Short rotation plantation

from Wikipedia, the free encyclopedia
2 month old poplar plantation
2 year old poplar plantation
Harvesting a willow plantation

A short rotation forestry (KUP, fast growing plantation, forest low short rotation) is a cultivation of fast-growing trees with the goal within a short rotations wood - chips as a renewable raw material to produce. If this is done exclusively for energy generation , it is also referred to as energy wood plantation or energy forest. Short rotation plantations are agricultural crops and not a forest within the meaning of the Federal Forest Act . In Germany, short rotation plantations may only be grown on arable land. A conversion of forest to short rotation plantations is excluded by law.

Tree species

Rash from a willow plantation harvested in winter (right), next to it on the left 3-year-old willow plantation

In a short rotation plantation, fast-growing and deciduous tree species, especially poplars (genus Populus ) or willows (genus Salix ) are used. Research and breeding focus on tree species that are suitable for temperate climates.

Among the poplars, the balsam poplars such as the western balsam poplar and Populus maximowiczii as well as their hybrids and crosses between balsam and black poplars are particularly suitable. Compared to pure black poplars and other tree species, these stand out in that they grow particularly quickly, do not need too much light and form a dense root system. Further goals in combination breeding of poplar trees are to increase biomass production , improve pest resistance, accept higher planting density, high stick rash and rapid growth in the first years of development in order to shorten harvest intervals. The fuel quality of the wood is also influenced by cultivation, in that forms with a high efficiency of nutrient use and a high, but nutrient-poor trunk content are selected.

Among the willows, the basket willow , the tub or kitten willow ( Salix × smithiana ) and the felt branch willow are particularly important. The cuttings of these species grow securely and tend to shoot with multiple shoots or to shrub . Tree species whose suitability for short rotation plantations is discussed but not yet researched are the robinia , the black alder and the silver birch .

History and economic situation

The short rotation plantation in the coppice has a historical forerunner , in which trees at regular intervals u. a. were placed on the stick to produce firewood .

The cultivation of fast-growing tree species for material use in the manufacture of wood-based materials has been practiced successfully in some European countries for many years. In Germany, however, wood fields have not got beyond the experimental cultivation stage since the 1970s, although the first research center for fast-growing tree species was founded in Hessen in 1974. On the one hand, this is due to a market that has so far only been limited for the end product wood chips . On the other hand, heating oil has been the most economical fuel for heat supply for years. However, this situation is changing in the course of increased prices for fossil fuels. Today short rotation plantations are mainly cultivated for energetic use.

Since about 1990 z. B. willow clones grown in large plantations. Sweden has many years of experience with short rotation pasture cultivation. 16,000 hectares were already being cultivated there in 1999; in the 2005/2006 financial year, around 15,000 hectares of wood fields were under cultivation. The yield of the newer varieties could be massively increased compared to the first wood fields and is currently at an annual increase of 8 to 12 tons of dry matter (atro) per hectare. In Germany, 5,968.5 hectares of short rotation plantations were cultivated in 2014 according to InVeKoS . Short rotation plantations are a very labor-intensive cultivation method in the field of agricultural production. The majority of the work can be carried out by farmers or foresters with their own machines. Special machines, which are usually provided by service providers, are only required for planting and harvesting.

use

In the short rotation plantation, so-called cuttings , i. H. Sections of annual, well-developed shoots, planted in rows and, depending on the type and climate, harvested mechanically or manually every 3 to 10 years. The rootstock remaining in the ground has the ability to erupt , and so the trees sprout again after the harvest without having to be replanted. Under good conditions, short rotation plantations can produce an average of around 10  tons of dry matter per year and hectare , and under very good conditions even twice as much. After about 20 years, the production power of the plants decreases, and the area should be rebuilt if it is used again.

Cultivation

Planting a short rotation plantation with the “Step-Planter”, the rods are cut into 20 cm long pieces in the machine and pressed into the ground
6 month old poplar (front) and willow plantation (back right)
4-year old poplar plantation (variety: Hybride 275)
4-year-old poplar plantation (variety: Max)

When creating short rotation plantations, deep loosening of the soil is strongly recommended, e.g. B. by plowing at least 25 cm deep. This enables rapid root growth and high wood growth rates. A good establishment success with heights of growth of over 1.5 m in the first vegetation period is usually only achieved if, in addition to careful soil preparation, the culture is largely kept free of weeds in the first vegetation period. This can usually be ensured by using pre-emergence herbicides directly after planting, as well as at least one mechanical maintenance cycle. Good cultivation care in the first year of growth significantly improves the competitive position of the energy crops as well as the survival rate and the yield potential. At the end of the second vegetation period, the end of the crop is already reached on most of the sites if the crop was kept weed-free in the first two years.

As a rule, short rotation plantations are created in spring (late March to early June). Either pre-produced 20 cm - 35 cm long cuttings , which are planted by machine or by hand, or approx. 2.50 meter long rods, which are cut into approx. 20 cm long cuttings in special planting machines, serve as planting material . When planting, make sure that the cuttings are inserted into the soil as vertically as possible with good contact with the soil. As a rule of thumb, the more difficult the location, the longer the cutting should be. Short cuttings are planted at ground level, longer cuttings (from 30 cm) can look about 1/3 out of the ground. In very difficult locations, planting rods> 100 cm in length is recommended, as these are much more robust against weeds and easier to care for. For cost reasons, however, the cultivation of plant rods is only recommended for longer rotation in quantities of 2,000 - 3,500 per hectare. Plant rods are planted at least 50 cm deep. The cultivation of short rotation plantations from seeds is not carried out because the seeds of poplar and willow trees cannot be stored and often cannot germinate after a few weeks. A significantly more expensive alternative to the cuttings, which are obtained from high-yield mother plants, is the use of tissue culture reproduction. However, this is currently not profitable and is therefore only used in research. Short rotation plantations are usually created with special planting machines. All leading suppliers of planting material also offer the planting service. The planting association depends on the type of tree, the planned product (energy or industrial wood) and the gauges of the machines to be used. In Germany, poplar energy wood is largely grown as a single row with a row spacing of 2.0–2.4 m and a distance between the plants in the row of 0.4–0.5 m. This results in a number of plants of around 10,000 per hectare. For the production of industrial poplar wood or energy wood with a low bark content and medium to long rotation, a plant layout of 2.0–2.4 m row spacing and a spacing within the row of 1 , 2–2.0 m recommended. This corresponds to a planting density of 2,000 - 5,000 pieces per hectare. Willow energy wood is also cultivated either in single rows or as double rows. The single row enables easier plantation maintenance and greater flexibility during harvest, the double row has the advantage that the plants are distributed more evenly over the area. Double rows are planted with a distance of 70 to 75 cm, which can be picked up by the harvesting machine (forage harvester) in one pass. There must be enough space between the double rows for the wheels of the harvester. This is approx. 1.8 m. The distance between the plants in the row is typically 55-60 cm for the double row of willows and approx. 35 cm for the single row of willows. Accordingly, plant densities of 13,500 plants per hectare are aimed for in willow.

Plant protection

Damage to a willow plantation by the blue willow leaf beetle ( Phratora vulgatissima )

The same problems occur in short rotation plantations as in forest crops . In addition to general dangers, pests specialized in individual species play a certain role.

The problem with the cultivation of short rotation plantations is the low genetic variability of the plants, which results from the vegetative propagation of the cuttings, and the crowding of the plants. This makes the entire population susceptible to pests, although so far only infestation by rust fungi of the genus Melampsora and poplar leaf beetles ( Chrysomela populi ) has led to greater yield losses. Effective insecticides from agriculture and forestry are available against harmful insects, but their use has so far only been carried out in rare individual cases.

In addition to mechanical plant protection methods such as fencing the cuttings against game bites , herbicides from grain cultivation are used against weeds during the establishment phase . For the application of pesticides on non-indicated crops in Germany, according to Section 18 b of the Plant Protection Act, an exemption from the responsible authorities is required . This is usually granted without any problems, as wood chips do not enter the food chain.

Under certain conditions it is necessary to completely or partially dispense with the use of herbicides . For example, this is the case in water protection zones or in organic farming . There are some alternative measures that can be taken for this: By early and multiple mechanical care and with the help of mulch films , the manager can prevent excessive accompanying vegetation. Mulch films reduce the maintenance measures and offer the trees protection and significant growth advantages. Willows as a quick starter are particularly suitable because, unlike poplars, they tend to get by without any maintenance measures. Mulching between the rows and raptor perches on the area help prevent mouse damage .

harvest

Harvesting a 4 year old willow plantation
Agricultural chopper with special equipment for harvesting energy wood
Truck loading of wood chips from short rotation plantations

Short rotation plantations are permanent crops that can usually be used for up to 20 years with an average of 3 to 6 crop rotations. The harvest takes place over several years, the stock has reached a height of 6 to 8 meters at harvest time. The yields for balsam poplar trees are between 10 and 15 tons per hectare and year, for willows between 5 and 10 tons per hectare and year. The best time to harvest is in winter after the leaves have fallen off, as this allows a large part of the nutrients to remain on the fields. Highly motorized , self-propelled forage harvesters with small wood infeed are mostly used as harvesting machines with short rotation times , as well as mounted mowers . Wood harvesters and bundlers from forest technology can also be used for higher-yielding crops and for longer rotation times. It is important not to compact the soil too much so that the trees can stand in well-ventilated soil.

Fresh wood chips usually have a water content of 50 to 60% and must be pre-dried for use. This happens when the schnitzel is stored outdoors or in pressed bales. For combustion in small and medium-sized systems, they should have a water content of a maximum of 30%. It is important to roughly chop the wood, as fine wood chips are difficult to store. The wood chips can be stored as heaps and burned, gasified or processed into pellets as required. Short rotation plantations sprout again after the harvest. Depending on the nutrient supply of the soil, fertilization of 50 to 70 kg nitrogen / ha can make sense after the harvest , but usually no fertilization is necessary, since hardly any nutrients are extracted from the area via the wood.

economics

Wood chip heater screw

Compared to established annual arable crops, SRCs require relatively high investments to establish a stand, a relatively long production period and generate irregular cash flows. At the same time, after a successful establishment, there are no significant additional costs for the management of the plantations, apart from the harvest costs. Finally, at the end of the useful life, the costs of converting the area back for arable use (removal of the root stocks) must be calculated. SRC therefore represent a greater business risk than annual crops; an extension only makes economic sense in the case of firm purchase agreements with binding prices.

In order to compare the profitability of SRC with that of annual crops, it is advisable to use the dynamic investment calculation instead of the contribution margin ; In this way, the irregular payment flows can be converted into an annuity that is constant every year . The calculated annuity can be compared directly with the contribution margin of annual crops. According to various studies, the annuity of poplars and willows can be around € 250 to € 500 per hectare and year under favorable conditions, but can also be negative under unfavorable conditions. The higher the number of rotations, with a rotation period of three to four years, the more likely positive annuities are achieved.

A profitability analysis of the cultivation of fast-growing tree species in short rotation plantations published by the University of Halle-Wittenberg on the basis of current literature and practical data shows that this is currently economical in the majority of cases, and from an average yield level of 11 to 12 tons of absolute dry matter per hectare and year can certainly compete with agricultural crop rotations. Compared with the average yields and prices of a crop rotation typical of Central Saxony (winter rape - winter wheat - winter wheat - winter barley) from 2006 to 2010, a farmer earns an average profit of 45 euros per hectare higher by growing energy wood. The activation of short rotation plantations as "ecological priority areas" can offer additional economic advantages.

The total costs for establishing a short rotation plantation are around 2,000 to 3,000 euros per hectare. The first harvest of poplar and willow plantations usually brings significantly lower yields than in subsequent years. From the 2nd harvest the annual growth rates are i. d. Usually at least 50% higher compared to the 1st harvest. In order to keep the specific harvest costs low, it is advisable to wait with the first harvest of a short rotation plantation until a total harvest of at least 25–30 t dry matter per hectare can be expected. However, care must be taken that the trunk thickness of the trees does not exceed the capabilities of the harvesting technology used.

In the heating market, woodchip firing systems are becoming economical due to the sharp rise in prices for fossil fuels, even with higher investment costs for the combustion and charging technology. The average energy content is between 15.5 and 18.5 MJ / kg, around 0.06 MJ / kg are consumed during harvest and crushing, which means that the energy balance is very good. It should be noted, however, that fast-growing plants also have a lower specific energy content, so that the volume of raw materials to be processed increases significantly. For example, one cubic meter of oak firewood provides approx. 1890 kWh, fast-growing poplar only 1110 kWh. This is not clear in the calorific value as it relates to the mass and not to the volume.

Legal

Germany

Since the amendment to the Federal Forest Act (BWaldG) in 2010, it has been made clear that short rotation plantations are not part of the forest. Before, it was controversial whether the creation of short rotation plantations is subject to forest law or not.

Short rotation plantations (official designation: coppice forest with short rotation) are classified as permanent agricultural crops, provided the rotation time is not longer than 20 years; d. H. at least one harvest must take place within 20 years. The total management period of energy wood plantations is not regulated. The areas are eligible for aid according to EC regulation 1120/2009.

The EC regulation 1120/2009 mandates the national states to draw up a list of permitted woody species. In Germany, willows, poplars, locust trees, birches, alders, the common ash as well as pedunculate, sessile and red oak were approved.

Short rotation plantations are recognized as ecological priority areas within the framework of so-called greening and are weighted with a factor of 0.3 from 2015. From this, short rotation plantations can possibly be assigned further economic advantages at the operational level. However, no mineral fertilizers or pesticides may be used on ecological priority areas with “coppice with short rotation”.

Particular areas of favor for the cultivation of pastures in short rotation can be found above all in lowlands, river plains and the glacial valleys of the North German lowlands. These landscape elements are often characterized by a high water availability, which has a positive influence on plant growth (maps and evaluations can be found in the source).

Austria

In Austria, conversions and new plantings are approved by the respective district authorities. The decision follows the management guidelines in the Cultural Area Protection Act . In addition, the European Regulation 1586/97, the Austrian Forest Act , the Fertilizer Act and the Water Law Act must be observed. In principle, the cultivation of short rotation plantations is possible on arable as well as set-aside areas; A minimum distance to neighboring crops of between three and ten meters must be observed in order to avoid damage to the neighboring fields through rooting and shading.

Short rotation plantations on devastated and urban areas

The global rise in food prices in 2007 and 2008 has led to a discussion as to whether and to what extent the manufacture of renewable raw materials for energy production has contributed to this increase. For this reason, too, pilot projects have been started to establish short rotation plantations on areas that do not compete with food production. Attempts in devastated areas of former opencast mines and on inner-city areas are to be emphasized. The latter was started in 2007/2008 by the Halle city utility on areas that were previously built on with residential buildings that were demolished as part of the so-called “ Stadtumaus Ost” in Halle (Saale) .

Climate protection effect

Climate protection performance and CO 2 avoidance costs of various bioenergy value chains

Bioenergy value chains based on short rotation plantations for electricity, heat and fuel production enable significantly higher CO 2 avoidance compared to traditional bioenergy processes. This is due to the extensive management, which means that the energy input in the form of fertilizers and pesticides or the use of machines is extremely low. The CO 2 avoidance costs are only a fraction compared to biofuels from rapeseed and grain or biogas from maize silage. The Scientific Advisory Board on Agricultural Policy at the Ministry of Agriculture writes in the study: Use of biomass for energy production - Recommendations to politicians: "Politicians could (...) achieve by changing course in funding (more biogas based on manure and electricity and heat based on wood chips SRC) that with constant use of resources and land, the contribution of bioenergy to climate protection would more than tripled. "

In addition, short rotation plantations offer the possibility of cultivating arable sites that have a particularly high drainage requirement. If willow and poplar clones are used, excessive drainage of these areas can therefore be avoided, which has a clearly positive effect on their CO 2 balance. If particularly moist locations are used in this context, a possible negative impact on the local water balance and thus sensitive ecosystems can be avoided.

Influence on biodiversity

When assessing the influence of short rotation plantations on biodiversity , the reference system used is crucial. Most studies come to the conclusion that short rotation has a positive effect on (plant) biodiversity compared to intensive arable land use, but has a low biodiversity compared to near-natural forest. When making this assessment, it should be noted that the conversion of forest into short rotation plantations is strictly prohibited and cultivation is exclusively concentrated on arable land. The NABU notes that the installation of SRC in arable regions contributes to the structuring of the landscape and to the creation of habitats and stepping stones for plant species. Up to now there have been no reliable studies for a comparison with grassland use . SRC, on the other hand, is not of great importance for biodiversity in terms of animal species, since endangered species are few or non-existent in intensively used regions. SRC would, however, bring animal-ecological advantages, since compared to annual arable crops, animals benefit from a longer soil dormancy, less use of fertilizers and pesticides and overall fewer disturbances.

See also

literature

  • Peter Liebhard: "Energy wood in short rotation - raw material of the future", 2nd edition 2010; Leopold Stocker Verlag - Graz, ISBN 978-3-7020-1150-5
  • F. Stockmann, H. Hagemann, M. Wenzelides: Woody Biomass in Agriculture - Practical Guide Part 2 , (2010), ACKER + plus 6/10 (31–37) ( Download ; PDF; 853 kB)
  • F. Stockmann, H. Hagemann, M. Wenzelides: Woody Biomass in Agriculture - Practical Guide Part 1 , (2010), ACKER + plus 4/10 (30–35) ( Download ; PDF; 762 kB)
  • Fachagentur Nachwachsende Rohstoffe e. V. (FNR): Energy wood production in agriculture , 3rd, revised edition (2009), 42 pages, available as nachwachsenderohstoffe.de
  • Federal Research Center for Forestry and Wood Management (BFH): Poplars, aspen and willows in Germany: use, conservation, research. Period 2000-2003. Federal Ministry for Consumer Protection, Food and Agriculture (BMVEL), 2004. ( Download ; PDF file; 1.10 MB)
  • M. Hofmann: Management of fast-growing tree species on agricultural areas in short rotation. Research Institute for Fast-Growing Tree Species, Hann. Münden 1998 ( Download ; PDF file; 270 kB)
  • Institute for Agricultural Engineering Bornim e. V. (Ed.): Energy wood production in agriculture. Potential, cultivation, technology, ecology and economy. Seminar January 29, 2004. Bornimer Agricultural Technical Reports Booklet 35, Potsdam-Bornim 2004.
  • D. Kauter, Iris Lewandowski & W. Claupein: Poplars in short rotation economy: Properties and quality management in the provision of solid fuel - an overview. Crop Science 5 (2), 2001; Pp. 64-74. ( Download ; PDF file; 1.11 MB)
  • Ralf Pude: Short rotation plantations. In: Klaus-Ulrich Heyland, Herbert Hanus, Ernst Robert Keller: Oil fruits, fiber plants, medicinal plants and special crops. Handbook of Plant Cultivation Volume 4, Eugen Ulmer KG, Stuttgart 2006; Pp. 588-591, ISBN 978-3-8001-3203-4
  • Ch. Röhricht, K. Ruscher: Cultivation recommendations for fast-growing tree species. Technical material Saxon State Agency for Agriculture, 2004. ( Download PDF)
  • C. Rösch, K. Raab, J. Skarka, V. Stelzer: Energy from grassland - sustainable development? Institute for Technology Assessment and Systems Analysis, Forschungszentrum Karlsruhe GmbH, Karlsruhe 2007. ( Download ; PDF file; 8.21 MB)
  • Angela Werner, Armin Vetter, Gerd Reinhold: Guideline for the efficient and environmentally friendly production of energy wood. Thuringian State Institute for Agriculture, 2006 ( Download ; PDF file; 222 kB)
  • Christoph Scheffknecht: Influence of sewage sludge fertilization on the pollutant content of energy forest trees. Investigations as part of a research project at the Dornbirn sewage treatment plant. Short report from the Environmental Institute of the State of Vorarlberg, 2002. ( Download ; PDF file; 391 kB)
  • Jens Hartwich: Assessment of the regional suitability of short rotation coppice in Germany . Dissertation. Free University of Berlin - Institute for Geographical Sciences, 2016. doi: 10.13140 / rg.2.2.17825.20326

Web links

Commons : Short rotation forestry  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e R. Schirmer: Aspects of plant breeding of fast-growing tree species for energy forests. In: F. Burger, N. Remler: Fast growing tree species, their cultivation and their utilization. Reports from the Bavarian State Institute for Forestry and Forestry 8; Pp. 6-18. Quoted from Pude 2006
  2. ↑ a b c d according to Kauter et al. 2001
  3. ^ L. Christersson: Theoretical background to and practical utalization of short-rotation and energy-forestry. In: L. Christersson, S. Ledin (Ed.): IEA. Bioenergy, Task 17: Short-rotation crops for energy purposes. Proceedings of the first meeting in Uppsala, Sweden. International Energy Agency , 1999; Pp. 5-19. Quoted from Kauter et al. 2001
  4. ↑ German Biomass Research Center, fast-growing tree species in Germany and their use for heat supply
  5. ↑ Recommended cultivation of short rotation plantations - planting of fast-growing wood plantations in agriculture ( Memento of March 4, 2016 in the Internet Archive )
  6. ↑ DLG: Short rotation plantations, planting, care, harvest and value creation
  7. ↑ Justify short rotation areas herbicide-free on waldwissen.net
  8. ↑ a b P. Wagner, J. Heinrich, M. Kröber, J. Schweinle, W. Große: Economic evaluation of short rotation plantations and classification of wood production in the cultivation structure of agricultural enterprises , in: T. Reeg, A. Bemmann, W. Konold , D. Murach, H. Spiecker (Ed.): Cultivation and use of trees on agricultural land , Wiley-VCH, Weinheim, 2009, p. 137. ISBN 978-3-527-32417-0
  9. ↑ Sächsische Landesanstalt für Landwirtschaft: Fast growing tree species  ( page can no longer be accessed , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.smul.sachsen.de  
  10. ↑ A. Bemmann, KH Feger, D. Gerold, W. Große, K.-U. Hartmann, R. Petzold, H. Röhle, J. Schweinle and C. Steinke: Short rotation plantations on agricultural areas in the Grossenhain region in the Free State of Saxony , Forest Archive 78, 2007, pp. 95–101. [1] (PDF).
  11. ↑ B. Stürmer, E. Schmid: Economic efficiency of willow and poplar in short rotation under Austrian conditions , summary, online trade journal of the Federal Ministry of Agriculture, Forestry, Environment and Water Management, year 2007. (PDF).
  12. ^ Mathias Kröber, Klaus Hank, Peter Wagner: On the profitability of short rotation plantations ( accessed on July 29, 2015 )
  13. ↑ Short rotation plantations could be interesting in 2015 ( lksh.de )
  14. ^ Regional energy Styria: Energy content of firewood added on February 8, 2012
  15. ↑ Thuringian State Research Center for Agriculture : Legal aspects of the cultivation of energy wood in short rotation plantations on agricultural areas. (PDF) 2010, accessed on August 7, 2014 .
  16. ↑ Electronic Federal Gazette, announcement 15/10/31 of May 12, 2010, changed on December 17, 2010
  17. ↑ thueringen.de (PDF) Greening commitments from 2015.
  18. ^ Jens Hartwich: Assessment of the regional suitability of short rotation coppice in Germany . Dissertation. Free University of Berlin - Institute for Geographical Sciences, Berlin January 20, 2017, doi : 10.13140 / rg.2.2.17825.20326 .
  19. ↑ Hartwich, J., J. Bölscher, A. Schulte, M. Schmidt, C. Pflugmacher & D. Murach: The transpiration water supply as a controlling factor for the production of energy from pastures in short rotation plantations - assessment of the bioenergy potential for Germany . In: hydrology and water management . tape 59 , no. 5 , 2015, p. 217–226 ( doi.bafg.de [PDF]).
  20. ↑ Peter Liebhard: Energy wood in short rotation. Stocker Verlag 1997; P. 15. ISBN 978-3-7020-1150-5 .
  21. ^ Scientific Advisory Board on Agricultural Policy at the BMELV, Use of Biomass for Energy Generation - Recommendations to Politics, p. 216, bmel.de
  22. ↑ Jens Hartwich, Jens Bölscher, Achim Schulte: Impact of short-rotation coppice on water and land resources . In: Water International . tape 39 , no. 6 , September 19, 2014, ISSN  0250-8060 , p. 813-825 , doi : 10.1080 / 02508060.2014.959870 .
  23. ↑ Jens Hartwich, Markus Schmidt, Jens Bölscher, Christian Reinhardt-Imjela, Dieter Murach: Hydrological modeling of changes in the water balance due to the impact of woody biomass production in the North German Plain . In: Environmental Earth Sciences . tape 75 , no. 14 , July 11, 2016, p. 1-17 , doi : 10.1007 / s12665-016-5870-4 .
  24. ↑ Naturschutzbund Deutschland ( NABU ) e. V. (Ed.): Energy wood production in agriculture - opportunities and risks from the point of view of nature and environmental protection nabu.de
  25. ↑ Bund für Umwelt und Naturschutz Deutschland ([BUND]) (Ed.): Short rotation plantations for energy wood production: opportunities and risks = position 55 ( bund.net ( Memento from May 16, 2011 in the Internet Archive ))