Sugarcane is a tall growing, jointed bunch grass that is cultivated as a perennial crop primarily for its ability to produce and store sucrose in its stem. It is a highly efficient “solar

Cellulosic Energy Cropping Systems, First Edition. Edited by Douglas L. Karlen. © 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.

cell” with an estimated energy in:energy out (I/O) ratio of 1:8 when it is allowed to grow for 12 months under tropical conditions and its harvested dry matter (sugar and fiber) is processed for ethanol instead of sugar [12-15]. Under more temperate environments, where sunlight duration and intensity fluctuates (seasonally and daily) and cooler temperatures and occasional frosts shorten the growing season, I/O ratios of 1:3 are easily obtainable with current sugarcane varieties if ethanol production from both sugar and fiber is the goal [9]. Solar energy recoveries for energy cane, sorghum, and tropical maize have independently been reported as 2.24, 2.23, and 2.85%, respectively [16,17]. Thus, energy cane is no more efficient in converting solar energy into chemical energy, but the extended growth phase allows it to capture more solar energy over an entire growth season relative to the other C4 grasses. This extended growth phase is attributed to tillers remaining functional and the continuous activity of apical meristems throughout most of the year. Moreover, continued stem elongation, increased internode density, and continued canopy development of tillers allows for storage of solar energy as dry biomass in an extended spatial area [17-19]. The theoretical maximum for aboveground sugarcane dry matter (DM) yield is estimated to be 140 Mg ha-1 annually [20]. This is dependent on temperature and sunlight, and would probably occur only under tropical conditions.

The theoretical maximum fresh weight yield of sugarcane biomass is 358 Mg ha-1 yr-1 [5]. Early generation hybrids between sugarcane and S. spontaneum have been shown to produce sustained biomass yields approaching the theoretical maximum in Louisiana over a five-year period [21]. Unfortunately, the high biomass yields in these early generation hybrids are the result of high fiber yields, and not high sucrose yields, and as such they are generally crossed back to elite clones of sugar cane two or three times before a sugarcane clone worthy of commercial sugarcane production can be released [7].

With the quest to produce second generation fuels from cellulosic biomass these early generation Fi hybrids are ideal biofeedstock candidates, that is, energy canes. Most of these hybrids can produce DM yields of 30 Mg ha-1 annually over four fall harvests, with about 20 Mg ha-1 being fiber and 10 Mg ha-1 being Brix [22]. One of the first sugarcane varieties developed for biomass production and utilization for the cogeneration of electricity was “L79-1002” [23]. The authors reported DM yields of 66.6 Mg ha-1 at a latitude of 30.4°N on 1.8-m wide rows. These yields from this variety were from fiber (27.9% on a fresh weight basis) and Brix (10.4% on a fresh weight basis).

Sugar and fiber levels in the harvested cane stalks are generally dependent on the variety, the length of the growing season, the amount of extraneous matter present, and the harvesting conditions. Sugarcane, once delivered to the raw sugar factory for milling, is separated into its water, Brix (soluble solids, of which approximately 80% is sucrose), fiber (bagasse) and sediment (ash, soil, etc.) fractions. The bagasse fraction in commercial sugar varieties consists of 38% cellulose, 19% hemicellulose, 22% lignin, 4% protein, and 3% ash, with the remaining 14% consisting of sugar, soil from harvesting, and other types of solids [21, 24]. The average fiber yield does not take into consideration leafy material removed in the field during the harvesting process, or the conditions under which the crop was harvested. When sugarcane is mechanically harvested for sugar without a pre-harvest burning of the standing cane, 4-6 Mg ha-1 of leaf litter is deposited back on the soil surface [25-27]. Moreover, in Louisiana, where sugarcane is grown on mineral soils, if the crop is harvested under wet and muddy conditions it is not uncommon to see 5-10% contamination with soil.

Competition from herbaceous and woody weeds can slow the growth of pines and this can delay harvest by as much as seven years. For some pine species, experienced foresters will use fire (i. e., prescribed burns) as a way to control hardwoods. Prescribed burns may be used after harvest to prepare the site for planting and they can be used in developing stands once the pines are large enough to tolerate the fire. Some pines (e. g., Pinus palustris) are more tolerant of fire than others (e. g., Pinus glabra), so fire is only appropriate for certain pine species. The timing of fires is also important (both on an age basis and a time-of-year basis). Periodic prescribed fires are used in the southern United States to control woody vegetation and improve wildlife habitat, especially in areas where the plantation is far from residential homes.

Controlling woody weeds with herbicides is now a common practice in pine plantations throughout the world. Depending on the degree of hardwood competition, controlling all hardwoods during the first three years of stand development can result in shortening the rotation by 1-5 years (i. e., the same amount of pine volume can be harvested 1-5 years sooner). Similar gains may result when controlling all herbaceous weeds (on sites with no woody weeds). However, controlling herbaceous weeds on sites with lots of hardwood competition might not affect pine growth at harvest. This is because controlling herbaceous weeds might benefit hardwoods more than pines.

Applying herbicides after harvesting but before planting is desirable from a biological point of view. Injury to planted seedlings is less (especially when applying non-selective herbicides) and higher herbicide rates can be applied (when compared to applying herbicides soon after planting). In the United States, the tax system once favored waiting three or four years after planting before applying herbicides. The cost of herbicide application could then be expensed (instead of capitalized when applied the same year as transplanting). Effective control was less since the woody competition was larger and more resistant (when herbicide rate was comparable). Now, most landowners may deduct up to $10 000 per year in weed control costs from their income (before calculating taxes). In other countries, foresters may deduct all weed control costs in the year that it occurs.

Application of herbicides are either made from the air (often with helicopters) or from the ground. Broadcast applications are typically cost effective and are often used prior to planting seedlings. Ground equipment or hand labor is used when applying herbicides in bands (e. g. treating 50% of the area in alternating strips). Ground application may also be preferred in areas where the risk of damage by herbicide drift to adjacent landscape plantings or agricultural crops is high.

Although sorghum is primarily self-pollinated it does outcross and researchers knew that hybrid vigor occurred in sorghum [71]. The development of sorghum hybrids did not occur until Stephens and Holland [72] identified methods to sterilize seed parents to produce hybrids by using a cytoplasmic male sterility system. This approach was first used to produce hybrids in 1956 and within five years hybrid sorghum seed was planted on over 90% of the total U. S. grain sorghum area. Soon after development of grain sorghum hybrids, forage sorghum hybrids for both hay and silage were developed and adopted. While hybrid forage sorghum cultivars have increased yield, another important consideration has been in the enhanced logistics of seed production (i. e., higher seed yield, easier harvest and better quality).

Over the past fifty years sorghum breeding programs have continued to improve and advance sorghum genetics. Traits such as increased yield with high inputs (e. g., water and fertilizer) became important, as was protection of yield potential from both biotic and abiotic stresses. These efforts have led to substantial improvements in yield potential, grain and forage quality, and the protection of this potential through abiotic and biotic stress tolerances. Further improvement relies on a thorough understanding of the crop and genetic control of traits of importance.

Another function of fast-growing tree species such as poplar is their potential role as an effective carbon sink. Intensive management of SRP poplar for biomass energy could help to partially offset carbon dioxide emissions due to short-term turnover of fine roots and long-term accumulation and decomposition associated with larger roots and stumps. Rytter

[66] provides calculations that are based not only on above and belowground biomass pro­duction data from field experiments, but also on fine root turnover, litter decomposition, and increased production levels from commercial plantations. Carbon accumulation in woody biomass, above and belowground, was estimated at 76.6-80.1 MgC ha-1 and accumulation of carbon in the soil at 9.0-10.3 MgC ha-1 over the first 20-22 seasons of plantation growth. The average rates of carbon sequestration were 3.5-4.0 MgC ha-1 yr-1 in woody biomass and 0.4-0.5 MgC ha-1 yr-1 in the soil. In each of his calculations, SRP poplar showed a higher carbon sink potential than for willow. Similar studies were carried out in China

[67] where they also found that SRP poplar had higher carbon sequestration capacity than any annual cropping system in their country. They reported that carbon concentrations in poplar organs ranged from 459 to 526 gC kg-1 DM with the highest levels in stemwood and the lowest concentrations in coarse roots.

Jaoude et al. [68] expressed doubts regarding the ability of poplar plantations to have a positive effect on carbon storage, arguing that if intensive management practices and commercial fertilizers were used, increasing emissions could reduce carbon storage in the soils. The processes for increasing carbon dioxide emission from short-rotation plantations were connected with soil respiration and included the following components: root respira­tion, heterotroph respiration (including microbial respiration of plant residues, turnover of soil organic matter, and rhizomicrobial respiration). It was found that coppicing increased carbon dioxide efflux from soil compared to the pre-coppicing period, but when nitrogen fertilizers were applied it caused a rapid and significant reduction of total soil carbon dioxide efflux by changing the metabolic pathways for both for hetero — and autotrophs.

The long-term effects of SRP poplar on soil properties is a matter of discussion in many countries, where some opponents of woody crop plantations have alleged that after 25 years of such management, soil nutrient levels are exhausted and special, long-lasting rehabilita­tion is needed. Recent studies in Germany [69] helped dispel this myth by providing data for sites where short-rotation poplar was grown for four rotations. The most important soil parameter (i. e. soil organic matter) was improved by 6.2 Mg ha-1 during the 12 years of poplar growth. Higher microbial activity was also recorded. There was some depletion in phosphorus and potassium but no negative yield effects and, furthermore, those nutrients can be easily supplemented with good management. With regard to soil physical properties, soil bulk density decreased and pore volume increased during the 12 years of short-rotation poplar growth.

Luo and Polle [70] evaluated effects of elevated atmospheric carbon dioxide concentra­tions on three poplar genotypes grown in SRPs to determine if the energy content would change. They found that changes in carbon dioxide concentration modified biomass com­position more than nitrogen fertilizers. Long-term elevated carbon dioxide concentrations increased the quantity of lignin in the wood. Since lignin has the highest calorific value of all wood components, this suggests that elevated carbon dioxide could actually result in better poplar biomass if it is burnt directly as a fuel. The other important observation was that higher nitrogen rates were necessary for the poplar to utilize the additional carbon dioxide in the atmosphere.

Environmental benefits associated with converting arable land to short-rotation poplar were presented by Updegraff et al. [71]. With regard to potential greenhouse gas mitigation, they noted high differences in calculations of carbon content. Other benefits included a reduction in erosion and agricultural runoff that can lead to surface water protection. They also pointed out that short-rotation poplar plantations cannot be treated as conservation system because of the intensive agricultural practices that are used to sustain the plantations, but the management strategies and environmental benefits are attained by the site and growing conditions. Updegraff et al. [71] also considered the environmental benefits of converting arable land into SRP poplar by constructing three scenarios of 10, 20, or 30% conversion in Minnesota, U. S.A. They assumed two scenarios for utilization of the poplar biomass — wood production or energy generation — and included an assumption that an offset for carbon sequestration would be introduced. Modeling of the three scenarios gave results that had a very high level of uncertainty because of difficulty in quantifying the most crucial environmental benefit (i. e. carbon sequestration). They simply could not obtain an accurate estimate of belowground biomass and carbon dynamics. Therefore, they concluded that the benefits, when treated as offsets in monetary terms, could only be estimated with a very wide range of between $44 and $96 ha-1.

4.3.2 Past and Current Projects

In Europe, the production potential of M. x giganteus has been investigated extensively in trials across northern Europe since 1983 [39]. Between 1993 and 1995, the Miscanthus productivity network, as part of the European agro-industry research program, carried out growth and yield trials on M. x giganteus in 16 locations throughout northern and southern Europe [15, 123]. Later, attention was given to breeding and genetics of Miscanthus. In 1997, the European Miscanthus Improvement (EMI) project was established to investigate the genetic diversity of Miscanthus. Through this project, the biomass productivity and chemical composition of 15 Miscanthus genotypes was assessed in different environments across Europe [3, 53]. The genotypic variation identified by the EMI project stimulated private and public breeding programs involving Miscanthus in the United States and Europe [3]. In 1998, the European BIOMIS project was focused on Miscanthus sinensis. Through a genetic approach, its final objective was to achieve a significant reduction of costs for expensive heat exchangers used in thermal conversion [124].

In 2011 a European project, OPTIMISC (Optimizing Miscanthus Biomass Production), was established between12 partners from Europe, China and Russia. OPTIMISC will run until 2016 and has been established to improve the bioenergy potential of Miscanthus via the trialing of novel elite genotypes across Europe, the Ukraine and Russia. The Miscanthus genotypes will be particularly investigated for their tolerance to water, salinity and cold stress and for their ability to be converted into biofuels and high-value bioproducts.

In France, a novel project called Biomass for the Future (BFF) started in 2012 with the aim of developing industrial clusters of biomass production from dedicated crops of Miscanthus (northern France) and sorghum (southern France). These crops will be improved for their performance in lignocellulosic biomass, with an environmental impact and a composition suitable for industrial applications (combustion, anaerobic digestion, building materials and plastics) and second-generation biofuels production. In the context of sustainable agriculture, BFF will contribute to the enhancement of marginal agricultural land and the development of a new green economy by involving all local stakeholders in a dedicated area. BFF is developed in synergy with biorefinery projects in France and other European countries.

In the United States, Miscanthus research started in 2001 at the University of Illinois at Urbana-Champaign has since expanded to other US universities (http://www. extension. org). Several public-private partnerships investigating aspects of Miscanthus have recently been created, including the Energy Biosciences Institute, the Mendel Biotech Company and the CERES Company. The Energy Biosciences Institute incorporates a range of partner institutions, including the University of California at Berkeley, the University of Illinois at Urbana-Champaign, the Department of Energy Lawrence Berkeley National Laboratory and the International Energy Company BP. In addition, Mendel Biotech in collaboration with the private German nursery company TINPLANT was involved in breeding services for Miscanthus from 2007 to 2011 (http://www. mendelbio. com/). Finally, the private com­pany California CERES is working with experts from IBERS (The Institute of Biological, Environmental and Rural Sciences at Aberystwyth University in the UK) to develop Mis­canthus varieties that can be sown more economically from seed (http://www. ceres. net/).

Other projects are focused on biofuels where Miscanthus constitutes one of the feed­stocks. Among others, the French research and development project Futurol aims to develop and market processes and technologies for second-generation bioethanol production from nonfood lignocellulosic feedstock such as Miscanthus. It runs from 2008 until 2016. Sup­ported by this project, the first pilot plant for second-generation agrofuels production was established in October 2011. In October 2010, the SUNLIBB (Sustainable Liquid

Biofuels from Biomass Bioreflning) project was established combining European and Brazilian research to improve the cell wall characteristics of Miscanthus for biofuel and production. The aim is to identify key genes involved in the biomass saccharification pro­cess and to develop genotypes with improved biofuel conversion efficiencies and clones with improved cell wall characteristics for biofuels, biochemicals and biomaterials.

Commercialization of Eucalyptus species mainly depends on its growth rate and ease of propagation. Most species that are commercially available are fast growers that can be easily propagated, have good form and are adapted to various soil conditions. Growth and yield of Eucalyptus varies from species to species as well as with the geographical area (Tables 9.1 and 9.2). Generally, the faster growing species such as E. grandis, E. urophylla and E. urograndis, which are usually the ideal species for tropical areas, have higher yields (Table 9.2). On the other hand, these tropical varieties do not tolerate the cold winter temperatures of subtropical areas. Therefore, their planting range in the United States is limited to South Florida and Hawaii. When these tropical species are planted further north, trees are killed back to the ground during winter months and coppice every year. Even if they survive the cold winter, their growth is compromised due to cold stress.

ArborGen has genetically engineered E. urograndis by inserting a freeze tolerant gene (Figure 9.1). Results from field trials suggest that the superior line has growth rates and productivity similar to the conventional base clone, with better freeze tolerance up to about -8 to -9°C [9]. With this freeze tolerance achievement, the species can be planted as far north as N 30.5°. TheU. S. Department of Agriculture’s Biotechnology Regulatory Services is currently reviewing the species for deregulation.

A continuing supply of early emerging, high stalk population, disease and insect resistant varieties from breeding stations has been the major contributor to the management of yield-robbing pests. Major diseases of sugarcane include: (1) viruses: potyviruses that cause mosaic (Sugarcane mosaic virus and Sorghum mosaic virus) and sugarcane yellow leaf (Sugarcane yellow leaf virus); (2) bacteria: ratoon stunting disease (Leifsonia xyli subsp. xyli), leaf scald (Xanthomonas albilineans), and sugarcane brown rust (Puccinia melanocephala); and (3) fungi: sugarcane smut (Ustilago scitaminea). This complex of bacterial, fungal, and viral diseases are threats to energy cane as race changes are common. In most cane growing regions, sugarcane is grown as a monoculture. deVries et al. [1] concluded that of the various energy feedstocks being considered, the risk of yield loss associated with the buildup of soil-borne diseases in a continuous cropping system was the least with sugarcane, especially if a short fallow period or a legume is included between cane cycles.

The stem borers (Lepidoptera: Crambidae), including the sugarcane borer [(Diatraea saccharalis (Fabricius)] and the Mexican rice borer [Eoreuma loftini (Dyar)], represent the major insect threats to both sugarcane and energy cane. Economical control of both of these stalk borers in sugarcane is currently obtained by an integrated pest manage­ment program (IPM) that utilizes varietal resistance, manipulation of cultural practices, biological control through natural predators, and the judicious use of insecticides includ­ing Lepidoptera-specific insecticides. Insecticides are applied only when pressures exceed established economic thresholds, and these are determined by using frequent scouting during the grand growth period [38]. The impact of these borers is primarily on sugar pro­duction; hence, their impact on energy cane has not been thoroughly researched. However, it is likely that pest management in energy cane will mirror IPM as practiced in sugar­cane. Borer preference appears to be more towards the low-fiber, high-sugar varieties and less towards the high-fiber, low-sugar varieties of sugarcane, which may be an advantage for energy cane [39]. Energy cane is expected to be grown to a large extent on low-rent, marginal, or underutilized land and in many cases adjacent to traditional food, feed, and fiber crops, where other types of disease and insect pressures may be encountered. Energy cane may harbor diseases and insect pests that may be injurious to the food crops as well; however, these canes may also serve as important overwintering sites for beneficial insects, thereby enhancing the role of biological control.

Broad spectrum pre-emergence and post-emergence herbicides are labeled for use in sugarcane, and presumably this labeling will allow their use in the non-food use energy cane as well [40]. The non-food use designation may also allow the use of herbicides not currently labeled for use in sugarcane. Perennial weeds, such as johnsongrass (Sorghum halepense),

Bermuda grass (Cynodon dactylon), and nutsedge (Cyperus spp.) and a multitude of annual species, but most importantly itchgrass [Rottboellia cochinchinensis) and morning glory (Ipomoea spp.), are particularly problematic, as cultivation is limited to only in the early spring and to the inter-row space for a period of five or more years [41]. The most critical applications of herbicide are at planting and at the start of each growing season of the crop cycle when the crop is in its infancy period [42]. Energy cane appears to be more competitive with weeds than sugarcane because it emerges faster and produces more shoots. Because of the wide row spacing to accommodate mechanical culture and harvesting, an application of herbicide at the start of each growing season is recommended for sugarcane. As energy cane may be more aggressive, applications of herbicide may not be needed after the first ratoon production year.

Some diseases and pests of pines are native to the region while others are exotic (also known as introduced pests). A few examples of exotic pests include Grosmannia huntii, Bursaphelenchus xylophilus (Table 10.5) and Sirex noctilo.

On a global basis, more pines die from stress and subsequent beetle infection than die from diseases [11]. Landscape-scale beetle mortality has occurred after stresses in Belize, Canada, China, Germany, Nicaragua and the United States. Dendroctonus spp. and Ips spp. are considered to be the most destructive insects of pines in North America. The risk of injury from these pests increases with age and stocking. Overstocked stands result in stressed pines that emit volatile compounds that attract beetles. Another beetle that may cause problems is Monochamus spp.

In some regions, regeneration weevils do not exist and, therefore, pines are planted just after the harvesting operation. However, in the United States and parts of Europe a delay occurs between harvesting and planting. This delay reduces the risk of injury from certain weevils (e. g. Hylobiuspales). For a regime harvesting pines when 17-years old, a one year delay in planting reduces the amount of energy captured by about 5%.

In some cases, early growth rates have been increased by controlling certain insects. For example, reducing the level of weed competition can increase both the number of shoots per tree and the number of shoots that are affected by the insect Rhyacionia frustrana. Some believe that applying insecticides to pine plantations during the first two years will be economically beneficial (Table 10.6).

Nematodes (unsegmented roundworms) are present in nearly all forests but most soils in the southern hemisphere do not have species that are adapted to feed on pine roots. The growth of pine is affected by the stubby-root nematode (Trichodorus christiei) and the lance nematode (Hoplolaimus galeatus). Some nematodes (Bursaphelencus spp.) can kill pines when they are planted as exotics.

Numerous fungi can affect the growth of pines. The most common disease of pines in the United States is Cronartium fusiforme f. sp. fusiforme, which can affect the stems and branches of several pines. In a few stands, over half of the trees are infected with this fungus.

Today’s sorghum breeding programs integrate both traditional and molecular approaches. When breeding new hybrids, each program develops inbred lines for test-cross evaluation. To develop inbred lines, most but not all sorghum breeding programs use some form of pedigree selection [4]. Test-cross evaluation is used to assess combining ability. Good general combining ability (GCA) is needed in the first test-cross and subsequent testing identifies the exact combinations with commercial potential. Predicting hybrid performance by evaluating inbred lines themselves is not typically an efficient use of resources [65].

If the new lines are seed parents (i. e., they do not restore fertility to male sterile inducing cytoplasm), they must be sterilized for use as a seed parent. Sterilization involves back — crossing to introgress sterility-inducing cytoplasm, which results in a sterile version of the seed parent. The use of off-season nurseries speeds the pace but sterilization and creation of an A-line (male sterile) version of the B-line (fertile seed parent) requires additional time. Since the advent of hybrids, sorghum germplasm has been placed into heterotic groups based on fertility restoration. While this classification was of necessity, there is some basis as most seed parents were in the kafir group while pollinator parents were typically cau- datum and durra types. Since then breeding has evolved these into legitimate heterotic groups [73].

Sorghum genetics and genomics are well advanced. The sorghum genome has been sequenced [74], two high-density genetic maps and one cytogenetic map have been con­structed [75-77]. Additionally, many agronomically important genes have been cloned [78-80] and a transformation system has been developed [81]. Finally, there are many published quantitative trait locus (QTL) studies in sorghum, and much of this information is being used for genetic characterization of sorghum germplasm in breeding programs.

Timothy A. Volk1, L. P. Abrahamson1, T. Buchholz2,

J. Caputo1, and M. Eisenbies1

1 College of Environmental Science and Forestry, State University of New York, U. S.A.
2Gund Institute for Ecological Economics, University of Vermont, and Spatial Informatics Group,

LLC, U. S.A.

12.1 Introduction

According to the U. S. Billion Ton Update (BT2) [1]), a federal investigation into the feasibility of replacing 30% of petroleum feedstocks with renewable biomass, perennial energy crops are projected to provide as much as 61% of the potential biomass in the United States by 2030 under the most favorable set of scenarios (highyield, $60 a ton price, 4% energy crop yield increases). The objective is to grow these crops on marginal agricultural and abandoned land to minimize the impact on production of other agricultural crops and to provide landowners with alternative crops and income from these areas. The northeast United States is well suited to production of perennial energy crops because there are large amounts of marginal agricultural land and reclaimed land. Studies indicate that there are over 2.8 million ha of idle or surplus low-cost agricultural land [2] and 0.5 million ha of disturbed mine land available for deploying perennial energy crops in the northeast [3]. Both woody [e. g., willow (Salix spp.) and hybrid poplar (Populus spp.)] and herbaceous perennial energy crops [e. g., switchgrass (Panicum virgatum), Miscanthus] have been identified as potential perennial energy crops on this land base.

Interest in shrub willows as a perennial energy crop for production of biomass has developed in Europe and North America over the past few decades because of concerns with energy security, environmental impact associated with the current mix of fossil fuels,

Cellulosic Energy Cropping Systems, First Edition. Edited by Douglas L. Karlen. © 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.

and economic challenges in rural areas. When deployed properly across the landscape, willow biomass crops can provide multiple environmental and rural development benefits [4-6], while providing a locally grown source of biomass that can be converted into a range of bioenergy, biofuels and bioproducts.

Initial trials with shrub willows as a biomass crop were conducted in the mid-1970s in Sweden and in the United States starting in 1986 [7]. Commercial expansion started in Sweden in the late 1980s and accelerated rapidly for several years because of favorable policies supporting biomass crop establishment. By the late 1990s, the acreage in Sweden had peaked at around 16 000 ha but since that time it has decreased slightly to about 14 000 ha of willow biomass crops [8-10]. An additional 18 500 ha of willow and poplar woody energy crops have been established in Germany, Italy and the United Kingdom [10].

Since the first research projects were initiated in upstate New York, U. S.A., in the mid-1980s, yield trials have been conducted or are underway in 15 states and six Cana­dian provinces, so that now over 500 ha of commercial scale willow biomass crops have been established. In addition to studies on potential yields of different varieties of willow across a range of sites, research has also been done on various aspects of the production cycle, including nutrient amendments and cycling, alternative tillage practices, incorpo­rating cover crops into these systems, spacing and density studies, harvesting systems development, growth characteristics important for biomass production, use of willow plan­tations by birds, changes in soil micro arthropod communities under willow, changes in soil carbon, economics of the production system, and life cycle assessments of willow bioen­ergy systems. In addition, a breeding and selection program for shrub willows has been developed and is producing improved varieties of willow for both the biomass production and agroforestry markets [11]. Results from this and other initiatives in North America and Europe have provided a base from which to begin to expand and deploy willow biomass crops.

The most recent development in the commercialization of willow biomass crops in North America has been the establishment in 2012 of a biomass crop assistance program (BCAP) project area in northern New York State [12]. BCAP is a U. S. Department of Agriculture (USDA) initiative intended to promote wide-scale deployment of biomass cropping and utilization, established in the Food, Conservation, and Energy Act of 2008 (P. L. 110-234, Sec. 9011). Under this program almost 500 ha of willow biomass crops will be managed for at least ten years. This program provides cost share support from the USDA for the establishment of willow biomass crops and an annual rental payment for land that is used to produce these crops. Long-term agreements are in place for the sale of all of the biomass produced from these fields to an end user in the region that is generating electricity and heat using wood chips. This program addressed some key barriers to the deployment of willow, including reducing upfront costs associated with establishing willow biomass crops and providing a secure long-term market for the biomass that is produced.