Short-rotation Woody Crop Plantations Research Articles

Accumulation of soil organic carbon after cropland conversion to short‐rotation willow and poplar

AbstractThe demand for bioenergy has increased the interest in short‐rotation woody crops (SRWCs) in temperate zones. With increased litter input and ceased annual soil cultivation, SRWC plantations may become soil carbon sinks for climate change mitigation. A chronosequence of 26 paired plots was used to study the potential for increasing soil organic carbon (SOC) under SRWC willow and poplar after conversion from cropland (CR) on well‐drained soils. We estimated SOC stocks in SRWC stands and adjacent CR and related the difference to time since conversion, energy crop species, SOC stock of the adjacent CR (proxy for initial SOC of SRWC) and the fine soil percentage (<63 μm) (FS). Soil cores to 40 cm depth were sampled and separated by layers of fixed depths (0–5, 5–10, 10–15, 15–25 and 25–40 cm). Additionally, soils were sampled from soil pits by genetic horizons to 100 cm depth. Comparisons of SOC stocks by equivalent soil masses showed that mean SOC stocks in SRWC were 1.7 times higher than those of CR in the top 5 cm of the soil (P < 0.001). The differences between SRWC and CR remained significant for the plough layer (0–25 cm) by a factor of 1.2 (P = 0.003), while no changes were detectable for the 0–40 cm (P = 0.32), or for the entire 0–100 cm soil layer (P = 0.29). The SOC stock ratio, that is the ratio of SOC stock in SRWC relative to CR, did not change significantly with time since conversion, although there was a tendency to an increase over time for the top 40 cm (P = 0.09). The SOC stock ratio was negatively correlated to SOC in CR and FS percentage, but there was no significant difference between willow and poplar at any depth. Our results suggest that SOC stocks in the plough layer increase after conversion to SRWC.

A traditional ground-based system for woody biomass harvesting in Short Rotation Woody Crop (SRWC) plantations – a case study in Michigan

ABSTRACTReconfigured forage harvesting equipment utilized for plantation biomass harvesting and processing is highly productive but is expensive and not yet widely used in short rotation woody crop (SRWC) production systems. Traditional timber harvesting equipment, on the other hand, has been widely used for decades and can be adapted for use in SRWC plantations. Productivity of these traditional systems is not well understood when utilized in such plantations. To that end, productivity and costs were evaluated for a traditional ground-based system (feller-buncher, skidder, loader, and grinder) in a 3.1-ha small-diameter hybrid poplar plantation in Escanaba, Michigan, USA. Operation cycle time predictive models were developed from a time and motion analysis. Operation productivity and costs were generated and then compared with published data for a reconfigured forage harvesting system. Compared values between the two systems included: machine hourly rate, in dollars per scheduled machine hour ($/SMH), the production cost, in dollars per oven dry ton ($/ODT), and the system production rate, in oven dry tons per productive machine hour (ODT/PMH). The machine hourly rate and production cost of the traditional system were found to be $284.00/SMH, and $22.30/ODT, respectively; while the production rate was found to be variably between 8.82–35.44 ODT/PMH. A sensitivity analysis was conducted on the traditional harvesting system to test the effect of machine utilization on production costs, where an equal utilization rate of 80% dropped production costs to $17.92/ODT. A net energy analysis was also conducted, demonstrating a net energy ratio of 24.8:1 for the traditional system.

Effect of Increased Soil Fertility on the Yield and Energy Value of Short-Rotation Woody Crops

Biomass is produced as a feedstock for energy generation and industrial processes from short-rotation woody crop plantations in Europe, the USA, and Canada. This study determined the impact of soil enrichment on the survival rate, productivity, energy value, and yield of three species of crops grown on poor soil in a 4-year harvest rotation based on two factors: species (willow, poplar, and black locust) and fertilization (lignin, mineral fertilization, mycorrhiza inoculation, and their combination). The highest average yield was obtained from willow, followed by poplar and black locust. The highest yield in the entire experiment was for poplar with lignin combined with mineral fertilization (10.5 odt ha−1 year−1). Using lignin combined with mineral fertilizers increased the yield by 8–14 % compared to mineral fertilizers alone for willow and poplar and nearly doubled the black locust yield. The energy value of the yield ranged from 28.6 to 176.7 GJ ha−1 year−1, respectively, for black locust grown on the control plot and for poplar grown with mineral fertilization combined with lignin.

Operational short rotation woody crop plantations: Manual or mechanised harvesting?

Harvesting is the most expensive, but the least investigated process in the cultivation of short rotation woody crops (SRWC). To get a better idea of the harvesting process (in terms of its performance, productivity, cost, soil compaction, cutting height and quality as well as biomass losses), we closely monitored the second harvest of a SRWC culture in Flanders (Belgium). We compared our results to the harvests of other, small European parcels. The trees at our site were harvested with both a manual and a mechanised (Stemster harvester) cut-and-store system, while the cut-and-chip system was analysed from an extensive literature survey. The production cost (to the edge of the field) at our site reached 426 (manual) and 94 (mechanised) € t−1, while the average values found in the literature are respectively 104 and 78 € t−1, versus 17 € t−1 for the cut-and-chip harvesting system. The productivity at our site reached 14 (manual) and 22 (mechanised) oven-dry tonnes per scheduled machine hour, while the average values found in the literature are respectively 15 and 23 t h−1. Based on the good performance (ha h−1) and productivity (t h−1) of the cut-and-chip system as well as its lower costs, this harvesting system is recommended for operational SRWC.

Comparative analysis of harvesting machines on an operational high-density short rotation woody crop (SRWC) culture: One-process versus two-process harvest operation

Short rotation woody crops (SRWCs) are being studied and cultivated because of their potential for bioenergy production. The harvest operation represents the highest input cost for these short rotation woody crops. We evaluated three different harvesting machines representing two harvesting systems at one operational large-scale SRWC plantation. On average, 8 ton ha−1 of biomass was harvested. The cut-and-chip harvesters were faster than the whole stem harvester; and the self-propelled harvester was faster than the tractor-pulled. Harvesting costs differed among the harvesting machines used and ranged from 388 € ha−1 to 541 € ha−1. The realized stem cutting heights were 15.46 cm and 16.00 cm for the tractor-pulled stem harvester and the self-propelled cut-and-chip harvester respectively, although a cutting height of 10 cm was requested in advance. From the potential harvestable biomass, only 77.4% was harvested by the self-propelled cut-and-chip harvester, while 94.5% was harvested by the tractor-pulled stem harvester. An increase of the machinery use efficiency (i.e. harvest losses, cost) is necessary to reduce costs and increase the competitiveness of biomass with other energy sources.

A STELLA Model to Estimate Soil CO2 Emissions from a Short-Rotation Woody Crop

The potential for climatic factors as well as soil–plant–climate interactions to change as a result of rising levels of atmospheric CO2 concentration is an issue of increasing international environmental concern. Agricultural and forest practices and managements may be important contributors to mitigating elevated atmospheric CO2 concentrations. A computer model was developed using the Structural Thinking and Experiential Learning Laboratory with Animation (STELLA) software for soil CO2 emissions from a short-rotation woody crop as affected by soil water and temperature regimes, root and microbial respiration, and surficial processes such as rainfall, irrigation, and evapotranspiration. The resulting model was validated with good agreement between the model predictions and the experimental measurements prior to its applications. Two scenarios were then chosen to estimate both diurnal and annual soil CO2 emissions from a 1-ha mature cottonwood plantation as affected by soil temperature, soil (i.e., root and microbial) respiration, and irrigation. The simulation resulted in typical diurnal soil respiration and CO2 emission patterns, with increases from morning to early afternoon and decreases from early afternoon to midnight. This pattern was driven by diurnal soil temperature variations, indicating that soil temperature was the main influence on soil respiration and CO2 efflux into the atmosphere. Our simulations further revealed that the average seasonal soil respiration rate in summer was 1.6 times larger than in winter, whereas the average seasonal CO2 emission rate in summer was 1.77 times larger than in winter. Characteristic annual variation patterns for soil respiration and CO2 emission also were modeled, with both increasing from January 1 through June 30 followed by steady declines from September 1 through December 31. These results suggest that the STELLA model developed is a useful tool for estimating soil CO2 emission from a short-rotation woody crop plantation.

Financial Analysis of the Cultivation of Short Rotation Woody Crops for Bioenergy in Belgium: Barriers and Opportunities

This paper analyses the financial performance of a poplar short rotation woody crop (SRWC) plantation in Belgium, from a farmer’s and an investor’s viewpoint, based on simulations from the newly developed model POPFINUA. The establishment, production and harvest costs were investigated to calculate the net present value (NPV) and the equivalent annual value (EAV) of the SRWC cultivation when the biomass chips were sold at a price of 40 € Mg−1 with a moisture content (m.c.) of 50 %. The calculated NPVs were 229 and −485 € ha−1, and the EAVs equalled 16.3 and −34.6 € ha−1 year−1 for the farmer’s and investor’s scenario, respectively. The break-even price at which the produced biomass could be sold at the farm gate excluding transport, handling, storage and profit margins of the involved companies was calculated using the levellised costs (LC) method and equalled 78.4 and 83.5 € oven-dried ton (odt)−1 for the farmer’s and investor’s viewpoint, respectively. Three harvesting strategies, applied on a SRWC plantation of 18.1 ha in Flanders (Belgium), were studied and compared. It became clear that preference should be given to more economic, small-scale harvesters instead of large-scale self-propelled harvesters, given the relatively limited surface available for SRWCs in Belgium. Furthermore, the inclusion of transportation over a distance of 50 km by truck increased the LC by 15.1 € odt−1. Moreover, subsidies such as establishment grants and/or yearly incentives proved indispensable to make this long-term investment profitable. This is particularly true for the scenario where an investor decides to cultivate SRWCs for energy purposes.

Harvest of Natural Shrubs with a Biobaler in Various Environments in Québec, Ontario and Minnesota

The biobaler is a novel approach to cut woody crops up to 150-mm basal diameter and compress the biomass into round bales. It can be used to harvest short-rotation woody crop plantations such as willow or hybrid poplar. It can also be used to clear wild brush, forest understory, and encroaching small trees to improve land management. A commercial version of the biobaler was evaluated for the latter purpose, i.e., to harvest natural shrubs in various environments in central Canada (at three sites in Qubec and two sites in Ontario) and in mid-western United States (at seven sites in Minnesota). More than 250 bales were harvested and monitored on natural stands in 2009 and 2010 to gain information on machinery management under wide-ranging conditions of crop species, density, and soil conditions. The harvest rate ranged from 2 to 26 bales/h (average of 14 bales/h). Bale mass averaged 477 kg at 46% moisture content [260 kg dry mass (DM)/bale at a density of 166 kg DM/m]. Diesel fuel consumption averaged 8.5 L/t DM. Harvesting cost with the biobaler was estimated at $33/t DM in high yield with rapid harvest (20 bale/h) and $64/t DM at low capacity (10 bales/h) which can be caused by lower yield or poor traction. The information will be helpful to evaluate the cost of environmental management of natural stands covered with brush and the potential biomass that may be recovered.

Woody biomass in the U.S. Cornbelt? Constraints and opportunities in the supply

The U.S. is clearly entering a new era of liquid fuel production; one that will be characterized by increasing degrees of renewable raw materials. Woody biomass is an especially compelling feedstock choice where available. Significant questions, however, exist regarding the potential of some landscapes to provide this feedstock. In an effort to answer these questions, we performed an exploratory spatial assessment of woody biomass production and supply capabilities in two-ecoregions Mississippi River corridor within the US Cornbelt. We used existing forest/timber inventories and conducted in-depth interviews with large regional sawmills to understand the accessibility of woody biomass from natural forests, availability of and general costs associated with woody biomass in the existing timber industry, and potential for production from short-rotation woody crop plantations. On an annual basis, taking into account only the annual net growth of non-sawlog species the Midwest Driftless Area currently produces 3.14 times the raw material required by a hypothetical facility using one-half million dry tons of woody biomass per year. Although allocated over a larger area, the Central Dissected Till Plain produces 3.94 times the required material. Throughout the entire region there would be an additional lower bound estimate of 107,000 dry Mg from easily transportable sawmill residues. The ecological state of US Cornbelt forests stand to gain from a developed market for woody biomass as proper woodland management to harvest trees, preserve wildlife, and reduce risk from disease, pests, and invasive species typically involves harvesting the low-value trees that will by and large drive the woody biomass system.

Changes in soil carbon and nutrient pools along a chronosequence of poplar plantations in the Columbia Plateau, Oregon, USA

Establishment of short-rotation woody crop (SRWC) plantations for meeting the demand of wood and bioenergy production necessitates reclamation of agricultural lands and desert soils, such as those in the southern Columbia Plateau of Oregon, USA. The effects of plantation management on soil carbon (C) storage and nutrient concentration were evaluated, using a chronosequence of poplar ( Populus spp.) stands on soils of eolian origin (Xeric Torripsamments). Stands of ages 1, 3, 4, 7, 9, and 10 years ( n = 3 per stand age), as well as adjacent agricultural and desert lands, were compared based on soil C, inorganic C (SIC), total nitrogen (N), and nutrient concentrations within the 0- to 50-cm soil depth. The 7- through 10-year-old stands that were in a first-rotation cycle were irrigated and fertilized. The 1- through 4-year-old stands in a second-rotation cycle received a mulch application treatment in addition to the irrigation and fertilization treatments. At age 11 years, the projected plantation C (147.5 Mg ha −1) accumulated almost entirely in the aboveground biomass (62.2%), forest floor (24.3%), and roots (11.7%). There were no significant increases in the mineral soil C and N pools with stand age, despite the presence of increasing trends within the surface layer. The accumulation of the mineral soil C pool (∼1.8%), from the first- (23.5 ± 1.7 Mg C ha −1) to the second-rotation stands (26.3 ± 3.5 Mg C ha −1), was partially offset by a loss of SIC due to irrigation. The SIC pool had a decreasing trend, which was related to dissolution of calcite along the soil profile, from the first- (16.7 ± 3.4 Mg C ha −1) to the second-rotation stands (8.4 ± 5.0 Mg C ha −1). Soil pH ( r > 0.6) and exchangeable acidity ( r = −0.5) patterns were dependent upon the concentration of exchangeable Ca 2+. Soil Mg 2+ and K + concentrations were correlated with soil C concentration in the surface layer ( r = 0.5). In coarse-textured soils, a decadal time scale was insufficient to measure significant changes in the mineral soil C pool. Carbon benefits may be gained, however, in aboveground (tree and forest floor) and belowground (roots) biomass accumulations. SRWC plantations are an effective land-use option to restore degraded lands of arid regions.

Avian species richness and reproduction in short-rotation coppice habitats in central and western New York

Capsule Species richness and density increase rapidly with coppice age, and are similar to estimates from early successional habitats. Aim To investigate avian species richness, density and breeding success in short-rotation woody crops (SRWC) planted as potential source of renewable bioenergy. Methods We carried out regular bird censuses and systematic nest searches in dense plantations of fast-growing willow and poplar clones coppiced at three- to five-year intervals in New York, USA. Results Thirty-nine species regularly used SRWC plantations; of these at least 21 were confirmed breeding on study plots. A total of 63% of the variation in bird species richness was explained by the number of years since coppicing and plot area together. Both the richness and overall density of avian species in SRWC plots was similar to estimates obtained from the Breeding Bird Census for more typical shrublands and successional habitats (e.g. abandoned fields, second-growth forest, regenerating clearcuts). Nesting success for the most common species was within the range of values from published studies in alternative nesting habitats, although often at the lower end of the range. Brood parasitism by Brown-headed Cowbirds Molothrus ater, often an important factor in nesting success, was extremely low on the study plots. Conclusion If planted on a fairly large scale with staggered coppicing schedules, SRWC plantations would help to maintain breeding populations of birds that range from open-habitat species to woodland species. There is no evidence that conversion of substantial land area to SRWC would result in an ‘ecological trap’ for species common in the farmland–small woodland landscapes of the northeastern USA.

Silviculture and biology of short-rotation woody crops in temperate regions: Then and now

Abstract Although its roots are in antiquity, the current concept of short-rotation woody crops (SRWC) for fiber and energy evolved scientifically from pioneering tree breeding work begun in the early 20th century. A natural outgrowth of this work was the culture of fast-growing trees on rotations of 1–15 years. Close-spaced tree culture received further impetus with the introduction of the “silage sycamore” concept in the southeastern US in the mid-1960s and the OPEC oil embargo in 1973, leading to statistically designed trials at numerous locations in North America, Europe, and Scandanavia. Early silvicultural research focused on spacing and species trials, propagation methods, site preparation, weed management, nutrition, growth, and yield. Because these trials were based on small plots, and the importance of pest depredations or site variation were not fully recognized, early biomass yield predictions tended to be overly optimistic. Soon physiologists and ecologists began to unravel the biological characteristics of SRWC plantations and their responses to environment. Knowledge of the influence and diversity of pests—insects, diseases, and animals—provided a necessary reality check. Many hardwood tree species and a few conifers have been evaluated over the years for SRWC in temperate regions of the world. Clones of Populus and Salix, however, became the dominant plantation material because of their inherently rapid growth and ease of propagation by hardwood cuttings. Among conifers, loblolly pine (Pinus taeda) also shows promise. Because genetic variation is readily exploitable in the dominant SRWC taxa, strongly focused breeding programs began to provide highly productive genotypes and seed sources in the last decades of the 20th century. A new plateau, with significant practical potential, was reached in the late 20th century when biotechnological methods were applied to tree taxa. Recently, the DNA in the Populus genome was sequenced. Thus, the few current commercial applications of SRWC rest on a substantial base of silvicultural and biological knowledge.

Clone preference by nesting birds in short-rotation coppice plantations in central and western New York

Interest in short-rotation woody crops (SRWC) for bioenergy production has been increasing in the northeastern United States. The possibility that substantial farmland could be converted to bio-fuel production has increased the importance of evaluating how this type of habitat might affect the populations of birds typically found in agricultural landscapes. In this study, we identified 39 species that regularly used SRWC plantations, and of these at least 21 were confirmed breeding on 12 study plots. Breeding birds constructed nests highly non-randomly with respect to willow/poplar clone. Nests were built more frequently than expected by chance in certain clones (e.g. S25 and S365) while fewer nests than expected were built in other clones (e.g. S301). Observed preferences may have been related to clone-specific differences in growth structure, which may affect the stability of the nest and/or concealment from predators. Although we found no significant correlation between reproductive success and the choice of clone for a nest site, the mix of clones chosen for large-scale SRWC plantations may affect the attractiveness of these sites for some species. We tentatively conclude that planting S25 and particularly S365, and perhaps avoiding the use of S301, might benefit avian breeding populations, and increase avian species richness.

Nitrogen supply and demand in short-rotation sweetgum plantations

Intensive management is crucial for optimizing hardwood plantation success, and nitrogen (N) nutrition management is one of the most important practices in intensive management. Because management of short-rotation woody crop plantations is a mixture of row-crop agriculture and plantation forestry, we tested the usefulness of an agronomic budget modified for deciduous perennial trees for estimating N fertilizer recommendations. We studied the foliar N demand, resorption, and uptake response of two sweetgum ( Liquidambar styraciflua L.) plantations on a converted agricultural field and a pine cutover site to biannual applications of three nitrogen (N) fertilizer rates: 0, 56 and 112 kg N ha −1. We also estimated soil N supply, foliar N uptake efficiency, and apparent fertilizer N uptake efficiency. Fertilization increased foliar demand (defined as total foliar N content), resorption, and uptake at both sites, but to a greater degree on the cutover site, which had lower soil N supply. Resorption efficiency did not increase with fertilization, but resorption proficiency, the N concentration of senesced leaves, was reduced (N concentrations higher) at the drier agricultural field site and in the fertilized trees. Based on our budget analysis, we recommend fertilizing sweetgum plantations with 50 kg N ha −1 for each 2000 kg ha −1 of foliage biomass, assuming they have 45–65 kg ha −1 of soil N supply.

Effects of Clone, Silvicultural, and Miticide Treatments on Cottonwood Leafcurl Mite (Acari: Eriophyidae) Damage in PlantationPopulus

Aculops lobuliferus (Keifer) is a little known pest of plantation Populus spp., which is capable of causing substantial damage. This is the first documented occurrence of A. lobuliferus in South Carolina. Previous anecdotal data indicated clonal variation in Populus susceptibility to A. lobuliferus damage. A damage rating scale was created to monitor mite damage in 2000–2001 in a short-rotation woody crop plantation; damage descriptions and seasonal phenology also were recorded. Foliar damage and terminal mortality were monitored on two Populus deltoides Bartr. clones, ST66 and S7C15, receiving one of three silvicultural treatments (irrigated [I], fertilized [F], or I+F) or no treatment (control). In 2001, early season foliar damage ratings were significantly higher on clone S7C15; however, damage on clone ST66 was greater after miticide treatments later in the year. Terminal mortality did not differ between clones. Silvicultural treatment significantly affected foliar damage levels in both clones. Trees receiving I+F and F treatments had higher damage ratings than did trees receiving irrigation alone or the control at times. Clone S7C15 trees receiving fertilizer had significantly less terminal mortality than their nonfertilized counterparts. Application of a commercially available miticide significantly reduced A. lobuliferus damage levels. This study demonstrates that A. lobuliferus damage levels can be influenced by Populus clone and silvicultural treatment. Foliar and terminal damage levels observed in this study indicate the potential for substantial economic impact of A. lobuliferus on plantation Populus. Although an effective control method may be to select and plant resistant Populus clones, chemical control remains a viable option.

Economic injury level for second-generation cottonwood leaf beetle (Coleoptera: Chrysomelidae) in two-year-old Populus.

The cottonwood leaf beetle, Chrysomela scripta F., is a major defoliating pest of Populus in North America. As the use of Populus in short-rotation woody crop plantations continues to increase, there are increasing economic and environmental needs to develop rational pest management programs to reduce the impact of this insect. Our objective was to determine the economic injury levels for the second generation of the cottonwood leaf beetle during plantation establishment. Integrating the cost of the management, market value, insect injury, and host response to the injury, the economic injury levels for second generation cottonwood leaf beetle on 2-yr-old Populus were determined to be from 0.2 to 0.9 egg masses per actively growing terminal.

Temporal and spatial scaling from individual trees to plantations: A modeling strategy

In order to effectively deploy short-rotation woody crop plantations for energy and fiber production at regional scales, biologically sound-field-level models of plant growth are required. Individual tree growth process models have proven effective at predicting growth based on environmental driving variables, but in the past these models have been too complex to use at the plantation scale. In this paper we describe an object-oriented strategy for scaling ECOPHYS, an individual tree growth process model for hybrid poplar, to a plantation. Included in this strategy are methods of scaling from an individual shoot to a tree, from individual trees to a patch, and from patches to a plantation. In describing interactions among trees, both above- and below-ground processes are considered. Finally, we describe methods for integrating the plantation level ECOPHYS with EPIC, a field scale model of soil productivity and erosion used in regional assessment.

Short rotation woody crop plantations in Brazil and the United States

The Short Rotation Woody Crop (SRWC) concept has been applied in the establishment of experimental and commercial plantations in both the United States and Brazil. The SRWC concept involves the application of agricultural principles to the production of tree crops for fiber or fuel. Although extensive SRWC research has occurred in the United States during the past 10 to 16 years, commercial applications have been rather limited. On the other hand, Brazil has made considerable progress in producing SRWC on a large-scale commercial basis while simultaneously conducting research. It seems clear that both countries can gain from each other's experience in SRWC experimentation and commercialization. This paper discusses and compares SRWC system developments in both countries and suggests means of improving and expanding SRWC systems use.