For short rotation coppicing (SRC) there are two main types of trees that stand out – willows and poplars – and choosing which one to plant largely depends on the local conditions.
In general, willows are the less demanding of the two and can grow 6ft (1.8m) or more a year, which means that after only three or four years, they are ready to be harvested for their energy value – though they’ll obviously need to be dried before use. Willows will grow in almost any conditions other than areas high in lime, and only need a metre or so of soil for their roots to do well – though obviously they perform better the more fertile the ground. They also show good wind and salt tolerance, which makes them suitable for many exposed and coastal sites – but even they cannot stand incessantly wild weather.
Poplars grow quickly too – they’re the fastest growing hardwood in Britain – but they are a little more fussy in their needs, which can rule them out for some sites. They are generally less wind and much less salt tolerant than willows and root more deeply, so they require more sheltered growing conditions with a deeper layer of soil. Unlike willows, poplars do not do well in permanently waterlogged sites.
The Value of Trials
Although it adds a year or two on establishing the SRC, it can often be a very worthwhile exercise to trial a few different varieties to demonstrate which one suit the local conditions best. You’ll need to get a rough idea of your soil chemistry – if you haven’t already – as this will be useful in narrowing down the most likely candidates to try.
If you pick some of the most apparently suitable types and plant them out in a trial bed, you should be able to see pretty quickly which ones seem to be doing best, but it’s important to do the trial on a big enough scale to make the results meaningful. We’re probably talking 10 or 20 specimens of each kind of tree – not one or two! If your plans and patience allow, it’s often useful to let the trial run for a couple of seasons because you can then get a good idea of which trees over-winter best and get going fastest in the spring, rather than just spotting which ones grow fastest in the summer.
Trees to Try
There are many different clones and varieties of willow to try and one or two kinds of poplar. Some of the most popular and successful forms include:-
- Willows Salix viminalis, S. burjatica (Germany), S. dasyclados, S. candida, S. caprea – particularly good for wetter soils – and S. x hirtei which is good for drought prone sites.
- Poplars Populus x interamericana, P. trichocarpa x deltoides and P. Nigra
If it all goes well, you should be able to get something between 6.5 and 16 dry tonnes per year out of your 2 acres once your SRC is established – so good luck with the project!