NERVO, G.; FACCIOTTO, G. - populus.it

Tercer Congreso Internacional de Salicáceas en Argentina

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Activities for sustainable poplar plantations management in Italy VIETTO, L.; NERVO, G.; FACCIOTTO, G.; CHIARABAGLIO, P.M. and COALOA, D. Research Unit for Intensive Wood Production (CRA-PLF) – Strada Frassineto 35, Casale Monferrato – Italy [email protected] Abstract In Italy, traditional poplar cultivation, based on ten-year rotation for plywood production, spread over about 70000 hectares, mainly in Po Valley, although other more plantations exist which are oriented to different purposes. At the Research Unit for Intensive Wood Production (CRAPLF) research carried out to improve the productivity and sustainable management of poplar plantations. Besides releasing new P. ×canadensis Moench clones tolerant to the most important biotic adversities, management protocols have been defined for a sustainable poplar cultivation (integrated control, nutrient management strategies and low tillage techniques for environmentally sensitive areas are considered). Based on these results, criteria and indicators for individual and group certification of sustainable poplar plantations management have been developed according to Forest Stewardship Certification (FSC) and Programme for the Endorsement of Forest Certification (PEFC) Standards. Low impact environment practices were also established for biomass production in short rotation plantation coppice (SRC). Using new poplar clones, characterized by good rooting capacity, fast growth-rate, tolerance to diseases and good re-sprouting capacity, it will be possible to reduce the economic and energy costs, making SRC cultivation more profitable. The Ministry of Agriculture and FAO supported projects for genetic resources conservation and exploitation and to re-establish European native poplars in fluvial areas. Plantations with Populus nigra L. and Populus alba L. selected genotypes have been established to evaluate their behaviour and performance related to different site conditions and cultivation techniques. In co-operation with fluvial parks several pilot trials were carried out on the Po river basin to create a network of black poplar stands to support a dynamic evolutionary process for this endangered species. A large number of native males and females could adapt to environmental changes and spontaneous dissemination could occur on fluvial banks in a short time. These afforested sites will serve also to separate areas subjected to frequent erosive events from intensive agricultural cultivation, to reduce river pollution by introducing buffer strips and to restore floodplain forests for recreational purposes. Key words: breeding; poplar cultivation; forest certification; short rotation coppice; genetic resources conservation; restoration

Introduction Through the creation of improved clones, poplar tree breeders have played a relevant role in the improvement and the sustainability of poplar cultivation. Over decades, they have built up huge collections of genotypes of the most important species and vast networks of experimental trials. At first they have continuously selected and mass-produced poplar clones dealing particularly with pest and diseases troubles and then they developed original methodologies in genetics and in related sciences to recombine, test, evaluate and analyse new materials. Recently, tree breeding R&D activities, though assisted by the development of new technologies (genomics, somatic embryogenesis), have become more complex due to environmental concerns (climatic changes, carbon sequestration, pressure from natural disaster) and socio-economic pressures (multi-functionality, sustainability). Indeed sustainable production policies have been adopted in Europe increasing demand for wood products and biodegradable materials for packaging & construction; moreover the achievement of renewable energy targets is strongly dependent on wood supply. As a consequence the European demand for wood is outstripping supply and


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wood use is forecast to exceed production (UNECE/FAO, 2008). There are many contributing factors. Reliance on imports leaves timber processing industries vulnerable to changeable international prices; undersupply of grown wood leads to increased prices for timber, wood products and wood fuel, reducing the competitiveness of wood-using industries. Strong European demand for timber places considerable pressure on natural forest stands both within and outside the EU, potentially leading to degradation of woodland habitats. as consumers become more educated about what they buy, sustainably-harvested products have gained a following and sustainable wood products and plantation management at present are not the exception any more. With regard to the Italian situation cultivated poplars occupy less than 2% of the total forest land, but yield more than 45% of the overall domestic wood production (ISTAT, 2009) The trend is negative even if the total area has remained rather stable since the early 1990’s; at present the poplar plantations area amounts to around 70 thousand hectares, more than 90% of which are situated in the Northern plains (MiPAAF, 2007). In 2007 poplar wood production was around 0,8 million cubic metres; to meet the industry demand around 500000 m3 of poplar round-wood were imported mainly from France and Hungary. Particularly on the Po river plain, poplar cultivation is going through an economic and technical crisis as regards management planning and methods of cultivation. In the last 20 years poplar growing has fallen out of favour. The main causes are environmental conflicts and increased competition for land (urbanization, agricultural exploitation, re-naturalization of floodplain areas), an unfavourable poplar market which has settled at a very low level (70 % of wood production is still related to the clone ‘I-214’) and lack of state contributions toward the establishment of poplar plantations in the areas particularly suited to this cultivation. To obtain trunks of good quality and to have a greater flexibility in the cultivation cycle the trend is establishing low density plantations (270-280 plants per hectare instead of 300-330), with relatively short rotations (about 9 to 13 years). This is being done to obtain young, medium-sized assortments capable of realizing more remunerative prices since the plywood industry is interested in these characteristics. As a result, other wood-using industries have followed this trend, installing equipment destined specifically for the processing and utilization of medium-sized poplar roundwood which was in good supply on the market. Contrariwise poplar plantations for paper and energy show positive trend. In some Administrative Departments (Regions), where biomass thermoelectric power plants are under construction, the establishment of Short Rotation Coppice plantations (SRC) is increasing (about 7000 hectares of SRC were planted over the last 5 years with public financial support for establishing biomass plantations only (Paris, 2010). Italy has a long tradition of poplar growing and use; specialist research institutions like the Poplar Research Institute have supported the development of faster growing and disease tolerant varieties since the 1930’s. The current CRA-Research Unit for Intensive Wood Production (CRA-PLF) is still carrying out research activities on poplars and willows; the experimental activity is chiefly aimed at developing new clones for traditional cultivation with particular qualities such as quick growth, disease tolerance and production of high-quality wood, adaptable to different soil conditions and to a wide range of uses. In the last years, considering the rising environmental awareness, techniques of intensive but sustainable cultivation have been investigated, in traditional plantations for biomass, as well as extensive or semi-extensive forestry models which respond better to the requirements of ecologically sustainable arboriculture, forest certification systems in particular. Likewise, cultivation models are studied for the regeneration of waste land and restoration of natural river-bank environments. To reduce significantly the expected gap between wood use and production in a sustainable approach and to support poplar growers and wood industries the CRA-PLF has developed some actions that will strengthen the poplar–wood chain and timber trading. Material and methods Diseases have influenced the evolution of specialized poplar growing right from the start of the domestication process. As a consequence of new pathological problems caused by rust (Melampsora spp.), woolly aphid (Phloeomyzus passerinii Sign.), bark necrosis (Discosporium populeum Sacc. Sutton) and disorders induced by environmental and cultivation factors and host’s genetic characteristics (“brown spots”), a vast poplar breeding program was set up in the


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early Eighties at the Poplar Research Institute. Based on a semi-reciprocal recurrent selection of P. deltoides and P. nigra it is aimed at producing improved populations of both species and obtaining parents of high breeding value to produce valuable P. ×canadensis hybrids. A systematic breeding approach integrating long-term (maintenance of genetic variation to create options for the future) and short-term breeding strategies (production and selection of new hybrids for intensive poplar cultivation and/or short rotation coppice) has been considered. A pool of promising clones (P. ×canadensis) selected for traditional cultivation within the individuals from the progeny test will join soon the materials listed recently in the National Register of Basic Forest Materials: ‘Lena’, ‘Neva’, ‘Dvina’, ‘Oglio’, ‘Soligo’, ‘Lambro’, ‘Taro’, ‘Brenta’, ‘Mella’, and ‘Timavo’. Besides other clones released for biomass production only (Baldo, ‘Orion’, ‘Imola’), new improved materials will be available in a short time as a result of a specific breeding program for commercial purposes started at the beginning of the 1990’s. Besides releasing new P. ×canadensis clones tolerant to the most important biotic adversities, the CRA-PLF has promoted a project proposal to develop management protocols for sustainable poplar cultivation (REGIONE PIEMONTE, 2002). Table 1 – Facing traditional and sustainable cultivation practices: main features. Extensive cultivation Intensive cultivation (traditional) (sustainable) Site choice

multi-sites

suitable sites only

Site preparation

deep tillage

Clone choice

monoclonal

shallow ploughing multiclonal by using tolerant varieties (rust, woolly aphid)

Planting density

medium (333 plants/hectare)

low (240-270 plants/hectare)

Fertilization

conventional

N supplies restricted to the 3 first years; P and K pre-planting application only

Soil/weed management

disk harrowing

weed shredding from 4th year on

Pest and diseases management

conventional

integrated (threshold-based crop protection); severe restrictions in floodplain areas

Irrigation

periodic submersion

during extended dry spells only

Rotation

8-10 years

8-13 years

The technical guidelines, resulting from the multi-year activity of a large working group (University, growers partnership, free lancers, accredited certification bodies, forest certification organization officers, stakeholders, natural areas managers) served as a baseline to define and include at a national level specific regulations for poplar plantation management in the Programme for Endorsement of Forest Certification (PEFC) and Forest Stewardship Council (FSC) Standards to be used for poplar plantations (Coaloa and Vietto, 2005). Sustainable poplar plantation management (table 1) consists mainly of a management plan and the implementation of an environmental monitoring system i.e. clonal diversification, implementation of measures to mitigate negative impacts of chemical product applications (disease control, nutrient supply), safe harvesting methods, water-course protection, irrigationwater management and control. All this results in a reduction of cultivation practices and costs (graphic 1; graphic 2) without affecting the wood quality. The main advantages obtained by forest enterprises with certification are: documentation of internationally-recognised ecological and social standards, safeguarding of existing market shares and customers, access to new markets, improvement of the company’s image and marketing advantages in general. The FSC and PEFC schemes allow a group of smallholders to join together under a single certificate and share certification costs among the group members; this can markedly reduce


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the costs for each owner (approximately 1-2% of gross product value, 40% are concentrated in the first year). 12.000

10.000 -13% 8.000 -16%

€/ha 6.000

Sustainable cultivation Traditional cultivation

4.000

2.000

- 4%

0 Cost for planting

Cost for management

Total cost

Graphic 1 – Percent of cost reduction due to growing hybrid poplars according to the extensive cultivation model. 2500

2000

1500 €/ha

Sustainable cultivation

- 31%

Traditional cultivation - 19%

1000

500 - 41% 0 Pest and diseases control

Soil management

Fertilization

Graphic 2 – Economic advantages (percent of cost reduction) of the sustainable cultivation model: costs shared among activities. As great interest has recently revived renewable energy owing to the increased costs of conventional energy sources, the CRA-PLF has also been active in the green energy sector looking for new materials and environmental friendly practices to manage SRC to reduce the demand for fossil fuels. The energy situation in Italy is rather critical, indeed energy from renewable sources accounts for 9% of the total (192.1 Mtoe/year-1), of which only 3% are from biomass (Enea, 2009). Research activities have been supported by ministerial funding with the aim to create a network of experimental trials, to achieve technical and economic information, to increase dry matter production per hectare and to achieve the objectives defined in the national strategy for rural biomass energy development. In this framework 60 experimental plantations have been


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established all over the Country under different environmental conditions following the “Very high density model” (5700-10000 plants per hectare) and the “High density model” (1100-1600 plants per hectare) and using poplar, willow, black locust, eucalyptus and other fast growing species. Table 2 : Biomass production (Oven Dry t ha-1/years-1) obtained in poplar trials with “very high density” after the 1st and 2nd harvesting. A: general mean, B: best clone average. Locality

Density -1 (n. stems ha )

Coppice cycle (years) st nd 1 2 2 2

Casale Monferrato (AL)

8170

Casale Monferrato (AL)

10000

2

2

Lombriasco (TO)

5747

3

3

Vinovo

5952

2

2

Bressana (PV)

4167

3

3

Santa Cristina (PV)

9376

1

1

Gazzo Bigarello (MN)

5952

2

2

Mira (VE)

5952

2

2

Meduna Livenza (TV)

7407

2

1

Osoppo (UD)

6163

2

2

Anzola (BO)

8333

2

2

Coltano (PI)

7100

2

6

Bagni Tivoli (RM)

10000

3

3

Monterotondo (RM)

8510

4

1

Mirto Crosìa (CS)

5500

2

2

A A B A B A B A B A B A B A B A B A B A B A B A B A B A B

Harvesting -1 -1 (O.D.t ha ·years ) st nd 1 cycle 2 cycle 12.1 18.4 12.5 16.6 5.8 6.7 11.5 15.0 2.6 4.2 5.4 7.4 5.2 5.7 15.1 21.5 9.5 13.1 7.5 8.8 16.6 21.7 7.1 9.4 8.1 11.2 5.5 9.1 11.1 17.7

7.4 11.6 22.5 28.0 11.6 14.8 3.7 5.9 7.6 12.6 7.1 11.1 20.3 24.0 16.7 24.7 5.7 8.9 9.4 15.4 7.9 13.5 11.8 19.5

The new poplar varieties ‘Orion’, ‘Imola’, ‘Baldo’ selected at the CRA-PLF and ‘Monviso’, ‘AF2’, ‘Sirio’, ‘Pegaso’, ‘AF8’ selected by the ALASIA Franco Company, characterized by good growth rate, disease and pests tolerance and better sprouting ability after repeated coppicing, have determined an increase of the productions reducing the economic and energetic costs. Site characteristic (soil fertility, climatic condition) and water availability (precipitation and irrigation) are the main limiting factors to productivity (Bergante et alii, 2010). The clones/provenances utilized in SRC trials have showed yields up to 25 Oven Dry tons (O.D.t.) ha-1year-1 (table 2); the yields in commercial plantations, where fertilization and irrigation are rarely applied by farmers, have been lower (average ranging from 6 to12 O.D.t ha-1year-1) (Paris et alii, 2010, Facciotto et alii, 2009). Coppice cycle in the “very high planting density” trials is generally short (2-3 years); the wood biomass produced has low quality owing to a high bark percentage (15-20%) and it is mostly used as chips for bio-energy power plants or for co-firing in thermo-electric plants and incinerators. In the case of “high planting density” the cycle is longer (5-6 years) and usually the yields obtained are within the range of 8 to 20 O.D.t ha-1year-1 (table 3); in this case the raw material has good quality, with lower bark percentage, and it is preferably used for pellet production or


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for other industrial uses such as pulp for paper or packaging. Table 3: Biomass production (Oven Dry t ha-1 years-1) obtained in poplar trials with “high density” after the 1st and 2nd harvesting. A: general mean, B: best clone average. Locality

Density -1 (n. stems ha )

Coppice cycle (years) st nd 1 2

Cavallermaggiore (CN) Motta dei Conti (VC) Casale Monferrato (AL) Lomello (PV)

1667 1330 1667 1667

5 5 5 5

Villanterio (PV)

1143

4

Corte dei Frati (CR) Gazzo Bigarello (MN)

1143 1111

4 4

6 5

A A A A B A B A A B

Harvesting -1 -1 (O.D.t ha ·years ) st nd 1 cycle 2 cycle 25.9 16.2 14.7 16.7 8.2 15.6 10.3 22.6 16.9 17.9 24.5 9.8 11.7 -

According to these preliminary results SRC recently planted show to be a good renewable energy source, although further research could improve the cultivation of dedicated woody crops. Currently the profitability of short rotation woody crops for farmers depends largely on public grants, giving the farmers have no alternative but to sell the biomass to the energy companies. Pilot experiences of farmers’ cooperatives which sell the energy obtained by their own biomass production show interesting profit margins (Paris et alii, 2010). Further developments of woody bio-energy crops will be connected to the implementation of the 5 years rotation model, along with improved cultivation techniques or associated with phytoremediation, and finally enlarging the choice of clone/species suitable to different site conditions especially in central and southern parts of the Country. The CRA-PLF has carried out activities on conservation and exploitation on native poplar genetic resources since 2000 with financial support from the Italian Ministry of Agriculture and FAO. Inventories and development of schemes whereby natural populations of poplar are protected as habitats and recognised as important germplasm pools are carried out; the aim is to provide material for breeding activities and to improve the genetic diversity thereby increasing tolerance of pest & disease pressure, adaptation to climatic stress and to environmental conditions in which poplar may be commercially grown. As a consequence of cereal surplus reduction policies and restrictions on hybrid cultivation on floodplain areas the importance of native poplars (Populus nigra and Populus alba) has increased in fields different from traditional intensive cultivation such as afforestation of fluvial areas and environmental restoration. Several pilot trials have been set up recently to show that native poplars can be successfully used in establishing plantations in fluvial ecosystems and, generally, in damp areas or agricultural flooded areas; as they are typical pioneer species and can grow in poor soil and start the natural evolution of forests (Vietto and Chiarabaglio, 2004). Moreover, recreating of an assemblage of native plant associations that mimic, as fully as possible, the early stage of mixed riparian forest, habitats that were lost as a result of urbanization and agricultural encroachment and also the movement of wildlife back into the riparian area can be enhanced Vietto et alii, 2008). Since P. nigra is in serious decline, a dynamic evolutionary process in the gene conservation strategies has been set up: selected pools of unrelated genotypes have been used to establish artificial in-situ gene conservation units (GCUs) in sites suitable for natural regeneration according to the EUFORGEN guidelines (Lefévre et alii, 2001). In order to increase the resilience to environmental and climate changes, large artificial populations of black poplar sets, with a balanced sex ratio and composed of individuals characterized by high genetic diversity have been planted. Together with other units created along the same river stretch over 200 hectares of artificial in-situ GCUs have been created recently on the Po river. These could be founder populations for new natural establishments over rather large distances, a source for gene flow (pollen and seeds) into neighbouring scattered stands and, lastly, a seed source for reproductive material to be used for restoration activities.


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A pool of black poplar genotypes characterized by growth performances similar to those of I-214 has been selected for cultivation in fluvial areas with restrictions on intensive agriculture and on use of poplar hybrids (graphic 3); a list of native P. nigra to be homologated for restoration activities has been furthermore identified. 120,00

Girth average (cm)

100,00 80,00 60,00 40,00 20,00

N 00 9 N 04 3 N 04 5 N 04 9 N 07 1 N 09 4 N 13 9 N 15 0 N 32 2 N 32 4 N 37 8 N 37 9 N 38 0 N 43 0 N 52 7 N 53 5 N 53 8 N 54 3 N J. 55 P 2 ou rte I-2 t 14

0,00

P.nigra genotypes

Graphic n. 3 – Growth rate in the 8th year of planting of P. nigra genotypes selected for cultivation in fluvial area with restrictions on intensive agriculture Results and discussion The sustainability of poplar cultivation and the robustness of the poplar industry will be hence increased through the diversification of the genetic pool of commercially grown poplar, reducing its vulnerability to the increased pest & disease pressures potentially brought about by climate change. Promoting sustainable development of multi-purpose poplar plantations the socio-economic development could take advantage and the environment could be markedly enhanced. At a European level there is a growing trend in business to grow and use certified wood from sustainable managed forests and plantations. Also in Italy where more than 45% of the domestic timber production comes from poplar plantations, there is a strong demand for certified poplar wood from domestic industries; at present at least 10% of the certified poplar wood is utilized by industry for plywood production and the market forecast suggests a positive trend (Coaloa and Vietto, 2008). Since 2007, about 4.500 hectares of poplar plantations have been certified (about 140 farms). A reduction of cultivation practices and costs without affecting the wood quality can be achieved by compiling with the “Standards for a sustainable poplar cultivation”; the new orientations of the agricultural policy should keep in due consideration and remunerate the increased environmental quality resulting from their application. In particular, given the demonstrated environmental value of poplar cultivation (one hectare absorbs 60-70 tonnes of carbon dioxide per year) it should hopefully benefit in the future from Community Agricultural Policies supporting measures. The development of alternatives to traditional fossil-based fuels for power, the reversion of farmlands into natural forest areas through cereal-surplus reduction policies, the rehabilitation of degraded sites, the re-establishment of forests in fluvial areas have all become common goals for central and regional government agencies at a European level. Energy plantations envisioned, on both agricultural and forest sites, are of excessive scale. However, plans are not yet finalized, and within the next 15 years the success of plantation programs will depend on appropriate genetic resources availability, the relative benefits and costs of plantation, as well as on effective research, development and management, innovation and technological advances. It will also depend increasingly on recognition of and respect for the principle of sustainability, in its full sense. Anyway only State incentives for renewable energy or positive trend in pricing for raw materials could encourage farmers to develop the biomass supply chain in the short term; these could be justified by increasing opportunities for


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rural economic development and by some environmental benefits such as fossil fuel substitution, carbon sink (stump and soil), positive impact on biodiversity compared to traditional food crops. A good perspective of environmental applications of poplars in these fields comes from the experiences carried out at the CRA-PLF. Restoration activities are useful to separate areas subject to frequent erosive events from intensive agricultural cultivations, to stream banks stabilization, to water pollution reduction by introducing buffer strips, to restore areas for recreational purposes, to promote economical land use exploiting of native poplar resources (Vietto et alii, 2007). Selected P. nigra genotypes for cultivation in fluvial areas with restrictions on intensive agriculture and on use of poplar hybrids will help to maintain poplar presence on rivers. Bibliografia Lefèvre, F.; Barsoum, N.; Heinze, B.; Kajba, D.; Rotach, P.; De Vries, S.M.G.;, Turok, J., 2001 EUFORGEN Technical Bulletin: In situ conservation of Populus nigra. International Plant genetic resources Institute, Rome, Italy.1-58. REGIONE PIEMONTE. 2002 - Disciplinare di produzione integrata per il pioppo - Relazione della Task 5, Sub-task 5.4. In: Progetto “Ecocertificazione della pioppicoltura” (ECOPIOPPO). http://www.regione.piemonte.it/montagna/pubblicazioni/dwd/eco_rel9.doc. 21 pp. Vietto, L.; Chiarabaglio, P.M. 2004 - Restoration of floodplain woodlands with native Poplars (Populus nigra and Populus alba) in Italy: some case studies on the Po river. In: 'River Restoration 2004. Principles, Processes, Practices.' Proceedings of the 3rd International Conference on River Restoration in Europe, Zagreb, Croatia, 17-21 May 2004. 375-381 Coaloa, D.; Vietto, L. 2005 - Pioppicoltura ecologicamente disciplinata. Costi di coltivazione del pioppeto secondo disciplinare produzione. SHERWOOD - Foreste ed Alberi Oggi n. 113 23-27 MiPAAF, 2007 – Inventario Nazionale delle Foreste e dei Serbatoi Forestali di Carbonio. Le stime di superficie 2005. Corpo Forestale dello Stato, Ispettorato generale. CRA-MPF- Trento. Vietto, L.; Chiarabaglio, P.M.; Nervo, G. 2007 - Environmental applications of poplar and willow germplasm in Italy: experiences and trends. [POSTER] Presented at the IPC - Environmental Applications of Poplar and Willow Working Party Workshop meeting, held in Montreal, Quebec, Canada June 5th - 8th 2007. UNECE/FA, 2008 - www.unece.org/trade/timber/workshops/2008/wood-balance/

Coaloa, D.; Vietto, L. 2008 - Forest certification for poplar plantations: a new market opportunity.[ABSTRACT] In: IPC 23rd Sess. 'Poplars, Willows and People's Wellbeing'. Abstracts of Submitted Papers. Beijing, China, 27-30 October 2008. p. 43 Vietto, L.; Vanden Broeck, A.; Van Looy, K.; Tautenhahn, M.; Chiarrabaglio, P.M. 2008 Matching the needs for the european black poplar (Populus nigra L.) gene conservation and river restoration: case studies in Italy, Belgium and Germany. In: Proceedings of the IV ECRR International Conference on River Restoration 2008. Venice, San Servolo Island, 16-19 June 2008. 157-166 ENEA. 2009 – Rapporto energia ambiente 2007-2008. L’analisi. 158 pp ISTAT - Annuario statistico italiano 2009, Agricoltura. Roma Facciotto, G.; Bergante, S.; Mughini, G.; Gras, M. L.; Nervo, G. 2009 - Biomass production with fast growing woody plants for energy purposes in Italy. In: Proceedings of the International Scientific Conference 'Forestry in achieving millenium goals' Held on 50th Anniversary of foundation of the Institute of Lowland Forestry and Environment. Novi Sad, Serbia 13-15 November 2008. 105-110 Bergante, S.; Facciotto, G.; Minotta, G. 2010 - Identification of the main site factors and management intensity affecting the establishment of short-Rotation-Coppices (SRC) in Northern Italy through Stepwise regression analysis. Central European Journal of Biology [1895-104X (Print) 1644-3632 (Online)]. 5: 4 522-530 Paris, P.; Facciotto, G.; Nervo, G.; Minotta, G.; Sabatti, M.; Scaravonati, A.; Tarchi, M.; Scarascia-Mugnozza, G. 2010 - Short Rotation Forestry of poplars in Italy: current situation and prospective. In Book of abstract of Fifth International Poplar Symposium, Poplars and willows:


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from research models to multipurpose trees for a bio-based society held in Orvieto, Italy 20-25 September 2010, 105-106.