Evaluation of poplar and willow performances for biomass ...

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Evaluation of poplar and willow performances for biomass ...

Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoEvaluation of poplar and willow performances for biomass production in Northern ItalyFacciotto G.; Bergante S.CRA- PLF Research unit for Intensive wood production, St. Frassineto Po 35, I-15033 CasaleMonferrato (AL) Italy Tel: +39 0142 330911; Fax: +39 0142 55580gianni.facciotto@entecra.it; sara.bergante@entecra.itAbstractThe Research Unit for Intensive Wood Production of Italian Agricultural Research Council(CRA-PLF) has contributed in the past to select poplars and willows for industrial usesparticularly for plywood and paper production. The best results were obtained with the poplarclones. The Populus ×canadensis clones, like ‘I-214’, ‘San Martino’ and others, selected fordisease resistance, growth, stem shape and wood quality, became the most important clonescultivated in Italy for these purposes. Willow clones were not utilized by the farmers; butbreeding, selection and conservation of these clones were carried out in the CRA-PLF. In thelast fifteen years the researches on woody biomasses for energy purposes give more emphasisto willows, selected and widely utilized in Northern Europe for energy production. Few speciesare evaluated and improved for fast growth in Italy: Salix alba L., Salix babylonica L. and Salixmatsudana Koidz. Currently in Italy poplar and willows for biomass production are cultivated inShort Rotation Coppice with high density of plantation (1100 - 8333 trees·ha -1 ) and harvestedevery two-three or five-six years. In order to find what are the clones more suitable for biomassproduction in Northern Italy, five experimental trials, three in Casale Monferrato (AL) one inLombriasco (TO) and one in Gazzo (MN), were established comparing poplar and willowclones. Other objective of these trials is to collect information on the characteristics of thebiomass and on the cultivation costs For each species from one to four clones have been used.A complete randomized block or a split-plot experimental design is utilized, with 3-4 replicationsfor trial. Production results are very variables but sometimes willow are able to produce morebiomass than poplars. Willow biomass production range from a minimum of 2,95 t·ha -1·y -1 insandy soil to 16,8 t·ha -1·y -1 in suitable environmental conditions. In the same trials poplar rangefrom 2 to 15,5 t·ha -1·y -1 . Rooting and survival results are very good for every clones withaverage of 90 %. The hybrids of S. matsudana named ‘S78-003’, ‘Drago’, ‘Levante’ and ‘S76-008’ show the best results. They are also resistant to repeated coppices, producing a highquantity of sprouts and biomass also in second and third rotation and show less sensibility todiseases and insects than poplar clones currently utilized in Italy.Two of these Willow clones ‘Drago’ and ‘Levante’ in 2008 obtained the European CommunityPlant Variety Right, a Patent for commercialization in EU.Keywords: Poplar, Willow, Biomass, SRC


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoIntroductionThe Research Unit for Intensive Wood Production of Italian Agricultural Research Council(CRA-PLF) has contributed in the past to select new poplars and willows clones for industrialuses, particularly for plywood and paper production. Clones were selected for diseaseresistance, growth, stem shape and wood quality. The best results were obtained with thepoplar species (Populus nigra, P. deltoides and their hybrids P. ×canadensis). The P.×canadensis clones, like ‘I-214’, ‘San Martino’ and others, became the most important clonescultivated in Italy for these purposes. Willow clones were not utilized by the farmers for qualitywood productions, but breeding, selection and conservation of these clones were carried out inthe CRA-PLF. The PLF maintain 590 genotypes from 30 species, a lot of which of Europeanand Asian origin as Salix jessoensis Seemen and S. matsudana Koidz. The greater number ofgenotypes come from Salix alba: 423 clones of Salix alba are in propagation, 207 of these wereobtained through controlled crossing (Vietto L. & Cagelli L., 2006).In the last fifteen years the researches on woody biomasses for energy purposes give moreemphasis to willows, selected and widely utilized in Northern Europe (Sweden) for energyproduction in very high density plantations (10000-20000 trees·ha -1 ) (Ledin S. & Willebrand E.,1995) Among the great variety of available genotypes, few willow species are evaluated andimproved for biomass production in Italy: Salix alba L., Salix babylonica L. and Salix matsudanaKoidz.(Facciotto G. et al., 2006; Facciotto G. et al., 2008)Currently in Italy poplar and willows for biomass production are cultivated with two ShortRotation Coppice models: with high plantation density (1100 trees·ha -1 ) and harvesting everyfive years, for biomass production and wood for industry (paper, pallets, particle boards), or withvery high plantation density (8300-10000 trees·ha -1 ) and harvesting every two years for biomassproduction and/or particle boards (Bergante S. & Facciotto G., 2006).Materials and methodsA total of five experimental plantations, with poplar and willow clones, located in Northern Italywere described in this paper.TurinMilan1 -2-34 5RomeFigure 1 – Location of experimental trials in Northern Italy. 1, 2, 3: Casale Monferrato (AL),“Mezzi” farm; 4: Lombriasco (TO), Salesiani’s farm; 5: Gazzo Bigarello (MN), ERSAF’s farm


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoThree experimental trials have been done in Casale Monferrato (AL), in “Mezzi” farm of CRA-PLF (1, 2, 3), one experimental trial in Lombriasco (4), near Torino, in the Salesiani Institutefarm, and one in Gazzo Bigarello (5), near Mantova, in the E.R.S.A.F. (Lombardy RegionalAgency for Services to Agriculture and Forestry) farm (Figure 1).Casale Monferrato (AL) trialsIn the “Mezzi” farm were planted three experimental trials of poplar and willow clones, with veryhigh plantation density model, harvested every two years for biomass production. Soil texture issandy.The trial 1 cover 5400 m 2 and was planted in 2002 utilizing Rotor machine and 20 cm longcuttings. Plantation density was 7500 trees·ha -1 corresponding to a spacing of 1,90 m x 0,70 m.In this trial were compared a miscellaneous of two poplar clones ‘I-214’ and ‘Neva’ (P.×canadensis), and two willow clones ‘Levante’ and ‘S76-008’ (S. matsudana hybrids). Soilpreparation consist on ploughing (40 cm dept), harrowing and manure (50 t per hectare).Herbicides, Metholaclor and Pendimethalin, were utilized for pre-emergency weeds control; twodisc harrowing were carried out during the first year after establishment and after each harvest.Two chemical spraying were applied to control insect: one during growing season to controlCrysomela populi L. and one at the sprouting of the second year to control Cryptorrhynchuslapathi L. Five sprinkler irrigations, using rotors, were applied during summer period (35 mm foreach irrigation). Plantation was harvested at the end of second and fourth year. After the firsttwo year of growing the plantation was coppiced utilizing circular saw applied to the tractor andthe trees were collected with a telescopic handler machine; subsequently the harvest was donewith corn foragers equipped with a modified header (Baratto et alii, 2008).The trial 2 was planted in 2004 and cover 1600 m 2 ; as plantation material were utilized 20 cmlong cuttings of the poplar clone ‘Orion’ (P. ×canadensis) and of two willows clones ‘Levante’and ‘S76-008’ (S. matsudana hybrids). Plantation density was 8170 trees·ha -1 corresponding toa spacing of 2,40 m x 0,51 m. Cultural management has been the same of the trial 1. Plantationwas harvested at the end of second and fourth year utilizing respectively Class and Kroneforagers with a modified header for biomass harvesting.The trial 3 was planted in 2004 and cover 2160 m 2 . Plantation density was 8333 trees·ha -1corresponding to a spacing of 2,40 m x 0,50 m. Plantation was carried out with Rotor machineutilizing poplar clone ‘I-214’ and willow clone ‘Levante’ cuttings, 20 cm long. Culturalmanagement has been the same of the trial 1. Plantation was harvested at the end of secondand fourth year utilizing respectively ‘Class’ and ‘Krone’ foragers.Lombriasco (TO) trialPlantation was made in spring 2004. Trial cover 5200 m 2 . The experimental design is arandomized complete block with three replication of ten clones (six poplars and four willows):‘Orion’, ‘I-214’ and ‘Ballottino’ (P. ×canadensis), ‘Baldo’, ’84-078’ and ’85-037’ (P. deltoides),‘Drago’, ‘Levante’, ‘S78-003’ and ‘S76-008’ (S. matsudana hybrids). Plantation density is 5747trees·ha -1 corresponding to a spacing of 2,90 m x 0,60 m. as plantation material were utilized 20cm long cuttings, manually planted. Soil texture is sandy-silt with an increasing percentage ofgravel toward the last part of the trial. Preparation consist of ploughing (40 cm dept), harrowingand P, K basic fertilization. Metholaclor and Pendimethalin were utilized for pre-emergencyweeds control. Two mechanical weeds controls were carried out during the first year afterestablishment and after each coppice. No irrigation or pest treatments were applied. Treeswere harvested at the end of third and fifth year utilizing ‘John Deere’ forager with headermodified for biomass harvesting.Gazzo Bigarello (MN) trialThe Gazzo Bigarello trial has different plantation model: plantation density was of 1100trees·ha -1 corresponding to a spacing of 3 m x 3 m. It was planted in spring 2006, utilizing poplarand willow one year old poles, without root. The plantation will be harvested at the end of fifthyear. Trial contains fifteen clones (10 of poplar and 5 of willow) compared in randomizedcomplete blocks with three replications: ‘Orion’, ‘Imola’, ’84.260.003’, ’83.120.036’, ’83.002.011’,’83.002.031’, ’84.048.032’ (P. ×canadensis), ‘Baldo’, ’85-037’, ’84-078’ (P. deltoides), ‘Drago’,


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo Técnico‘Levante’, ‘S76-008’ (S. matsudana hybrids), ‘131-25’ (S. babylonica x S. alba), ‘SI64-017’ (S.alba). In this farm texture soil is clay-loam, with pour drainage and oxygenation, difficultconditions for salicaceae. Soil preparation consist on ploughing (40 cm dept), harrowing and N,P, K basic fertilization. Two mechanical weeds control were carried out during the first threeyears. One chemical treatment against insects (Cryptorrhynchus lapathi L) was spayed eachyear at the sprouting. Two irrigation (flooding) during every growing season.Data collectionAt the end of the growing season in all the trials have been done the following measures:1) rooting (%) at the end of the first year and survival (%) at the end of each year;2) diameter (mm) at breast height (dbh) of stem on a sample of 30 trees/stumps;3) number of sprouts per tree/stumpOn a sample of tree per each clone/density were measured dbh, wet and dry weight (afterdrying process 103°C in oven up to attainment of co nstant weight). Four different regressionequations (power) were been calculated to evaluate trees weight (poplars and willows in veryhigh plantation density, poplar and willow in high plantation density): equations correlatediameter with dry weight (in grams) of tree/shoot. Growth and production results of poplar andwillow are reported in oven dry tons·ha -1 (Odt·ha -1 , 0% moisture), at the end of each rotation,and in oven dry ton·ha -1 per year (Odt·ha -1·y -1 , average) at the end of cycle of two-threerotations. Data were analyzed with ANOVA (p= 0,05) utilizing SPSS Statistic software. A ‘Posthoc’ test was applied in case of significative resultsResults and DiscussionCasale Monferrato, trial 1Rooting was the same for poplar and willow genotypes (92 %). At the end of fourth year survivalwas lower, specially for poplar miscellaneous (63 %). Poplar clones utilized for this trial wereselected for traditional cultivation and show a lower resistance to repeated harvesting. Willowsshow a better resistance to coppicing and a higher biomass production both in first and secondrotation (table 1).Table 1- Casale Monferrato, trial 1. Average and ANOVA analysis of rooting (Root.) at the endof first year (S1R1), survival (Surv.) at the end of fourth year (S2R4) and total oven dry biomass(B) at the end of first (S2R2) and second (S2R4) biennial rotation.Root. (%) Surv. (%) B (Odt· ha -1 ) B (Odt· ha -1 )Specie S1R1 S2R4 S2R2 S2R4Poplar 92 63 18,80 6,77Willow 92 88 22,55 23,69Average 92,3 75,7 20,67 15,23F values n.s. 26,1** n.s. 29,4**Casale Monferrato, trial 2Rooting was, both for poplar and willow not so high, probably due to hot temperature in the firstyear and summer drought. Willow ‘S76-008’ gives the best result of rooting and survival (94%and 91%). The average value of dry biomass production of the trial at the end of first rotationwas 12,69 Odt·ha -1 , without significant differences between clones. After harvesting, duringsecond rotation, the differences between the clones become statistically significant (table 2):willow clones show the best productions, particularly ‘S76-008’ that produce 32,53 Odt·ha -1 intwo years (16,3 Odt·ha -1·y -1 ).


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoTable 2- Casale Monferrato, trial 2. Average and ANOVA analysis of rooting (Root.) at the endof first year (S1R1), survival (Surv.) at the end of fourth year (S2R4) and total oven dry biomass(B) at the end of first (S2R2) and second (S2R4) biennial rotationRoot. (%) Surv. (%) B (Odt· ha -1 ) B (Odt· ha -1 )Clone S1R1 S2R4 S2R2 S2R4Orion 90 87 12,09 18,4Levante 89 88 12,89 28,09S76-008 94 91 13,1 32,53Average 91 89 12,69 26,34F values n.s n.s. n.s. 4,8 *Casale Monferrato, trial 3Also in this trial both species/clones show rooting problems, maybe for hot temperatures in thefirst year and summer drought. Accordingly, the production in the first rotation is not so high, thewillow clone ‘Levante’ give the best result with 19,07 Odt·ha -1 . During second rotation the poplarclone maintain the same behavior and production, while the willow clone reach a very high yield(probably due to a production of great number of sprouts) of 38,34 Odt·ha -1 in two years (19,2Odt·ha -1·y -1 ) (table 3).Table 3 - Casale Monferrato, trial 3. Average and ANOVA analysis of rooting (Root.) at the endof first year (S1R1), survival (Surv.) at the end of fourth year (S2R4) and total oven dry biomass(B) at the end of first (S2R2) and second (S2R4) biennial rotationRoot. (%) Surv. (%) B (Odt· ha -1 ) B (Odt· ha -1 )Clone S1R1 S2R4 S2R2 S2R4I-214 88 82 13,80 13,97Levante 84 83 19,07 38,34Average 86,2 82,6 16,44 26,15F values n.s n.s 29,8 * 68,4 *Lombriasco (TO)At Lombriasco rooting was good for all clones. The average was 94,4% and best rooting valuewas for Salix matsudana hybrid clone ‘S76-008’ (99%).Table 4 - Lombriasco. Average and ANOVA analysis of rooting (Root.) at the end of first year(S1R1), survival (Surv.) at the end of the first triennial rotation (S3R3) and at the end of second(S2R5) and third (S2R7) biennial rotation.


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoRoot. (%) Surv. (%) Surv. (%) Surv. (%)Clone S1R1 S3R3 S2R5 S2R785-037 92 D 91 BC 89 AB 87 AB84-078 91 D 91 BC 89 AB 82 BCBallottino 91 D 90 C 89 AB 85 ABOrion 96 ABCD 95 ABC 93 AB 90 ABBaldo 93 BCD 93 BC 92 AB 92 ABI-214 97 ABCD 97 ABC 95 AB 90 ABS78-003 98 AB 97 AB 70 C 49 DS76-008 99 A 99 A 97 A 97 ABDrago 97 ABC 97 ABC 81 BC 70 CLevante 92 CD 92 BC 92 AB 90 ABAverage 94,4 94,2 88,8 83,2F values 7,47** 4,40** 7,24** 16,9**The same clone maintain a high survival value until to end of first rotation (S3R3), andgenerally, for all clones, the survival has been unchanged in comparison to the rooting values(94,2%). After the first harvest, some stumps die; two willow clones, ‘Drago’ and ‘S78-003’ showa high mortality, but generally the trial maintain a good survival values with an average around89%. After second harvest the two willow clones show again high mortality, while generally thetrial maintain a good values (83,2 %), (table 4).During first rotation differences in growth values (diameter, number of shoots per root) andbiomass production between clones were significant: P. deltoides clones ‘85-037’ and ‘84-078’at the end of third year have the greater diameter (over 50 mm) but generally the trees of thisspecies produce only one shoot per root during first rotation, so better biomass production wasreached by willow clones, particularly ‘Drago’ and ‘Levante’ that have a high growth in diameterand produce many shoots. During second rotation the two P. deltoides clones maintain a gooddiameter growth and produce many new shoots, so even if the differences between biomassvalues are not significant, the clone ‘84-078’ produce a higher quantity of dry matter (57,7Odt·ha -1 in two years). At the end of third rotation the best clone was the willow ‘Levante’ thatproduce 59,60 Odt·ha -1 in two years followed by ‘S78-003’, it has compensated the elevatedmortality with a greater number of shoots per stump. Between poplar clones the best was‘Baldo’ that produce 53,58 Odt·ha -1 in the last biennial rotation (table 5).Table 5 - Lombriasco. Average and ANOVA analysis of diameter (Diam), number of shoots perstump (sh/r) and total dry biomass (Odt·ha -1 ) at the end of first triennial rotation (S3R3), second(S2R5) and third (S2R7) biennial rotation.S3R3 S2R5 S2R7Clone Diam (mm) sh/s (n.) B (Odt·ha -1 ) Diam (mm) sh/s (n.) B (Odt·ha -1 ) Diam (mm) sh/s (n.) B (Odt·ha -1 )85-037 51,5 A 1,0 B 18,59 ABC 36,1 AB 5,0 C 42,56 39,3 A 4,2 D 44,29 abc84-078 52,0 A 1,0 B 19,86 ABC 36,6 A 6,3 ABC 57,70 33,3 ABC 5,8 CD 40,32 bcBallottino 43,8 ABC 1,1 B 14,60 C 29,3 CDE 7,3 ABC 39,30 27,1 BC 8,2 ABCD 39,98 bcOrion 41,7 ABC 1,2 AB 15,79 BC 31,5 ABCD 5,6 ABC 37,82 28,2 BC 6,6 BCD 38,80 abcBaldo 48,3 AB 1,1 B 17,09 ABC 33,1 ABC 5,4 BC 37,46 35,7 AB 6,1 CD 53,58 abcI-214 48,3 AB 1,1 B 17,77 ABC 27,4 CDE 7,3 ABC 36,58 24,5 C 7,9 ABCD 37,12 cS78-003 32,2 C 1,7 A 16,96 ABC 27,0 DE 8,9 A 42,45 23,8 C 10,7 A 54,90 abS76-008 36,7 BC 1,5 AB 19,11 ABC 25,7 E 8,5 AB 55,89 21,6 C 10,0 ABC 52,45 abcDrago 43,6 ABC 1,4 AB 22,63 A 30,6 BCDE 6,7 ABC 48,83 24,9 C 10,6 AB 48,60 abcLevante 46,4 AB 1,2 B 21,32 ABC 26,8 DE 7,7 ABC 51,08 26,8 BC 8,1 ABCD 59,60 aAverage 44,45 1,24 18,37 30,41 6,89 44,97 28,51 7,82 46,963F values 5,30** 4,34** 3,60 ** 10,12** 3,63** n.s. 6,80** 5,82** 2,45*Table 6 - Lombriasco. Average and ANOVA of total dry biomass obtained in a cycle of 7 years(three rotation).


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoTot. B Tot. B/7Clone Odt·ha -1 -1Odt·ha-1·y85-037 83,30 11,90 ABC84-078 97,72 13,96 ABCBallottino 73,89 10,56 BCOrion 73,01 10,43 CBaldo 81,34 11,62 ABCI-214 72,91 10,42 CS78-003 86,86 12,41 ABCS76-008 101,22 14,46 ABDrago 95,76 13,68 ABCLevante 102,20 14,60 AAverage 86,820 12,403F values 3,81**To compare clones the productivity of a cycle of seven year, the yields of the first, second andthird rotation are been added for each clone to obtain an average of annual biomass production(Table 6). The differences among the clones are statistically significant; the S. matsudanahybrid clone ‘Levante’ shows best production with a mean of 14,6 Odt·ha -1·y -1 . Between poplar-1clones the best is ‘84-078’ that produce 13,96 Odt·ha-1·yGenerally in Lombriasco the productions resulted low during first triennial rotation, and speciallyduring first and second year. This was due probably to summer drought. After the first rotationbiomass productions (Odt·ha -1·y -1 ) increased of 3,7 times and became very good both forwillows and poplars.Gazzo Bigarello (MN)In this trial rooting was lower than in the other trials. This was probably due to soil texture, tooclay. Differences in biomass production was not significant. Plantation reach in four years ofgrowth 39,2 Odt·ha -1 , corresponding to a annual production of 9,80 Odt·ha -1·y -1 . The best-1production was reached by P. ×canadensis clone “Imola” that produce 10,8 Odt·ha-1·yTable 7- Gazzo Bigarello. Total average and ANOVA of rooting (Root.) in the first year (S1R1),survival (Surv.) in the fourth year (S4R4), and dry biomass, total and average annual.S1R1S4R4S4R4Root. (%) Surv. (%) B (Odt·ha -1 ) B (Odt·ha -1·y -1 )83.141.020 94 94 39,1 9,885-037 88 86 43,7 10,9Baldo 90 90 47,0 11,784-078 72 68 33,4 8,3Imola 99 99 43,1 10,884.260.003 85 85 42,4 10,683.120.036 88 88 42,5 10,683.002.011 89 89 43,0 10,883.002.031 69 67 29,3 7,384.048.032 85 84 38,8 9,7131-25 93 93 39,5 9,9Drago 94 94 36,2 9,1Levante 95 95 35,7 8,9SI64-017 85 85 35,1 8,8S76-008 88 88 39,0 9,7Average 87,3 86,7 39,2 9,80F values n.s n.s n.s n.s


Tercer Congreso Internacional de Salicáceas en ArgentinaTrabajo TécnicoConclusionThe biomass production and rooting/survival of clones tested are very variable. Generally newwillow clones, hybrids of S. matsudana, give good results, accordingly with others onesdescribed in literature (Facciotto G. et al., 2006; Facciotto G. et al., 2008; Cerrillo T. et al.,2008). Rooting and survival can reach 94%. in very high density plantations, stump mortalityafter harvest is counterbalanced by production of a great number of shoots per stump. InCasale Monferrato willow clones give in all the trials best production, specially during thesecond rotation. In Lombriasco the best production was reached by a P. deltoides clone ‘84-078’ but, in average, willow clones maintain a production 17% higher than poplar ones. InGazzo Bigarello willow production is more less the same of poplar one, and this results isprobably due to cultivation model of this plantation. Biomass production of willow is generallycorrelated with the presence of many shoots, but utilizing poles without roots at theestablishment, at the end of fourth year the productions of willow clones are lower than poplarones. Between poplars the P. deltoides clones show good productions but generally P.×canadensis clones have better rooting and survival values during all the cycle length.High biomass productions can be obtained using the “very high density model”; but in this casethe higher costs for planting, for weed and pest control and for the site restoration must beconsidered. The “high density model” gives more flexibility and opportunities for diversificationof the biomass production (pulp & paper, packaging and particle board); anyway somedisadvantages must be taken into consideration also in this case: a greater surface areacovered and a longer rotation period is necessary.References- Baratto G., Bergante S., Facciotto G., Annunziati M. (2008) - Studies of poplar and willowshort rotation coppice establishment. IPC 23rd Sess. 'Poplars, Willows and People'sWellbeing'. Beijing, China, 27-30 October 2008. 27 pp. url: www.fao.org/forestry/ipc2008- Bergante S., Facciotto G. (2006) – Impianti annuali, biennali, quinquennali. Produttivitàe costi in alcune realtà del Nord Italia. SHERWOOD - Foreste ed Alberi Oggi n. 128 25-30.- Cerrillo T., Facciotto G., Bergante S. (2008) - Biomass production of different willow’scombinations – preliminary results. Proceedings of '16° European Conference &Exhibition, from Research to Industry and Markets. 2-7 June 2008. Valencia. Spain. 567-569.- Facciotto G., Bergante S., Lioia C., Rosso L., Mughini G., Zenone T., Nervo G. (2006) -Produttività di cloni di pioppo e salice in piantagioni a turno breve. Forest@. 3: 2 238-252- Facciotto G., Di Candilo M., Bergante S., Baratto G., Diozzi M. (2008) - Willow clones’ forbiomass production in SRC plantations. Proceedings of '16° European Conference &Exhibition, from Research to Industry and Markets. 2-7 June 2008. Valencia. Spain. 611-613.- Ledin S., Willebrand E. (1995) – Handbook on how to grow short rotation forests. IEABioenergy. Swedish University of Agricultural Sciences. Department of Short Rotationforestry.- Vietto L., Cagelli L. (2006) – Raccolta, conservazione e gestione del germoplasma delleSalicaceae. Manuale per la raccolta, studio, conservazione e gestione del germoplasma.APAT 140-147.

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