Development and validation of aboveground biomass estimations for four Salix clones in central New York

Commercial and research scale plantings of short-rotation woody crops require reliable and efficient estimations of biomass yield before time of harvest. Biomass equations currently exist but the accuracy and efficiency of estimation procedures at the level of specificity needs to be quantified for clones being used in North America. Diameter-based allometric equations for aboveground biomass for four clones of willow (Salix discolor, Salix alba, Salix dasyclados, and Salix sachalinensis), between two sites (Canastota and Tully, NY), and across four years (1998–2001), were developed using ordinary least-squares regression (OLSR) on log-transformed variables, weighted least squares regression (WLSR) on log-transformed variables, and nonlinear regression (NLR) methods and validated using independent data sets. Biomass estimations derived from clone, age, and site (Specific) using OLSR equations had highest R² and lowest percent bias (<2.3%) allowing for accurate estimations of standing biomass. Values for specific equations using WLSR were similar, but bias was higher for NLR (0.7–12.5%). However, the amount of time and effort required to develop specific equations, is large and in many situations prohibitive. Biomass estimates derived from clone and age, regardless of site (Intermediate), resulted in small increases in prediction error and a small increase in percent bias using OLSR (<0.4%) and WLSR (<1.7%). The increase in percent bias was larger (1.1–5.7%) for NLR equations. Intermediate models correspond to the loss of only a small amount of accuracy while gaining more efficiency in estimating standing biomass. Estimates of biomass derived from clone alone (general) equations, considering neither age nor site, had the weakest prediction abilities that may lead to large errors for biomass estimations using OLSR (7.0–9.5%), WLSR (1.1–21.7%) or NLR (31.9–143.4%).     

Performance of 14 hybrid poplar clones grown in Beijing,China

Evaluating the performance of poplar clones to be used in short-rotation intensive culture (SRIC) and selecting superior clones are critical to increase wood production and ecological effects. This study described the growth and aboveground biomass production of 14 hybrid poplar clones after three growing seasons, evaluated the clones with cluster analysis on multiple basis. At the end of each growing season, total tree height, basal diameter and biomass were measured. Highest production was found for clone NE-353 and DN-70 with mean annual biomass production 22 Mg ha^?1 year^?1. Lowest performance was observed for clone 311-93 and 309-74 with biomass production 0.29 and 0.75 Mg ha^?1 year^?1. Cluster analysis was conducted with survival and tree volume index, all measured at the end of the third growing season. The clones were grouped into four classes. Clone R-247, DN-70 and Simplot had higher survival and highest tree volume index, appeared to well adapted to the region; clone 52-225, 58-280, NE-353, DN-34, PC-01 and OP-367 exhibited moderate survival and Growth; clone DN-14273, R-419 showed moderate survival and low growth; clone 195-529, 311-93 and 309-74 performed poorest with lowest survival and tree volume index and these clones may not suitable for biomass producers in this region.     

Size matters? – The diverging influence of cutting length on growth and allometry of two Salicaceae clones

Short rotation coppices (SRC) are often established by inserting cuttings vertically into the soil. Longer cuttings are generally regarded as superior to establish plants on stress-prone sites. However, knowledge about above- and belowground biomass production, plant allometry and root characteristic of clones established through different lengths of cuttings is scarce.The experiment was performed with 2 common SRC clones (Populus clone Max 4, Salix clone Inger) and 2 cutting length (20 cm and 40 cm). Above- and belowground biomass and leaf and root morphology were determined after one growing season. Longer cuttings produce more biomass but have a diverging influence on the shoot:root allocation of both clones. Long cuttings of Populus cl. Max produce more aboveground biomass, mostly leaves, than 20 cm cuttings, while 40 cm Salix cl. Inger cuttings have more fine roots. Leaf and root morphology are only marginally influenced by cutting length.Choosing longer Populus cl. Max cuttings might not be a good strategy when considering SRC establishment on more stress-prone sites, since their larger above-ground biomass will e.g. increase transpirational demand. Because of the lower shoot:root ratio, longer Salix cl. Inger cuttings seem to be more suitable to establish SRC on fields with (partially) restricted water and nutrient supply than shorter cuttings. Thus, planting difficulties and higher costs of longer cuttings may be offset by higher survival and greater aboveground productivity only in some clones. In the future, optimal cutting lengths must be evaluated not only for different environmental conditions but also for different SRC species/clones.     

Yield traits of eight common osier clones in the first three years following planting in Poland

This study presents the results of investigations concerning variations in traits that effect structure of biomass yield in eight selected clones of common osier (Salix viminalis L.) from the willow collection at the University of Warmia and Mazury in Olsztyn. Additionally, analysis of clone/genotype interactions with years was performed for these traits. The study was conducted on two clones from the oldest Polish forms of common osier, namely, Paskówka and Gigantea. Three newer collected Polish common osier clones, and three clones from Swedish cultivars of common osier, were also used in this study. Early development stages of willow plants were investigated in field experiments. The study began with the planting of the willows and ended with harvesting after the third year of growth. The experiment was performed in the random block design in three replications. Analysis of variance on the tested clones of common osier with terms of their yield structure traits was performed on plant height, tillering, shoot diameter and yield. The analysis showed that a significant variation between clones begins in the second year of growth. Moreover, a significant genotype and environment interaction was found for all the willow clones, in terms of yield, which is expressed by the weight of one plant. However, this interaction for other traits was significant only in relation to certain clones. In the third year of cultivation old Polish willow clones in comparison with the Swedish and new Polish clones have higher plant weight (yield), tillering and shoot diameter.     

Biomass production of Salix viminalis in southern Finland and the effect of soil properties and climate conditions on its production and survival

Ten Salix viminalis clones were cultivated in 35 experimental plantations situated on privately-owned farms in southern and central Finland. Management instructions were given to the farmers who established and tended the study plots. The biomass production and survival of the clones were recorded by inventory every year during the first rotation period, which consisted of the establishment year and three following growing seasons. The greatest amount of biomass production exceeded 30 above-ground tonne of dry matter/3 years, but amounts varied greatly between the experimental plantations. The main reasons causing this variation were the low frost hardiness of most of the S. viminalis clones and unsuccessful weed control during the year the plantations were established. Early autumn frost in particular caused severe damage. S. viminalis grew rather well on a wide variety of soil types. Sufficient amounts of nitrogen, potassium and organic matter seem to be the properties which most clearly have an effect on the biomass production and survival of S. viminalis in mineral soils. A relatively small amount of manganese in wet and low oxygenic soils is recommended, because a high content may cause toxic effects. In this study S. viminalis clones only succeeded well in southernmost Finland, where properly managed plantations produced rather high biomass yields. In other parts of southern and central Finland more research work on frost resistance and the breeding of new clones is needed. To conclude, in the climatic conditions of Finland energy willow husbandry is a compromise between high biomass yield and frost hardiness.     

Rapid biomass estimation using optical stem density of willow (Salix spp.) grown in short rotation

Quick and accurate biomass estimation of willow (Salix spp.) grown under short rotation intensive culture (SRIC) is essential for carbon accounting and management decisions. Currently, most estimates of tree biomass, including willow, rely on measurement of stem diameter. This is a suitable approach for single-stem species but for measurements of multi-stem species such as willow, there is an increase in the time and effort required as well as the need to include site, clone and age specific information. Therefore, we developed a new method which calculates optical stem density from digital photographs taken at predetermined locations and angles within a plantation during the fall or winter when the willow is without leaves. We then calibrated a mathematical model using destructive sampling to convert the measurements of optical stem density into estimates of biomass. The method produced very strong relationships (adjusted r² = 0.97) between the predicted and actual harvested biomass for the plots studied. Being new, the method still requires further testing and possibly adjustments for different planting designs and clones.     

A simple technique for estimating above-ground biomass in short-rotation willow plantations

Successful purpose-grown willow production systems require regular monitoring of willow growth to apply timely management techniques for increased productivity and timing of harvest for maximizing profit. The objective of this study was to assess the efficacy of a novel method of estimating above-ground willow biomass, involving measuring light attenuation through the willow canopy, to calculate a ‘stem area index’ for relating to harvested willow biomass. Two different willow clones, with contrasting growth form, were used: single stem (Charlie) and multi-stem (SV1). Given the strong correlations (r² > 0.97; p < 0.05) between the measured stem area index and harvested willow biomass, regardless of growth form, it appears that this simple mensurative technique is a promising alternative for estimating above-ground biomass in short-rotation willow plantations.     

Short-term growth and morphological responses to nitrogen availability and plant density in hybrid poplars and willows

Morphological characteristics of poplar and willow clones were determined in order to identify main characteristics leading to superior growth under increased plant competition with low or high nitrogen (N) availability. Seven hybrid poplar (Populus spp. including one hybrid aspen) and five willow (Salix spp.) clones were grown under greenhouse conditions for 13 weeks at three spacings (20 × 20, 35 × 35, and 60 × 60 cm) and two N levels (20 and 200 mg kg⁻¹). The decrease in spacing from 60 to 20 cm reduced leaf area by 50% but clones had similar aboveground biomass per tree under all spacings, with increasing their height per unit leaf area. More productive clones had greater leaf area (+102%), leaf area per unit plant biomass (+12%) and lower root-to-shoot ratios (−27%) compared to less productive clones. There were positive relationships between leaf area and above-ground biomass per tree for both more and less productive clones. Compared to low N level and 60 cm spacing, trees growing in high N level and 20 cm spacing reached similar root collar diameter, crown width, and leaf area values and even greater height, suggesting that an addition of N could help mitigate negative effects of tree competition.     

Short-rotation forestry of birch,maple, poplar and willow in Flanders (Belgium) I—Biomass production after 4 years of tree growth

During the last three decades, oil crises, agricultural surpluses and global climate change enhanced the interest in short-rotation forestry (SRF). In this study, the biomass production of birch (Betula pendula Roth), maple (Acer pseudoplatanus L.—Tintigny), poplar (Populus trichocarpa × deltoides—Hoogvorst) and willow (Salix viminalis—Orm) growing under a short-rotation (SR) management system were compared after a 4 years period. The plantation was established on former agricultural land. The sandy soil had a mean pH of 4.5 and a mean carbon content of 1.0%. Survival rates after 4 years were 75.8%, 96.8%, 86.3% and 97.6% for birch, maple, poplar and willow, respectively. The mean actual annual biomass production for these four species amounted to 2.6, 1.2, 3.5 and 3.4 t DM ha⁻¹ yr⁻¹, respectively. The large variation in biomass production at the different plots of the plantation could not be explained by the measured soil parameters. Biomass production results found here were in the lower range of values reported in literature. However, in contrast to most other studies, no weed control, fertilisation or irrigation was applied in this experiment. As marginal agricultural soils are suboptimal for the growth of poplar and willow, birch can be considered as a very interesting alternative for the establishment of SR plantations in Flanders.     

Physiological adaptability of Poplar clones selected for bioenergy purposes under non-irrigated and suboptimal site conditions: A case study in Central Italy

New Poplar clones for biomass production are currently under evaluation in Italy to be cultivated in Mediterranean site conditions, where the evapotranspirative demand is not balanced by rainfall supply. The study aims to evaluate the dynamic responses of leaf gas exchanges, budding, foliar morphology and yield in three modern hybrids Poplar clones (AF2, AF6 and Monviso) under non-irrigated and suboptimal site conditions in a Short Rotation Forestry plantation of Central Italy. During the drought season, the stomatal closure was gradual in AF2 and AF6 but rapid in Monviso. These traits were associated with the best yields (expressed as dry matter) in AF2 (8.74 Mg ha⁻¹ year⁻¹) and AF6 (6.53 Mg ha⁻¹ year⁻¹) compared to Monviso (5.72 Mg ha⁻¹ year⁻¹). Monviso was advised as sensitive clone to summer drought even if it has showed higher photosynthetic potential traits such as earlier budding and maximum leaf area. AF2 and AF6 were advised as tolerant and moderately-tolerant clones to summer drought as they maintained higher and relatively-higher stomatal conductance (gs) values over a growing season, summer photosynthetic assimilation rates (A) and intrinsic water-use efficiency (A/gs ratio) compared to Monviso, respectively. We pointed out the occurrence of main physiological processes (budding, maximum and minimum gs, maximum leaf area) to highlight the key-periods leading the growth under these site conditions by identifying the air temperature thresholds and precipitation patterns along a growing season. We provided recommendations to Italian Poplar practitioners for cultivations of these clones in Mediterranean areas affected by summer drought.     

Long-term biomass productivity of willow bioenergy plantations maintained in southern Quebec,Canada

Maintaining the long-term productivity of short-rotation coppice plantations is very important to ensure the large-scale deployment of biomass as a renewable energy source. In Quebec (Canada), willow short rotation coppice has been studied since the early ‘90s, thereby allowing long-term analysis of the dynamic performance of several species and hybrids as well as management practices. In this study, we report on the long-term productivity of two trials maintained in southern Quebec and carried out to compare a) growth and biomass yield of willow Salix viminalis (cultivar 5027) grown for 15 years under fertilized and unfertilized conditions and b) growth of different willow cultivars over three successive rotations (10 years). The first trial showed that after four rotations, sludge-fertilized S. viminalis 5027 produced significantly more biomass, 19.2 odt ha⁻¹ yr⁻¹, whereas unfertilized plots yielded 13.8 odt ha⁻¹ yr⁻¹. The second trial showed that among the wide variety of commercial willow cultivars available, SX64 and SX61 along with some indigenous species (i.e. S25, S365, S546) were the most suitable for short-rotation forestry in southern Quebec.     

Biomass production and soil nutrients in organic and inorganic fertilized willow biomass production systems

The use of organic waste materials as nutrient sources for willow biomass production is an attractive means to decrease fertilization costs, increase biomass production and reduce greenhouse gas emissions associated with the system. In this study, changes in soil nutrients and biomass production of two willow varieties (Salix miyabeana–SX64 and Salix purpurea–9882-34) in organic and synthetic fertilized systems were compared at three locations in Northeastern U.S.A: Middlebury VT (MID), Delhi NY (DEL) and Fredonia NY (FRE). A 150 and 200 kg available N ha⁻¹ of urea as commercial fertilizer (CF), biosolid compost (BC) and digested dairy manure (DM) and a control (CT0) treatments were applied in June 2008 to the willow which was re-sprouting after coppice. There was no significant difference (p > 0.05) in biomass production among the fertilization treatments at any of the three sites and for either of the varieties. First rotation biomass production of 9882-34 ranged from 9.0 to 11.6 Mg ha⁻¹ yr⁻¹ at DEL, 3.4–8.8 Mg ha⁻¹ yr⁻¹ at MID and 3.5–7.7 Mg ha⁻¹ yr⁻¹ at FRE. For SX64, biomass production ranged from 13.2 to 19.0 Mg ha⁻¹ yr⁻¹ at DEL, 9.0–15.0 Mg ha⁻¹ yr⁻¹ at Mid and 5.5–9.3 Mg ha⁻¹ yr⁻¹ at FRE. SX64 deployed small numbers of large stems and produced more biomass than 9882-34 which deployed large numbers of small stems. Application of BC significantly increased soil N and P levels at MID in both 2008 and 2009 (p < 0.05). At DEL, BC and DM treatments increased soil N, Ca, Mg and OM levels in both 2008 and 2009 (p < 0.05). The fertilization treatments had no significant effect on any soil nutrients at FRE. This study indicates that willow biomass can be produced without fertilizer additions in the first rotation across this range of sites due to the nutrient status of these sites and high internal nutrient cycling in these systems.     

Wood ash effects on plant and soil in a willow bioenergy plantation

Intensive management for biomass production results in high rates of nutrient removal by harvesting. We tested whether wood ash generated when burning wood for energy could be used to ameliorate negative soil effects of short-rotation harvesting practices. We measured the temporal and spatial dynamics of soil nutrient properties after wood ash applications in a willow plantation in central New York State and determined the influence of wood ash application on willow growth. Wood ash was applied annually for 3 years at the rates of 10 and 20 Mg ha⁻¹ to coppiced willow, Salix purpurea, clone SP3. Wood ash application significantly increased soil pH in the 0–10 cm soil layer from 6.1 in the control to 6.9 and 7.1 in the 10 and 20 Mg ha⁻¹ treated plots. Wood ash application significantly increased soil extractable phosphorus, potassium, calcium, and magnesium concentrations. Potassium was the element most affected by wood ash treatment at all soil depths. Wood ash had no significant effect on nutrient concentrations of foliar, litter, and stem tissue. Wood ash did not affect either individual plant growth or plot biomass production, which declined over the course of the study; it did increase the size of stems, but this effect was balanced by a decrease in the number of stems. Applying nitrogen as well as wood ash might be required to maintain the productivity of this SRIC system.     

Allometric relationships from coppice structure of seven North American willow (Salix) species

Biomass yield and component coppice growth traits were assessed in up to 20 clones from seven native North American willow species, Salix amygdaloides (SAM), Salix bebbiana (BEB), Salix discolor (DIS), S eriocephala (ERI), Salix humilis (HUM), Salix interior (INT), and Salix nigra (NIG), established together in a clonally replicated common-garden field test. Aboveground mass, coppice stem number, stem length, and stem basal diameter measurements on up to 20 of the largest stems from 2-yr-old coppiced plants showed that ERI had the greatest aboveground mass, followed by INT, and then a close grouping of BEB, DIS, and HUM; the “tree” willows, AMY and NIG, had the lowest yields. The tree willows were not as prolific in coppice stem sprout production as were the shrub willows. The greatest number of stem sprouts was produced by ERI, with one coppice producing 67 2-yr-old stem sprouts, and ERI also showed an atypical, non-negative relationship between stem size and stem number; whereas the other six willows showed a varying but expected negative relationship between coppice stem size and stem number. Species differences in allometric relationships highlight the need to develop species-specific models for more accurate non-destructive biomass yield estimation.     

The effect of water availability on stand-level productivity,transpiration, water use efficiency and radiation use efficiency of field-grown willow clones

The effect of water availability on stand-level productivity, transpiration, water use efficiency (WUE) and radiation use efficiency (RUE) is evaluated for different willow clones at stand level. The measurements were made during the growing season 2000 in a 3-year-old plantation in Scania, southernmost Sweden. Six willow clones were included in the study: L78183, SW Rapp, SW Jorunn, SW Jorr, SW Tora and SW Loden. All clones were exposed to two water treatments: rain-fed, non-irrigated treatment and reduced water availability by reduced soil water recharge. Field measurements of stem sap-flow and biometry are up-scaled to stand transpiration and stand dry substance production and used to assess WUE. RUE is estimated from the ratio between the stand dry substance production and the accumulated absorbed photosynthetic active radiation over the growing season. The total stand transpiration rate for the 5 months lies between 100 and 325 mm, which is fairly low compared to the Penman–Monteith transpiration for willow, reaching 400–450 mm for the same period. Mean WUE of all clones and treatments is 5.3 g/kg, which is high compared to earlier studies, while average RUE is 0.31 g/mol, which is slightly low compared to other results. Generally, all clones, except for Jorunn, seem to be better off concerning biomass production, WUE and RUE than the reference clone. Jorr, Jorunn and Loden also seem to be able to cope with the reduced water availability with increase in the water use efficiency. Tora performs significantly better than the other clones concerning both growth and efficiency in light and water use, but the effect of the dry treatment on stem growth shows sensitivity to water availability. The reduced stem growth could be due to a change in allocation patterns.     

Effects of competition between short-rotation willow and weeds on performance of different clones and associated weed flora during the first harvest cycle

In order to assess the ability of willow clones to compete with weeds, willow shoot biomass and plant mortality were measured over the first harvest cycle for 10 commercial and two breeding clones at three different sites in southern Sweden. Two levels of weed pressure (weeded and not weeded) were employed and the effects of cutback or not after the first growing season were compared for willow clones under weed pressure. There were significant differences between clones in their ability to compete with weeds, measured as willow shoot growth reduction in plots with weeds, at two of the three sites. However, shoot biomass reduction due to weeds was large in all the clones, with Stina and SW Inger among the least affected. Mean shoot growth reduction after the first harvest cycle for the commercial clones was 68.3%, 91.2% and 94.3% at the three sites and the corresponding plant mortality was 9.8%, 57.3% and 56.2% under weed pressure. Significant clonal differences in yield, under weed-free conditions, were found at all three sites. Significant clone-site interactions were found for both growth reduction and biomass production. Cutting back shoots after the establishment season, under weed pressure, resulted in higher mean plant mortality and lower mean willow shoot biomass after one harvest cycle at two of the three sites. The weed flora was initially dominated by annuals, but became dominated by perennial weeds during the first harvest cycle.     

Impacts of paper sludge and manure on soil and biomass production of willow

Land application of organic wastes to short rotation woody crops (SRWC) can reduce the environmental impacts associated with waste disposal and enhance the productivity of biomass production systems. Understanding the potential impacts of organic amendments however, requires the examination of changes in soil characteristics and plant productivity. This study was conducted to evaluate the effect of paper sludge and dairy manure on biomass production of shrub willow (Salix dasyclados SV1) and to determine the impacts of these amendments on soil chemical properties. Treatments included urea, dairy manure and paper sludge separately and in combination, and a control. These materials were applied in the summer of 2005 to two fields of SV1 at different stages of growth: An old field with one year old shoots on a 10 year old root system and a young field which was beginning regrowth after being coppiced at the end of its first growing season. Foliar nutrient concentrations and soil chemical properties were analyzed at the end of the second growing season after treatment application to determine plant response to the fertilization regimes and to determine the effects of fertilization on soil characteristics. Fertilization did not increase biomass production in either field. However, application of the N-poor paper sludge did not reduce yield either. In general, fertilization did not influence soil or foliar chemistry, although there were some exceptions. The lack of response observed in this study is probably related to the nutrient status of the site or losses of applied nutrients.     

A novel approach to simulate growth of multi-stem willow in bioenergy production systems with a simple process-based model (3PG)

An important requirement for commercialization of willow biomass production in short-rotation crop (SRC) plantations is the reliable and cost-efficient estimation of biomass yield. Predictions and simulations of willow stand biomass have been problematic due to issues with modeling the multi-stem growth form of willow. The aim of this paper was to develop a new approach for managing allometric measurements from multi-stemmed willow for stand growth simulations. The 3PG model (Physiological Principles in Predicting Growth) was parameterized for willow and was used for biomass yield simulation for an entire 22-yr cycle (seven 3-yr rotations) of willow in SRC plantations. The multi-stemmed growth form was transformed into a single-stem modeling form by deriving whole plant willow allometric relationships using detailed stem-level measurements of basal area, stem biomass and volume. 3PG model predictions for plant diameter, height, biomass, and stand biomass and volume were within the 95% confidence range of mean plot values. Model simulations showed that after seven 3-yr rotations only 20% of planted cuttings would survive (a decrease from 15,152 to 3022 plants ha⁻¹), but stand volume would increase continuously with each subsequent rotation. 3PG predictions for cumulative (for 22 yr) aboveground biomass was 272 Mg ha⁻¹ and mean annual yield was 12 Mg ha⁻¹ yr⁻¹, comparing favorably with other findings. To our knowledge, this work is the first where the 3PG model was calibrated and used for willow species. Once parameterized for a specific willow clone, 3PG can predict biomass accumulation for any agricultural land in North America using only available soil and climate data.     

Yield comparison of four lignocellulosic perennial energy crop species

From 2006 to 2009, block template experiments were conducted to evaluate the biomass yield of four crop species—Amur silvergrass, Giant Miscanthus, Virginia fanpetals, and two Basket willow clones—at the University of Life Science, Lublin, Poland. The dry matter (d m) yields and number of shoots were determined each November, while biomass moisture levels were determined every November and March. The averages of the 4-year research datasets indicated that Giant Miscanthus produced the greatest biomass (16.5 t ha⁻¹ d m), while the two Basket willow clones (8.8–10.2) t ha⁻¹ d m, and Amur silvergrass (6.2 t ha⁻¹ d m) produced the lowest biomass. The mean yield of Virginia fanpetals was 13.0 t ha⁻¹ d m. The largest number of shoots per one m² were produced by Miscanthus species (55 units), with Basket willow and Virginia fanpetals producing half this amount (24–28 units). Similar moisture levels were obtained for Basket willow biomass harvested in autumn (49.5–54.6)% and winter (48.4–49.7)%. The biomass moisture levels of the other species in March was approximately two times lower (14–29)% than that in November (27–70)%.In a second experiment, the effect of varying plant density (10 000 and 30 000 plants per ha) on the yield of Giant Miscanthus was investigated. Double the biomass yield was obtained in crops with a density of 30 000 plants per hectare compared to 10 thousand. The higher yields were accompanied by larger, heavier, taller, but thinner shoots.