Niclas Scott Bentsen

Biomass for energy in the European Union - a review of bioenergy resource assessments

This paper reviews recent literature on bioenergy potentials in conjunction with available biomass conversion technologies. The geographical scope is the European Union, which has set a course for long term development of its energy supply from the current dependence on fossil resources to a dominance of renewable resources. A cornerstone in European energy policies and strategies is biomass and bioenergy. The annual demand for biomass for energy is estimated to increase from the current level of 5.7 EJ to 10.0 EJ in 2020. Assessments of bioenergy potentials vary substantially due to methodological inconsistency and assumptions applied by individual authors. Forest biomass, agricultural residues and energy crops constitute the three major sources of biomass for energy, with the latter probably developing into the most important source over the 21st century. Land use and the changes thereof is a key issue in sustainable bioenergy production as land availability is an ultimately limiting factor.

The state of forest vegetation management in Europe in the 21st century

COST (COST is an intergovernmental framework for European cooperation in science and technology. COST funds network activities, workshops and conferences with the aim to reducing the fragmentation in European research) Action E47, European Network for Forest Vegetation Management—Towards Environmental Sustainability was formed in 2005 and gathered scientists and practitioners from eighteen European countries with the objective of sharing current scientific advances and best practice in the field of forest vegetation management to identify common knowledge gaps and European research potentials. This paper summarizes the work of the COST action and concludes that although diverse countries have by necessity adopted different means of addressing the challenges of forest vegetation management in Europe in the 21st century, some common themes are still evident. In all countries, there is a consensus that vegetation management is a critical silvicultural operation to achieve forest establishment, regeneration, growth and production. It appears that herbicides are still in use to some degree in all the countries reviewed, although at a lower intensity in many of the northern countries compared to other regions. The most common alternatives to herbicides adopted are the use of mechanical methods to cut vegetation and achieve soil cultivation; overstorey canopy manipulation to control vegetation by light availability; and in some instances the use of mulches or biological control. Any reductions in herbicide use achieved do not seem to have been driven solely by participation in forest certification schemes. Other factors, such as national initiatives or the availability of additional resources to implement more expensive non-chemical approaches, may be equally important. The development of more cost-effective and practical guidance for managers across Europe on non-chemical control methods can best be brought about by future collaborative research into more sustainable and holistic methods of managing forest vegetation, through the identification of silvicultural approaches to reduce or eliminate pesticide use and through gaining a better understanding of the fundamental mechanisms and impacts of competition.

Forest vegetation management under debate: an introduction

is anintegral part of silvicultural practices in many parts of theworld (Wagner et al. 2006; Richardson et al. 2006; Newton2006). However, there are substantial differences betweenthe continents with regard to the preferred methods. Theimplementation of tending measures to control woodycompetitors is common in European even-aged stands as inother parts of the world. In contrast, the use of herbicidesfor weed control is much less common in Europe than forexample in North America, South Africa, Australia andNew Zealand where chemical vegetation control, inparticular, is used and promoted strongly in plantationforestry (Newton 2006). If at all, in Europe, herbaceousvegetation is controlled predominantly by mechanical sitepreparation, mulching or other techniques (McCarthy et al.2010, this issue). An overwhelming amount of literaturehas shown that chemical vegetation control can result inhuge gains in wood volume (Wagner et al. 2006). This hadlet to favourable reports of chemical vegetation control asthe following statements may indicate: ‘in most instances,forests cannot be managed economically without herbi-cides if the goal is to grow seedlings at the potential of thesite and the plant community includes sprouting hardwoodsand shrubs of rhizomatous forbs and ferns’ (McDonald andFiddler 1993); ‘most regeneration efforts around the worldwould fail or be severely delayed without effective forestvegetation management … primarily using herbicides’(Wagner et al. 2006); ‘reducing competition for desirabletrees with modern chemicals has less impact on soil andwildlife habitat and lowers human health risk per unitof effectiveness than mechanical or manual methods’(Newton 2006). In contrast, in Europe at present there ispolitical consensus for a reduction in the use of herbicidesas much as possible (i.e. The EU Thematic strategy on theSustainable Use of Pesticides). Society perceives Europeanforests as the last quasi-natural compartments of a land-scape which has been entirely manipulated for more than2,000 years. In this context, herbicides are view by thepublic as a serious threat for the maintenance of the set ofmultiple functions that forests provide (Merlo and Croitoru2005; Schmithu¨sen 2007; Ammer and Puettmann 2009).

Status and prospects for renewable energy using wood pellets from the southeastern United States

The ongoing debate about costs and benefits of wood‐pellet based bioenergy production in the southeastern United States (SE USA) requires an understanding of the science and context influencing market decisions associated with its sustainability. Production of pellets has garnered much attention as US exports have grown from negligible amounts in the early 2000s to 4.6 million metric tonnes in 2015. Currently, 98% of these pellet exports are shipped to Europe to displace coal in power plants. We ask, ‘How is the production of wood pellets in the SE USA affecting forest systems and the ecosystem services they provide?’ To address this question, we review current forest conditions and the status of the wood products industry, how pellet production affects ecosystem services and biodiversity, and what methods are in place to monitor changes and protect vulnerable systems. Scientific studies provide evidence that wood pellets in the SE USA are a fraction of total forestry operations and can be produced while maintaining or improving forest ecosystem services. Ecosystem services are protected by the requirement to utilize loggers trained to apply scientifically based best management practices in planning and implementing harvest for the export market. Bioenergy markets supplement incomes to private rural landholders and provide an incentive for forest management practices that simultaneously benefit water quality and wildlife and reduce risk of fire and insect outbreaks. Bioenergy also increases the value of forest land to landowners, thereby decreasing likelihood of conversion to nonforest uses. Monitoring and evaluation are essential to verify that regulations and good practices are achieving goals and to enable timely responses if problems arise. Conducting rigorous research to understand how conditions change in response to management choices requires baseline data, monitoring, and appropriate reference scenarios. Long‐term monitoring data on forest conditions should be publicly accessible and utilized to inform adaptive management.

Comparing predicted yield and yield stability of willow and Miscanthus across Denmark

To achieve the goals of energy security and climate change mitigation in Denmark and the EU, an expansion of national production of bioenergy crops is needed. Temporal and spatial variation of yields of willow and Miscanthus is not known for Denmark because of a limited number of field trial data. The semi‐mechanistic crop model BioCro was used to simulate the production of both short‐rotation coppice (SRC) willow and Miscanthus across Denmark. Predictions were made from high spatial resolution soil data and weather records across this area for 1990–2010. The potential average, rain‐fed mean yield was 12.1 Mg DM ha−1 yr−1 for willow and 10.2 Mg DM ha−1 yr−1 for Miscanthus. Coefficient of variation as a measure for yield stability was poorest on the sandy soils of northern and western Jutland, and the year‐to‐year variation in yield was greatest on these soils. Willow was predicted to outyield Miscanthus on poor, sandy soils, whereas Miscanthus was higher yielding on clay‐rich soils. The major driver of yield in both crops was variation in soil moisture, with radiation and precipitation exerting less influence. This is the first time these two major feedstocks for northern Europe have been compared within a single modeling framework and providing an important new tool for decision‐making in selection of feedstocks for emerging bioenergy systems.

Bioenergy, sustainability, and the second law

A recent study in GCB Bioenergy (Harsono et al., 2012) analyses a number of scenarios for palm biodiesel production. The authors calculate energy and greenhouse gas balances as measures of environmental sustainability; the better balance the more sustainable. The argumentation is not unique; it has been applied in numerous studies also recently, e.g., González-Garcı́a et al., 2012. We question the argumentation that the better energy balance ensures more sustainability. Sustainable development is a common mantra, also in the debate on energy supply, and much attention is devoted to cater the development of sustainable energy systems. The Brundtland definition of sustainable development targets two generations: the current and any future. However, forecasts of future energy technologies and societal development have a long history of failure (Smil, 2005), and future generation’s needs and demands for energy are known only very generally. Consequently, a sustainable approach to the development of an energy sector must target flexibility and the potential for providing a variety of options for generations to come. A subtle concept, sustainability, and its science does not build on one particular scientific discipline. We argue that basic understanding of the laws of thermodynamics can help reducing unsustainability in our stewardship of energy resources. The first law of thermodynamics tells that energy (E) neither can be created nor be destroyed, it can only change form. Energy is subject to the law of conservation, DEsystem = Ein Eout. Take the biosphere as an example. The amount of energy received from the sun almost equals the amount radiated back to space. The biosphere is more or less in energetic equilibrium. How is life then created and maintained if it does not build on consumption of energy? The second law of thermodynamics explains this apparent paradox. The second law tells that the conversion of energy from one form to another generates entropy (S). If the process is reversible the entropy level stays constant, but in real life there are no or only very few reversible processes, DEsystem = 0. Entropy is a measure of the dispersedness of energy (Lambert, 2011) and may be used as an indicator of the quality of energy forms. The incoming solar radiation has lower entropy (=higher quality) than the reradiated infrared radiation, and life on earth is created and maintained not through energy consumption but through energy quality consumption. Based on the second law a quality hierarchy of energy forms can be illustrated as a flight of stairs (Fig. 1). Energy can be moved up and down the stairs but (1) eventually it ends at the bottom step, and (2) every move comes at an ‘entropy cost’ and big steps has higher costs than smaller steps. The best use of biomass resources in the energy sector is intensely debated in the scientific literature; consensus does not prevail. Here, six options for using cereal straw in the energy sector are analyzed according to the first and second law. The second law analysis applies the concept of exergy (Ex). Exergy is a measure of energy’s potential to be converted into mechanical energy and builds on the first and second laws of thermodynamics (Dincer & Rosen, 2009). Material and energy balances, and energy and exergy performances of the six options are presented in Table 1. In scenarios 1, 2, and 4 the efficiency measured as energy or exergy is comparable, they rank identically. In scenarios 3, 5, and 6 the energy and exergy analysis diverge. Whereas the energy analysis finds these options very efficient, the exergy analysis finds them less efficient, most pronounced in scenario 6 with the highest energy efficiency and the lowest exergy efficiency. What characterizes these scenarios is the generation of heat, the energy form of lowest quality (cf. Fig. 1). The analysis leads to quite different conclusions, whether it is interpreted according to the first or the second law, but which makes most sense and provides most useful information? In a time where resources are considered more or less infinite or the consequences of their exploitation is not emphasized, which has been the case in the greater part of the 20th century, the first law has made sufficient sense. The last few decades, the perception of resources as finite and concern over the Correspondence: Niclas Scott Bentsen, tel. + 45 3533 1714, e-mail: nb@life.ku.dk