National Activities - UK The UK Network of experimental sites for short rotation coppice

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The UK Network of experimental sites for short rotation coppice.

Introduction
In order to assess the performance of willow and poplar clones at a range of site types a network of 49 sites was established by Forest Research (FR) on contract to ETSU for the Department of Trade and Industry (DTI) between 1994/95 and 1995/96. It has long been known that the early performance of willow and poplar is very dependent on good site preparation and management, and particularly on rigorous elimination of weed competition. Given good husbandry, yield depends on interactions between the genetic material, soil conditions and climate. In order to evaluate such interactions sites were selected throughout the UK to cover the major soil types suitable for poplar and willow, over a wide range of climatic conditions. The resulting data will be used to construct yield models which can be used to advise planners, energy producers and growers of the most suitable clones to plant in a given area and to indicate the likely average yield.

Experimental

Energy coppice should employ clones of poplar and willow which are disease resistant and vigorous coming from breeding programmes that continually develop new clones. Yield models must be generalised and adaptable for new clones, since it is unlikely that the list of clones recommended in future will be the same as those available now. Hence, good examples, such as pure Salix viminalis or Populus interamericana hybrids were selected from each parent group. These are being examined for variations in yield over a large number of sites using a relatively simple experiment design. Predictions of yield for clones not included can then be approximations based on the representative clonal type. In addition a small number of larger experiments each containing a more comprehensive range of clones has been established to help verify assumptions used, in combination with records of the climatic conditions, as inputs to empirical growth models developed from the simpler trials. The arrangements are as follows:

• A completely randomised design was used for the majority of sites with 2 species x 3 clones x 3 replications. Fifteen of the sites include the same clones combined in additional mixture plots
• A randomised block design was used at a few of sites with 2 species x 16 clones x 3 replications
• Plot size is 100 trees (10 x 10) with a 36 tree (6 x 6) assessment plot. Spacing is alternately 1.5 m and 0.75 m between rows, and 0.9 m in the rows, to give a stocking equivalent to around 10,000 cuttings/ha. This plot size is sufficient to provide some extra guard rows to allow for a small amount of destructive sampling, whilst minimising edge-effects. The mixture plots are 10 double rows wide, and 20 'columns' deep, and contain an assessment plot of 9 x 9 trees
• Site selection was based on the need to cover the major soil types suitable for poplar and willow, at an elevation of <250 m above sea level
• Sites were also selected to cover the wide range of climate types found in the UK, based on warmth and wetness
• Sites were sampled to obtain a representative soil profile and analysed for physical and chemical properties
• The sites with more clones have been equipped with instruments to measure a full range of climatic conditions, with air temperature, soil temperature and rainfall measured at all sites
• Sites were sprayed with a contact herbicide to eliminate perennial weeds prior to ploughing
• Ploughed sites were power-harrowed immediately before planting with 25 cm unrooted cuttings
• Residual herbicides were applied immediately after planting and the sites kept weed-free by further applications of herbicide throughout the year
• At the end of the first growing season failures were replaced and all trees stumped back to 10 cm above ground level to encourage the stools to become multistemmed. Harvesting is planned to follow a standard 3-year cutting cycle, so that data will be readily comparable between sites and with data from other research.

An annual assessment of yield will be made by measuring the diameter of all stems in the inner assessment plots on a per stool basis. Some selected stems will be used to determine the height/diameter relationship non-destructively. A minimum number of sample stems taken from the guard rows will be used to convert volume to dry weight.

Pest and disease

Poplars and willows are host to a wide range of phytophagous insect species and fungal pathogens. Assessments are being made twice a year at all sites to record the levels of damage from pests and disease.

Participants and funding

The first phase of this work that established 28 sites was funded by the DTI through ETSU. Phase two, which covered data collection and management until May 1998, was funded by DTI (through ETSU), Forestry Commission (FC), MAFF, Department of Agriculture for Northern Ireland (DANI) and the trade organisation British Biogen. Day to day management is carried out by Forest Research and DANI research staff.

The progress of the project is overseen by a steering committee An international modelling panel with representatives from Sweden, Belgium, Denmark, Switzerland and USA, as well as the UK has been set up to advise on the most appropriate models to use and which parameters to assess. Thanks are due to the landowners who offered sites for trials, staff of Forest Research who established plots and gathered and analysed data, staff of IACR for DNA analysis of willows, and staff of DANI for assessments in Northern Ireland.