Short Rotational Coppice - Best Practice Guidelines (PB7135)

Poplar SRC

Poplar has been used as a short rotation coppice crop on a small scale to date, often planted adjacent to willow SRC to provide visual diversity.

Site

Poplar grows best in deep fertile soils, although it will grow in most conditions. The main exceptions are shallow soils and sites that remain waterlogged. Soil pH  should ideally fall in the range 5.5 - 7.5, although research suggests that there are varieties tolerant to soil pH outside this range.

Preparation of the site should be the same as that for willow SRC, taking care to ensure eradication of all weeds. The soil should be well cultivated to a depth of at least 25cm. Where compaction is present, sub-soiling should be carried out to a depth of 40cm.

Planting material

Most new poplar varieties have been bred for high yield but as a single stem crop. Also a number of varieties planted in the mid-1990s succumbed to rust as their resistance broke down. However, current breeding programmes aim to produce high yielding varieties that will coppice more readily and have long term resistance to rust. The current recommended and approved poplar varieties for SRC are listed in the Forestry Commission Information Note, Poplar and willow varieties for short rotation coppice (Tabbush and Tubby 1999 / Tabbush, Parfitt and Tubby 2002). Poplar varieties are controlled under the Forest Reproductive Material Regulations, which are in place to improve the quality of poplar varieties, increase production and ensure that the most suitable varieties are used. These Regulations also control the marketing of poplar varieties so that reproductive material is only available from registered sources.

Planting

SRCfig15.jpg (27326 bytes) Planting should take place as early as possible in the spring but avoiding frost. The density of planting has generally been lower than that for willow at 10-12,000 cuttings/ha. The cuttings are 20-25cm long and must have an apical bud within 1cm of the top of the cutting. This means that poplar cannot be planted using step planters, as the cuttings have to be manually processed to ensure the presence of the apical bud. Consequently, modified cabbage planters have to be used but due to the ridged nature of poplar stems, the cuttings occasionally block the planter mechanisms.

The lay-flat planter is currently being tested for planting poplar rods.

Management

Weed control is very important in the establishment year, so after planting and rolling a residual herbicide should be applied within 3-5 days. Cutback takes place late in the winter following planting. Due to its apical dominance, poplar will generally produce only 1-3 shoots after cutback. Melampsora rust is also the most common disease of poplar, although different species of rust affect poplar and willow. Different poplar varieties have different susceptibilities to rust so it is important to read the latest version of the Forestry Commissions varieties Information Note referred to above. As with willow, it is recommended that a mix of varieties be planted.

Willow beetles are also an important pest of poplars and should be treated either by spraying localised colonies or, if the population reaches 100 or more adult beetles per square metre of canopy, edge spraying the coppice in early spring. Overspraying the entire plantation would be ecologically and financially inadvisable.

Yields

Research has shown that poplar can often outperform willow in terms of yield but this appears to be site specific and highlights the fact that choosing the appropriate varieties for a site is essential. Unlike willow, poplar tends to produce better yields when allowed to grow for four years or more from cutback.

Harvesting

As poplar produces fewer, heavier stems, careful consideration must be given to the harvesting machinery used; it must be capable of dealing efficiently with large diameter, rigid stems. Details of the latest machinery available to buy or hire can be obtained from British Biogens Energy Crops Network (see Contacts section).

Removal

The removal of poplar SRC at the end of its life is more problematic than willow. The rooting system of poplar includes a large taproot that grows down into the soil. Removal of the stools (following final harvest and spraying off of the shoots) will generally require a large excavator.

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011