ESTABLISHMENT AND MONITORING OF LARGE SCALE TRIALS OF SHORT ROTATION COPPICE FOR ENERGY ETSU B/W2/00514/REP Contractor University of Aberdeen Prepared by C P Mitchell E A Stevens M P Watters The work described in this report was carried out under contract as part of the New & Renewable Energy Programme, managed by ETSU on behalf of the Department of Trade and Industry. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of ETSU or the Department of Trade and Industry.__________________________________ First published 1998 © Crown copyright 1998 executive summary This report covers the progress and results of the twelve year research and development project: Establishment And Monitoring Of Large Scale Trials Of Short Rotation Coppice For Energy; ETSU Contracts E/5A/CON/1171/ 1413, E/5A/CON/ 1255/2079, E/ 5A/ CON/1384/ 2835 and E/ 5A/ CON/ 514/ 00/ 00. The objectives of the project were to obtain information on cost, logistics, productivity and overall biology of short rotation coppice crops in order to evaluate their potential for producing wood for fuel. the trials As part of the Depatment of Trade and Industry's_ continued commitment to renewable energy Aberdeen University, Wood Supply Research Group were sponsored to establish 7 Salix and 3 Populus coppice trials across the UK on sites representing a wide range of latitudes, climatic conditions and soil types. The trials were planted using a range of genera, species and clones thought to have potential for biomass production in the UK. The production plots were established on a larger scale than had previously been used for research to provide technical and economic data that would better reflect commercial production. The twelve year project was funded in 4, three yearphases. The trials were established during the first two phases, allowing the evaluation of establishment techniques and the development of best practice guidelines. The latter 2 phases concentrated on the collection of technical and economic data on the management of SRC systems, particularly: weed control, crop nutrition, pest and pathogen control, harvesting and crop removal. Throughout the twelve year programme, the trials have formed the basis of numerous add­ on studies covering many aspects of SRC management. These studies, where relevant, are summarised and cited in this report. Each of the 10 trials sites have been individually managed using the bestknowledge available at the time. A full history of site management together with the data obtained from each trial is given in Section One of this report. As a result of this project, significant advances have been made in the level of knowledge and quality of SRC management, these are described and discussed in Section Two of this report. The work was initiated by the Department of Energy in 1986, and adopted by the Department of Trade and Industry in 1989. site selection The trials were established on sites thought to be representative of land that might become available for SRC in the UK, covering a range of soil, climate and land use types. The work highlighted three factors of primaryimportance when determining the suitability of sites for SRC: climate, soil type, and ease and efficiency of mechanisation. Climate Climatic factors including, quantity and type of precipitation, quantity and quality of radiation, and maximum and minimum daily temperatures, directly affect crop growth potential. In addition, climate influences the development of pest and disease populations, which also impact on plant growth. Ironically, climatic conditions that promote rapid coppice growth also favour the development of the leaf rust Melampsora spp. Levels of the leaf rust, on both willow and poplar, are higher in areas with high annual rainfall and above average winter temperatures. Prior to this project, susceptibility to frost damage, particularly in early autumn and late spring, were thought to restrict the geographic range of SRC poplar to the south of England. Results from the project indicate that poplars can be established and managed in more northerly latitudes; plant survival rates and mean first rotation yields at Markington, North Yorkshire, (84% and 5.9 odt/ha/yr respectively) are comparable with those achieved at the more southerly sites of Swanbourne and Water Eaton. Soil Type Soil type, particularly pH and nutrient levels, influence potential growth rate. The highest growth rates have been recorded at trials established on deep, fertile sites, generally ex­ arable land, with good water availability but without prolonged waterlogging. Several of the sites selected for early trials were established on marginal grassland areas which suffered winter waterlogging. As well as impeding crop development, the site conditions restricted effective ground preparation and weed control, and preclude the use of mechanised harvesting. In general the crops at these sites produced low yields, suffered high stool mortality and incurred high management and harvesting costs; marginal, wet sites are not considered appropriate for the establishment of commercial SRC. Mechanisation of operations The efficacy of many management operations is dependent on a high degree of mechanisation, including planting, weed control (chemical and mechanical) and harvesting. Sites should be selected, and plantations designed to maximise the efficiency of these operations. Ideally, sites should be flat with long straight rows and the soil should contain a minimum of large stones that might cause damage to equipment. Harvesting of SRC occurs during winter when ground conditions are also soft, and trafficking of heavy machinery can lead to soil and crop damage; sites that are prone to winter waterlogging are not considered suitable for commercial SRC. suitability of genera The project tested the suitability of five genera, thought to have potential for use in SRC for energy systems. Salix Seven sites were planted with willow ranging from Buckfast in Devon, to Brahan in Inverness- shire. In general, the clones used were easily established from cuttings, frost tolerant and coppiced well. However, many of the clones used in the programme suffered from infection by the leaf rust Melampsora spp. which reduced crop growth and plant survival rates. The highest levels of infection are recorded at sites where warm, wet climate conditions favoured rust development, and where crops were weakened by other pest and weed problems. Melampsora epitea has been shown to have numerous distinct pathotypes or ‘races’, each infecting specific clones. The use of clonal mixtures to reduce the impact of rust infection by slowing the spread of individual pathotypes through a crop was investigated at three sites: Castle Archdale, Parbold and Buckfast. Results are conflicting; the evidence from Castle Archdale clearly indicates a higher yield in the mixed plots over the mono-clonal plots, but the figures from the other two trials show no yield benefit from the mixtures. Plant survival rates of two of the clones in the five way mixture is down to below 50%, indicating that inter-clonal competition will eventually reduce the mixture to three clones, reducing any potential disease protection. New breeding programmes are generating clones with multi-gene disease resistance, which when planted in non-competitive mixtures, should offer long term protection from rust infection. The insect pest Phyllodecta spp. (Brassy willow beetle) has been identified as a serious threat to SRC willow. In the worst case, at Long Ashton, Avon, it defoliated over one hectare of crop and resulted in a plant mortality rate of over 80% and the abandonment of the trial. Populus Three production trials were established using poplar: Swanbourne, Buckinghamshire, Water Eaton, Wiltshire and Markington, North Yorkshire. In addition screening plots were established at three further sites. Poplar was found to be more difficult to establish than willow, requiring increased care with ground preparation and early weed control. Once established however, management requirements of the two genera were similar. Poplar was seen not to respond to cut-back in the same way as willow, tending to remain as a single stem crop until after the first harvest. It is recommended that poplar is not cut-back at the end of year one, unless access is required for remedial weed control. During the project, the poplar crops have not suffered the same level of pest and disease pressure as willow plantations. However, Melampsora spp. infection, first seen in summer 1994, has been noted as occurring earlier in the season and resulting in higher levels of infection and crop damage. It is thought that a new race of the rust has become established in the UK which may result in the removal of two of the highest yielding Belgain clones (Beaupre and Boelare) from the Forestry Authority approved planting list. Phyllodecta spp. were noted at all the poplar trials during the project but only caused minor leaf damage; they are not considered a barrier to the use of poplar SR C. Eucalyptus Eucalyptus was established in a number of small screening trials at Long Ashton, Avon. The species and clones used proved easy to establish from seedlings, with plant survival rates in the year after planting of 98% During their first five year cycle the plots suffered no pest or disease problems and were not affected by frost as was hypothesised prior to the trial. However, following their first harvest, the plants were infected by Chrondrostereum purpureum (silver leaf disease), which reduced survival rates to below 20% forcing the abandonment of the trial. Despite generating the highest yields of anytrial in the project (18.0 odt/ ha/ yr), the risk of silver leaf disease precludes the use of eucalyptus in SRC for energy systems. Northofagus Four screening plots of Northofagus were established at Long Ashton, Avon using nursery transplants (1+0). By the end of the first year plant survival was below 50% and at the end of the second growth season the plots were abandoned.