment are low at 2 to 7 tons ha-1, which is insufficient to merit harvest in most cases. The establishment phase lasts between 2 and 5 years depending on the site conditions, e.g. climate and soil. Irrigation of newly planted rhizomes appears to improve establishment rates under drier conditions. Fertilizers are not needed in the first years, but weed control is very important for rapid establishment. After the establishment phase, fields are subject to different mechanical treatments to break up and multiply the rhizomes into smaller pieces. Micro-propagation offers potentially much higher multiplication rates compared to mechanical treatments, but these techniques are currently considerably more expensive than mechanical rhizome division. During the period of main use the above ground biomass is harvested in spring of the following year. Mineral nutrient fertilization will be required at most sites during the phase of main use to replace the amounts exported in harvested biomass. Biomass is harvested, for example with a common chopping forage harvester, at the end of the growing season. Although harvests can be taken between maturity in the fall and plant re-growth the following spring, the crop is typically harvested when the stems are fully dried out, although biomass yield drops by more than 25 % during the drying period. Late winter and spring harvests result in higher quality feedstock for combustion and considerably increased nutrient mobilization in the crop. Biomass yields depend very much on climate and soil conditions, and the highest yields are reported under warm climate and high availability of water and mineral nutrients, e.g. Southern Europe.

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4.2. Salix In spite of the fact that Salix is a woody species, the establishment of willow coppice plantations has more in common with agricultural crops than forestry. A Salix energy crop plantation consists of densely planted, high-yielding varieties of willow. The above-ground shoots are harvested during winter on a 2 to 5 yr cycle. The rootstock or stools remain in the ground after harvest with new shoots emerging the following spring. A plantation could be viable for more than 20 years before re-planting becomes necessary, although this depends on the productivity of the stools and the development of pests and diseases. As for Miscanthus, ground preparation is carried out using conventional agricultural machinery and methods. Planting takes place in spring and early summer (March-June) and is performed either by planting machines (most commercial plantations) or manually. The planting material consists of one-year- old willow shoots, which are cut into pieces of approximately 20 cm length planted by simply pushing them into the cultivated soil. The cuttings are planted in a twin row formation to allow the specialized harvest machinery to harvest two rows at a time. The distance between the rows usually alternates at 75 and 150 cm and the distance between the plants within rows is around 60 cm, which gives a plantation density of approximately 15 000 cuttings ha-1. Other plantation schemes are also in use, but it is important to adjust the plantation scheme to the harvest machinery if the plantation should be run commercially. During the establishment year, weed control (mechanical or chemical) is very important, but no mineral nutrient fertilizer needs to be applied. In the winter following planting, shoots are frequently cut back (using a mower) in order to prepare for vigorous re-growth during next spring. In Salix coppice, the developing shoots grow for 2 to 4 yr, depending on the site conditions before harvest; other species, e.g. poplars, are often grown for longer periods before harvest. In the year following establishment and after each harvest, nutrient fertilization is usually applied to ensure high yield and prevent nutrient depletion of the soil. The fertilization is most commonly done by means of commercial fertilizer, but in Sweden also sludge from municipally waste treatment plants is also used, supplemented by some extra nitrogen. Biomass harvesting takes place in winter (November to April), when growth has ceased and leaves are shed. Harvests are performed using specialized machinery that cuts the shoots and directly processes them into wood chips, which are transported to the end-user (Fig. 5). If the shoot diameter exceeds approximately 8 cm, e.g. in single-stem cultures of poplar grown at longer cutting cycles than Salix, the stands need to be harvested by using less effective forestry machinery. A willow coppice plantation can be grown for more than five cutting cycles, before it needs to be re- established. The termination of a Salix energy crop plantation is not particularly complicated, because the roots in a plantation are relatively shallow and degrade easily.

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5. Breeding A major challenge in breeding of perennial crops is the production of plant material with guaranteed high productivity over many years. The cyclic nature of perennial production systems, with harvests every year or every 2 to 5 yr for a period of up to 25 yr, also stresses the need for specific breeding goals compared to the breeding of an annual agricultural crop. In order to be considered economically viable, the key requirements for perennial crops include high yielding genotypes with natural resistances to pathogens and pests, and with the ability to withstand abiotic stresses such as drought and frost, which are of particular importance, given the length of time that perennial crops are in the ground. 5.1. Miscanthus Several trials to evaluate the biomass production capacity of Miscanthus species have been established in Europe and North America during the late 1990s, but breeding programs have been initiated only a decade later. Most of the Miscanthus material being tested so far has a rather narrow genetic base, which may slow breeding improvements. Thus, growing large areas of identical or closely related genotypes may imply increased risk for pests and diseases, and a collection of only few high-yielding Miscanthus genotypes is a poor basis for the breeding towards genotypes that are adapted to different climates and quality requirements. For example, extensive field trials of Miscanthus species in Europe have shown that the most widely planted clone, M. x giganteus, has insufficient frost tolerance in some regions, and that the highest-yielding genotypes in one region were among the lowest-yielding genotypes in another region. A broad genetic base including a selection of genetically diverse Miscanthus genotypes is required to facilitate successful breeding. Some large breeding programs for Miscanthus have been launched in Europe (e.g., Germany), North America and China. Breeding methods include both traditional and molecular (marker-assisted) breeding,

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and the goal is to develop a new platform for molecular breeding. Breeding materials consist of the previously used species and genotypes (M. x giganteus, M. sinensis) as well as new collections of native genotypes from Asia. Specific breeding objectives include increased biomass production but also improvements in winter-hardiness and combustion quality. Some new genotypes with thick stems, decreased leaf loss during winter and improved winter hardiness have been produced so far. 5.2. Salix Willows show considerable variation in terms of growth habits, ranging from small creeping bushes to tall trees, but the bush-type species have proven to be best suited for coppicing and biomass production. In addition, willows are unusual in that hybrids (crosses) between distinct species are easy to make. In certain cases, hybrids have been produced that grow better than either of the parents, an effect that is utilized in various commercial available hybrid willows. Apart from growth habit and biomass production, willows are highly diverse and great natural genetic variation exists in most traits relevant for breeding, e.g. sensitivity to drought and frost, and sensitivity/tolerance for pests and diseases. The broad genetic base is a necessary prerequisite for successful breeding. Breeding programs for biomass Salix were launched in Europe during the 1980s and in North America some years later. The early breeding programs were based on traditional crossings and breeding methods, whereas modern breeding programs, e.g. in the UK and Sweden, increasingly attempt to utilize molecular methods and marker assisted breeding. Specific breeding objectives for biomass willows focus not only on biomass production, but also growth habit (to adapt the crop to commercial harvesting machinery), water use efficiency and drought tolerance, frost and disease resistance, and also biomass quality characters. Salix is taxonomically close to Populus, and the Populus genome has been sequenced. The close taxonomic relationship between the two genera which make up the family Salicaceae will enable breeders to use the genetic information on Populus for Salix breeding also. These possibilities indicate a great potential to gain maximized benefit in the breeding of complex crop characters important for the long- term performance of this perennial crop.

6. Environmental Aspects The establishment and possible large-scale deployment of perennial energy crop plantations is often controversial due to, for example, presumed negative and long-lasting influences on biodiversity and the cultural heritage landscape, along with negative public attitudes. Critics of plantations of perennial energy crops include those who argue that they harm wildlife, water and soil resources and biodiversity. Indeed, planting of intensively managed perennials, especially plantation forests in the Tropics, frequently has had negative impacts, but the problems of these plantation forests are frequently associated with inappropriate location and management. Thus, the localization and management of plantations of perennial energy crops should be planned carefully, in order to reduce the risks for the environment, and they should utilize at best their potential to improve environmental and landscape quality. 6.1. Soil and Water Energy crop plantations, like many other plantations, can imply the risk of negative effects on the environment in terms of herbicide use, deterioration of soil properties, nutrient losses and damage on drains caused by roots. However, when compared to conventional annual crops, the perennial character of the crops considered here commonly leads to reduced herbicide application, because herbicide treatment is typically required only during establishment. Thus, the risk of ground water contamination by agro- chemicals is usually low in cultures of perennial crops.

The culture of perennials on former arable land can often have positive effects on soil properties due to less frequent use of heavy machinery, especially when the use of harvesters is restricted to the period of frozen ground in cold-winter regions. For example, carbon sequestration and water holding capacity were found to increase in formerly arable soils that were planted with Salix or Miscanthus for 5 to 10 yr. The perennial nature of the crops also leads to less nutrient loss compared to conventional annual crops, provided that the rate and timing of fertilization is adjusted to the nutrient delivery and nutrient holding capacity of the soil in relation to the uptake capacity of the crops. In contrast to the potential risks of nutrient leakage from fertilized plantations, plantations of fast-growing perennials can offer great possibilities for environmental control at a local scale in terms of, e.g. phyto- remediation. Thus, based on the large nutrient quantities taken up by fast-growing perennials, the plantations can be used as recipients for municipal wastewater and industrial sludge and simultaneous biomass production (multifunctional biomass plantations). This possibility has been realized with Salix plantations in Sweden. 6.2. Biodiversity The effects of perennial crop cultures on biodiversity can be positive or negative, depending on location, management and previous land use. Studies on biodiversity often arrive at contradictory conclusions, especially when different kinds of organisms are considered. Thus, the land use context, e.g. forestry or agriculture, along with the type of use that was replaced by the plantation as well as the spatial scale aspects, e.g. size or shape of plantations, influence the impact of energy crop plantations on biodiversity. In addition, many animals use multiple habitats and, therefore, depend on habitat combinations. Hence, it is mainly the diversity of land use types in a given landscape that can have large impacts on biodiversity. In comparison to managed forests and farmland in Sweden and the UK, Salix energy plantations have been shown frequently to increase vascular-plant diversity. Similar observations have been made for Miscanthus plantations. Also fauna diversity (birds and mammals) is frequently found to be higher in Salix and Miscanthus stands compared to agricultural croplands. Thus, the more extensive management in plantations of perennials compared to intensively managed annual crops can improve habitat quality for many organisms including plants, birds, and insects. However, the location of the plantations within the landscape exerts a strong influence on their effect on biodiversity. A native wood nearby a Salix plantation will facilitate the migration of birds, insects and plants and, thus, increase biodiversity. In large plantations, different parcels of the stand can be established and harvested in different years in order to enhance structural diversity and biodiversity. The same goal could be achieved by establishing a large number of smaller plantations, which are harvested in different years. Mixtures of different species and/or varieties can be established either by planting them in different blocks across the field or random mixtures within each row. These mixtures increase structural and functional diversity and contribute to reduce the impact of pests and diseases. Thus, a mosaic of plantations with different species, e.g. Salix and Miscanthus intermixed with annual food crops, and possibly with different primary goals, e.g. purely commercial and environmental, probably would contribute most to maximize the positive effects on environment and biodiversity. It hence appears that plantations of perennial energy crops can increase the abundance and diversity of many organisms, particularly in landscapes today dominated by either conventional agricultural fields or managed forests, by increasing structural diversity. However, plantations should be avoided close to open habitats of high conservation values such as certain types of wet meadows and buffer zones along streams, because such sites often have a conservation value linked to openness of the habitat. Also public foot path access to landscape as well as local archaeology should be taken into account when energy crop plantations are planned. With these restrictions in mind, especially small-scale plantations of perennial

crops (or sub-divided larger plantations) grown on agricultural land may have the potential to positively affect biodiversity in many farmland regions, where the set-aside of agricultural land from food production suggests the development of alternative uses. There is a risk that Miscanthus and Salix (probably also other perennial energy crops), as they are introduced species in most regions, might invade local floras and threaten biodiversity. For the genotypes used so far this does not seem to be a problem, because most varieties used for biomass production have been around for many years or decades without showing signs of invasiveness. This is perhaps related to the fact that these genotypes, when grown in non-native environments, are poor competitors in the juvenile plant stage and require weed control in order to establish properly. If new varieties are produced in the future with characteristics making them stronger competitors, e.g. to reduce the costs for weed control, the risk of threatening local floras might greatly increase. 6.3. Landscape Plantations of fast-growing perennials may already after few years of growth be up to 6 or 8 m high, and it is important to consider the impact this will have on the landscape at the early planning stages of an energy crop plantation. Many concerns are raised regarding the impact of plantations of perennial energy crops on the landscape: Will the open agricultural landscape be "darkened"? How will the new crop be adapted to the traditional field crops of agricultural landscapes? Will we soon experience a total transformation of our ingrained cultural heritage? Similar to biodiversity evaluations, studies regarding the effects of plantations of perennial energy crops on visual landscape perception usually arrive at different conclusions, e.g. the more open the landscape is, the larger can the size of the plantations be and particularly small plantations placed in open agricultural landscape can enrich landscape perception. In spite of wide-spread negative attitudes expressed by people who are afraid to lose the traditional cultural landscape, a frequently made positive comment is that plantations of fast-growing perennials are an exciting new feature of the landscape and that these plantations indeed can enhance the aesthetic value of landscape by adding variation, e.g. autumn colors in Salix, and structure in homogeneous agricultural landscape.

7. Conclusions A significant and increasing fraction of agricultural land in Europe and worldwide is likely to be dedicated to the culture of energy crops for the production of bio-fuels in the near future. Also, a shift from so-called first-generation bio-fuels, such as bio-diesel and bio-ethanol produced from annual crops, towards second-generation bio-fuels, produced mainly from perennial crops, is expected for the future (see also: Growth and Production of Herbaceous Energy Crops: Making Bio-fuels from Crops). Perennial grasses and tree crops can achieve high biomass yields with relatively low inputs of nitrogen fertilizer and have a very positive energy balance, i.e. energy input per harvested biomass. Miscanthus and Salix are often regarded as front-runners in the search for commercially viable perennial biomass crops, and breeding programs have been launched for both crops. Key targets for perennial crop breeding include high yield along with high resistance towards pathogens, pests, drought and frost. When compared to conventional annual crops, perennial crops commonly require reduced herbicide application and the risk of ground water contamination by agro-chemicals is usually low in cultures of perennial crops. Plantations of perennial energy crops can increase the abundance and diversity of many organisms, particularly in landscapes today dominated by conventional agricultural fields.

Glossary Biodiversity : The variation in genotypes, species or life forms found in an environment of a given spatial and temporal scale. Bio-fuel : Solid, liquid or gas fuel derived from living biological material such as plants and microorganisms. Biomass : Living biological material that can be used as fuel, for agronomic or industrial production. C3 and C4 : Plants characterized by C3 and C4 carbon fixation, respectively, which are two plant different biochemical mechanisms to bind carbon dioxide for sugar production through photosynthesis. Carbon : The process by which carbon sinks, e.g. in oceans and plants, and thus removes sequestration carbon dioxide from the atmosphere. Energy crop : A plant which is grown and exploited for its energy content. Commercial energy crops are typically densely planted, high yielding crop species. Hybridization : Process of combining different varieties or species of organisms to create a hybrid. In plant breeding, hybrids are commonly produced and selected because they have desirable characteristics not found or inconsistently present in the parent plants. Ligno-cellulosic : Plant biomass that is composed of cellulose, hemicellulose, and lignin. This type of biomass is produced in large amounts by woody plants, e.g. trees, and some fast- growing rhizomatous grasses. Micro- : The practice of rapidly multiplying stock plant material to produce a large number of propagation offspring by using tissue culture methods. Perennial : A plant that lives for more than 2 yr such as woody plants like shrubs and trees, and rhizomatous grasses. Phyto- : Any process that uses plants or their enzymes to return the natural environment remediation altered by contaminants to its original condition. Rhizomatous : Members of the grass (Poaceae) family with under-ground horizontal stems and grass shoots. Short rotation : Characteristic of a biomass production system in which the above-ground shoots of trees or shrubs are harvested on 2 to 20 yr cycles. Tissue culture : The growth of tissues and/or cells separate from the organism in a liquid, semi-solid or solid growth media such as agar.

Bibliography Clifton-Brown, J.C., Stampfl, P.F. and Jones, M.B. (2004). Miscanthus Biomass Production for Energy in Europe and its Potential Contribution to Decreasing Fossil Fuel Carbon Emissions. Global Change Biology, 10: 509-518. [This document describes the potential contribution of Miscanthus culture to ameliorate the consequences of climate change.] DEFRA [Dept. for Environment, Food and Rural Affairs] (2008). Planting and Growing Miscanthus - Best Practice Guidelines. http://www.defra.gov.uk/erdp/pdfs/ecs/miscanthus-guide.pdf. [This booklet is designed to introduce farmers to the energy crop Miscanthus] Gibson, L. and Barnhart, S. (2007). Miscanthus Hybrids for Biomass Production. Iowa State University, Dept. of Agronomy (www.agron.iastate.edu), 2 pp. [This document very briefly describes Miscanthus agriculture from a North American perspective.]

FAO (2008). The State of Food and Agriculture 2008. Bio-fuels: Prospects, Risks and Opportunities. FAO, Rome, Italy. 138 p. [This document surveys the current state of the debate on bio-fuels and explores its implications for the environment, food security and the poor.] Larsson, S., Nordh, N.-E., Farrell, J. and Tweddle, P. (2007). Manual for SRC Willow Growers. Lantmännen Agroenergi AB (www.agroenergi.se), Örebro, Sweden. 18 p. [This document is a grower’s manual for Salix culture on agricultural land.] Hein, K.R.G. (2005). Future Energy Supply in Europe - Challenges and Chances. Fuel, 84: 1189-1194. [This document reviews the current discussion on energy supply and the need for energy crops from a European perspective.] Kahle, P., Beuch, S., Boelcke, B., Leinweber, P. and Schulten, H.-R. (2001). Cropping of Miscanthus in Central Europe: Biomass Production and Influence on Nutrients and Soil Organic Matter. European Journal of Agronomy, 15: 171-184. [This document describes Miscanthus culture and its effects on soils.] Karp, A. and Shield, I. (2008). Bioenergy from Plants and the Sustainable Yield Challenge. New Phytologist, 179: 15-32. [This document gives an up-to-date overview on the biology of energy crops grown on agricultural land.] Styles, D., Thorne, F. and Jones, M.B. (2008). Energy Crops in Ireland: An Economic Comparison of Willow and Miscanthus Production with Conventional Farming Systems. Biomass and Bio-energy, 32: 407-421. [This document is a case study of the economic result of Salix and Miscanthus culture in comparison to conventional agricultural crops.] Weih, M. (2004). Intensive Short Rotation Forestry in Boreal Climates: Present and Future Perspectives. Canadian Journal of Forest Research, 34: 1369-1378. [This document describes the specific problems and possibilities associated with Salix short rotation forestry in cool-temperate regions.] Weih, M. and Nordh, N.-E. (2007). Biomass Production with Fast-growing Trees on Agricultural Land in Cool- temperate Regions: Possibilities, Limitations, Challenges. In: Environmental Research Advances. New York, Nova Science Publishers, pp. 155-170. [This document describes the possibilities and limitations of Salix agriculture from both commercial and environmental perspectives.] Wright, L. (2006). Worldwide Commercial Development of Bio-energy with a Focus on Energy Crop-based Projects. Biomass and Bio-energy, 30: 706-714. [This document describes the development of energy crops worldwide during the late 1990s and early 2000s.]

Biographical Sketch Martin Weih, PhD, is a Professor of crop eco-physiology at the Department of Crop Production Ecology at the Swedish University of Agricultural Sciences (SLU) in Uppsala. He has more than 15 years of experience in ecological research on birch, willow, poplar, bamboo and other species. His main interest is in plant eco-physiology and ecological questions related to biodiversity. Major research activities focus on the production ecology and physiology of energy crops - mainly perennial biomass crops such as Salix and Populus grown on agricultural land - and the genetic basis of production traits. Effects of plantations of fast-growing trees on the environment (e.g., biodiversity) and landscape are another important research interest. He is participating in several EC projects. Author of more than 55 peer-reviewed publications in scientific journals and books.