20 September 1996

Exploiting full potential from

poplar sets…

Realising poplar potential

With environmental payments on the political agenda, interest in forestry is bound to rise. Jeremy Hunt kicks off this special feature with a look at poplars

HYBRID poplar trees capable of growing 4m (13ft) in their first year are undoubtedly one of the most exciting developments in forestry for many years.

And even though 12,000ha (30,000 acres) of poplars are currently being grown in the UK – the area is increasing at the rate of 500ha/year (1230 acres/year) – there is still a huge oppportunity for more farmers to integrate commecial poplar growing into their traditional agricultural practices.

Poplar trees have had a chequered history in the UK. Match manufacturer Bryant and May generated interest among commercial growers after the war because poplar timber peeled easily and making matches from the wood was a straightforward process. But in the late 1970s the market for poplar timber collapsed.

It was not until the mid-1980s that information concerning new Belgian-bred poplar cultivars began to filter back to the UK. Trials in Belgium in 1987 produced astonishing results achieving a hundred-fold increase in yield.

The last 10 years have seen a steady rise in poplars grown as commercial timber. Now more farmers are beginning to recognise the potential and versatility of poplars as the Forestry Commission and other organisations strive to restructure timber growing and seek to bring trees "down the hill" and into the curtilage of the lowland farm.

Many silviculturalists agree that there is no better commercial lowland tree than the poplar. The new varieties reach maturity in as little as 25 years – half the time taken by trees such as Sitka Spruce.

The growth potential of the most recently developed poplars will produce trees measuring 50cm (20in) diameter by 12 years old, growing twice as fast as the traditional variety Robusta.

According to Tillhill Economic Forestry, the cost of planting and managing poplars in the first 10 years is half the average cost of establishing broad-leaved and mixed woodland. And some farmers are already taking advantage of this potential.

Full tree planting grants are now only available on poplars planted at 1110 trees/ha (450 trees/acre), but this close planting arrangement is already being exploited by some growers. They are claiming successful first thinnings of trees of 10cm (4in) in diameter at five to six years onwards. The intention is to reduce numbers to 156 trees/ha (63 trees/acre) within 10-12 years, and then leave the remaining crop until it reaches 25-30 years old when it will be capable of producing high quality veneer timber.

The profitability of the 10cm (4in) thinnings for sale as firewood is questionable, but the 20cm (8in) thinnings at eight to nine years is certainly classed as "small timber".

Another use for poplars is in the rehabilitation of derelict woodland. Random planting of unrooted "sets" at a third of their depth is now widely successful; for many farmers and landowners this has been their introduction to poplars. Needless to say it is an introduction that often leads to a more formal approach to growing poplars.

Poplars have also found favour with those developing biomass projects. Closely planted, unrooted cuttings measuring around 20cm (8in) long will successfully strike, and on weed-free cultivated land will produce a first year thinning suitable as biomass. Coppicing after the first year encourages multi-stemmed regrowth, producing biomass for 10-12 years.

Poplars offer several options to farmers, but possibly the most exciting is the development of poplar growing in-between drilled rows of arable cropping.

Planted as 2m (6ft 6in) unrooted "sets" in rows 6-8m (20-26ft) apart, the "alleys" in between can be cultivated. A trial evaluating this practice is now in its fifth year in Yorkshire and the results are extremely encouraging. There appears to have been no loss of yield from cereal crops grown with poplars. If a decision is taken to return the land to pasture the spacing of the trees and the upright habit create only a minimal level of shade.

Pasture in between the trees can be used as valuable grazing whereas a similar plantation of other species would dominate the land use.

A tree crop grown in this way is worth around £6000-£7000/ha (£2400-£2800/acre) at current timber value. A rough guide to output/ha based on 156 trees/ha (63 trees/acre) would be 350-400cu m/ha (5000-5700cu ft/acre) after 25 years. The current price is around £25/cu m (70p/cu ft).n

Poplars – the future

Promoters of poplar growing say there is unlimited potential for the UK to become a major supplier of poplars to produce plywood. Any interested farmers should contact Maj David Davenport, The Poplar Forum, Foxley Estate Office, Mansel Lacy, Hereford. HR4 7HQ (01981-590224).

Poplars have good potential as a commercial lowland tree.