Woody energy crops in the southeastern United States: Two centuries of practitioner experience

Forest industry experts were consulted on the potential for hardwood tree species to serve as feedstock for bioenergy in the southeastern United States. Hardwoods are of interest for bioenergy because of desirable physical qualities, genetic research advances, and growth potential. Yet little data is available regarding potential productivity and costs. This paper describes required operations and provides a realistic estimate of the costs of producing bioenergy feedstock based on commercial experiences. Forestry practitioners reported that high productivity rates in southeastern hardwood plantations are confined to narrow site conditions or require costly inputs. Eastern cottonwood and American sycamore grow quickly on rich bottomlands, but are also prone to pests and disease. Sweetgum is frost hardy, has few pest or disease problems, and grows across a broad range of sites, yet growth rates are relatively low. Eucalypts require fewer inputs than do other species and offer high potential productivity but are limited by frost to the lower Coastal Plain and Florida. Further research is required to study naturally regenerated hardwood biomass resources. Loblolly pine has robust site requirements, growth rates rivaling hardwoods, and lower costs of production. More time and investment in silviculture, selection, and breeding will be needed to develop hardwoods as competitive biofuel feedstock species. Because of existing stands and fully developed operations, the forestry community considers loblolly pine to be a prime candidate for plantation bioenergy in the Southeast.     

Soil carbon, after 3 years, under short-rotation woody crops grown under varying nutrient and water availability

Soil carbon contents were measured on a short-rotation woody crop study located on the US Department of Energy's Savannah River Site outside Aiken, SC. This study included fertilization and irrigation treatments on five tree genotypes (sweetgum, loblolly pine, sycamore and two eastern cottonwood clones). Prior to study installation, the previous pine stand was harvested and the remaining slash and stumps were pulverized and incorporated 30 cm into the soil. One year after harvest soil carbon levels were consistent with pre-harvest levels but dropped in the third year below pre-harvest levels. Tillage increased soil carbon contents, after three years, as compared with adjacent plots that were not part of the study but where harvested, but not tilled, at the same time. When the soil response to the individual treatments for each genotype was examined, one cottonwood clone (ST66), when irrigated and fertilized, had higher total soil carbon and mineral associated carbon in the upper 30 cm compared with the other tree genotypes. This suggests that root development in ST66 may have been stimulated by the irrigation plus fertilization treatment.     

An analysis of the feasibility for increasing woody biomass production from pine plantations in the southern United States

In the near future, wood from the 130 000 km² of pine plantations in the southern United States could provide much of the feedstock for emerging bioenergy industries. Research and operational experience show that total plantation biomass productivity exceeding 22.4 Mg ha^?1 y^?1 green weight basis with rotations less than 25 years are biologically possible, financially attractive, and environmentally sustainable. These gains become possible when intensively managed forest plantations are treated as agro-ecosystems where both the crop trees and the soil are managed to optimize productivity and value. Intensive management of southern US pine plantations could significantly increase the amount of biomass available to supply bioenergy firms. Results from growth and yield simulations using models and a financial analysis suggest that if the 130 000 km² of cutover pine plantations and an additional 20 000 km² of planted idle farmland are intensively managed in the most profitable regimes, up to 77.5 Tg green weight basis of woody biomass could be produced annually. However, questions exist about the extent to which intensive management for biomass production can improve financial returns to owners and whether they would adopt these systems. The financial analysis suggests providing biomass for energy from pine plantations on cutover sites is most profitable when intensive management is used to produce a mixture of traditional forest products and biomass for energy. Returns from dedicated biomass plantations on cutover sites and idle farmland will be lower than integrated product plantations unless prices for biomass increase or subsidies are available.     

Modeling the role of forests in a regional carbon mitigation plan

Biomass from the forest sector can be an important source of renewable energy and can contribute to climate change mitigation and bioenergy development. However, the removal of biomass from forests has significant impacts on the forest ecosystem. For instance, it modifies soil litter which is particularly important to preserve soil characteristics and to sustain a diversity of organisms. Our aim is to analyze alternatives of sustainable forest management and compare how they perform in terms of carbon savings in order to assess the role of the sector in a regional emission reduction plan. The analysis is performed applying CO2FIX, a well-known carbon accounting model to the forests of the Italian region of Emilia-Romagna. The behavior of the most important forest macro-categories is investigated under common management alternatives: no harvest activities, maintenance of a constant stock, different rotation lengths, and maximization of harvested biomass. We evaluate their impact at landscape level on the regional carbon budget, thus estimating the maximum potential contribution from the forest sector.     

Soil disturbance concerns regarding the use of forest biomass as a source of energy: Examples from Pacific Northwestern North America

Increased biomass removals may affect long-term site productivity and hydrologic function through harvesting effects on soils. This paper reviews the current soil disturbance context for biomass harvesting in the Pacific Northwest of North America, and discusses environmental sustainability concerns that should be of interest to all parties involved in the generation or purchase of bio-energy. In the Pacific Northwest many dense stands of low-value timber exist and are seen by some as a source of cheap biomass energy; however, intensive biomass harvest may involve more machine traffic during harvest, increasing concerns about protection of the soil resource. Both the United States Department of Agriculture, Forest Service, and British Columbia Forest Service have developed and implemented soil quality standards to keep activity-induced soil disturbance within defined limits. Examples of soil disturbance data collected over the past 20 years from various harvesting systems are discussed to demonstrate the higher-than-usual level of disturbance that can occur from biomass harvesting. Comparison of such monitoring results within or between forest management jurisdictions is often difficult because of differing definitions of detrimental soil disturbance and different soil disturbance assessment protocols. Recommendations are provided regarding more comparable and rigorous means of conducting soil quality assessments, including common terminology, which are needed to enable demonstration that long-term productivity and hydrologic function are being protected during biomass harvest under various international protocols and their respective criteria and indicators, and third-party certification schemes.     

Social availability of residual woody biomass from nonindustrial private woodland owners in Minnesota and Wisconsin

An important and potentially underused source of biomass that could be utilized in energy production is from nonindustrial private woodlands. We employ the Theory of Planned Behavior to estimate the social availability of woody biomass as a function of landowner behavior intent, landowner characteristics, forest land characteristics, and biomass price on stated willingness to harvest biomass in conjunction with a commercial timber harvest. A mail survey was administered to 1109 nonindustrial private woodland owners in a 26-county region in northeast Minnesota and northwest Wisconsin during the fall of 2009. Using binary logistic regression, we found payment level offered to harvest biomass plays a significant role in landowners' decisions, but that non-monetary factors are also important. Landowner attitudes and opinions regarding soil impacts, aesthetics, and energy independence were important predictors of stated willingness to harvest. Social norms as manifested through the influence of neighbors were also significant. These findings expand existing research and are useful for profiling nonindustrial private woodland owners to identify sustainable sources of biomass to supply a burgeoning bioenergy sector in the Lake States.     

Balancing biofuel production and biodiversity: Harvesting frequency effects on production and community composition in planted tallgrass prairie

Native perennial grasslands have been proposed as a source of feedstocks for the production of second-generation lignocellulosic biofuels in the Midwestern USA. Although the consequences of some management decisions for biomass production and plant community composition are well understood (e.g. fertilization), less is known about the effects of harvesting frequency. We compared a once- and twice-annual harvesting regime at two restored prairies in southwestern Michigan established with identical seed mixtures as part of a large-scale bioenergy experiment. We determined biomass production and species composition in experimental plots and also measured the availability of light, inorganic nitrogen and soil moisture. The plant communities that established at the two sites differed markedly in composition and there was little evidence of convergence after five years. At the site dominated by warm-season C₄ grasses, single harvests generally produced more biomass than double harvests. By contrast, biomass production was unaffected by harvesting at the more diverse site. Contrary to our prediction that a summer harvest would increase diversity, we found small and subtle effects on plant community composition. This may be due in part to the timing of our harvest treatment. Our results suggest that a single, end-of-season harvest is the best practice for maximizing biomass production in prairies, especially at sites where warm-season grasses dominate. However, at more diverse sites, two harvests can produce the same total biomass and may support other beneficial ecosystem services. This study indicates that in the short term, double harvests are unlikely to affect plant species diversity or community composition in prairie plantings.     

Exploring the potential of Eucalyptus for energy production in the Southern United States: Financial analysis of delivered biomass. Part I

Eucalyptus plantations in the Southern United States offer a viable feedstock for renewable bioenergy. Delivered cost of eucalypt biomass to a bioenergy facility was simulated in order to understand how key variables affect biomass delivered cost. Three production rates (16.8, 22.4 and 28.0 Mg ha⁻¹ y⁻¹, dry weight basis) in two investment scenarios were compared in terms of financial analysis, to evaluate the effect of productivity and land investment on the financial indicators of the project. Delivered cost of biomass was simulated to range from $55.1 to $66.1 per delivered Mg (with freight distance of 48.3 km from plantation to biorefinery) depending on site productivity (without considering land investment) at 6% IRR. When land investment was included in the analysis, delivered biomass cost increased to range from $65.0 to $79.4 per delivered Mg depending on site productivity at 6% IRR. Conversion into cellulosic ethanol might be promising with biomass delivered cost lower than $66 Mg⁻¹. These delivered costs and investment analysis show that Eucalyptus plantations are a potential biomass source for bioenergy production for Southern U.S.     

Biomass retention following whole-tree, energy wood harvests in central Maine: Adherence to five state guidelines

The expansion of the bioenergy industry in Maine has led to an increase in integrated roundwood and energy wood whole-tree harvesting. A better understanding of the amounts of logging residue left unrecovered on whole-tree harvested sites will enable the refinement of available forest residue estimates for Maine and the assessment of the potential effect of such harvesting on forest health. Several states have developed biomass harvesting guidelines in response to concerns generated from an expanding bioenergy industry. In this study downed wood and snags were inventoried on twelve sites in central Maine that had recently been whole-tree harvested for roundwood and energy wood. The percentage of harvested material retained as residue on the study sites was determined. On average, 45% of the energy wood generated during the harvest was left on site. This removal efficiency must be considered when developing forest residue availability estimates. Additionally, the volumes of logging residue were compared to measurable criteria from biomass and biodiversity guidelines of several states. We found that enough fine woody material (<15 cm diameter) remained on the harvest sites to meet the guideline criteria; however, the quantities of coarse woody material (≥15 cm diameter), large logs (≥38 cm dbh), and snags (≥25 cm dbh) were insufficient to meet the guideline criteria. These deficiencies likely resulted from prior forest practices rather than from the current energy wood removal. Retaining more trees of larger sizes in the future can address this concern.     

Harvesting productivity and costs when utilizing energywood from pine plantations of the southern Coastal Plain USA

For woody biomass to make a significant contribution to the United States' energy portfolio, harvesting contractors must economically harvest and transport energywood to conversion/processing facilities. We conducted a designed operational study in the Coastal Plain of North Carolina, USA with three replications of three treatments to measure harvesting productivity and costs when utilizing woody biomass. The treatments were: a conventional roundwood only harvest (control), an integrated harvest in which merchantable roundwood was delivered to mills and residuals were chipped for energy, and a chip harvest in which all stems were chipped for energy use. The harvesting contractor in this study typically delivers 2200–2700 t of green roundwood per week and is capable of wet-site harvesting. Results indicate that onboard truck green roundwood costs increased from 9.35 $ t⁻¹ in the conventional treatment to 10.98 $ t⁻¹ in the integrated treatment as a result of reduced felling and skidding productivity. Green energy chips were produced for 19.19 $ t⁻¹ onboard truck in the integrated treatment and 17.93 $ t⁻¹ in the chip treatment. Low skidding productivity contributed to high chip costs in the integrated treatment. Residual green biomass was reduced from 18 t ha⁻¹ in the conventional treatment to 4 and 3 t ha⁻¹ in the integrated and chip treatments, respectively. This study suggests that until energywood prices appreciate substantially, loggers are unlikely to sacrifice roundwood production to increase energywood production. This research provides unique information from a designed experiment documenting how producing energywood affects each function of a harvesting system.     

Biomass and nutrient removal by willow clones in experimental bioenergy plantations in New York State

The development of short-rotation intensive cultural (SRIC) willow systems as a source of bioenergy and bioproducts is growing in the northeastern and midwestern United States. Important data for sustainable management such as nutrient removal and nutrient use efficiency in willow bioenergy plantations is lacking. This study reports wood biomass production, annual removal of nutrients, and nutrient use efficiency in experimental plantings of SRIC willow and poplar at Tully, New York. Effects of clone, fertilization, irrigation, planting density, and harvest cycle were analyzed.

Annual biomass production of 15–22 dryMg/ha removed 75–86, 10–11, 27–32, 52–79 and 4–5 kg/ha/year of N, P, K, Ca and Mg, respectively. For all the variables studied, the responses depended on clone. Fertilization and irrigation increased rates of nutrient removal by means of increased biomass production. Unlike planting density, harvest cycle significantly affected rates of nutrient removal and nutrient use efficiency. For clone SV1 (Salix dasyclados), an irrigated and fertilized planting with a density of 36,960 trees/ha harvested on a 3-year rotation had the highest biomass production and nutrient use efficiency, and the lowest rates of nutrient removal. The annual harvest cycle had the lowest nutrient use efficiency and the highest annual removal of nutrients suggesting that this choice would be most appropriate for biomass crops that are to be used as buffer strips to manage nutrient runoff from agricultural fields. An appropriate choice of clone, planting density, and harvest cycle could tailor the rates of nutrient removal and nutrient use efficiency to match the objective of the planting.     

The effects of slash and stump removal on productivity and quality of forest regeneration operations—preliminary results

The object of this study was to survey the effects of slash and stump removal on work productivity and work quality, as well as on the technology of forest regeneration operations. Site preparation and planting were studied in different conditions. Slash and stump treatments “removal” and “no removal” were established at each site. Time studies were made during site preparation and planting. The quality of mounding and planting was analysed by measurements of the seedlings.After slash removal, the increase of work productivity (E₀) in mechanized planting was 18 per cent with a Bräcke planting machine and 0 per cent with an Ecoplanter planting machine. The quality of mechanized planting was slightly improved by slash removal.After slash removal, the productivity (E₀) of excavator-mounted mounders was 22 per cent higher with a mounding blade and 53 per cent higher with a ditching bucket. The quality of mounding was the same for both slash treatments. The productivity (E₀) of three forwarder-mounted mounders was 5 per cent lower after slash removal, but at the same time the quality of the mounding was much better.In combined stump extraction and mounding, the time consumption of the mounding phase was about 40 per cent lower than for separate mounding after stump removal.The results show that slash and stump removal will improve work productivity and quality when using mechanized mounding and planting methods. In addition after slash and/or stump removal it may be possible and cost-effective to use new planting and site preparation methods based on forwarder-mounted mounders.     

Factors affecting nonindustrial private forest landowners' willingness to supply woody biomass for bioenergy

Bioenergy is a renewable form of potential alternative to traditional fossil fuels that has come to the forefront as a result of recent concerns over high price of fuels, national security, and climate change. Nonindustrial private forest (NIPF) landowners form the dominant forest ownership group in the southern United States. These forests often tend to have large quantities of small diameter trees. Use of logging residues and non-marketable small diameter trees for bioenergy production can create economic opportunities for NIPF landowners. The results demonstrated that landowners’ willingness to harvest woody biomass was influenced by their ownership objectives, size of the forest, structure and composition of tree species, and demographic characteristics. The model found that relatively younger landowners who owned large acres of forestland with pine plantations or mix forests had the potential to become a preferable choice for contractors, extension foresters and bioenergy industries as they were more likely to supply woody biomass for bioenergy. Findings of this study will be useful to bioenergy industries, extension foresters, nonindustrial private forest landowners and policy makers.     

Long-term yield potential of switchgrass-for-biofuel systems

Limited information is available regarding biomass production potential of long-term (>5- yr-old) switchgrass (Panicum virgatum L.) stands. Variables of interest in biomass production systems include cultivar selection, site/environment effects, and the impacts of fertility and harvest management on productivity and stand life. We studied biomass production of two upland and two lowland cultivars under two different managements at eight sites in the upper southeastern USA during 1999–2001. (Sites had been planted in 1992 and continuously managed for biomass production.) Switchgrass plots under lower-input management received 50 kg N ha⁻¹ yr⁻¹ and were harvested once, at the end of the season. Plots under higher-input management received 100 kg N ha⁻¹ (in two applications) and were harvested twice, in midsummer and at the end of the season. Management effects on yield, N removal, and stand density were evaluated. Annual biomass production across years, sites, cultivars, and managements averaged 14.2 Mg ha⁻¹. Across years and sites, a large (28%) yield response to increased inputs was observed for upland cultivars; but the potential value of higher-input management for lowland cultivars was masked overall by large site×management interactions. Nitrogen removal was greater under the higher-input system largely due to greater N concentrations in the midsummer harvests. Management recommendations (cultivar, fertilization, and harvest frequency), ideally, should be site and cultivar dependent, given the variable responses reported here.     

Fibre use,net calorific value,and consumption of forest-derived bioenergy in British Columbia,Canada

The lack of data about current bioenergy production in British Columbia severely limits stakeholder analyses of the true value and growth potential of bioenergy within the province and the forest industry's sustainability. Fifty-two facilities were surveyed to gather statistics on rates of fibre use for energy, thermal and electrical energy capacity and net production. We estimated that from 2000 to 2011, on average 9.4 Mt of wood fibre (oven-dry) was used annually to produce energy, which was about one-third of the total harvested biomass. However, bioenergy does not drive the harvest. Bioenergy uses residual fibre from other operations—primarily black liquor from pulp mills. In total, the forest sector produced approximately 118 PJ of thermal and electrical energy in 2011, based on the net calorific value provided by respondents. Based on these results, we concluded that wood-based bioenergy supplied approximately 10% of British Columbia's energy demands in 2011. Forestry sector commodity and economic statistics likely underestimate the more than 640 M$ worth of energy it produced. The survey results also showed a wide variation in the efficiency of energy production between different facilities. Given the large discrepancy between the theoretical high heating values and what the producers achieved, it may be prudent to use an operationally-derived net calorific value or low heating value for estimating energy supply from biomass, especially for policy or business development.     

Using a decision support system to optimize production of agricultural crop residue Biofeedstock

For several years the Idaho National Laboratory (INL) has been developing a Decision Support System for Agriculture (DSS4Ag) which determines the economically optimum recipe of various fertilizers to apply at each site in a field to produce a crop, based on the existing soil fertility at each site, as well as historic production information and current prices of fertilizers and the forecast market price of the crop at harvest. In support of the growing interest in agricultural crop residues as a bioenergy feedstock, we have extended the capability of the DSS4Ag to develop a variable-rate fertilizer recipe for the simultaneous economically optimum production of both grain and straw. In this paper we report the results of 2 yr of field research testing and enhancing the DSS4Ag's ability to economically optimize the fertilization for the simultaneous production of both grain and its straw, where the straw is an agricultural crop residue that can be used as a biofeedstock. For both years, the DSS4Ag reduced the cost and amount of fertilizers used and increased grower profit, while reducing the biomass produced. The DSS4Ag results show that when a biorefinery infrastructure is in place and growers have a strong market for their straw it is not economically advantageous to increase fertilization in order to try to produce more straw. This suggests that other solutions, such as single-pass selective harvest, must be implemented to meet national goals for the amount of biomass that will be available for collection and use for bioenergy.     

The role of forest and bioenergy strategies in the global carbon cycle

Forest and bioenergy strategies offer the prospect of reduced CO₂ emissions to the atmosphere. Such strategies can affect the net flux of carbon to the atmosphere through 4 mechanisms: storage of C in the biosphere; storage of C in forest products; use of biofuels to displace fossil-fuel use; use of wood products which often displaces other products that require more fossil fuel for their production. We use the mathematical model GORCAM (Graz/Oak Ridge Carbon Accounting Model) to examine these mechanisms for 16 land-use scenarios. Over long time intervals the amount of C stored in the biosphere and in forest products reaches a steady state and continuing mitigation of C emissions depends on the extent to which fossil fuel use is displaced by the use of bioenergy and wood products. The relative effectiveness of alternative forest and bioenergy strategies and their impact on net C emissions strongly depend, for example, on the productivity of the site, its current usage, and the efficiency with which the harvest is used. When growth rates are high and harvest is used efficiently, the dominant opportunity for net reduction in C emissions is seen to be fossil-fuel displacement. At the growth rates and efficiencies of harvest utilization adopted in many of our base scenarios, the net C balance at the end of 100 years is very similar whether trees are harvested and used for energy and traditional forest products, or reforestation and forest protection strategies are implemented. The C balance on a plantation system that provides a constant output of biomass products can look different than the balance of a single parcel of land.     

Forest treatment residues for thermal energy compared with disposal by onsite burning: Emissions and energy return

Mill residues from forest industries are the source for most of the current wood-based energy in the US, approximately 2.1% of the nation's energy use in 2007. Forest residues from silvicultural treatments, which include limbs, tops, and small non-commercial trees removed for various forest management objectives, represent an additional source of woody biomass for energy. We spatially analyzed collecting, grinding, and hauling forest residue biomass on a 515,900 ha area in western Montana, US, to compare the total emissions of burning forest residues in a boiler for thermal energy with the alternatives of onsite disposal by pile-burning and using either natural gas or #2 distillate oil to produce the equivalent amount of useable energy. When compared to the pile-burn/fossil fuel alternatives, carbon dioxide emissions from the bioenergy alternative were approximately 60%, methane emissions were approximately 3%, and particulate emissions less than 10 μm were 11% and 41%, respectively, for emission control and no-control boilers. Emissions from diesel consumption for collecting, grinding, and hauling biomass represented less than 5% of the total bioenergy emissions at an average haul distance of 136 km. Across the study area, an average 21 units of bioenergy were produced for each unit of diesel energy used to collect, grind, and haul biomass. Fossil fuel energy saved by the bioenergy alternative relative to the pile-burn/fossil fuel alternatives averaged 14.7–15.2 GJ t^?1 of biomass.     

Assessing and mapping biomass potential productivity from poplar-dominated riparian forests: A case study

River systems are subjected to continuous physical changes as a result of their sediment transport. River dynamics is mainly determined by the seasonal variation of weather conditions and, together with the nature of the catchment and land management, affects flow patterns on a local scale. Riparian vegetation is well adapted to this periodical disturbance. It naturally regenerates on the new mineral soil created by the redistribution of river sediments during floods, playing an important role in the maintenance of streams and riverbanks stability. The high level of resilience and productivity of riparian tree species like Populus, contributes to the rapid biomass accumulation of riparian vegetation making these ecosystems of potential interest for biomass production for energy. This paper presents an operational methodology for investigating the biomass potential from riparian forests by coupling airborne laser scanning data and field survey. A case study on assessing and mapping biomass dynamics over a seventeen year period along a tract on the Paglia river, in Central Italy, is presented and discussed. The results highlight that the surface of the poplar-dominated riparian vegetation has significantly changed over the 1989–2006 period. More than 70 ha of new poplar forest were naturally regenerated during the analyzed period. The total amount of aboveground woody biomass of the riparian forest at the second inventory occasion has been estimated in 88 Mg ha⁻¹, evidencing a large amount of technically available resources for bioenergy production (around 80% of the standing woody biomass). The innovative strategy here proposed to assess and map at a very high spatial resolution the aboveground woody biomass of riparian forest meets the monitoring requirements to support energy production based on modern, non-conventional biomass harvest planning options.     

Economic analysis of alternative logistics systems for Tennessee-produced switchgrass to penetrate energy markets

Growing biomass crops for energy production on low productivity lands not used for food production has been suggested as an alternative to reduce dependence on fossil fuels and to mitigate greenhouse gas emissions from transportation fuel. Switchgrass is considered a potential feedstock in various states, including Tennessee, given its high biomass content in a wide range of environments. However, its low density relative to energy value and resulting high logistics costs impede the profitability of switchgrass-based bioenergy. The objective of this study is to determine the optimal logistics configuration for a collection/distribution hub to market Tennessee-produced switchgrass for bioenergy production. A mathematical programming model integrated with a geographic information system is used to maximize the net present value of profit from a hub that serves switchgrass producers and bioenergy markets. Six logistics configurations delivering switchgrass to local or international bioenergy markets are evaluated. The results highlight the economic challenges of penetrating energy markets for a switchgrass collection/distribution hub – only one logistics configuration that targets the local market is profitable. However, serving local and international markets becomes more feasible as investment risk declines. The results imply that a clear direction for national bioenergy policy is crucial to developing a biomass feedstock for the U.S. bioenergy industry.